Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND COMPOSITIONS
USING BUTYRATE ESTERS OF THREITOL
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the use of
butyrate esters of threitol, alone or in combination with
other agents, in pharmaceutical compositions and methods
for increasing fetal hemoglobin and gamma globin in a
patient. These methods are particularly useful in
treating ~-hemoglobinopathies, such as sickle cell
syndromes and ~-thalassemia syndromes. Compositions
comprising butyrate esters of threitol, alone or in
combination with antiproliferative and differentiating
agents are also useful in methods for inducing cell-
differentiation in malignant cells. These methods are
useful in treating cancer, particularly the tetrabutyrate
ester.
BACKGROUND OF THE INVENTION
~-hemoglobinopathies are a group of inherited
~ disorders of ~-globin biosynthesis. Although efforts
have concentrated on a variety of therapeutic regimens,
feasible clinical treatments for these debilitating
diseases remain scarce.
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Various therapies have been utilized in the
treatment of ~-hemoglobinopathies, each accompanied by
drawbacks [G.P. Rogers et al., "Current and Future
Strategies for the Managements of Hemoglobinopathies and
Thalassemia", Hematology 1994, Education Program American
Society of Hematology, pp. 9-20 (1994)]. Although
hydroxyurea stimulates fetal hemoglobin production and
reduc~s sickling crisis in sickle cell ane~a p~tients,
its use is potentially limited by myelotoxicity and the
risk of carcinogenesis. Potential long term
carcinogenicity is also a drawback of 5-azacytidine-based
therapies. Red blood cell transfusions expose patients
to the potential of a wide range of infectious viral
agents, allo;~ml~nization and iron overload. Bone marrow
transplants are not a readily available option for a
large number of patients. Erythropoietin-based therapies
have not proved consistent among a range of patient
populations. Such varying drawbacks contraindicate the
long term use of such agents or therapies.
It is clear from multicenter studies involving
numerous patients with sickle cell disease that increased
blood levels of fetal hemoglobin are associated with
lower events of sickle cell crisis and longer survival
time [Platt et al., "Pain in Sickle Cell Disease, New
Eng. J. Med., 325, pp. 11-16 (1991); Platt et al.,
"Mortality ion Sickle Cell Disease", New Eng. J. Med.,
330, pp. 1639-44 (1994)~. Accordingly., in an effort to
avoid the disadvantages of conventional therapies for ~-
hemoglobinopathies, therapies have centered around ways
to increase fetal hemoglobin production. Recent clinical
trials have focused on the use of butyrate analogs,
including arginine butyrate and isobutyramide, to
stimulate fetal hemoglobin production as a means of
'12
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treatment [S. Perrine et al., "A Short Term Trial of
Butyrate to Stimulate Fetal-Globin-Gene Expression in the
~-globin Disorders", N. Eng. J. Med., 328, pp. 81-86
(1993); S.P. Perrine et al., "Isobutyramide, an Orally
Bioavailable Butyrate Analogue, Stimulates Fetal Globin
Gene Expression in vitro and in vivo," British J.
Haematology, 88, pp. 555-61 (1994); A.F. Collins et al.,
"Or~l Sodi~m Phenyl~utyrate Therapy in Homo2ygous 8-
Thalassemia: A Clinical Trial", Blood, 85, pp. 43-49
(1995)]. Clinical trials have also employed sodium
phenylbutyrate as a hemoglobin switching agent for 8-
thalassemia [Collins et al., supra].
Following the observation that butyric acid
induces cell differentiation in vitro [A. Leder and P.
