Synergistic effect of hydrotrope and surfactant on solubility and dissolution of atorvastatin calcium: screening factorial design followed by ratio optimization.

The present study was aimed at investigating the effect of hydrotrope and surfactant on poor solubility of atorvastatin calcium. Excipients screening followed by factorial design was performed to study effect of excipients and manufacturing methods on solubility of drug. Three independent factors (carrier, surfactant and manufacturing method) were evaluated at two levels using solubility as a dependant variable. Solid-state characterisation was performed using Fourier transform infrared spectroscopy and differential scanning calorimetry. Optimised complex were incorporated into orally disintegrating micro tablets and in vitro dissolution test was performed. Nicotinamide, Plasdone and sodium dodecyl sulphate were emerged as promising excipients from excipient screening. General regression analysis revealed only the type of carrier has significantly enhanced (P<0.05) the solubility of drug while other factors were found to be nonsignificant. Ratio optimisation trial revealed that drug to nicotinamide ratio is more critical in enhancing the solubility of drug (40 fold increases in solubility compared to pure drug) in comparison to drug-surfactant ratio; however the presence of surfactant deemed essential. Significantly higher rate and extent of dissolution was observed from solid dispersion complex and tablets compared to dissolution of pure drug (P<0.05). Study revealed hydrotrope and surfactant have synergistic effect on solubility and dissolution of atorvastatin calcium and this can be explored further.

Multi-targeted antifolates aimed at avoiding drug resistance form covalent closed inhibitory complexes with human and Escherichia coli thymidylate synthases.

Crystal structures of four pyrrolo(2,3-d)pyrimidine-based antifolate compounds, developed as inhibitors of thymidylate synthase (TS) in a strategy to circumvent drug-resistance, have been determined in complexes with their in vivo target, human thymidylate synthase, and with the structurally best-characterized Escherichia coli enzyme, to resolutions of 2.2-3.0 A. The 2.9 A crystal structure of a complex of human TS with one of the inhibitors, the multi-targeted antifolate LY231514, demonstrates that this compound induces a "closed" enzyme conformation and leads to formation of a covalent bond between enzyme and substrate. This structure is one of the first liganded human TS structures, and its solution was aided by mutation to facilitate crystallization. Structures of three other pyrrolo(2,3-d)pyrimidine-based antifolates in complex with Escherichia coli TS confirm the orientation of this class of inhibitors in the active site. Specific interactions between the polyglutamyl moiety and a positively charged groove on the enzyme surface explain the marked increase in affinity of the pyrrolo(2,3-d)pyrimidine inhibitors once they are polyglutamylated, as mediated in vivo by the cellular enzyme folyl polyglutamate synthetase.

Novel cryptophycin antitumor agents: synthesis and cytotoxicity of fragment "B" analogues.

A general synthetic approach to novel cryptophycin analogues 6 is described. N-Hydroxysuccinimide active ester 15, a key common intermediate, was converted to beta-epoxide 6 in three steps, via initial coupling with unprotected amino acid 9, followed by deprotection/macrolactamization of acyclic precursor 16, and final oxidation of styrene 7 to install the C7-C8 beta-epoxide. Cryptophycin styrenes 7 and beta-epoxides 6, bearing diverse side chains in fragment "B", were evaluated for cytotoxic activity. beta-Epoxides 6, in general, were significantly more potent than the corresponding alpha-epoxides 17 and styrenes 7. A benzyl side chain was required for potent activity, with beta-epoxide 6u, possessing a 3-Cl,4-(dimethylamino)benzyl moiety, as the most potent cytotoxic agent prepared, with an IC(50) = 54 pM, only 2-fold less than that of Cryptophycin-52 (3).

Role of thymidylate synthase in the antitumor activity of the multitargeted antifolate, LY231514.

The cytotoxicity of LY231514 was only partially alleviated by thymidine addition (5 microM) in GC3 human colon carcinoma cells, and complete protection required the addition of both hypoxanthine (100 microM) and thymidine. In contrast, the cytotoxic activity of tomudex (raltitrexed, ZD1694) was completely reversed by thymidine alone. MCF-7 human breast and H630 human colon carcinoma cells selected for resistance to tomudex and 5-fluorouracil, respectively via thymidylate synthase (TS) amplification demonstrated only modest resistance to LY231514 compared to tomudex. LY231514-induced cytotoxicity in these resistant cell lines was completely prevented by the addition of hypoxanthine (100 microM), indicating inhibition of purine de novo biosynthesis as a secondary target for LY231514 action. Thymidine at physiologic levels in mouse plasma (approximately 1 microM) produced only a 2.6-fold shift in the IC50 for LY231514-mediated cytotoxicity in GC3/cl1 cells compared to a 128-fold shift for tomudex. LY231514 treatment (i.p., qd x 10) significantly delayed tumor growth in the GC3 carcinoma xenograft model. However, a thymidine kinase-deficient mutant of this same tumor line demonstrated heightened sensitivity to the in vivo antitumor activity of LY231514 with complete regression of established tumors and a large number of tumor-free survivors after one course of treatment. The data demonstrate that inhibition of thymidylate synthase is a prominent mechanism for antitumor activity by LY231514, but important secondary sites of action exist for this multitargeted molecule.

