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Description  |
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The present invention relates to novel drugs and their use in treating
diseases or disorders. The invention is particularly concerned with the
provision of a special type of drug which is effective in irreversibly
inhibiting the enzyme aldose reductase in the eye and which is, therefore,
useful in treating diabetic cataracts or related eye problems which may be
caused by aldose reductase. However, as will be evident from the
description which follows, the invention is of broader application in
relating to what may be termed "target-entrapped" drugs.
Target-entrapped drugs (hereinafter referred to as "T-E" drugs) constitute,
according to the invention, a new class of drugs whose effectiveness is
potentiated at a specific anatomic site by a variety of techniques, such
as electromagnetic irradiation of that site or treating with any other
energy such as thermal energy, so as to produce a tight or irreversible
drug-receptor bond, e.g. a covalent bond.
In the conventional use of a typical drug, the drug rapidly equilibrates
throughout the body soon after administration, reversibly binds to its
specific receptor site and produces its pharmacological effect. The
effectiveness of such drug increases to a maximum, then falls to zero as
the drug is detoxified and excreted from the system, usually over a period
of hours. In contrast, a T-E drug, according to the invention, differs in
that, after administration, if one appropriately irradiates or otherwise
appropriately energizes a selected specific anatomical target site when
the pharmacological effect of the drug is at a maximum, a tight or
irreversible drug-receptor bond is produced. This prevents detoxification
and excretion of the drug from that specific targeted site and thus
prevents a decrease of pharmacological effect. Upon irradiation, a
reversible drug-receptor interaction is caused to change into a tight or
irreversible drug-receptor interaction. Consequently, the half-life of
effectiveness for a T-E drug is the biological turnover time of the
drug-receptor complex or neosynthesis of the receptor in contrast to that
for a typical conventional drug whose half-life is a function of the rate
of detoxification and excretion of the drug.
The selected target site may be a specific receptor, such as an enzyme, in
a specific organ, such as the kidney. The same receptor may be present in
many organs, but if the target organ alone is irradiated, then the drug
will function for a prolonged period only in that organ thereby
eliminating potential complications and side-effects as a result of
repeated administration of the drug. Since they will generally function by
covalently binding to receptor sites, smaller doses of T-E drugs will be
needed because lesser amounts will serve to achieve and retain therapeutic
levels. In addition, if a drug produces undesirable side-effects at a
therapeutic dose level, several still smaller doses may be administered
over a relatively short time so that a cumulative effective dose will be
attained in the irradiated specific target site area.
The electromagnetic irradiation employed to initiate the covalent coupling
of T-E drug to receptor site can be of any type such as visible light,
ultra-violet light, and X-rays. The anatomic target site can be as large
or small as desired and is limited only by the nature of the
electromagnetic radiation used, the equipment available and the techniques
of irradiation.
A second action of T-E drugs is the formation of soluble-immobilized or
membrane-immobilized drugs. Although a T-E drug may have extremely high
affinity for its receptor site, some of the drug present in the anatomic
target site will not be bound to receptor sites. Upon irradiation, these
molecules of T-E drug will react non-specifically. Some of the T-E drug
will bond to extra- or intra-cellular membrane surfaces; some will bond to
soluble proteins (e.g. a soluble-immobilized drug) in the cytoplasm or
subcellular organelle of cells. This non-specifically bound (e.g.
covalently bound) T-E drug will retain its ability to reversibly bind to
receptor sites and produce its physiological response. In either case,
this drug, too, will be retained in the target area and will be long
acting because it will not diffuse out or be detoxified by normal
detoxification processes. The drug action by the membrane-bound and
soluble-immobilized drug will simply be added to the specific T-E drug
action. The overall contribution of non-specifically bound drug can vary
from insignificant to highly significant.
