Rapid, radiometric in vitro assay for the evaluation of the anti-leprosy activity of clofazimine and its analogues.

The effect of c10fazimine and 6 analogues (B 369 1 , B 3 7 1 3 , B 3640, B 3648, B 720 and B 749) on the viabi l i ty of Mycobacterium /eprae was tested i n a rapid, radiometric, ill vitro assay. Thi rteen human and I armadi l lo-derived freshly-extracted M. /eprae, maintained in peritoneal macro phages, incorporated 3H -thymidine to significant levels as compared to paral lel cu l tures with heat-k i l led baci l l i . Exposure of such cul tures to c10fazimine for 48 h showed significant inh ibi t ion of the radiolabel uptake without any adverse effects on the host macrophages. A sharp l i near i ncrease i n i nhibi t ion was observable at concentra­ tions from I to 10 ng/ml , with a plateau up to 40 ng/m l . Further i ncreases of drug concentration up to 1 00 ng/ml showed marginal increase i n the percentage inhibit ion of 3H-thymidine i ncorporat ion . The analogues tested showed levels of inhibit ion s imi lar to that of c10fazimine when left for 72 h and 1 5 days i n M. /eprae macrophage cul tures . However, they were less effect ive than c10fazimine when tested for the shorter duration of 48 h at the lower concentration of 5 ng/m l .