Potentiation of Adriamycin Cytotoxicity in P388 Murine Leukemia Sensitive and Resistant to Adriamycin by use of Lonidamine and Hyperthermia

The in vitro effect of adriamycin (ADR) and lonidamine alone and in combination, at 37 °C and 43 °C, was investigated on murine leukemia P388 sensitive (P388/S) and resistant (P388/ADR) to adriamycin. The sensitive and the resistant cells were exposed in vitro with and without the drugs for 1 h at 37 °C and 43 °C. These cells were inoculated ip (10⁶ cells/mouse) into groups of BDF, mice. Cytotoxic effect of the treatment was assessed on the basis of percentage increase in life span (% ILS) of these animals, compared to the animals receiving cells which did not receive any treatment but exposed only to 37 °C for 1 h. It was observed that exposure of P388/ADR cells to lonidamine or adriamycin alone at 43 °C for 1 h resulted in greater cell kill, thus enhancing the % ILS of the experimental animals receiving those cells, compared to that of mice receiving the cells exposed to the same drugs for 1 h at 37 °C. However, the combination of lonidamine (0.02 mM) and adriamycin (10 μg/ml) at 43 °C for 1 h showed more than a synergistic effect, resulting in a % ILS of 120. Similar results were seen in the case of P388/S; however, the observations pertaining to P388/ADR are encouraging, since the mode of treatment has reversed the acquired resistance of P388 leukemia cells to adriamycin.