Enhancement of an anti‐tumor effect of interferon by dipyridamole in established human malignant melanoma cell lines

Enhancement of the anti-proliferative effect of human interferon (HuIFN) preparations (alpha, beta and gamma) by dipyridamole was detected in a human malignant melanoma cell line, MM-ICB, which we originally established. Cell growth was inhibited by HuIFN alone, but a marked increase in inhibition was noted in vitro and in vivo when dipyrydamole was added. Cellular DNA synthesis, as determined by 3H-deoxythymidine incorporation into the acid-insoluble cellular fraction, was more inhibited by combined treatment than by any of the agents used alone. Two other melanoma cell lines that we established, MM-2CB and MM-3CB, also exhibited sensitivity to combined treatment both in vitro and in vivo. Furthermore, the HMV-I and SEKI melanoma cell lines were susceptible to the combination. Even non-cytotoxic concentrations of dipyridamole could enhance the effect of HuIFN on MM-ICB, MM-2CB, and SEKI cells.