Pharmacodynamic Activity of [18F]-Fluorthanatrace Poly(ADP-ribose) Polymerase Positron Emission Tomography in Patients With BRCA1/2-Mutated Breast Cancer Receiving Talazoparib.

PURPOSE: We tested the ability of [18F] fluorthanatrace (FTT), a radiolabeled analog of poly(ADP-ribose) polymerase (PARP)-1 inhibitors, to demonstrate target engagement on positron emission tomography (PET) scans from patients with newly diagnosed primary breast cancer receiving the PARP inhibitor (PARPi) talazoparib. METHODS: Seven patients with germline BRCA1/2 pathogenic variants underwent [18F]FTT PET-computed tomography scanning at baseline, and five underwent repeat scanning 14 days after talazoparib initiation. Maximum uptake on PET was quantified in the primary tumor, involved nodes, contralateral pectoralis muscle, and lumbar vertebra body level 3, and compared between the two time points. RESULTS: Blocking of [18F]FTT was observed on the second scan. Potentially strong but nonsignificant correlations were found between changes in tumor volume (on ultrasound at 1 month v baseline) and percentage changes in tumor-to-muscle uptake ratio at 14 days from baseline (Spearman rank correlation coefficient r = 1; P = .083); and between the highest-grade hematologic toxicity and baseline bone marrow-to-muscle (B/M) uptake ratio (r = 0.72; P = .068) and percentage change in B/M ratio at 14 days from baseline (r = 0.87; P = .058). CONCLUSION: We conclude that [18F]FTT can image target engagement by PARPi, but larger studies are needed to determine whether [18F]FTT uptake can predict response to PARPi and whether uptake of [18F]FTT in bone marrow may be an early predictor of hematologic toxicity.

PIKing up and AKTing on Resistance Mutations in Osimertinib-Treated EGFR-Mutated NSCLC.

A recent study identified high rates of PI3K-AKT pathway mutations from the FLAURA and AURA3 osimertinib trials and pre-clinically validated that these mutations decreased osimertinib sensitivity in EGFR-mutated non-small cell lung cancer. The AKT inhibitor capivasertib was found to overcome this resistance, providing an important rationale for the development of AKT inhibitors in non-small cell lung cancer. See related article by Grazini et al., p. 4143.

Targeting DNA Damage Response Deficiency in Thoracic Cancers.

Thoracic cancers comprise non-small cell lung cancers (NSCLCs), small cell lung cancers (SCLCs) and malignant pleural mesotheliomas (MPM). Collectively, they account for the highest rate of death from malignancy worldwide. Genomic instability is a universal feature of cancer, which fuels mutations and tumour evolution. Deficiencies in DNA damage response (DDR) genes amplify genomic instability. Homologous recombination deficiency (HRD), resulting from BRCA1/BRCA2 inactivation, is exploited for therapeutic synthetic lethality with poly-ADP ribose polymerase (PARP) inhibitors in breast and ovarian cancers, as well as in prostate and pancreatic cancers. However, DDR deficiency and its therapeutic implications are less well established in thoracic cancers. Emerging evidence suggests that a subset of thoracic cancers may harbour DDR deficiency and may, thus, be effectively targeted with DDR agents. Here, we review the current evidence surrounding DDR in thoracic cancers and discuss the challenges and promise for achieving clinical benefit with such therapeutics.

Long-Term Echocardiographic and Clinical Outcomes After Invasive and Non-Invasive Therapies for Sub-Massive and Massive Acute Pulmonary Embolism.

