DNA Repair Mutations Research Articles

The Pivotal Role of Germline BRCA2 Pathogenic Variants in "Apparently Sporadic" Pancreatic Cancer.

In 1996, Goggins and colleagues demonstrated the importance of germline BRCA2 pathogenic variants in the development of apparently sporadic pancreatic ductal adenocarcinoma (PDAC). Previously, the group identified homozygous deletion of the 13q region in PDACs, enabling the identification of the BRCA2 gene. This 1996 article first revealed loss of BRCA2, both germline and somatic, as a key driver of PDAC at a time when there was still doubt if PDAC even had an inherited component. Contrary to the prevailing wisdom, not all individuals with inherited pathogenic BRCA2 variants had a family history of cancer. The innovative bedside-to-bench nature of this work revealed that individuals with these variants would be missed if genetic testing was limited only to those meeting the family history criteria. Therefore, Goggins and colleagues advocated that universal genetic testing may be indicated for pancreatic cancer at a time when genetic testing was in its infancy. Twenty-three years later, in 2019, universal testing for pancreatic cancer became standard of care in the United States. Additionally, this work and future-related publications by the Kern Laboratory set the stage for targeting BRCA2 and related DNA repair mutations in pancreatic cancer via a synthetic lethal therapeutic approach. The provocative discussion initiated by this team in this publication is still inspiring the field today. In this seminal publication, Goggins and colleagues profoundly impacted the direction of pancreatic cancer research, leading to a more sophisticated approach to designing earlier detection and precision treatment strategies for pancreatic cancer. See related article by Goggins and colleagues, Cancer Res 1996;56:5360-4.

Abstract IA003: Molecular subtypes and clinical benefit from neoadjuvant chemotherapy: A ten-year update

Abstract Ten years ago TCGA and two private groups reported that muscle-invasive bladder cancers (MIBCs) could be grouped into basal and luminal molecular subtypes that shared features with the corresponding subtypes of breast cancer. These and earlier studies by the group at Lund University demonstrated that molecular subtype membership was prognostic: patients whose tumors were assigned to basal/squamous subtypes had shorter survival than did patients whose tumors were assigned to the luminal subtypes, and these relationships were confirmed in subsequent studies. In addition, one of the studies included tumors from patients treated with neoadjuvant cisplatin-based combination chemotherapy (NAC), where patients whose tumors were infiltrated with smooth muscle cells and fibroblasts (the MD Anderson p53-like subtype) had the lowest response rates. Parallel comparisons of patients who either did or did not receive NAC concluded that patients with basal tumors derived the most clinical benefit in terms of disease-specific or overall survival. Thus, in addition to being prognostic, there was a suggestion that molecular subtypes might also be used to predict resistance to NAC. This work led to the design of two large collaborative projects that were designed to validate these observations and the conclusion that inactivating mutations in several DNA damage and repair (DDR) genes were also associated with response. One leveraged the S1314 Phase-2 “CoXEN” trial that was designed to prospectively validate another gene expression-based biomarker, and the other exploited pretreatment samples from the CALGB/Alliance 90601 Phase-3 trial of gemcitabine/cisplatin with or without bevacizumab in patients with advanced or metastatic disease. Comparisons of response rates as a function of molecular subtype membership in S1314 failed to validate the original link between the MD Anderson p53-like subtype and resistance, and patients with basal/squamous tumors in 90601 did not have better outcomes than did patients with luminal tumors. Thus, while the prognostic value of molecular subtype membership was confirmed, the predictive value was not. Developing biomarkers to predict response to chemotherapy remains a challenge not only for bladder cancer but also for other solid and hematopoietic malignancies. It seems likely that success will require the integration of measurements using multiple platforms, including liquid biopsies and others. The exciting results of the EV-302 clinical trial of enfortumab vedotin plus pembrolizumab have shifted the focus of biomarker work to these and other novel agents. Citation Format: David J McConkey. Molecular subtypes and clinical benefit from neoadjuvant chemotherapy: A ten-year update [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr IA003.

Predictive and Prognostic Biomarkers and Tumor Antigens for Targeted Therapy in Urothelial Carcinoma.

Urothelial carcinoma (UC) is the fourth most prevalent cancer amongst males worldwide. While patients with non-muscle-invasive disease have a favorable prognosis, 25% of UC patients present with locally advanced disease which is associated with a 10-15% 5-year survival rate and poor overall prognosis. Muscle-invasive bladder cancer (MIBC) is associated with about 50% 5 year survival when treated by radical cystectomy or trimodality therapy; stage IV disease is associated with 10-15% 5 year survival. Current therapeutic modalities for MIBC include neoadjuvant chemotherapy, surgery and/or chemoradiation, although patients with relapsed or refractory disease have a poor prognosis. However, the rapid success of immuno-oncology in various hematologic and solid malignancies offers new targets with tremendous therapeutic potential in UC. Historically, there were no predictive biomarkers to guide the clinical management and treatment of UC, and biomarker development was an unmet need. However, recent and ongoing clinical trials have identified several promising tumor biomarkers that have the potential to serve as predictive or prognostic tools in UC. This review provides a comprehensive summary of emerging biomarkers and molecular tumor targets including programmed death ligand 1 (PD-L1), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), fibroblast growth factor receptor (FGFR), DNA damage response and repair (DDR) mutations, poly (ADP-ribose) polymerase (PARP) expression and circulating tumor DNA (ctDNA), as well as their clinical utility in UC. We also evaluate recent advancements in precision oncology in UC, while illustrating limiting factors and challenges related to the clinical application of these biomarkers in clinical practice.

