Journal
TOXICOLOGY IN VITRO
Volume 14, Issue 1, Pages 53-59Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0887-2333(99)00092-2
Keywords
Lactobacillus leichmannii; cytotoxicity; dihydrofolate reductase; inhibition; Pergularia pallida; pergularinine; tylophorinidine
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The phenanthroindolizidine plant alkaloids pergularinine (PGL) and tylophorinidine (TPD) isolated from the Indian medicinal herb Pergularia pallida have been evaluated for their biological activity and assessed for the first time employing dihydrofolate reductase (DHFR) (5,6,7,8-THF: NADP(+) oxidoreductase, EC 1.5.1.3) as the probe in the present investigations. The enzyme is a key target in cancer chemotherapy and has been purified from Lactobacillus leichmannii. Cytotoxicity studies showed that both PGL and TPD are potently toxic and inhibited the growth of L. leichmannii cells (IC50 = 45 and 40 mu M. respectively). Both the alkaloids significantly inhibited DHFR activity (IC50 = 40 and 32 mu M for PGL and TPD, respectively). Alkaloid concentrations greater than 75-95 mu M resulted in a complete loss of DHFR activity. Our results are suggestive of the alkaloids as potential antimicrobial and antitumour compounds. Alkaloid binding to DHFR is slow and reversible. Inhibition kinetics revealed K-i values of 9 x 10(-6) hr and 7x10(-6) hr for PGL and TPD, respectively for the enzyme and inhibition in both the cases was a simple linear 'non-competitive' type. (C) 2000 Elsevier Science Ltd. AII rights reserved.
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