75 Transcriptional Correlates of ARNT Expression and Its Impact on Survival Outcomes in Clear-Cell Renal Cell Carcinoma (Ccrcc)

Abstract Background Encoded by ARNT, hypoxia-inducible factor-1β (HIF1β) is a constitutively expressed obligate binding partner for HIF1α and HIF2α, enabling their transcriptional activation of HIF-target pathways, such as angiogenesis. Here, we examine the relation of ARNT expression with hypoxia and immune programs, and its impact on survival outcomes in ccRCC. Methods We included patients (pts) with RNA-seq data from TCGA-KIRC (stages I-IV; n = 529), and 2 first-line clinical trials in metastatic ccRCC involving VEGF-pathway inhibitor alone vs in combination with immunotherapy (Trial 1: n = 741, Trial 2: n = 403). Transcripts per million (TPM) were log2-transformed and scaled per 1 SD change. Buffa Hypoxia Score (BHS) was computed per prior reports (Bhandari et al., 2020): expression for each of the score’s 50 genes per patient was assigned +1, if ≥ median for this gene, or -1 if < median, then summed. The immune signatures, IMmotion150 Angio, Teff and Myeloid, JAVELIN and Tumor Inflammatory Score (TIS) were calculated as means of their genes’ log2-transformed TPMs. Spearman correlation associated ARNT expression, with each of these signatures, and EPAS1 and HIF1A expressions. Multivariable Cox models evaluated the association of ARNT expression with progression-free (PFS) and overall (OS) survival per each full cohort, adjusted for age, sex, stage and sarcomatoid features for KIRC, and for age, sex, IMDC risk, treatment arm and sarcomatoid features for the trials. Likelihood ratio test (LRT) assessed interaction between ARNT and treatment arm in predicting survival. Results Across three cohorts, higher ARNT expression correlated with higher BHS (ρ = 0.23-0.49), higher Angio signature (ρ = 0.14-0.57) and higher TIS (ρ = 0.14-0.21) (p < 0.05). Higher ARNT correlated with higher Teff and JAVELIN signatures in KIRC (Teff: ρ = 0.19, p = 8.3 × 10⁻⁶; JAVELIN: ρ = 0.16, p = 1.8 × 10⁻⁶) and Trial 1 (Teff: ρ = 0.16, p = 1.2 × 10⁻5; JAVELIN: ρ = 0.17, p = 1.8 × 10⁻⁶) but not Trial 2 (ρ = 0.09 for both, p > 0.05). A positive correlation was identified between Myeloid signature and higher ARNT expression in Trial 1 (ρ = 0.17, p = 2.3 × 10⁻⁶) and Trial 2 (ρ = 0.12, p = 0.02), but not KIRC (ρ = 0.05, p = 0.24). A consistent correlation was observed between ARNT and EPAS1 expressions (ρ = 0.19-0.61), and HIF1A (ρ = 0.30-0.51), across all cohorts (p < 0.05). Multivariable Cox models revealed no significant association between ARNT expression and PFS and OS (Table), independent of treatment arm per trial (LRT p > 0.05). Conclusions ARNT expression tracks with hypoxia, angiogenic and immune transcriptional states in ccRCC but is not independently prognostic, suggesting biologic relevance without clear predictive value in current VEGF- and immunotherapy-based regimens.