Note: Descriptions are shown in the official language in which they were submitted.
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USE OF CATIONIC DEXTRAN DERIVATIVES FOR PROTECTING
DOSE-LIMITING ORGANS
The Field of the Invention
The present invention is related to the use of cationic dextran derivatives
for protecting
dose-limiting organs especially, kidneys during systemic treatment of cancer
or other
diseases. Also disclosed is a method for protecting dose-limiting organs in
patients
subjected to systemic therapy by administrating cationic dextran derivatives.
The cationic
dextran derivatives not only protect the dose-limiting organs, but are better
tolerated and
have less side effects than conventionally used protective agents.
The Background of the Invention
Systemic therapy refers to the intravenous infusion of therapeutic drugs.
Drugs in this
context can be cytostatic pharmaceuticals, compounds carrying cytostatic
pharmaceuticals,
antibiotics, radionuclides or compounds carrying radionuclides. These drugs,
including
other therapeutically active chemicals are known to have substantial side
effects on certain
vital organs including kidneys. The intensity of the systemic treatment, i.e.
the infused
dose and its frequency, is limited by said dose-limiting organs. Two important
dose-limiting organs are kidneys and bone marrow. This means that for each
drug or drug
combination there is a maximum dose that these organs can tolerate. Above this
dose
maximum the organs are seriously and permanently damaged by side effects
caused by the
drug. This restricts the drug dose that can be used and the frequency of its
administration.
If the dose can be increased without damaging the organs, the probability of
successful
treatment increases.
Currently, there are few drugs available for protecting dose-limiting organs
during
systemic therapy. Some protective agents are described in the patent US
5,290,538, which
discloses the use of nephroprotective infusion solutions containing soluble L-
amino acids,
which are administered intravenously to patients to protect their kidneys from
nephrotoxic
agents. The patent application DE 34 14 491 discloses a mixture of L-amino
acids,
which is developed for this purpose. However, said amino acid mixtures may
have
detrimental effects on the kidney, by inducing acute renal failure or
potentiating a
preexisting acute renal failure. The commonly known amino acid mixtures are
not suitable
for kidney protection against the toxic effects of cytostatic and
immunosuppressive agents.
The patent publications US 5,087,441, US 5,010,092 and EP 0 434 470 disclose
the use
of methimazole or carbimazole for reducing nephrotoxicity due to antibiotics,
radiological
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contrast media, metal or metal compounds as well as environmental toxins. To
achieve
the desired kidney protection, large amounts i. e. gram quantities of kidney
protective
agents are required. Such large doses are known to be connected with
pronounced and
sometimes serious side effects, e. g. nausea and vomiting, including grade I
and II
gastrointestinal toxicity, and sometimes disturbance of electrolyte balance
affecting heart
function. Consequently, there is a need for new methods and more effective
agents with
less side effects for protecting dose-limiting organs, including kidneys. The
objective of
the present invention is to provide novel alternative agents having
significant less side
effects for manufacturing medicines effectively protecting dose-limiting
organs, especially
kidneys.
The Summary of the Invention
The objectives of the present invention are achieved by employing cationic
dextran
derivatives that is dextran substituted with positively charged substitutents,
particularly
amino acid residues from a group consisting of lysine, arginine, histidine,
ornithine and
mixtures thereof.
The present invention provides the use of such cationic dextran derivatives
for
manufacturing medical compositions, including infusion solutions and
injectable
formulations for the protection of dose-limiting organs particularly kidneys
during
systemic therapy in treatment of cancer as well as other diseases. The
cationic dextran
derivatives not only protect the dose-limiting organs, but are better
tolerated and have
minimal side effects compared to conventional protective agents.
