DNA Repair Gene Defects Research Articles

Upper Tract Urothelial Carcinoma: A Rare Malignancy with Distinct Immuno-Genomic Features in the Era of Precision-Based Therapies.

Upper tract urothelial carcinoma (UTUC) is a rare malignancy, occurring in 5-10% of patients diagnosed with UC, and involves the renal pelvis, calyces, or ureters. UTUC can be sporadic or hereditary as a clinical manifestation of Lynch syndrome. Therapeutic management of these patients is challenging. Following risk stratification of localized disease, patients with low-grade UTUC may undergo kidney-sparing surgery or radical nephroureterectomy (RNU) and/or chemoablation with mitomycin-c instillation to reduce recurrence. In high-grade disease, RNU followed by adjuvant chemotherapy remains the standard of care. For decades, platinum-based chemotherapy has been the cornerstone of treatment for locally advanced and metastatic disease. The aim of the present review is to summarize recent advances in UTUC's therapeutic management through the lens of its genomic and immune landscape. Accumulating knowledge on the genetic and immune aspects of UTUC tumors has increased our understanding of their underlying biology, supporting a luminal papillary, T-cell depleted contexture and enrichment in fibroblast growth factor receptor (FGFR) expression. These advances have fueled successful clinical testing of several precision-based therapeutic approaches, including immune checkpoint inhibitors (ICIs), the antibody-drug conjugates (ADCs) enfortumab vedotin and sacituzumab govitecan, and agents targeting the FGFR axis such as erdafitinib and other kinase inhibitors, allowing their entry into the therapeutic armamentarium and improving the prognosis of these patients. Not all patients respond to these precision-based targeted therapies; thus, validating and expanding the toolkit of potential biomarkers of response or resistance, including molecular subtypes, FGFR pathway gene alterations, DNA repair gene defects, tumor mutational burden (TMB), circulating tumor DNA (ctDNA), nectin-4, TROP2, and programmed death ligand-1 (PD-L1), are key to maximizing the benefit to these particular subgroups of patients.

Combining next-generation hormonal therapy with PARP inhibition in metastatic castration-resistant prostate cancer

In a paradigm of precision oncology, elegant preclinical work showed that inhibition of poly(ADP-ribose) polymerase (PARP) proteins can exploit a deficiency of cancer cells to repair DNA double-strand breaks through homologous recombination repair (HRR), 1 Lord CJ Ashworth A PARP inhibitors: synthetic lethality in the clinic. Science. 2017; 355: 1152-1158 Crossref PubMed Scopus (1411) Google Scholar and the resulting synthetic lethality was first shown to be clinically effective in ovarian cancer carrying a germline deleterious mutation in BRCA1 or BRCA2, key HRR genes. 2 Banerjee S Moore KN Colombo N et al. Maintenance olaparib for patients with newly diagnosed advanced ovarian cancer and a BRCA mutation (SOLO1/GOG 3004): 5-year follow-up of a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet Oncol. 2021; 22: 1721-1731 Summary Full Text Full Text PDF PubMed Scopus (92) Google Scholar For prostate cancer, the discovery of alterations in BRCA2 and other HRR-related genes in up to 20% of advanced disease 3 Robinson D Van Allen EM Wu YM et al. Integrative clinical genomics of advanced prostate cancer. Cell. 2015; 161: 1215-1228 Summary Full Text Full Text PDF PubMed Scopus (2077) Google Scholar led to the development of several biomarker-driven trials of PARP inhibitors in patients with metastatic castration-resistant prostate cancer (mCRPC) 4 Abida W Patnaik A Campbell D et al. Rucaparib in men with metastatic castration-resistant prostate cancer harboring a BRCA1 or BRCA2 gene alteration. J Clin Oncol. 2020; 38: 3763-3772 Crossref PubMed Scopus (309) Google Scholar , 5 de Bono JS Mehra N Scagliotti GV et al. Talazoparib monotherapy in metastatic castration-resistant prostate cancer with DNA repair alterations (TALAPRO-1): an open-label, phase 2 trial. Lancet Oncol. 2021; 22: 1250-1264 Summary Full Text Full Text PDF PubMed Scopus (79) Google Scholar , 6 Hussain M Mateo J Fizazi K et al. Survival with olaparib in metastatic castration-resistant prostate cancer. N Engl J Med. 2020; 383: 2345-2357 Crossref PubMed Scopus (289) Google Scholar , 7 Smith MR Scher HI Sandhu S et al. Niraparib in patients with metastatic castration-resistant prostate cancer and DNA repair gene defects (GALAHAD): a multicentre, open-label, phase 2 trial. Lancet Oncol. 2022; 23: 362-373 Summary Full Text Full Text PDF PubMed Scopus (41) Google Scholar and to the regulatory approval of rucaparib and olaparib as monotherapy for the treatment of mCRPC harbouring mutations in BRCA2 and other HRR genes. Talazoparib plus enzalutamide in men with first-line metastatic castration-resistant prostate cancer (TALAPRO-2): a randomised, placebo-controlled, phase 3 trialTalazoparib plus enzalutamide resulted in clinically meaningful and statistically significant improvement in rPFS versus standard of care enzalutamide as first-line treatment for patients with mCRPC. Final overall survival data and additional long-term safety follow-up will further clarify the clinical benefit of the treatment combination in patients with and without tumour HRR gene alterations. Full-Text PDF

