Immune checkpoint inhibitor sensitivity of DNA repair deficient tumors.

Faithful DNA replication is necessary to maintain genome stability and implicates a complex network with several pathways depending on DNA damage type: homologous repair, nonhomologous end joining, base excision repair, nucleotide excision repair and mismatch repair. Alteration in components of DNA repair machinery led to DNA damage accumulation and potentially carcinogenesis. Preclinical data suggest sensitivity to immune checkpoint inhibitors in tumors with DNA repair deficiency. Here, we review clinical studies that explored the use of immune checkpoint inhibitor in patient harboring tumor with DNA repair deficiency.

[Recent therapeutic trends in triple-negative metastatic breast cancers: PARP inhibitors, immunotherapies and antibody-drug conjugates]. / PARPi, immunothérapies et anticorps monoclonaux conjugués dans les cancers du sein triple-négatifs.

Compared with other breast cancer subtypes, patients with metastatic triple-negative breast cancer (TNBC) are younger and have a worst overall survival with a median of 15 to 18 months. These tumors have long suffered from a purely negative definition, but the last few years have witnessed many breakthrough genomic and molecular findings, that could dramatically improve our understanding of the biological heterogeneity of TNBC. Moreover, based on these genomic analyses, new generation of clinical trials, using many innovative therapies directed against novel targets, had been conducted. Some TNBC have DNA damage response defects, particularly linked to germinal BRCA1/2 mutations. At the present time, two poly(ADP-ribose) polymerase (PARP) inhibitors have been approved for patients with germinal BRCA1/2 mutation. Breast cancers are not the more immunogenic solid tumors, but some of them have a high percentage of tumor infiltrating lymphocytes (TILs), express PD-L1 (about 40%) or have a high tumor mutational burden. These features of TNBC have given a strong rational to investigate the role of immune checkpoint inhibitors. One of them has been approved by FDA in association with a cytotoxic as a first line treatment. At last, targeting surface receptors outside genomic landscape with antibody drug conjugate (ADC) is a new strategy for metastatic TNBC. Sacituzumab-govitecan is the first ADC approved by FDA in advanced TNBC beyond two lines of treatment.

A Very Long-Acting PARP Inhibitor Suppresses Cancer Cell Growth in DNA Repair-Deficient Tumor Models.

PARP inhibitors are approved for treatment of cancers with BRCA1 or BRCA2 defects. In this study, we prepared and characterized a very long-acting PARP inhibitor. Synthesis of a macromolecular prodrug of talazoparib (TLZ) was achieved by covalent conjugation to a PEG40kDa carrier via a ß-eliminative releasable linker. A single injection of the PEG∼TLZ conjugate was as effective as ∼30 daily oral doses of TLZ in growth suppression of homologous recombination-defective tumors in mouse xenografts. These included the KT-10 Wilms' tumor with a PALB2 mutation, the BRCA1-deficient MX-1 triple-negative breast cancer, and the BRCA2-deficient DLD-1 colon cancer; the prodrug did not inhibit an isogenic DLD-1 tumor with wild-type BRCA2. Although the half-life of PEG∼TLZ and released TLZ in the mouse was only ∼1 day, the exposure of released TLZ from a single safe, effective dose of the prodrug exceeded that of oral TLZ given daily over one month. µPET/CT imaging showed high uptake and prolonged retention of an 89Zr-labeled surrogate of PEG∼TLZ in the MX-1 BRCA1-deficient tumor. These data suggest that the long-lasting antitumor effect of the prodrug is due to a combination of its long t 1/2, the high exposure of TLZ released from the prodrug, increased tumor sensitivity upon continued exposure, and tumor accumulation. Using pharmacokinetic parameters of TLZ in humans, we designed a long-acting PEG∼TLZ for humans that may be superior in efficacy to daily oral TLZ and would be useful for treatment of PARP inhibitor-sensitive cancers in which oral medications are not tolerated. SIGNIFICANCE: These findings demonstrate that a single injection of a long-acting prodrug of the PARP inhibitor talazoparib in murine xenografts provides tumor suppression equivalent to a month of daily dosing of talazoparib.

Homologous recombination repair deficiency as a therapeutic target in sarcoma.

