Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF DRUG FORMULATION BASED ON INCREASING THE AFFINITY OF
CRYSTALLINE MICROPARTICLE SURFACES FOR ACTIVE AGENTS
This is a divisional of Canadian Patent Application Serial No. 2,621,806
having a filing date of September 14, 2006.
[0001] The present application is related to United States Provisional
Application Serial No. 60/717,524 filed on September 14, 2005, and United
States
Provisional Application Serial No. 601744,882, filed on April 14, 2006.
FIELD OF THE INVENTION
[0002] This invention is generally in the area of drug formulations
and is
particularly related to methods of coating active agents onto the surface of
crystalline
microparticles.
[0002a] It will be understood that any references to "the present
invention" or
the like in this specification may relate to subject-matter of this divisional
or its parent.
BACKGROUND OF THE INVENTION
[0003] Delivery of therapeutic agents has been a major problem. Oral
administration is one of the most common and preferred routes of delivery due
to
ease of administration, patient compliance, and decreased cost. However, the
disadvantages of this route include low or variable potency and inefficient
adsorption
of the therapeutic. This is particularly evident when the compound to be
delivered is
unstable under conditions encountered in the gastrointestinal tract. A variety
of
coatings and encapsulation methods have been developed in the art, but only a
few
are effective in addressing this issue. Still, there are therapeutic compounds
that
tend to be less active in the conditions of the gastrointestinal tract and
must be
administered in higher dosages to be adsorbed into the bloodstream in an
effective
amount.
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[0004] A broad range of drug formulation systems have been developed
to
address the problem of optimal drug delivery and are based on incorporation of
drug
into a matrix that acts as p carrier. Factors considered in drug formulation
include
requirements that the system be non-toxic, non-reactive with the drug to be
delivered,
economical to manufacture, formed of readily available components, and
consistent
with respect to final composition and physical characteristics, including
stability and
release rate. It is also preferable that the drug delivery system is formed of
materials
easily removed from the body by normal physiologic processes.
[0005] Microparticle drug formulations can be used in numerous routes
of
administration, but are particularly well suited to pulmonary delivery.
Advantages of
the lungs for delivery of agents having systemic effects include the large
amount of
surface area and ease of uptake by the mucosal surface. United States Patent
No.
6,071,497,
1a
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describes a pulmonary drug delivery system based on the
formation of diketopiperazine microparticles as well as polymer-based
microparticles.
SUMMARY OF THE INVENTION
[0006] Methods are provided = for forming a coating of active agent on
crystalline
microparticles. In general, microparticles are coated with an active agent by
modifying the
surface properties of the microparticles such that the active agent has a
higher affinity for the
microparticle surface than for remaining in solution.
[0007] The present invention to provide improved methods for coating
crystalline
particles such as fumaryl diketopiperazine (FDKP) microparticles with active
agents, such as
proteins, using electrostatically, hydrophobically, or hydrogen-bond driven
associations. In
the present invention, liquid can optionally be removed (for recovery of
active agent coated
microparticles) by filtration or drying, or replaced by exchanging for a
different solution
medium. In any case, removal of the liquid medium is not an obligatory step in
formation of
the active agent-microparticle complex. This invention discloses a method for
microparticle
coating based on changing the surface properties of the crystalline
microparticles to achieve
adsorption of active agent to the microparticle.
[0008] In particular embodiments of the present invention, there is
provided a method
of coating a preformed crystalline microparticle in suspension with an active
agent
comprising; i) adjusting the energetic interaction between the active agent
and the crystalline
microparticle independent of solvent removal; and ii) allowing time for the
active agent to
adsorb onto the surface of the microparticle. In some embodiments, the method
of coating a
preformed crystalline microparticle in suspension with an active agent can
further comprise a
step of removing or exchanging the solvent without substantial effect on the
interaction
between active agent and microparticle.
[0009] In other particular embodiments of the present invention, the
method of coating
the microparticle with active agent is accomplished by modifying the surface
properties of
the microparticle. Modification of the surface properties of the microparticle
is achieved by
altering solution conditions. These conditions, in a non-limiting manner,
comprise changing
the pH. In other embodiments of the invention, the surface properties of the
microparticle
are modified by: 1) altering the polarity of the solution; 2) the addition of
monovalent or
multivalent ions; and 3) chemical derivatization of the microparticle.
[0010] In yet another embodiment, the present invention further
comprises a step of
dissolving the active agent in the fluid phase of the suspension of
microparticles and
subsequently changing the pH. Such step of dissolving the active agent in a
fluid phase
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refers to the dissolving of a solid. In addition, such step of dissolving the
active agent refers
to the addition of a more concentrated solution of the active agent in
addition to adding solid.
[0011] In still yet another embodiment, the pH conditions of the
microparticle
suspension are altered to favor interactions between active agent and
microparticle prior to,
or after, the addition of active agent.
[0012] In other embodiments, the active agent has more than one type
of energetically
favorable interaction with the microparticle surface.
[0013] In another particular embodiment of the present invention, the
active agent is
insulin or an analog thereof. =
[0014] In other particular embodiments of the present invention, the
surface properties
that create a favorable interaction between the active agent and microparticle
are selected
from the group consisting of electrostatic properties, hydrophobic properties,
and hydrogen
bonding properties.
[0015] In another embodiment of the present invention, the
microparticle is porous and
has interior surfaces. accessible to the bulk fluid of the solution. In one
embodiment, the
microparticle comprises a diketopiperazine such as fumaryl diketopiperazine
but is not
limited to such.
[0016] In embodiments of the present invention, the method of coating
produces a
monolayer of active agent on the microparticle surface. In other embodiments
of the-
invention, the monolayer is continuous. In other embodiments of the invention,
the active
agent in the monolayer can have a preferred orientation.
[0017] In yet another embodiment, a method is provided for coating a
pre-formed
crystalline microparticle in suspension with insulin comprising adjusting the
energetic
interaction between the active agent and the crystalline microparticle
independent of solvent
removal; and absorbing the insulin onto the surface of the microparticles.
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[0017a] According to another aspect of the present invention, there is
provided
a method of coating a preformed crystalline microparticle in suspension with
an active
agent, the method comprising the steps in the sequence set forth of; i)
obtaining
crystalline diketopiperazine microparticles; ii) providing a suspension
comprising the
microparticles, the active agent and a solvent; iii) altering conditions in
the
suspension to modify an energetic interaction between the active agent and the
crystalline diketopiperazine microparticles by modifying the surface
properties of the
microparticle, wherein altering conditions in the suspension comprise at least
one of
changing the pH of the suspension, altering the polarity of the suspension, or
adding
multivalent or monovalent ions to the suspension, wherein the altering step
does not
include a step of removing solvent from the suspension; and iv) adsorbing the
active
agent onto a surface of the microparticle to provide a coating of active agent
on the
microparticle without removing solvent from the suspension, and wherein the
altering
step causes the adsorbing.