AIM: Acute pulmonary embolism (PE) is a significant cause of mortality in the hospital setting. The objective of this study was to outline the long-term outcomes after surgical and non-surgical management for patients with massive and submassive PE. METHODS: Population cohort observational study evaluating all patients who presented to three tertiary hospitals in the state of Western Australia with access to cardiothoracic services over 5 years (2013-2018). Reviewed notes of all patients as well as radiology, linked mortality data and all available echocardiography studies at the primary hospital. RESULTS: In total, 245 patients were identified, of which 41 received surgical management and 204 non-surgical management; demographic data was similar. Clinically, the surgical group had higher rates of shock requiring vasopressors, severe bradycardia, or cardiopulmonary resuscitation prior to intervention. The 28-day mortality was not statistically significantly different between the surgical embolectomy group (2/41 [4.2%]) and the non-surgical group (17/201 [8.3%]) (p=0.382). There was no difference in 12-month mortality, including when this was adjusted for vasopressors, right ventricular (RV) strain, troponin, and brain natriuretic peptide. In the massive PE sub-group, 28-day mortality was not significantly different: 2/29 (6.9%) surgical group vs 7/34 (20.2%) non-surgical group (p=0.064). Higher rates of severe RV impairment and dilatation were present in the surgical group. All patients with available echocardiography studies at outpatient follow-up returned to normal or mild RV impairment. CONCLUSION: Patients who presented with massive or submassive PE had similar outcomes whether treated with surgical or non-surgical management. Surgical embolectomy is a safe option in a cardiothoracic centre setting.

Poly(ADP-Ribose) Polymerase Inhibitor Development: Promising Strategies to Move Beyond Approved Indications.

Biomarker-based patient selection and rational combinations show promise in expanding the use of PARP inhibitors.

Ataxia telangiectasia and Rad3-related (ATR) inhibitor camonsertib dose optimization in patients with biomarker-selected advanced solid tumors (TRESR study).

BACKGROUND: Camonsertib is a selective oral inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase with demonstrated efficacy in tumors with DNA damage response gene deficiencies. On-target anemia is the main drug-related toxicity typically manifesting after the period of dose-limiting toxicity evaluation. Thus, dose and schedule optimization requires extended follow-up to assess prolonged treatment effects. METHODS: Long-term safety, tolerability, and antitumor efficacy of 3 camonsertib monotherapy dosing regimens were assessed in the TRESR study dose-optimization phase: 160 mg once daily (QD) 3 days on, 4 days off (160 3/4; the preliminary recommended Phase II dose [RP2D]) and two step-down groups of 120 mg QD 3/4 (120 3/4) and 160 mg QD 3/4, 2 weeks on, 1 week off (160 3/4, 2/1w). Safety endpoints included incidence of treatment-related adverse events (TRAEs), dose modifications, and transfusions. Efficacy endpoints included overall response rate, clinical benefit rate, progression-free survival, and circulating tumor DNA (ctDNA)-based molecular response rate. RESULTS: The analysis included 119 patients: 160 3/4 (n = 67), 120 3/4 (n = 25), and 160 3/4, 2/1w (n = 27) treated up to 117.1 weeks as of the data cutoff. The risk of developing grade 3 anemia was significantly lower in the 160 3/4, 2/1w group compared with the preliminary RP2D group (hazard ratio = 0.23, 2-sided P = .02), translating to reduced transfusion and dose reduction requirements. The intermittent weekly schedule did not compromise antitumor activity. CONCLUSION: The 160 3/4, 2/1w dose was established as an optimized regimen for future camonsertib monotherapy studies offering a substantial reduction in the incidence of anemia without any compromise to efficacy. CLINICAL TRIAL ID: NCT04497116.

Loss of the DNA Repair Gene RNase H2 Identifies a Unique Subset of DDR-Deficient Leiomyosarcomas.