The present invention provides cationic dextran derivatives for manufacturing
medical
compositions for protecting dose-limiting organs, such as kidneys and bone
marrow
during systemic therapy of certain diseases, particularly cancer. The cationic
dextran
derivatives comprise dextran the sugar monomers of which are substituted with
substituents having positively charged cationic side groups, preferably amino
groups. The
dextran moiety has a molecular weight of 50 kDa or less, preferably a
molecular weight
between 10-50 kD, more preferably 20-40 kD. The positively charged cationic
side
groups are selected from a group consisting of the positively charged amino
acids such
as lysine, arginine, histidine, ornithine and mixtures thereof. A particularly
useful
substituent is lysine. A substantially sufficient substitution degree is 0.05 -
25 mol cationic
residues / mol dextran, preferably 0.5 - 20 mol cationic residues / mol
dextran, most
preferably 5 - 10 mol cationic residues / mol dextran. 10-25 mol cationic
substituents / mol dextran being a particularly suitable range.
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The present invention provides a method for protecting a subject from damages
in
dose-limiting organs caused by effects of radioactive or cytotoxic agents
during
systemic treatment. The method comprises the administration of an effective
amount of a
cationic dextran derivative that is dextran provided with substituents having
positively
charged cationic side groups, to a subject in association with or before the
administration
of a chemotherapeutic, radioactive or immunosuppressive agent. The present
invention
particularly provides a method of protecting a subject from renal damage
caused by
nephrotoxic effects of radioactive or cytotoxic agents during systemic
treatment of cancer.
Said method comprises the administration of a kidney protecting amount of a
cationic
dextran derivative provided with a substituent having positively charged
cationic side
groups to the subject in association with or before the administration of a
chemotherapeutic, radioactive or immunosuppressive agent. In the method of the
present
invention the cationic dextran derivative is provided in an intravenously
administrable
dosage form or they are intravenously co-administrated or co-infused with the
drugs used
in the systemic therapy.
Brief description of the drawings
Figure 1A depicts whole body images showing the anterior (front) and exterior
(back) of a
patient 3 hours after infusion without renal protection.
Figure 1B depicts whole body images showing the anterior (front) and exterior
(back) of a
patient 3 hours after infusion with renal protection.
Figure 2A depicts blood clearance and kidney uptake as demonstrated by a curve
indicating the percentage injected activity in blood as a function of time in
the same
patient without renal protection (basal), with prior art protection (amino
acid) and with
lysine substituted dextran (dextran+Lysine).
Figure 2B depicts blood clearance and kidney uptake as demonstrated by a curve
indicating the percentage injected activity in kidneys as a function of time
in the same
patient without renal protection (basal), with prior art protection (amino
acid) and with
lysine substituted dextran (dextran+Lysine).
The Detailed Description of the Invention
Definitions
In the present invention the terms used have the meaning they generally have
in the fields
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of biochemistry, radiology, physiology and pharmacology, but some terms are
used with a
somewhat deviating or broader meaning than in the normal context. Accordingly,
in order
to avoid uncertainty caused by terms with unclear meaning some of the terms
used in the
specification and in the claims are defined in more detail below.
The term "systemic therapy" means the medication including cytostatic agents,
radioactive substances and/or immunosuppressants pertaining to or affecting
the body as a
whole e. g. via blood circulatory system. Systemic therapy in cancer treatment
refers to the
intravenous infusion of therapeutic drugs. Drugs in this context can be
cytostatic
pharmaceuticals, compounds carrying cytostatic pharmaceuticals, radionuclides
or
compounds carrying radionuclides. The intensity of the systemic treatment,
i.e. the
infused dose and its frequency, is limited by so called dose-limiting organs.
The term "dose-limiting organs" refers to those organs e.g. the kidneys and
bone marrow
that are seriously and permanently damaged when a systemically administered
drug is
administered above a certain dose. This means that for each drug or drug
combination
there is a maximum dose that these organs can tolerate. This dose limits the
efficacy of the
drug, since a higher dose; which would be useful for treating the cancer or
other disease is
detrimental and not be used because it has toxic side effects on the sensitive
organs.