Abstract 6082: Assessing difference in the tumor and immune microenvironment of BRCA1/2 mutated versus BRCA wild type high grade serous ovarian cancers

Abstract Ovarian cancer (OvCa) is the deadliest gynecological malignancy in the United States. Surgery and chemotherapy are the primary treatments for OvCa, but 80% of late-stage OvCa patients experience chemo-resistant recurrence, which necessitates the development of new treatment strategies. The genomic diversity within a tumor and the interactions among various cell types within its microenvironment are considered key factors contributing to therapeutic efficacy. Specifically, women who harbor germline BRCA1 or BRCA2 mutations are at increased risk of developing high grade serous ovarian cancer (HGSC). To understand the genomic consequences, including somatic alterations, associated with defective DNA repair, tumor DNA and RNA was isolated from fresh frozen OCT embedded sections from 15 HGSC patients with BRCA1/2 mutation and 10 without any alterations in the BRCA genes (BRCA-wt). Whole exome sequencing (WES) and total RNA-seq was performed to determine the association of homologous recombination (HR) DNA repair gene defects with tumor mutation burden (TMB), neoantigen load (NL), and immunological assessment of tumor microenvironment. TMB was calculated from mutation rates of somatic WES. Germline exome analysis was used to validate inherited BRCA mutations. To identify the somatic mutations, somatic single nucleotide variants and InDels were detected using Strelka. TP53 mutations were most common with several other genes showing only modest mutation frequency. Mutation signatures were also detected with maftools and compared to the COSMIC mutational signature database. BRCA-mutated samples displayed a unique mutational signature associated with defects in HR DNA repair pathway. We also observed heterogeneity in copy number variation profiles amongst cases, as determined by the tool Sequenza. Furthermore, gene set enrichment analysis indicated differential enrichment of P53 pathway, MAPK pathway, and PTEN pathway, in addition to numerous pathways related to immune cell signaling and immune response. RNA-seq data was analyzed with CIBERSORTx and revealed different proportions of 22 immune effector cell types that accompany tumor cells within the HGSC microenvironment. Additional analyses are underway, including measuring differences in NL in BRCA-mutated versus BRCA-wt cases. This work will represent a significant advancement in our fundamental knowledge regarding the complexities of the TME and effective immunological responses in OvCa. Citation Format: Jing Qian, Lynda D. Roman, Seeta Rajpara, Monica Neuman, Varun Khetan, David W. Craig, Joseph Carlson, John D. Carpten. Assessing difference in the tumor and immune microenvironment of BRCA1/2 mutated versus BRCA wild type high grade serous ovarian cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6082.

A review of treatments targeting DNA-repair gene defects in metastatic castration resistant prostate cancer.

Prostate cancer is the most common cancer in men. About 6% of those diagnosed will develop metastatic disease. Unfortunately, metastatic prostate cancer is fatal. Prostate cancer can be castration sensitive or castration resistant. Many treatments have been shown to improve progression free survival and overall survival in metastatic castration resistant prostate cancer (mCRPC). In recent years, studies have been exploring targeting mutations in the DNA Damage Repair (DDR) response that may amplify oncogenes. In this paper, we aim to discuss DDR, new approved targeted therapies, and the most recent clinical trials in the setting of metastatic CRPC.

Loss of tRNA methyltransferase 9 and DNA damage response genes in yeast confers sensitivity to aminoglycosides.

tRNA methyltransferase 9 (Trm9)-catalysed tRNA modifications have been shown to translationally enhance the DNA damage response (DDR). Here, we show that Saccharomyces cerevisiae trm9Δ, distinct DNA repair and spindle assembly checkpoint (SAC) mutants are differentially sensitive to the aminoglycosides tobramycin, gentamicin and amikacin, indicating DDR and SAC activation might rely on translation fidelity, under aminoglycoside stress. Further, we report that the DNA damage induced by aminoglycosides in the base excision repair mutants ogg1Δ and apn1Δ is mediated by reactive oxygen species, which induce the DNA adduct 8-hydroxy deoxyguanosine. Finally, the synergistic effect of tobramycin and the DNA-damaging agent bleomycin to sensitize trm9Δ and the DDR mutants mlh1Δ, rad51Δ, mre11Δ and sgs1Δ at significantly lower concentrations compared with wild-type suggests that cells with tRNA modification dysregulation and DNA repair gene defects can be selectively sensitized using a combination of translation inhibitors and DNA-damaging agents.

