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.

A Phase I Expansion Cohort Study Evaluating the Safety and Efficacy of the CHK1 Inhibitor LY2880070 with Low-dose Gemcitabine in Patients with Metastatic Pancreatic Adenocarcinoma

PURPOSE

Combining gemcitabine with CHK1 inhibition has shown promise in preclinical models of pancreatic ductal adenocarcinoma (PDAC). Here, we report the findings from a phase I expansion cohort study (NCT02632448) investigating low-dose gemcitabine combined with the CHK1 inhibitor LY2880070 in patients with previously treated advanced PDAC.

PATIENTS AND METHODS

Patients with metastatic PDAC were treated with gemcitabine intravenously at 100 mg/m2 on days 1, 8, and 15, and LY2880070 50 mg orally twice daily on days 2-6, 9-13, and 16-20 of each 21-day cycle. Pretreatment tumor biopsies were obtained from each patient for correlative studies and generation of organoid cultures for drug sensitivity testing and biomarker analyses.

RESULTS

Eleven patients with PDAC were enrolled in the expansion cohort between August 27, 2020 and July 30, 2021. Four patients (36%) experienced drug-related grade 3 adverse events. No objective radiologic responses were observed, and all patients discontinued the trial by 3.2 months. In contrast to the lack of efficacy observed in patients, organoid cultures derived from biopsies procured from two patients demonstrated strong sensitivity to the gemcitabine/LY2880070 combination and showed treatment-induced upregulation of replication stress and DNA damage biomarkers, including pKAP1, pRPA32, and γH2AX, as well as induction of replication fork instability.

CONCLUSIONS

No evidence of clinical activity was observed for combined low-dose gemcitabine and LY2880070 in this treatment-refractory PDAC cohort. However, the gemcitabine/LY2880070 combination showed in vitro efficacy, suggesting that drug sensitivity for this combination in organoid cultures may not predict clinical benefit in patients.

Phase II Study of Olaparib and Temozolomide for Advanced Uterine Leiomyosarcoma (NCI Protocol 10250)

PURPOSE

Uterine leiomyosarcoma (uLMS) is an aggressive subtype of soft-tissue sarcoma with frequent metastatic relapse after curative surgery. Chemotherapy provides limited benefit for advanced disease. Multiomics profiling studies have identified homologous recombination deficiency in uLMS. In preclinical studies where olaparib and temozolomide provided modest activity, the combination was highly effective for inhibiting uLMS tumor growth.

PATIENTS AND METHODS

NCI Protocol 10250 is a single-arm, open-label, multicenter, phase II study evaluating olaparib and temozolomide in advanced uLMS. Patients with progression on ≥1 prior line received temozolomide 75 mg/m2 orally once daily with olaparib 200 mg orally twice a day both on days 1-7 in 21-day cycles. The primary end point was the best objective response rate (ORR) within 6 months. A one-stage binomial design was used. If ≥5 of 22 responded, the treatment would be considered promising (93% power; α = .06). All patients underwent paired biopsies that were evaluated with whole-exome sequencing (WES)/RNAseq and a RAD51 foci formation assay.

RESULTS

Twenty-two patients were evaluable. The median age was 55 years, and 59% had received three or more prior lines. Best ORR within 6 months was 23% (5 of 22). The overall ORR was 27% (6 of 22). The median progression-free survival (mPFS) was 6.9 months (95% CI, 5.4 months to not estimable). Hematologic toxicity was common (grade 3/4 neutropenia: 75%; thrombocytopenia: 32%) but manageable with dose modification. Five of 16 (31%) of tumors contained a deleterious homologous recombination gene alteration by WES, and 9 of 18 (50%) were homologous recombination-deficient by the RAD51 assay. In an exploratory analysis, mPFS was prolonged for patients with homologous recombination-deficient versus homologous recombination-proficient tumors (11.2 v 5.4 months, P = .05) by RAD51.

CONCLUSION

Olaparib and temozolomide met the prespecified primary end point and provided meaningful clinical benefit in patients with advanced, pretreated uLMS.

Abstract 6210: Combination of M1774 and niraparib can overcome ATR and PARP inhibitor resistance in BRCA1 mutated ovarian cancer models

PARP inhibitors are being used in maintenance treatment of BRCA-mutated high-grade serous ovarian cancer (HGSOC). However, de novo and acquired resistance to PARP inhibitors, resulting from restoration of homologous recombination repair or stabilization of replication forks, is a pressing clinical problem. ATR inhibitors are known to reverse both of these mechanisms of PARP inhibitor resistance and are currently in clinical development. In this study, we assessed the activity of a novel ATR inhibitor, M1774, as a monotherapy and in combination with PARP inhibition in HGSOC preclinical models. M1774 exhibited single-agent activity across a panel of ovarian cancer cell lines with induction of DNA damage. We used a panel of BRCA1-mutated patient-derived xenograft (PDX) models of HGSOC with acquired PARP inhibitor resistance and identified two M1774-sensitive models and one M1774-resistant model. M1774 monotherapy demonstrated anti-tumor activity in mice bearing sensitive PDX models of HGSOC with PARP inhibitor resistance. In the M1774-sensitive models, the combination of M1774 and niraparib augmented the degree and durability of response compared with M1774 monotherapy. The combination of M1774 and niraparib also demonstrated synergistic anti-tumor activity in the M1774-resistant model, indicating that the combination could overcome monotherapy resistant to either agent. We also generated organoid cultures from these PDX models. Treatment of the organoid models with M1774, niraparib or the combination faithfully recapitulated the anti-tumor activities seen in vivo. Mechanistically, M1774-resistant organoid cultures demonstrated stable replication forks and an absence of replication stress. The combination of M1774 with niraparib resulted in destabilization of the replication forks. In contrast, M1774-sensitive organoids exhibited unstable replication forks, which were further destabilized by the niraparib combination. In addition, the sensitive models demonstrated higher basal levels of replication stress, as detected by increased levels of phospho-RPA. Collectively, these results indicate that the combination of M1774 and niraparib can overcome PARP inhibitor resistance and ATR inhibitor resistance in BRCA1-mutant ovarian cancer PDX models and demonstrate the utility of organoid cultures for discerning mechanisms of resistance and strategies to restore drug sensitivity. Combined M1774-mediated ATR inhibition and PARP inhibition may be a promising therapeutic strategy for the treatment of ovarian cancer.

