naloxone and Fibrosarcoma

New strategies that stimulate cell-mediated immunity (CMI) against tumors and inhibit regulatory T cells are needed to improve the outcome of cancer immunotherapy. The aim of this study was to enhance the anti-tumor immunity of gp96 vaccine through naloxone administration. Therefore, we used BALB/c mouse model of fibrosarcoma tumor and analyzed the tumor size, splenocyte proliferation, spleen and tumor-infiltrated lymphocytes. Tumor and spleen CD4+CD25+Foxp3+ regulatory T lymphocytes, cytotoxic activity of the splenocytes, IFN-gamma and IL-4 secretion were assessed to describe the anti-tumor immune response. Our findings showed that co-administration of gp96 and naloxone has resulted in a significant reduction in CD4+CD25+Foxp3+ regulatory T cells in the spleen. The results indicated that on days 27 and 32 the tumors in the gp96+Nal group grew significantly slower. Moreover, co-administration of gp96 and naloxone significantly increased the intra-tumor CD8+ T cells and cytotoxic activity. In addition the results indicated a significant increase in the proliferation of splenocytes and IFN-gamma production. Our results demonstrate that naloxone is an effective immunoadjuvant in cancer immunotherapy.

Topics: Animals; Antigens, Neoplasm; CD4 Antigens; Cell Line, Tumor; Cell Proliferation; Cytotoxicity, Immunologic; Female; Fibrosarcoma; Forkhead Transcription Factors; Interferon-gamma; Interleukin-2 Receptor alpha Subunit; Interleukin-4; Lymphocytes, Tumor-Infiltrating; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Neoplasm Transplantation; Spleen; T-Lymphocytes, Regulatory; Tumor Burden

Recent evidence has implicated enkephalins as immunomodulators. Several studies have reported the regulation of tumor growth by methionine enkephalin (ME). However, there has been little effort to relate the immunological significance of enkephalins to the development of anticancer drugs. The present study had three aims: first, to compare the antitumor activity of the synthetic peptide, D-[Ala2]methionine enkephalinamide (MEA), with endogenous enkephalins on PYB6 fibrosarcoma tumor growth; second, to determine whether tumor growth inhibition was mediated by an opiate receptor; and third, to investigate the effects of MEA on selected immune responses. Female B6C3F1 mice were injected i.p. daily for 7 days with 50-4000 micrograms/kg of ME, MEA, leucine enkephalin (LE) or D-[Ala2]leucine enkephalinamide (LEA), beginning 1 day after PYB6 inoculation. ME and MEA, but not LE or LEA, decreased the PYB6 growth rate. The dose of 50 micrograms/kg MEA exerted the maximum inhibition of tumor growth (nearly 72% on day 15 post tumor transplantation). MEA was not directly toxic to PYB6 tumor cells, as evaluated by the measurement of DNA synthesis and cellular ATP levels of PYB6 cells exposed to MEA in vitro. No [3H]-etorphine specific bindings were detected on the cell membrane or sonicates of splenic lymphocytes or PYB6 cells. Therefore, the antitumor activity by MEA is likely mediated by an indirect mechanism. Immunological studies indicated that MEA selectively enhanced the lymphoproliferative response to the T-cell mitogen, concanavalin A, but not to the B-cell mitogen, lipopolysaccharide.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adjuvants, Immunologic; Animals; Antibody Formation; Antineoplastic Agents; Enkephalin, Methionine; Enkephalins; Female; Fibrosarcoma; Killer Cells, Natural; Lymphocyte Activation; Mice; Naloxone; Receptors, Opioid; Tumor Cells, Cultured