Growth inhibitory effects of pegylated IFN-α 2 b and 5-fluorouracil in combination on renal cell carcinoma cell lines in vitro and in vivo

We investigated the effects of pegylated IFN-α2b (PEG-IFN-α2b) alone and PEG-IFN-α2b plus 5-fluorouracil (5-FU) in vitro on the proliferation of renal cell carcinoma (RCC) cell lines. After the transplantation of RCC cells into nude mice, we administered IFN (PEG-IFN-α2b or IFN-α2b) alone, 5-FU alone, or IFN (PEG-IFN-α2b or IFN-α2b) plus 5-FU; and investigated tumor volume, tumor weight, the numbers of apoptotic cells and artery-like blood vessels, relative mRNA expression levels of enzymes which relate to 5-FU metabolism, angiogenesis factor, and type I interferon receptor. RCC cells in vitro were generally and relatively resistant to the anti-proliferative effects of PEG-IFN-α2b, but the addition of 5-FU augmented IFN-induced anti-proliferative effects with the induction of apoptosis. PEG-IFN-α2b in vivo presented stronger anti-tumor effects than IFN-α2b, and its combination with 5-FU augmented the effects. The significant anti-tumor effect of the combination treatment was the increase in apoptotic cell number, but there were no significant differences in the suppression of angiogenesis, expression of IFN receptor, and the actions of metabolic enzymes of 5-FU. In conclusion, PEG-IFN-α2b presents stronger anti-tumor effects than non-pegylated IFN, and the effects are augmented in the combination with 5-FU. Our findings suggest the clinical usefulness of PEG-IFN-α2b in the treatment of RCC. Introduction Renal cell carcinoma (RCC) is highly resistant to conventional chemotherapy. The objective response rate is 6-9% for vinblastine and 5-8% for 5-fluorouracil (5-FU) (1). The response rates of treatment regimens using interleukin-2 are 6-31% (2), and the therapeutic response rates of interferon (IFN)-α are 4-33% in patients with metastatic RCC (3). The response rates of immunochemical therapies that utilize chemotherapeutic agents with IFN-α or interleukin-2 range between 8 and 39% (4). Immunochemical therapy is the best treatment for advanced RCC, but potential synergetic effects of the medicines as well as their mechanisms remain to be elucidated. Wadler and Wienik (5) for the first time proposed a combination therapy of IFN-α and 5-FU in 1988 in their study using colon cancer cell lines. Later, this combination therapy was applied to various types of human malignancies including RCC and hepatocellular carcinoma (HCC). 5-FU has two major anti-tumor mechanisms: one involves its active metabolite 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP), inhibiting the activity of thymidylate synthase (TS) and consequently DNA synthesis; the other is related to the incorporation of 5-FU metabolite into RNA and DNA, thereby disrupting normal RNA processing and function. The sensitivity of cancer cells to 5-FU is often influenced by the enzymes affecting 5-FU metabolism, including TS, dihydropyrimidine dehydrogenase (DPD), orotate phosphoribosyl transferase (OPRT), thymidine phosphorylase (TP), uridine phosphorylase (UP) and thymidine kinase (TK). PEG-IFN-α2b, a new interferon, is a covalent conjugate of recombinant IFN-α2b with monomethoxy polyethylene glycol (PEG) in a 1:1 molar ratio that produces a 31,000-Da molecule (6). PEG conjugation increases the size of the molecule, therefore, the absorption of the pegylated molecule is slower, its serum half-life is longer, and its rate of clearance from the plasma is lower than that of the unmodified molecule. PEG-IFN-α2b thereby increases patient exposure INTERNATIONAL JOURNAL OF ONCOLOGY 33: 647-655, 2008 647 Growth inhibitory effects of pegylated IFN-α2b and 5-fluorouracil in combination on renal cell carcinoma cell lines in vitro and in vivo FUKUKO MORIYA1-3, SACHIKO OGASAWARA1,3, YUJI BASAKI4, JUN AKIBA1,3, SAKIKO KOJIRO1,3, SUGURU FUKAHORI1,3, HIRONORI ISHIZAKI1-3, NAOYO NISHIDA1,3, KEI MATSUOKA2,3, MASAMICHI KOJIRO1,3, MICHIHIKO KUWANO3,4 and HIROHISA YANO1,3 Departments of 1Pathology and 2Urology, Kurume University School of Medicine, 3Research Center of Innovative Cancer Therapy of the 21st Century COE Program for Medical Science, Kurume University, 67 Asahi-machi, Kurume, Fukuoka 830-0011; 4Station-II for Collaborative Research Center, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan Received May 16, 2008; Accepted July 18, 2008 DOI: 10.3892/ijo_00000050 _________________________________________ Correspondence to: Dr F. Moriya, Department of Pathology, Kurume University School of Medicine, 67 Asahi-machi, Kurume, Fukuoka 830-0011, Japan E-mail: moriya_fukuko@kurume-u.ac. jp