Targeting the DNA damage response (DDR) pathway is an emerging therapeutic approach for leiomyosarcoma (LMS), and loss of RNase H2, a DDR pathway member, is a potentially actionable alteration for DDR-targeted treatments. Therefore, we designed a protein- and genomic-based RNase H2 screening assay to determine its prevalence and prognostic significance. Using a selective RNase H2 antibody on a pan-tumor microarray (TMA), RNase H2 loss was more common in LMS (11.5%, 9/78) than across all tumors (3.8%, 32/843). In a separate LMS cohort, RNase H2 deficiency was confirmed in uterine LMS (U-LMS, 21%, 23/108) and soft-tissue LMS (ST-LMS; 30%, 39/102). In the TCGA database, RNASEH2B homozygous deletions (HomDels) were found in 6% (5/80) of LMS cases, with a higher proportion in U-LMS (15%; 4/27) compared with ST-LMS (2%; 1/53). Using the SNiPDx targeted-NGS sequencing assay to detect biallelic loss of function in select DDR-related genes, we found RNASEH2B HomDels in 54% (19/35) of U-LMS cases with RNase H2 loss by IHC, and 7% (3/43) HomDels in RNase H2 intact cases. No RNASEH2B HomDels were detected in ST-LMS. In U-LMS patient cohort (n = 109), no significant overall survival difference was seen in patients with RNase H2 loss versus intact, or RNASEH2B HomDel (n = 12) versus Non-HomDel (n = 37). The overall diagnostic accuracy, sensitivity, and specificity of RNase H2 IHC for detecting RNA-SEH2B HomDels in U-LMS was 76%, 93%, and 71%, respectively, and it is being developed for future predictive biomarker driven clinical trials targeting DDR in U-LMS.

BRCA1-Mediated Dual Regulation of Ferroptosis Exposes a Vulnerability to GPX4 and PARP Co-Inhibition in BRCA1-Deficient Cancers.

Resistance to poly (ADP-ribose) polymerase inhibitors (PARPi) limits the therapeutic efficacy of PARP inhibition in treating breast cancer susceptibility gene 1 (BRCA1)-deficient cancers. Here we reveal that BRCA1 has a dual role in regulating ferroptosis. BRCA1 promotes the transcription of voltage-dependent anion channel 3 (VDAC3) and glutathione peroxidase 4 (GPX4); consequently, BRCA1 deficiency promotes cellular resistance to erastin-induced ferroptosis but sensitizes cancer cells to ferroptosis induced by GPX4 inhibitors (GPX4i). In addition, nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy and defective GPX4 induction unleash potent ferroptosis in BRCA1-deficient cancer cells upon PARPi and GPX4i co-treatment. Finally, we show that xenograft tumors derived from patients with BRCA1-mutant breast cancer with PARPi resistance exhibit decreased GPX4 expression and high sensitivity to PARP and GPX4 co-inhibition. Our results show that BRCA1 deficiency induces a ferroptosis vulnerability to PARP and GPX4 co-inhibition and inform a therapeutic strategy for overcoming PARPi resistance in BRCA1-deficient cancers. Significance: BRCA1 deficiency promotes resistance to erastin-induced ferroptosis via blocking VDAC3 yet renders cancer cells vulnerable to GPX4i-induced ferroptosis via inhibiting GPX4. NCOA4 induction and defective GPX4 further synergizes GPX4i with PARPi to induce ferroptosis in BRCA1-deficient cancers and targeting GPX4 mitigates PARPi resistance in those cancers. See related commentary by Alborzinia and Friedmann Angeli, p. 1372.

Comparison of intraocular pressure profiles during the water drinking test and the modified diurnal tension curve.