Inherited Germline DNA Repair Gene Defects Are Prevalent Among Thai Patients with Myeloid Neoplasms

Certain germline mutations increase the risk of developing myeloid neoplasms (MNs) accompanied by second hit somatic events, such as therapy-related or oxidation-induced DNA damages. Aberrancy in DNA damage response (DDR) pathways leads to genomic instability giving rise to cancer. Previous data showed that the prevalence of pathogenic germline mutations in young adult Caucasian MN patients was 13-19%.1, 2 The most commonly affected pathways were involved in telomere biology and transcription factors, while the defects in DDRs were found in 15-25%. However, data in Asians are limited. In this study, we investigated the prevalence and landscape of germline variants in cancer predisposition genes in a cohort of Thai patients diagnosed with MNs. Targeted next generation sequencing of 23 germline predisposition genes was performed using the SureSelect custom kit and the Illumina HiSeq 2500 system. The total of 127 unselected adult (> 15 years old) patients from 3 medical centers comprising MDS (66%), MDS/MPN (14%) secondary AML (sAML, 20%) were enrolled. The median age was 66 years old (range 16-93) and 50% were male. Variants reported in COSMIC, the frequency of higher than 0.01% in the Genome Aggregation Database (gnomAD) or Thai exome database (consisted of 1084 Thai exome controls) and variant allelic frequency of less than 30% were excluded. New or exceeding rare nonsense variants or indels, as well as missense variants predicted to be deleterious by at least 4/6 in silico software, were included. The variants were classified according to American College of Medical Genetics (ACMG) classification. 14pathogenic and likely pathogenic germline variants were identified in 15 patients (15/127; 12%). One patient had 2 variants including heterozygous CEBPAP75fs and MSH2A604G. Of the 16 variants, there were 8 (50%) missense, 7 (44%) frameshift, and 1 (6%) nonsense, with a median VAF of 51%, ranging 36-83%. The variants affected the DDR pathway (8/16; 50%), transcriptional regulation pathway (4/16; 25%) and signal transduction pathway (2/16; 13%). Two variants were recurrent i.e.,FANCAAla1219GlyfsTer59 and BRCA2Glu626delinsAspPro and the others were identified in BRCA1/2, MSH2, MSH6, GATA2, CEBPA, DDX41, CBL and NF1. The median age of patients harboring germline variants was younger (58 vs. 66 years old) than those who did not. Half of the cases (6/12) were characterized by normal cytogenetics without enrichment of -7 or complex karyotype, comparable to patients with no germline variants. Of note, 28% (4/14) patients had previous history of gastrointestinal stromal tumor, Graves’ disease, Immune thrombocytopenia, and aplastic anemia (FANCA mutation) for years before MNs were diagnosed. None of the patients reported family history of hematological malignancies. In conclusion, the prevalence of germline predisposition to MNs in Southeast Asian populations is as high as in Caucasians and the identified variants are more commonly involved in the DDR pathway. The defects in the DDR pathway suggested an important role of genomic instability in leukemogenesis. This subset of patients should preferably receive non-cytotoxic treatments to avoid oxidative damages that possibly lead to further clonal evolution. ReferencesKeel SB, Scott A, Sanchez-Bonilla M, Ho PA, Gulsuner S, Pritchard CC, et al. Genetic features of myelodysplastic syndrome and aplastic anemia in pediatric and young adult patients. Haematologica 2016 Nov; 101(11): 1343-1350. Feurstein S, Churpek JE, Walsh T, Keel S, Hakkarainen M, Schroeder T, et al. Germline variants drive myelodysplastic syndrome in young adults. Leukemia 2021 2021/08/01; 35(8): 2439-2444.