Citation Format: Jie Hao, Arindam Bose, Golbahar Sadatrezaei, David B. Martignetti, Yuqing Jiao, Alexandre André B. da Costa, Jean-Bernard Lazaro, Bose Kochupurakkal, Huy Nguyen, Kalindi Parmar, Alan D. D’Andrea, Geoffrey I. Shapiro. Combination of M1774 and niraparib can overcome ATR and PARP inhibitor resistance in BRCA1 mutated ovarian cancer models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6210.

A phase Ia/Ib study of talazoparib in combination with tazemetostat in metastatic castration-resistant prostate cancer (mCRPC)

TPS5098

Background: Enhancer of zeste homolog 2 (EZH2) is frequently overexpressed in metastatic castration-resistant prostate cancer (mCRPC), and is linked to lineage plasticity and therapy resistance. In pre-clinical studies, EZH2 directly regulates DNA damage repair (DDR) gene expression, and pharmacologic inhibition of EZH2 sensitizes prostate cancer cells to genotoxic stress as induced by poly-ADP ribose polymerase (PARP) inhibition. The PARP inhibitor talazoparib and EZH2 inhibitor tazemetostat are currently under study in mCRPC, and we are conducting a Phase 1 clinical trial of the combination. Methods: Phase 1a of the study will define the recommended phase 2 dose (RP2D) and Phase 1b will better assess safety and preliminary clinical activity of the combination at the RP2D. Eligible patients must have progressive disease after at least one secondary hormonal therapy and taxane-based chemotherapy (or felt not to be more appropriate for taxane), have disease evaluable for response (PSA ≥ 2 ng/ml or measurable disease by RECIST 1.1) and have a metastatic lesion amenable to biopsy adequate for next generation sequencing. In Phase 1a (n = 9-18), the starting doses are talazoparib 0.75 mg daily and tazemetostat 600 mg BID, with dose escalation/de-escalation of both agents by up to 2 dose levels [DLs] based on a 3+3 design. The RP2D is the maximum tolerated dose (MTD) or DL +2 (talazoparib 1 mg daily + tazemetostat 800 mg BID) if the MTD is not reached. After 6 patients are treated at the RP2D, phase 1b will enroll an additional 20 patients to an expansion cohort. The primary endpoint of safety and tolerability is based on incidence of dose-limiting toxicities [DLTs] and incidence and grade of adverse events [AEs] by CTCAE version 5.0. For the secondary endpoint of overall response rate (ORR; defined as PSA reduction by ≥ 50% OR radiographic response by RECIST 1.1), with a sample size of 26 (6 patients from dose escalation and 20 from expansion), we deem talazoparib+tazemetostat effective if ORR is ≥ 5/26 (19%). The probability of concluding that the treatment strategy effective is 0.11 if its true response rate is 10% and at least 0.93 if the true response rate exceeds 30%. Mandatory pre-treatment and on-treatment (8-week) biopsies will undergo targeted genetic sequencing, transcriptomic profiling, ChIP (Chromatin ImmunoPrecipitation)-seq, and immunohistochemistry (IHC) for DDR and differentiation markers; blood specimens will undergo circulating cell-free DNA and circulating tumor cell profiling – these studies will nominate possible predictive biomarkers for therapeutic response and serve as pharmacodynamic markers of combined PARP and EZH2 inhibition. The goal of this study is to expand treatment options in mCRPC through a novel approach to exploit EZH2 as a therapeutic target through co-targeting the DDR response. Enrollment began in July 2021. Clinical trial information: NCT04846478.

Correlative results from NCI protocol 10250: A phase II study of temozolomide and olaparib for the treatment of advanced uterine leiomyosarcoma

11509

Background: uLMS is an aggressive sarcoma subtype of smooth muscle origin. Chemotherapy provides limited benefit for advanced disease. 18-25% of uLMS harbor deleterious alterations in homologous recombination (HR) DNA repair genes. uLMS exhibits high levels of replicative stress. These findings prompted a phase 2 study of O+T in pretreated uLMS where O+T demonstrated activity: ORR 27%, mPFS 6.9 mos (Ingham M. et. al. ASCO 2021: #11506) Methods: NCI protocol #10250 is a single-arm, multicenter, phase 2 trial evaluating O+T in advanced uLMS pts with progression on ≥1 prior line. Pre-treatment (Pre) and on-treatment (On) biopsies were collected from 22 pts. In prespecified analysis, we evaluated for a relationship between clinical outcomes and HR gene alterations by whole exome sequencing (WES), SLFN11/MGMT expression by RNAseq, and RAD51 foci formation (functional assay). HRD scores were calculated from WES using scarHRD. Gene expression was evaluated using a Spearman rank-order correlation analysis to identify genes associated with PFS (p < 0.01) and overexpressed in sensitive (S: PFS > 240d) or resistant (R: PFS < 240d) pts. Gene set enrichment analysis (GSEA) was performed (q = FDR-adjusted p value). Pts with available results: WES/RNAseq (16), Pre HRD score (13), Pre RAD51 foci (12). Results: 31% (5/16) pts had a mutation (Mut) or homozygous deletion (Hd) in the HR panel: ATRX Mut (2), ATR Mut, PALB2 Hd, RAD51B Hd. Pts with PALB2 and RAD51B Hd had longest PFS on study. Recurrent alterations also occurred in TP53 (56%) and RB1 (19%). Median HRD score in Pre samples was 51 (range 36-66) and 10/13 had HRD scores ≥ 42. Pre and On SLFN11 and MGMT RNA expression were not correlated with ORR/PFS. 6/13 Pre samples were HR-deficient by the RAD51 foci assay. Of pts with PFS ≥ 200d, 4/6 were HR-deficient. In Pre samples, 81 genes were overexpressed in S pts and 73 in R pts. In On samples, 146 genes were overexpressed in S pts and 127 in R pts. In On samples, GSEA identified the epithelial-mesenchymal transition enriched in S pts (q = 3.38e-7) and cell cycle pathways (E2F targets, G2M checkpoint) in R pts (q = 7.43e-4). Only 2 genes, CXCL10 and PCDH15, were differentially expressed between paired Pre and On samples (both increased in On). Gene expression signatures for replicative stress showed borderline association with worse PFS. Conclusions: Most uLMS tumors exhibit HR defects as measured by HRD scores. A subset of pts with greater benefit from O+T were identified by WES for HR genes and the RAD51 assay. There was no correlation between SLFN11 and MGMT expression and outcomes. GSEA identified pathways differentially expressed in S and R pts in On samples. O+T induced CXCL10 which has been associated with T-cell trafficking to tumors. A randomized phase 3 trial of O+T versus investigator’s choice is planned. These results provide insight into which pts may benefit most from this novel drug combination. Clinical trial information: NCT03880019.