Leder, "Butyric Acid, a Potent Inducer of Erythroid
Differentiation in Cultured Erythroleukemic Cells", Cell,
5, pp. 319-22 (1975)], that compound was found to
demonstrate promising effects in leukemia patients, by
inducing cell differentiation [A. Novogrodsky et al.,
"Effect of Polar Organic Compounds on Leukemic Cells",
Cancer, 51, pp. 9-14 (1983)]. Aside from their use in
treating ~-hemoglobinopathies, butyrate derivatives such
as arginine butyrate, an arginine salt of butyric acid,
have been shown to exert anti-tumor and anti-leukemia
effects in mice [C. Chany and I. Cerutti, "Antitumor
Effect Of Arginine Butyrate in Conjunction with
Corynebacterium Parvum and Interferon", Int. J. Cancer,
30, pp. 489-93 (1982); M. Otaka et al., "Antibody-
Mediated Targeting of Differentiation Inducers To Tumor
Cells: Inhibition of Colonic Cancer Cell Growth in vitro
and in vivo", Biochem. Biophys. Res. Commun.,158, pp.
202-08 (1989)].
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Butyrate salts induce differentiation of colon
cancer cell lines and arrest the growth of neoplastic
colonocytes tO. C. Velazquez, H. M. Lederer, and J. L.
Rombeau, "Butyrate and the Colonocyte. Implications for
Neoplasia", Dig. Dis. Sci., 41, pp.727-39 (1996)].
Sodium butyrate has been shown to induce apoptosis in
colorectal carcinoma cell lines [A. Hague, D. J. Elder,
D. J. Hicks, and C. Paraskeva, "Apoptosis in Colorectal
Tumour Cells: Induction by the Short Chain Fatty Acids
Butyrate, Propionate And Acetate and by the Bile Salt
Deoxycholate", Int. J. Cancer, 60, pp.400-6 (1995)].
Although butyrate salts have the advantage of
low toxicity as compared with conventional
chemotherapeutic agents, their short half-lives in vivo
have been viewed as a potential obstacle in clinical
settings [A. Miller et al., "Clinical Pharmacology of
Sodium Butyrate in Patients with Acute Leukemia", Eur. J.
Clin. Oncol., 23, pp. 1283-87 ~1987); Novogrodsky et al.,
supra]. The rapid clearance of these agents results in
an inability to deliver and maintain high plasma levels
of butyrate and necessitates administration by
intravenous infusion. Another potential obstacle to the
use of butyrate salts is salt overload and its
physiological sequelae.
In view of these observations, various prodrugs
of butyric acid have been proposed for use in 8-
hemoglobinopathy and leukemia differentiation therapies.
Such prodrugs include tributyrin and n-butyric acid mono-
and polyesters derived from monosaccharides [Z. Chen and
T. Breitman, "Tributyrin: A Prodrug of Butyric Acid for
Potential Clinical Application in Differentiation
Therapy", Cancer Res., 54, pp. 3494-99 (1994); H. Newmark
et al., "Butyrate as a Differentiating Agent:
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Pharmacokinetics, Analogues and Current Status", Cancer
Letts., 78, pp. 1-5 (1994); P. Pouillart et al.,
"Pharmacokinetic Studies of N-Butyric Acid Mono- and
Polyesters Derived From Monosaccharides", J. Pharm.
Sci., 81, pp. 241-44 (1992)]. Such prodrugs have not
proved useful as therapeutics, however, due to factors
such as low bioavailability, lack of effective oral
deliverability, short half life, low CmaX or high
pharmacokinetic variability. Other prodrugs, such as AN9
and AN-10, elicit metabolites that may produce
formaldehyde in vivo, which may lead to toxic effects in
patients.
To date, conventional methods and therapeutic
agents have not proved to be safe and effective for all
patients in the long term treatment of ~-
hemoglobinopathies. This is also the case for diseases
characterized by neoplastic, tumorigenic or malignant
cell growth, or malignant hematological disorders.
Accordingly, the need exists for alternatives having
advantages over, and avoiding the disadvantages of, such
conventional methods and agents, while providing
effective therapy for those target diseases.
DISCLOSURE OF THE INVENTION
The present invention solves these problems by
providing methods and compositions utilizing butyrate
esters of threitol for increasing fetal hemoglobin and
gamma globin production in a patient. These butyrate
esters demonstrate good bioavailability, effective oral
deliverability, good half-life, good Cmax and surprisingly
low pharmacokinetic variability between individual
patients. This last factor increases their utility as
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agents to deliver therapeutically effective amounts of
systemic butyrate.
