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

Abstract
Enhancement of the anti‐proliferative effect of human interferon (HuIFN) preparations (α, β and γ) by dipyridamole was detected in a human malignant melanoma cell line, MMICB, which we originally established. Cell growth was inhibited by HulFN alone, but a marked increase in inhibition was noted in vitro and in vivo when dipyrydamole was added. Cellular DNA synthesis, as dletermined 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 HulFN on MM‐ICB, MM‐2CB, and SEKI cells.