OBJECTIVES: To compare intraocular pressure (IOP) during the water drinking test (WDT) and modified diurnal tension curve (mDTC) in open-angle glaucoma (OAG) patients, using multimodal, observer-masked tonometry. METHODS: Open-angle glaucoma subjects were prospectively enroled, excluding those who had undergone glaucoma filtration or laser surgery. Two-hourly mDTC Goldmann applanation (GAT) and rebound tonometry (RT) was performed between 8:00 and 16:00, and every 15 min for 45 min after ingestion of 800mls of water. Blood pressure, heart rate, pupillometry measurements, and optical coherence tomography (AS-OCT) were also recorded. RESULTS: Forty-two subjects' right eyes were included. 48% were using topical glaucoma medication. Mean baseline IOP was 14.9 ± 4.52 mmHg, with mean visual field mean deviation (±SD) -5.05 ± 5.45 dB. Strong association was found between maximum IOP during mDTC and WDT (r = 0.90, 95% CI 0.82-0.95 p < 0.0001) with agreement (mDTC-WDT) bias -0.82 mmHg, 95% LoA -1.46 to -0.18. During the WDT, mean systolic blood pressure (±SD) increased from 140.0 ± 20.0 to 153.3 ± 24.0 mmHg (p < 0.0001), mean heart rate ( ± SD) reduced from 69.5 ± 11.3 bpm to 63.6 ± 10.0 bpm (p < 0.0001), and temporal iridocorneal angle increased from 29.2 ± 6.0° to 29.6 ± 5.2° (p = 0.04). CONCLUSION: This study presents repeated, observer-masked IOP data showing strong correlation between maximum IOP during mDTC and WDT using multimodal tonometry. This supports WDT as a meaningful alternative to mDTC when investigating diurnal IOP characteristics in clinic, with reduced time requirements and associated costs.

First-in-Human Study of the Ataxia Telangiectasia and Rad3-Related (ATR) Inhibitor Tuvusertib (M1774) as Monotherapy in Patients with Solid Tumors.

PURPOSE: Tuvusertib (M1774) is a potent, selective, orally administered ataxia telangiectasia and Rad3-related (ATR) protein kinase inhibitor. This first-in-human study (NCT04170153) evaluated safety, tolerability, maximum tolerated dose (MTD), recommended dose for expansion (RDE), pharmacokinetics (PK), pharmacodynamics (PD), and preliminary efficacy of tuvusertib monotherapy. PATIENTS AND METHODS: Ascending tuvusertib doses were evaluated in 55 patients with metastatic or locally advanced unresectable solid tumors. A safety monitoring committee determined dose escalation based on PK, PD, and safety data guided by a Bayesian 2-parameter logistic regression model. Molecular responses (MR) were assessed in circulating tumor DNA samples. RESULTS: Most common grade ≥3 treatment-emergent adverse events were anemia (36%), neutropenia, and lymphopenia (both 7%). Eleven patients experienced dose-limiting toxicities, most commonly grade 2 (n = 2) or 3 (n = 8) anemia. No persistent effects on blood immune cell populations were observed. The RDE was 180 mg tuvusertib QD (once daily), 2 weeks on/1 week off treatment, which was better tolerated than the MTD (180 mg QD continuously). Tuvusertib median time to peak plasma concentration ranged from 0.5 to 3.5 hours and mean elimination half-life from 1.2 to 5.6 hours. Exposure-related PD analysis suggested maximum target engagement at ≥130 mg tuvusertib QD. Tuvusertib induced frequent MRs in the predicted efficacious dose range; MRs were enriched in patients with radiological disease stabilization, and complete MRs were detected for mutations in ARID1A, ATRX, and DAXX. One patient with platinum- and PARP inhibitor-resistant BRCA wild-type ovarian cancer achieved an unconfirmed RECIST v1.1 partial response. CONCLUSIONS: Tuvusertib demonstrated manageable safety and exposure-related target engagement. Further clinical evaluation of tuvusertib is ongoing.

Limited Independent Follow-Up with Germline Testing of Variants Detected in BRCA1 and BRCA2 by Tumor-Only Sequencing.