Abstract 4133: High prevalence and heterogeneity of emergence of BRCA reversion mutations at progression on niraparib treatment in BRCA-mutant metastatic castration-resistant prostate cancer (mCRPC) patients

Abstract In the phase 2 GALAHAD study (NCT02854436), the PARP inhibitor (PARPi) niraparib, was evaluated in heavily pre-treated patients with mCRPC and DNA-repair gene defects (DRD) who progressed after androgen-receptor (AR) targeted therapy and taxane-based chemotherapy. The results showed that objective response rate (ORR) was 34.2% for patients with measurable disease having biallelic BRCA1/2 alterations (n=76). The development of BRCA reversion mutations, a type of secondary mutation that restores protein function, has been proposed as a key resistance mechanism to PARP inhibition. We aimed to evaluate the relationship between reversion mutations and treatment response in BRCA1/2 altered patients treated with niraparib in the GALAHAD study. Thirty-three patients with biallelic BRCA alterations (excluding patients with homozygous deletions) had donated an end-of-treatment (EOT) ctDNA sample. We performed sequencing to detect reversion mutations using the Resolution Bioscience ctDx-HRD assay. Mutation patterns at baseline included splice site, nonsense, missense, and frameshift mutations, with the latter being the most common (24/33; 73%). No reversions were detected at baseline and the baseline BRCA alterations were detected at EOT for every patient. Most BRCA patients (28/33; 85%) had at least 1 reversion mutation (range: 1-38 different BRCA alterations) at EOT. Of the 28 patients with reversions, 5 were classified as low reversions: 3 patients had only one reversion mutation, 1 patient had 2 reversions at low allele frequency and 1 patient had 4 reversions at low allele frequency. Patients with reversion mutations showed better composite response (defined as ORR by RECIST 1.1, or CTC conversion to <5/7.5 mL blood, or ≥50% decline in prostate specific antigen) (74.2% vs 25.8%, p=0.01) and longer duration on treatment (median 6.9 vs 3.7 mo, p<0.05) compared to those without or low reversions. Additionally, patients with reversions trended to have longer median radiographic progression-free survival compared to those without or low reversions (8.1 vs 5.5 mo, p=0.12). In conclusion, the high prevalence of patients with BRCA reversion mutations and the displayed longer benefit from niraparib underscores the dependence of these tumors on BRCA mutation as an oncogenic driver and reversion mutations as a marker of secondary resistance to niraparib treatment. Citation Format: Karen Urtishak, Gerhardt Attard, Tokuwa Kanno, Shibu Thomas, Gary E. Mason, Byron Espina, Eugene Zhu, Natalie Hutnick, Mary Guckert, Adam del Corral, Mark Li, Angela Lopez-Gitlitz, Kim Chi, William Kevin Kelly, Evan Y. Yu, Karim Fizazi, Matthew Smith. High prevalence and heterogeneity of emergence of BRCA reversion mutations at progression on niraparib treatment in BRCA-mutant metastatic castration-resistant prostate cancer (mCRPC) patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4133.

Abstract IA-007: Exploiting DNA repair defects in head and neck squamous cell carcinoma

Abstract DNA damage repair pathways govern genomic integrity and determine cellular sensitivities to radiation and chemotherapeutic agents. Recent genetic studies highlight the identification of an increasing number of DNA repair gene defects in many different cancer types. DNA damage response and repair inhibitors on the other hand provide opportunities to exploit such defects inherent to cancer cells. Combined with radiotherapy they are highly effective radiosensitizers that show some tumor specificity in that they cause greater radiation dose enhancement in cells with repair defects. To optimize such potent combinations, robust and sensitive biomarkers are needed to 1) assess effectivity and guide clinical trial designs and 2) to identify repair defects in individual patients. Radiotherapy is a mainstay in the treatment of advanced HPV-negative head and neck squamous cell carcinoma (HNSCC). There is a need for improved treatment options in this patient population. Indicating particular crosslink repair sensitivity and frequent cancer cell repair defects, cumulative cisplatin dose is an important factor in determining patient outcomes after chemoradiotherapy. Indeed, preclinical and genetic data highlight the frequent manifestation of DNA crosslink repair defects in HNSCC. Genetic biomarkers have therefore been generated and tested to support the identification of patients in need for novel treatment options and of crosslink repair defects in HNSCC for combination with PARP inhibitors. Citation Format: Conchita Vens. Exploiting DNA repair defects in head and neck squamous cell carcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr IA-007.

Prostate carcinogenesis: inflammatory storms.

Prostate cancer is a major cause of cancer morbidity and mortality. Intra-prostatic inflammation is a risk factor for prostate carcinogenesis, with diet, chemical injury and an altered microbiome being causally implicated. Intra-prostatic inflammatory cell recruitment and expansion can ultimately promote DNA double-strand breaks and androgen receptor activation in prostate epithelial cells. The activation of the senescence-associated secretory phenotype fuels further 'inflammatory storms', with free radicals leading to further DNA damage. This drives the overexpression of DNA repair and tumour suppressor genes, rendering these genes susceptible to mutagenic insults, with carcinogenesis accelerated by germline DNA repair gene defects. We provide updates on recent advances in elucidating prostate carcinogenesis and explore novel therapeutic and prevention strategies harnessing these discoveries.