As will be appreciated from the foregoing, the principal object of the
present invention is to provide a novel drug design concept such that drug
therapy may be directed to a specific anatomical site and retain its
effectiveness over an extended period of time. Another object of the
invention is to provide a T-E drug that will irreversibly bind to a
selected receptor site or sites to give the results and advantages
generally referred to above. A more specific object is to provide a drug
composition which can be used to irreversibly inhibit the enzyme aldose
reductase in a selected target organ, e.g. an eye or eye lens. Another
specific object of the invention is to provide a T-E drug for effectively
dealing with diabetic cataracts and related eye diseases. Other objects,
all based on the concept of providing a T-E drug that will tightly or
irreversibly bind to the drug receptor site in the anatomic target site,
will also be hereinafter apparent.
Broadly stated, the T-E drug of the invention comprises a chemical
combination of three components (1) a therapeutically active component or
drug portion, e.g. an aldose reductase inhibitor segment; (2) a linking
component intended to bind the drug portion to the target site; and (3) a
portion activatable by an energy source such as electromagnetic radiation,
e.g. an azide component which is light sensitive or X-ray sensitive and
which, on exposure to light or X-ray when the T-E drug is located at the
desired target site, liberates the combination of (1) and (2) for binding
to the site to irreversibly effect the desired therapeutic result.
It will be appreciated that a wide variety of drugs may be designed using
the concept broadly described above. Thus, while the invention is
hereinafter exemplified by reference to the preparation of a specific
compound which is called "Asub-Q" for convenience, and its use as a T-E
drug for binding to the enzyme aldose reductase, it will be recognized
that the invention is of much broader scope.
It is known that various medical problems are caused by the enzyme aldose
reductase. For example, it is presently believed that diabetic
complications, such as cataract formation, retinopathy, neuropathy and
others are the result of the high production of sorbitol by aldose
reductase. In the case of diabetic cataracts, it appears that the enzyme
aldose reductase rapidly catalyzes the reduction of glucose to sorbitol in
diabetics whose blood glucose is at higher than normal concentrations.
Sorbitol cannot be rapidly metabolized nor can it rapidly diffuse out of
the lens. Thus, there is a tendency for its concentration to increase. As
this occurs, osmotic pressure in the lens increases inducing water to be
absorbed and swelling of the lens to occur. This swelling of the lens
promotes changes such as in protein conformation which results in opacity
of the lens, i.e. cataract formation.
It will be appreciated from the foregoing that the inhibition of aldose
reductase in diabetics should be useful in preventing diabetic cataracts
and various related diabetic complications (Fagius and Jameson, J. Neur,
Neurosurg, and Psych 44, 991-1001 (1981); Robinson et al. Sci 222,
1177-1779 (1983); Chem & Eng. News, Sept. 5, 1983, p. 5). The product
herein called "Asub-Q", which is representative of the invention, is photo
or X-ray activatable to irreversibly and effectively bind to aldose
reductase. As a consequence, this product should be useful to prevent the
formation of diabetic cataracts. It is also believed that, in view of its
demonstrated irreversible aldose reductase inhibiting activity, Asub-Q
should be more effective than simple reversible aldose reductase
inhibitors such as quercitrin or sorbanil in preventing diabetic
retinopathy and diabetic neuropathy that occur in tissues other than lens.
Additionally, since many humans with senile cataracts are hyperglycemic,
it appears that these cataracts may be similar to diabetic cataract and
should also be effectively treated with an aldose reductase inhibitor such
as Asub-Q.
The invention is more specifically described by reference to the
accompanying drawings, a preferred design of T-E drug, according to the
invention, being shown in FIG. 1. As there shown, (I) represents the drug
component, e.g. an inhibitor, which by itself is only capable of acting
reversibly, i.e. it only reversibly binds to a receptor site. The drug
portion (I) is reacted, as shown at (1) with a bifunctional reagent which
comprises an electromagnetic radiation-sensitive or activatable group
N.sub.3 (e.g. an azide group) and a convenient reactive group (X), e.g.
halogen joined together by a linking component (LC). On reacting (I) and
the bifunctional reagent through the reactive group (X), the T-E drug is
obtained as a product as shown in FIG. 1. This drug functions to
reversibly inhibit an enzyme (E) (or other receptor) as shown in (2) until
the T-E drug is subjected to light (or other electromagnetic activating
means) as shown at (3). This then liberates the azide or other activatable
group (N.sub.3) to provide irreversible inhibition by binding the enzyme
(E) to the inhibitor (I) through the connecting chain (LC).