Introduction: Genomic profiling is performed in patients with advanced or metastatic cancer, in order to direct cancer treatment, often sequencing tumor-only, without a matched germline comparator. However, because many of the genes analyzed on tumor profiling overlap with those known to be associated with hereditary cancer predisposition syndromes (HCPS), tumor-only profiling can unknowingly uncover germline pathogenic (P) and likely pathogenic variants (LPV). In this study, we evaluated the number of patients with P/LPVs identified in BRCA1 and BRCA2 (BRCA1/2) via tumor-only profiling, then determined the germline testing outcomes for those patients. Methods: A retrospective chart review was performed to identify patients with BRCA1/2 variants on tumor-only genomic profiling, and whether they had germline testing. Results: This study found that of 2923 patients with 36 tumor types who underwent tumor-only testing, 554 had a variant in BRCA1/2 (19.0%); 119 of the 554 patients (21.5%) had a P/LP BRCA1/2 variant, representing 4.1% of the overall population who underwent genomic profiling. Seventy-three (61.3%) of 119 patients with BRCA1/2 P/LPV on tumor-only testing did not undergo germline testing, 34 (28.6%) had already had germline testing before tumor-only testing, and 12 (10.1%) underwent germline testing after tumor-only testing. Twenty-eight germline BRCA1/2 P/LPVs were detected, 24 in those who had prior germline testing, and 4 among the 12 patients who had germline testing after tumor-only testing. Conclusion: Tumor-only testing is likely to identify P/LPVs in BRCA1/2. Efforts to improve follow-up germline testing is needed to improve identification of germline BRCA1/2 alterations.

Targeting ATR in patients with cancer.

Pharmacological inhibition of the ataxia telangiectasia and Rad3-related protein serine/threonine kinase (ATR; also known as FRAP-related protein (FRP1)) has emerged as a promising strategy for cancer treatment that exploits synthetic lethal interactions with proteins involved in DNA damage repair, overcomes resistance to other therapies and enhances antitumour immunity. Multiple novel, potent ATR inhibitors are being tested in clinical trials using biomarker-directed approaches and involving patients across a broad range of solid cancer types; some of these inhibitors have now entered phase III trials. Further insight into the complex interactions of ATR with other DNA replication stress response pathway components and with the immune system is necessary in order to optimally harness the potential of ATR inhibitors in the clinic and achieve hypomorphic targeting of the various ATR functions. Furthermore, a deeper understanding of the diverse range of predictive biomarkers of response to ATR inhibitors and of the intraclass differences between these agents could help to refine trial design and patient selection strategies. Key challenges that remain in the clinical development of ATR inhibitors include the optimization of their therapeutic index and the development of rational combinations with these agents. In this Review, we detail the molecular mechanisms regulated by ATR and their clinical relevance, and discuss the challenges that must be addressed to extend the benefit of ATR inhibitors to a broad population of patients with cancer.

Development of a Practical Nomogram for Personalized Anemia Management in Patients Treated with Ataxia Telangiectasia and Rad3-related Inhibitor Camonsertib.

PURPOSE: Camonsertib is a highly selective and potent inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase. Dose-dependent anemia is a class-related on-target adverse event often requiring dose modifications. Individual patient risk factors for the development of significant anemia complicate the selection of a "one-size-fits-all" ATR inhibitor (ATRi) dose and schedule, possibly leading to suboptimal therapeutic doses in patients at low risk of anemia. We evaluated whether early predictors of anemia could be identified to ultimately inform a personalized dose-modification approach. PATIENTS AND METHODS: On the basis of preclinical observations and a mechanistic understanding of ATRi-related anemia, we identified several potential factors to explore in a multivariable linear regression modeling tool for predicting hemoglobin level ahead of day 22 (cycle 2) of treatment. RESULTS: In patients treated with camonsertib monotherapy (NCT04497116), we observed that hemoglobin decline is consistently preceded by reticulocytopenia, and dose- and exposure-dependent decreases in monocytes. We developed a nomogram incorporating baseline and day 8 hemoglobin and reticulocyte values that predicted the day 22 hemoglobin values of patients with clinically valuable concordance (within 7.5% of observations) 80% of the time in a cross-validation performance test of data from 60 patients. CONCLUSIONS: The prediction of future hemoglobin decrease, after a week of treatment, may enable a personalized, early dose modification to prevent development of clinically significant anemia and resulting unscheduled dose holds or transfusions.

Phase 1/2 trial of avelumab combined with utomilumab (4-1BB agonist), PF-04518600 (OX40 agonist), or radiotherapy in patients with advanced gynecologic malignancies.

