Mutational Analysis of PBRM1 and Significance of PBRM1 Mutation in Anti-PD-1 Immunotherapy of Clear Cell Renal Cell Carcinoma

Chromatin Remodelers Are Regulators of the Tumor Immune Microenvironment

Immune checkpoint inhibitors show remarkable responses in a wide range of cancers, yet patients develop adaptive resistance. This necessitates the identification of alternate therapies that synergize with immunotherapies. Epigenetic modifiers are potent mediators of tumor-intrinsic mechanisms and have been shown to regulate immune response genes, making them prime targets for therapeutic combinations with immune checkpoint inhibitors. Some success has been observed in early clinical studies that combined immunotherapy with agents targeting DNA methylation and histone modification; however, less is known about chromatin remodeler-targeted therapies. Here, we provide a discussion on the regulation of tumor immunogenicity by the chromatin remodeling SWI/SNF complex through multiple mechanisms associated with immunotherapy response that broadly include IFN signaling, DNA damage, mismatch repair, regulation of oncogenic programs, and polycomb-repressive complex antagonism. Context-dependent targeting of SWI/SNF subunits can elicit opportunities for synthetic lethality and reduce T-cell exhaustion. In summary, alongside the significance of SWI/SNF subunits in predicting immunotherapy outcomes, their ability to modulate the tumor immune landscape offers opportunities for therapeutic intervention.

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.

Identification of pyroptosis-related subtypes and comprehensive analysis of characteristics of the tumor microenvironment infiltration in clear cell renal cell carcinoma

Pyroptosis is a kind of programmed cell death triggered by the inflammasome. Growing evidence has revealed the crucial utility of pyroptosis in tumors. However, the potential mechanism of pyroptosis in clear cell renal cell carcinoma (ccRCC) is still unclear. In this research, we systematically analyze the genetic and transcriptional alterations of pyroptosis-related genes (PRGs) in ccRCC, identify pyroptosis-related subtypes, analyze the clinical and microenvironmental differences among different subtypes, develop a corresponding prognostic model to predict the prognosis of patients, and interpret the effect of pyroptosis on ccRCC microenvironment. This study provides a new perspective for a comprehensive understanding of the role of pyroptosis in ccRCC and its impact on the immune microenvironment, and a reliable scoring system was established to predict patients' prognosis.

PBRM1 mutation as a predictive biomarker for immunotherapy in multiple cancers

Background: There has been evidence that Polybromo-1 (PBRM1) mutation was closely associated with immunotherapy response in clear cell renal cell carcinoma (ccRCC). However, it remains incompletely unclear whether PBRM1 mutations correlate with ICI response in pan-cancer. Methods: The clinical data and whole exome sequencing (WES) data were collected from seven published immunotherapy studies to evaluate the association between PBRM1 mutation and ICIs efficacy in the discovery cohort. In order to provide further insight into the relationship between PBRM1 and immunity, we analyzed a relatively large sample as a validation cohort. Moreover, we also collected the clinical data and mutation information of 134 non-small cell lung cancer (NSCLC) patients from the First Affiliated Hospital of Nanjing Medical University to verify the findings. Gene set enrichment analysis (GSEA) was used to evaluate the relationship between PBRM1 and immune-related pathway. Results: Our results found that PBRM1 mutation were associated with immune response in the discovery cohort (Progression free survival [PFS]: hazard ratio (HR) = .51, 95% CI: .28-.95, p = .030; objective response rate [ORR]: 47.92% vs. 28.21%, p = .0044; disease control rate [DCR]: 72.92% vs. 47.53%, p = .0008). In the validation cohort, the patients with PBRM1 mutation had a longer overall survival (OS) (hazard ratio = .69, 95% CI: .53-.91, p = .006). In our non-small cell lung cancer cohort, PFS, objective response rate and disease control rate had obvious superiority in the patients with PBRM1 mutation than those without PBRM1 mutation (PFS: HR = .268, 95% CI: 084-.854, p = .04, ORR: 55.56% vs. 20.00%, p = .027, DCR: 100% vs. 75.20%). Using the Gene set enrichment analysis (GSEA) in TCGA cohorts, PBRM1 mutation was closely related to immune efficacy and immune microenvironment, including killer cell mediated immunity regulation, cell cytokine production, CD8⁺ T-cell activation and MHC protein binding process. Conclusion: There is a strong correlation between PBRM1 mutation and prognosis and immune response. Based on the findings, PBRM1 mutation may be a promising immunotherapeutic signature that could guide clinical management and personalized immunotherapy.