The compositions and methods of the invention
are especially useful for treating or reducing the
advancement, severity, symptoms or effects of ~-
hemoglobinopathies, including sickle cell syndromes and
~-thalassemia syndromes. In addition, the methods and
~om~osit Gns accordins to the present inventior. are
useful for stimulating cell differentiation in malignant
cells. Such compositions and methods are useful for
treating cancer.
Accordingly, the methods and compositions of
this invention are not beset by the variety of side
effects which typically characterize conventional therapy
regimens.
DETAILED DESCRIPTION OF THE INVENTION
In order that the invention herein described
may be more fully understood, the following detailed
description is set forth.
According to one embodiment, this invention
provides pharmaceutical compositions comprising a
butyrate ester of threitol represented by the formula:
OR
RO ~ OR
O
~~ .
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wherein R is or hydrogen, provided that at
o
least one R is ~ ; and the stereochemistry at
the chiral carbons is independently
selected from R or S and a phArm~ceutically acceptable
o
carrier or adjuvant. Preferably each R is
More preferably, the pharmaceutical
compositions of this invention comprise an approximately
equimolar mixture of (R) and (S) configurations
represented by the following Fischer projections:
O o
OC ( CH2 ) 2CH3 OC ( CH2 ) 2CH3
O O
CH3(CH2)2CO - OC(CH2)2CH
O O
OC(CH2)2CH3 CH3(CH2)2CO
O O
OC (CH2) 2CH3 --OC (cH2) 2CH3
The tetrabutyrate esters of threitol and the
partially esterified analogs of threitol useful in the
methods and compositions of the present invention may be
synthesized by conventional techniques. Advantageously,
these compounds are conveniently synthesized from
commercially available starting materials. For example,
they may be prepared from the D-, L- or D,L-forms of
threitol using an appropriate activated reagent, such as
an activated butyric acid derivative, in conventional
c esterification techniques. For instance, reaction with
an activated carboxylate, such as an acyl halide (e.g.,
acid fluorides, acid chlorides, and acid bromides), an
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acyl cyamide of acyl imidazolide, an activated ester such
as nitrophenyl ester or 1-hydroxysuccinimide (HOSU)
ester, an anhydride such as the symmetrical anhydride or
isobutyl mixed carbonic anhydride, or mixed carbonic-
phosphoric or carbonic-phosphonic anhydrides with an
appropriate alcohol, will yield the corresponding ester.
Other methods of forming esters from alcohols
and carboxylic acids or their derivatives are also well
known to those of skill in the art. These include
removal of water by Dean-Stark distillation, Fischer
esterification and transesterification. Various
catalysts and additives, including protic and/or Lewis
acids, bases or zeolites may be used to increase the ease
or efficiency of these reactions. Enzymatic methods to
form esters are also well known in the art.
Specific modifications of these methods, as
well as other means of forming esters are known by those
of skill in the art. It will be readily recognized that
in order to facilitate specific reactions, the protection
of one or more potentially reactive groups followed by
subsequent removal of that group may be required. Such
modifications are within the skill of the art.
In any synthesis method, the desired compound
may be isolated by any technique, including, for example,
distillation, chromatographic techniques, such as normal
phase, reverse phase, ion-exchange, affinity, or gel
permeation, as well as extraction, crystallization, or
other means. The relative ease of synthesis of the
compounds of this invention represents an advantage in
their large scale production.
It should also be understood that the butyrate
esters of threitol used in the compositions of this
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invention may be modified by appending appropriate
functionalities to enhance selective biological
properties. Such modifications are well recognized in
the art and include sustenance of plasma and/or whole
blood butyrate concentration, increased oral
availability, altered metabolism and altered rate of
excretion of butyric acid or butyric acid prodrugs.