As will be evident, the photosensitive irreversible inhibitor or T-E drug
contemplated herein comprises three components which are chemically
combined, i.e. the inhibitor component I, the component N.sub.3
activatable by electromagnetic radiation and the linking component LC. It
will be appreciated that the inhibitor component is selected to deal with
the particular enzyme or other receptor of concern. A photosensitive azide
component N.sub.3 is a preferred activatable group although other
activatable groups may be used to replace the N.sub.3 depending on the
nature of the desired external activating means.
The linking component (LC) may also be varied, its essential characteristic
being that, on removal of the activatable group (e.g. azide) by exposure
to light (or otherwise) at the desired site, it is capable of binding the
inhibitor to the enzyme or other receptor site.
As indicated earlier, a preferred T-E drug according to the invention is
Asub-Q which may also be called "NAP-Hex-quercitrin" the latter being
derived from the compound's chemical name, i.e. N-(2-nitro-4-azidophenyl)
hexylenediamine-N-(2'-O-quercitrin) and isomers such as those shown in
FIG. 3. These are representative of a general class of photosensitive
azide-substituted quercitrins which can be used to irreversibly inhibit
aldose reductase.
The chemical structure of Asub-Q (or NAP-Hex-quercitrin) is shown in FIG.
2. As will be evident, the product consists of three chemically bound
component units, i.e. quercitrin which is the reversible inhibitor (I) of
aldose reductase, the photosensitive nitrophenylazide component (N.sub.3)
and the spacer unit (LC) derived from hexamethylene diamine, the unit (LC)
chemically binding together component (I) and (N.sub.3). On activation by
light or X-ray, N.sub.2 from the N.sub.3 radical of Asub-Q is liberated to
leave a site for covalent binding of the quercitrin inhibitor component
via the nitrophenyl moiety linked to the polymethylene diamine spacer to
the aldose reductase to irreversibly and selectively inhibit the latter's
activity.
While Asub-Q includes the hexamethylene diamine spacer unit (LC), it will
be appreciated that the nature of this component may be varied. However,
it appears essential for optimum binding to use a spacer chain length of
greater than 2 or 3 carbons. A polymethylene group of 5-6 carbon atoms
appears to be preferable for best effects although somewhat longer chain
lengths may be used. Desirably the spacer unit is terminated at each end
with an amino group although it is possible that other terminal
substituents, and even substitution on the polymethylene chain, could
function satisfactorily provided such substitution does not interfere with
the inhibiting effect of the inhibitor component (I).
The invention is illustrated by the following examples:
EXAMPLE 1
This example illustrates the preparation of Asub-Q (or NAP-Hex-quercitrin).
(a) Synthesis of NAP-HEX-AMINE
N-(2-nitro-4-azidophenyl)hexylenediamine (NAP-Hex-Amine) was synthesized by
a modification of the methods of Rogers and Ladunski (see Biochem 18,
135-140 (1979)) and of Darfler and Marinetti (see Biochem Biophys. Res.
Comm 79, 1-7 (1977)), then purified.
All operations carried out with azide compounds were performed under red
light. 1.0 gm of 4-fluoro-3-nitrophenyl azide (5.5 mmoles) (FNPA) was
gently stirred with 6.4 gm of 1,6-hexylenediamine (55 mmoles) in 10 ml of
freshly distilled dimethylsulphoxide (DMSO) under nitrogen at 50.degree.
C. for 30 minutes. The product was recovered from the solution by
lyophilization.
The resulting crude NAP-Hex-Amine (150 mg) was dissolved in 4 ml of solvent
(benzene/methanol/acetic acid, 70:15:15) and purified on a solvent-washed
Bio-Sil A, 200-325 mesh, column (2.5.times.10.0 cm) by elution with the
same solvent. The pure product was isolated by lyophilization of the peak
fractions. Yield was 68%.