Abstract CT261: Phase II trial of nivolumab in combination with talazoparib in patients with unresectable or metastatic melanoma and mutations in BRCA or BRCA-ness

Abstract Novel therapies are needed for anti-PD-1 refractory metastatic melanoma. Few therapies rationally target biologically selected subpopulations of melanoma. In the Cleveland Clinic Familial Melanoma Registry, a high rate of germline mutations in proteins that regulate DNA repair were seen. PARP inhibitors can lead to synthetic lethality and clinical benefit in patients with BRCA mutations or mutations associated with DNA damage repair (“BRCAness phenotype”). Additionally, preclinical models have shown that PARP inhibitors lead to STING activation, raising the hypothesis that combination therapy with anti-PD-1 could augment immune responses. We conducted a phase II trial evaluating the combination of the PARP inhibitor talazoparib with nivolumab in patients with metastatic melanoma harboring germline or somatic DNA repair mutations. We enrolled a cohort of patients with multiple melanoma subtypes including cutaneous melanoma (3), melanoma arising from a blue nevus (2) and uveal melanoma (2). Mutant DNA repair genes included BAP1 (4), BRCA2 (1), ATM (1), ATR (1) and ARID2 (1), 3 of which were germline. The patient population had highly refractory disease with 6 of 7 patients having progression after ipilimumab + nivolumab (5 of these were primary progression). The 7th patient had a recurrence after adjuvant nivolumab. Of the 7 patients enrolled, all progressed within 6 months (using RECIST and iRECIST criteria).The toxicity profile was consistent with known profile of PARP inhibitors (anemia). Although patient enrollment was limited, this study suggests that in heavily pretreated patients selected for DNA repair mutations the combination of PARP inhibitors and anti-PD-1 has no effect on RECIST-based tumor response. Additional studies are needed. Possible alternative selection strategies include evaluating for genomic evidence of homologous recombination repair deficiency (HRD) or targeting specific mutations (BRCA). TABLE 1: NAND Patient Characteristics and Treatment Outcome Age Subtype of Melanoma Gene Alteration Somatic or Germline TMB BRAF Status Prior Therapy Status of Prior IO response Clinical Trial Response 76 Cutaneous ATM Germline N/A WT Nivolumab Progression after Adjuvant Progression 32 Cutaneous ATR Somatic 4.2 V600E Ipilimumab + Nivolumab Primary Progression Progression 75 Uveal BRCA2 and BAP1 Germline 1.3 WT Ipilimumab + Nivolumab Primary Progression Progression 45 Cutaneous/Blue Nevus BAP1 Somatic 0.0 WT Ipilimumab + Nivolumab Primary Progression Progression 51 Cutaneous/Blue Nevus BAP1 Germline 1.6 WT Ipilimumab + Nivolumab Primary Progression Progression 69 Uveal BAP1 Somatic 1.6 WT Pembrolizumab Primary Progression Progression 61 Cutaneous ARID2 Somatic 17.9 WT Ipilimumab + Nivolumab Secondary Resistance Progression Citation Format: James Isaacs, Tamara A. Sussman, Lucy B. Kennedy, Joshua Arbesman, Brian Gastman, Millennia Zhou, Emily Zabor, Claudia Diaz-Montero, Jennifer Ko, Pauline Funchain. Phase II trial of nivolumab in combination with talazoparib in patients with unresectable or metastatic melanoma and mutations in BRCA or BRCA-ness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT261.

The effect of germline DNA repair mutations on radiosensitivity in pancreatic ductal adenocarcinoma.

703 Background: The association between homologous recombination deficiency (HRD) in pancreatic ductal adenocarcinoma (PDAC) and sensitivity to platinum-based chemotherapy highlights the need to further understand how germline DNA repair mutations influence the efficacy of different therapies. Given the recent ALLIANCE data that chemotherapy alone is an acceptable standard of care to enhance R0 resection, the focus has shifted towards the contribution of radiotherapy. However, the relationship between germline DNA repair mutations in general and radiosensitivity remains less understood. This study explores the relationship between germline mutations and the Radiosensitivity Index (RSI) gene signature. Methods: After obtaining institutional review board approval, a retrospective analysis was performed of patients who had both RSI and germline mutation testing (i.e., BRCA1, BRCA2, BLM, ATM, MLH1, MSH2, MSH6, PMS2, and BARD mutations) between 1999 and 2023 at a single institution. Student T, Chi squared, Kaplan Meier (KM), Cox univariate log regression (UVA), and Mann-Whitney U (MWU) tests were used for statistical analyses. Results: A total of 25 patients were included, 13 with mutations and 12 without. MWU analysis demonstrated a significant difference in RSI values, where patients with mutations exhibited greater radiosensitivity (mean 0.379 vs. 0.464, p=0.040). The median age at diagnosis, max diameter of tumor, and baseline CA 19-9 were 67 years (range 47 – 77), 3.4 cm (range 0.8 – 8.2), and 288 (9.5 – 26,100), respectively. Most of the tumors were resectable (84%), stage IIB (36%), and grade 2 (68%). All patients underwent resection, with the majority without neoadjuvant therapy (96%). Most patients received chemotherapy (n=18; 72%), most commonly gemcitabine monotherapy (n=14/18). A majority also received radiation therapy (n=15; 60%), with 93% receiving chemoradiation (n=14/15). The median follow-up was 20.8 months. KM analysis yielded a median overall survival (OS) of 20.0 months (95% CI: 7.1-33.0) and progression-free survival (PFS) of 15.1 months (95% CI: 12.3-18.0) for the entire cohort. At the time of analysis, 15.4% of patients with mutations were alive (>10 years), compared to none without mutations (p=0.157). There were no statistically significant differences between the two cohorts for clinical outcomes on KM analysis. On UVA, worse OS was correlated with stage III (HR 7.9, 95% CI 1.2 – 50.2) and IV (HR 11.8, 95% CI 1.4 – 102.3). No other variables were associated with OS on UVA or on mutant-only subgroup analysis. Conclusions: Our findings demonstrate an increased radiosensitivity in patients with germline DNA repair mutations, suggesting these cancers might be more susceptible to radiation-induced DNA damage. Since our results are constrained by the small sample size, further studies are needed to understand the relationship between PDAC with DNA repair mutations.

