Interferon-alpha potentiates the antiproliferative activity of CPT-11 against human colon cancer xenografts in nude mice.

Recently cytokines have been reported to potentiate the antiproliferative effects of chemotherapeutic agents against a variety of malignant tumors. We studied the antiproliferative effect of recombinant human interferon-alpha (rHuIFN-α) and CPT-11 on transplantable human colon cancer H-110 in nude mice. CPT-11 was administered to the H-110-bearing nude mice intraperitonealy every 4 days and rHuIFN-α was administered subcutaneously every day. The weight of the individual tumor was estimated by the tumor size. The cell cycle was analyzed by flow cytometry. The single administration of rHuIFN-α failed to show any antiproliferative activity. The antiproliferative effects of CPT-11 alone were observed in a dose and time dependent manner. This antiproliferative activity was markedly (p<0.05) enhanced by combination with rHuIFN-α. Flow cytometric analysis revealed that treatment with rHuIFN-α accumulated cells in the S phase. rHuIFN-α can enhance the antiproliferative effects of CPT-11, probably through the accumulation of the tumor cells in the S phase.