(b) Activation of Quercitrin
Activation of quercitrin was performed in an ice bath using a closed
stirred system. Nitrogen, bubbled through the system, was released through
a mineral oil trap. Quercitrin (0.5 mmoles) was added to 5 ml of 3N sodium
hydroxide solution. This was followed by the dropwise addition of 1.0 ml
of BrCN (1.0 gm). The pH was monitored and 3N sodium hydroxide was added
to maintain pH 10.5-11.5. Fifteen minutes after acid production ceased,
any remaining unreacted BrCN was removed by extraction with ether three
times.
(c) Coupling NAP-HEX-AMINE to Activated Quercitrin
The freshly activated quercitrin was added to NAP-Hex-Amine (0.5 mmoles)
dissolved in 8 ml DMSO at room temperature and maintained at pH 11.0-11.5
by addition of 3N sodium hydroxide under a nitrogen atmosphere. After 4
hours, the solution was acidified, using 3N HCl, to pH 5.0 and put in the
cold for 2 hours. The precipitate was collected on a Buchner funnel,
redissolved in fresh solvent, and then dried by flash evaporation at
50.degree. C. The crude product was purified chromatographically using the
same system as described above in (a). Thin layer analysis with HPTLC
silica gel 60 plates using benzene/methanol/acetic acid (70:15:15) as
solvent showed one major spot and two minor spots with Rf values of 0.60,
0.53 and 0.70, respectively. The three spots are isomers and each was
found to inhibit aldose reductase reversibly. However, when photolyzed,
the isomers inhibited the aldose reductase irreversibly. Yield was 46%.
The synthesis described above is summarized in FIG. 3 which shows the
preparation of NAP-Hex-Amine, the activation of quercitrin and its
coupling to NAP-Hex-Amine yielding three isomers, respectively.
(d) Spectral Analysis of Asub-Q
FIG. 4 shows the UV-Visible spectrum before and after 20 minutes of
photolysis in a Rayonet Photochemical Reactor with a light source having
maximum at 350 nM. The differential spectra is seen in FIG. 5. The
decrease in absorbance at 262 nm and 462 mm and the increase in absorbance
at 325 nm and 365 nm upon photolysis can be easily seen by eye
particularly on thin layer plates. The different extinction coefficients
are -855, -247, 263 and 263, respectively.
EXAMPLE 2
This example illustrates the synthesis of gamma-globulin
NAP-Hex-quercitrin.
200 mg of bovine g-globulin were dissolved in 2 ml of 0.1M sodium phosphate
buffer, pH 6.3 by gently stirring for 30 minutes at room temperature.
After 0.2 ml of NAP-Hex-Quercitrin (0.9 mg) was added to the solution, it
was split into two fractions, one was photolyzed for 10 minutes while the
other was kept in the dark. The adduct was separated from the inhibitor
solution by passing through a Sephadex G-25 column (0.7.times.7.0 cm, 0.5
ml/minute). The purple protein elutes at the void volume cleanly separated
from the inhibitor. Prior photolysis of the protein alone or the inhibitor
alone had no effect on its elution whether run alone or together on the
column. In the control, the colorless protein was also cleanly separated
from the inhibitor. When a BioRad P-15 column was used in place of the
Sephadex column the results were the same. Exhaustive dialysis against
buffer did not separate the inhibitor from the protein. It was concluded
from this that the inhibitor was covalently linked to the g-globulin.
EXAMPLE 3
This example illustrates the inhibition of aldose reductase by Asub-Q.
(a) REVERSIBLE INHIBITION
Tests to determine the inhibiting activity of Asub-Q against aldose
reductase indicate that Asub-Q reversibly inhibits aldose reductase in a
crude extract of rat lens with a Ki (the binding constant representative
of the inhibiting activity of a compound) similar to quercitrin itself.
Lens aldose reductase used for test purposes was extracted and assayed by
the technique reported by Hayman and Kinoshita (see J.Biol. Chem. 240,
877-882 (1965)). The extract was usually adjusted to pH 7.0 and
lyophilized. This product is stable indefinitely in the cold and provides
particularly reliable assay results since day to day rates are
reproducible.