BACKGROUND: Immune checkpoint blockade has shown mixed results in advanced/recurrent gynecologic malignancies. Efficacy may be improved through costimulation with OX40 and 4-1BB agonists. The authors sought to evaluate the safety and efficacy of avelumab combined with utomilumab (a 4-1BB agonist), PF-04518600 (an OX40 agonist), and radiotherapy in patients with recurrent gynecologic malignancies. METHODS: The primary end point in this six-arm, phase 1/2 trial was safety of the combination regimens. Secondary end points included the objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors and immune-related Response Evaluation Criteria in Solid Tumors, the disease control rate (DCR), the duration of response, progression-free survival, and overall survival. RESULTS: Forty patients were included (35% with cervical cancer, 30% with endometrial cancer, and 35% with ovarian cancer). Most patients (n = 33; 83%) were enrolled in arms A-C (no radiation). Among 35 patients who were evaluable for efficacy, the ORR was 2.9%, and the DCR was 37.1%, with a median duration of stable disease of 5.4 months (interquartile range, 4.1-7.3 months). Patients with cervical cancer in arm A (avelumab and utomilumab; n = 9 evaluable patients) achieved an ORR of 11% and a DCR of 78%. The median progression-free survival was 2.1 months (95% CI, 1.8-3.5 months), and overall survival was 9.4 months (95% CI, 5.6-11.9 months). No dose-limiting toxicities or grade 3-5 immune-related adverse events were observed. CONCLUSIONS: The findings from this trial highlight that, in heavily pretreated patients with gynecologic cancer, even multidrug regimens targeting multiple immunologic pathways, although safe, did not produce significant responses. A DCR of 78% in patients with cervical cancer who received avelumab and utomilumab indicates that further research on this combination in select patients may be warranted.

Effects of COVID-19 pandemic on glaucoma appointment scheduling in a tertiary hospital in London, UK.

PURPOSE: To investigate the impact of the delay in patient appointments caused by the COVID-19 pandemic and the triage system on the glaucomatous disease of patients in a London tertiary hospital. METHODS: Observational retrospective study that randomly selected 200 glaucoma patients with more than 3 months of unintended delay for their post-COVID visit and other inclusion and exclusion criteria. Demographic information, clinical data, number of drugs, best-corrected visual acuity (BCVA), intraocular pressure (IOP), visual field (VF) mean deviation (MD), and global peripapillary retinal nerve fibre layer (pRNFL) thickness were obtained from the pre- and post-COVID visit. At the post-COVID visit, the clinical outcomes subjective clinical concern and change of treatment or need for surgery were also annotated. The variables were stratified by glaucoma severity (according to the MD into early, moderate and advanced) and by delay time (more and less than 12 months) and analysed using SPSS. RESULTS: We included 121 eyes (from 71 patients). The median patient age was 74 years (interquartile range -IQR- 15), 54% were males and 52% Caucasians. Different glaucoma types and all glaucoma severities were included. When data was stratified for glaucoma severity, at the pre-COVID visit, significant differences in BCVA, CCT and IOP were observed and there were significantly higher values in the early glaucoma group. The median follow-up delay was 11 months (IQR 8), did not differ between the glaucoma severity groups and did not correlate to the glaucoma severity. At the post-COVID visit, significant differences in BCVA, IOP, and Global pRNFL thickness were observed between the glaucoma severity groups, as lower BCVA and higher IOP and pRNFL thickness were observed in the early glaucoma group. At the post-COVID visit there was cause for concern in 40 eyes: 5 were followed more closely, 22 had a change of treatment and 13 were booked for surgery (3 for cataract and 10 for glaucoma surgery). However, the number of eyes with causes for concern were similar between the glaucoma severity groups and there was no correlation between these clinical outcomes and the delay of the post-COVID visit. The number of topical hypotensive medications increased significantly after the post-COVID visit, higher number of medications were observed in the advanced glaucoma group. When differences of IOP, MD and pRNFL thickness between the pre and post-COVID visit, only the MD difference was significantly different between the glaucoma severity groups because it was higher in the severe group. When data was stratified for delay longer or shorter than 12 months, no differences were observed between the groups except at the pre-COVID visit, when the numbers of patients with MD deviation >-6 dB had longer delay time. When differences in IOP, MD and RNFL thickness were calculated, only the pRNFL thickness showed significant differences between the delay groups, because it was higher in the longer delay group. Finally, when paired analysis of the variables at the pre- and post-COVID visits, stratified by glaucoma severity and delay were conducted, although there were no significant differences in IOP in any group, the BCVA decreased significantly in the overall group and in the longer delay groups, the number of hypotensive drugs increased significantly overall and in the moderate and advanced glaucoma, the MD of the VF worsened significantly in the overall group and in the early glaucoma and longer delay groups and the pRNFL thickness decreased significantly in all groups. CONCLUSIONS: We document that delayed care impacts negatively on the glaucomatous disease of our patients because at the post-COVID visit there were reasons for clinical concern in a third of eyes that resulted in change of treatment or surgery. However, these clinical consequences were not related to IOP, glaucoma severity or delay time and reflect that the triage methods implemented worked adequately. The most sensitive parameter to indicate progression in our sample was the pRNFL thickness.

