Exploratory Multi-Level Analysis of the HIF Axis in Clear-Cell Renal Cell Carcinoma and Evaluation of GN44028 as an Experimental HIF Pathway-Modulating Compound

Clear-cell renal cell carcinoma (ccRCC) is characterised by constitutive activation of hypoxia-inducible factors (HIFs) following VHL loss, which contributes to tumour progression and therapeutic resistance. Given the limitations of VEGFR-targeted therapies, we investigated the biological and potential therapeutic relevance of the HIF axis in ccRCC. Nuclear and cytoplasmic HIF1A and EPAS1/HIF2A expression were assessed by immunohistochemistry in tumours from 40 patients and correlated with clinicopathological parameters and cancer-specific survival. The functional effects of HIF pathway inhibitors (GN44028, KC7F2, and FM19G11) and sunitinib were analysed in VHL-mutant 786-O and VHL-wild-type Caki-1 cell lines using SRB viability assay, cell cycle analysis, wound closure assay, and RT-qPCR of HIF-related genes, with comparison to non-malignant HK-2 cells. TCGA-ccRCC data from advanced-stage patients (III–IV, n = 185) were analysed as a complementary transcriptomic context. Nuclear, but not cytoplasmic, HIF1A and EPAS1/HIF2A expression was associated with advanced stage and shorter survival in univariable analyses. GN44028 showed the most pronounced antiproliferative effect under tested conditions and was associated with broad suppression of HIF-related transcription, whereas sunitinib was associated with increased expression of selected HIF-related genes. GN44028 did not demonstrate clear selectivity over non-malignant HK-2 cells. Overall, nuclear HIF activation is associated with aggressive ccRCC biology, and broader HIF pathway modulation warrants further experimental investigation; however, the clinical findings remain exploratory, and therapeutic selectivity and translational relevance are not yet established.