Antineoplastic activity of the combination of interferon and cytotoxic agents against experimental and human malignancies: a review.

The combination of interferon (IFN) and conventional chemotherapeutic agents offers a promising therapeutic approach for the treatment of cancer. However, there is as yet no consensus on optimal strategies for combining this family of compounds with other cancer therapies. While in vitro studies have demonstrated both direct cytotoxic and cytokinetic effects for IFN, a more interesting role derives from its ability to synergistically potentiate the activity of a wide variety of cytotoxic agents against multiple human and rodent tumors, both in vitro and in animal models. The interaction between IFN and cytotoxic agents in vitro is complex and depends not only on the choice of cytotoxic agent but also on the concentrations, ratios, duration, and sequence of exposure to the two drugs. Preliminary data suggest that some combinations are not merely additive but rather that IFN may biochemically modulate the cellular uptake or metabolism of the cytotoxic agent resulting in synergistic antineoplastic activity. In vivo interactions between IFN and cytotoxic agents involve an additional layer of complexity because of the potential effects of the biological agent on the host immune system and drug-metabolizing enzymes. Furthermore, IFN may have a protective effect on normal host tissues which theoretically could allow for the delivery of higher doses of cytotoxic agents. The results of early clinical trials using combinations of IFN with chemotherapeutic agents have generally been disappointing. This may be due to the inability of preclinical models to accurately predict the clinical situation or alternatively from a failure to incorporate information on dose, scheduling, and sequence of drug administration into clinical trials. Preliminary clinical studies with IFN-alpha and the fluorinated pyrimidine, 5-fluorouracil, in patients with advanced colorectal carcinoma suggest that IFN may enhance the effects of the antimetabolite. Confirmatory trials are in progress. Further trials designed to exploit the preclinical experience with combinations of IFN and cytotoxic agents are warranted.