Randomized Phase II Study of Gemcitabine With or Without ATR Inhibitor Berzosertib in Platinum-Resistant Ovarian Cancer: Final Overall Survival and Biomarker Analyses

PURPOSE

The multicenter, open-label, randomized phase 2 NCI-9944 study (NCT02595892) demonstrated that addition of ATR inhibitor (ATRi) berzosertib to gemcitabine increased progression-free survival (PFS) compared to gemcitabine alone (hazard ratio [HR]=0.57, one-sided log-rank P = .044, which met the one-sided significance level of 0.1 used for sample size calculation).

METHODS

We report here the final overall survival (OS) analysis and biomarker correlations (ATM expression by immunohistochemistry, mutational signature 3 and a genomic biomarker of replication stress) along with post-hoc exploratory analyses to adjust for crossover from gemcitabine to gemcitabine/berzosertib.

RESULTS

At the data cutoff of January 27, 2023 (>30 months of additional follow-up from the primary analysis), median OS was 59.4 weeks with gemcitabine/berzosertib versus 43.0 weeks with gemcitabine alone (HR 0.79, 90% CI 0.52 to 1.2, one-sided log-rank P = .18). An OS benefit with addition of berzosertib to gemcitabine was suggested in patients stratified into the platinum-free interval ≤3 months (N = 26) subgroup (HR, 0.48, 90% CI 0.22 to 1.01, one-sided log-rank P =.04) and in patients with ATM-negative/low (N = 24) tumors (HR, 0.50, 90% CI 0.23 to 1.08, one-sided log-rank P = .06).

CONCLUSION

The results of this follow-up analysis continue to support the promise of combined gemcitabine/ATRi therapy in platinum resistant ovarian cancer, an active area of investigation with several ongoing clinical trials.

Biological basis of extensive pleiotropy between blood traits and cancer risk

BACKGROUND

The immune system has a central role in preventing carcinogenesis. Alteration of systemic immune cell levels may increase cancer risk. However, the extent to which common genetic variation influences blood traits and cancer risk remains largely undetermined. Here, we identify pleiotropic variants and predict their underlying molecular and cellular alterations.

METHODS

Multivariate Cox regression was used to evaluate associations between blood traits and cancer diagnosis in cases in the UK Biobank. Shared genetic variants were identified from the summary statistics of the genome-wide association studies of 27 blood traits and 27 cancer types and subtypes, applying the conditional/conjunctional false-discovery rate approach. Analysis of genomic positions, expression quantitative trait loci, enhancers, regulatory marks, functionally defined gene sets, and bulk- and single-cell expression profiles predicted the biological impact of pleiotropic variants. Plasma small RNAs were sequenced to assess association with cancer diagnosis.

RESULTS

The study identified 4093 common genetic variants, involving 1248 gene loci, that contributed to blood-cancer pleiotropism. Genomic hotspots of pleiotropism include chromosomal regions 5p15-TERT and 6p21-HLA. Genes whose products are involved in regulating telomere length are found to be enriched in pleiotropic variants. Pleiotropic gene candidates are frequently linked to transcriptional programs that regulate hematopoiesis and define progenitor cell states of immune system development. Perturbation of the myeloid lineage is indicated by pleiotropic associations with defined master regulators and cell alterations. Eosinophil count is inversely associated with cancer risk. A high frequency of pleiotropic associations is also centered on the regulation of small noncoding Y-RNAs. Predicted pleiotropic Y-RNAs show specific regulatory marks and are overabundant in the normal tissue and blood of cancer patients. Analysis of plasma small RNAs in women who developed breast cancer indicates there is an overabundance of Y-RNA preceding neoplasm diagnosis.

CONCLUSIONS

This study reveals extensive pleiotropism between blood traits and cancer risk. Pleiotropism is linked to factors and processes involved in hematopoietic development and immune system function, including components of the major histocompatibility complexes, and regulators of telomere length and myeloid lineage. Deregulation of Y-RNAs is also associated with pleiotropism. Overexpression of these elements might indicate increased cancer risk.

Targeting MCL-1 triggers DNA damage and an anti-proliferative response independent from apoptosis induction

MCL-1 is a high-priority target due to its dominant role in the pathogenesis and chemoresistance of cancer, yet clinical trials of MCL-1 inhibitors are revealing toxic side effects. MCL-1 biology is complex, extending beyond apoptotic regulation and confounded by its multiple isoforms, its domains of unresolved structure and function, and challenges in distinguishing noncanonical activities from the apoptotic response. We find that, in the presence or absence of an intact mitochondrial apoptotic pathway, genetic deletion or pharmacologic targeting of MCL-1 induces DNA damage and retards cell proliferation. Indeed, the cancer cell susceptibility profile of MCL-1 inhibitors better matches that of anti-proliferative than pro-apoptotic drugs, expanding their potential therapeutic applications, including synergistic combinations, but heightening therapeutic window concerns. Proteomic profiling provides a resource for mechanistic dissection and reveals the minichromosome maintenance DNA helicase as an interacting nuclear protein complex that links MCL-1 to the regulation of DNA integrity and cell-cycle progression.

Dynamics of the DYNLL1-MRE11 complex regulate DNA end resection and recruitment of Shieldin to DSBs

The extent and efficacy of DNA end resection at DNA double-strand breaks (DSB) determine the repair pathway choice. Here we describe how the 53BP1-associated protein DYNLL1 works in tandem with the Shieldin complex to protect DNA ends. DYNLL1 is recruited to DSBs by 53BP1, where it limits end resection by binding and disrupting the MRE11 dimer. The Shieldin complex is recruited to a fraction of 53BP1-positive DSBs hours after DYNLL1, predominantly in G1 cells. Shieldin localization to DSBs depends on MRE11 activity and is regulated by the interaction of DYNLL1 with MRE11. BRCA1-deficient cells rendered resistant to PARP inhibitors by the loss of Shieldin proteins can be resensitized by the constitutive association of DYNLL1 with MRE11. These results define the temporal and functional dynamics of the 53BP1-centric DNA end resection factors in cells.

An autoinhibited state of 53BP1 revealed by small molecule antagonists and protein engineering

The recruitment of 53BP1 to chromatin, mediated by its recognition of histone H4 dimethylated at lysine 20 (H4K20me2), is important for DNA double-strand break repair. Using a series of small molecule antagonists, we demonstrate a conformational equilibrium between an open and a pre-existing lowly populated closed state of 53BP1 in which the H4K20me2 binding surface is buried at the interface between two interacting 53BP1 molecules. In cells, these antagonists inhibit the chromatin recruitment of wild type 53BP1, but do not affect 53BP1 variants unable to access the closed conformation despite preservation of the H4K20me2 binding site. Thus, this inhibition operates by shifting the conformational equilibrium toward the closed state. Our work therefore identifies an auto-associated form of 53BP1-autoinhibited for chromatin binding-that can be stabilized by small molecule ligands encapsulated between two 53BP1 protomers. Such ligands are valuable research tools to study the function of 53BP1 and have the potential to facilitate the development of new drugs for cancer therapy.

Serum miRNA-based signature indicates radiation exposure and dose in humans: A multicenter diagnostic biomarker study

PURPOSE

Mouse and non-human primate models showed that serum miRNAs may be used to predict the biological impact of radiation doses. We hypothesized that these results can be translated to humans treated with total body irradiation (TBI), and that miRNAs may be used as clinically feasible biodosimeters.

METHODS

To test this hypothesis, serial serum samples were obtained from 25 patients (pediatric and adults) who underwent allogeneic stem-cell transplantation and profiled for miRNA expression using next-generation sequencing. miRNAs with diagnostic potential were quantified with qPCR and used to build logistic regression models with lasso penalty to reduce overfitting, identifying samples drawn from patients who underwent total body irradiation to a potentially lethal dose.