[001713] According to still another aspect of the present invention, there
is
provided a method of coating a preformed crystalline microparticle with
insulin in
suspension, the method comprising the steps in the sequence set forth of: i)
obtaining
a crystalline diketopiperazine microparticle; ii) forming a suspension
comprising the
microparticles, insulin and a solvent; iii) altering conditions in the
suspension to
modify the energetic interaction between the insulin and the crystalline
microparticle,
wherein altering conditions in the suspension comprise at least one of
changing the
pH of the suspension, altering the polarity of the suspension, or adding
multivalent or
monovalent ions to the suspension; v) adsorbing the insulin onto the surface
of the
microparticles to provide a coating of insulin on the microparticle without
removing
solvent from the suspension and wherein the altering step causes adsorption of
insulin onto a surface of the microparticle; and vi) removing or exchanging
the solvent
after the adsorbing step.
[0017c] According to still another aspect of the present invention,
there is
provided a microparticle comprising an fumaryl diketopiperazine (FDKP) core
and an
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81771478
insulin coating; wherein at least a portion of the insulin is bound to a
surface of the
FDKP core, and wherein the surface of the FDKP core to which the insulin is
bound
contains a plurality of carboxylic acid groups, part of which are ionized;
wherein the
plurality of carboxylic acid groups are ionized in an amount that is
equivalent to the
amount of ionized carboxylic acid groups that would be present on the surface
if the
FDKP core were dispersed in an aqueous solution having a pH of about 4 to
about 5.
[0017d] According to still another aspect of the present invention,
there is
provided a pharmaceutical microparticle comprising a preformed fumaryl
diketopiperazine (FDKP) microparticle and an insulin coating, wherein the
pharmaceutical microparticle is prepared by a process comprising providing a
dispersion of the preformed FDKP microparticle and the insulin in an aqueous
solution having a pH of about 4.2 to about 5 to adjust the surface charge
density of
the preformed FDKP microparticle; or the preformed FDKP microparticle, in
admixture with the insulin, has a surface charge density that is equivalent to
a
preformed FDKP microparticle that has been dispersed in an aqueous solution
having a pH of about 4.2 to about 5.
[0017e] According to still another aspect of the present invention,
there is
provided a method for coating a crystalline microparticle with insulin and an
insulin
analog in a suspension, the method comprising the following sequential steps:
(i) dissolving the insulin or insulin analog in a solvent; (ii) obtaining a
crystalline
diketopiperazine microparticle wherein the crystalline diketopiperazine
microparticle
does not comprise an active agent; (iii) forming a suspension comprising the
crystalline diketopiperazine microparticle, the insulin or insulin analog, and
the
solvent; (iv) increasing pH of the suspension to between about 4 and about 5;
(v) adsorbing the insulin or insulin analog onto a surface of the crystalline
diketopiperazine microparticle to provide a coating of the insulin or insulin
analog on
the crystalline diketopiperazine microparticle; (vi) removing or exchanging
the solvent
after step (v).
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[0017f] According to still another aspect of the present invention,
there is
provided a microparticle comprising a fumaryl diketopiperazine (FDKP) core and
an
active agent coating; wherein at least a portion of the active agent is bound
to a
surface of the FDKP core, and wherein the surface of the FDKP core to which
the
active agent is bound contains a plurality of carboxylic acid groups, part of
which are
ionized; wherein the plurality of carboxylic acid groups are ionized in an
amount that
is equivalent to the amount of ionized carboxylic acid groups that would be
present
on the surface if the FDKP core were dispersed in an aqueous solution having a
pH
of about 4 to about 5.
[00171] According to still another aspect of the present invention, there
is
provided a microparticle comprising a fumaryl diketopiperazine (FDKP) core
microparticle and an insulin coating, wherein the insulin coating is about 9%
to about
12% of the total weight of the microparticle.
[0018] Solvent, as used herein, refers to the fluid medium in which
the active
agent and microparticle are "bathed." It should not be interpreted to require
that all
components are in solution. Indeed in many instances it may be used to refer
to the
liquid medium in which the microparticles are suspended.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The following drawings form part of the present specification
and are
included to further demonstrate certain aspects of the examples disclosed
herein.
The invention may be better understood by reference to one or more of these
drawings in combination with the detailed description of specific embodiments
presented herein.
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[0020] Figure 1 depicts the ultrasonic HCI titration profiles for
separate components of
fumaryl diketopiperazine (FDKP) suspension, FDKP particles and buffer,
according to the
teachings of the present invention. The magnitude of the changes in ultrasonic
velocity
titration profile (Figure '1; Panel A) reflects hydration changes caused by
protonation cif
ionizable carboxylate groups of the sample components. The excess ultrasonic
attenuation
peaks (Figure 1; Panel B) result from fast relaxation in the proton exchange
reaction at the
. point of saturation. Frequency (F) is 16 MHz, temperature is 25 C.
[0021] Figure 2 depicts the ultrasonic glacial acetic acid titration
profiles for FDKP
particles + insulin and FDKP particles alone according to the teachings of the
present
invention. The ultrasonic velocity profile was calculated by subtracting the
insulin
contribution; frequency is 8 MHz, temperature is 25 C. Excess ultrasonic
attenuation as a
function of the concentration of glacial acetic acid added is also depicted.
Two stages of
glacial acetic acid induced acidification are similar to that observed by HCI
titration. The
inset panel on the left ,(Panel A) depicts the association of the active agent
with the FDKP
microparticle at pH greater than about 2.9. The inset panel on the right
(Panel B) depicts the
reduced interaction between the active agent and the microparticle at pH below
about 2.9.
, [0022] Figure 3 depicts protein adsorption onto ionizable
microparticles according to
the teachings of the present invention. Protein was added to the microparticle
suspension
after pH adjustment, unbound protein was filtered away and the microparticles
dissolved to
release bound protein.
[0023] Figure 4 depicts the pH dependence for the adsorption of active
agents onto
FDKP microparticles according to the teachings of the present invention.
Figures 4A depicts
insulin adsorption; Figure 4B depicts anti-SSX-24149 monoclonal antibody
adsorption, Figure
4C depicts parathyroid hormone (PTH) adsorption and Figure 4D depicts ghrelin
adsorption.
[0024] Figure 5 depicts the pH dependence of insulin adsorption onto
FDKP
microparticles with limiting insulin concentration according to the teachings
of the present
invention.
[0025] Figure 6 depicts the change in ultrasonic velocity in FDKP
microparticle
suspension (11 mg/mL) upon stepwise titration of FDKP microparticles with
protein
(10 mg/mL) according to the teachings of the present invention. The
contribution of free
protein and the effect of FDKP microparticle dilution were subtracted.
Temperature is 25 C.
[0026] Figure' 7 depicts the saturation curves for adsorption of the
active agent onto
FDKP microparticles according to the teachings of the present invention.