Liquid Biopsy as a Powerful Therapeutic Tool in Veteran Patients with Prostate Carcinoma

Abstract Introduction/Objective The National Comprehensive Cancer Network (NCCN) guidelines currently recommend somatic tumor molecular testing for alterations in homologous recombination (HR) DNA repair genes in patients with metastatic prostate cancer, which can be performed on either the sampled tumor tissue itself or by liquid biopsy. Particularly when the sampled tumor tissue may be limited, liquid biopsy with next generation sequencing is a recently available attractive alternative that is minimally invasive (requiring just phlebotomy). Based on the information gathered from circulating tumor cells (CTC), a tumor molecular profile can be obtained that can impact treatment, particularly if a HR DNA repair mutation is found as that may predict response to a poly (ADP-ribose) polymerase (PARP) enzyme inhibitor such as Olaparib. However, the literature of metastatic prostate cancers targeted by liquid biopsies and the mutations found is sparse, particularly for the veteran population. Methods/Case Report A retrospective review was performed of all patients with a submitted liquid biopsy specimen at a Veteran Affairs Medical Center (VAMC) October 23rd, 2019, to March 3rd, 2023 to examine those patients with metastatic prostate cancer. Information on mutations detected was collected. Results (if a Case Study enter NA) There were a total of 64 patient specimens with a history of metastatic prostate cancer, from which 56 had an available liquid biopsy report with the first liquid biopsy collection occurring on October 23rd, 2019. HR DNA repair mutations found included CHEK2 (6/56), ATM (4/56), and BRCA1 (1/56). Outside of HR DNA repair genes, relatively common detected mutations were found in TP53 (25/56), PTEN (6/56), BRAF (4/56), and an AR amplification (4/56). 7 of the 56 reports had no reportable genomic alterations detected. Conclusion Liquid biopsies continues to be a minimally invasive, highly useful powerful therapeutic tool in veteran patients with metastatic prostate carcinoma for molecular profiling. Not uncommonly in the Veteran population, these molecular findings include mutations in HR DNA repair genes that as noted by the NCCN may predict response to PARP inhibitor chemotherapy.

Tumor-derived biomarkers predict efficacy of B7H3 antibody-drug conjugate treatment in metastatic prostate cancer models.

Antibody-drug conjugates (ADCs) are a promising targeted cancer therapy; however, patient selection based solely on target antigen expression without consideration for cytotoxic payload vulnerabilities has plateaued clinical benefits. Biomarkers to capture patients who might benefit from specific ADCs have not been systematically determined for any cancer. We present a comprehensive therapeutic and biomarker analysis of a B7H3-ADC with pyrrolobenzodiazepine(PBD) payload in 26 treatment-resistant, metastatic prostate cancer (mPC) models. B7H3 is a tumor-specific surface protein widely expressed in mPC, and PBD is a DNA cross-linking agent. B7H3 expression was necessary but not sufficient for B7H3-PBD-ADC responsiveness. RB1 deficiency and/or replication stress, characteristics of poor prognosis, and conferred sensitivity were associated with complete tumor regression in both neuroendocrine (NEPC) and androgen receptor positive (ARPC) prostate cancer models, even with low B7H3 levels. Non-ARPC models, which are currently lacking efficacious treatment, demonstrated the highest replication stress and were most sensitive to treatment. In RB1 WT ARPC tumors, SLFN11 expression or select DNA repair mutations in SLFN11 nonexpressors governed response. Importantly, WT TP53 predicted nonresponsiveness (7 of 8 models). Overall, biomarker-focused selection of models led to high efficacy of in vivo treatment. These data enable a paradigm shift to biomarker-driven trial designs for maximizing clinical benefit of ADC therapies.

19 DNA repair mutations aid in Mycobacterium avium adaptation to antibiotic stress during chronic cystic fibrosis respiratory infection

19 DNA repair mutations aid in Mycobacterium avium adaptation to antibiotic stress during chronic cystic fibrosis respiratory infection

A phase 1/2 study of combination olaparib and radium-223 in men with metastatic castration-resistant prostate cancer with bone metastases (COMRADE): A trial in progress.