RESULTS

Differential expression results were consistent with previous studies in mice and non-human primates. miRNAs with detectable expression in this and two prior animal sets allowed for distinction of the irradiated from non-irradiated samples in mice, macaques and humans, validating the miRNAs as radiation-responsive through evolutionarily conserved transcriptional regulation mechanisms. Finally, we created a model based on the expression of miR-150-5p, miR-30b-5p and miR-320c normalized to two references and adjusted for patient age with an AUC of 0.9 (95%CI:0.83-0.97) for identifying samples drawn after irradiation; a separate model differentiating between high and low radiation dose achieved AUC of 0.85 (95%CI: 0.74-0.96).

CONCLUSIONS

We conclude that serum miRNAs reflect radiation exposure and dose for humans undergoing TBI and may be used as functional biodosimeters for precise identification of people exposed to clinically significant radiation doses.

An autoinhibited state of 53BP1 revealed by small molecule antagonists and protein engineering

The recruitment of 53BP1 to chromatin, mediated by its recognition of histone H4 dimethylated at lysine 20 (H4K20me2), is important for DNA double-strand break repair. Using a series of small molecule antagonists, we demonstrate a conformational equilibrium between an open and a pre-existing lowly populated closed state of 53BP1 in which the H4K20me2 binding surface is buried at the interface between two interacting 53BP1 molecules. In cells, these antagonists inhibit the chromatin recruitment of wild type 53BP1, but do not affect 53BP1 variants unable to access the closed conformation despite preservation of the H4K20me2 binding site. Thus, this inhibition operates by shifting the conformational equilibrium toward the closed state. Our work therefore identifies an auto-associated form of 53BP1 - autoinhibited for chromatin binding - that can be stabilized by small molecule ligands encapsulated between two 53BP1 protomers. Such ligands are valuable research tools to study the function of 53BP1 and have the potential to facilitate the development of new drugs for cancer therapy.

Identification of BRCA1/2 mutation female carriers using circulating microRNA profiles

Identifying germline BRCA1/2 mutation carriers is vital for reducing their risk of breast and ovarian cancer. To derive a serum miRNA-based diagnostic test we used samples from 653 healthy women from six international cohorts, including 350 (53.6%) with BRCA1/2 mutations and 303 (46.4%) BRCA1/2 wild-type. All individuals were cancer-free before and at least 12 months after sampling. RNA-sequencing followed by differential expression analysis identified 19 miRNAs significantly associated with BRCA mutations, 10 of which were ultimately used for classification: hsa-miR-20b-5p, hsa-miR-19b-3p, hsa-let-7b-5p, hsa-miR-320b, hsa-miR-139-3p, hsa-miR-30d-5p, hsa-miR-17-5p, hsa-miR-182-5p, hsa-miR-421, hsa-miR-375-3p. The final logistic regression model achieved area under the receiver operating characteristic curve 0.89 (95% CI: 0.87-0.93), 93.88% sensitivity and 80.72% specificity in an independent validation cohort. Mutated gene, menopausal status or having preemptive oophorectomy did not affect classification performance. Circulating microRNAs may be used to identify BRCA1/2 mutations in patients of high risk of cancer, offering an opportunity to reduce screening costs.

Dynamics of the DYNLL1/MRE11 complex regulates DNA end resection and recruitment of the Shieldin complex to DSBs

Extent and efficacy of DNA end resection at DNA double strand break (DSB)s determines the choice of repair pathway. Here we describe how the 53BP1 associated protein DYNLL1 works in tandem with Shieldin and the CST complex to protect DNA ends. DYNLL1 is recruited to DSBs by 53BP1 where it limits end resection by binding and disrupting the MRE11 dimer. The Shieldin complex is recruited to a fraction of 53BP1-positive DSBs hours after DYNLL1 predominantly in the G1 cells. Shieldin localization to DSBs is dependent on MRE11 activity and is regulated by the interaction of DYNLL1 with MRE11. BRCA1-deficient cells rendered resistant to PARP inhibitors by the loss of Shieldin proteins can be re-sensitized by the constitutive association of DYNLL1 with MRE11. These results define the temporal and functional dynamics of the 53BP1-centric DNA end resection factors in cells.

Abstract P017: Early detection of ovarian cancer in high-risk individuals using circulating miRNAs: The MiDe study

Background: Epithelial ovarian cancers generally carry a poor prognosis due to late-stage presentation and a high rate of disease recurrence. In contrast, diagnosis of early-stage disease is associated with a high rate of durable remission. Prior studies using archival samples have suggested that a neural network analysis of circulating miRNA expression levels may be an informative biomarker for early-stage ovarian cancer diagnosis. Methods: The miRNA Detection Study (MiDe Study) is a prospective, observational clinical trial open to individuals in all 50 U.S. states. Persons with at least one ovary classified as being at high-risk for ovarian cancer, either due to known genetic predisposition or family history suggestive of possible hereditary breast and ovarian cancer syndrome or Lynch syndrome, are eligible to enroll. Study subjects will submit a blood sample every 6 months for up to 5 years. Neural network analysis of serum miRNA profiles will be correlated with the subsequent diagnosis of ovarian cancer or serous tubal intraepithelial carcinoma, either clinically or at the time of risk-reducing salpingectomy or salpingo-oophorectomy. The primary outcomes are the sensitivity and specificity of the neural network for anticipating a diagnosis of epithelial ovarian cancer or a cancer precursor within 2 years of the index blood sample. The goal recruitment is 1000 study subjects. Based on a presumed cancer incidence of 0.5-1% per year among this population, approximately 25 incident cancers or precursors are expected to be diagnosed over the timespan of the study. Results: Enrollment began in September 2019. As of August 1, 2022, 372 subjects had consented to the study. Among study subjects, 270/372 (72.5%) carry a known mutation in BRCA1/2, 63/372 (16.9%) carry a known mutation in a different high-risk gene (e.g., PALB2, BRIP1), and 39/372 (10.5%) are considered high-risk due to a mutation in a gene potentially related to ovarian cancer (e.g., ATM, CHEK2) or based on family history alone. To date, 215 (57.8%) participants have contributed at least one sample, among whom 90/215 (41.9%) of subjects have contributed multiple blood samples. Among the study subjects who have given a sample, 2/215 (0.9%) have been later diagnosed with ovarian cancer. Conclusions: The MiDe Study seeks to establish the feasibility of a circulating miRNA-based test for early diagnosis of epithelial ovarian cancer among high-risk individuals. The results of this study will clarify the performance of the neural network test among a high-risk population and inform subsequent interventional trials.

Citation Format: Kevin M. Elias, Dipanjan Chowdhury, Judy Garber, Ryan C. Buehler. Early detection of ovarian cancer in high-risk individuals using circulating miRNAs: The MiDe study. [abstract]. In: Proceedings of the AACR Special Conference: Precision Prevention, Early Detection, and Interception of Cancer; 2022 Nov 17-19; Austin, TX. Philadelphia (PA): AACR; Can Prev Res 2023;16(1 Suppl): Abstract nr P017.

Targeting replication stress in cancer therapy

Replication stress is a major cause of genomic instability and a crucial vulnerability of cancer cells. This vulnerability can be therapeutically targeted by inhibiting kinases that coordinate the DNA damage response with cell cycle control, including ATR, CHK1, WEE1 and MYT1 checkpoint kinases. In addition, inhibiting the DNA damage response releases DNA fragments into the cytoplasm, eliciting an innate immune response. Therefore, several ATR, CHK1, WEE1 and MYT1 inhibitors are undergoing clinical evaluation as monotherapies or in combination with chemotherapy, poly[ADP-ribose]polymerase (PARP) inhibitors, or immune checkpoint inhibitors to capitalize on high replication stress, overcome therapeutic resistance and promote effective antitumour immunity. Here, we review current and emerging approaches for targeting replication stress in cancer, from preclinical and biomarker development to clinical trial evaluation.

