Enhancement of the anti-tumor effect of melphalan in experimental mice by some vaso-active agents

Abstract A comparison is made between the vaso-active agents hydralazine, nifedipine, and verapamil for their ability to increase the anti-tumor effectiveness of melphalan. Treatment of mice with hydralazine (5 mg/kg) 15 mins after melphalan increases by a factor of ∼2.5 melphalan-induced delay in growth of either the RIF-1 or KHT tumors. Similar enhancements are obtained when measurement is made of the surviving fraction of tumor cells in vitro following treatment in vivo with hydralazine and melphalan. Further, tumor cell kill is also increased when nifedipine is administered with melphalan compared with the effect of melphalan alone. These enhanced effects are observed if the vaso-active agents are given before or after melphalan. Hydralazine (5 mg/kg) induces close to 100% radiobiological hypoxia in the RIF-1 and KHT tumors. In contrast, Nifedipine has no effect on tumor hypoxic fraction at a dose of 10 mg/kg although the anti-tumor effectiveness of melphalan is substantially increased. However, a higher dose of 50 mg/kg nifedipine causes a large increase in tumor hypoxic fraction, an effect that persists for several hours. Verapamil causes no change in the fraction of hypoxic cells in the KHT tumor and increases, only slightly, the anti-tumor effect of melphalan.