Genetic and epigenetic profiling of BRCA1/2 in ovarian tumors reveals additive diagnostic yield and evidence of a genomic BRCA1/2 DNA methylation signature

Poly-ADP-ribose-polymerase inhibitor (PARPi) treatment is indicated for advanced-stage ovarian tumors with BRCA1/2 deficiency. The “BRCAness” status is thought to be attributed to a tumor phenotype associated with a specific epigenomic DNA methylation profile. Here, we examined the diagnostic impact of combined BRCA1/2 sequence, copy number, and promoter DNA methylation analysis, and evaluated whether genomic DNA methylation patterns can predict the BRCAness in ovarian tumors. DNA sequencing of 172 human tissue samples of advanced-stage ovarian adenocarcinoma identified 36 samples with a clinically significant tier 1/2 sequence variants (point mutations and in/dels) and 9 samples with a CNV causing a loss of function in BRCA1/2. DNA methylation analysis of the promoter of BRCA1/2 identified promoter hypermethylation of BRCA1 in two mutation-negative samples. Computational modeling of genome-wide methylation markers, measured using Infinium EPIC arrays, resulted in a total accuracy of 0.75, sensitivity: 0.83, specificity: 0.64, positive predictive value: 0.76, negative predictive value: 0.74, and area under the receiver’s operating curve (AUC): 0.77, in classifying tumors harboring a BRCA1/2 defect from the rest. These findings indicate that the assessment of CNV and promoter DNA methylation in BRCA1/2 increases the cumulative diagnostic yield by 10%, compared with the 20% yield achieved by sequence variant analysis alone. Genomic DNA methylation data can partially predict BRCAness in ovarian tumors; however, further investigation in expanded BRCA1/2 cohorts is needed, and the effect of other double strand DNA repair gene defects in these tumors warrants further investigations.

Niraparib in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and biallelic DNA-repair gene defects (DRD): Correlative measures of tumor response in phase II GALAHAD study.

118 Background: Niraparib, a highly potent and selective poly (ADP-ribose) polymerase inhibitor (PARPi) received breakthrough designation by US FDA for treatment of pts with BRCA1,2 mutant mCRPC who progressed on taxane and androgen receptor-targeted therapy. Circulating tumor cells (CTC) detection associates with poor outcomes, with declining counts consistent with improved survival [1,2]. Methods: GALAHAD study assessed niraparib (300 mg daily) in pts with mCRPC+DRD (NCT02854436). Patients with non-measurable soft tissue disease by RECIST 1.1 were required to have a baseline CTC count ≥1 cell/7.5 mL blood. CTC response was defined as CTC conversion to <5 for pts with baseline CTC≥5 and CTC drop to 0 post-baseline for pts with ≥1 baseline CTC. Alkaline phosphatase (ALP) was collected at each monthly cycle. Results: For primary efficacy population of pts with BRCA1/2 mutations, the objective response rate (ORR) by RECIST 1.1 criteria was 41.4%. CTC response rates for this population were as high as ORR regardless of measurability (Table). Time to CTC response for each CTC responder will be shown. Radiographic progression-free survival (rPFS) durations were similar for patients with a measurable disease response and patients with CTC conversion. Median duration of treatment for responders of any type was 6.7mo (range: 2–27). DRD status, both BRCA and non- BRCA, for each responder will also be discussed. Trends in disease burden and markers of bone metabolism will also be quantitatively explored including 24% pts who were on treatment for at least one cycle who had ≥25% decreased unfractionated ALP from baseline. Conclusions: Niraparib showed clinical activity with CTC response and decline in ALP levels in mCRPC pts having biallelic BRCA mutations, which further supports its recent breakthrough designation. Clinical trial information: NCT02854436. [Table: see text]

Phase Ib study of niraparib plus androgen receptor-targeted therapy (ART) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC).

