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N Ravi, A Ravi, P Hamilton; Quantitative Structure Toxicity Relationship of Picolinic Acid Analogs . Invest. Ophthalmol. Vis. Sci. 2002;43(13):460.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previously (ARVO, 2001), the inhibitory effects of picolinic acid and fusaric acid (5-butyl picolinic acid) were compared with that of EDTA as a possible method of inhibiting Posterior Capsular Opacification (PCO) after cataract surgery. In this study, the growth inhibitory effects and toxicity of picolinic acid (PA) with 10 of its analogs were analyzed. Methods: Based on the method described by Senderoff et al. (IOVS Vol 31 #12 pp2572-2578, 1990), CHO cells were used as a cell model. Cell counts were performed varying the analog concentration from 1-5000 µg/ml, and were expressed as a percentage of the treated cell counts with respect to the untreated or control cell counts. From plots of the percentage cell count versus concentration, the IC50 (i.e. concentration at which treated cell counts are 50% of the control) was established, and this was used as a measure of toxicity. Results: The 11 compounds tested, in order of their decreasing toxicity are as follows: Fusaric acid, 3-Hydroxy picolinic acid, Picolinic acid, Picloram, 6-Bromo picolinic acid, 6-Methyl picolinic acid, Di-picolinic acid, Iso-nicotinic acid, Picolinic acid N-oxide, Nicotinic acid, and 6-Hydroxy picolinic acid. The IC50 ranged from 0.032 mM to 25.85 mM. Depending on the PA analog used, the morphology of the CHO cells varied markedly. Quantitative Structure Toxicity Relationship (QSTR) showed that charge on nitrogen and logP (hydrophobicity) were the two most important molecular descriptors. Conclusion: Analogs of picolinic acid differ greatly in their toxicity. While EDTA primarily chelates Ca2+ and Mg2+ ions, picolinic acid mainly chelates Zn2+ and Fe2+. Zinc and iron are essential for the biological activity of zinc finger and iron binding proteins, which are involved in DNA replication and cell division. Picolinic acid is known to decrease the zinc and iron content of the cell and hence, inhibit cell growth, while at the same time showing decreased toxicity to non-proliferating cells. On the basis of the QSTR the growth inhibitory effects of the analogs depend on two main factors: 1) Ability to chelate zinc, (partial charge on nitrogen) and 2) Ability to cross cell membranes (logP).
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