Microsatellite instability and prostate cancer: clinical and pathological implications

Recent Research Advances in Double-Strand Break and Mismatch Repair Defects in Prostate Cancer and Potential Clinical Applications

Prostate cancer remains a leading cause of cancer-related death in men worldwide. Recent research advances have emphasized the critical roles of mismatch repair (MMR) and double-strand break (DSB) in prostate cancer development and progression. Here, we provide a comprehensive review of the molecular mechanisms underlying DSB and MMR defects in prostate cancer, as well as their clinical implications. Furthermore, we discuss the promising therapeutic potential of immune checkpoint inhibitors and PARP inhibitors in targeting these defects, particularly in the context of personalized medicine and further perspectives. Recent clinical trials have demonstrated the efficacy of these novel treatments, including Food and Drugs Association (FDA) drug approvals, offering hope for improved patient outcomes. Overall, this review emphasizes the importance of understanding the interplay between MMR and DSB defects in prostate cancer to develop innovative and effective therapeutic strategies for patients.

The promising role of new molecular biomarkers in prostate cancer: from coding and non-coding genes to artificial intelligence approaches

Background

Risk stratification or progression in prostate cancer is performed with the support of clinical-pathological data such as the sum of the Gleason score and serum levels PSA. For several decades, methods aimed at the early detection of prostate cancer have included the determination of PSA serum levels. The aim of this systematic review is to provide an overview about recent advances in the discovery of new molecular biomarkers through transcriptomics, genomics and artificial intelligence that are expected to improve clinical management of the prostate cancer patient.

Methods

An exhaustive search was conducted by Pubmed, Google Scholar and Connected Papers using keywords relating to the genetics, genomics and artificial intelligence in prostate cancer, it includes “biomarkers”, “non-coding RNAs”, “lncRNAs”, “microRNAs”, “repetitive sequence”, “prognosis”, “prediction”, “whole-genome sequencing”, “RNA-Seq”, “transcriptome”, “machine learning”, and “deep learning”.

Results

New advances, including the search for changes in novel biomarkers such as mRNAs, microRNAs, lncRNAs, and repetitive sequences, are expected to contribute to an earlier and accurate diagnosis for each patient in the context of precision medicine, thus improving the prognosis and quality of life of patients. We analyze several aspects that are relevant for prostate cancer including its new molecular markers associated with diagnosis, prognosis, and prediction to therapy and how bioinformatic approaches such as machine learning and deep learning can contribute to clinic. Furthermore, we also include current techniques that will allow an earlier diagnosis, such as Spatial Transcriptomics, Exome Sequencing, and Whole-Genome Sequencing.

Conclusion

Transcriptomic and genomic analysis have contributed to generate knowledge in the field of prostate carcinogenesis, new information about coding and non-coding genes as biomarkers has emerged. Synergies created by the implementation of artificial intelligence to analyze and understand sequencing data have allowed the development of clinical strategies that facilitate decision-making and improve personalized management in prostate cancer.

MSH2 Loss in Primary Prostate Cancer

Purpose: Inactivation of mismatch repair (MMR) genes may predict sensitivity to immunotherapy in metastatic prostate cancers. We studied primary prostate tumors with MMR defects.Experimental Design: A total of 1,133 primary prostatic adenocarcinomas and 43 prostatic small cell carcinomas (NEPC) were screened by MSH2 immunohistochemistry with confirmation by next-generation sequencing (NGS). Microsatellite instability (MSI) was assessed by PCR and NGS (mSINGS).Results: Of primary adenocarcinomas and NEPC, 1.2% (14/1,176) had MSH2 loss. Overall, 8% (7/91) of adenocarcinomas with primary Gleason pattern 5 (Gleason score 9-10) had MSH2 loss compared with 0.4% (5/1,042) of tumors with any other scores (P < 0.05). Five percent (2/43) of NEPC had MSH2 loss. MSH2 was generally homogenously lost, suggesting it was an early/clonal event. NGS confirmed MSH2 loss-of-function alterations in all (12/12) samples, with biallelic inactivation in 83% (10/12) and hypermutation in 83% (10/12). Overall, 61% (8/13) and 58% (7/12) of patients had definite MSI by PCR and mSINGS, respectively. Three patients (25%) had germline mutations in MSH2 Tumors with MSH2 loss had a higher density of infiltrating CD8+ lymphocytes compared with grade-matched controls without MSH2 loss (390 vs. 76 cells/mm2; P = 0.008), and CD8+ density was correlated with mutation burden among cases with MSH2 loss (r = 0.72, P = 0.005). T-cell receptor sequencing on a subset revealed a trend toward higher clonality in cases versus controls.Conclusions: Loss of MSH2 protein is correlated with MSH2 inactivation, hypermutation, and higher tumor-infiltrating lymphocyte density, and appears most common among very high-grade primary tumors, for which routine screening may be warranted if validated in additional cohorts. Clin Cancer Res; 23(22); 6863-74. ©2017 AACR.

