The effects of ALK5 inhibition and simultaneous inhibition or activation of HIF-1alpha in melanoma tumor growth and angiogenesis

Abstract

BACKGROUND: Hypoxia is the most common signature of the tumor microenvironment that drives tumorigenesis through the complex crosstalk of a family of transcription factors called hypoxia-inducible factors (HIFs), with other intercellular signaling networks. Hypoxia increases transforming growth factor-beta (TGF-beta) expression. TGF-beta and HIF-1alpha play critical roles in several malignancies and their interactions in melanoma progression remain unknown. Therefore, the aim of this study was to assess the impact of inhibiting activin receptor-like kinase-5 (ALK5), a TGF-beta receptor, on the response to HIF-1alpha activation or inhibition in melanoma tumor progression. MATERIALS AND METHODS: Tumors were induced in C57BL/6J mice by subcutaneous inoculation with B16F10 melanoma cells. Mice were divided into HIF-1alpha inhibitor, ALK5 inhibitor (1 mg/kg) and HIF-1alpha inhibitor (100 mg/kg), ALK5 inhibitor, HIF-1alpha activator (1000 mg/kg), HIF-1alpha activator and ALK5 inhibitor, and control groups to receive inhibitors and activators through intraperitoneal injection. The expression of E-cadherin was evaluated by RT-qPCR. Vessel density and platelet-derived growth factor receptor beta (PDGFR)-beta+ cells around the vessels were investigated using immunohistochemistry. RESULTS: The groups receiving HIF-1alpha inhibitor and activator showed lower and higher tumor growth compared to the control group, respectively. E-cadherin expression decreased in all groups compared to the control group, illustrating the dual function of E-cadherin in the tumor microenvironment. Vascular density was reduced in the groups given HIF-1alpha inhibitor, ALK5 inhibitor, and ALK5 and HIF-1alpha inhibitor simultaneously. The percentage of PDGFR-beta+ cells was reduced in the presence of HIF-1alpha inhibitor, ALK5 inhibitor, HIF-1alpha and ALK5 inhibitors, and upon simultaneous treatment with HIF-1alpha activator and ALK5 inhibitor. CONCLUSION: Despite increased expression and interaction between TGF-beta and HIF-1alpha pathways in some cancers, in melanoma, inhibition of either pathway alone may have a stronger effect on tumor inhibition than simultaneous inhibition of both pathways. The synergistic effects may be context-dependent and should be further evaluated in different cancer types.