The ph~rm~ceutical compositions of this
invention are characterized by the presence of a butyrate
ester of threitol in an amount effective to increase the
production of fetal hemoglobin or stimulate cell
differentiation in a patient and a pharmaceutically
acceptable carrier or adjuvant. More specifically, these
compositions are designed to treat a patient suffering
from a ~-hemoglobinopathy or a malignant disease. The
term "malignant disease", as used herein denotes a
condition characterized by neoplastic, tumorigenic or
malignant cell growth, or a hematological disorder.
An amount effective to increase the production
fetal hemoglobin or stimulate cell differentiation in a
patient will depend, of course, on the particular disease
to be treated, the severity of the disease, the physical
condition of the patient and the judgment of the treating
physician. Preferably, the prodrug of Formula I will be
present in an amount capable of producing a plasma
butyric acid concentration of between about 0.03 mM and
3.0 mM within 8 hours of administration. More
preferably, the prodrug of formula I is present in an
amount that produces a plasma butyric acid concentration
of between about 0.1 mM and 1.O mM within 6 hours of
administration. Most preferably, the prodrug in the
composition is present in an amount that produces a
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plasma butyric acid concentration of between about 0.1 mM
and 1.O mM within 2 hours of administration and the
concentration r~m~; ns at those levels for at least 2
hours. Dosages of between 25 mg/kg and 3000 mg/kg body
weight of butyrate ester of threitol administered one or
more time per day will produce the desired serum butyrate
concentration. Preferably, the patient will be
administered the prodrug between 1 and 4 times per day.
In a preferred embodiment, these compositions
additionally comprise a conventional agent used in the
treatment of ~-hemoglobinopathies. The conventionaL
agent may be present in the same amount or less than that
normally required to treat ~-hemoglobinopathies in a
monotherapy. The normal dosages of these conventional
agents are well known in the art. Such agents include
hydroxyurea, clotrimazole, isobutyramide, erythropoietin
and salts of short-chain fatty acids, such as
phenylacetic acid, phenylbutyric acid and valproic acid.
According to an alternate preferred embodiment,
the compositions comprise a butyrate ester of threitol
and a conventional agent used in the treatment of
diseases characterized by neoplastic, tumorigenic or
malignant cell growth, or a hematological disorder in a
patient. This additional agent may be present in an
amount equal to or less than that normally required to
treat such diseases in a monotherapy. The normal dosages
of these conventional agents are well known in the art.
Such agents include, erythropoietin, or cancer
chemotherapeutic agents, such as hydroxyurea or 5-
azacytidine.
The carriers and adjuvants useful in thepharmaceutical compositions of this invention include,
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for example, ion exchangers, alumina, aluminum stearate,
lecithin, serum proteins, such as human serum albumin,
buffer substances, such as phosphates, glycine, sorbic
acid, potassium sorbate, partial glyceride mixtures of
saturated vegetable fatty acids, water, salts or
electrolytes such as prolamine sulfate, disodium hydrogen
phosphate, sodium chloride, zinc salts, colloidal silica,
magnesium, trisilicate, polyvinyl pyrrolidone, cellulose-
based substances and polyethylene glycol. Adjuvants for
topical or gel base forms may be selected from the group
consisting of sodium carboxymethylcellulose,
polyacrylates, polyoxyethylene-polyoxypropylene-block
polymers, polyethylene glycol and wood wax alcohols.
The compositions of the present invention may
be in a variety of conventional depot forms. These
include, for example, solid, semi-solid and liquid dosage
forms, such as tablets, pills, powders, liquid solutions
or suspensions, emulsions, oil dilutions, liposomes,
capsules, suppositories, injectable and infusible
solutions. The preferred form depends upon the intended
mode of administration and therapeutic application.