The Ki and type of inhibition of aldose reductase by Asub-Q (0.274 mM) was
determined at pH 6.3 in 0.1M phosphate buffer using a saturating
concentration of NADPH (121 uM). The results are plotted in FIG. 6. Asub-Q
was found to be a noncompetitive inhibitor with a Ki of 0.48 uM, very
similar to quercitrin.
(b) IRREVERSIBLE-INHIBITION INDUCED BY PHOTOIRRADIATION
When the mixture of Asub-Q and extract is irradiated with light (maximum at
350 nM) followed by chromatographic removal of small molecules, it is
found that the enzyme is inhibited. Kinetic analysis shows that both
specific irreversible inhibition and non-specifically bound reversible
(soluble immobilized inhibitor) inhibition occur.
Photolysis of Asub-Q and aldose reductase was studied in the presence and
absence of saturating substrate concentrations (0.274 mM glyceraldehyde,
and 0.111 mM NADPH) in 0.1M phosphate buffer, pH 6.3. Photolysis was
performed in 3 ml quartz spectrophotometer cuvettes in a Rayonet
photochemical reactor with a 350 nm maxima light source. The enzyme was
separated from the non-covalently bound inhibitor by passing the
photolyzed solution through a Sephadex G-25 column as described above. The
results are plotted in FIG. 7. The results show that aldose reductase with
no inhibitor present was not affected by the photolysis. The enzyme
photolyzed with inhibitor in the presence or absence of substrate is 80%
inhibited after 10 minutes. It was found that irreversible inhibition is
quite rapid, roughly 40% in one minute.
(c) IRREVERSIBLE INHIBITION INDUCED BY X-RAY IRRADIATION
When a mixture of Asub-Q and rat lens extract is irradiated with X-rays
followed by chromatographic removal of small molecules, it is found that
aldose reductase is extensively irreversibly inhibited. X-ray irradiation
was performed with a General Electric Maximum-100 type X-ray machine using
the following settings: 100 kVp, 5 ma, 3 mm Al added, HUL=2.6 mm Al,
calibrated output=175 R/min. at 15 cm. Two ml of solution with components
at the same concentrations used in photolysis experiments were X-rayed in
50 mm diameter open petri dishes placed at 15.9 cm from the X-ray source.
The dosages were varied from 5 to 100 Rads, requiring 1, 2, 3, 4, 34 and
51 seconds exposure, respectively. Typical results of duplicate samples
recorded in Table 1 and plotted in FIG. 8 show that at 20 Rads irradiation
or above the enzyme has lost approximately two thirds of its activity.
TABLE 1
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X-RAY INDUCED IRREVERSIBLE INHIBITION
OF ALDOSE REDUCTASE BY ASUB-Q
System Rads Relative Activities
______________________________________
(Enzyme + Asub-Q)*
5 30, 30
(Enzyme + Asub-Q)*
10 26, 23
(Enzyme + Asub-Q)*
20 16, 19
(Enzyme + Asub-Q)*
50 11, 11
(Enzyme + Asub-Q)*
100 11, 13
Enzyme* + Asub-Q
100 40, 32
Enzyme + Asub-Q*
100 38, 42
Enzyme* + Asub-Q*
100 41, 43
Enzyme + Asub-Q 40, 46
Enzyme* 100 41, 43
Enzyme 42, 45
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*Irradiated components are indicated by asterisk with the parenthesis
showing which components were irradiated after mixing.
(d) REVERSIBLE INHIBITION BY SOLUBLE IMMOBILIZED ASUB-Q
(1) Aldose reductase inhibition by means of the
g-Globulin-NAP-Hex-quercitrin prepared in Example 2 was also investigated.
The Ki and type of inhibition was established by use of a Lineweaver-Burk
plot of the rate data. The results presented in FIG. 9 show that the
globulin product is acting as an noncompetitive inhibitor with
glyceraldehyde as the variable substrate. The assay system contains 3.75
mg/ml of the inhibitor. Since the crude lens extract consists of many
proteins in addition to aldose reductase, just as the lens itself does, it
is expected that the Asub-Q inhibited enzyme preparation contains
inhibitor bound irreversibly to other proteins and behaves similar to the
soluble immobilized g-globulin.
