Background: Renal cell carcinoma (RCC) is a top ten malignancy in the U.S. Overexpression of the proviral integration site for moloney murine leukemia virus 1 (PIM1) kinase is associated with poor clinical outcomes in RCC patients. PIM1 is a constitutively active serine/threonine kinase promoting cell proliferation, apoptosis resistance, invasion, and migration. The mechanisms underlying PIM1 expression and its function in RCC are not fully delineated. IL-6 is a pleiotropic cytokine that activates the JAK/STAT signaling cascade. High serum IL-6 levels are associated with the poor prognosis of RCC patients and may contribute to RCC invasion and metastasis. STAT3/5 binds directly to the PIM1 promoter inducing PIM1 expression. An IL-6/ STAT3/PIM1 axis exists in pancreatic and breast cancer. We previously reported that PIM1 is overexpressed in a panel of human RCC cell lines relative to renal proximal tubule epithelial cells. We also identified that RCC cells secrete IL-6. Our prior studies suggest that differential expression of PIM1 may be linked to autocrine IL-6 signaling. We thus hypothesize that an IL6/JAK/STAT pathway regulates the expression of PIM1 in RCC.

Methods: Retrospective review of DNA (592-gene or whole exome) and RNA (whole transcriptome) NGS data from real-world patient samples profiled at a CLIA-certified lab (Caris Life Sciences). Pathway analysis of differentially expressed genes was assessed using GSEA. Overall survival was calculated from insurance claims data. To understand how IL-6 signaling through the JAK/STAT pathway may regulate PIM1 expression in RCC cells, we examined whether IL-6 blockade using anti-IL-6 antibody or tocilizumab, would modulate PIM1 expression. Similarly, we assessed whether ruxolitinib, and LLL12, a STAT3 inhibitor could regulate PIM1 expression.

Results: Transcriptome analyses show that PIM1 expression is significantly increased in metastatic RCC relative to primary RCC. Survival curves demonstrate that PIM1 overexpression is associated with decreased overall survival for RCC patients, independent of treatment received. IL-6 expression was up to 6.5-fold higher in RCC patients with PIM1 overexpression. In RCC cell lines, IL-6 blockade through either anti-IL-6 antibody or tocilizumab was sufficient to decrease PIM1 protein levels. Treatment with ruxolitinib leads to a dose and time-dependent decrease in PIM1 levels. Incubation with a STAT3 inhibitor also resulted in decreased PIM1 levels in RCC cells.

Conclusions: These results suggest that differential expression of PIM1 in RCC may be linked to autocrine IL-6 signaling. Furthermore, poor survival in PIM1-overexpressing RCC patients is independent of treatment received, and therefore necessitates use of targeted therapies against this axis. Multiple FDA-approved agents are available that target this pathway. Further investigation is required to determine the efficacy of these agents in pre-clinical models and clinical trials. Research Sponsor: Kidney Cancer Association; National Institutes of Health; Brown University.