122 Background: Poly ADP-ribose polymerase (PARP) inhibitor and abiraterone acetate + prednisone (AA+P) has activity in pts with mCRPC regardless of DNA repair gene defects (DRD). Methods: This phase 1b study (Bedivere; NCT02924766) began with a 3+3 dose escalation of niraparib (Part 1), followed by expansion (Part 2) of the recommended phase 2 dose (RP2D) of nira + AA+P. Pts with mCRPC received nira 200 or 300 mg/day with AA+P. Dose-limiting toxicities (DLTs) were evaluated the first 28 days. Serial PK for nira were collected on cycle 1 day 1 (C1D1) over 24 h; PK for nira and abiraterone were collected on C2D1 over 10 h. Results: Nira 200 mg + 1000 mg AA+P was selected as the RP2D dose. 4 pts in 200 mg cohort and 8 pts in 300 mg cohort were enrolled in Part 1. During Part 1, 1 patient in the 300 mg cohort had two DLTs: Gr 3 fatigue and Gr 4 increased gamma glutamyltransferase. Therefore, the 200 mg dose was evaluated in 15 pts in Part 2. In 19 total pts treated with 200 mg niraparib, 12 (63%) pts had Gr 3-4 AEs, 5 (26%) pts had an AE with outcome of drug discontinuation and 1 (5%) patient had an AE with outcome of death (general physical health deterioration; unrelated). AEs of special interest were: 6 pts (32%) thrombocytopenia, 6 pts (32%) hypertension, 5 pts (26%) anemia and 3 pts (16%) neutropenia of any grade. 21% pts in 200 mg cohort had treatment emergent serious AE (TESAE) while 50% treated with 300 mg had TESAE. The exposure (AUC24h) on Day 1 of Cycle 2 for 200 mg niraparib with 1000 mg of AA were 17745±9380 ng.h/mL and 712±140 ng.h/mL, respectively. These exposures are consistent with single agent PK. Summaries of all responses will be provided, including a patient with primarily bone disease and carrying an ATM mutation who had a circulating tumor cell conversion and was on study treatment for 22.1 mo. Conclusions: The safety and PK findings support the choice of nira 200 mg in combination with AA+P in pts with mCRPC. The efficacy of nira + AA+P is being evaluated in an ongoing phase 3 MAGNITUDE study (NCT03748641). Clinical trial information: NCT02924766.

1412P - Analytical performance of the resolution-HRD plasma assay used to identify mCRPC patients with biallelic disruption of DNA repair genes for treatment with niraparib

BackgroundMetastatic castration-resistant prostate cancer (mCRPC) patients with DNA repair gene defects (DRD) have a shorter life expectancy than patients without DRD and may benefit from treatment with PARP inhibitors. Niraparib is a highly selective PARP inhibitor, with activity against PARP-1/2 DNA-repair polymerases. Detection of DRD in cell free DNA (cfDNA) isolated from blood is minimally invasive and of special benefit to mCRPC patients, including patients without accessible lesions. The assay would also have the advantage of a shorter turnaround time (TAT) than genotyping of tissue. However, using cfDNA to identify biallelic disruption of DNA-repair genes is technically challenging. MethodsResolution-HRD identifies patients with biallelic pathogenic alterations of the ATM, BRCA1, BRCA2, BRIP1, CHEK2, FANCA, HDAC2, or PALB2 genes, by targeted NGS sequencing of cfDNA. Analytical performance of Resolution-HRD was validated using cfDNA from mCRPC patient plasma, cfDNA from healthy donor plasma, and contrived samples with a wide spectrum of technically challenging genetic aberrations. ResultsThe LOD95 at a cfDNA input level of 40ng ranged from 0.2 to 1.37 for SNVs and indels, and 6-12 for CNL. APA for intra-run and inter-run studies at the 1X LOD was 95% and 95% respectively. No false-positives were detected in any samples from healthy donors (N=60). Resolution-HRD has been validated to give consistent results across the 10-75ng input range. Resolution-HRD is used to identify patients for enrollment in the GALAHAD Phase II Efficacy and Safety Study (64091742PCR2001) of Niraparib in Men with mCRPC and DNA-Repair Anomalies. As of April 2019, over 2000 patients are tested successfully (0.88% failure rate) with a median TAT of 8.6 days (range 5-12 days). ConclusionsThe analytical performance of the Resolution-HRD assay offers highly sensitive, specific and robust test results, and meets analytical requirements for clinical applications. This test is currently being evaluated in several clinical trials for prospective identification of mCRPC patients with DRD for treatment with niraparib. Legal entity responsible for the studyResolution Bioscience. FundingJanssen Research and Development. DisclosureI. Pekker: Shareholder / Stockholder / Stock options, Full / Part-time employment: resolution bioscience. L. Lim: Leadership role, Shareholder / Stockholder / Stock options, Licensing / Royalties, Full / Part-time employment, Officer / Board of Directors: Resolution Bioscience. J.S. Simon: Leadership role, Shareholder / Stockholder / Stock options: Janssen. M. Gormley: Shareholder / Stockholder / Stock options, Full / Part-time employment: Janssen. Z. Li: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. J. Pollak: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. K. Potts: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. S. Watford: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. J. Posey: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. P. Chan: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. K. Urtishak: Shareholder / Stockholder / Stock options, Full / Part-time employment: Janssen. K. Garg: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. A. Hosseini: Shareholder / Stockholder / Stock options, Full / Part-time employment: Resolution Bioscience. M. Li: Leadership role, Shareholder / Stockholder / Stock options, Full / Part-time employment, Officer / Board of Directors: Resolution Bioscience.