Loading curves
are shown for active agent/FDKP microparticles as a function of active agent
concentration
at pH 5Ø Figure 7A depicts glucagon-like peptide 1 (GLP-1) adsorption;
Figure 78 depicts
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PTH adsorption; Figure 7C depicts anti-SSX241..49 monoclonal antibody
adsorption and
Figure 7D depicts anti-MOPC-21 monoclonal antibody adsorption.
[0027] Figure 8 depicts adsorption of active agents onto microparticles
at pH 5.0 as
influenced by increasing concentrations of salt according to the teachings of
the present
invention. The active agent was added to the microparticle suspension after pH
adjustment,
unbound agent was filtered away and the microparticles dissolved to release
bound agent.
Figure 8A depicts insulin adsorption, Figure 8B depicts anti-SSX-241-49
monoclonal antibody
adsorption, Figure 8C depicts PTH adsorption and Figure 8D depicts ghrelin
adsorption.
DETAILED DESCRIPTION OF THE INVENTION
Agents to be delivered
[0028] The substance to be coated onto the crystalline microparticle is
referred to
herein as the active agent. Examples of classes of active agent include
pharmaceutical
compositions, synthetic compounds, and organic macromolecules that have
therapeutic,
prophylactic, and/or diagnostic utility.
[0029] Generally, any form of active agent can be coated onto the
surface of a
crystalline microparticle. These materials can be organic macromolecules
including nucleic
acids, synthetic organic compounds, polypeptides, peptides, proteins,
polysaccharides and
other sugars, and lipids. Peptides, proteins, and polypeptides are all chains
of amino acids
linked by peptide bonds. Peptides are generally considered to be less than 30
amino acid
residues, but may include more. Proteins are polymers that can contain more
than 30 amino
acid residues. The term polypeptide as is know in the art and as used herein,
can refer to a
peptide, a protein, or any other chain of amino acids of any length containing
multiple
peptide bonds, though generally containing at least 10 amino acids. The active
agents used
in the coating formulation can fall under a variety of biological activity
classes, such as
vasoactive agents, neuroactive agents, hormones, anticoagulants,
immunomodulating
agents, cytotoxic agents, antibiotics, antiviral agents, antigens, and
antibodies. More
particularly, active agents may include, in a non-limiting manner, insulin and
analogs thereof,
growth hormone, parathyroid hormone (PTH), ghrelin, granulocyte macrophage
colony
stimulating factor (GM-CSF), glucagon-like peptide 1 (GLP-1), Texas Red,
alkynes,
cyclosporins, clopiogrel and PPACK (D-phenyialanyl-L-prolyl-L-arginine
chloromethy I
ketone), antibodies and fragments thereof, including, but not limited to,
humanized or
chimeric antibodies; F(ab), F(ab)2, or single-chain antibody alone or fused to
other
polypeptides; therapeutic or diagnostic monoclonal antibodies to cancer
antigens, cytokines,
infectious agents, inflammatory mediators, hormones, and cell surface
antigens. Non-
limiting examples of antibodies to tumor antigens include anti-SSX-241_49
(synovial sarcoma,
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X breakpoint 2), anti-NY-ESO-1 (esophageal tumor associated antigen), anti-
PRAME
(preferentially expressed antigen of melanoma), anti-PSMA (prostate-specific
membrane
antigen), anti-Melan-A (melanoma tumor associated antigen), anti-tyrosinase
(melanoma
tumor associated antigen), and anti-MOPC-21 (myeloma plasma¨cell protein).
Delivery System -Crystalline Microparticles
[0030] Essentially, the term "microparticle" refers to a particle
with a diameter of about
0.5-1000 pm, irrespective of the precise exterior or interior structure.
Within the broad
category of microparticles, nmicrospheres" refers to microparticles with
uniform spherical
= shape. Crystalline microparticles as used herein refers to microparticles
that have the
internal structure though not necessarily the external form of a crystal and
have a regular
arrangement of atoms in a space lattice. Ionizable crystalline surfaces refer
to crystalline
microparticles that have the additional capacity to carry an electrical
charge.
[0031] Preferably, the chemical substance composing the crystalline
microparticle is
reversibly reactive with the active agent to be delivered, as well as
nonkto)dc and not
metabolized, at least by rodents and humans. In addition, the crystalline
structure of
preferred microparticles is not substantially disrupted in the process of
coating with active
agent. The composition of the crystalline microparticle determines what type
of chemical
interactions can be manipulated to drive adsorption of an active agent to the
microparticle
surface.
[0032] A number of substances can be used to form crystalline
microparticles.
Microparticles as such have an outer surface, the properties of which can be
manipulated in
the coating process. Representative materials from which crystalline -
microparticles can be
=
=
formed include but are not limited to: aromatic amino acids, salts with
limited solubility in a
= defined pH range such as diketopiperazines and morpholine sulfates.
[0033] United States' Patent Nos. 5,352,461 and 5,503,852,
describe a drug delivery system based on formation of
diketopiperazine.(DKP) microparticles from diketopiperazine derivatives such
as 3,6-bis[N-
. fumaryl-N-(n-butyl)amino] (also referred to as fumaryl diketopiperazine
or FDKP; also termed
(E)-3,6-bis[4-(N-carboxy-2-propenyl)amidobutyI]-2,5-diketopiperazine) that are
stable at low
pH and dissolve at the pH of blood or the small intestine. As disclosed in the
above patents,
the drug to be delivered is combined or loaded with the diketopiperazine
particles by forming
DKP microparticles in the presence of drug (payload). A system based on
diketopiperazine
structural elements, or one of its substitution derivatives, including, but
not limited to,
diketomorpholines and diketodioxanes, forms microparticles with desirable size
distributions
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and pH ranges as well as good payload tolerance. A wide range of stable, -
reproducible
characteristics can be generated with appropriate manipulations of the
substituent groups.
[0034] Other diketopiperazines that may be contemplated in the
present invention may
include 3,6-di(4- aminobutyI)-2,5-diketopiperazine; 3,6-di(succiny1-4-
aminobuty1)-2,5-
.
diketopiperazine (succinyl diketopiperazine or SDKP); 3,6-di(maley1-4-
aminobuty1)-2,5-
diketopiperazine; 3,6-di(citracony1-4-aminobuty1)-2-5-diketopiperazine; 3,6-
di(glutary1-4-
aminobuty1)-2,5-diketopiperazine; 3,6-di(ma)ony1-4-aminobuty1)-2,5-
diketopiperazine; 3,6-
di(oxaly1-4-aminobuty1)-2,5-diketopiperazine and derivatives therefrom.
Diketopiperazine
= salts may also be utilized in the present invention and may included, for
example, a
pharmaceutically acceptable salt such as the Na, K, Li, Mg, Ca, ammonium, or
mono-, di- or
tri-alkylammoniurn (as derived from triethylamine, butylamine, diethanotamine,
triethanolamine, or pyridines, and the like). The salt may be a mono-, di-, or
mixed salt.