Characterization of the Functional Interplay between the BRD7 and BRD9 Homologues in mSWI/SNF Complexes

Bromodomains (BRDs) are a family of evolutionarily conserved domains that are the main readers of acetylated lysine (Kac) residues on proteins. Recently, numerous BRD-containing proteins have been proven essential for transcriptional regulation in numerous contexts. This is exemplified by the multi-subunit mSWI/SNF chromatin remodeling complexes, which incorporate up to 10 BRDs within five distinct subunits, allowing for extensive integration of Kac signaling to inform transcriptional regulation. As dysregulated transcription promotes oncogenesis, we sought to characterize how BRD-containing subunits contribute molecularly to mSWI/SNF functions. By combining genome editing, functional proteomics, and cellular biology, we found that loss of any single BRD-containing mSWI/SNF subunit altered but did not fully disrupt the various mSWI/SNF complexes. In addition, we report that the downregulation of BRD7 is common in invasive lobular carcinoma and modulates the interactome of its homologue, BRD9. We show that these alterations exacerbate sensitivities to inhibitors targeting epigenetic regulators─notably, inhibitors targeting the BRDs of non-mSWI/SNF proteins. Our results highlight the interconnections between distinct mSWI/SNF complexes and their far-reaching impacts on transcriptional regulation in human health and disease. The mass spectrometry data generated have been deposited to MassIVE and ProteomeXchange and assigned the identifiers MSV000089357, MSV000089362, and PXD033572.

Chromatin regulators-related lncRNA signature predicting the prognosis of kidney renal clear cell carcinoma and its relationship with immune microenvironment: A study based on bioinformatics and experimental validation

Background: Kidney Renal Clear cell carcinoma (KIRC) is a major concern in the urinary system. A lot of researches were focused on Chromatin Regulators (CRs) in tumors. In this study, CRs-related lncRNAs (CRlncRNAs) were investigated for their potential impact on the prognosis of KIRC and the immune microenvironment.

Methods: The TCGA database was used to obtain transcriptome and related clinical information. CRs were obtained from previous studies, whereas CRlncRNAs were obtained by differential and correlation analysis. We screened the lncRNAs for the signature construction using regression analysis and LASSO regression analysis. The effectiveness of the signature was evaluated using the Kaplan-Meier (K-M) curve and Receiver Operating Characteristic curve (ROC). Additionally, we examined the associations between the signature and Tumor Microenvironment (TME), and the efficacy of drug therapy. Finally, we further verified whether these lncRNAs could affect the biological function of KIRC cells by functional experiments such as CCK8 and transwell assay.

Results: A signature consisting of 8 CRlncRNAs was constructed to predict the prognosis of KIRC. Quantitative Real-Time PCR verified the expression of 8 lncRNAs at the cell line and tissue level. The signature was found to be an independent prognostic indicator for KIRC in regression analysis. This signature was found to predict Overall Survival (OS) better for patients in the subgroups of age, gender, grade, stage, M, N0, and T. Furthermore, a significant correlation was found between riskScore and immune cell infiltration and immune checkpoint. Finally, we discovered several drugs with different IC50 values in different risk groups using drug sensitivity analysis. And functional experiments showed that Z97200.1 could affect the proliferation, migration and invasion of KIRC cells.

Conclusion: Overall, the signature comprised of these 8 lncRNAs were reliable prognostic biomarkers for KIRC. Moreover, the signature had significant potential for assessing the immunological landscape of tumors and providing individualized treatment.

Deciphering the functional mechanism of zinc ions of PARP1 binding with single strand breaks and double strand breaks

Poly(ADP-ribose)polymerase 1 (PARP1) is a key target for the treatment of cancer-related diseases, and plays an important role in biological processes such as DNA repair, regulating a variety of metabolic and signal transduction processes. Understanding the dynamic binding mechanisms between each domain of PARP1 and DNA is of great significance to deepen the understanding on the function of PARP1 and to facilitate the design of inhibitors. Herein, strategies such as classical molecular dynamics simulation, conformational analysis, binding free energy calculation and energy decomposition were used to shed light on the binding mechanisms of different DNA binding domains (DBDs, including ZnF1, ZnF2 and ZnF3) in PARP1 with DNA and on the influences of zinc ions on the binding process. On one hand, during binding with DNA, ZnF2 tends to expand its space to identify the DNA damage sites and ZnF1/ZnF2 recognizes the interfaces on both sides of DNA damage rather than one side during the process of DNA repair. More importantly, the stable secondary structure of L₂ of ZnF2 (PRO146 to MET153) is the key conformational change for ZnF1 and ZnF2 to recognize DNA damage. Meanwhile, ZnF3 has little effect on the binding mechanisms of PARP1. On the other hand, for the structural differences of DBD domains, zinc ions in ZnF1 and ZnF2 (Zn1 and Zn2) have an impact not only on the conformational changes of PARP1, but also on the conformational changes brought by the interaction of double strand breaks (DSB) and single strand breaks (SSB). And meanwhile, Zn3 also has little effect on ZnF3 for the system of ZnF3/DSB. The findings presented in this work deepen the understanding on the functional mechanism of PARP1 and provide a theoretical basis for further study on the interaction between different inhibitors and DBD domains to design more potential inhibitors.