A phase Ia/Ib study of talazoparib in combination with tazemetostat in metastatic castration-resistant prostate cancer (mCRPC)

TPS195

Background: Enhancer of zeste homolog 2 (EZH2) is frequently overexpressed in metastatic castration-resistant prostate cancer (mCRPC), and is linked to lineage plasticity and therapy resistance. In pre-clinical studies, EZH2 directly regulates DNA damage repair (DDR) gene expression, and pharmacologic inhibition of EZH2 sensitizes prostate cancer cells to genotoxic stress as induced by poly-ADP ribose polymerase (PARP) inhibition. The PARP inhibitor talazoparib and EZH2 inhibitor tazemetostat are currently under study in mCRPC, and we are conducting a phase 1 clinical trial of the combination. Methods: Phase 1a of the study will define the recommended phase 2 dose (RP2D) and phase 1b will better assess safety and preliminary clinical activity of the combination at the RP2D. Eligible patients must have progressive disease after at least one secondary hormonal therapy and taxane-based chemotherapy (or felt not to be more appropriate for taxane), have disease evaluable for response (PSA ≥ 2 ng/ml or measurable disease by RECIST 1.1) and have a metastatic lesion amenable to biopsy adequate for next generation sequencing. In phase 1a (n=9-18), the starting doses are talazoparib 0.75 mg daily and tazemetostat 600 mg BID, with dose escalation/de-escalation of both agents by up to 2 dose levels [DLs] based on a 3+3 design. The RP2D is the maximum tolerated dose (MTD) or DL +2 (talazoparib 1 mg daily + tazemetostat 800 mg BID) if the MTD is not reached. After 6 patients are treated at the RP2D, phase 1b will enroll an additional 20 patients to an expansion cohort. The primary endpoint of safety and tolerability is based on incidence of dose-limiting toxicities [DLTs] and incidence and grade of adverse events [AEs] by CTCAE version 5.0. For the secondary endpoint of overall response rate (ORR; defined as PSA reduction by ≥ 50% OR radiographic response by RECIST 1.1), with a sample size of 26 (6 patients from dose escalation and 20 from expansion), we deem talazoparib+tazemetostat effective if ORR is ≥ 5/26 (19%). The probability of concluding that the treatment strategy effective is 0.11 if its true response rate is 10% and at least 0.93 if the true response rate exceeds 30%. Mandatory pre-treatment and on-treatment (8-week) biopsies will undergo targeted genetic sequencing, transcriptomic profiling, ChIP (Chromatin ImmunoPrecipitation)-seq, and immunohistochemistry (IHC) for DDR and differentiation markers; blood specimens will undergo circulating cell-free DNA and circulating tumor cell profiling – these studies will nominate possible predictive biomarkers for therapeutic response and serve as pharmacodynamic markers of combined PARP and EZH2 inhibition. The goal of this study is to expand treatment options in mCRPC through a novel approach to exploit EZH2 as a therapeutic target through co-targeting the DDR response. Enrollment began in July 2021. Clinical trial information: NCT04846478.

Phase 1 Combination Study of the CHK1 Inhibitor Prexasertib and the PARP Inhibitor Olaparib in High-grade Serous Ovarian Cancer and Other Solid Tumors

PURPOSE

Checkpoint kinase 1 (CHK1) plays a central role in the response to replication stress through modulation of cell-cycle checkpoints and homologous recombination (HR) repair. In BRCA-deficient cancers with de novo or acquired PARP inhibitor resistance, the addition of the CHK1 inhibitor prexasertib to the PARP inhibitor olaparib compromises replication fork stability, as well as HR proficiency, allowing for sensitization to PARP inhibition.

PATIENTS AND METHODS

This study followed a 3+3 design with a 7-day lead-in of olaparib alone, followed by 28-day cycles with prexasertib administered on days 1 and 15 in combination with an attenuated dose of olaparib on days 1-5 and 15-19. Pharmacokinetic blood samples were collected after olaparib alone and following combination therapy. Patients enrolled to the expansion phase of the study underwent paired tumor biopsies for pharmacodynamic (PD) assessments.

RESULTS

Twenty-nine patients were treated. DLTs included grade 3 neutropenia and grade 3 febrile neutropenia. The MTD/recommended phase 2 dose (RP2D) was prexasertib at 70 mg/m² i.v. with olaparib at 100 mg by mouth twice daily. Most common treatment-related adverse events included leukopenia (83%), neutropenia (86%), thrombocytopenia (66%), and anemia (72%). Four of 18 patients with BRCA1-mutant, PARP inhibitor-resistant, high-grade serous ovarian cancer (HGSOC) achieved partial responses. Paired tumor biopsies demonstrated reduction in RAD51 foci and increased expression of γ-H2AX, pKAP1, and pRPA after combination exposure.

CONCLUSIONS

Prexasertib combined with olaparib has preliminary clinical activity in BRCA-mutant patients with HGSOC who have previously progressed on a PARP inhibitor. PD analyses show that prexasertib compromises HR with evidence of induction of DNA damage and replication stress.

A first-in-class Polymerase Theta Inhibitor selectively targets Homologous-Recombination-Deficient Tumors

DNA polymerase theta (POLθ) is synthetic lethal with Homologous Recombination (HR) deficiency and thus a candidate target for HR-deficient cancers. Through high-throughput small molecule screens we identified the antibiotic Novobiocin (NVB) as a specific POLθ inhibitor that selectively kills HR-deficient tumor cells in vitro and in vivo. NVB directly binds to the POLθ ATPase domain, inhibits its ATPase activity, and phenocopies POLθ depletion. NVB kills HR-deficient breast and ovarian tumors in GEMM, xenograft and PDX models. Increased POLθ levels predict NVB sensitivity, and BRCA-deficient tumor cells with acquired resistance to PARP inhibitors (PARPi) are sensitive to NVB in vitro and in vivo. Mechanistically, NVB-mediated cell death in PARPi-resistant cells arises from increased double-strand break end resection, leading to accumulation of single-strand DNA intermediates and non-functional RAD51 foci. Our results demonstrate that NVB may be useful alone or in combination with PARPi in treating HR-deficient tumors, including those with acquired PARPi resistance. (151/150).

