| Summary: | 博士 === 國立中山大學 === 生物醫學研究所 === 101 === Despite the development of novel target therapy drugs in recent years, metastatic cancer remains refractory to current cancer therapies and accounts for the majority of cancer mortalities worldwide. Metastasis consists of multiple steps including angiogenesis, extravasion, escape from immune surveillance, adhesion, and clonal expansion in different organs that a systemic therapy is required for effective control of metastasis. The pro-inflammatory nuclear factor kappa B (NFκB) pathway plays an important role during each of these metastatic events and constitutes an excellent target for metastasis control. Stress hormone pro-opiomelanocortin (POMC) and its derived neuropeptides including corticotrophin (ACTH), α-, β-, and γ-melanocyte–stimulating hormone (α-, β-, and γ-MSH), β-endorphin are potent inhibitors of NFκB pathway. Other than the central regulation of stress response and energy homeostasis, POMC also regulates the skin pigmentation, inflammatory processes, and immune reactions in the peripheral system. Since adenovirus–mediated POMC gene delivery leads to hepatic POMC expression, it seems plausible that POMC gene therapy may elicit systemic production of anti-inflammatory POMC-derived peptides and hold promises for control of primary and metastatic cancers. In B16-F10 melanoma models, POMC gene delivery elevated the circulating ACTH levels for more than 8 weeks and suppressed the growth of established melanoma, thereby prolonging the life span of tumor-bearing mice. Moreover, combination of POMC therapy with cisplatin further enhances the survival outcome. Subsequent analysis reveals that POMC gene therapy inhibits the growth and metastasis of melanoma through apoptosis, angiogenesis inhibition, and modulation of epithelial-mesenchymal transition. Besides, α-MSH/melanortin-1 receptor (MC-1R) pathway is involved in the POMC-mediated melanoma suppression.
To investigate whether POMC therapy could be applied to other types of tumor, we evaluated the therapeutic efficacy of POMC gene therapy in Lewis lung carcinoma (LLC) cells which lack MC-1R. Interestingly, POMC gene delivery effectively inhibited the proliferation and colony formation of LLC cells in vitro and the growth of established LLC in mice. Histological analysis indicated that POMC gene delivery attenuated LLC through proliferation inhibition, apoptosis induction, and angiogenesis blockade. Moreover, POMC gene delivery perturbed β-catenin signaling by reducing protein levels of β-catenin and its downstream proto-oncogenes, including cyclin D1 and c-myc. These results support the existence of an MC-1R-independent pathway for POMC gene therapy and expand the therapeutic spectrum of POMC therapy for multiple types of cancer.
To elucidate the role of host immunity in anti-neoplastic mechanism underlying POMC therapy, we compared the treatment efficacy of POMC gene therapy for B16-F10 melanoma between severe combined immune-deficient (SCID) and immune-competent C57BL/6 mice, and found similar extent of tumor suppression in both strains of mice. In addition, POMC gene therapy reduced the spleen weight and the number of circulating lymphocytes in B6 mice. These findings suggest that POMC therapy was not dependent on host immunity, yet instead induced immune suppression of animals through ACTH/cortisol production. To minimize such side effect of POMC therapy, we generated a series of adenovirus vectors encoding POMC with mutations in ACTH domain (ACTH-K15A/R17A), which fails to stimulate cortisol synthesis in vitro and in vivo. Gene delivery of ACTH (K15A/R17A) remained capable of suppressing the primary and metastatic melanoma, but had no effect on immune functions in mice. In conclusion, we have characterized the anti-neoplastic function and mechanism of POMC therapy for cancer. Furthermore, we have developed improved POMC gene vectors to minimize its adverse effect for future cancer therapy.
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