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Background: PLEKHA5 has previously been identified as a novel molecule implicated in melanoma brain metastasis, a disease that continues to portend a poor prognosis. The aim of this study was to further investigate the functional role of PLEKHA5 in disseminated melanoma., Methods: The impact of PLEKHA5 on proliferation and tumor growth was examined in vitro and in melanoma xenograft models, including brain-tropic melanomas (melanomas tending to disseminate to the brain). In vitro loss- and gain-of-function studies were used to explore the underlying mechanisms of PLEKHA5-mediated tumor growth and the crosstalk between PLEKHA5 and PI3K/AKT/mTOR or MAPK/ERK signaling. The clinical relevance of PLEKHA5 dysregulation was further investigated in a cohort of matched cranial and extracranial melanoma metastases., Results: PLEKHA5 stable knockdown negatively regulated cell proliferation by inhibiting the G 1 -to-S cell cycle transition, which coincided with upregulation of the cell cycle regulator PDCD4. Conversely, ectopic PLEKHA5 expression exhibited the inverse effect. PLEKHA5 knockdown significantly inhibited tumor growth, whereas its overexpression upregulated the growth of tumors, which was induced by cranial and subcutaneous inoculation of cells in nude mice. PLEKHA5 modulation affected PDCD4 protein stability and was coupled with changes in PI3K/AKT/mTOR pathway signaling. High PDCD4 expression in cerebral specimens was associated with better overall survival., Conclusions: This study further supports the role of PLEKHA5 as a regulator of melanoma growth at distant sites, including the brain. Furthermore, the results highlight the significance of PDCD4 dysregulation in disseminated melanoma and implicate PDCD4 as a possible causal link between PLEKHA5 and cell proliferation and growth., (© 2019 American Cancer Society.)

Background: Inhibiting src kinases (non-receptor tyrosine kinase signaling intermediates) reduces melanoma cell proliferation and invasion. Dasatinib inhibits c-kit, PDGFβR, and EPHA2 and src kinases c-src, c-Yes, Lck, and Fyn. A phase 2 trial of dasatinib in melanoma was conducted to assess response rate (RR), progression-free survival (PFS), and toxicity., Methods: Adults with stage 3/4 chemotherapy-naïve unresectable melanoma were eligible. Dasatinib was initially administered at 100 mg twice daily continuously to 17 patients. Due to toxicity, the starting dosage was decreased to 70 mg twice daily. Tumor assessments occurred every 8 weeks., Results: Thirty-nine patients were enrolled, 36 of whom were evaluable for activity and toxicity. Five, 4, and 3 patients had acral-lentiginous, ocular, or mucosal primaries, respectively. Two patients had confirmed partial responses lasting 64 and 24 weeks (RR 5%). Three patients had minor responses lasting 136, 64, and 28 weeks, and 1 patient who was responding discontinued due to noncompliance. The median PFS was 8 weeks; the 6-month PFS rate was 13%. One patient with an exon-13 c-kit mutation had a partial response, whereas disease in another patient with an exon-11 c-kit mutation progressed. Common toxicities were fatigue, dyspnea, and pleural effusion., Conclusions: Daily dasatinib has minimal activity in unselected melanoma patients, excluding those with c-kit mutations. The study did not meet the prespecified endpoints of 30% response rate or 6-month PFS. Dasatinib was poorly tolerated overall, often requiring dose reduction or interruption. Because activity was observed in a small subset without c-kit mutations, identifying predictive biomarkers is important for future development of dasatinib in melanoma alone or in combination trials., (2010 American Cancer Society.)