The elevated expression of a mismatch repair protein is a predictor for biochemical recurrence after radical prostatectomy

PURPOSE

The inability to predict clinical outcome of prostate cancer is a major impediment to effective treatment decisions and patient counseling. New markers of recurrence are needed to improve the accuracy of risk assessment and treatment of prostate cancer. Our previous studies identified a mismatch repair protein, PMS2, to be elevated in prostate cancer; here, we investigate the prognostic potential of this marker. We hypothesized that the elevation of PMS2 would correlate with disease outcome.

EXPERIMENTAL DESIGN

Retrospective quantitative immunohistochemistry was done to measure PMS2 in high-grade cancers of 166 men treated by radical prostatectomy with a biochemical recurrence rate of 56%. Associations between PMS2 levels, pathologic variables, and biochemical recurrence over time were determined.

RESULTS

The mean level of PMS2 protein was consistently higher in both cancer-associated benign epithelium and cancer cells of patients who recurred, compared with nonrecurrent patients. PMS2 was an independent predictor of time-to-recurrence in Cox multivariate analyses and significantly stratified patients based on outcome. PMS2 was able to improve the sensitivity of total percent Gleason 4/5 as a risk factor for recurrence in this cohort.

CONCLUSIONS

PMS2 protein levels were shown to be a predictor of time-to-recurrence after surgery. This study is the first to document that the elevation of a mismatch repair protein negatively correlates with prognosis and has implications in patient diagnosis and molecular profiling.

Elevated levels of the mismatch repair protein PMS2 are associated with prostate cancer

BACKGROUND

Defects in mismatch repair (MMR) proteins have been identified in various types of cancer. However, an association with prostate cancer has been controversial. Defective MMR results in genome instability with detrimental consequences that significantly contribute to tumorigenesis. This study determined alterations in key MMR protein levels in prostate cancer with the goal to identify prognostic markers.

METHODS

Prostatectomy samples were immunohistochemically stained and the relative presence or absence of key proteins MSH2, MLH1, and PMS2 determined. Cancer tissue of distinct grades was compared with the normal surrounding tissue. Microsatellite instability (MSI) in altered tissues was determined according to NCI guidelines.

RESULTS

In contrast to reports that associate a lack of individual MMR proteins with tumorigenesis, a significant increase in PMS2 levels was identified in PIN lesions and prostate cancer tissue. This elevation in PMS2 was independent of changes in levels in its heterodimeric partner, MLH1. Prostate tumors with elevated levels of PMS2 were genetically unstable, which was corrected by MLH1 co-elevation.

CONCLUSIONS

This is the first documentation of detrimental consequences associated with the increase in a MMR protein in human cancer. This study recognizes PMS2 elevation as a prognostic marker in pre-neoplastic and prostate cancer lesions. This result has significant implications for future diagnostic and treatment measures.

Preliminary evidence that the allogeneic response might trigger antitumour immunity in patients with advanced prostate cancer

OBJECTIVE

To explore the possibility that allogeneic responses might, by chance, encompass cross-reactive T cell clones specific for neo-antigenic tumour determinants, and thereby activate antitumour immunity; such cross-reactions are well documented for antiviral immunity, and genetic instability in developing cancers generates many neo-antigenic determinants as potential targets for immune responses, but the biology inevitably favours tumour progression.

PATIENTS AND METHODS

Fourteen patients with hormone-refractory prostate cancer received full-thickness skin allografts from different, unrelated donors (fellow patients) until each had received six grafts. Serum prostate-specific antigen (PSA) level was used as a surrogate for tumour mass.

RESULTS

One patient had a remarkable decline in PSA level, with levels at 1 year lower than before grafting. A second patient had stable PSA levels for almost 2 years. A third patient had stable PSA levels for 10-12 months before they resumed an exponential rise. Of four patients with PSA levels of > 10 ng/mL, three required surgery or radiotherapy for obstructive symptoms during or shortly after grafting.