897TiP - A phase III randomized, placebo-controlled, double-blind study of niraparib plus abiraterone acetate and prednisone versus abiraterone acetate and prednisone in patients with metastatic prostate cancer (NCT03748641)

897TiP - A phase III randomized, placebo-controlled, double-blind study of niraparib plus abiraterone acetate and prednisone versus abiraterone acetate and prednisone in patients with metastatic prostate cancer (NCT03748641)

LBA50 - Pre-specified interim analysis of GALAHAD: A phase II study of niraparib in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and biallelic DNA-repair gene defects (DRD)

LBA50 - Pre-specified interim analysis of GALAHAD: A phase II study of niraparib in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) and biallelic DNA-repair gene defects (DRD)

Phase II study of niraparib in patients with metastatic castration-resistant prostate cancer (mCRPC) and biallelic DNA-repair gene defects (DRD): Preliminary results of GALAHAD.

202 Background: New therapies are needed for patients (pts) with mCRPC progressing after androgen-receptor signaling inhibitors (ARSIs) and taxane therapies. Niraparib is a once daily highly selective inhibitor of poly (ADP-ribose) polymerase (PARP-1 and 2). Methods: GALAHAD is an ongoing open label Ph 2 study assessing niraparib (300 mg daily) in pts with DRD progressing on/after ARSIs and taxane chemotherapy. Using a validated plasma assay, DRD status was defined as pathogenic mutations (including homozygous deletions) of BRCA1/2, ATM, FANCA, PALB2, CHEK2, BRIP1 or HDAC2. Composite response rate (RR) was defined as an objective response by RECIST 1.1 for measurable disease, circulating tumor cell (CTC) conversion to < 5/7.5 mL blood or prostate-specific antigen (PSA) decline of ≥50% (PSA50). Here, preliminary data on RR and adverse events (AEs) are reported in pts with biallelic DRD. Results: As of 10 Sep 2018, 123 pts with mCRPC and DRD were enrolled, of whom 39 had biallelic DRD (23 BRCA1/2). The median follow-up was 5.7 mo (2.0–23.7). Table depicts RRs for pts with biallelic DRD by BRCA status. Composite and objective RRs were 65% and 38% in pts with biallelic BRCA1/2, respectively. 3/8 pts (38% [2/5 BRCA1/2 and 1/3 non-BRCA]) with measurable visceral metastases showed objective response. Among the 20 biallelic responders, the duration of treatment (tx) has exceeded 4 mo in 13 pts and 6 mo in 8 pts; 14 pts remain on tx. The most common grade 3/4 hematologic AEs were anemia (25%) and thrombocytopenia (15%) (manageable by dose reduction/interruption). The most common grade 3/4 nonhematologic AEs were asthenia (6%) and hypertension (5%). Conclusions: These results suggest niraparib has compelling activity as monotherapy for pts with treatment-resistant mCRPC, particularly those with biallelic BRCA1/2 identified by a blood assay. Clinical trial information: NCT02854436. [Table: see text]

PARP Inhibitors in Prostate Cancer.

The genomic landscape of metastatic prostate cancer (mPCa) reveals that up to 90% of patients harbor actionable mutations and >20% have somatic DNA repair gene defects (DRD). This provides the therapeutic rationale of PARP inhibition (PARPi) to achieve "synthetic lethality" in treating this fatal disease. Clinical trials with PARP inhibitors have shown significant response rates up to 88% for PCa patients having DRD like BRCA1/2 or ATM mutations. The FDA has awarded "breakthrough designation" to develop the PARPi olaparib in treating this subset of metastatic PCa patients. The search for predictive biomarkers has expanded the realm of DNA repair genetic defects and combination genetic platforms are being evaluated as tools to assess potential "BRCAness" of tumors. Ongoing clinical trials seek to determine the optimal timing and sequence of using these agents in current PCa treatment algorithms. Combination strategies of PARPi with chemo-, radiation, and hormonal therapies, targeted agents, and immunotherapy are promising avenues of current research. Multi-center international collaborations in well-designed biomarker-driven clinical trials will be key to harness the potential of PARPi in managing a heterogeneous disease like prostate cancer.

Contribution of classical end-joining to PTEN inactivation in p53-mediated glioblastoma formation and drug-resistant survival

DNA repair gene defects are found in virtually all human glioblastomas, but the genetic evidence for a direct role remains lacking. Here we demonstrate that combined inactivation of the XRCC4 non-homologous end-joining (NHEJ) DNA repair gene and p53 efficiently induces brain tumours with hallmark characteristics of human proneural/classical glioblastoma. The murine tumours exhibit PTEN loss of function instigated by reduced PTEN mRNA, and increased phosphorylated inactivation and stability as a consequence of aberrantly elevated CK2 provoked by p53 ablation and irrevocably deregulated by NHEJ inactivation. This results in DNA damage-resistant cytoplasmic PTEN and CK2 expression, and the attenuation of DNA repair genes. CK2 inhibition restores PTEN nuclear distribution and DNA repair activities and impairs tumour but not normal cell survival. These observations demonstrate that NHEJ contributes to p53-mediated glioblastoma suppression, and reveal a crucial role for PTEN in the early DNA damage signalling cascade, the inhibition of which promotes tumorigenicity and drug-resistant survival.