The term "protection of dose-limiting organs" or specifically "kidney (nephro)
protection" means the protection of the sensitive organ, specifically
protection against
renal damage in a patient receiving systemic cancer therapy with potentially
nephrotoxic
drugs. In the present invention the protection is achieved by infusion of
cationic dextran
derivatives which provides the negatively charged kidney with a layer, which
allows a
smooth and rapid passage of the drug preventing uptake in kidneys, thus
preventing
nephrotoxicity.
The term "dextran" is applied to polysaccharides, i.e. high-molecular-weight
polymers of
D-glucose, produced by glycosyltransferase on the cell surface of certain
lactic acid
bacteria growing on a sucrose substrate. Several organisms produce dextrans,
but only
Leuconostoc mesentroides and L. dextranicum have been used commercially. The
chemical
and physical properties of the dextrans vary with the method of production.
Native
dextrans usually have a high molecular weight; lower molecular weight clinical
dextrans
are usually prepared by depolymerization and subsequent fractionation of the
native
dextrans .
The dextrans used for kidney protection preferably have a molecular weight,
which is
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below the kidney filtration threshold for clinical dextrans, i.e. 50 kD or
less. Dextrans
with a molecular weight above 50 kD are not filtrated through the kidneys. The
molecular
weight of the invention preferably varies between 10-50 kD. The average
molecular
weight being 40 kD. This means that the cationic dextran derivatives for
kidney protection
comprises on average 222 glucose monomers, the mean range being ~50 glucose
monomers.
In the present invention the term "cationic dextran derivatives" means
dextrans having
the structure, properties and functions defined above for "dextrans", but
which dextrans
are substituted with positively charged side groups, such as amino groups,
preferably
amino acid residues. The positively charged groups, which preferably are amino
acid
residues, are selected from a group of amino acids including lysine, arginine,
histidine,
ornithine an mixtures thereof, but also other positively charged substituents
can be used.
Diaminated alkyl chains are examples of other such substituents.
The degree of substitution should be such that the positive charge of the
cationic dextran
derivatives is sufficiently high to be attracted by the negatively charged
kidney, but not so
high that it is permanently attached to the kidney and cannot be removed from
the kidney.
A sufficient substitution degree is 0.05 - 25 mol substituents / mol dextran,
more
preferably 0.5 - 20 mol substituents / mol dextran, most preferably 5 - 10 mol
substituents / mol dextran. An optimal substitution degree is obtained when 10
- 25 mol
substituents / mol dextran are coupled.
In addition to the positively charged substituents, which preferably are the
amino acid
residues listed above, the cationic dextran derivatives of the present
invention can be
chemically substituted forming dextran derivatives including for example,
alkylated,
esterified, etherified or amidized forms with a low substitution degree.
Especially
advantageous are small molecule substituents having aminated methyl or ethyl
groups as
substituents. The substitution should not disturb the protective properties
and functions of
the cationic dextran derivatives.
The General Description of the Invention
When studying patients with somatostatin receptor positive tumors and
investigating the
renal protective efficacy of different agents, it was surprisingly observed
that a cationic
dextran polymer to which lysine was covalently linked, showed a high kidney
protection
capacity and had no side effects.
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Based on this preliminary observation, it was deducted that dextrans
substituted with
cationic side groups, preferably amino acids carrying positively charged side
groups,
particularly lysine-dextran conjugates can be used to protect kidneys when
administering
potentially nephrotoxic drugs. It was demonstrated that the dosage of the drug
could be
increased by 25-30 % because of the effective inhibition of the
nephrotoxicity. This means
that a significantly higher dose of the drug could be used. In fact, said
increased dosage of
drug may provide the additional efficacy necessary for curative treatment of
the disease
e.g. cancer.
Accordingly, the present invention is based on studies, in which it has been
demonstrated
for the first time that infused dextrans, substituted with lysine or another
positively
charged side group, including amino acid residues such as arginine, histidine,
ornithine
and mixtures, covalently linked to the dextran via an amine bond, protect the
kidneys
during systemic therapy more effectively than commonly used nephroprotective
agents,
such as amino acid mixtures and positively charged proteins. Additionally, the
cationic
dextran derivatives show no significant side effects.