Sarcoma is a rare cancer arising from soft tissue and bone and consists of more than 50 distinct subtypes. There is an increasing emphasis on understanding the cancer biology of individual sarcoma subtypes to inform the development of targeted and immunotherapy-based treatment approaches. While some advances have recently been made in this respect, most sarcomas are still treated with chemotherapy. The homologous recombination DNA repair pathway plays an important role in repairing highly cytotoxic double-stranded DNA breaks and restarting stalled replication forks. A subset of human cancers, notably ovarian, breast, prostate, and pancreatic cancers, harbor defects in components of the homologous recombination repair pathway, such as mutation or loss of BRCA1/2, and are sensitive to treatments which induce double stranded DNA breaks or replication fork arrest, including oral small molecule poly-ADP-ribose polymerase (PARP) inhibitors. Our understanding of DNA repair defects in sarcoma remains at an early stage. Recently, uterine leiomyosarcoma was identified as a sarcoma subtype with characteristic defects in the homologous recombination repair pathway and frequent BRCA2 loss. Preclinical data, presented here, demonstrates marked activity for the PARP inhibitor olaparib in combination with the alkylating agent temozolomide in leiomyosarcoma models. Ongoing research promises to identify other sarcomas with DNA repair defects and may offer a new opportunity for the targeted treatment of this rare, aggressive cancer.

Activity of Platinum-Based Chemotherapy in Patients With Advanced Prostate Cancer With and Without DNA Repair Gene Aberrations.

Importance: DNA repair gene aberrations occur in 20% to 30% of patients with castration-resistant prostate cancer (CRPC), and some of these aberrations have been associated with sensitivity to poly(ADP-ribose) polymerase (PARP) inhibition platinum-based treatments. However, previous trials assessing platinum-based treatments in patients with CRPC have mostly included a biomarker-unselected population; therefore, efficacy in these patients is unknown. Objective: To characterize the antitumor activity of platinum-based therapies in men with CRPC with or without DNA repair gene alterations. Design, Setting, and Participants: In this case series, data from 508 patients with CRPC treated with platinum-based therapy were collected from 25 academic centers from 12 countries worldwide. Patients were grouped by status of DNA repair gene aberrations (ie, cohort 1, present; cohort 2, not detected; and cohort 3, not tested). Data were collected from January 1986 to December 2018. Data analysis was performed in 2019, with data closure in April 2019. Exposure: Treatment with platinum-based compounds either as monotherapy or combination therapy. Main Outcomes and Measures: The primary end points were as follows: (1) antitumor activity of platinum-based therapy, defined as a decrease in prostate-specific antigen (PSA) level of at least 50% and/or radiological soft tissue response in patients with measurable disease and (2) the association of response with the presence or absence of DNA repair gene aberrations. Results: A total of 508 men with a median (range) age of 61 (27-88) years were included in this analysis. DNA repair gene aberrations were present in 80 patients (14.7%; cohort 1), absent in 98 (19.3%; cohort 2), and not tested in 330 (65.0%; cohort 3). Of 408 patients who received platinum-based combination therapy, 338 patients (82.8%) received docetaxel, paclitaxel, or etoposide, and 70 (17.2%) received platinum-based combination treatment with another partner. A PSA level decrease of at least 50% was seen in 33 patients (47.1%) in cohort 1 and 26 (36.1%) in cohort 2 (P = .20). In evaluable patients, soft tissue responses were documented in 28 of 58 patients (48.3%) in cohort 1 and 21 of 67 (31.3%) in cohort 2 (P = .07). In the subgroup of 44 patients with BRCA2 gene alterations, PSA level decreases of at least 50% were documented in 23 patients (63.9%) and soft tissue responses in 17 of 34 patients (50.0%) with evaluable disease. In cohort 3, PSA level decreases of at least 50% and soft tissue responses were documented in 81 of 284 patients (28.5%) and 38 of 185 patients (20.5%) with evaluable disease, respectively. Conclusions and Relevance: In this study, platinum-based treatment was associated with relevant antitumor activity in a biomarker-positive population of patients with advanced prostate cancer with DNA repair gene aberrations. The findings of this study suggest that platinum-based treatment may be considered an option for these patients.

Durable benefit from immunotherapy and accompanied lupus erythematosus in pancreatic adenocarcinoma with DNA repair deficiency.