A phase 2 study of berzosertib (M6620) in combination with carboplatin compared with docetaxel in combination with carboplatin in metastatic castration-resistant prostate cancer

5034

Background: Alterations in DNA damage repair (DDR) genes are common in metastatic castration-resistant prostate cancer (mCRPC), and are implicated in responses to carboplatin [carbo], PARP inhibitors and immunotherapeutics. Inhibitors of the ATR kinase, which is involved in the DDR response, have been demonstrated to have synergistic activity with platinum compounds in preclinical models. We therefore conducted a phase 2 study of the ATR inhibitor berzosertib [berzo]+carbo vs. docetaxel [doce]+carbo in mCRPC. Methods: Patients (pts) previously treated with at least one secondary hormonal therapy and taxane underwent mandatory pre-treatment biopsy and were randomized 1:1 to receive Arm A (doce 60 mg/m2 day 1 + carbo AUC 4 day 1) or Arm B (berzo 90 mg/m2 days 2,9 + carbo AUC 5 day 1) every 21 days. Pts randomized to Arm A who were not candidates for doce received carbo AUC 5 monotherapy. Stratification factors were 1) prior PARP inhibitor (yes vs. no) and 2) evaluable disease by RECIST 1.1 (yes vs. no). Pts on Arm A crossed over to Arm B (berzo+carbo) at the earlier of PSA or radiographic progression. The primary endpoint was overall response rate (ORR; PSA reduction by ≥ 50% or radiographic response by RECIST 1.1). Secondary endpoints included time to PSA progression, radiographic PFS (rPFS), PFS by PCWG3 criteria, and adverse events (AEs) in each arm. Planned enrollment was 136 pts (for 130 to be treated), with interim analysis for futility after 65 pts were treated. Results: 73 pts were randomized between 6/2019 and 7/2020; 34 pts were treated on Arm A (26 carbo+doce; 8 carbo alone) and 31 on Arm B. Median number of prior systemic therapies (excluding ADT, 5α-reductase inhibitors, 1st generation antiandrogens) was 4 (range 2-8). Median treatment duration was 3 cycles, and 4 pts in each arm discontinued for AEs. Grade 3 or higher treatment-related AEs (TrAE) were seen in 13(38%) pts in Arm A and 21(68%) in Arm B. Pts in Arm B had greater frequency of grade 3-4 thrombocytopenia (8[26%] vs. 3[9%]). 1 pt in Arm B had grade 5 sepsis attributed to study treatment. ORR was 15% in Arm A (5/34; 5/26[19%] in pts who received carbo+doce) and 0% in Arm B (0/31). 14 pts in Arm A crossed over, with no subsequent responses seen. Median rPFS was 2.1(95% CI:2.0,3.2) mo in Arm A and 2.4(1.9,4.2) mo in Arm B. At planned interim analysis, trial enrollment and crossover to Arm B were halted due to futility. Conclusions: Carbo+berzo led to fewer overall responses and a higher rate of grade 3 or higher TrAEs compared to carbo+doce. All responses seen were in pts who received carbo+doce despite requirement for prior progression on taxane, suggesting that this combination is favored over carbo+berzo or carbo monotherapy in a heavily pre-treated biomarker-unselected population. Extensive genetic and molecular studies for DDR assessment from tissue and cfDNA are in progress. Clinical trial information: NCT03517969.

NCI protocol 10250: A phase II study of temozolomide and olaparib for the treatment of advanced uterine leiomyosarcoma

11506

Background: Uterine leiomyosarcoma (uLMS) is an aggressive sarcoma subtype with frequent metastatic relapse. After failure of front-line chemotherapy, remaining options provide limited benefit (trabectedin: ORR 11%, mPFS 4.0 mos; pazopanib: ORR 11%, median PFS 2.9 mos; dacarbazine: ORR 9%, mPFS 1.5 mos). Recent molecular studies suggest uLMS harbors characteristic defects in the homologous recombination (HR) DNA repair pathway, including somatic biallelic BRCA2 deletion in 10%, implicating potential sensitivity to PARP-inhibitor based treatment approaches. In preclinical uLMS models in which temozolomide (T, an oral equivalent to dacarbazine) or the PARP inhibitor olaparib (O) showed limited single agent activity, the combination of T + O was highly effective in inhibiting uLMS tumor growth and promoting apoptosis. Methods: NCI protocol #10250 is a single-arm, open-label, multi-center phase II study evaluating T + O in advanced uLMS. Pts had progression on ≥ 1 prior line and ECOG PS ≤ 2. Pts received T 75 mg/m2 PO daily + O 200 mg PO BID days 1-7 in 21-day cycles. Primary endpoint was ORR. A one-stage binomial design was used. If ≥ 5/22 responded, the treatment was considered promising (95% power; α = 0.06). All pts underwent paired tumor biopsies. Correlative assays to evaluate for HR deficiency (whole exome sequencing/RNAseq, RAD51 foci formation) and for intrinsic PARP inhibitor resistance (SLFN11 expression) will be correlated with response. Results: 22 patients were evaluable (median age 55, median prior treatment lines 3). Median follow-up was 10.8 mos. Primary endpoint, ORR within 6 mos of initiating treatment, was 23% (5/22). Overall ORR was 27% (6/22). Median PFS was 6.9 mos (95% CI: 5.4 mos – not estimable (NE)). Median duration of response (DOR) was 12.0 mos (95% CI: 9.5 mos – NE). Hematologic toxicity was common (grade 3/4 neutropenia, 77%; thrombocytopenia 32%) but manageable with dose modification. Correlative assays are ongoing with plans to present at the meeting. An immunohistochemical assay for RAD51 foci has been adapted for uLMS samples and clearly distinguishes BRCA2- deleted and wild-type tumors. Conclusions: NCI 10250 met the prespecified primary efficacy endpoint of ORR in a population of patients with heavily pre-treated uLMS. Responses are durable (median DOR 12 mos). Correlative assays are being completed to evaluate whether uLMS tumors with HR deficiency or with preserved SLFN11 expression are most sensitive to T + O and may underlie durable responses. A randomized study of the combination is planned. Clinical trial information: NCT03880019.

Clinical Efficacy and Molecular Response Correlates of the WEE1 Inhibitor Adavosertib Combined with Cisplatin in Patients with Metastatic Triple-Negative Breast Cancer

PURPOSE

We report results from a phase II study assessing the efficacy of the WEE1 inhibitor adavosertib with cisplatin in metastatic triple-negative breast cancer (mTNBC).