A druggable addiction to de novo pyrimidine biosynthesis in diffuse midline glioma

Diffuse midline glioma (DMG) is a uniformly fatal pediatric cancer driven by oncohistones that do not readily lend themselves to drug development. To identify druggable targets for DMG, we conducted a genome-wide CRISPR screen that reveals a DMG selective dependency on the de novo pathway for pyrimidine biosynthesis. This metabolic vulnerability reflects an elevated rate of uridine/uracil degradation that depletes DMG cells of substrates for the alternate salvage pyrimidine biosynthesis pathway. A clinical stage inhibitor of DHODH (rate-limiting enzyme in the de novo pathway) diminishes uridine-5'-phosphate (UMP) pools, generates DNA damage, and induces apoptosis through suppression of replication forks-an "on-target" effect, as shown by uridine rescue. Matrix-assisted laser desorption/ionization (MALDI) mass spectroscopy imaging demonstrates that this DHODH inhibitor (BAY2402234) accumulates in the brain at therapeutically relevant concentrations, suppresses de novo pyrimidine biosynthesis in vivo, and prolongs survival of mice bearing intracranial DMG xenografts, highlighting BAY2402234 as a promising therapy against DMGs.

TOPBPing up DSBs with PARylation

Zhao et al. (2022) demonstrate that HIV Tat-specific factor 1, an RPA PARylation reader, recruits Topoisomerase IIβ-binding protein 1 to double-strand break sites specifically in the S phase of the cell cycle to promote homologous recombination.

Abstract 3065: Establishment and characterization of a platform of endometrial cancer organoids

Background: Endometrial cancer is the most commonly diagnosed gynecologic cancer in the US; the incidence is rising, and survival rates for this cancer are decreasing. There is a paucity of effective treatment for recurrent endometrial cancer, especially high grade endometrial cancers (HGEC) which include serous, carcinosarcoma, endometrioid, and clear cell histologies. Models that mimic the clinical and molecular characteristics of HGEC are lacking. To support the development of next generation therapeutics for endometrial cancer, we report on the establishment of 3D endometrial patient-derived organoids (PDOs) from HGEC.

Methods: 26 Tumors from 21 different patients with HGEC (Serous, Carcinosarcoma, Clear Cell and High-grade Endometrioid subtypes) who underwent surgical resection (n= 13), biopsy (n = 7), paracentesis (n = 3) or thoracentesis (n = 3) were passaged as 3D organoid cultures in Matrigel in an optimized media. Robust models (defined by average days to passage <14 days) were viably banked. 3 frozen models were also thawed and re-cultured to assess the viability post freezing. PDOs were collected for H&E staining and their histology was compared to the original diagnosis. DNA replication rate and the effect of replication stress on organoid growth were assessed by the DNA Fiber Assay and immunofluorescence (IF). Finally, an established clear cell endometrial cancer organoid model was engrafted in mice to generate a Patient-Derived Xenograft (PDX) model.

Results: Endometrial PDOs were successfully developed from 19 of 26 original samples for an overall success rate of 73.1%. Successful PDOs were developed from multiple histologies, including 8 carcinosarcoma, 6 uterine serous, 2 endometrioid, 2 clear cell and 1 mixed uterine serous and endometrioid. Though biopsy samples had initially fewer viable cells, our overall success rate was similar at 85.7% compared to 84.6% for surgical resections and higher than 66.7% for paracenteses. Samples obtained via thoracentesis did not form PDOs. Endometrial PDOs were histologically validated to match the primary patient tumor. Freeze thawing had no effect on morphology and growth characteristics. DNA fiber assays could be successfully conducted in PDOs, with a reduction in replication rate observed in PDO models treated with ATR or WEE1 inhibitors, with concurrent increase in y-H2AX and decrease in pRPA2 observed by IF. We also successfully generated a validated PDX model from organoids. Studies to determine molecular fidelity between the original patient tumor and established organoids are ongoing.

Conclusions: We describe the successful establishment of 19 endometrial PDO models which retain original tumor morphology and demonstrate sensitivity to drug-induced DNA damage. 3D endometrial organoids can therefore be used for further target discovery and validation as well as biomarker studies to advance targeted therapies for high-grade endometrial cancer.

Citation Format: Aisha L. Saldanha, Ha V. Vo, Kevin Vasquez, Kenneth Ngo, Shrabasti Roychoudhury, Carina Feeney, Courtney H. Qi, Swati Narayan, Jennifer D. Curtis, Prafulla C. Gokhale, Dipanjan Chowdhury, Cloud P. Paweletz, Marisa R. Nucci, Ursula A. Matulonis, Elena Ivanova, Joyce F. Liu. Establishment and characterization of a platform of endometrial cancer organoids [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 3065.

A Translational Model to Improve Early Detection of Epithelial Ovarian Cancers

Neural network analyses of circulating miRNAs have shown potential as non-invasive screening tests for ovarian cancer. A clinically useful test would detect occult disease when complete cytoreduction is most feasible. Here we used murine xenografts to sensitize a neural network model to detect low volume disease and applied the model to sera from 75 early-stage ovarian cancer cases age-matched to 200 benign adnexal masses or healthy controls. The 14-miRNA model efficiently discriminated tumor bearing animals from controls with 100% sensitivity down to tumor inoculums of 50,000 cells. Among early-stage patient samples, the model performed well with 73% sensitivity at 91% specificity. Applied to a population with 1% disease prevalence, we hypothesize the model would detect most early-stage ovarian cancers while maintaining a negative predictive value of 99.97% (95% CI 99.95%-99.98%). Overall, this supports the concept that miRNAs may be useful as screening markers for early-stage disease.

Combined PARP and HSP90 inhibition: preclinical and Phase 1 evaluation in patients with advanced solid tumours

PURPOSE

PARP inhibitor resistance may be overcome by combinatorial strategies with agents that disrupt homologous recombination repair (HRR). Multiple HRR pathway components are HSP90 clients, so that HSP90 inhibition leads to abrogation of HRR and sensitisation to PARP inhibition. We performed in vivo preclinical studies of the HSP90 inhibitor onalespib with olaparib and conducted a Phase 1 combination study.

PATIENTS AND METHODS

Tolerability and efficacy studies were performed in patient-derived xenograft(PDX) models of ovarian cancer. Clinical safety, tolerability, steady-state pharmacokinetics and preliminary efficacy of olaparib and onalespib were evaluated using a standard 3 + 3 dose-escalation design.

RESULTS

Olaparib/onalespib exhibited anti-tumour activity against BRCA1-mutated PDX models with acquired PARPi resistance and PDX models with RB-pathway alterations(CDKN2A loss and CCNE1 overexpression). Phase 1 evaluation revealed that dose levels up to olaparib 300 mg/onalespib 40 mg and olaparib 200 mg/onalespib 80 mg were safe without dose-limiting toxicities. Coadministration of olaparib and onalespib did not appear to affect the steady-state pharmacokinetics of either agent. There were no objective responses, but disease stabilisation ≥24 weeks was observed in 7/22 (32%) evaluable patients including patients with BRCA-mutated ovarian cancers and acquired PARPi resistance and patients with tumours harbouring RB-pathway alterations.

CONCLUSIONS

Combining onalespib and olaparib was feasible and demonstrated preliminary evidence of anti-tumour activity.

P–761 Can modified luteal support in fresh cycle after agonist trigger “rescue” the cumulative live birth rate (CLBR) in high responders

Study question

Can modified luteal support in fresh cycle “rescue” the cumulative live birth rate (CLBR) in high responders who receive agonist trigger?

Summary answer

Live birth rate in high responders who had agonist trigger in fresh cycle was significantly reduced despite modified luteal support.