Poly(ADP-ribose)polymerase 1 (PARP1) is a key target for treatment of cancer-related diseases. Detailed structural changes DBD in PARP1 during the binding process with DNA were investigated and the dynamic conformational differences of DBD caused by zinc ions were revealed.

RRM2 gene expression depends on BAF180 subunit of SWISNF chromatin remodeling complex and correlates with abundance of tumor infiltrating lymphocytes in ccRCC

About 40% of clear cell renal cell carcinoma (ccRCC) cases carry the pbrm1 mutation inactivating BAF180 subunit of the SWI/SNF chromatin remodeling complex (CRC). Here we show that the majority of transcriptomic changes appear at the stage I of ccRCC development. By contrast, the stage II ccRCC exhibits hyperactivation of DNA replication demonstrated by the overexpression of several genes, e.g., RRM1 and RRM2 genes encoding subunits of ribonucleotide reductase (RNR) complex. We found that the degree of RRM1 and RRM2 upregulation in ccRCC patients depends on pbrm1 mutation. We show that the BAF180 protein product of the PBRM1 gene directly binds to RRM1 and RRM2 loci. The BAF180 binding regions are targeted by regulatory proteins previously reported as SWI/SNF CRC interacting partners. BAF180 binding to RRMs loci correlates with enrichment of H3K27me3 in case of RRM1 and H3K14Ac on RRM2, indicating the existence of differential regulatory mechanism controlling expression of these genes. We found that the strong overexpression of RRM2 in ccRCC patient samples correlates with T cell infiltration. Surprisingly, the majority of tumor infiltrating lymphocytes (TILs) consisted of CD4+ T cells. Furthermore, we show that exhausted CD4+ T cells induced the expression of the RRM2 gene in the primary ccRCC cell line. Collectively, our results provide the link between PBRM1 loss, RRM2 expression and T cell infiltration, which may lead to the establishment of new treatment of this disease.

Successful treatment using immunotherapy in combination with chemotherapy for metastatic squamous cell carcinoma of unknown primary origin with bulky abdominal mass: A case report

RATIONALE

Cancer of unknown primary (CUP) means that the primary focus cannot be found after preliminary clinical evaluation. It accounts for 2.3% to 5% of newly diagnosed cancer cases. Due to the lack of standard treatment, CUP is usually associated with poor prognosis and is the third to fourth most common cause of cancer-related deaths.

PATIENT CONCERNS

We report the case of a 42-year-old female patient who was admitted to the hospital for intermittent right abdominal pain and abdominal distension. Abdominal computed tomography (CT) showed a large abdominal mass of unknown origin, which was difficult to resect due to its close relationship with surrounding tissues. Twenty days later, the patient had enlarged left supraclavicular lymph nodes, and percutaneous biopsy revealed squamous cell carcinoma. In addition, next-generation sequencing (NGS) of tissue and blood samples showed immune-related mutations and PD-L1 expression.

DIAGNOSES

The patient was diagnosed with metastatic squamous cell carcinoma of unknown primary origin, with a bulky abdominal mass.

INTERVENTIONS

The patient was treated with carboplatin, albumin-binding paclitaxel, and immune checkpoint inhibitor (carilizumab). After 6 cycles, the patient was switched to maintenance treatment with carilizumab.

OUTCOMES

The general condition of the patient improved, and the lesion was significantly reduced. The treatment efficacy was assessed as partial remission according to Response Evaluation Criteria in Solid Tumors. The patient benefited from immunotherapy combined with chemotherapy.

LESSONS

There is no recommended standard treatment for most CUPs, which leads to their poor prognoses. By performing NGS for patients and targeting immune-related positive predictors, immunotherapy combined with chemotherapy may prolong the overall survival of patients. This case report suggests that immunotherapy combined with chemotherapy is feasible and effective in patients with CUP.

Molecular Mechanisms of Resistance to Immunotherapy and Antiangiogenic Treatments in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most common histological subtype arising from renal cell carcinomas. This tumor is characterized by a predominant angiogenic and immunogenic microenvironment that interplay with stromal, immune cells, and tumoral cells. Despite the obscure prognosis traditionally related to this entity, strategies including angiogenesis inhibition with tyrosine kinase inhibitors (TKIs), as well as the enhancement of the immune system with the inhibition of immune checkpoint proteins, such as PD-1/PDL-1 and CTLA-4, have revolutionized the treatment landscape. This approach has achieved a substantial improvement in life expectancy and quality of life from patients with advanced ccRCC. Unfortunately, not all patients benefit from this success as most patients will finally progress to these therapies and, even worse, approximately 5 to 30% of patients will primarily progress. In the last few years, preclinical and clinical research have been conducted to decode the biological basis underlying the resistance mechanisms regarding angiogenic and immune-based therapy. In this review, we summarize the insights of these molecular alterations to understand the resistance pathways related to the treatment with TKI and immune checkpoint inhibitors (ICIs). Moreover, we include additional information on novel approaches that are currently under research to overcome these resistance alterations in preclinical studies and early phase clinical trials.