PATIENTS AND METHODS

Patients with mTNBC treated with 0-1 prior lines of chemotherapy received cisplatin 75 mg/m2 i.v. followed 21 days later by cisplatin plus adavosertib 200 mg oral twice daily for five doses every 21 days. The study had 90% power to detect the difference between null (20%) and alternative (40%) objective response rates (ORR) with a one-sided type I error of 0.1: an ORR >30% was predefined as making the regimen worthy of further study. RNA sequencing and multiplex cyclic immunofluorescence on pre- and post-adavosertib tumor biopsies, as well as targeted next-generation sequencing on archival tissue, were correlated with clinical benefit, defined as stable disease ≥6 months or complete or partial response.

RESULTS

A total of 34 patients initiated protocol therapy; median age was 56 years, 2 patients (6%) had BRCA2 mutations, and 14 (41%) had one prior chemotherapy. ORR was 26% [95% confidence interval (CI), 13-44], and median progression-free survival was 4.9 months (95% CI, 2.3-5.7). Treatment-related grade 3-5 adverse events occurred in 53% of patients, most commonly diarrhea in 21%. One death occurred because of sepsis, possibly related to study therapy. Tumors from patients with clinical benefit demonstrated enriched immune gene expression and T-cell infiltration.

CONCLUSIONS

Among patients with mTNBC treated with 0-1 prior lines, adavosertib combined with cisplatin missed the prespecified ORR cutoff of >30%. The finding of immune-infiltrated tumors in patients with clinical benefit warrants validation.

A phase II study of M6620 in combination with carboplatin compared with docetaxel in combination with carboplatin in metastatic castration-resistant prostate cancer

TPS5597

Background: Alterations in DNA damage repair genes are common in metastatic castration-resistant prostate cancer (mCRPC), and are implicated in responses to carboplatin, PARP inhibitors and immunotherapeutics. The ATR kinase is involved in the DNA damage response, and ATR inhibitors have been demonstrated in preclinical models to have synergistic activity with platinum compounds due to induction of replication stress. Methods: This is a randomized open-label Phase 2 study of the ATR inhibitor M6620 + carboplatin vs. docetaxel + carboplatin in mCRPC. Patients (pts) previously treated with at least one secondary hormonal therapy and taxane-based chemotherapy undergo mandatory pre-treatment biopsy and are randomized 1:1 to receive Arm A (docetaxel 60 mg/m2 day 1 + carboplatin AUC 4 day 1) or Arm B (M6620 90 mg/m2 days 2,9 + carboplatin AUC 5 day 1) every 21 days. Pts randomized to Arm A who are not candidates for docetaxel receive carboplatin AUC 5 monotherapy. Stratification factors are 1) prior PARP inhibitor (yes vs. no) and 2) evaluable disease by RECIST 1.1 (yes vs. no). Pts on Arm A crossover to Arm B (M6620+carboplatin) at the earlier of PSA or radiographic progression. For the primary endpoint of overall response rate (ORR; PSA reduction by ≥ 50% or radiographic response by RECIST 1.1), with 65 pts on each arm (total N = 130), there will be 80% power to distinguish ORR of 40% vs. 20% using a chi-square test (one sided α = 0.05). 136 pts will be enrolled to account for 5% dropout. Secondary endpoints include time to PSA progression, radiographic PFS, PFS by PCWG3 criteria, safety and adverse events in each arm. Biomarker studies include whole exome sequencing, RAD51 focus formation, and ATM IHC from tumor specimens. Circulating cell-free DNA from pre-treatment and progression plasma specimens will undergo ultra-low pass whole genome sequencing and deep targeted sequencing. The goal of this study is to expand therapeutic options in mCRPC through a novel approach to targeting the DNA damage response, and to identify biomarkers associating with response and resistance to both standard and trial therapy. Enrollment began June 2019 (NCI/ETCTN #10191, NCT03517969). Clinical trial information: NCT03517969 .

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.

Reversion and non-reversion mechanisms of resistance to PARP inhibitor or platinum chemotherapy in BRCA1/2-mutant metastatic breast cancer

BACKGROUND

Little is known about mechanisms of resistance to poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) and platinum chemotherapy in patients with metastatic breast cancer and BRCA1/2 mutations. Further investigation of resistance in clinical cohorts may point to strategies to prevent or overcome treatment failure.

PATIENTS AND METHODS

We obtained tumor biopsies from metastatic breast cancer patients with BRCA1/2 deficiency before and after acquired resistance to PARPi or platinum chemotherapy. Whole exome sequencing was carried out on each tumor, germline DNA, and circulating tumor DNA. Tumors underwent RNA sequencing, and immunohistochemical staining for RAD51 foci on tumor sections was carried out for functional assessment of intact homologous recombination (HR).

RESULTS

Pre- and post-resistance tumor samples were sequenced from eight patients (four with BRCA1 and four with BRCA2 mutation; four treated with PARPi and four with platinum). Following disease progression on DNA-damaging therapy, four patients (50%) acquired at least one somatic reversion alteration likely to result in functional BRCA1/2 protein detected by tumor or circulating tumor DNA sequencing. Two patients with germline BRCA1 deficiency acquired genomic alterations anticipated to restore HR through increased DNA end resection: loss of TP53BP1 in one patient and amplification of MRE11A in another. RAD51 foci were acquired post-resistance in all patients with genomic reversion, consistent with reconstitution of HR. All patients whose tumors demonstrated RAD51 foci post-resistance were intrinsically resistant to subsequent lines of DNA-damaging therapy.

CONCLUSIONS

Genomic reversion in BRCA1/2 was the most commonly observed mechanism of resistance, occurring in four of eight patients. Novel sequence alterations leading to increased DNA end resection were seen in two patients, and may be targetable for therapeutic benefit. The presence of RAD51 foci by immunohistochemistry was consistent with BRCA1/2 protein functional status from genomic data and predicted response to later DNA-damaging therapy, supporting RAD51 focus formation as a clinically useful biomarker.