What is known already

Previous studies, including small randomised controlled trials, claimed that good live birth rate could be achieved at fresh transfer in “high responders” who had GnRHa trigger with modified luteal phase support. However, majority of these studies exclude the true high responders (patients with 20 and above oocytes) and average number of collected eggs reported in many of these studies in the range of 9 to 12. The data on outcome of fresh transfer in true high responders is very limited.

Study design, size, duration

A prospective observational study was conducted in 407 patients, aged 23–42 years who were expected to be at risk of high response (AFC>18, AMH>20 pmol/l) undergoing controlled ovarian stimulation between 2014–2019 triggered either with HCG or GnRH agonist. Live birth rate (LBR) in a fresh and subsequent 3 frozen transfers were compared in groups with different triggers and freeze all.

Participants/materials, setting, methods

Patients were stimulated in short antagonist protocol. The trigger was chosen based on the background characteristics, peak oestradiol and clinician discretion. Triggering was achieved either with 0.5 mg buserelin (GnRHa) 0.5mgin 230 patients (A) or with 250 mcg of hCG(H) in 177 patients. Modified luteal support included vaginal progesterone, oral oestrogen and 1500 iu of hCG on the day of egg retrieval. The later was omitted with more than 20 oocytes.

Main results and the role of chance

The mean age, AFC, number of previous cycles, number of embryos transferred were 33.3, 22.4, 0.26 and 1.2 respectively and did not have significant difference between different triggers. Whereas AMH (53 pmol/l (A) vs 43.1 pmol/l (H), P = 0.003), peak oestradiol (15140.74 (A) vs 9738.59 (H), P = 5.59X10–14), and number of oocytes collected (21 vs.17, P = 5.63X10–7) were significantly higher in GnRHa group. Seventeen patients in buserelin group had elective freeze all. Ovarian Hyperstimulation Syndrome (OHSS) rate was 3.9% in buserelin group (more then half of these cases had a bolus of hCG at egg collection; most were mild/moderate). On the other hand, hCG group had 2.5% of OHSS (all severe). Live birth rate in fresh cycle was 31% in hCG and 21% in GnRHa groups. If freeze all was undertaken in fresh cycle after GnRHa trigger, then LBR in the first frozen cycle of this group was 53% (P = 0.003, fresh vs frozen GnRHa group). CLBR was not different between GnRHa and hCG groups (51%). However, this was significantly lower than CLBR in GnRHa trigger freeze all group 76% (P = 0.03)

Limitations, reasons for caution

The limitation of this study is its non-randomised nature. However, since it is one of the biggest studies for high responders it has a power to minimise bias by adjusting for multiple variables.

Wider implications of the findings: Proceeding with fresh transfer in high responders after GnRHa trigger with modified luteal support not only maintains the risk of OHSS (equivalent to hCG group) but also significantly impairs the LBR not compensated even after 3 subsequent frozen embryo transfers. Therefore, freeze-all approach should be preferred in this group.

Trial registration number

NA

HGG-38. DE NOVO PYRIMIDINE SYNTHESIS INHIBITION INDUCES REPLICATION CATASTROPHE MEDIATED CELL DEATH IN DIFFUSE MIDLINE GLIOMA

Diffuse midline gliomas (DMG) are aggressive and lethal pediatric brain tumors that cannot be cured by conventional therapeutic modalities. Using a genome wide CRISPR screen we identified the de novo pyrimidine biosynthesis pathway as a metaboilic vulnerability in DMGs. BAY2402234 is a small molecule inhibitor of DHODH -a rate liminting enzyme in the de novo pyrimidine biosynthesis pathway. BAY2402234 induces cell death in DMG cells at low nanomolar concentrations while sparing adult glioblastoma cells and normal astrocytes. Further investigations revealed drammatic reduction in cellular UMP pools, the precursor for all pyrimidine nucleotides, after DHODH inhibition, specifically in DMG cells. Cytotoxicity of DHODH inhibition in DMG cells is rescued by exogenous uridine, supporting UMP depletion as the mechanism underlying DMG cell death and also showing that cell death is an “on target” response to BAY2402234. Cell death induced by BAY2402234 is a consequence of replication fork stalling as evident by accumulation of chromatin-bound RPA foci and g-H2AX. Stalled replication forks eventually collapse, resulting in replication catastrophy and apoptosis. Cytotoxic effects of DHODH inhibition are further exacerbated by inhibition of the intra-S checkpoint protein, ATR. Combined treatment of DMG cells with DHODH and ATR inhibitors resulted in enhanced accumulation of chromatin-bound RPA, g-H2AX, replication fork collapse and apoptosis. Importantly, in vivo studies verify that both BAY2402234 (DHODHi), and BAY1895344 (ATRi), cross the blood-brain barrier, accumulate in the brain at therapeutically relevant concentrations, and induce DNA damage in intracranial DMG xenografts in mice. Taken together, our studies have identified DHODH inhibition as a DMG-specific vulnerability resulting in cell death; the mechanism of DHODHi-induced cell death led us to identify combined inhibition of DHODH and ATR as a synergistic therapy against DMG tumors.

TIRR inhibits the 53BP1-p53 complex to alter cell-fate programs

53BP1 influences genome stability via two independent mechanisms: (1) regulating DNA double-strand break (DSB) repair and (2) enhancing p53 activity. We discovered a protein, Tudor-interacting repair regulator (TIRR), that associates with the 53BP1 Tudor domain and prevents its recruitment to DSBs. Here, we elucidate how TIRR affects 53BP1 function beyond its recruitment to DSBs and biochemically links the two distinct roles of 53BP1. Loss of TIRR causes an aberrant increase in the gene transactivation function of p53, affecting several p53-mediated cell-fate programs. TIRR inhibits the complex formation between the Tudor domain of 53BP1 and a dimethylated form of p53 (K382me2) that is poised for transcriptional activation of its target genes. TIRR mRNA expression levels negatively correlate with the expression of key p53 target genes in breast and prostate cancers. Further, TIRR loss is selectively not tolerated in p53-proficient tumors. Therefore, we establish that TIRR is an important inhibitor of the 53BP1-p53 complex.

DDRE-32. THERAPEUTIC TARGETING OF A NOVEL METABOLIC ADDICTION IN DIFFUSE MIDLINE GLIOMA

Diffuse midline glioma (DMG) is a uniformly fatal pediatric cancer that is in need of urgent “outside the box” therapeutic approaches. Recent studies show that tumor cells adapt to stresses created by oncogenic mutations and these oncogene-induced adaptations create vulnerabilities that can be exploited to therapeutic ends. To uncover these oncogene-induced vulnerabilities in DMGs we conducted a genome-wide CRIPSR knockout screen in three DMG lines. The top common DMG dependency pathway that we discovered is de novo pyrimidine biosynthesis. Under normal conditions pyrimidine nucleotide needs are met through the salvage pathway. However, in DMG tumorigenesis, pyrimidine nucleotide synthesis is rewired such that the cells become dependent on the de novo biosynthesis pathway. De novo pyrimidine synthesis is catalyzed by CAD, DHODH and UMPS; all three genes are identified as dependencies in our screen and have been validated using shRNA mediated gene knockdown. Interestingly, DMG cells did not exhibit a dependency on the de novo purine biosynthesis pathway. Using a small molecule inhibitor of DHODH, BAY2402234 [currently studied in phase I trial for myeloid malignancies (NCT03404726)], we have demonstrated and validated, (i) efficacy and specificity of de novo pyrimidine synthesis inhibition in vitro in DMG cells; (ii) de novo pyrimidine addiction is not attributable to cell proliferation; (iii) DHODH inhibition induces apoptosis by hindering replication and inciting DNA damage; (iv) DHODH and ATR inhibition act synergistically to induce DMG cell death; and (v) critical in vivo efficacy. The in vivo experiment documents that BAY2402234 crosses the blood-brain barrier, is present in the brain at therapeutically relevant concentrations, suppresses de novo pyrimidine biosynthesis in intracranial DMG tumors in mice, and prolongs survival of orthotopic DMG tumor bearing mice. Taken together, our studies have identified a novel metabolic vulnerability that can be translated for the treatment of DMG patients.