TPS5110 Background: Radium-223, an α-emitting radioisotope inducing DNA double-stranded breaks leading to cell death has demonstrated improvement in overall survival (OS) in men with metastatic castration-resistant prostate cancer (mCRPC) with bone metastases. PARP inhibitors prevent the repair of DNA single-stranded breaks and have demonstrated clinical efficacy as monotherapy in mCRPC patients harboring alterations in the homologous recombination repair (HRR) pathway and in combination with androgen receptor signaling inhibitors irrespective of DNA repair mutation status. In preclinical models, PARP inhibitors have shown efficacy as radio sensitizing agents. We designed a phase 1/2 trial to identify the recommended phase 2 dose (RPD2) of olaparib and radium-223 and test the hypothesis that radium-223 + olaparib will demonstrate anti-tumor activity in mCRPC irrespective of homologous recombination repair deficiency (HRD) status (NCT03317392). Methods: This open-label, multicenter, phase 1/2 study evaluates the dosing, safety and efficacy of olaparib with radium-223 in men with mCRPC with bone metastases. The phase 1 component used a 3+3 dose escalation design to determine the olaparib recommended phase 2 dose (RP2D) + fixed dose radium-223 (55 kBq/kg IV every 4 weeks x 6). The phase 1 portion has completed accrual (n = 12) and demonstrated that the RP2D of olaparib is 200 mg by mouth twice daily when combined with standard dose radium-223. The phase 2 component of the study which was activated in 1/2021 is an open-label, randomized trial (1:1) evaluating olaparib + radium-223 compared to radium-223 alone. The inclusion criteria include patients with mCRPC with any number of prior therapy lines for mCRPC and ≥2 bone metastases by imaging and at least 1 lesion which has not been treated with prior radiation. Patients with visceral metastases or malignant lymphadenopathy ( > 4 cm in short diameter) are excluded. The primary endpoint for phase 2 is radiographic progression-free survival (rPFS) per PCWG3 guidelines for bone metastases and RECIST v1.1 for non-bone disease. The integrated biomarker is Oncopanel assay to determine HRR status. A key secondary endpoint will evaluate rPFS in biomarker positive and negative patients. Other secondary endpoints include time to PSA progression, PSA response, time to subsequent therapy, time to first skeletal event, and OS. Exploratory endpoints include WES/WTS of baseline biopsy tissue, assessment of RAD51 IHC and correlation with outcomes, ctDNA assessment and correlation with responses, evaluation of changes in the tumor immune microenvironment, and quality of life assessment. Target accrual is 133 patients. Clinical trial information: NCT03317392 .

Abstract 5272: 3D cell-culture strategy for screening novel agents in Fanconi anemia chemoprevention

Abstract Fanconi anemia (FA) patients have DNA repair mutations predisposing them to oral cancers so treatment with non-DNA damaging agents is highly desired. As cancer experimental therapeutics advance towards study paradigms that more carefully mimic physiology, e.g. organoids and spheroids. Presently, we are using a 3D cell culture method emphasizing layers of extracellular matrix (ECM) as FA premalignant lesions retain epithelial architecture. We conducted 3D screening studies using 2 layered geometries: 1) nanofibers coated with 1 ng/mL 2:1 Collagen III/IV (C3C4) then 100 pg/mL 2.75:1 Tenascin C/Fibronectin (TNFN) and 2) polystyrene layered with 50 ug/mL C3C4 then 3.5 ug/mL TNFN. We developed these coatings to maximize lipid raft recovery, a drug transport feature lost in 2D culture. The ECM impact on FA cell drug transport was characterized by comparing effective nuclear delivery of a 20nm nanoencapsulated FITC-labeled RNAi compound (s50-TBG-RNAi3UTR), known to require lipid rafts, to the same oligo formulated with Dotap in a FA HNSCC cell line (FA1). Using confocal microscopy and IMARS software to segment delivery at maximal nuclear intensity into nuclear or endolysosomal compartments, we found, for FA1 cells on ECM, nuclear oligo signal colocalization with nuclear compartment ± coefficient of variation was 62 ± 2.2% for the capsule vs 9.8 ± 8.5% for Dotap oligo. On glass, nuclear delivery was 10 ± 52% for s50 capsule vs 25 ± 32% for Dotap. Endolysosomal compartment sequestration was respectively 28 ± 12, 62 ± 10, 44 ± 19 and 51 ± 15%. This illustrates a relevant decrease in variation in FA cell biology from ECM addition. Next, we studied metformin (Met) and pioglitazone (Pio)(agents in current oral cancer prevention studies) combined with G2/M blockade inhibitors, MK1775 (Wee1 kinase inhibitor) and GSK461364 (PLK inhibitor) in FA1s. Inhibiting G2/M blockade, already induced by FA-derived DNA damage, could promote inappropriate cell division, mitotic catastrophe (MOC) and death. In initial 2D FA1 growth studies, increased death was observed with Met plus MK1775. 3D studies, in contrast, showed increased cell death for FA1s treated with Pio plus either MK1775 or s50-TBG-RNAiCK2 (RNAiCK2). Confocal mechanistic studies in cells plated on ECM and treated for 18 hours, indicated Pio + MK1775 inhibited Survivin and ß-catenin upregulation and FA1 cells did proceed into MOC and death. For Pio (PPARg agonist) + RNAiCK2, RXRa was dephosphorylated at S260, enabling its escape from cytosolic sequestration to bind nuclear PPARg, initiating differentiation. Differentiation was indicated by upregulation panKeratin and Transglutaminase-3. We conclude combination therapies with high interest agents in FA-associated oral cancer can be performed in 3D culture systems and might confirm drug mechanisms of action, thus augmenting other standard methods of cancer drug evaluation and screening (e.g. cell proliferation and clonogenicity). Citation Format: Gretchen M. Unger, Beverly R. Wuertz, Mary E. Brown, Sanjana Arji, Janeen H. Trembley, Frank G. Ondrey. 3D cell-culture strategy for screening novel agents in Fanconi anemia chemoprevention. [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 5272.