Targeting DNA Repair: The Role of PARP Inhibition in the Treatment of Castration-Resistant Prostate Cancer.

Several genomic studies have identified DNA repair gene defects in prostate cancer in the last 5 years. The mechanisms by which these DNA repair defects promote carcinogenesis and tumor progression in the prostate have not been fully elucidated, but their presence in at least 20-25% of metastatic castration-resistant prostate cancers (CRPCs) provides an opportunity for a therapeutic strategy that turns a tumor strength into its weakness and may lead to arguably the first molecularly stratified treatment for this disease.Poly(ADP-ribose) polymerase (PARP) inhibitors have been developed as an anticancer synthetic lethal therapeutic strategy for tumors with impaired homologous recombination DNA repair, based on a synthetic lethal effect. Poly(ADP-ribose) polymerase inhibitors have shown to induce significant tumor responses in cancer patients carrying germline BRCA1/2 mutations. Recent evidence from a phase II clinical trial supports further testing of PARP inhibitors for the treatment of metastatic CRPC with either germline or somatic defects in BRCA2, ATM, PALB2, and other DNA repair genes.We review the current evidence of how this strategy is relevant for the treatment of advanced prostate cancers, the available data from trials with PARP inhibitors in metastatic CRPC, and the ongoing studies analyzing combinations of these drugs with other therapies.

Deletion of Nono, a Novel Double-Strand Break Repair Factor, Leads to Hematopoietic Stem Cell Defects

Three genes, SFPQ, NONO, and PSPC1 encode for a small family of tandem RRM domain-containing proteins with diverse functions in RNA processing, transcription, and DNA repair. Our previous work has shown that an SFPQ•NONO complex promotes a distinct sub-pathway of non-homologous end joining (NHEJ) in vitro, implicating it as a novel double-strand break (DSB) repair factor. Consistently, attenuation of NONO function in human fibroblasts leads to partial radiosensitivity, delayed resolution of DNA repair foci, and an increase in radiation-dependent chromosome aberrations. To investigate the in vivo function of this complex, we knocked out Nono, the mouse homolog of the human NONO gene. We hypothesized that a DSB repair deficiency would lead to stem cell exhaustion, sensitivity to DNA damaging agents, or both. First, we investigated hematopoietic stem cells (HSCs), which are known to be sensitive to impairment of DNA repair. Nono-deficient (gt/0) mice showed reduced bone marrow and spleen cellularity, potentially due to reduced body size. The proportion of HSCs (LSK-SLAM) in relation to total bone marrow cells was similar in Nono-deficient and wild type (WT) mice, and bone marrow cell cultures yielded similar numbers and types of colonies. However, HSCs from Nono-deficient mice showed severe impairment in competitive repopulation assays in primary and secondary recipients. HSCs from gt/0 mice also displayed significantly higher levels of ROS and proliferation (accessed via BrdU incorporation), as well as higher percentage of Ki-67 positivity when compared to HSCs from WT mice. Together, these results indicate that Nono-deficient HSCs exhibit impaired capacity for self-renewal that may be caused by excessive HSC proliferation, a primary defect in response to genotoxic stress or a combination of both. To further elucidate this phenomenon, we investigated potential differences in sensitivity to the DNA crosslinking agent mitomycin C (MMC) and radiation. As previously observed in other genomic instability models (e.g., Fanconi anemia), colony-forming-cells from Nono-deficient mice were highly sensitive to MMC and X-rays (2 Gγ). Utilizing FACS-sorted HSCs, we determined that NONO protein levels are induced after X-ray treatment, and that Nono-deficient HSCs show delayed resolution of γ-H2AX foci and increased apoptosis. We also evaluated changes in the testis, another organ frequently affected by DNA repair gene mutations. Accordingly, testes of Nono-deficient mice showed growth retardation that became apparent between 18 and 26 days of postnatal development. The co-occurrence of hematopoietic and germ cell defects is reminiscent of other DNA repair gene defects, including those seen in Fanconi anemia. Collectively, our data identify NONO as a novel and important regulator of both HSC maintenance and germ cell function. Its potential effect in other organ systems and mechanism of action are under investigation. DisclosuresNo relevant conflicts of interest to declare.