Tumor protein expression of the DNA repair gene BRCA1 and lethal prostate cancer

DNA repair genes are commonly altered in metastatic prostate cancer, but BRCA1 mutations are rare. Preliminary studies suggest that higher tumor expression of the BRCA1 protein may be associated with worse prognosis. We undertook a prospective study among men with prostate cancer in the Health Professionals Follow-up Study and evaluated BRCA1 via immunohistochemical staining on tissue microarrays. BRCA1 was expressed in 60 of 589 tumors. Prevalence of BRCA1 positivity was 43% in the 14 men with metastases at diagnosis compared with 9% in non-metastatic tumors [difference, 33 percentage points; 95% confidence interval (CI), 7-59]. BRCA1-positive tumors had 2.16-fold higher Ki-67 proliferative indices (95% CI, 1.18-3.95), higher tumor aneuploidy as predicted from whole-transcriptome profiling, and higher Gleason scores. Among the 575 patients with non-metastatic disease at diagnosis, we evaluated the association between BRCA1 expression and development of lethal disease (metastasis or cancer-specific death, 69 events) during long-term follow-up (median, 18.3 years). A potential weak association of BRCA1 positivity with lethal disease (hazard ratio, 1.61; 95% CI, 0.82-3.15) was attenuated when adjusting for age, Gleason score and clinical stage (hazard ratio, 1.11; 95% CI, 0.54-2.29). In summary, BRCA1 protein expression is a feature of more proliferative and more aneuploid prostate tumors and is more common in metastatic disease. While not well suited as a prognostic biomarker in primary prostate cancer, BRCA1 protein expression may be most relevant in advanced disease.

Silver Trauma- a true challenging entity

Historically trauma has been identified as the leading cause of death in the younger under 40’s population (1). However, with an aging population there is a higher incidence of trauma sustained in the elderly population. Silver trauma is defined as elderly patient of retirement age or over the age of 65 years. This has been taken into consideration when trauma guidelines have been incorporated. To name a few examples, the CCSR (Canadian C-spine rule) includes the at-risk population as those >/= 65 years of age in the context of potential cervical spine injury. In various major trauma trial tools, the >65 years of age group are considered to be a high risk of deteoriation group. Through clinical practice clinicians have noted that in this group of patients’ injuries can be missed which would be detrimental to the overall outcome of these patients. Through this article I aim to highlight the main issues that make the initial management of the elderly trauma patient at times challenging. Furthermore, suggestion for potential management strategies will also be highlighted.

CHK1 Inhibitor Blocks Phosphorylation of FAM122A and Promotes Replication Stress

While effective anti-cancer drugs targeting the CHK1 kinase are advancing in the clinic, drug resistance is rapidly emerging. Here, we demonstrate that CRISPR-mediated knockout of the little-known gene FAM122A/PABIR1 confers cellular resistance to CHK1 inhibitors (CHK1is) and cross-resistance to ATR inhibitors. Knockout of FAM122A results in activation of PP2A-B55α, a phosphatase that dephosphorylates the WEE1 protein and rescues WEE1 from ubiquitin-mediated degradation. The resulting increase in WEE1 protein expression reduces replication stress, activates the G2/M checkpoint, and confers cellular resistance to CHK1is. Interestingly, in tumor cells with oncogene-driven replication stress, CHK1 can directly phosphorylate FAM122A, leading to activation of the PP2A-B55α phosphatase and increased WEE1 expression. A combination of a CHK1i plus a WEE1 inhibitor can overcome CHK1i resistance of these tumor cells, thereby enhancing anti-cancer activity. The FAM122A expression level in a tumor cell can serve as a useful biomarker for predicting CHK1i sensitivity or resistance.

Abstract IA03: PARP inhibitor and platinum resistance in ovarian cancer-genome wide CRISPR screens

High-grade serous ovarian carcinoma (HGSOC) patients with germline mutations in BRCA1/2 exhibit high sensitivity and improved outcome to platinum-based drugs and PARP inhibitors. Three PARP inhibitors (olaparib, rucaparib, niraparib) have recently gained FDA approval for the treatment of HGSOCs. However, de novo and acquired resistance to these agents is common even in the BRCA mutation carriers and pose a significant, unsolved clinical challenge. Here we identify multiple gene complexes involved in PARPi resistance through a loss-of-function CRISPR screen. High-confidence hits include previously identified 53BP1, PARP1, shieldin complex, and ATMIN/DYNLL1 complex. Only for DYNLL1 does low expression correlate with worse outcome in BRCA1-mutant ovarian cancer patients; incidentally, all these patients had platinum-based therapy. In BRCA1-defective HGSOC patients, DNA end resection is greatly compromised and contributes to the loss of HR and PARP inhibitor sensitivity. DNA end resection is a vital process that initiates homologous recombination (HR)-mediated repair of double-stranded DNA breaks and consequently influences genome stability. Loss of DYNLL1 allows DNA end resection and restores HR in BRCA1-mutant cells, thereby inducing resistance to platinum drugs and PARP inhibitors. In primary ovarian carcinomas low BRCA1 expression correlates with increased chromosomal aberrations, and the junction sequences of somatic structural variants indicate the loss of HR. Concurrent decrease in DYNLL1 expression in BRCA1-low ovarian cancers “rescued” this phenotype with reduced genomic alterations and increased homology at putative lesions. From the mechanistic standpoint, we observed that DYNLL1 limits nucleolytic degradation of DNA ends by interacting with the DNA end resection machinery (MRN complex, BLM helicase, and DNA2) in cells. The impact of DYNLL1 on end resection can be recapitulated in vitro; this is dependent on direct interaction with MRE11. Furthermore, DYNLL1 mutants that do not interact with MRE11 phenocopy the PARPi resistance phenotype of DYNLL1/BRCA1-deficient cells. Therefore, we infer that DYNLL1 is an important antiresection factor that significantly influences genomic stability and response to DNA-damaging chemotherapy in ovarian cancer patients.

Citation Format: Dipanjan Chowdhury. PARP inhibitor and platinum resistance in ovarian cancer-genome wide CRISPR screens [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr IA03.

Berzosertib plus gemcitabine versus gemcitabine alone in platinum-resistant high-grade serous ovarian cancer: a multicentre, open-label, randomised, phase 2 trial

BACKGROUND

High-grade serous ovarian cancers show increased replication stress, rendering cells vulnerable to ATR inhibition because of near universal loss of the G1/S checkpoint (through deleterious TP53 mutations), premature S phase entry (due to CCNE1 amplification, RB1 loss, or CDKN2A mRNA downregulation), alterations of homologous recombination repair genes, and expression of oncogenic drivers (through MYC amplification and other mechanisms). We hypothesised that the combination of the selective ATR inhibitor, berzosertib, and gemcitabine could show acceptable toxicity and superior efficacy to gemcitabine alone in high-grade serous ovarian cancer.

METHODS

In this multicentre, open-label, randomised, phase 2 study, 11 different centres in the US Experimental Therapeutics Clinical Trials Network enrolled women (aged ≥18 years) with recurrent, platinum-resistant high-grade serous ovarian cancer (determined histologically) and Eastern Cooperative Oncology Group performance status of 0 or 1, who had unlimited previous lines of cytotoxic therapy in the platinum-sensitive setting but no more than one line of cytotoxic therapy in the platinum-resistant setting. Eligible patients were randomly assigned (1:1) to receive intravenous gemcitabine (1000 mg/m²) on day 1 and day 8, or gemcitabine plus intravenous berzosertib (210 mg/m²) on day 2 and day 9 of a 21-day cycle until disease progression or intolerable toxicity. Randomisation was done centrally using the Theradex Interactive Web Response System, stratified by platinum-free interval, and with a permuted block size of six. Following central randomisation, patients and investigators were not masked to treatment assignment. The primary endpoint was investigator-assessed progression-free survival, and analyses included all patients who received at least one dose of the study drugs. The study is registered with ClinicalTrials.gov, NCT02595892, and is active but closed to enrolment.

