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Intravenous administration of N-(beta-alanyl-L-leucyl-L-alanyl-L-leucyl)doxorubicin (4) induces an acute toxic reaction, killing animals in a few minutes. This results from its positive charge at physiological pH combined with its propensity to form large aggregates in aqueous solutions. Negatively charged N-capped versions of 4 such as the succinyl derivative 5 can be administered by the iv route at more than 10 times the LD(50) of doxorubicin without inducing the acute toxic reaction, and they are active in vivo.

Oligopeptidic derivatives of anthracyclines unable to penetrate cells were prepared and screened for their stability in human blood and their reactivation by peptidases secreted by cancer cells. N-beta-alanyl-L-leucyl-L-alanyl-L-leucyl-doxorubicin was selected as a new candidate prodrug. The NH2-terminal beta-alanine allows a very good blood stability. A two-step activation by peptidases found in conditioned media of cancer cells ultimately yields N-L-leucyl-doxorubicin. In vitro, when MCF-7/6 cancer cells are exposed to the prodrug, they accumulate about 14 times more doxorubicin than MRC-5 normal fibroblasts, whereas when exposed to doxorubicin the uptake is slightly higher in fibroblasts than in MCF-7/6 cells. This increased specificity of the prodrug over doxorubicin was confirmed in cytotoxicity assays using the same cell types. In vivo, the prodrug proved about nine times less toxic than doxorubicin in the normal mouse and also much more efficient in two different experimental chemotherapy models of human breast tumors.

The synthesis and antiviral activity of an original series of 6-benzoyl-benzoxazolin-2-one and 6-benzoyl-benzothiazolin-2-one derivatives are described. Several compounds were found to have a selective inhibitory activity against human cytomegalovirus (HCMV) and varicella-zoster virus (VZV) in vitro, being inactive against a variety of other DNA and RNA viruses. 6-(3-fluorobenzoyl)benzoxazolin-2-one, 6-(3-fluorobenzoyl)benzothiazolin-2-one, 6-(3-bromobenzoyl)benzothiazolin-2-one, 6-(3-iodobenzoyl)benzothiazolin-2-one, 3-methyl-6-(3-fluorobenzoyl)benzothiazolin-2-one, 3-benzyl-6-benzoyl-benzothiazolin-2-one, 3-benzyl-6-(3-fluorobenzoyl)benzothiazolin-2-one and 3-benzoyl-6-(3-fluorobenzoyl)benzothiazolin-2-one were the most active of the series against HCMV and VZV with a selectivity index (CC50/IC50) ranging from 10 to 20. They displayed similar activity against thymidine kinase competent (TK+) and deficient (TK-) VZV strains, and also proved to be active against clinical HCMV isolates that were resistant to ganciclovir (GCV). Time-of-addition experiments revealed a site of interaction with the HCMV replicative cycle that may be close or similar to that of GCV and cidofovir (HPMPC). The compounds showed poor, if any, activity against herpes simplex virus type 1 (HSV-1) and HSV-2, and were not inhibitory against human immunodeficiency virus and other DNA and RNA viruses. Therefore, these compounds may represent a novel lead for the development of specific HCMV and VZV drugs.

This work is aimed at further exploring the concept that phenytoin-related compounds might present with an anti-HIV potential. We screened for anti-HIV activity, selected compounds whose structural design rests on pharmacophores successfully shown to convey phenytoinergic anticonvulsant activity. We determined the corresponding anticonvulsant protective doses in mice via the i.p. route of administration using the maximal electroshock seizure test (a test in which the anticonvulsant activity of phenytoin is well expressed). Firstly, 4-aminophthalimide pharmacophores were utilized with either N-(2,6-dimethyl)phenyl or N-(1-adamantyl) substitutions. While the former was found to be highly potent, the latter was devoid of significant activity. Secondly, the pharmacophores N-(2,6-dimethylphenyl)phthalimide and N-(1-adamantyl)phthalimide were compared for antiviral (antiHIV-1 and antiHIV-2) properties in CEM (human T-lymphocyte) cells infected with HIV-1 or HIV-2 strains. Various phthalimide C4-substitutions (H, NO2, NH2, Cl, CH3, OCH3, COOH) of these pharmacophores were studied. From this set of experiments, 4-amino-N-(1-adamantyl)phthalimide emerged with EC50 (effective concentration-50) values of 16 and 27 microM against HIV-1 and HIV-2, respectively. The CC50 (cytostatic concentration-50) of this compound was 30 microM. Thirdly, the N-(2,6-dimethylphenyl) and N-(1-adamantyl) substitutions of the 4-aminobenzamide pharmacophore (another known phenytoinergic anticonvulsant platform) were shown to be devoid of anti-HIV activities. A similar negative result was obtained for amantadine. Taken as a whole, the present data indicate that both the 4-aminophthalimide pharmacophore and N-(1-adamantyl) substitutions are required for anti-HIV properties. Molecular modeling studies further provide clues for this dual requirement.

A series of original 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives were evaluated for their affinity at sigma1 and sigma2 receptor subtypes in competition binding experiments, using [3H](+)-pentazocine or [3H]1,3-di-o-tolyl-guanidine (DTG) in the presence of 100 nM (+)-N-allylnormetazocine (NANM) in guinea-pig brain membranes. Several of these derivatives showed preferential selectivity for sigma1 binding sites. Compound 1 [3-(1-piperidinoethyl)-6-propylbenzothiazolin-2-one] emerged as a potent sigma1 receptor ligand (Ki = 0.6 nM) and displayed a moderate selectivity over the sigma2 receptor subtype (Ki for sigma2/Ki for sigma1 = 29). Compounds 2 [3-(1-piperidinopropyl)-6-propanoylbenzothiazolin-2-one] and 3 [3-(1-piperidinopropyl)-6-propanoylbenzoxazolin-2-one] still showed rather high affinities for sigma1 binding sites with Ki values of 2.3 and 8.5 nM, respectively. On the contrary, they had 87- and 58-fold less affinity at sigma2 receptors, respectively. Unlike their potent affinity for sigma binding sites, these compounds had negligible affinity for mu-, delta- and kappa-opioid receptors, 5-HT2, dopamine D2, and muscarinic M2 receptors. Sigma receptor ligands may affect neuronal transmission and display, in animal models, antipsychotic, cognitive, motor, neuroprotective and anticonvulsant activity. Therefore, on the basis of these findings, these novel sigma receptor ligands were assayed, in mice, in three tests: maximal electroshock, subcutaneous pentylenetetrazol and rotarod neurotoxicity. Compound 1, administered intraperitoneally, was the most effective against maximal electroshock-induced seizures and was devoid of significant neurotoxic effects.