(2) If fresh aldose reductase is assayed in the presence of Asub-Q
photo-inhibited aldose reductase, the fresh enzyme is inhibited reversibly
by the photo-inhibited enzyme. FIG. 10 is a plot of relative enzyme
activity as a function of fresh enzyme concentration when 1 mg/ml of
photo-inhibited enzyme is present. FIG. 11 is similar, but 2.5 mg/ml of
photo-inhibited enzyme is added in addition. The resulting decrease in
slope is produced by the inhibition of fresh enzyme by photo-inhibited
enzyme that is functioning as a soluble-immobilized enzyme in this system.
EXAMPLE 4
This illustrates the inhibition of cataract formation in lens organ culture
by a single dose of Asub-Q irradiated with lenses.
(A) EFFECT OF ASUB-Q ON CATARACT FORMATION IN RAT LENSES IN ORGAN CULTURE
EXPERIMENTS: LIGHT IRRADIATED
Organ culture was performed by a modification of the method of Kinoshita et
al (see Biochem. Biophys. Acta 158, 472-475 (1968)) with a modified TC 199
medium using 50-75 gm Sprague-Dawly male rats, care being taken to avoid
contamination of the system. Fresh rat lenses were treated with Asub-Q in
the manner hereinafter described and incubated in the presence of fructose
and in the presence of galactose, in order to determine the effect of the
Asub-Q. The Asub-Q treatment involved the following:
(a) rat lenses were incubated in the dark in an incubation medium
containing Asub-Q for two hours to permit the drug to diffuse into the
lens;
(b) the lenses were then placed into a fresh medium and irradiated for 10
minutes for complete inhibition of aldose reductase;
(c) the lenses were then placed into a fresh medium for two hours with four
changes in medium in the first 24 hours to permit non-covalently bound
drug to diffuse out; and
(d) the lenses were then incubated in a medium containing fructose or
galactose.
In a typical experiment four groups of 20 lens, four to a Petri dish, were
used. The first group was supplemented with fructose (30 mM); the second,
with galactose (30 mM); the third, with fructose (30 mM) and treated with
Asub-Q (0.145 mM); and the fourth, with galactose (30 mM) and treated with
Asub-Q (0.145 nM). The lens were photographed with color film on a red
background and evaluated on a O to V scale with O assigned to a clear lens
and V to a lens with a totally opaque cataract. The procedure for
treatment and photolysis of the lens was described above. The results are
summarized in Table 2.
TABLE 2
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EFFECT OF ASUB-Q ON RAT LENS IN ORGAN CULTURE
Asub-Q Asub-Q
+ +
Days
Fructose Fructose Galactose Galactose
__________________________________________________________________________
0 -- -- -- --
1 -- -- -- I(15) + II(5)
2 -- -- -- III(16) + II(4)
3 O(16) + I(4)
-- -- V(20)
7 O(16) + I(4)
O(16) + I(4)
--
10 O(12) + I(8)
O(16) + I(4)
O(12) + I(8)
15 O(8) + I(12)
O(12) + I(8)
O(8) + I(12)
21 O(8) + II(8) +
O(12) + I(4) +
O(8) + I(4) +
III(4) II(4) III(8)
35 V(20) II(8) + III(4) +
III(4) + IV(8) +
V(4) V(8)
__________________________________________________________________________
The number outside the parenthesis is the status of the lenses: O to V. The
number inside the parenthesis is the number of the lenses.
All of the lenses with galactose supplements exhibited total cataracts
after three days as previously reported by Kinoshita et al (See Biochem.
Biophys. Acta 158, 472-475 (1968)). Four of the fructose containing
control lenses showed very slight clouding while the remainder remained
totally clear. All of the lenses containing Asub-Q remained clear. By day
21, roughly half of all the remaining lens stayed clear and half became
cloudy. By day 35 all the lenses incubated with fructose were totally
opaque, whereas those treated with Asub-Q were not nearly as advanced.
These data indicate that lens containing Asub-Q are at least as impervious
to cataract formation as control lenses that were incubated with fructose.