FINDINGS

Between Feb 14, 2017, and Sept 7, 2018, 88 patients were assessed for eligibility, of whom 70 were randomly assigned to treatment with gemcitabine alone (36 patients) or gemcitabine plus berzosertib (34 patients). At the data cutoff date (Feb 21, 2020), the median follow-up was 53·2 weeks (25·6-81·8) in the gemcitabine plus berzosertib group and 43·0 weeks (IQR 23·2-69·1) in the gemcitabine alone group. Median progression-free survival was 22·9 weeks (17·9-72·0) for gemcitabine plus berzosertib and 14·7 weeks (90% CI 9·7-36·7) for gemcitabine alone (hazard ratio 0·57, 90% CI 0·33-0·98; one-sided log-rank test p=0·044). The most common treatment-related grade 3 or 4 adverse events were decreased neutrophil count (14 [39%] of 36 patients in the gemcitabine alone group vs 16 [47%] of 34 patients in the gemcitabine plus berzosertib group) and decreased platelet count (two [6%] vs eight [24%]). Serious adverse events were observed in ten (28%) patients in the gemcitabine alone group and nine (26%) patients in the gemcitabine plus berzosertib group. There was one treatment-related death in the gemcitabine alone group due to sepsis and one treatment-related death in the gemcitabine plus berzosertib group due to pneumonitis.

INTERPRETATION

To our knowledge, this is the first randomised study of an ATR inhibitor in any tumour type. This study shows a benefit of adding berzosertib to gemcitabine in platinum-resistant high-grade serous ovarian cancer. This combination warrants further investigation in this setting.

FUNDING

US National Cancer Institute.

The most important attribute: stakeholder perspectives on what matters most in a physician

Background

Most people can think of important attributes that they believe physicians should have. The canmeds framework defines domains of attributes in medical training (Leader, Medical Expert, Scholar, Communicator, Advocate, Collaborator, and Professional). Whether some are more valued by various stakeholders is unknown. Previous research has shown that patients can receive suboptimal care if physician and patient expectations of a health care encounter differ. In the present study, we sought to identify what various stakeholders identified as the single most important attribute for a physician to possess.

Methods

A simple survey asked the question "What is the single most important attribute a physician should have?" at a single academic teaching hospital and affiliated medical school. The survey was administered to medical students, doctors, nurses, patients, and caregivers. Age and sex were also collected. Responses were assigned to domains and analyzed to identify trends. The primary outcome is a descriptive analysis of the findings.

Results

From 362 individuals who responded, 109 different responses were obtained. The single most common answer was "compassion" (n = 86). Responses were categorized into these 5 domains: Caring, n = 209; Professional or Collaborator, n = 58; Medical Expert, n = 54; Communicator, n = 32; and Other, n = 9. Compared with men, women chose attributes in the Caring domain more frequently (64% vs. 49%), although that domain was the most popular for both sexes. Medical students were less likely to highly value Communicator attributes.

Conclusions

All stakeholder group identified attributes in the Caring domain as being most important. Although all canmeds roles are important, our research highlights the priorities of stakeholders.

Author Correction: Immunogenomic profiling determines responses to combined PARP and PD-1 inhibition in ovarian cancer

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Immunogenomic profiling determines responses to combined PARP and PD-1 inhibition in ovarian cancer

Combined PARP and immune checkpoint inhibition has yielded encouraging results in ovarian cancer, but predictive biomarkers are lacking. We performed immunogenomic profiling and highly multiplexed single-cell imaging on tumor samples from patients enrolled in a Phase I/II trial of niraparib and pembrolizumab in ovarian cancer (NCT02657889). We identify two determinants of response; mutational signature 3 reflecting defective homologous recombination DNA repair, and positive immune score as a surrogate of interferon-primed exhausted CD8 + T-cells in the tumor microenvironment. Presence of one or both features associates with an improved outcome while concurrent absence yields no responses. Single-cell spatial analysis reveals prominent interactions of exhausted CD8 + T-cells and PD-L1 + macrophages and PD-L1 + tumor cells as mechanistic determinants of response. Furthermore, spatial analysis of two extreme responders shows differential clustering of exhausted CD8 + T-cells with PD-L1 + macrophages in the first, and exhausted CD8 + T-cells with cancer cells harboring genomic PD-L1 and PD-L2 amplification in the second.

Tumor protein expression of BRCA1 and development of lethal prostate cancer

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Background: DNA repair genes including BRCA1 are commonly altered in metastatic prostate tumors. However, mutations and copy number aberrations in these genes are rare in primary tumors. Instead, preliminary studies suggest that higher tumor expression of the BRCA1 protein may be associated with worse prognosis. Methods: We undertook a prospective study of tumor BRCA1 protein expression and lethal prostate cancer among men with clinically localized prostate cancer in the Health Professionals Follow-up Study. We performed immunohistochemical staining for BRCA1 on tumor tissue microarrays using a validated antibody and scored expression as positive or negative. We also assessed tumor proliferation by immunostaining for Ki67, angiogenesis by immunostaining for CD34, and apoptosis using a TUNEL assay. Proportional hazards regression was used to evaluate the association between BRCA1 protein expression and development of lethal prostate cancer (metastasis or cancer-specific death). Results: Ten percent of tumors (60 of 589) stained positive for the BRCA1 protein. BRCA1-positive tumors were characterized by higher Gleason scores, a higher proliferative index, and a higher apoptotic index. During a median follow-up of 14.3 years, 18 men (34%) in the BRCA1-positive group and 74 men (14%) in the BRCA1-negative group developed lethal prostate cancer. There was a strong positive association between BRCA1 protein expression and lethal prostate cancer in both unadjusted analyses (HR 2.71, 95% CI 1.73–4.26) and after adjusting for clinical factors (HR 2.00, 95% CI 1.26–3.18). The positive association with BRCA1 protein expression was also independent of proliferation index. Conclusions: Primary prostate tumors expressing the BRCA1 protein have a highly proliferative phenotype and are more likely to progress to lethal disease, independent of its higher proliferative index. Assessing tumor protein expression of BRCA1 may help elucidate the Janus-faced role of DNA repair pathways in prostate cancer progression.[Table: see text]

Circulating microRNAs as Biomarkers of Radiation Exposure: A Systematic Review and Meta-Analysis

PURPOSE

MicroRNAs (miRNAs) were hypothesized to be robust and easily measured biomarkers of radiation exposure, which has led to multiple studies in various clinical and experimental scenarios. We sought to identify evolutionary conserved, radiation-induced circulating miRNAs through a multispecies, integrative systematic review and meta-analysis of miRNAs in radiation.

METHODS AND MATERIALS

The systematic review was registered in the PROSPERO database (ID: 81701). We downloaded a list of studies with the query: (circulating OR plasma OR serum) AND (miRNA or microRNA) AND (radiat* OR radiotherapy OR irradiati*) from MEDLINE (103 studies), EMBASE (364 studies), and Cochrane Database of Systematic Reviews (0 studies). After deleting 116 duplicates, the remaining 351 abstracts were reviewed. Inclusion criteria were experimental study; human, mice, rat or nonhuman primate study; and serum or plasma miRNA expression measured before and after radiation exposure.