Higher order salts are also contemplated for diketopiperazines in which the R
groups contain
more than one acid group. In other aspects of the invention, a basic form of
the agent may
be mixed with the diketopiperazine in order to form a drug salt of the
diketopiperazine, such
that the drug is the counter cation of the diketopiperazine.
[0035] United States Patent No. 6,444,226, and 6,652,885,
describe preparing and providing microparticles of DKP in
aqueous suspension to which a solution of active agent is.added, and then the
critical step of
= lyophilizing the suspension to yield microparticles having a coating of
active agent. The
basis for this formulation is that the coating of microparticle with active
agent is driven by
removal of the liquid medium by lyophilization. (See also United States Patent
No.
= 6,440,463). In contrast to teachings
in the prior art, the present invention provides means for adjusting the
association of active
agent with the microparticle prior to solvent removal. Thus, removal of the
liquid medium by
= bulk physical methods (e.g., filtration or sedimentation) or evaporative
methods (e.g.,
lyophilization or spray-drying) can result in comparable loads.
Controlled Coating of Crystalline Microparticles =
[0036] Controlled coating refers to the directed process of
adsorbing active agent onto
the surface of a crystalline microparticle. The coating process involves
changing the surface
properties of crystalline microparticles in a fluid suspension either by
changing solution
conditions (such as pH, temperature, polarity, ionic strength, and co-
solvents), by
= complexation to mono- or multi-valent ions, or by chemical
derivatization. Altering the
surface properties of the microparticle either before or after addition of
active agent affects
its chemical interactions with active agent, thereby resulting in adsorption
of active agent to
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the crystalline microparticle. Chemical interaction between the microparticle
and active agent
drives adsorption and results in a monolayer of the active agent on the
surface of the
microparticle. Once a molecule of active agent is adsorbed, that portion of
the microparticle
surface is not exposed for further interaction and adsorption of additional
active agent at that
particular surface point: The resulting monolayer can be either continuous (no
gaps
between adsorbed active agent molecules over the accessible surface) or non-
continuous
(gaps of exposed microparticle surface between adsorbed active agent
molecules.
Adsorption of Active Agent onto Microparticles
[0037] As discussed above, adsorption of the active agent onto the
microparticle
results in mono-layering (coating) of the active agent onto the microparticle.
However, there
is more than one mechanism at play in the adsorption of an active agent, such
as insulin for
example, to crystalline microparticles:
100381 The monolayer of an active agent, such as insulin, that coats the
microparticle is
one stage of the loading process of insulin onto the microparticle but is not
necessarily the
end result in the loading process as both monomeric and multimeric layers can
be formed
based on the energetics of the system.
[0039] Under conditions of permissive solubility, such as low insulin
concentration
and/or low pH (substantially below pH 5.0), attractive forces between insulin
and the FDKP
particle surface are much greater than the self-associative forces for
insulin. Thus coating of
insulin onto the microparticle occurs in a monolayer manner and saturation is
observed
without aggregation or multilayering onto the microparticle surface (see
Example 6). As
solubility approaches saturation, due to high insulin concentration and/or pH
close to 5.0 (a
solubility minimum for wild-type insulin), insulin self-association becomes
more energetically
favorable. Thus coating can proceed past the point of a saturated monolayer
and further
layers of insulin can be added to the particle. Two forms of self-association
can be
recognized: multimerization and aggregation. Multimerization is characterized
by specific
intermolecular interactions and fixed stoichiometry. Aggregation is
characterized by
unspecific intermolecular interactions and undefined stoichiometry. Speaking
generally,
multimeric active agents can be adsorbed in the multimeric state, or
disassociated into
monomers, or lower order multimers, and adsorbed to the surface in that state.
In either
case aggregation can mediate layering of the active agent onto the
microparticle. According
to the inventors current understanding, under the general conditions used in
the examples of
the present disclosure (such as dissolution of insulin in acetic acid)
deposition of additional
layers of insulin proceed as aggregation of non-hexameric insulin.
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Method for Coating Microparticles
[0040] The procedure for coating crystalline microparticles, such as
.preformed
crystalline microparticles, with active agents is described generally as
follows: crystalline
microparticles previously formed by precipitation, or another method, are
suspended in liquid
medium, such as water; and the medium is adjusted to alter the particles'
surface either
before or after addition of active agent. At this point the active agent will
adsorb to the
microparticle surface and after an interval of time (for example <1, 1, 2, 8,
4, 5, 6, 7, 8, 9, or
minutes; preferably from <1 to at least 5 minutes) the loading process will be
complete.
The liquid medium may be removed by any means including filtration,
centrifugation,
= lyophilization or spray-drying or replaced by media exchange. Adsorption
may be confirmed
by either of two experimental approaches: 1) demonstrating the absence of
significant
amounts of active agent in a filtrate or supernatant and/or 2) demonstrating
presence of the
= active agent in the solid phase while showing that active agent does not
precipitate when
taken through the same procedure in the absence of the microparticles.
Manipulating Microparticle Surface Properties
[0041] As disclosed elsewhere herein, the surface properties of the
microparticle can
be manipulated by various means. The microparticle surface properties that can
be
manipulated include, but are not limited to, electrostatic, hydrophobic, and
hydrogen bonding
properties. In various embodiments these manipulations are carried out in the
absence or
= presence of-the active agent, or before or after the microparticles and
the active agent are
mixed together. When the manipulation takes place in the presence of the
active agent, for
example by altering solution condition, there can also be effects on the
active agent that will
modify its affinity for the surface. Thus in some embodiments of the present
invention,
. coating of the microparticle can involve manipulation of surface
properties and modification
of properties of the active agent. Methods directed to the latter are
disclosed in
US. Patent 7,803, 404 entitled
METHOD OF DRUG FORMULATION BASED ON INCREASING THE AFFINITY OF
=
ACTIVE AGENTS FOR CRYSTALLINE MICROPART1CLE SURFACES filed on date even
with the instant application.
[0042] Electrostatic interactions are attractions between opposite
charges or repulsions
between like charges that grow stronger as the charges come closer to each
other.
Electrostatic interactions constitute a key component in understanding
interactions between
charged bodies in ionic solutions. For example, the stability of colloidal
particles dispersed
in a solvent can be explained by considering the competition between repulsive
electrostatic
interactions and the attractive van der Weals interactions. Also, the chemical
functionality
(for example, but not limited to COOH, NH, etc.) of the microparticle surface
can be utilized
9
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as the counter ion to an ionized active agent such that the active
agent/particle composite
comprises a salt. Electrostatic interactions are also of importance when
considering
interaction and adhesion between particles.