BACKGROUND: Clinical trials showed limited benefit of anti-PD-1 (programmed cell death 1) monotherapy in pancreatic adenocarcinoma patients and immune-related adverse events caused by immune checkpoint inhibitors were rarely reported in pancreatic adenocarcinoma. Here, we report the first case of durable benefit along with systemic lupus erythematosus following immunotherapy in mismatch repair-proficient pancreatic cancer. CASE PRESENTATION: We describe a 57-year-old woman with resected stage ⅢB pancreatic cancer who underwent several lines of conventional chemotherapy after multiple lymph node metastases. When the disease progressed again, the patient received an off-label treatment with pembrolizumab (100 mg every 3 weeks). After four cycles of immunotherapy treatment, CA19-9 level rapidly decreased to normal and the lymph node metastases reduced dramatically in volume, demonstrating a partial response to the therapy by RECIST 1.1 criteria. She continued on pembrolizumab and a total of eight cycles of administration she had received. Her lesions showed consistent reduction in size even when the medication had been stopped. Actually the patient experienced durable benefit from anti-PD-1 therapy for more than 4 years and she is still in good condition without tumor relapses to date. Besides, she was diagnosed with systemic lupus erythematosus 2 months after the last dose of pembrolizumab. Molecular profiling identified two deleterious PALB2 alterations including a germline mutation (PALB2 c.3114-1G>A) and a somatic mutation (PALB2 c.2514+1G>C) in this patient, suggesting the potential of DNA homologous recombination deficiency. Multiplex immunohistochemistry and RNA-seq results revealed a brisk immune cell infiltration in her resected primary lesion. Additionally, humanleukocyte antigen (HLA) typing assay identified two previously reported systemic lupus erythematosus risk alleles HLA-DRB1*15:01 and HLA-DQB1*06:02 in this patient. CONCLUSIONS: The deleterious mutations of PALB2 closely related to homologous recombination deficiency or alterations of DNA damage response and repair genes might be promising biomarkers for predicting efficacy of immune checkpoint inhibitors in pancreatic adenocarcinoma. Genetic correlation behind immunotherapy-induced systemic lupus erythematosus and associated mechanism remain to be elucidated.

Hexavalent Chromium-Induced Chromosome Instability Drives Permanent and Heritable Numerical and Structural Changes and a DNA Repair-Deficient Phenotype.

A key hypothesis for how hexavalent chromium [Cr(VI)] causes cancer is that it drives chromosome instability (CIN), which leads to neoplastic transformation. Studies show chronic Cr(VI) can affect DNA repair and induce centrosome amplification, which can lead to structural and numerical CIN. However, no studies have considered whether these outcomes are transient or permanent. In this study, we exposed human lung cells to particulate Cr(VI) for three sequential 24-hour periods, each separated by about a month. After each treatment, cells were seeded at colony-forming density, cloned, expanded, and retreated, creating three generations of clonal cell lines. Each generation of clones was tested for chromium sensitivity, chromosome complement, DNA repair capacity, centrosome amplification, and the ability to grow in soft agar. After the first treatment, Cr(VI)-treated clones exhibited a normal chromosome complement, but some clones showed a repair-deficient phenotype and amplified centrosomes. After the second exposure, more than half of the treated clones acquired an abnormal karyotype including numerical and structural alterations, with many exhibiting deficient DNA double-strand break repair and amplified centrosomes. The third treatment produced new abnormal clones, with previously abnormal clones acquiring additional abnormalities and most clones exhibiting repair deficiency. CIN, repair deficiency, and amplified centrosomes were all permanent and heritable phenotypes of repeated Cr(VI) exposure. These outcomes support the hypothesis that CIN is a key mechanism of Cr(VI)-induced carcinogenesis.Significance: Chromium, a major public health concern and human lung carcinogen, causes fundamental changes in chromosomes and DNA repair in human lung cells. Cancer Res; 78(15); 4203-14. ©2018 AACR.

DNA Repair Deficiency Is Common in Advanced Prostate Cancer: New Therapeutic Opportunities.

UNLABELLED: : Advances in DNA sequencing technology have created a wealth of information regarding the genomic landscape of prostate cancer. It had been thought that BRCA1 and BRCA2 mutations were associated with only a small fraction of prostate cancer cases. However, recent genomic analysis has revealed that germline or somatic inactivating mutations in BRCA1 or BRCA2, or other genes involved in the homologous recombination (HR) pathway of DNA repair collectively occur in as much as 20%-25% of advanced prostate cancers. A synthetic lethal therapeutic approach using poly(ADP-ribose) polymerase inhibitor therapy has been developed for BRCA mutant- and HR deficient-related cancers (those with "BRCAness") and is being studied in multiple clinical trials. This article discusses the current understanding of the genomic landscape of prostate cancer, focusing on the occurrence of DNA repair mutations and the therapeutic opportunities that this presents. IMPLICATIONS FOR PRACTICE: This review aims to update oncologists about the increased understanding of the genomes of prostate cancers and, in particular, the prevalence of mutations in DNA repair genes. These observations provide potential new therapeutic opportunities for the use of poly(ADP-ribose) polymerase inhibitors and other therapies, especially in advanced forms of the disease. Of note is the recent U.S. Food and Drug Administration breakthrough therapy designation of olaparib for the treatment of BRCA1/2- or ATM-mutated metastatic castration-resistant prostate cancer. The implications of this new knowledge for clinical practice now and in the future are discussed.