RESULTS

The screening procedure yielded 62 research studies. After verification, 30 articles contained data on miRNA expression change after irradiation. Thus, we obtained a database of 131 miRNAs from 96 pairwise post-/preirradiation comparisons reporting 2508 fold changes (FCs) of circulating miRNAs. The meta-analysis showed 28 miRNAs with significant radiation-induced change of their expression in the serum. In metaregression analysis, 7 miRNAs-miR-150 (FC = 0.40; 95% confidence interval [CI], 0.35-0.45), miR-29a (FC = 0.87; 95% CI, 0.79-0.96), miR-29b (FC = 0.85; 95% CI, 0.76-0.96), miR-30c (FC = 1.19; 95% CI, 1.09-1.30), miR-200b (FC = 1.34; 95% CI, 1.21-1.48), miR-320a (FC = 1.13; 95% CI, 1.05-1.23), and miR-30a (FC = 1.18; 95% CI, 1.07-1.30)-significantly correlated with either total or fraction dose of radiation. Additionally, miR-150, miR-320a, miR-200b, and miR-30c correlated significantly with time elapsed since irradiation.

CONCLUSIONS

Circulating miRNAs reflect the impact of ionizing radiation irrespective of the studied species, often in a dose-dependent manner. This makes circulating miRNAs promising biomarkers of radiation exposure.

A systemic approach to screening high-throughput RT-qPCR data for a suitable set of reference circulating miRNAs

Background

The consensus on how to choose a reference gene for serum or plasma miRNA expression qPCR studies has not been reached and none of the potential candidates have yet been convincingly validated. We proposed a new in silico approach of finding a suitable reference for human, circulating miRNAs and identified a new set of endogenous reference miRNA based on miRNA profiling experiments from Gene Expression Omnibus. We used 3 known normalization algorithms (NormFinder, BestKeeper, GeNorm) to calculate a new normalization score. We searched for a universal set of endogenous miRNAs and validated our findings on 2 new datasets using our approach.

Results

We discovered and validated a set of 13 miRNAs (miR-222, miR-92a, miR-27a, miR-17, miR-24, miR-320a, miR-25, miR-126, miR-19b, miR-199a-3p, miR-30b, miR-30c, miR-374a) that can be used to create a reliable reference combination of 3 miRNAs. We showed that on average the mean of 3 miRNAs (p = 0.0002) and 2 miRNAs (p = 0.0031) were a better reference than single miRNA. The arithmetic means of 3 miRNAs: miR-24, miR-222 and miR-27a was shown to be the most stable combination of 3 miRNAs in validation sets.

Conclusions

No single miRNA was suitable as a universal reference in serum miRNA qPCR profiling, but it was possible to designate a set of miRNAs, which consistently contributed to most stable combinations.

TRIP13 regulates DNA repair pathway choice through REV7 conformational change

DNA double-strand breaks (DSBs) are repaired through homology-directed repair (HDR) or non-homologous end joining (NHEJ). BRCA1/2-deficient cancer cells cannot perform HDR, conferring sensitivity to poly(ADP-ribose) polymerase inhibitors (PARPi). However, concomitant loss of the pro-NHEJ factors 53BP1, RIF1, REV7-Shieldin (SHLD1-3) or CST-DNA polymerase alpha (Pol-α) in BRCA1-deficient cells restores HDR and PARPi resistance. Here, we identify the TRIP13 ATPase as a negative regulator of REV7. We show that REV7 exists in active 'closed' and inactive 'open' conformations, and TRIP13 catalyses the inactivating conformational change, thereby dissociating REV7-Shieldin to promote HDR. TRIP13 similarly disassembles the REV7-REV3 translesion synthesis (TLS) complex, a component of the Fanconi anaemia pathway, inhibiting error-prone replicative lesion bypass and interstrand crosslink repair. Importantly, TRIP13 overexpression is common in BRCA1-deficient cancers, confers PARPi resistance and correlates with poor prognosis. Thus, TRIP13 emerges as an important regulator of DNA repair pathway choice-promoting HDR, while suppressing NHEJ and TLS.

P1727 Large coronary artery to pulmonary artery fistula as primary source of pulmonary blood supply in tetralogy of fallot with pulmonary atresia

Funding Acknowledgements

Not Applicable

OnBehalf

Not Applicable

Introduction

Pulmonary blood supply in patients of Tetralogy of Fallot with pulmonary atresia is usually from patent arterial duct or major aortopulmonary collaterals (MAPCAs) arising from descending thoracic aorta. We describe a case in which large coronary to pulmonary artery fistula was the primary source of pulmonary blood supply.

Case Report

A 17 years old female was referred to our hospital for diagnostic workup of suspected congenital heart disease. She was previously undiagnosed and now complains of progressive shortness of breath for last few months.

On physical examination she was non-dysmorphic with oxygen saturation of ∼ 77 % in room air, blood pressure of ∼ 117/72 mmHg, pulse rate of ∼ 89 beats per minute and respiratory rate of ∼ 24 breaths per minute. She was clinically cyanosed with grade 3 clubbing and polycythemic. Cardiovascular examination revealed quiet precordium with normally placed apex beat, grade 2 parasternal heave with single second heart sound and grade 3/6 continuous murmur along left mid sternal border.

Twelve lead electrocardiogram (ECG) showed normal sinus rhythm, right axis deviation and right ventricular hypertrophy. There was no evidence of ischemia. Chest X-ray revealed "boat shaped heart" with oligaemic lung fields. Transthoracic echocardiography showed large conoventricular ventricular septal defect with bidirectional flow. There was aortic over-ride with dilated left main coronary artery. No forward flow was seen across right ventricular outflow tract. Considering hugely dilated left main coronary artery, suspicion of coronary to pulmonary artery fistula was made and cardiac computed tomography followed by conventional angiography was done, both confirmed the diagnosis of Tetralogy of Fallot with pulmonary atresia and large coronary artery to main pulmonary artery fistula as a primary pulmonary blood supply. Two small collaterals (MAPCAs) were also identified supplying small part of right and left lungs.

Conclusion

This case highlights unusual source of pulmonary blood supply in Tetralogy of Fallot with pulmonary atresia. Correct pre-operative diagnosis is essential for appropriate surgical planning and better outcome.

Abstract P1727 Figure. TOF-PA with CA to PA Fistula

Abstract GMM-027: DYNLL1 INHIBITS DNA END RESECTION IN BRCA1-DEFICIENT CELLS AND REGULATES PARP INHIBITOR SENSITIVITY

High-grade serous ovarian carcinoma (HGSOC) patients with germline mutations in BRCA1/2 exhibit high sensitivity and improved outcome to double strand DNA break (DSB)-inducing agents [i.e. platinum and Poly(ADP-ribose) polymerase inhibitors (PARPi)] due to underlying defects in DNA repair via homologous recombination (HR). Due to their effectiveness, three PARP inhibitors (olaparib, rucaparib, niraparib) have recently gained FDA approval for the treatment of HGSOCs. However, de novo and acquired resistance to these agents is common even in the BRCA mutation carriers, and pose a significant, and unsolved, clinical challenge. Therefore, we adopted a systematic approach to comprehensibly identify unexplored factors/pathways that could be responsible for PARPi/platinum resistance in BRCA-defective HGSOC patients.