The substituted cationic dextran derivative of the present invention comprises
dextrans or
dextran derivatives substituted with residues having positively charged side
groups,
preferably amino acids, which are covalently coupled to the activated hydroxyl
groups of
the glucose monomers in the dextran chains either by ether, ester or amine
bonds.
The substituted cationic dextran derivatives, substituted with aminated alkyl
groups,
lysine, histidine, arginine, ornithine or mixtures thereof, are cationic
polymers having an
overall positive effective charge, whereas kidney is charged negatively
leading to an
effective blocking of the toxic effects of the drugs.
The nephroprotective effect is believed to be obtained by the fact that the
positively
charged cationic dextran derivatives of the present invention are attracted
(attached) to the
negatively charged tissues of kidney and other dose-limiting organs and
thereby allow the
cytotoxic and radioactive agents as well as immunosuppressives to pass the
kidneys thus
preventing uptake of the drug through the proximal tubuli of the kidneys. By
preventing
the uptake by the kidneys of radioactive and/or cytotoxic drugs, higher doses
can be used
thus increasing treatment efficacy.
Since the cationic dextran derivatives are macromolecules they seem to block
the uptake of
drugs more effectively than monomers, such as conventionally used amino acids
or amino
acid mixtures used as such. The positively charged macromolecule, preferably
the cationic
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dextran derivatives blocks the negative charges of the proximal tubules tissue
more
effectively than amino acids per se. Also the time a macromolecule blocks the
drug uptake
in kidneys is longer than that of a monomer. Since a smaller amount can be
used due to
the good binding capacity of the dextran derivatives less, if any side effects
occur.
Intravenous administration of the cationic dextran derivatives of the present
invention to
patients subject to cytostatic treatment counteracts toxic renal damage
resulting from
cytostatic drugs or that resulting from immunosuppressive agents.
The dose of the cationic dextran derivatives of the present invention as well
as the time of
administration is optimized in such a way that the accumulation kinetics in
the tumor and
the elimination of the drug produces an optimal radiation dose relation
between the tumor
and the rest of the organism.
The use of the present invention is preferably aimed at renally healthy
patients who are at
risk of being subjected to renal damage due to systemic treatment of another
ailment with
cytostatic pharmaceuticals, compounds carrying cytostatic pharmaceuticals,
radionuclides
or compounds carrying radionuclides. The composition is specifically directed
to block
toxic effect of said cytostatic pharmaceutical compounds used in systemic
therapy.
It is generally known that the charge of the polydisperse macromolecule is
highly affected
by the media in which the macromolecule of interest is situated. Said media
dependent so
called effective surface charge can deviate remarkably from the theoretical
electric charge
of the molecule based on the amount of dissociated groups. Said deviation is
especially
remarkable in a physiological medium, for example, in a human being, injected
with said
drug.
The evaluation of the effective surface charge is carried out with a multitude
of different
test systems, e.g. measuring of zeta-potentials. According to the generally
accepted
opinion, methods based on electrophoresis give the values, which best describe
the actual
situation. The effective surface charge can be determined exactly with test
system based
on convective electrophoresis.
Synthetic methods described in the dissertations of Anders Holmberg, Dextran
Conjugates
for Tumour Targeting, Synthesis and Characterisation, Comprehensive Summaries
of
Uppsala Dissertations from the Faculty of Medicine 546, ACTA Universitatis
Upsaliensis,
Uppsala, Sweden, 1995 and Jin Du, Derivatives of Dextran Synthesis and
Application in
Oncology, Academic Dissertation from the Faculty of Mathematics and Natural
Sciences
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of the University of Jyvaskyla, Jyvaskyla, Finland (2001) can be used for
preparing the
cationic dextran derivatives of the present invention.
The cationic dextran derivatives of the present invention can be purified with
conventional
methods including chromatography and ultrafiltration.