Internet-Based Germline Genetic Testing for Men With Metastatic Prostate Cancer.

Germline mutations in DNA repair genes are present in approximately 10% of men with metastatic prostate cancer (mPC), and guidelines recommend genetic germline testing. Notable barriers exist, including access to genetic counseling, insurance coverage, and out-of-pocket costs. The GENTleMEN study was designed to determine the feasibility of an Internet-based, patient-driven germline genetic testing approach for men with mPC. In this prospective cohort study, men with mPC provided informed consent via an Internet-based platform and completed a questionnaire including demographics and family cancer history. Supporting medical data were also collected. Genetic testing was performed using the Color Genomics 30-gene targeted panel of cancer predisposition genes on a mailed saliva sample. Men whose test results identified a germline pathogenic or likely pathogenic variant received results by phone or telehealth genetic counseling; other participants received results by email with an option for phone-based or telehealth genetic counseling. As of August 18, 2021, 816 eligible men were consented, of whom 68% (551) completed genetic testing, and 8.7% (48 of 551) were found to carry a pathogenic or likely pathogenic variant in a germline DNA repair gene: CHEK2 (17), BRCA2 (15), ATM (6), NBN1 (3), BRCA1 (2), PALB2 (2), PMS2 (2), and MSH6 (1). Participants were more likely to complete the testing process if they were non-Hispanic White, married, highly educated, or from a higher-income bracket. Here, we show the feasibility of delivering germline (inherited) genetic testing by a voluntary, patient-driven, Internet-based platform to men with mPC. Preliminary results show rates of germline DNA repair mutations, consistent with other cohorts. Although feasible for some, reduced steps for participation, more dedicated diverse outreach and participant support, and identification and addressing of additional barriers is needed to ensure equitable access and optimization.

TRIUMPH: Phase II trial of rucaparib monotherapy in patients with metastatic hormone-sensitive prostate cancer harboring germline DNA repair gene mutations.

190 Background: Androgen deprivation therapy (ADT) is the backbone of treatment for patients (pts) with metastatic prostate cancer (PCa), but many pts find this difficult to tolerate. Treatment with non-castrating regimens may avoid or delay the toxicities of hormonal therapy. The activity of PARP inhibitors (PARPi) in pts with homologous recombination DNA-repair (HRD) mutations (muts) and metastatic castration-resistant PCa has been established. We hypothesized here that the benefit of ARPi can be maintained in the absence of ADT in a biomarker-selected (HRD mutated) population with PCa. We designed a Phase 2 study in men with hormone-naïve, metastatic PCa who harbored a germline HRD mut treated with rucaparib monotherapy (without ADT). Methods: This was a multi-center, single arm Phase 2 study (NCT03413995) in men with asymptomatic hormone-sensitive metastatic PCa who received rucaparib 600mg by mouth daily. During consenting, pts were informed and had to opt out of ADT-based therapy. Pts must have had a germline mutation in an HRD gene on clinical-grade testing. The primary endpoint was confirmed PSA50 response rate. Key secondary endpoints included safety, objective response rate (ORR), and radiographic progression-free survival (rPFS). The trial was designed to detect a 25% absolute increase in PSA50 response from a null of 50%. Results: 12 pts were enrolled, 7 with BRCA1/2 and 5 with CHEK2 muts. The confirmed PSA50 response rate to rucaparib was 41.7% (N=5/12, 95% CI: 19.3-68.1%), which did not meet the pre-specified efficacy boundary to enroll additional patients to 2nd stage. In pts with measurable disease, the ORR was 60% (N=3/5, all with BRCA2). Median rPFS on rucaparib was 10.3 months (95% CI: 4.0 mo - NR). At the time of the interim analysis, 3 pts remained on study. The majority of adverse events (AE) were Grade ≤2 and expected. Translational studies are ongoing. Conclusions: Rucaparib can induce clinical responses in a biomarker-selected PCa population without concurrent ADT. However, the pre-specified threshold of PSA50 response was not met. Although durable responses were observed in a subset of pts, PARPi without ADT in metastatic hormone sensitive PCa will not be pursued. Clinical trial information: NCT03413995 . [Table: see text]

Impact of somatic DNA repair mutations on bone-related efficacy endpoints in patients with metastatic castration-resistant prostate cancer (mCRPC): A retrospective analysis.

214 Background: Up to 80% of mCRPC have bone metastases and about 25% of metastatic prostate cancer harbor mutations in DNA damage repair defects (DDR). DDR gene mutations are a negative prognostic factor, being associated with short metastasis-free survival and cancer-specific survival. We analyzed the impact of somatic mutations in DDR genes on bone-related efficacy endpoints in mCRPC. Methods: We retrospectively analyzed the mutational status of mCRPC patients per FoundationOne analysis in tissue biopsy or, when it was not possible, in liquid biopsy (performed at the onset of mCRPC). We evaluated the impact of DDR gene mutations on bone-related efficacy endpoints at the time of mCRPC diagnoses, by dividing patients in two main groups (mutated DDR, specifically, mutations in at least one of BRCA1/2, ATM, FANCA, ATR, CHEK2, RAD51, PALB2, and CDK12 genes: group A; wild-type DDR: group B). We investigated differences between the two groups in terms of time from bone metastases onset to death, skeletal metastatic tumor burden (sites and number of lesions), skeletal-related events (SRE) incidence, and time to first on-study SRE. Results: Of the 131 patients with mCRPC enrolled, 115 had bone metastases. Clinical data distribution, according to molecular profile, is presented. There is no difference in terms of sites of metastases and time from bone metastases onset to death between the 2 groups. Mutated DDR status was associated with bone metastases volume (p = 0.0325), but did not affect SRE incidence and time to SRE onset. Conclusions: In our analysis, mutated DDR status was associated with higher bone metastases volume, although a not detrimental effect on the other bone-related efficacy endpoints was observed. [Table: see text]