For example, oral administration may be by any
orally acceptable dosage form including, but not limited
to, capsules, tablets, and aqueous or non-aqueous
suspensions and solutions. In the case of tablets for
oral use, carriers which are commonly used include
lactose and corn starch. Lubricating agents, such as
magnesium stearate, are also typically added. For oral
administration in a hard gelatin capsule form, useful
diluents include lactose and dried corn starch. Soft
gelatin capsules incorporating oils and/or polyethylene
glycols as excipients may also be used. Fluid unit
dosage forms for oral administration include shakes,
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syrups and suspensions. For example, the butyrate ester
of threitol may be dissolved in an aqueous vehicle
together with sugar, sweetening or flavoring agents and
preservatives to form a shake or a syrup. Suspensions
may be prepared with an aqueous vehicle and a dispersing
agent, such as acacia, tragacanth or methylcellulose.
Preferably, the pharmaceutical compositions of
this invention are formulated for oral or rectal
administration. A preferred form of oral administration
employs emulsions comprising between about 5 to 40% (w/w)
of the prodrug of formula I and an ionic or non-ionic
surfactant with the resulting composition having an HLB
value of between 0-40. Preferred surfactants include
Tween-20, Tween-80, Spam20, Spam-40 and poloxamers, such
as S-108.
A preferred form of rectal administration uses
a rectal suppository or an enema using a suitable fluid
dosage form. An enema is a more preferred form of rectal
administration.
The butyrate esters of threitol which
characterize the compositions of this invention are
characterized by several advantages. They are
metabolized to yield therapeutic butyric acid plasma
concentrations over a sustained period of time, resulting
in therapeutically effective exposure to butyric acid.
Additionally, they are orally bioavailable, unlike sodium
butyrate -- which is rapidly cleared before therapeutic
plasma concentration levels can be reached. They are
also non-toxic, thus avoiding, for example, sodium
overload and irritation which may be associated with
injections of hyperosmolalic solutions.
The most surprising and unexpected feature of
the butyrate esters of threitol that characterize the
-
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pharmaceutical compositions of this invention is that
they exhibit significantly lower pharmacokinetic
variability over conventional prodrugs of butyric acid.
Pharmacokinetic variability is the measure of differences
in the serum butyrate concentrations between different
patients administered the same amount of butyrate esters
of threitol. Pharmacokinetic variability is quantified
by dividing the stAn~rd deviation for a ~iven parameter,
such as Cmax or AUC, by the mean value of that parameter,
in a series of patients given dose the same dosage of
butyrate ester of threitol.
In particular, the tetrabutyrate ester of
mesothreitol is characterized by a pharmacokinetic
variability of 35-40~, as compared with conventional
prodrugs of butyric acid, such as tributyrin, which has a
pharmacokinetic variability of 70%. This reduced
variability means that the compositions of this invention
provide sustained release and produce more consistent
plasma concentrations of butyric acid among individual
patients. This, in turn, m;n;m; zes the potential for
cellular toxicity, which, based on our own in vitro cell
culture studies, has been observed at butyric acid
concentrations above 3.0 mM under certain in vitro
conditions.
According to another e-m-bodiment~ the invention
provides methods for treating a ~-hemoglobinopathy in a
patient. This method comprises the step of treating the
patient with any of the compositions described above.
The term "treating", as used herein includes reducing the
severity, symptoms or effects of the ~-hemoglobinopathy.
Preferably, the method provides a serum butyric acid
concentration of between about 0.03 mM and 3.0 mM within
about 8 hours of administration. More preferably, this
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produces a plasma butyric acid concentration of between
about 0.1 mM and 1.0 mM within about 6 hours of
administration. Most preferably, the prodrug in the
composition is present in an amount that produces a
plasma butyric acid concentration of between about 0.1 mM
and 1.0 mM within 2 hours of administration and the
concentration r~m~; nS within that range for at least 2
hours. These plasma levels are achieved by administering
a butyrate ester of threitol to the patient at a dose of
between about 25-3000 mg/kg body weight one or more times
per day. Preferably, the patient will be administered
the prodrug between 1 and 4 times per day.
