Expression of PBRM1 as a prognostic predictor in metastatic renal cell carcinoma patients treated with tyrosine kinase inhibitor

PBRM1 loss is associated with increased sensitivity to MCL1 and CDK9 inhibition in clear cell renal cancer

MCL1 is a member of the BCL2 family of apoptosis regulators, which play a critical role in promoting cancer survival and drug resistance. We previously described PRT1419, a potent, MCL1 inhibitor with anti-tumor efficacy in various solid and hematologic malignancies. To identify novel biomarkers that predict sensitivity to MCL1 inhibition, we conducted a gene essentiality analysis using gene dependency data generated from CRISPR/Cas9 cell viability screens. We observed that clear cell renal cancer (ccRCC) cell lines with damaging PBRM1 mutations displayed a strong dependency on MCL1. PBRM1 (BAF180), is a chromatin-targeting subunit of mammalian pBAF complexes. PBRM1 is frequently altered in various cancers particularly ccRCC with ~40% of tumors harboring damaging PBRM1 alterations. We observed potent inhibition of tumor growth and induction of apoptosis by PRT1419 in various preclinical models of PBRM1-mutant ccRCC but not PBRM1-WT. Depletion of PBRM1 in PBRM1-WT ccRCC cell lines induced sensitivity to PRT1419. Mechanistically, PBRM1 depletion coincided with increased expression of pro-apoptotic factors, priming cells for caspase-mediated apoptosis following MCL1 inhibition. Increased MCL1 activity has been described as a resistance mechanism to Sunitinib and Everolimus, two approved agents for ccRCC. PRT1419 synergized with both agents to potently inhibit tumor growth in PBRM1-loss ccRCC. PRT2527, a potent CDK9 inhibitor which depletes MCL1, was similarly efficacious in monotherapy and in combination with Sunitinib in PBRM1-loss cells. Taken together, these findings suggest PBRM1 loss is associated with MCL1i sensitivity in ccRCC and provide rationale for the evaluation of PRT1419 and PRT2527 for the treatment for PBRM1-deficient ccRCC.

Treatment strategies for clear cell renal cell carcinoma: Past, present and future

Clear cell renal cell carcinoma (ccRCC) is the most prevalent histological subtype of kidney cancer, which is prone to metastasis, recurrence, and resistance to radiotherapy and chemotherapy. The burden it places on human health due to its refractory nature and rising incidence rate is substantial. Researchers have recently determined the ccRCC risk factors and optimized the clinical therapy based on the disease's underlying molecular mechanisms. In this paper, we review the established clinical therapies and novel potential therapeutic approaches for ccRCC, and we support the importance of investigating novel therapeutic options in the context of combining established therapies as a research hotspot, with the goal of providing diversified therapeutic options that promise to address the issue of drug resistance, with a view to the early realization of precision medicine and individualized treatment.

PBRM1 Immunohistochemical Expression Profile Correlates with Histomorphological Features and Endothelial Expression of Tumor Vasculature for Clear Cell Renal Cell Carcinoma

Simple Summary

The PBRM1 protein, whose gene is the most frequently mutated one in clear cell renal cell carcinoma (ccRCC) following von Hippel-Lindau, has been proposed as a potential biomarker for ccRCC. However, the association of the PBRM1 immunohistochemical expression with histomorphological features of ccRCC and the endothelial expression of tumor vasculature, which is an important role of the tumor microenvironment related to treatment response, is little known. Recently, our research team has established a vascularity-based architectural classification of ccRCC correlated with angiogenesis and immune gene expression signatures, which could provide prognostic information and function as a surrogate for treatment selection. In the present study, we found the PBRM1 expression was correlated with the architectural patterns. Furthermore, we demonstrated that endothelial expression tended to be lost in cases with low PBRM1 expression. This correlation implied the orchestrated expression of PBRM1, raising the possibility that the cancer cells and their microenvironment interact in ccRCC.

Abstract

Loss of the polybromo-1 (PBRM1) protein has been expected as a possible biomarker for clear cell renal cell carcinoma (ccRCC). There is little knowledge about how PBRM1 immunohistochemical expression correlates with the histomorphological features of ccRCC and the endothelial expression of tumor vasculature. The present study evaluates the association of architectural patterns with the PBRM1 expression of cancer cells using a cohort of 425 patients with nonmetastatic ccRCC. Furthermore, we separately assessed the PBRM1 expression of the endothelial cells and evaluated the correlation between the expression of cancer cells and endothelial cells. PBRM1 loss in cancer cells was observed in 148 (34.8%) patients. In the correlation analysis between architectural patterns and PBRM1 expression, macrocyst/microcystic, tubular/acinar, and compact/small nested were positively correlated with PBRM1 expression, whereas alveolar/large nested, thick trabecular/insular, papillary/pseudopapillary, solid sheets, and sarcomatoid/rhabdoid were negatively correlated with PBRM1 expression. PBRM1 expression in vascular endothelial cells correlated with the expression of cancer cells (correlation coefficient = 0.834, p < 0.001). PBRM1 loss in both cancer and endothelial cells was associated with a lower recurrence-free survival rate (p < 0.001). Our PBRM1 expression profile indicated that PBRM1 expression in both cancer and endothelial cells may be regulated in an orchestrated manner.