[0043] Altering
the pH of the surrounding solution system can change electrostatic
properties of ionizable crystalline microparticles in suspension. As
demonstrated in Example
3, changing the pH of the solution changes the ionization of a microparticle
such that active
agent adsorbs to the microparticle surface. Specifically, Example 4 shows that
microparticles
composed of FDKP (3,6-bis[N-fumaryl-N -(n-butyl)amino]2,5-diketopiperazine)
are ionizable.
The microparticles are insoluble in water below pH 3.5 but solubility
increases rapidly
between pH 3.5 and 5.0, presumably due to the ionization of the carboxyl
groups. The FDKP
microparticle is partially ionized at pH 5 prior to complete dissolution at
higher pH, which can
be observed indirectly via ultrasonic spectroscopy. Example 5 demonstrates the
controlled
coating of protein onto the FDKP microparticle surface. In one
embodiment,
diketopiperazine microparticles are suspended in an acidic solution, active
agent is added to
the suspension, and the pH of the solution is raised after the active agent
and microparticles
are mixed together. The increased pH alters the surface properties of the
microparticles to
create an environment in which the active agent has a higher affinity for the
microparticle
than for the solvent.
[0044]
Alternatively, the pH of the microparticle suspension can be raised
immediately
prior to addition of active agent to the solution. The surface charge
properties of the
microparticle are altered by the change in pH such that active agent has a
higher affinity for
the microparticle than for remaining in solution and is adsorbed to the
microparticle surface
upon addition.
[0045] Examples
6 and 7 demonstrate loading of insulin onto FDKP particles by
manipulation of pH conditions. Finally, the saturation of the microparticle by
protein
adsorption and the formation of a monolayer are described in Example 6.
Other Methods of Manipulating the Surfaces of Microparticles
[0046] In
addition to electrostatic properties, other properties of a microparticle
surface
can be exploited to control adsorption of active agent. Microparticles
containing compounds
with imidazole, pyridine, Schiff bases, ketone, carboxylic acid bioisosteres,
amides, or other
functional groups that can exist in multiple structures could be manipulated
to modify surface
properties.
[0047]
Hydrophobic interactions are associations of non-polar groups with each other
in
aqueous solutions because of their insolubility in water. Hydrophobic
interactions can affect
a number of molecular processes including, but not limited to, structure
stabilization (be it of
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single molecules, complexes of two or three molecules, or larger assemblies)
and dynamics,
and make important contributions to protein-protein and protein-ligand binding
processes.
These interactions are also known to play a role in early events of protein
folding, and are
involved in complex assembly and self-assembly phenomena (e.g., formation of
membranes).
[0048]
Hydrophobic interactions can be manipulated by changing the protonation of
crystalline microparticles composed of histidine. Protonating the histidine
will reduce the
nucelophilicity of the crystalline microparticles and impart a positive
charge.
[0049] Hydrogen
bonding interactions are especially strong dipole-dipole forces
between molecules; a hydrogen atom in a polar bond (e.g., H-F, H-0 or H-N) can
experience
an attractive force with a neighboring electronegative molecule or ion, which
has an
unshared pair of electrons (usually an F, 0 or N atom on another molecule).
Hydrogen
bonds are responsible .for the unique properties of water and are very
important in the
organization of biological molecules, especially in influencing the structure
of proteins and
DNA.
[0050] In the
present invention, the hydrogen bonding properties of the microparticle
surface can be controlled by chemical derivatization. Hydrogen bond
donors/acceptors can
be added chemically to alter the microparticle surface. For example, the
hydrogen in an N-H
bond can undergo hydrogen bonding to the oxygen in a C=0 bond. If the N-H is
replaced by
an N-CH3, then this particular hydrogen bonding interaction is removed.
Likewise,
replacement of the C=0 group with a C=C group also removes this particular
bonding
interaction.
[0051]
Microparticles with surfaces containing ionizable aromatic groups are polar
when ionized but hydrophobic in their un-ionized state. Starting with
protonated surfaces and
manipulating solution conditions to reduce particle surface ionization causes
hydrophobic or
aromatic active agents to coat the microparticle surface.
[0052]
Microparticles with ketone surface groups could be manipulated by changing the
solution polarity. By reducing solvent polarity (adding low polarity organic
solvents to an
aqueous solution) the end- form is made the predominant species at the
particle surface.
This enol- form is a hydrogen bond donor whereas the keto- form is a hydrogen
bond
acceptor. The adsorption of nitrogen-containing drugs onto the microparticle
surface is
promoted in this manner.
[0053]
Microparticles with surface groups that undergo pH- or temperature-induced
isomerization can also. be induced to adsorb drug molecules by manipulating
solution
conditions. In the case of these surfaces, the introduction of a kink in a
linear surface group
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due to isomerization increases the mobility (fluidity) of the groups at the
microparticle
surface. This allows the surface to form more contacts with the active agent
than are
possible with an ordered surface. If the additional interactions with the
active agent are each
favorable, then the net interaction energy becomes favorable and the drug
adsorbs to the
microparticle surface.
Fluid Medium Removal Techniques
[0054] Removal of solvent after controlled coating of the crystalline
surfaces with active
agent can be achieved by methods including, but not limited to, sedimentation,
filtration, or
drying. Drying techniques include, but are not limited to, lyophilization and
spray-drying.
These techniques are known to those skilled in the art. In one embodiment of
the present
invention, solvent is removed by spray-drying., Methods of spray-drying
diketopiperazine
microparticles are disclosed in, for example, U.S. Provisional Patent
Application No.
60/776,605 filed on February 22, 2006
regarding spray-drying diketopiperazine microparticles.
Analysis of Surface Property Modifications
[0055] The present invention employs the technique of ultrasonic
spectroscopy to
analyze the changes in the surface properties of crystalline microparticles in
a fluid
suspension, which promote or enhance adsorption of an active agent to the
crystalline
microparticle. As disclosed elsewhere herein, such changes involve changing
solution
conditions (such as pH, temperature, polarity, ionic strength, and co-
solvents), by
complexation to mono- or multi-valent ions, or by chemical derivatization to
alter the surface
properties of the microparticle either before or after addition of active
agent.
[0056] Ultrasonic spectroscopy is an analytical tool known to the
skilled artisan. In
brevity, ultrasonic spectroscopy employs sound waves. In particular, it uses a
high frequency
acoustical wave which probes intermolecular forces in samples/materials.
Oscillating
compression (and decompression) in the ultrasonic wave causes oscillation of
molecular
arrangements in the sample, which responds by intermolecular attraction or
repulsion.
[0057] Traveling through samples, the ultrasonic wave loses its energy
(a decrease in
amplitude) and changes its velocity. This decrease in amplitude and change in
velocity are
analyzed as characteristics of the sample. Therefore, propagation of
ultrasonic waves is
determined by ultrasonic velocity and attenuation.
[0058] Ultrasonic velocity is determined by the elasticity and the
density of the medium.