The ~-hemoglobinopathies which may be treated
by this method include sickle cell syndromes, such as
sickle cell anemia, hemoglobin SC disease, hemoglobin SS
disease and sickle ~-thalassemia; ~-thalassemia
syndromes, such as ~-thalassemia; other genetic mutations
of the ~-globin gene locus that lead to unstable
hemoglobins, such as congenital Heinz body anemia, ~-
globin mutants with abnormal oxygen affinity and
structural mutants of ~-globin that result in thalassemic
phenotype. These diseases are described in The Molecular
Basis of Blood Disease, vol. II, G. Stamatoyannopoulos et
al., eds., pp. 157-244 (1994).
According to a preferred embodiment, the above-
described method comprises the additional step of
treating the patient with an agent that is normally used
to such ~-hemoglobinopathies. That agent may be
administered prior to, se~uentially with or after
treatment with the butyrate prodrug-cont~in;ng
composition. Of course, if the composition used to treat
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the disease is one that already contains such
conventional agent, this additional step can be omitted.
The amount of conventional agent administered
in these methods is preferably less than that normally
required to treat such diseases in a monotherapy. The
normal dosages of these conventional agents are well
known in the art. Such agents include hydroxyurea,
clotrimazole, isobutyramide, erythropoietin and salts of
short-chain fatty acids, such as phenylacetic acid,
phenylbutyric acid and valproic acid.
According to another embodiment, the invention
provides a method for treating diseases characterized by
neoplastic, tumorigenic or malignant cell growth, as well
as malignant hematological disorders. Treatment includes
prevention of the progression the disease or its
recurrence. Such diseases include carcinomas, myelomas,
mel~nsm~s, lymphomas and leukemias. According to a
preferred embodiment, the present invention provides a
method for treating colo-rectal cancer and prostate
cancer. According to a more preferred embodiment, the
method of the present invention is used to treat colo-
rectal cancer and prostate cancer using a formulation
suitable for oral or rectal administration.
According to another preferred embodiment, the
method of the present invention is used to treat prostate
cancer using a formulation suitable for oral or rectal
administration.
According to a preferred embodiment, the above-
described method comprises the additional step of
treating the patient with an agent that is normally used
to such malignancies. That agent may be administered
prior to, sequentially with or after treatment with the
butyrate prodrug-containing composition. Of course, if
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the composition used to treat the disease is one that
already contains such conventional agent, this additional
step can be omitted.
The amount of conventional agent administered
in these methods is preferably less than that normally
required to treat such diseases in a monotherapy. In
those instances, the occurrence of any side effects
associated with that agent may be reduced or avoided.
The normal dosages of these conventional agents are well
known in the art. Such agents include, erythropoietin,
or cancer chemotherapeutic agents, such as hydroxyurea or
5-azacytidine.
Combination therapies with conventional agents
according to this invention (whether part of a single
composition or administered separate from the prodrugs of
this invention) may also exert an additive or synergistic
effect, particularly when each component acts to treat or
prevent the target disease via a different mechanism.
In order that the invention described herein
may be more fully understood, the following examples are
set forth. It should be understood that these examples
are set forth for illustrative purposes only and are not
to be construed as limiting this invention in any manner.
EXAMPLE 1
Synthesis of d-, l- and
d,l-Threitol Tetrabutyrate Esters
We synthesized d-threitol tetrabutyrate ester
as follows. We added 17 ml of Et3N to 3.0 g of D-threitol
dissolved in CH2Cl2 and cooled the mixture to O~C. We
then added 11 ml of CH3(CH2)2COCl in 5 ml CH2Cl2 over 30
minutes. The reaction mixture was stirred at room
temperature overnight. We then diluted the reaction with
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ether and filtered the resulting material. The
precipitate was washed once over a filter with ether.
The filtrates were combined, washed twice with water,
once with saturated NaCl and dried over MgSO4, filtered
and concentrated.
The resulting yellow oil was run on an MPLC
column in 90:10 (hexane:EtOAc). The yield of purified
product was 8.35g of a light yellow oil.