LY231514, a pyrrolo[2,3-d]pyrimidine-based antifolate that inhibits multiple folate-requiring enzymes.

N-[4-[2-(2-amino-3,4-dihydro-4-oxo-7H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl ]-benzoyl]-L-glutamic acid (LY231514) is a novel pyrrolo[2,3-d]pyrimidine-based antifolate currently undergoing extensive Phase II clinical trials. Previous studies have established that LY231514 and its synthetic gamma-polyglutamates (glu3 and glu5) exert potent inhibition against thymidylate synthase (TS). We now report that LY231514 and its polyglutamates also markedly inhibit other key folate-requiring enzymes, including dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyltransferase (GARFT). For example, the Ki values of the pentaglutamate of LY231514 are 1.3, 7.2, and 65 nM for inhibition against TS, DHFR, and GARFT, respectively. In contrast, although a similar high level of inhibitory potency was observed for the parent monoglutamate against DHFR (7.0 nM), the inhibition constants (Ki) for the parent monoglutamate are significantly weaker for TS (109 nM) and GARFT (9,300 nM). The effects of LY231514 and its polyglutamates on aminoimidazole carboxamide ribonucleotide formyltransferase, 5,10-methylenetetrahydrofolate dehydrogenase, and 10-formyltetrahydrofolate synthetase were also evaluated. The end product reversal studies conducted in human cell lines further support the concept that multiple enzyme-inhibitory mechanisms are involved in cytotoxicity. The reversal pattern of LY231514 suggests that although TS may be a major site of action for LY231514 at concentrations near the IC50, higher concentrations can lead to inhibition of DHFR and/or other enzymes along the purine de novo pathway. Studies with mutant cell lines demonstrated that LY231514 requires polyglutamation and transport via the reduced folate carrier for cytotoxic potency. Therefore, our data suggest that LY231514 is a novel classical antifolate, the antitumor activity of which may result from simultaneous and multiple inhibition of several key folate-requiring enzymes via its polyglutamated metabolites.

Novel acid labile COL1 trityl-linked difluoronucleoside immunoconjugates: synthesis, characterization, and biological activity.

LY207702 (1) is a difluorinated purine nucleoside that exhibits impressive antitumor activity in preclinical models. This agent, however, also possesses cardiotoxicity which limits the potential clinical utility of this novel drug candidate. We therefore developed linker chemistry whereby regioselective N6-tritylation of LY207702 (1) allowed this drug to be coupled to epsilon-lysine amino groups of mAb's reactive with human tumor-associated antigens. The resulting immunoconjugates 3 possessed conjugation ratios ranging from 5 to 7 mol of LY207702/mol of mAb, minimal aggregate content (5-10%), and good immunoreactivity. The electronic nature of substituents on the aromatic rings of the trityl group dictated the degree of acid lability of the trityl linker. Increased electronic stabilization of the transient trityl carbocation led to increase in the release rate of free drug, i.e., m-DMT 10a = p-DMT 10b > p-MMT 10d > p-T 10f. Consequently, the more acid labile DMT conjugates 3a and 3b proved to be the most potent cytotoxic agents, and the most stable p-T conjugate 3f exhibited the least antitumor activity when evaluated in vitro and in vivo. p-MeT-linked conjugate 3e, the most stable construct that retained excellent in vivo antitumor activity, was selected for more extensive evaluation. No detectable free drug or metabolite was observed in mouse plasma at a single intravenous dose of p-MeT conjugate 3e, which was consistent with its predicted stability under physiological conditions. This construct did, however, exhibit significant antigen-mediated antitumor activity in vivo. No cardiotoxicity was detected in mice dosed with conjugate 3e (6 mg/kg free drug content per day for 21 days) equivalent to approximately 8 times the total dose required for complete regression of well-established (approximately 1 g) HC1 human colon tumor xenografts in nude mice. Cardiotoxicity was induced in 20% of free drug 1 treated group at the equivalent dose. Cardiomyopathy was, however, observed when the dose of conjugate 3e was increased to 8 mg/kg per day for 21 days. These data suggest that antitumor activity of LY207702 (1) was maintained and its cardiotoxic potential reduced when this agent was administered to human tumor xenograft bearing nude mice as COL1-N6-p-MeT-207702 conjugate 3e.