Gynecologic Cancers: Emerging Novel Strategies for Targeting DNA Repair Deficiency.

The presence of a BRCA mutation, somatic or germline, is now established as a standard of care for selecting patients with ovarian cancer for treatment with a PARP inhibitor. During the clinical development of the PARP inhibitor class of agents, a subset of women without BRCA mutations were shown to respond to these drugs (termed "BRCAness"). It was hypothesized that other genetic abnormalities causing a homologous recombinant deficiency (HRD) were sensitizing the BRCA wild-type cancers to PARP inhibition. The molecular basis for these other causes of HRD are being defined. They include individual gene defects (e.g., RAD51 mutation, CHEK2 mutation), homozygous somatic loss, and whole genome properties such as genomic scarring. Testing this knowledge is possible when selecting patients to receive molecular therapy targeting DNA repair, not only for patients with ovarian cancer but also endometrial and cervical cancers. The validity of HRD assays and multiple gene sequencing panels to select a broader population of patients for treatment with PARP inhibitor therapy is under evaluation. Other non-HRD targets for exploiting DNA repair defects in gynecologic cancers include mismatch repair (MMR), checkpoint signaling, and nonhomologous end-joining (NHEJ) DNA repair. This article describes recent evidence supporting strategies in addition to BRCA mutation for selecting patients for treatment with PARP inhibitor therapy. Additionally, the challenges and opportunities of exploiting DNA repair pathways other than homologous recombination for molecular therapy in gynecologic cancers is discussed.

Leveraging DNA repair deficiency in gynecologic oncology.

PURPOSE OF REVIEW: The review discusses DNA repair deficiencies in ovarian cancer and how this has become the target for poly (ADP-ribose) polymerase (PARP) inhibition as a successful therapeutic strategy. RECENT FINDINGS: Hereditary ovarian cancers arise from germline mutations in BRCA1, BRCA2, or other important genes in the DNA repair process of homologous recombination. Sporadic ovarian cancers can also acquire a phenotype of homologous recombination deficiency through various other mechanisms. Recent studies have found the class of drugs called PARP inhibitors to selectively target ovarian cancers with homologous recombination deficiency. There are eight PARP inhibitors in various phases of clinical development with four being actively studied in phase III trials in ovarian cancer. In December 2014, the first-in-human PARP inhibitor olaparib was approved for ovarian cancer patients with two different clinical indications in Europe and the United States. SUMMARY: Ovarian cancer has become a model for the successful translation of targeted therapy against DNA repair deficiencies in cancer.

Evolution of DNA repair defects during malignant progression of low-grade gliomas after temozolomide treatment.

Temozolomide (TMZ) increases the overall survival of patients with glioblastoma (GBM), but its role in the clinical management of diffuse low-grade gliomas (LGG) is still being defined. DNA hypermethylation of the O (6) -methylguanine-DNA methyltransferase (MGMT) promoter is associated with an improved response to TMZ treatment, while inactivation of the DNA mismatch repair (MMR) pathway is associated with therapeutic resistance and TMZ-induced mutagenesis. We previously demonstrated that TMZ treatment of LGG induces driver mutations in the RB and AKT-mTOR pathways, which may drive malignant progression to secondary GBM. To better understand the mechanisms underlying TMZ-induced mutagenesis and malignant progression, we explored the evolution of MGMT methylation and genetic alterations affecting MMR genes in a cohort of 34 treatment-naïve LGGs and their recurrences. Recurrences with TMZ-associated hypermutation had increased MGMT methylation compared to their untreated initial tumors and higher overall MGMT methylation compared to TMZ-treated non-hypermutated recurrences. A TMZ-associated mutation in one or more MMR genes was observed in five out of six TMZ-treated hypermutated recurrences. In two cases, pre-existing heterozygous deletions encompassing MGMT, or an MMR gene, were followed by TMZ-associated mutations in one of the genes of interest. These results suggest that tumor cells with methylated MGMT may undergo positive selection during TMZ treatment in the context of MMR deficiency.

Optimizing chemotherapy in triple-negative breast cancer: the role of platinum.

Although characterization of triple-negative breast cancer (TNBC) using mRNA gene expression profiling has certainly provided important insights, the concept of targeting DNA repair defects with DNA damaging therapeutics such as platinum in TNBC has been advanced from studies focusing on both germline and somatic genetic alterations associated with this breast cancer subtype. A growing body of preclinical and clinical data suggests that platinum chemotherapy has a potential role to play in the treatment of both early-stage and advanced TNBC, though results are not yet definitive. Randomized clinical trials that incorporate biomarkers of response, including germline BRCA1 and BRCA2 mutation status as well as tumor-based measures of genomic "scarring" resulting from the accumulation of DNA damage in tumors with deficient repair capacity, will help to clarify the optimal use and activity of platinum in TNBC.