Solids have the strongest interactions between the molecules followed by
liquids and gases
and are therefore more rigid compared with liquids and gases. Ultrasonic
attenuation is a
measure of the energy that ultrasonic waves lose as they traveling through a
sample. It
12
=
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characterizes the ultrasonic transparency of the sample and can be seen as a
reduction of
amplitude of the wave.
[0059] Multi-frequency measurement of ultrasonic attenuation in
homogeneous
systems allows the analysis of fast chemical reactions such as, but not
limited to, proton
exchange, .structural transitions (e.g.,. isomerization), self-association
(e.g., dimerization),
aggregation, binding of ligands to macromolecules etc.
EXAMPLES
[0060] The following examples are included to demonstrate
embodiments of the
present invention. It should be appreciated by those of skill in the art that
the techniques
disclosed in the examples which follow represent techniques discovered by the
inventor to
function well in the practice of the present invention, and thus can be
considered to
constitute preferred modes for its practice.
Example 1
General Procedure For Loading Microparticles With Active Agents
[0061] Table 1 below is an example of electrostatically driven
coating of an ionizable
crystalline- microparticle (FDKP microparticles) utilizing pH-controlled
adsorption. In these
=
experiments, FDKP microparticle suspensions were prepared at pH 2.0 and 4.5.
Protein
(growth hormone) was then added to each to give final conditions of 5 mg/mL
FDKP
particles and 200 ug/mL protein. After mixing, the bulk liquid was removed
from suspension
by filtration. The material trapped on the filter was then dissolved and
collected. The protein
concentration in all of the fractions was quantitated by HPLC.
[0062] At low pH (2.0), the protein did not adsorb to the
particles and all protein was
found in the first filtrate. By increasing the pH to 4.5, the surface
properties of the particles
were changed to have a high affinity for the protein. Under these conditions,
the protein
bound to the microparticles and was not seen in the filtrate. To determine the
amount of
protein associated with the microparticles, the protein was recovered when the
microparticles were dissolved. The particle-free controls demonstrate that the
protein, by
itself, was not retained on the filter under the conditions used, i.e., the
protein did not self-
associate or otherwise aggregate into particles larger than the filter pores.
13
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Table 1. Protein concentrations in an adsorption experiment with FDKP
microparticles.
pH 2.0 pH 2.0 pH 4.5 pH 4.5
Fraction with particles no particles with particles no
particles
Initial conc. (pg/mL) 200 200 200 200
Filtrate (unbound protein) 146 181 0 145
Dissolved Particles 0 0 180 0
Values shown are results from HPLC quantitation of the solutions after
filtration
Example 2
Controlling FDKP Microparticle Ionization by Manipulating the pH
[0063] FDKP is a rod-shaped molecule with a carboxylic acid functional
group at each
end which is essentially insoluble in water below pH 3.5 when the carboxylic
acids are
protonated and carry no charge. The solubility of FDKP increases rapidly above
pH 3.5
corresponding to ionization of the carboxyl groups. Modeling of FDKP crystals,
which form
as plates with two large, flat faces and narrow edges, indicates that the rod-
like FDKP
molecules align perpendicular to the edges of the plates so that the
carboxylic acid ends of
the molecule are arrayed on the large faces of the plates. On a theoretical
basis, the
surfaces of FDKP crystals should be partially ionized around pH 5.0, where the
solubility is
about 1 mg/mL, just below the pH at which a 10 mg/mL suspension of
microparticles will
dissolve.
[0064] The ionization of FDKP crystal surfaces has been observed
indirectly with
ultrasonic spectroscopy. In Figure 1, the ultrasonic titration curve of FDKP
microparticles and
buffer are shown. In this experiment, a solution containing 200 mM HCI was
added in small
aliquots to a stirred 10 mg/mL suspension of FDKP microparticles in 20 mM
ammonium
acetate buffer. The initial pH was 4.8. After each addition of HCI, the system
was permitted
to equilibrate and ultrasonic data was collected.
[0065] The decrease in ultrasonic velocity observed with increasing acid
concentration
(decreasing pH) reflects the protonation of carboxylic acid groups in the
system. As the
groups were protonated and became uncharged, the water structure around them
relaxed
and ultrasonic waves were transmitted more slowly (the ultrasonic velocity
decreases).
Because FDKP microparticles carboxylate surfaces and the carboxylate group in
the acetate
buffer are chemically very similar, the curves were also similar. The
differences, however,
were caused by the FDKP microparticles. First, the magnitude of the velocity
change with
FDKP microparticles was larger. This difference results from protonation of
ionized
carboxylate groups on the FDKP microparticle surface. The peak in the
attenuation curve,
which occurs near the point of complete protonation, was shifted to slightly
higher acid
14
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concentration in the FDKP suspension. Finally, both FDKP parameters continued
to change
as the pH was reduced from 3.5 to 2.3. These changes reflect additional
modifications in the
surface properties of the particles that may include ordering of the surface
carboxyl groups
or other microstructure! modifications.
Example 3
Loading Protein onto FDKP Microparticles by pH Manipulation of the Surface
Properties
[0066] The adsorption of proteins onto ionizable microparticle surfaces
by pH
manipulation can be achieved in two ways. The protein can be added and then
the pH
adjusted to cause ionization of the surface with concomitant adsorption of
protein. This
process is reversible. Alternatively the pH of the particle suspension can be
adjusted to
cause ionization of the surface before the protein is added.
[0067] The ultrasonic titration data shown in Figure 2 indicates the
association of
protein (insulin) with the FDKP microparticles at pH greater than about 2.9
and reduced
interaction at pH below about 2.9.
[0068] A suspension of FDKP microparticles was prepared in 20 mM
ammonium
acetate buffer, pH 4.8, and combined with an insulin stock solution to give
800 pL of
suspension with a final concentration of 10 mg/mL FDKP microparticles and
insulin
concentration of 1 mg/mL. This suspension was introduced into an ultrasonic
spectrometer.
While stirring gently, glacial acetic acid was gradually added in 5 pL
aliquots to lower the pH.
At each step in the titration ultrasonic data was collected.
[0069] The change in ultrasonic velocity was related (proportional) to
the amount of
surface area (hydration water) of the particles and/or macromolecules in the
sample. Figure
2 illustrates that above pH of about 2.9 (10% v/v acetic acid added), the
velocity curves for
microparticles alone (FDKP particles) and microparticles with insulin (FDKP
particles +
Insulin) coincided. This indicated that the amount of surface area in the
system is essentially
the same as the surface area of FDKP microparticles alone. The insulin had a
negligible
contribution because it is very small compared to the microparticles. Below pH
2.9, the
FDKP particles and FDKP particles + Insulin curves diverged. Ultrasonic
velocity of the
FDKP particles + Insulin curve was higher here, which indicated that there was
more surface
area exposed to water than in the FDKP particles alone sample. This additional
surface area
was from free insulin in the suspension. As the pH increased from about 2.7 to
about 2.9,
the insulin surface area was lost by adsorption of insulin to FDKP
microparticle surfaces, and
the higher intensity of the FDKP microparticles + Insulin curve disappeared as
free insulin
disappeared from the system.