A phase II study of M6620 in combination with carboplatin compared with docetaxel in combination with carboplatin in metastatic castration-resistant prostate cancer

TPS252

Background: Alterations in DNA damage repair genes are common in metastatic castration-resistant prostate cancer (mCRPC), and are implicated in responses to carboplatin, PARP inhibitors and immunotherapeutics. The ATR kinase is involved in the DNA damage response, and ATR inhibitors have been demonstrated in preclinical models to have synergistic activity with platinum compounds due to induction of replication stress. Methods: This is a randomized open-label Phase 2 study of the ATR inhibitor M6620 + carboplatin vs. docetaxel + carboplatin in mCRPC. Patients (pts) previously treated with at least one secondary hormonal therapy and taxane-based chemotherapy undergo mandatory pre-treatment biopsy and are randomized 1:1 to receive Arm A (docetaxel 60 mg/m2 day 1 + carboplatin AUC 4 day 1) or Arm B (M6620 90 mg/m2 days 2,9 + carboplatin AUC 5 day 1) every 21 days. Pts randomized to Arm A who are not candidates for docetaxel receive carboplatin AUC 5 monotherapy. Stratification factors are 1) prior PARP inhibitor (yes vs. no) and 2) evaluable disease by RECIST 1.1 (yes vs. no). Pts on Arm A crossover to Arm B (M6620+carboplatin) at the earlier of PSA or radiographic progression. For the primary endpoint of overall response rate (ORR; PSA reduction by ≥ 50% or radiographic response by RECIST 1.1), with 65 pts on each arm (total N = 130), there will be 80% power to distinguish ORR of 40% vs. 20% using a chi-square test (one sided α = 0.05). 136 pts will be enrolled to account for 5% dropout. Secondary endpoints include time to PSA progression, radiographic PFS, PFS by PCWG3 criteria, safety and adverse events in each arm. Biomarker studies include whole exome sequencing, RAD51 focus formation, and ATM IHC from tumor specimens. Circulating cell-free DNA from pre-treatment and progression plasma specimens will undergo ultra-low pass whole genome sequencing and deep targeted sequencing. The goal of this study is to expand therapeutic options in mCRPC through a novel approach to targeting the DNA damage response, and to identify biomarkers associating with response and resistance to both standard and trial therapy. Enrollment began June 2019 (NCI/ETCTN #10191). Clinical trial information: NCT03517969.

Abstract P3-10-08: A phase II study of cisplatin and the Wee1 inhibitor adavosertib in metastatic triple-negative breast cancer (mTNBC)

Introduction: mTNBC progresses rapidly on first-line chemotherapy. For instance, in the TNT trial, median progression-free survival (PFS) was 3 months on first-line carboplatin. Selective inhibition of Wee1, a negative regulator of the G2 cell cycle checkpoint, may enhance the efficacy of DNA-damaging agents by reducing DNA damage repair. We report the results of the first phase II study assessing the efficacy of the Wee1 inhibitor adavosertib (AZD-1775) with cisplatin in mTNBC.

Methods: mTNBC patients (pts) with 0-1 prior lines of chemotherapy in the metastatic setting were eligible. Pts received cisplatin 75 mg/m2 IV followed by combination therapy 21 d later with cisplatin plus adavosertib 200 mg oral twice daily x 5 doses over 2.5 d every 21 d. Tumor biopsies were mandatory for patients with safely accessible tumors, and occurred 5-48 h after monotherapy and 5-8 h after the last adavosertib dose in the first combination therapy cycle. The study used a Simon optimal two-stage design that had 90% power to detect the difference between null (20%) and alternative (40%) response rates with a one-sided type I error of 0.1. The primary endpoint was objective response rate (ORR): an ORR &gt; 30% would identify the regimen as worthy of further study. Key secondary endpoints were PFS and overall survival (OS). Exploratory analyses evaluated the association of response, defined as clinical benefit rate (CBR) &gt; 6 months (CR + PR + SD &gt; 6 mos), with transcriptional and immunostaining profiles of on-treatment tumors (n = 16), as well as with targeted panel genomic alterations in archival tissue. Tumor immune cell composition was assessed by CIBERSORT.

Results: 34 pts initiated protocol therapy; median age was 56 yrs, 2 (6%) pts had known BRCA2 mutations, and 14 (41%) had 1 prior line of chemotherapy. Median follow-up was 13 mos. ORR was 29% (3 CR + 7 PR), median PFS 4.9 months (95% CI, 2.3-5.8 mos), CBR 35%, and preliminary OS 14.0 mos (95% CI, 11.8-21.8 mos). All-cause AEs occurred in 100% of pts (G3-4, 56%; most commonly diarrhea, 21%), including one death due to sepsis possibly related to study therapy. The primary tumor of the longest responding patient had a possible biallelic loss-of-function alteration (missense mutation and loss of heterozygosity) in the homologous recombination-related gene FANCM. In Hallmark gene set enrichment analyses of 26 on-treatment biopsies across 16 pts, responding tumors (n = 4) demonstrated enriched expression of immune response gene sets (allograft rejection FDR q &lt; 0.001, IL2-STAT5 signaling FDR q = 0.001, inflammatory response FDR q = 0.003), while non-responding tumors (n = 12) showed enrichment of cell cycle gene sets (E2F targets FDR q &lt; 0.001, G2M checkpoint FDR q &lt; 0.001). In the same on-treatment biopsies, responding tumors (n = 4) had higher tumor infiltrating lymphocytes (46% v. 29%, Mann-Whitney p = 0.04) and lower M0 macrophages (3% v. 17%, Mann-Whitney p = 0.04) than non-responding tumors (n =12). Updated data, including OS and tissue immunostaining results, will be presented.

Conclusions: Among mTNBC pts, the combination of adavosertib and cisplatin was associated with a 29% ORR, failing to meet the pre-determined ORR of &gt; 30% required to support further investigation. Responses were associated with immune-related gene expression and TILs detected by RNA sequencing.

Citation Format: Tanya E. Keenan, Zhenying Tan-Wasielewski, Lorenzo Trippa, Bose Kochupurakkal, Jennifer L. Guerriero, Rie K. Tahara, Grace Winship, Wafa Osmani, Chelsea Andrews, Jake R. Conway, Meng X He, Ricardo Pastorello, Adam Tracy, Robert E. Godin, Beth A. Overmoyer, Eric P. Winer, Elizabeth A. Mittendorf, Geoffrey I Shapiro, Eliezer M Van Allen, Sara M Tolaney. A phase II study of cisplatin and the Wee1 inhibitor adavosertib in metastatic triple-negative breast cancer (mTNBC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-10-08.

Abstract AP10: REAL-TIME ASSESSMENT OF HGSC DNA DAMAGE REPAIR DEFECTS AND DEFECT-INDUCED RESPONSE TO THERAPY IN OVARIAN CANCER ORGANOIDS

Patients with High Grade Serous Ovarian Cancer (HGSC) have limited therapeutic options. Immuno-oncologic (IO) agents have had limited effect. DNA damage repair gene mutations that may confer repair defects have been identified in up to 50% of HGSCs, making therapies that target repair defects, like PARP, CHK1, and ATR inhibitors, additional options. We have no means of predicting which patients will respond to any of these therapies.