Specific Clonal Mutations Are Predictive of Therapy-Related Myeloid Neoplasms (tMN) after Autologous Peripheral Blood Stem Cell Transplantation (aPBSCT) for Lymphoma

Background: tMN is a lethal complication of aPBSCT for Hodgkin (HL) and non-Hodgkin lymphoma (NHL). Clonal somatic mutations in leukemia-associated genes (clonal hematopoiesis [CH]) are observed in peripheral blood of healthy older adults, and are associated with an elevated risk for subsequent leukemia. In cancer patients, CH mutations are differentially selected by therapeutic exposures. We examined the association between CH in the PBSC product and risk of post-aPBSCT tMN. Methods: We constructed a retrospective cohort of 1,328 patients (NHL=1,000; HL=328) who received aPBSCT between 1980 and 2016 at a single institution. Information on demographics (sex, race), clinical characteristics (HL/NHL, age at aPBSCT, CD34 counts in PBSC product) and therapeutic exposures (pre-aPBSCT cyclophosphamide equivalent dose [CED], doxorubicin equivalence dose, radiation; total body irradiation [TBI]) was abstracted from medical records. Using cryopreserved aliquots of PBSC product from all patients, we performed sequencing of target regions in 91 genes selected for association with CH or myeloid malignancies (Illumina NovaSeq platform; >1000x), to identify pathogenic mutations (variant allele frequency [VAF] ≥1%). Logistic regression identified demographic/clinical/treatment factors associated with CH. Fine-Gray proportional sub-distribution hazard regression determined the role of CH (yes/no; number of mutations [0, 1, 2+]; specific mutations) in development of subsequent tMN, adjusting for above factors. We also examined the role of CH in post-aPBSCT mortality. Results: Median age at aPBSCT was 50y (range: 18-78); 62% male; 61% non-Hispanic white. CH in the PBSC was identified in 435 patients (33%); single mutation: 276 (21%); >1 mutation: 159 (12%). Most commonly mutated genes included DNMT3A (192, 14.5%), PPM1D (118, 8.9%), TET2 (82, 6.2%), TP53 (44, 3.3%). Seventy-five patients developed tMN, yielding an 8y cumulative incidence of 5.9%. Predictors for CH in PBSC: Older age at aPBSCT (odds ratio [OR]per_y_inc=1.07, p=5.9x10-34 and high pre-aPBSCT alkylating agent exposure [CED=1-12,000: OR=1.58, p=0.01; CED >12,000: OR=2.03, p=0.057) were independently associated with CH. CH in PBSC and post-aPBSCT t-MN: Among the 435 patients with CH, 38 (9%) developed tMN. The 8y cumulative incidence of tMN was highest in patients with >1 mutations (14.6%) vs. single mutation (6.9%), vs. no mutation (4.0%), p=2.4x10-6. Multivariable analysis (Table 1) revealed >1 mutation as an independent predictor of tMN (HR=2.38, p=0.003; single mutation: HR=1.27, p=0.47; reference: no mutations); other factors associated with tMN are in Table 1. Specific mutations in PBSC andpost-aPBSCTtMN: The role of specific mutations in the development of tMN is detailed in Table 2. tMN incidence in patients with DNMT3A mutations alone did not differ from patients with no mutations (8y incidence: 4.2% vs. 4.0%, p=0.95), but was increased in patients with PPM1D (9.4% vs. 4.0%, p=0.06) and TP53 (9.5% vs. 4.0%, p=0.22) mutations alone, although not reaching statistical significance. The co-occurrence of mutations in DNMT3A + PPM1D (21.4% vs. 4.0%, p=0.0006), DNMT3A +TP53 (33.3% vs. 4.0%, p <0.001) or PPM1D + TP53 (42.9% vs. 4.0%, p <0.001) was associated with significantly higher tMN incidence compared with no CH mutations. Taken together, individuals with the combination of mutations in genes involved in epigenetic regulation (DNM3TA, TET2 and/or ASXL1) and DNA repair (TP53, PPM1D, ATM, and/or SRCAP) had significantly higher tMN incidence compared to those with mutations in genes involved in epigenetic regulation alone (26.6% vs. 5.4%, p=1.1x10-5). Specific mutations at time of tMN: In available samples (peripheral blood or bone marrow: n=40), TP53 (n=13, 32.5%), PPM1D (n=12, 30%), DNMT3A (n=12, 30%) and TET2 (n=4, 10%) were the most frequently mutated genes. CH in PBSC and mortality: All-cause mortality at 8y from aPBSCT was significantly higher in patients with CH (38.4%) vs. those without (30.1%), p=0.0009. Conclusion and Relevance: CH is associated with increased risk of tMN after aPBSCT for lymphoma, but most patients with CH do not develop tMN. This study shows that the co-occurrence of multiple key somatic mutations in the PBSC product increases tMN risk. Importantly, mutations in DNA repair/ damage response genes, especially in combination with epigenetic regulatory genes, increase the risk of tMN. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Pathogenic variants in SLF2 and SMC5 cause segmented chromosomes and mosaic variegated hyperploidy