Here we identify DYNLL1 as a negative regulator of DNA end resection through a loss-of-function CRISPR screen in BRCA1-mutant ovarian carcinoma cells. DNA end resection is a vital process that initiates homologous recombination (HR)-mediated repair of double-stranded DNA breaks (DSBs), and consequently influences genome stability. In BRCA-defective HGSOC patients, DNA end resection is greatly compromised and contribute to the loss of HR and PARP inhibitor sensitivity. Loss of DYNLL1 allows DNA end resection and restores HR in BRCA1-mutant cells, thereby inducing resistance to platinum drugs and PARP inhibitors. In primary ovarian carcinomas low BRCA1 expression correlates with increased chromosomal aberrations, and the junction sequences of somatic structural variants indicate the loss of HR. Concurrent decrease in DYNLL1 expression in BRCA1 low ovarian cancers ‘rescued' this phenotype with reduced genomic alterations and increased homology at putative lesions. DYNLL1 limits nucleolytic degradation of DNA ends by interacting with the DNA end resection machinery (MRN complex, BLM helicase and DNA2) in cells. The impact of DYNLL1 on end resection can be re-capitulated in vitro and this is dependent on direct interaction with MRE11. In the absence of exogenous stress, depletion of DYNLL1 slows DNA replication fork progression due to ectopic activity of MRE11. Therefore, we infer that DYNLL1 is an important anti-resection factor that significantly influences genomic stability and response to DNA damaging chemotherapy.

Citation Format: Yizhou Joseph He, Khyati Meghani, Marie-Christine Caron, Chunyu Yang, Daryl A. Ronato, Jie Bian, Anchal Sharma, Jessica Miller, Niraj Joshi, Alexandre Detappe, John G. Doench, Gaelle Legube, David E. Root, Alan D. D'Andrea, Pascal Drané, Subhojyoti De, Panagiotis Konstantinopoulos, Jean-Yves Masson, and Dipanjan Chowdhury. DYNLL1 INHIBITS DNA END RESECTION IN BRCA1-DEFICIENT CELLS AND REGULATES PARP INHIBITOR SENSITIVITY [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-027.

PDTM-41. INHIBITION OF DNA DOUBLE STRAND BREAK REPAIR PATHWAYS AS A PROMISING THERAPEUTIC TARGET IN DIFFUSE INTRINSIC PONTINE GLIOMAS (DIPGs)

METHODS

To identify pathways critical for DIPG cell survival, genome wide CRISPR-Cas9 screen was performed on patient derived DIPG cell lines followed by gene set enrichment analyses. To monitor the effects of pathway inhibition on survival, apoptosis, DNA damage and repair, assays were performed to measure cell proliferation, cleaved-caspase3, gamma-H2AX and reporter based-DNA repair efficiency.

RESULTS

Our unbiased CRISPR approach to uncover vulnerabilities in DIPGs identified DNA double strand break (DSBs) repair pathways as essential for DIPG cell proliferation and survival. Further studies revealed high basal DSBs in DIPG cells compared to neural stem cells and primary astrocytes that suggest dependence of DIPG cell survival on specific DSB repair pathways. We confirmed the intrinsic reliance of DIPG cells on the specific DSB repair pathway of mutagenic end-joining, and defined a key role for DNA repair in suppressing endogenous DNA damage-induced apoptotic cell death.

CONCLUSION

DIPG cells have high endogenous DNA damage levels and escape catastrophic genomic instability and cell death by engaging DNA repair pathways, in particular the mutagenic end-joining DNA repair pathway. Inhibition of this specific DNA repair pathway represents a promising new avenue for the treatment of DIPGs.

Spatio-temporal distribution analysis of circulating genotypes of dengue virus type 1 in western and southern states of India by a one-step real-time RT-PCR assay

Dengue virus type 1 (DENV-1) Asian and American/African (AM/AF) genotypes were reported to be co-circulating in southern and western states of India based on envelope (E) gene sequencing of few representative samples. The objective of the present study was to develop a one-step real-time RT-PCR to discriminate between Asian and AM/AF genotypes of DENV-1 and investigate the spatio-temporal distribution of the DENV-1 genotypes in southern and western states of India. A one-step real-time RT-PCR to discriminate the Asian and AM/AF genotypes of DENV-1 was developed and validated using 40 samples (17 Asian and 23 AM/AF), for which the envelope (E) gene sequence data was available. DENV-2, DENV-3 and DENV-4 isolates, one each and DENV negative samples (n = 17) were also tested by the assay. Additional 296 samples positive for DENV-1 from selected Southern and Western states of India were genotyped using the real-time RT-PCR assay. Among the samples used for validation, the genotyping results were concordant with sequencing results for 39 samples. In the one discordant sample which was positive for AM/AF by sequencing, the genotyping assay tested positive for both Asian and AM/AF genotype. DENV-2, DENV-3 and DENV-4 isolates were not reactive in the assay. None of the DENV negative samples were positive (sensitivity 100% and specificity 98.2%). A total of 336 samples (40 samples with sequence data and 296 samples without sequence data) were used for spatio-temporal distribution analysis. The results revealed that the Asian genotype was the predominant genotype in Tamil Nadu and Kerala, the southern states. The AM/AF genotype was the predominant genotype in Maharashtra, a western state of India. In Nashik district of Maharashtra, Asian genotype was observed in 32.6% of DENV-1 samples during 2017 while the same decreased to 7.3% during 2018. In Pune district, Asian genotype was observed in 40.0% of DENV-1 samples during 2018 only. To conclude, a one step real-time RT-PCR has been developed for discriminating Asian and AM/AF genotypes of DENV-1. This assay can act as a complement to sequencing but not a substitute and can be utilized in resource limited settings for molecular surveillance of DENV-1. DENV-1 Asian genotype was the dominant genotype in South India while, AM/AF genotype was dominant in Western India.

A mitotic CDK5-PP4 phospho-signaling cascade primes 53BP1 for DNA repair in G1

Mitotic cells attenuate the DNA damage response (DDR) by phosphorylating 53BP1, a critical DDR mediator, to prevent its localization to damaged chromatin. Timely dephosphorylation of 53BP1 is critical for genome integrity, as premature recruitment of 53BP1 to DNA lesions impairs mitotic fidelity. Protein phosphatase 4 (PP4) dephosphorylates 53BP1 in late mitosis to allow its recruitment to DNA lesions in G1. How cells appropriately dephosphorylate 53BP1, thereby restoring DDR, is unclear. Here, we elucidate the underlying mechanism of kinetic control of 53BP1 dephosphorylation in mitosis. We demonstrate that CDK5, a kinase primarily functional in post-mitotic neurons, is active in late mitotic phases in non-neuronal cells and directly phosphorylates PP4R3β, the PP4 regulatory subunit that recognizes 53BP1. Specific inhibition of CDK5 in mitosis abrogates PP4R3β phosphorylation and abolishes its recognition and dephosphorylation of 53BP1, ultimately preventing the localization of 53BP1 to damaged chromatin. Our results establish CDK5 as a regulator of 53BP1 recruitment.

Multifaceted Impact of MicroRNA 493-5p on Genome-Stabilizing Pathways Induces Platinum and PARP Inhibitor Resistance in BRCA2-Mutated Carcinomas

BRCA1/2-mutated ovarian cancers (OCs) are defective in homologous recombination repair (HRR) of double-strand breaks (DSBs) and thereby sensitive to platinum and PARP inhibitors (PARPis). Multiple PARPis have recently received US Food and Drug Administration (FDA) approval for treatment of OCs, and resistance to PARPis is a major clinical problem. Utilizing primary and recurrent BRCA1/2-mutated carcinomas from OC patients, patient-derived lines, and an in vivo BRCA2-mutated mouse model, we identified a microRNA, miR-493-5p, that induced platinum/PARPi resistance exclusively in BRCA2-mutated carcinomas. However, in contrast to the most prevalent resistance mechanisms in BRCA mutant carcinomas, miR-493-5p did not restore HRR. Expression of miR-493-5p in BRCA2-mutated/depleted cells reduced levels of nucleases and other factors involved in maintaining genomic stability. This resulted in relatively stable replication forks, diminished single-strand annealing of DSBs, and increased R-loop formation. We conclude that impact of miR-493-5p on multiple pathways pertinent to genome stability cumulatively causes PARPi/platinum resistance in BRCA2 mutant carcinomas.