A model system that allows for functional assays to assess for DNA damage repair defects, prediction of response to therapies targeting such defects, and assessment of the functionality of the tumor immune infiltrate and its response to IO agents is needed. Organoids are three-dimensional structures derived from human normal or tumor tissue cells that anatomically and functionally mimic the developed human organ. Organoids mimicking the parent tumor from which they were derived have aided in the study of multiple tumor types. They are inexpensive and easily manipulated and may be an ideal model system for studying ovarian cancer.

We have devised a functional assay platform to profile the DNA damage repair capacity and immune targetability of short-term patient-derived HGSC organoids. The organoids mimic the tumors from which they were derived morphologically, molecularly, and genetically.

We have tested 33 organoid cultures derived from 21 HGSC patients for homologous recombination (HR) and replication fork protection capacity and compared the functional results to the tumor genomic profile. Regardless of repair gene mutational status, an HR functional defect in the organoids correlated with PARP inhibitor sensitivity. A fork protection functional defect correlated with carboplatin, and ATR and CHK1 inhibitor sensitivity. Importantly, this work has led to the discovery of potential therapeutic combinations, such as a CHK1 inhibitor plus carboplatin or gemcitabine that may be useful in treating tumors otherwise resistant to most therapies. Drugs such as carboplatin or gemcitabine can synergize with a CHK1 inhibitor by enhancing replication stress and fork deprotection.

In parallel, we have immune phenotyped the parent tumors and organoid cultures from 15 patients, and shown that the organoid cultures retain lymphocytes expressing relevant IO receptors in the short term. Upon treatment with carboplatin, olaparib, and pembrolizumab as single agents or in combination, we detect changes in IO receptor expression and production of different cytokines in the cultures, suggesting an immune response induced by these agents. We have detected receptor and cytokine alterations that would create an immune suppressive environment with specific drug combinations in tumors with specific repair defects, suggesting that these may be inappropriate combinations for harnessing the immune system in tumors with specific repair capacities.

Continued combined immune and DNA damage repair phenotyping analyses of the organoids will lead to a better understanding of which mechanistic defects are needed to confer sensitivity to DNA damage repair agents, what functional properties and immune milieu lead to sensitivity to IO agents, and how best to combine such therapies. In addition, through further correlation with patient responses over time, HGSC organoids may become a useful tool for rapidly predicting patient response to therapeutic agents.

Citation Format: Sarah J. Hill, Brennan Decker, Emma A. Roberts, Chunyu Yang, Neil S. Horowitz, Michael G. Muto, Michael J. Worley Jr., Colleen M. Feltmate, Marisa R. Nucci, Elizabeth M. Swisher, Ryuji Morizane, Bose Kochupurakkal, Khanh T. Do, Panagiotis Konstantinopoulos, Joyce F. Liu, Joseph V. Bonventre, Ursula A. Matulonis, Geoffrey I. Shapiro, Ross S. Berkowitz, Christopher P. Crum, and Alan D. D'Andrea. REAL-TIME ASSESSMENT OF HGSC DNA DAMAGE REPAIR DEFECTS AND DEFECT-INDUCED RESPONSE TO THERAPY IN OVARIAN CANCER ORGANOIDS [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 AP10.

Fanconi-BRCA pathway mutations in childhood T-cell acute lymphoblastic leukemia

BRCA2 (also known as FANCD1) is a core component of the Fanconi pathway and suppresses transformation of immature T-cells in mice. However, the contribution of Fanconi-BRCA pathway deficiency to human T-cell acute lymphoblastic leukemia (T-ALL) remains undefined. We identified point mutations in 9 (23%) of 40 human T-ALL cases analyzed, with variant allele fractions consistent with heterozygous mutations early in tumor evolution. Two of these mutations were present in remission bone marrow specimens, suggesting germline alterations. BRCA2 was the most commonly mutated gene. The identified Fanconi-BRCA mutations encode hypomorphic or null alleles, as evidenced by their inability to fully rescue Fanconi-deficient cells from chromosome breakage, cytotoxicity and/or G2/M arrest upon treatment with DNA cross-linking agents. Disabling the tumor suppressor activity of the Fanconi-BRCA pathway is generally thought to require biallelic gene mutations. However, all mutations identified were monoallelic, and most cases appeared to retain expression of the wild-type allele. Using isogenic T-ALL cells, we found that BRCA2 haploinsufficiency induces selective hypersensitivity to ATR inhibition, in vitro and in vivo. These findings implicate Fanconi-BRCA pathway haploinsufficiency in the molecular pathogenesis of T-ALL, and provide a therapeutic rationale for inhibition of ATR or other druggable effectors of homologous recombination.

Functional profiling of nucleotide Excision repair in breast cancer

Homologous recombination deficiency conferred by alterations in BRCA1 or BRCA2 are common in breast tumors and can drive sensitivity to platinum chemotherapy and PARP inhibitors. Alterations in nucleotide excision repair (NER) activity can also impact sensitivity to DNA damaging agents, but NER activity in breast cancer has been poorly characterized. Here, we apply a novel immunofluorescence-based cellular NER assay to screen a large panel of breast epithelial and cancer cell lines. Although the majority of breast cancer models are NER proficient, we identify an example of a breast cancer cell line with profound NER deficiency. We show that NER deficiency in this model is driven by epigenetic silencing of the ERCC4 gene, leading to lack of expression of the NER nuclease XPF, and that ERCC4 methylation is also strongly correlated with ERCC4 mRNA and XPF protein expression in primary breast tumors. Re-expression of XPF in the ERCC4-deficient breast cancer rescues NER deficiency and cisplatin sensitivity, but does not impact PARP inhibitor sensitivity. These findings demonstrate the potential to use functional assays to identify novel mechanisms of DNA repair deficiency and nominate NER deficiency as a platinum sensitivity biomarker in breast cancer.

Abstract CT050: Expansion cohort of Phase I study of oral sapacitabine and oral seliciclib in patients with metastatic breast cancer and BRCA1/2 mutations

Introduction: Sapacitabine, a nucleoside analog, and seliciclib, a cyclin-dependent kinase 2/9 inhibitor, constitute a novel oral regimen aimed at augmenting DNA damage and impairing cell cycle checkpoints. The initial phase I cohort investigating this combination demonstrated a 25% response rate in BRCA carriers. Hence, we developed an expansion cohort to assess the safety and efficacy of this regimen in patients with metastatic breast cancer and BRCA1/2 mutations.

