Preliminary in vitro toxicological evaluation of a series of 2-pyridylcarboxamidrazone candidate anti-tuberculosis compounds III

We have evaluated the cytotoxicity of a series of novel anti-tubercular 2-pyridyl carboxamidrazones through incubation with human mononuclear leucocytes (MNL), with and without a rat microsomal metabolising system. Isoniazid (INH), the closest structurally related agent, was used as a positive control. Incubation of the 3-benzyloxy-benzylidene, dimethylpropyl-benzylidene and 4-phenyl-benzylidene with MNL showed no significant toxicity in comparison with either INH or DMSO vehicle control. However, the 4-N,N-dimethylamino-1-naphthylidene derivative exerted more than sevenfold greater toxicity compared with INH, while the 4-N,N-dimethylamino-1-naphthylidene, 2-benzyloxy-3-methoxy-benzylidene, 2-t-butylthio-benzylidene and 4-i-propyl-benzylidene derivatives showed toxicity which ranged from five to fourfold that of INH. In the presence of either rat microsomes with or without NADPH, the 3-benzyloxy-benzylidene, dimethylpropyl-benzylidene and 4-phenyl-benzylidene derivatives showed no metabolically-mediated cytotoxicity. The latter two derivatives showed a combination of low toxicity and considerable efficacy against Mycobacteria tuberculosis in vitro and show promise for future development. © 2001 Elsevier Science B.V.

The use of computational QSAR analysis in the toxicological evaluation of a series of 2-pyridylcarboxamidrazone candidate anti-tuberculosis compounds

A series of N1-benzylidene pyridine-2-carboxamidrazone anti-tuberculosis compounds has been evaluated for their cytotoxicity using human mononuclear leucocytes (MNL) as target cells. All eight compounds were significantly more toxic than dimethyl sulphoxide control and isoniazid (INH) with the exception of a 4-methoxy-3-(2-phenylethyloxy) derivative, which was not significantly different in toxicity compared with INH. The most toxic agent was an ethoxy derivative, followed by 3-nitro, 4-methoxy, dimethylpropyl, 4-methylbenzyloxy, 3-methoxy-4-(-2-phenylethyloxy) and 4-benzyloxy in rank order. In comparison with the effect of selected carboxamidrazone agents on cells alone, the presence of either N-acetyl cysteine (NAC) or glutathione caused a significant reduction in the toxicity of INH, as well as on the 4-benzyloxy derivative, although both increased the toxicity of a 4-N,N-dimethylamino-1-naphthylidene and a 2-t-butylthio derivative. The derivatives from this and three previous studies were subjected to computational analysis in order to derive equations designed to establish quantitative structure activity relationships for these agents. Twenty-five compounds were thus resolved into two groups (1 and 2), which on analysis yielded equations with r2 values in the range 0.65-0.92. Group 1 shares a common mode of toxicity related to hydrophobicity, where cytotoxicity peaked at logP of 3.2, while Group 2 toxicity was strongly related to ionisation potential. The presence of thiols such as NAC and GSH both promoted and attenuated toxicity in selected compounds from Group 1, suggesting that secondary mechanisms of toxicity were operating. These studies will facilitate the design of future low toxicity high activity anti-tubercular carboxamidrazone agents. © 2003 Elsevier Science B.V. All rights reserved.