Targeting ATR in Cancer Medicine.

As a key component of the DNA Damage Response, the Ataxia telangiectasia and Rad3-related (ATR) protein is a promising druggable target that is currently widely evaluated in phase I-II-III clinical trials as monotherapy and in combinations with other rational antitumor agents, including immunotherapy, DNA repair inhibitors, chemo- and radiotherapy. Ongoing clinical studies for this drug class must address the optimization of the therapeutic window to limit overlapping toxicities and refine the target population that will most likely benefit from ATR inhibition. With advances in the development of personalized treatment strategies for patients with advanced solid tumors, many ongoing ATR inhibitor trials have been recruiting patients based on their germline and somatic molecular alterations, rather than relying solely on specific tumor subtypes. Although a spectrum of molecular alterations have already been identified as potential predictive biomarkers of response that may sensitize to ATR inhibition, these biomarkers must be analytically validated and feasible to measure robustly to allow for successful integration into the clinic. While several ATR inhibitors in development are poised to address a clinically unmet need, no ATR inhibitor has yet received FDA-approval. This chapter details the underlying rationale for targeting ATR and summarizes the current preclinical and clinical landscape of ATR inhibitors currently in evaluation, as their regulatory approval potentially lies close in sight.

SPOP Mutations Target STING1 Signaling in Prostate Cancer and Create Therapeutic Vulnerabilities to PARP Inhibitor-Induced Growth Suppression.

PURPOSE: Speckle-type POZ protein (SPOP) is important in DNA damage response (DDR) and maintenance of genomic stability. Somatic heterozygous missense mutations in the SPOP substrate-binding cleft are found in up to 15% of prostate cancers. While mutations in SPOP predict for benefit from androgen receptor signaling inhibition (ARSi) therapy, outcomes for patients with SPOP-mutant (SPOPmut) prostate cancer are heterogeneous and targeted treatments for SPOPmut castrate-resistant prostate cancer (CRPC) are lacking. EXPERIMENTAL DESIGN: Using in silico genomic and transcriptomic tumor data, proteomics analysis, and genetically modified cell line models, we demonstrate mechanistic links between SPOP mutations, STING signaling alterations, and PARP inhibitor vulnerabilities. RESULTS: We demonstrate that SPOP mutations are associated with upregulation of a 29-gene noncanonical (NC) STING (NC-STING) signature in a subset of SPOPmut, treatment-refractory CRPC patients. We show in preclinical CRPC models that SPOP targets and destabilizes STING1 protein, and prostate cancer-associated SPOP mutations result in upregulated NC-STING-NF-κB signaling and macrophage- and tumor microenvironment (TME)-facilitated reprogramming, leading to tumor cell growth. Importantly, we provide in vitro and in vivo mechanism-based evidence that PARP inhibitor (PARPi) treatment results in a shift from immunosuppressive NC-STING-NF-κB signaling to antitumor, canonical cGAS-STING-IFNß signaling in SPOPmut CRPC and results in enhanced tumor growth inhibition. CONCLUSIONS: We provide evidence that SPOP is critical in regulating immunosuppressive versus antitumor activity downstream of DNA damage-induced STING1 activation in prostate cancer. PARPi treatment of SPOPmut CRPC alters this NC-STING signaling toward canonical, antitumor cGAS-STING-IFNß signaling, highlighting a novel biomarker-informed treatment strategy for prostate cancer.