The cationic dextran derivatives of the present invention comprise less than
20 % (w/w),
preferably 5-15 % (w/w), more preferably 15-20 % (w/w), most preferably 20 %
(w/w)
of substituents or residues, preferably amino acid residues.
Preferably, the charged substituents or residues are bound to 15-30 % of the
glucose
monomers of said dextran.
The compounds according to the invention in the basic form or in combination
with
pharmaceutically acceptable additives, carriers, adjuvants, etc. are valuable
protective
agents for dose-limiting organs and particularly valuable nephroprotective
agents.
The cationic dextran derivatives of the present invention can be provided in
free form or
as salts. Salts include salts formed from acid, e.g. organic acids, polymeric
acids or
inorganic acids, of which hydrochlorides and acetates are examples and forms
of salts,
which are formed from carboxylic groups or sulfonic acids.
The kidney protective efficacy of the cationic dextran derivatives of the
present invention
can be demonstrated in patients with somatostatin receptor positive tumors.
The systemic
therapy can be carried out by administering the cationic dextrans of the
present invention
before or simultaneously with the radioactive drug intravenously or by other
suitable
means of administration. Kidney dose reduction after infusion of the
protective agents can
be evaluated by different means, including Medical Internal Radiation Dose
(MIRD)
formalism, followed by intrapatient analysis.
The invention is demonstrated by the following example, which is provided for
illustrative
purposes and should not be used to limit the scope of invention.
Example 1
Renal protective effects of dextran-lysine (DxL), arginine-lysine (LAL)
mixture and a
standard cationic protein used in hospitals
Fifteen patients (5 patients/group) with somatostatin receptor positive
tumors, which are
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characterized by high-density somatostatin receptors, were studied to
investigate the renal
protective efficacy of three different agents i.e. dextran-lysine (DxL),
arginine-lysine
mixture (LA) and a positively charged protein, i.e. avidine (caP), which is
used as a
standard at Instituto Europeo di Oncologia, Divisione di Midicina Nucleare,
Milano,
Italia. Each patient underwent two dosimetric evaluations within two weeks,
the first
without protective agent and the second with infusion of protective agent (DxL
2 mg/kg,
LA 400 mg/kg and caP 2 mg/kg). In both cases 185 Mbq 111lndotatoc was
administered
intravenously (i.v). Whole body images were acquired at 30 min, 3, 16, 24 and
48 h post
injection. Pharmacokinetics was determined by collecting blood and urine
samples up to
50 h post injection. Kidney dose reduction after infusion of the protective
agents was
evaluated by Medical Internal Radiation Dose (MIRD) formalism with an
intrapatient
analysis.
The mean kidney absorbed dose was reduced ca. 31 t25 % with the conventional
lysine-arginine (LA) mixture, ca. 50~ 13 % with the positively charged protein
(caP) more
than 5024% with dextran-lysine compound (DxL). No relevant differences were
found
in blood clearance with or without Cationic-Dextran. Urinary excretion curves
were
similar, except for a slight faster ( 10 % ) rate within the first few hours
after injection with
a cationic dextran derivative (DxL). Apart from kidney uptake, the
biodistribution in other
organs was not significantly modified. Time-activity curves for kidneys showed
the same
trend with and without protection, but with a lower uptake as demonstrated by
percentage
injected activity ( % IA) at all time points.
Side effects occurred with LA and caP i.e. grade I-II gastrointestinal
toxicity. No side
effects were observed with dxL. In conclusion, dextran-lysine shows high
kidney
protection capacity without side effects.
The results are also shown in Figures 1A-1B and 2A-2B. In Figure 1 whole body
images
in anterior (from the front) and posterior (from the back) views of the same
patient 3 h
after injection are shown. 1A shows images without renal protection and 1B
shows images
with renal protection using dextran-lysine (DxL). Figure 1B shows reduced
doses of
kidney absorption and higher activities in the bladder. In Figure 2 blood
clearance and
kidney uptake without renal protection (basal), with amino acids protection
and with DxL
protection are shown for the same patient.