Embryonic development is dictated by tight regulation of DNA replication, cell division and differentiation. Mutations in DNA repair and replication genes disrupt this equilibrium, giving rise to neurodevelopmental disease characterized by microcephaly, short stature and chromosomal breakage. Here, we identify biallelic variants in two components of the RAD18-SLF1/2-SMC5/6 genome stability pathway, SLF2 and SMC5, in 11 patients with microcephaly, short stature, cardiac abnormalities and anemia. Patient-derived cells exhibit a unique chromosomal instability phenotype consisting of segmented and dicentric chromosomes with mosaic variegated hyperploidy. To signify the importance of these segmented chromosomes, we have named this disorder Atelís (meaning - incomplete) Syndrome. Analysis of Atelís Syndrome cells reveals elevated levels of replication stress, partly due to a reduced ability to replicate through G-quadruplex DNA structures, and also loss of sister chromatid cohesion. Together, these data strengthen the functional link between SLF2 and the SMC5/6 complex, highlighting a distinct role for this pathway in maintaining genome stability.

EP-334 The Impact of Combined DNA Repair and Oncogene Mutations in Colorectal Cancer Survival

Abstract Aims To examine the coexistent effect of either KRAS or BRAF gene status with MMR gene status on patient outcomes in a rural population of colorectal cancer patients. Methods Using a colorectal cancer database, results for patient mutation status for mismatch repair genes and other oncogenes, obtained by DNA sequencing and immunohistochemical analysis, were assessed to see if there were significant differences in survival probability in patients with and without single and combined risk factors. Kaplan-Meier survival analyses were performed to examine overall survival probability in the different groups of patients. Results Comparison of survival outcomes in patients with and without KRAS and MLH1 mutations showed a significant difference (p=0.018). Pairwise analysis reveals that this difference is mostly between the group with wild-type status for both genes and a patient with mutant KRAS and EGFR status with wildtype MLH1 status (p=0.062 with bonferroni correction). Combined KRAS and PMS2 status results in a borderline insignificant (p=0.056) survival difference as well. The effects of mutations in other combinations of oncogenes, as well as sex or tumour sidedness and mutation statuses, were not significant on survival probability. Conclusions These preliminary results should be interpreted with caution owing to the relatively small sample size. This study supports previous findings that mutant oncogenes, combined with altered MMR genes can be predictive of colorectal cancer survival outcome.

Abstract 2075: Systemic small molecule TREX1 inhibitors to selectively activate STING in the TME of metastatic disease

Abstract Genetic evidence from human disease and mouse genetic knock-out studies identify the Stimulator of Interferon Genes (STING) pathway as a critical innate immune sensor for the development of immunity. Tumor cells can evolve to avoid immune recognition through inactivating the STING pathway by diverse mechanisms, indicating that it is important to generating tumor-specific immunity. However, the clinical activity of STING agonists given by intratumoral (IT) administration has not compared well to preclinical studies. The scientific hypothesis supporting these first clinical studies is that localized CD8+ T cell priming would have activity against distal non-injected tumors, but findings that tumors in advanced malignancies have unique antigenic repertoires suggests that this approach may have limited activity against distal tumors. Global innate activation in metastases may therefore be necessary to prime a broadly active CD8+ T cell population targeting diverse antigens, in addition having the benefit of reversing the immune suppressive tumor microenvironment (TME). However, ubiquitous expression of STING presents a significant challenge to achieving a therapeutic index with systemic delivery of direct STING agonists. Selective activation of the STING pathway may be achieved through targeted inhibition of TREX1, a cytosolic DNA exonuclease that modulates cGAS/STING signaling. Expression of TREX1, in contrast to STING, is increased in tumor cells due to elevated levels of cytosolic DNA resulting from genetic instability, DNA repair mutation, inflammatory mediators or DNA-modifying anti-cancer therapies. These observations provide the principal scientific rationale to selectively activate the STING pathway in metastatic disease through targeted inhibition of TREX1. Utilizing published TREX1 X-ray crystal structures to guide medicinal chemistry, we discovered small molecule inhibitors of TREX1 and transformed these molecules from &amp;gt;100 µM leads into a series with drug-like physicochemical properties and picomolar potency against both human and mouse TREX1. We evaluated the activity of lead molecules in cell-based assays, in which TREX1 inhibition enhanced cGAS/STING signaling, and advanced molecules with desired pharmacokinetic profiles to mouse tumor studies. We observed significant anti-tumor activity in mice with CT26 tumors given a combined therapy of low dose doxorubicin to induce dsDNA breaks and increase TME TREX1 expression along with lead series TREX1 molecule inhibitors. Recognizing that TREX1 is a DNA repair enzyme, we also showed that TREX1 inhibitors were cytotoxic in DNA repair deficient human tumor cell lines, informing advancement of this new class of STING therapeutics as a clinical approach to both activate the cGAS/STING pathway to initiate immune recognition, as well as to inhibit DNA repair orthogonal to existing tumor-driver DNA repair mutations. Citation Format: Brian Francica, Dara Burdette, Ryan Clark, Jamie Cope, David Freund, Anja Holtz, Peppi Prasit, Chan Whiting, Thomas W. Dubensky. Systemic small molecule TREX1 inhibitors to selectively activate STING in the TME of metastatic disease [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 2075.

