Dipyridamole as a modulator of multidrug-resistance in tumor-cells in-vitro.

The aim of the present study was to investigate in vitro the effect on LoVo cells (LoVo-S, doxorubicin-sensitive, and LoVo-R, doxorubicin-resistant) on the association of dipyridamole and certain antiblastic drugs (doxorubicin, idarubicin, mitoxantrone, teniposide) with different mechanisms of action. The cells were treated for 48 hours with the drugs, or were left for 24 hours without treatment (recovery period). The results demonstrate that dipyridamole possesses an inhibitory effect on cell growth, and that it potentiates the cytotoxic effect of the tested antiblastic drugs, particularly on LoVo-R cells. In the recovery period the inhibitory effect of dipyridamole on LoVo-S and LoVo-R cells was reversible, while the effect of the antitumour drugs, either alone or in association with dipyridamole, persisted. We suggest that dipyridamole has a synergistic effect on LoVo cell growth when associated with antiblastics; the increased effect produced on LoVo-R cells is indicative for a reversion of multidrug resistance, probably via a mechanism related to transmembrane transport system.