BMN 673, a novel and highly potent PARP1/2 inhibitor for the treatment of human cancers with DNA repair deficiency.

PURPOSE: PARP1/2 inhibitors are a class of anticancer agents that target tumor-specific defects in DNA repair. Here, we describe BMN 673, a novel, highly potent PARP1/2 inhibitor with favorable metabolic stability, oral bioavailability, and pharmacokinetic properties. EXPERIMENTAL DESIGN: Potency and selectivity of BMN 673 was determined by biochemical assays. Anticancer activity either as a single-agent or in combination with other antitumor agents was evaluated both in vitro and in xenograft cancer models. RESULTS: BMN 673 is a potent PARP1/2 inhibitor (PARP1 IC50 = 0.57 nmol/L), but it does not inhibit other enzymes that we have tested. BMN 673 exhibits selective antitumor cytotoxicity and elicits DNA repair biomarkers at much lower concentrations than earlier generation PARP1/2 inhibitors (such as olaparib, rucaparib, and veliparib). In vitro, BMN 673 selectively targeted tumor cells with BRCA1, BRCA2, or PTEN gene defects with 20- to more than 200-fold greater potency than existing PARP1/2 inhibitors. BMN 673 is readily orally bioavailable, with more than 40% absolute oral bioavailability in rats when dosed in carboxylmethyl cellulose. Oral administration of BMN 673 elicited remarkable antitumor activity in vivo; xenografted tumors that carry defects in DNA repair due to BRCA mutations or PTEN deficiency were profoundly sensitive to oral BMN 673 treatment at well-tolerated doses in mice. Synergistic or additive antitumor effects were also found when BMN 673 was combined with temozolomide, SN38, or platinum drugs. CONCLUSION: BMN 673 is currently in early-phase clinical development and represents a promising PARP1/2 inhibitor with potentially advantageous features in its drug class.

Cytosine-based nucleoside analogs are selectively lethal to DNA mismatch repair-deficient tumour cells by enhancing levels of intracellular oxidative stress.

BACKGROUND: DNA mismatch repair deficiency is present in a significant proportion of a number of solid tumours and is associated with distinct clinical behaviour. METHODS: To identify the therapeutic agents that might show selectivity for mismatch repair-deficient tumour cells, we screened a pair of isogenic MLH1-deficient and MLH1-proficient tumour cell lines with a library of clinically used drugs. To test the generality of hits in the screen, selective agents were retested in cells deficient in the MSH2 mismatch repair gene. RESULTS: We identified cytarabine and other related cytosine-based nucleoside analogues as being selectively toxic to MLH1 and MSH2-deficient tumour cells. The selective cytotoxicity we observed was likely caused by increased levels of cellular oxidative stress, as it could be abrogated by antioxidants. CONCLUSION: We propose that cytarabine-based chemotherapy regimens may represent a tumour-selective treatment strategy for mismatch repair-deficient cancers.

Chromosomal instability syndromes are sensitive to poly ADP-ribose polymerase inhibitors.

Poly ADP-ribose polymerase inhibitors have been shown to target cells with homologous recombination DNA repair defects. We report that poly ADP-ribose polymerase inhibitors induces apoptosis in cells deficient in other key DNA repair components. Chromosomal instability disorders, Fanconi Anemia and Bloom's syndrome have dysfunctional DNA repair and an increased likelihood of leukemic transformation. PI addition to Fanconi Anemia and Bloom's syndrome cells resulted in significant apoptosis. Furthermore, poly ADP-ribose polymerase inhibitors induced apoptosis in DNA repair signaling defective ATM(-/-) and NBS(-/-) fibroblasts. Immunocytochemistry showed homologous recombination was abrogated in NBS(-/-) and ATM(-/-) fibroblasts, compromised in Fanconi anemia and normal in Bloom's syndrome cells in response to poly ADP-ribose polymerase inhibitors. Strikingly, poly ADP-ribose polymerase inhibitors increases non-homologous end joining repair activity, whilst non-homologous end joining deficient cells are extremely sensitive to poly ADP-ribose polymerase inhibitors. These data suggest poly ADP-ribose polymerase inhibitors target cells with DNA repair and signaling defects rather than solely defects in homologous recombination improving the potential of poly ADP-ribose polymerase inhibitors therapy in a wider range of cancers.