CONCLUSION

Transplant rejection involves mechanistically atypical T cell recognition of allogeneic major histocompatibility complex antigens, with massive polyclonal T cell activation. This unique aspect of T cell biology might represent a novel approach for initiating cross-reactive antitumour responses.

XPA versus ERCC1 as chemosensitising agents to cisplatin and mitomycin C in prostate cancer cells: role of ERCC1 in homologous recombination repair

Nucleotide excision repair is the principal mechanism for the removal of bulky DNA adducts caused by a range of chemotherapeutic drugs, and contributes to cisplatin resistance. In this study, we used synthetic siRNAs targeted to XPA and ERCC1 and compared their effectiveness in sensitising mismatch repair deficient prostate cancer cell lines to cisplatin and mitomycin C. Downregulation of ERCC1 sensitised DU145 and PC3 cells to cisplatin and mitomycin C. In contrast, XPA downregulation did not sensitise either cell line to mitomycin C, and only sensitised DU145 cells to cisplatin. The effects of ERCC1 downregulation may be due to its role in homologous recombination repair. Excision repair of cisplatin adducts in PC3 cells was attenuated to a similar extent by XPA and ERCC1 downregulation. Downregulation of XPA but not ERCC1 caused an increase in the number of cisplatin-induced RAD51 foci in PC3 cells, suggesting that HRR is able to substitute for NER in these cells. We observed co-localisation of ERCC1 and RAD51 in cisplatin treated PC3 cells by immunofluorescence and co-immunoprecipitation, which may represent recruitment of ERCC1/XPF to sites of recombination repair. These results indicate that ERCC1 is a broader therapeutic target than XPA with which to sensitise cancer cells to chemotherapy because of its additional role in recombination repair.

Biomarkers for the detection and prognosis of prostate cancer

Recent studies have cast doubt on the reliability of serum total prostate-specific antigen as a biomarker for the detection and prognosis of prostate cancer. Biomarkers that can identify those men at risk for clinically significant prostate cancer are desperately needed. The search for biomarkers that may improve the detection of biologically consequential prostate cancer is one of the most active areas under current investigation. In this review, we highlight some of these ongoing efforts. Proper validation of newly discovered biomarkers is of paramount importance.

Analysis of Candidate Genes for Prostate Cancer

Considerable evidence demonstrates that genetic factors are important in the development and aggressiveness of prostate cancer. To identify genetic variants that predispose to prostate cancer we tested candidate SNPs from genomic regions that show linkage to prostate cancer susceptibility and/or aggressiveness, as well as genes that show a significant difference in mRNA expression level between tumor and normal tissue. Cases had histologically verified prostate cancer. Controls were at least 65 years old, never registered a PSA above 2.5 ng/ml, always had digital rectal examinations that were not suspicious for cancer, and have no known family history of prostate cancer. Thirty-nine coding SNPs and nine non-coding SNPs were tested in up to 590 cases and 556 controls resulting in over 40,000 SNP genotypes. Significant differences in allele frequencies between cases and controls were observed for ID3 (inhibitor of DNA binding), p = 0.05, HPN (hepsin), p = 0.009, BCAS1 (breast carcinoma amplified sequence 1), p = 0.007, CAV2 (caveolin 2), p = 0.007, EMP3 (epithelial membrane protein 3), p < 0.0001, and MLH1 (mutL homolog 1), p < 0.0001. SNPs in three of these genes (BCAS1, EMP3 and MLH1) remained significant in an age-matched subsample.

Cadmium is a mutagen that acts by inhibiting mismatch repair

Most errors that arise during DNA replication can be corrected by DNA polymerase proofreading or by post-replication mismatch repair (MMR). Inactivation of both mutation-avoidance systems results in extremely high mutability that can lead to error catastrophe. High mutability and the likelihood of cancer can be caused by mutations and epigenetic changes that reduce MMR. Hypermutability can also be caused by external factors that directly inhibit MMR. Identifying such factors has important implications for understanding the role of the environment in genome stability. We found that chronic exposure of yeast to environmentally relevant concentrations of cadmium, a known human carcinogen, can result in extreme hypermutability. The mutation specificity along with responses in proofreading-deficient and MMR-deficient mutants indicate that cadmium reduces the capacity for MMR of small misalignments and base-base mismatches. In extracts of human cells, cadmium inhibited at least one step leading to mismatch removal. Together, our data show that a high level of genetic instability can result from environmental impediment of a mutation-avoidance system.