(B) EFFECT OF ASUB-Q ON CATARACT FORMATION IN RAT LENSES IN ORGAN CULTURE
EXPERIMENTS: X-RAY IRRADIATED
This experiment was similar to the photoirradiation experiment except that
the lenses were irradiated with 175 Rads of X-rays in place of light.
After eight days each of the 4 control lenses incubated with fructose
showed slight cataract (I) formation, as expected. Lenses incubated with
galactose would be completely opaque (V). The X-ray irradiated lenses
incubated with galactose were found to consist of 5 clear lenses (O) and 6
with a slight cataract (I). This experiment indicates that X-ray
irradiation of Asub-Q with rat lenses results in 100% protection from
sugar induced cataracts.
The foregoing shows that Asub-Q is effective as a reversible inhibitor with
activity about the same as quercitrin. On irradiation, the compound
functions as a photo- or X-ray sensitive irreversible affinity inhibitor
for aldose reductase. The data also show that Asub-Q non-specifically
forms soluble immobilized reversible inhibitor. This can potentially
supplement the direct irreversible inhibition of aldose reductase in its
action as an anti-diabetic cataract drug. Organ culture studies show 100%
effectiveness in protecting lens from forming diabetic cataracts induced
by galactose. Finally, Asub-Q serves as a good example of a new class of
drugs target-directed drugs.
EXAMPLE 5
This example illustrates the inhibition of cataract formation in rats by
irradiation of Asub-Q treated animals.
EFFECT OF ASUB-Q ON CATARACT FORMATION IN RATS: LIGHT IRRADIATED
Approximately 5-10 .mu.l of Asub-Q (0.65 mM) dissolved in DMSO was injected
into the aqueous humour of the right eye of each of three 75 g. rats.
After 1 hour, when the drug had diffused into the lens, the rat was
irradiated for 30 minutes in a Rayonet Photochemical Reactor. The rats
were fed ad-libinum with a mix of 1:1 chow:galactose. The control eyes
(left eye) developed detectable cataracts after 3 days. After 7 days, the
cataracts in the control eyes got more extensive (III) but no cataract was
observed in the treated right eyes. This was repeated on thirty rats with
equivalent results.
It will be appreciated that the T-E drugs of the invention may be
administered in conventional form, e.g. as tablets, capsules or pills for
oral administration or as sterile solutions for intravenous
administration. The composition form selected for use will depend, in
large measure, on the disorder which is being treated. In the treatment of
eye or ear problems, for example, topical administration may be most
advantageous. The essential point is to have the composition in the form
which will best center on the target site and lend itself to be
irreversibly bound thereby, for example, pervasive or electromagnetic
radiation such as visible light, X-rays, etc. It is particularly
advantageous to have the drug irreversible receptor-binding capability
activatable by light since many skin and body openings are readily
accessible to light. Asub-Q is therefore especially useful as an
anti-diabetic cataract drug since the eye is directly accessible to light.
Other T-E drugs utilizing light as the activating energy source can
similarly be prepared for use in the ears, nose, mouth and the total G.I.
system as well as the skin. Additionally, if the activating sources are
X-rays or other pervasive radiation, it is possible to design the T-E drug
so that it can be applied to internal organs or even smaller anatomic
sites in the body.
The amount of T-E drug administered will vary depending, for example, on
the disorder and drug involved, mode of administration and other factors
as will be understood by those in the art. Broadly speaking, however, the
amount of T-E drug administered will usually fall in the range employed
for the parent drug itself although, because of the improved efficiency
using the T-E drug, it should be possible to reduce the effective dosages
and amounts of the parent drug by as much as 25-50% or even more. In fact,
a major advantage of a drug according to the invention is that the
functional half-life should be much greater than that of typical drugs
since its effective half-life should be dependent on neosynthesis of
receptor sites, in place of the typically more rapid normal drug
detoxification routes. This should allow for a much more conservative drug
administration regimen such as one dose a month in place of three doses a
day.
It will be appreciated that various modifications may be made in the
invention as described above. Hence, the scope of the invention is defined
in the following claims.
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