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[0070] As noted above, the second pH-driven method of coating particles
with protein
is to suspend particles in a fluid medium and adjust solution conditions to
ionize the particle
surface. The protein can then be added to the suspension and protein molecules
will
immediately adsorb. Figure 3 illustrates the amount of protein (insulin) that
was adsorbed
upon addition to pH-adjusted suspensions of FDKP microparticles.
[0071] FDKP microparticle suspensions were prepared at 5 mg/mL and an
excess of
protein (2 mg/mL) was added. (An excess of protein, as referred to herein, is
that amount
over what is believed to be necessary to form a monolayer covering the
accessible surface
of the FDKP microparticle). After incubation, non-adsorbed protein was removed
by filtration.
The solids retained on the filter (retentate) were dissolved and the amounts
of FDKP
microparticles and protein retained on the filter were quantitated by HPLC.
The
protein/particle mass ratio was determined from this quantitation. Based on
the known
surface area of these particles and the molecular dimensions of the protein, a
continuous
monolayer of adsorbed protein was estimated to occur at a mass ratio of about
0.07. On the
basis of that estimate it can be seen from this example that a continuous
monolayer was
formed at pH 5.0 and that non-continuous monolayers formed at pH 3.5 through
pH 4.5.
[0072] Additionally, different lots of dried active agent-coated FDKP
microparticles were
suspended in either an acid solution (final pH about 2.0) or water (final pH
about 4.5). The
different active agents included insulin, growth hormone and insulin aspart (a
fast-acting type
of insulin), as shown in Table 2. The solvent was filtered from these
suspensions and the
retained particles were dissolved and collected. The amount of active agent in
all of these
samples was quantitated by HPLC. The results are shown in Table 2.
[0073] For each of the lots, the active agent was released from the
particles in the
acidic solution. Therefore, by protonating the surfaces of the microcrystals,
the active agent
desorbs from the crystal surfaces. When the particles were resuspended in
water, which
does not change the ionization state of the particle surface, the protein
remained adsorbed.
Table 2. Active agents coated onto FDKP microparticles
G rowthInsulin
Insulin
Hormone Aspart
Active Agent Standard solution 250 1103 1099
Resuspended in Acidic solution 240 980 893
Redissolved after filtering away acidic
0 49 29
solution
Resuspended in water 0 4 0
Redissolved after filtering away water 191 936 982
Values in the table are integrated peak areas from HPLC quantitation
(mAU*sec at 215nm).
16
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Example 4
Characterization of pH Driven Adsorption of Insulin onto FDKP Microparticles
[0074] Insulin
was adsorbed (loaded) onto FDKP microparticles in a pH-controlled
process by mixing an aqueous suspension of FDKP microparticles with an aqueous
solution
of insulin. To characterize the effect of pH on insulin binding to FDKP
microparticles, a 5
mg/mL suspension of FDKP particles at varying pH values was prepared. An
excess of
dissolved insulin was then added, allowed to adsorb for about 5 minutes, after
which the
unbound insulin was removed by filtration. The solid particles with adsorbed
insulin were
recovered from the filter (retentate), dissolved and collected. The amounts of
insulin and
dissolved FDKP microparticles were quantitated by HPLC. The amount of adsorbed
insulin
was calculated as a fraction of the total mass of retentate. The pH dependence
of insulin
adsorption is shown in Figure 4A; insulin adsorption increased as a function
of pH. Similar
= results were obtained for SSX-241.49 monoclonal antibody, PTH, and
ghrelin as illustrated in
Figures 413, C, and D respectively.
[0075]
Additionally, FDKP particles were suspended in insulin solutions (10 mg/mL) of
different pHs. The mass ratio of FDKP particles to insulin was 10:1. The
unbound insulin
concentration in the supernatant was determined by HPLC after the supernatant
had been
separated from the particles by centrifugation. Insulin binding was determined
as the
difference from the initial insulin concentration. The data reported in Figure
5 demonstrate
that increasing pH resulted in reduced insulin in solution and in-creased
insulin content on the
FDKP particles.
[0076] Thus,
insulin binding to FDKP particles increases with increasing pH from about
pH 3.0 up to about pH 5. Preferably, the insulin solution is added at pH 3.6
and under these
conditions approximately 75% of the insulin is adsorbed from solution onto the
particles.
Insulin binding increases to > 95% as pH increases to 4Ø Substantially
complete binding
is achieved at about pH 42,
preferably about 4.4. At pH higher than 5.0, the FDKP
microparticles begin to. dissolve and no longer retain the structure of a
crystalline
microparticle.
Example 5
Description of Loading FDKP Microparticles With Insulin
[0077] In a
production scale format (2-5 kg), microparticles of FDKP are formed by acid
precipitation with acetic acid and washed. An insulin solution at pH 3.6 is
added to the
FDKP particle suspension. The insulin stock solution is 10 wt% insulin and 2.5
wt% acetic
acid (pH of approximately 3.6). Ammonium hydroxide is used to adjust the pH of
the mixture
to 4.5. Table 3 indicates the amounts of the various components per kilogram
of formulation
17
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used to prepare particles containing ¨11.4% insulin by weight. Polysorbate 80
can be
incorporated during particle formation and can improve the handling
characteristics of the
final particles. Time is allowed for insulin adsorption onto the FDKP
particles and to ensure
thorough mixing. The mixture is then added dropwise to liquid nitrogen to
flash freeze the
suspension. The fluid medium is removed by lyophilization to produce FDKP
particle/insulin
bulk drug product Alternatively the mixture is spray-dried. Table 4 indicates
the amounts of
the various components in the bulk product after removal of the fluid medium.
Table 3. Composition of FDKP particles/Insulin Batch Formula
Component 11.4% FDKP/Insulin
(Grams per kg of formulation)
Insulin, USP 114 g
FDKP 870g
Polysorbate 80, USP* 34.8 g
Strong Ammonia Solution, NF 572 g
Acetic acid (glacial), NF 3680 g
Purified Water, NF 179000 g
Nitrogen, NF as needed
Table 4. Composition of FDKP particles/Insulin
11_4% FDKP/Insulin, process
Component
(Quantity per gram formulation)
Insulin, USP 3.0 IU (0.11 mg)
FDKP 0.87 mg
Polysorbate 80, USP* 0.007 mg
Strong Ammonia Solution, NF Removed during process
Acetic acid (glacial), NF Removed during process
Purified Water, NF 0.012 mg
Nitrogen, NF Removed during process
In Tables 3 and 4 above, NF denotes ¨ National Formulary
* Polysorbate 80 content is estimated by an HPLC/MS assay.
**The FDKP/Insulin formulation contains about 1.2% residual
water after lyophilization. Trace quantities of acetic acid and
ammonium hydroxide may also be present.