We synthesized d-, 1-threitol tetrabutyrate
ester using the same methodology replacing D-threitol
with D,L-threitol using the same ratio of equivalents
(1:5:4.5i threitol:Et3N:CH3(CH2)2COCl).
The structure of the purified compounds was
confirmed by NMR.
EXAMPLE 2
Oral Availability of Butyrate
Esters of Threitol in Rats
We evaluated oral bioavailability and
sustenance of plasma concentrations of butyric acid in
rats receiving tetrabutyrate esters of threitol and
tributyrin by oral gavage.
This assay was carried out according to the
protocol described in Daniel et al., Clinica Chimica
A ., 181, pp. 255-64 (1989); Planchon et al., J. Pharm.
Sci., 82, pp. 1046-48 (1993); Pouillart et al., J. Pharm.
Sci., 81, pp. 241-44 (1992). Each compound was tested in
five to six rats (Sprague Dawley; Harlan Labs, Inc.)
weighing approximately 300 grams each. The relevant
pharmacokinetic parameters for these agents are listed in
the table below. In that table, data are expressed as
mean + standard deviation (range) and were compared using
the unpaired Student's t-test.
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Table 1. Pharmacokinetics of butyrate esters of threitol in
rats
Dose Nu Tber of AUC C~ Plasma tu2
Compound (arrl/kg) animals (mM.hr) (mM) (mins)
~butyrin 3.0 6 1.59iO.930.51iO.46157.2i70.2
-threitol tetr~bubrate 2.4 5 1.20iO.400.58iO.1366.0~12.0
~6~
d-threitol tetra-butyrate2.8 6 0.~26 0.47iO.1458.8~19.8
ester
dl-threitol tetra-butyrate 3.0 5 1.25~0.220.39iO.12 106~+~
ester
' Si~nificanUy differentfrom l-threitol tetrabutyrate ester and d-threitol tetrabutyrate ester (p<0.01).
As shown above, the tetrabutyrate esters of
threitol were found to release butyric acid in vivo with
lower variability than tributyrin. oral administration of
each of those prodrugs of butyric acid also increased the
"apparent" plasma half-life of butyric acid to
significantly longer than the 6 minutes observed in
leukemia patients after continuous infusions of sodium
butyrate [Miller et al., supra]. The area under the
plasma concentration-time curve and the observed Cmax
15 values for butyric acid were not significantly different
for any of the tetrabutyrate esters or tributyrin
(following dose-normalization). Advantageously and
unexpectedly, the butyrate ester of D,L-threitol was
found to have an "apparent" butyric acid plasma half-life
which was significantly longer than that observed for the
tetrabutyrate ester of either D-threitol or L-threitol.
A closer ~x~m;n~tion of the data showed that
the release of butyric acid from tributyrin was more
variable when compared to that obtained following oral
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administration of the tetrabutyrate ester of D,L-
threitol. The pharmacokinetic variability with
tributyrin oral administration is demonstrated by the
wide range of C~x (0.295 to 1.46 mM) ; AUC (0.72 to 3.23
mM.hr); and plasma half-life (67.2 to 259.8 minutes). on
the other hand, the ranges for Cm~x AUC and plasma half-
life for orally administered tetrabutyrate ester of D,L-
threitol were 0.26 to 0.545 mM, 0.95 to 1.53 mm.hr and
79.2 to 126.9 minutes, respectively. Thus, both
tributyrin and the tetrabutyrate ester of D,L-threitol
are orally bioavailable to provide therapeutic plasma
levels of butyric acid. However, a clear advantage of
that tetrabutyrate ester is its reduced pharmacokinetic
variability -- signifying a consistent pharmacokinetic
profile which, in turn, enables more reliable clinical
treatment regimens than those based on tributyrin.
While we have hereinbefore described a number
of embodiments of this invention, it is apparent that our
basic constructions can be altered to provide other
embodiments which utilize the processes and compositions
of this invention. Therefore, it will be appreciated
that the scope of this invention is to be defined by the
claims appended hereto rather than by the specific
embodiments which have been presented hereinbefore by way
of example.
