Opposing effects of suramin and DL-alpha-difluoromethylornithine on polyamine metabolism contribute to a synergistic action on B16 melanoma cell growth in vitro.

Polyamines are crucial for normal and neoplastic cell growth. Treatment with the polyanionic drug suramin has pronounced antigrowth activity in several tumor cell lines, but its clinical use has been hampered by its toxicity. We have earlier shown that suramin affects cellular polyamine metabolism and transport, and that these effects were, in some respects, opposite to those of alpha-difluoromethylomithine (DFMO), a specific inhibitor to ornithine decarboxylase, a key metabolic enzyme for polyamines. DFMO has been used in anticancer trials, although with limited success. Combinations of suramin and DFMO were, hence, evaluated in vitro and were found to strongly inhibit B16 melanoma cell proliferation. DFMO alone induced melanoma cell differentiation, and suramin used in combination with DFMO did not abrogate this DFMO-induced differentiation. Synergy analysis demonstrated a pronounced growth-inhibitory synergism between suramin and DFMO. The results suggest that the efficacy of combinations of DFMO with suramin or its analogues should be further explored, especially in cells requiring high levels of polyamines for their growth.