Novel therapeutic targeting of apoptosis and survival pathways in melanoma

• Main Author: Karst, Alison Marie
• Language: English
• Published: University of British Columbia 2008
• Subjects: Cancer; Genetics
• Online Access: http://hdl.handle.net/2429/2473

Cutaneous malignant melanoma is an aggressive form of skin cancer, characterized by strong chemoresistance and poor patient prognosis. The molecular mechanisms underlying its resistance to chemotherapy remain unclear but are speculated to involve dysregulation of apoptosis and reinforcement of survival signaling. In this work, we show that aberrant expression of two key proteins, PUMA and p-Akt, is associated with melanoma tumor progression and poor patient survival. We report that PUMA expression is reduced in melanoma tumors compared to dysplastic nevi, while p-Akt expression is elevated in melanoma tissue compared to dysplastic nevi. We propose a two-pronged therapeutic strategy of (1) boosting PUMA expression and (2) inhibiting Akt phosphorylation. We demonstrate that exogenous overexpression of PUMA, via adenoviral-mediated gene expression (ad-PUMA), forces melanoma cells to undergo rapid mitochondrial-mediated apoptosis in vitro. We also report that a small molecule Akt inhibitor, API-2, greatly inhibits melanoma cell growth in vitro. Using a SCID mouse melanoma xenograft model, we show that combination treatment of ad-PUMA and API-2 dramatically suppresses tumor growth in an additive manner, leading to over 80% growth inhibition compared to controls. We also investigate the role of NF-κB overexpression in melanoma. Our lab previously reported that expression of the p50 subunit of NF-κB, in particular, correlates with melanoma progression and poor patient survival. Here, we use cDNA microarray analysis to show that p50 overexpression upregulates IL-6 in melanoma cells. We further demonstrate that p50-mediated IL-6 expression stimulates the growth of endothelial cells in vitro and promotes angiogenesis in vivo. This work supports the hypothesis that melanoma cells exploit multiple mechanisms to sustain a survival advantage, including: 1) suppression of apoptosis (via PUMA down-regulation), 2) increased activation of survival pathways (via increased p-Akt), and 3) upregulation of pro-angiogenic factors (via p50-mediated IL-6 induction). This work suggests that the specific targeting of one or more key mediators of these processes may be an effective therapeutic strategy for treating malignant melanoma.