18
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Example 6
Saturation of Microparticle Surfaces by Protein (Formation of a Continuous
Monolayer)
[0078] The surface coating of a microparticle with a monolayer should be
a saturable
process. That is, its accessible surface area and the diameter of the active
agent molecule
will dictate the capacity of the microparticle surface. Figure 6 illustrates
this saturation.
[0079] A suspension of FDKP microparticles was prepared and the pH was
adjusted to
between pH 3.0 and pH 3.5 at which point the surfaces partially ionize. In
this. procedure,
higher pH could not be used because it would have caused self-association of
the active
agent, insulin. Small portions of a concentrated insulin solution were added
to the stirred
suspension. After each addition, the sample was allowed to stabilize and
ultrasonic data was
collected.
[0080] Figure 6 shows that a reduction in ultrasonic velocity is
observed as the protein
concentration was increased. This type of change in the ultrasonic velocity is
typical for
ligand binding in aqueous solutions and indicates adsorption of the active
protein to the
FDKP microparticle surfaces. The velocity decrease results from the release of
hydration
water from the FDKP microparticle and protein surfaces. When the hydration
water is
displaced by adsorption of the active agent, its structure relaxes and
produces a net
decrease in the ultrasonic velocity through the sample. When all the binding
sites on the
surface of the FDKP micrOparticles have been saturated, i.e., a protein
monolayer has
formed, the curve levels off. Monolayer formation was also demonstrated by the
data in
Figures 7A-7D which showed that the adsorption of various active agents (GLP-1
[Figure
7A]; PTH [Figure 76]; anti-SSX-24149 monoclonal antibody [Figure 7C]; and anti-
MOPC-21
monoclonal antibody [Figure 7D3), onto microparticles reached saturation as
the
concentration of the active agent is increased at a constant concentration of
FDKP
microparticles (5 mg/rriL). These studies were conducted at pH 5.0 where
optimal
adsorption of the active agent to microparticles is observed. GLP-1 does not
self associate
at the concentrations used (as disclosed in U.S. Provisional Patent
Application No.
60/744,882).
Example 7
Evidence for Electrostatic Interaction Mechanism
[0081] Evidence for an electrostatic mechanism of interaction is the
ability to interfere
with adsorption by weakening electrostatic interactions. This is demonstrated
by adding salt
to the ionized-particle/active agent system. Figures 8A-8D illustrate that
increasing ionic
strength in an active agent-FDKP microparticle system reduced the adsorption
of the active
agent onto the microparticle.
19
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[0082] A series of samples were prepared at pH 5.0 where adsorption of
the active
agent onto FDKP microparticle surfaces is strong. Each sample contained a
different
quantity of salt (sodium chloride), as indicated under each bar in Figures 8A-
8D (units are
. mM). The active agent was mixed into the suspension to give a final
concentration of 5
mg/mL FDKP microparticles and 0.75 mg/mL insulin (an excess; Figure BA). After
a brief
incubation, unbound active agent was removed by filtration and the particles
with adsorbed
active agent were redissolved. The amount of active agent and particle
recovered was
quantitated by HPLC, and expressed as a mass ratio (% loading). Figures 8A-8D
illustrate
that increasing ionic strength in a active agent-FDKP microparticle system
reduced the
extent of adsorption of active agents including anti-SSX-241.49 monoclonal
antibody (0.2
mg/mL; Figure 8B), ghrelin (0.1 mg/mL; Figure 8C) and PTH (0.25 mg/mL; Figure
8D) in the
presence of 5 mg/mL FDKP microparticles.
[0083] Figure 8 shows an inverse correlation between the measured
adsorption and
the salt concentration in the loading suspension. This can be interpreted as
evidence that
the salt competed with the active agent for interaction with the particle
surface. As the salt
concentration was increased, it competed strongly and effectively for surface
binding sites,
and essentially displaced the active agent from the particle surfaces. It is
also speculated,
that decrease binding of the active agent to microparticle may be attributable
to Debye
shielding.
[0084] Unless otherwise indicated, all numbers expressing quantities of
ingredients,
properties such as molecular weight, reaction conditions, and so forth used in
the
specification and claims are to be understood as being modified in all
instances by the term
"about." Accordingly, unless indicated to the contrary, the numerical
parameters set forth in
the following specification and attached claims are approximations that may
vary depending
upon the desired properties sought to be obtained by the present invention. At
the very
least, and not as an attempt to limit the application of the doctrine of
equivalents to the scope
of the claims, each numerical parameter should at least be construed in light
of the number
of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding
that the numerical ranges and parameters setting forth the broad scope of the
invention are
approximations, the numerical values set forth in the specific examples are
reported as
precisely as possible. Any numerical value, however, inherently contains
certain errors
necessarily resulting from the standard deviation found in their respective
testing
measurements.
[0085] The terms "a'' and "an" and "the" and similar referents used in
the context of
describing the invention (especially in the context of the following claims)
are to be construed
CA 02818900 2013-06-12
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=
to cover both the singular and the plural, unless otherwise indicated herein
or clearly
contradicted by context. Recitation of ranges of values herein is merely
intended to serve as
a shorthand method of referring individually to each separate value falling
within the range.
Unless otherwise indicated herein, each individual value is incorporated into
the specification
as if it were individually recited herein. All methods described herein can be
performed in
any, suitable order unless otherwise indicated herein or otherwise clearly
contradicted by
context. The use of any and all examples, or exemplary language (e.g. "such
ad') provided
herein is intended merely to better illuminate the invention and does not pose
a limitation on
the scope of the invention otherwise claimed. No language in the specification
should be
construed as indicating any non-claimed element essential to the practice of
the invention.
[0086] The use of the term "or" in the claims is used to mean "and/or"
unless explicitly
indicated to refer to alternatives only or the alternatives are mutually
exclusive, although the
disclosure supports a definition that refers to only alternatives and
"and/or."
[0087] Groupings of alternative elements or embodiments of the
invention disclosed
herein are not to be 'construed as limitations. Each group member may be
referred to
individually or in any combination with . other members of the group or other
elements found herein. One or more members of a group may be
included in, or deleted from, a group for reasens.of convenience and/or
patentability.
[0088] Preferred embodiments of this invention are described herein,,
including the best
mode known to the inventors for carrying out the invention. Of course,
variations on those
preferred embodiments will become apparent ,to those of ordinary skill in the
art upon
reading the foregoing description. The inventor expects skilled artisans to
employ such
variations as appropriate.
[0089] Furthermore, numerous references have been Made to patents and
printed
publications throughout this specification.
21
CA 02818900 2013-06-12
51432-39D1
[0090]
Further, it is to be understood that the embodiments of the invention
disclosed
herein are illustrative of the principles of the present invention. Other
modifications that may
be employed are within the scope of the invention. Thus, by way of example,
but not of
limitation, alternative configurations of the present invention may be
utilized in accordance
with the teachings herein.
=
22
