Potentiation of the antiproliferative effect in vitro of doxorubicin, cisplatin and genistein by new analogues of vitamin D

Numerous vitamin D-3 analogues have been synthesised in recent years in order to obtain compounds with a favourable biological and therapeutic (antipsoriatic and/or antitumour) activity. Our results showed that pre-treatment for 72 hours of HL-60 human promyelocytic leukaemia cells with calcitriol or its new analogues significantly potentiated their sensitivity to the antiproliferative effect in vitro of cisplatin, doxorubicin or genistein. Moreover, for all cytotoxic agents tested a synergistic antiproliferative effect was observed. This effect was expressed as a significant decrease of the ID50 (inhibitory dose 50%) values for each cytotoxic agent applied after pretreatment with calcitriol or its analogues of HL-60 cells in comparison with the effect of cytotoxic agent applied alone. The observed in vitro potentiated antiproliferative effect of cytotoxic drugs used in combination with vitamin D or its analogues may raise the question as to whether such an effect could be expected in the in vivo situation.