INFLUENCE OF VERAPAMIL ON TUMOR-CELL GROWTH IN-VITRO FOLLOWING TREATMENT WITH ANTIBLASTIC DRUGS

The effect of antiblastic drugs with different mechanisms of action ha s been investigated in LoVo cells (on the resistant line LoVo R and th e parental LoVo S) for 48 h and for further 24 h in drug-free medium ( recovery time) in order to evaluate drug action after its removal. Our results show that the drug effect persists in time, particularly in L oVo R cells. The inhibitory effect on cell growth was enhanced when th e drugs were associated with verapamil, while no difference was detect ed with cisplatin and 4-hydroperoxycyclophosphamide, drugs which are n ot involved in P-glycoprotein-mediated multidrug resistance. These res ults demonstrate that verapamil is an effective agent in association w ith those drugs which are actively transported out of the tumour cells , while it is ineffective on drugs which can induce resistance by diff erent mechanisms.