Implications of MEK and VEGFR2 inhibition on melanoma CXCR4-CXCL12 chemotaxis, survival and tumour progression

Abstract

Both uveal and cutaneous metastatic melanoma remain incurable, largely due to the deregulation of signalling networks that facilitate drug resistance and tumour dissemination for which CXCR4-CXCL12 chemotaxis, MAPK signalling and angiogenesis play key roles. While hyper-activating mutations in MAPK signalling promote tumour survival/drug resistance, CXCR4-CXCL12 chemotaxis and angiogenesis, promote melanoma migration. Known individually to drive melanoma escape from the localised microenvironment, how these pathways interact remains largely undefined. The principle aim of the present study was thus to define the role and crosstalk of CXCR4-CXCL12, MAPK and VEGFR2 signalling in uveal and cutaneous melanoma, to inform on more efficacious targeted approaches to prevent metastasis. Results revealed increased CXCR4 expression as a putative prognostic biomarker for AJCC stage II cutaneous melanomas, while CXCL12 expression within the epidermis likely prevents metastasis. Additionally, CXCL12 secretion by melanomas was associated with autocrine CXCR4-CXCL12 signalling and MAPK activation. VEGFR2 was expressed by primary melanomas and associated with cutaneous metastasis to lymph nodes, with VEGF treatment promoting melanoma cell migration. Analysis of CXCR4-CXCL12-mediated chemotaxis demonstrated enhanced migration of melanoma cells towards CXCL12, either recombinant of derived from primary dermal fibroblast supernatants, the effect of which was inhibited by both the MEK inhibitor, trametinib, and the VEGFR2 inhibitor, pazopanib. Interestingly, the concurrent increase in autophagy observed in response to trametinib, prevented by co-treatment of uveal/cutaneous melanoma cells with chloroquine, suggest the efficacy of MEK inhibition may be potentiated with dual inhibition of pro-survival autophagy. Given that both CXCR4-CXCL12 and VEGF-VEGFR2 signalling activate MAPK pathway, and alone promote melanoma migration. Results demonstrated combined trametinib and pazopanib, potentiated both inhibition of uveal and cutaneous melanoma cell viability as well as CXCR4-CXCL12-mediated migration. Collectively these studies confirm the intimate relationship between CXCR4-CXCL12/VEGFR2/MAPK signalling, highlighting potential novel combinational approaches through which to prevent melanoma survival and migration.