Durvalumab (D) in combination with olaparib (O) for advanced, previously treated non-small cell lung cancer (NSCLC).

e21153 Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) show variable clinical activity in individuals with advanced cancers. In the lung-MAP substudy S1400G, talazoparib alone was not sufficiently active in squamous lung cancers with homologous recombinant repair deficiency. Combinations of PARPi with immune checkpoint inhibitors (ICIs) are under investigation since preclinical studies show an immunostimulatory effect of PARPi that can potentially increase responsiveness to ICIs. To test this hypothesis, we evaluated the PARPi, O with the ICI, D in individuals with advanced NSCLC who had received at least one prior platinum-based regimen. Methods: Eligible participants were enrolled in an expansion cohort of a proof-of-concept phase I/II study (NCT02484404) and received O 300 mg PO BID with D 1500 mg IV every 4 weeks until disease progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS). Results: Between July 2016 and July 2021, 15 participants with recurrent NSCLC were enrolled (median age: 66 years; stage IV: 12; adenocarcinoma 11; prior ICI: 9). After median potential follow-up of 39.6 months (mo), median PFS (mPFS) was 3.2 mo (95% CI: 0.9-7.6). Among 14 subjects with known EGFR mutation status, mPFS was longer in 11 individuals with EGFR-WT tumors (5.7 vs. 0.9 mo; p = 0.001). DNA repair mutation ( APC, BAP1, BRCA1, BRCA2, CHEK2, FANCI, FANCL and PALB2) status was known for 9 subjects; mPFS of subjects with (n = 7) or without (n = 2) DNA repair mutations was 3.2 vs. 18.1 mo (p = 0.68), respectively. Tumor PD-L1 expression &gt; 50% (n = 3/10) and prior ICI therapy (n = 9/15) was associated with longer, albeit not statistically significant, mPFS: 7.6 vs. 1.8 mo; p = 0.22, and 5.7 vs. 1.8 mo; p = 0.39, respectively. Two (13%) partial responses, 7 (47%) stable disease and 6 (40%) cases of progressive disease were observed. Four (27%) subjects, including 3 previously treated with ICIs, achieved durable response or stability for up to 3 years. Treatment-related adverse events (TRAEs) were generally mild (grade 1 or 2). The most common TRAEs were anemia (40%), thrombocytopenia (27%), anorexia, fatigue, pain, and hypophosphatemia (each observed in 20%). Grade &gt; 3 TRAEs occurred in 4 (27%) subjects (all hematologic). Immune-related AEs occurred in 4 (27%) individuals. Two subjects developed myelodysplasia after 12 and 36 mo of treatment. Three (20%) subjects required dose reductions or discontinuation of O due to anemia. There were no treatment-related deaths. Accrual will continue until 20 eligible participants are enrolled. Conclusions: O+D has acceptable safety and modest efficacy in an unselected population with recurrent NSCLC. Sufficient clinical activity is not observed in individuals with EGFR-mutated tumors. Genomic and immunological analyses are being performed to identify predictive biomarkers in individuals with durable benefit and will be reported. Clinical trial information: NCT02484404.

Review of second-generation androgen receptor inhibitor therapies and their role in prostate cancer management.

We review the published literature on the indications of second-generation androgen receptor inhibitors, Poly(ADP-Ribose) Polymerase (PARP) inhibitors, combination therapies, and their evolution throughout the advanced prostate cancer continuum. Enzalutamide trials have published data supporting its use in metastatic hormone-sensitive prostate cancer (mHSPC), nonmetastatic castration-resistant prostate cancer (nmCRPC), and metastatic castration-resistant prostate cancer (mCRPC). Apalutamide trials have supported its indication for mHSPC and nmCRPC. Darolutamide trials currently support its use for nmCRPC. Abiraterone trials have supported its use in mCRPC and mHSPC. Olaparib and rucaparib have shown clinical benefit in heavily pretreated patients with mCRPC and DNA repair mutation genes. Phase 3 trials and peer-reviewed literature demonstrate that enzalutamide, apalutamide, and darolutamide prolong overall survival (OS) in men with nmCRPC. Abiraterone, enzalutamide, and apalutamide improve OS in men with mHSPC. Abiraterone and enzalutamide have data supporting improvement in OS in men with mCRPC.

Radiotherapy and radiosensitivity syndromes in DNA repair gene mutations.

Ionizing radiation DNA damage is the main mechanism of radiotherapy (RT) action and the outcome of treatment and healthy tissue toxicity is influenced by a number of external and internal factors, including mutations in DNA damage recognition and repair. Disorders of DNA repair may result in increased sensitivity to cancer treatment. The mechanism of DNA repair and an overview of genetic syndromes with mutations in genes involved in DNA repair clarify the accelerated carcinogenesis and increased radiosensitivity in RT cancers. Most radiosensitivity syndromes are autosomal recessively inherited; examples are ataxia teleangiectasia, Nijmegen breakage syndrome, xeroderma pigmentosum, Cockayne syndrome, Bloom syndrome and Werner syndrome. Radiotherapy is contraindicated in most homozygous patients with recessive radiosensitivity syndromes. Asymptomatic heterozygotes may have an increased risk of tumor incidence and a small part of them slightly increased risk of RT intolerance; however, this does not limit RT treatment. The high risk of secondary malignancies after radiotherapy is a contraindication to adjuvant RT in Li-Fraumeni syndrome.