A HUWE1 defect causes PARP inhibitor resistance by modulating the BRCA1-∆11q splice variant.

Although PARP inhibitors (PARPi) now form part of the standard-of-care for the treatment of homologous recombination defective cancers, de novo and acquired resistance limits their overall effectiveness. Previously, overexpression of the BRCA1-∆11q splice variant has been shown to cause PARPi resistance. How cancer cells achieve increased BRCA1-∆11q expression has remained unclear. Using isogenic cells with different BRCA1 mutations, we show that reduction in HUWE1 leads to increased levels of BRCA1-∆11q and PARPi resistance. This effect is specific to cells able to express BRCA1-∆11q (e.g. BRCA1 exon 11 mutant cells) and is not seen in BRCA1 mutants that cannot express BRCA1-∆11q, nor in BRCA2 mutant cells. As well as increasing levels of BRCA1-∆11q protein in exon 11 mutant cells, HUWE1 silencing also restores RAD51 nuclear foci and platinum salt resistance. HUWE1 catalytic domain mutations were also seen in a case of PARPi resistant, BRCA1 exon 11 mutant, high grade serous ovarian cancer. These results suggest how elevated levels of BRCA1-∆11q and PARPi resistance can be achieved, identify HUWE1 as a candidate biomarker of PARPi resistance for assessment in future clinical trials and illustrate how some PARPi resistance mechanisms may only operate in patients with particular BRCA1 mutations.

Actionability classification of variants of unknown significance correlates with functional effect.

Genomically-informed therapy requires consideration of the functional impact of genomic alterations on protein expression and/or function. However, a substantial number of variants are of unknown significance (VUS). The MD Anderson Precision Oncology Decision Support (PODS) team developed an actionability classification scheme that categorizes VUS as either "Unknown" or "Potentially" actionable based on their location within functional domains and/or proximity to known oncogenic variants. We then compared PODS VUS actionability classification with results from a functional genomics platform consisting of mutant generation and cell viability assays. 106 (24%) of 438 VUS in 20 actionable genes were classified as oncogenic in functional assays. Variants categorized by PODS as Potentially actionable (N = 204) were more likely to be oncogenic than those categorized as Unknown (N = 230) (37% vs 13%, p = 4.08e-09). Our results demonstrate that rule-based actionability classification of VUS can identify patients more likely to have actionable variants for consideration with genomically-matched therapy.

PARP inhibitors: enhancing efficacy through rational combinations.

Poly (ADP-ribose) polymerase inhibitors (PARPi) have significantly changed the treatment landscape for tumours harbouring defects in genes involved in homologous repair (HR) such as BRCA1 and BRCA2. Despite initial responsiveness to PARPi, tumours eventually develop resistance through a variety of mechanisms. Rational combination strategies involving PARPi have been explored and are in various stages of clinical development. PARPi combinations have the potential to enhance efficacy through synergistic activity, and also potentially sensitise innately PARPi-resistant tumours to PARPi. Initial combinations involving PARPi with chemotherapy were hindered by significant overlapping haematologic toxicity, but newer combinations with fewer toxicities and more targeted approaches are undergoing evaluation. In this review, we discuss the mechanisms of PARPi resistance and review the rationale and clinical evidence for various PARPi combinations including combinations with chemotherapy, immunotherapy, and targeted therapies. We also highlight emerging PARPi combinations with promising preclinical evidence.