Methods: We enrolled 20 patients with HER2-negative metastatic breast cancer and germline or somatic BRCA1/2 mutations, who were treated with sapacitabine 50 mg twice daily for days 1-7 followed by seliciclib 800 mg twice daily for days 8-10 of a 21-day cycle. Baseline or archival biopsies underwent RAD51 immunohistochemistry to assess for functional homologous recombination proficiency. Available tissue was sent for whole exome and transcriptome sequencing, and pre- and post-treatment blood was submitted for cell-free DNA sequencing to assess for genomic correlates of response.

Results: Participants received a median of 2 prior lines of chemotherapy for metastatic disease. Of the 9 patients who received a prior platinum agent, 6 progressed on this therapy. In addition to chemotherapy, 7 patients received and progressed on a prior PARP inhibitor. The overall response rate for sapacitabine and seliciclib in this cohort was 10%, consisting of 2 patients with partial responses lasting 4.7 and 9.0 months, respectively. The clinical benefit rate (CR + PR + SD ≥ 6 months) was 30%, and durations of stable disease ≥ 6 months ranged from 7.4 to 11.7 months. For all patients, median PFS was 3.7 months. The most frequent grade 3/4 adverse events were neutropenia (25% of patients), transaminitis (20%), and rash (10%). No patients who progressed on prior PARP inhibitor therapy and 6 of 13 patients (46%) with no history of PARP inhibitor resistance experienced clinical benefit (p = 0.052 by Fisher’s exact test). In contrast, 1 of 6 patients (17%) who progressed on prior platinum chemotherapy and 5 of 14 patients (36%) with no history of platinum resistance experienced clinical benefit (p = 0.61 by Fisher’s exact test). Notably, the tumors of some resistant patients harbored BRCA reversion mutations. Additional genomic analyses and RAD51 immunohistochemistry will be presented.

Conclusions: The combination of sapacitabine and seliciclib was safe and led to durable clinical benefit in some patients with metastatic breast cancer and BRCA1/2 mutations. Prior progression on PARP inhibitors predicted resistance to this combination, associated in some cases with BRCA reversion mutations. Based on these results, the combination of sapacitabine and the PARP inhibitor olaparib is now being investigated in patients with PARP-naïve metastatic HER2-negative breast cancer and germline BRCA1/2 mutations.

Citation Format: Tanya Keenan, David Liu, Haitham Elmarakeby, Daniel Stover, Bose Kochupurakkal, Adam Tracy, Elaine Danielczyk, Leilani Anderson, Chelsea Andrews, Brendan Reardon, Beth Overmoyer, Eric Winer, Daniella Zheleva, Judy Chiao, David Blake, Eliezer Van Allen, Geoffrey I. Shapiro, Sara Tolaney. Expansion cohort of Phase I study of oral sapacitabine and oral seliciclib in patients with metastatic breast cancer and BRCA1/2 mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT050.

Abstract CT128: Palbociclib in combination with fulvestrant or tamoxifen as treatment for hormone receptor positive metastatic breast cancer with prior chemotherapy for advanced disease (TBCRC 035): A Phase II study with pharmacodynamic markers

Background: Addition of the cyclin dependent kinase 4/6 inhibitor (CDK4/6i) palbociclib to endocrine therapy significantly improves progression free survival (PFS) in patients with HR+ MBC. The primary toxicity is neutropenia (ntp). TBCRC035 explored rates of neutropenia in patients with prior chemotherapy for MBC with 2 dose levels of palbociclib, and correlated changes in retinoblastoma protein phosphorylation (pRB) and Ki67 expression in proliferating keratinocytes and tumor, as well as mutations in cell-free DNA (cfDNA) with response.

Methods: TBCRC035 is a 1:1 randomized multicenter Phase II study evaluating palbociclib at either 125 or 100 mg in combination with physician choice fulvestrant or tamoxifen. Eligible patients (pts) with HR+ MBC had received 1-3 lines of chemotherapy for MBC, any number of hormone therapies, and were naïve to CDK4/6i. The primary endpoint was grade 3/4 ntp; secondary endpoints included PFS, clinical benefit rate (CBR), safety/tolerability, inhibition of RB phosphorylation (pRB) and change in Ki67 expression in skin and tumor (FFPE sections of skin and tumor biopsies) at day 14-21 of treatment compared to baseline, and correlation of response with mutations in cell free DNA (cfDNA). FFPE sections of skin punch and tumor biopsies were stained using antibodies to Ki67, total RB, and phospho-RB-S780 using BOND polymer red detection. Stained slides were scanned into the Aperio image analysis platform; the percentage of marker positive cells was determined. Whole blood was collected at baseline & processed for plasma; cfDNA was extracted. Using a combination of digital PCR and ultradeep next generation sequencing, cfDNA was analyzed for ESR1 and PIK3CA mutations.

Results: 70 pts were enrolled; 35 were randomized to 100 vs 125 mg of palbociclib respectively. 12 pts (100 mg), and 19 pts (125 mg) had &gt;1 episode of grade 3/4 ntp (p=0.091). Pts on 100 mg had fewer total episodes of grade 3/4 ntp (p=0.036). Dose reductions were more frequent in patients starting with 125 mg compared to those starting with 100 mg (12 vs6). CBR and PFS were similar (100 vs 125 mg; CBR: 67 vs 74%; PFS: 6.5 vs 10 mo,p=0.18). In skin and tumor, the % of Ki67-positive nuclei was significantly lower in post-treatment biopsies (p&lt;0.0001 for both) and was similarly reduced for pRb in skin, (tumor data pending); there was no significant difference in % change in pRB and Ki67 by palbociclib dose, or by CBR or PFS. Higher baseline tumor Ki67 was associated with worse PFS (p=0.006), regardless of dose. Presence of PIK3CA mutations in cfDNA correlated with worse PFS (p=0.008), but ESR1 mutations did not.

Conclusion: In pts with prior chemotherapy for HR+ MBC, treatment with 100 mg of palbociclib significantly reduced episodes of ntp and dose reductions; efficacy was comparable to patients treated with 125mg. Reductions in expression of Ki67 in tumor and keratinocytes and pRB in keratinocytes were comparable between dose levels indicating robust inhibition of CDK4/6 at both doses. The presence of PIK3CA mutations correlated with reduced PFS. These data suggest that dose reduction of palbociclib to mitigate toxicity should not compromise efficacy and provide additional prognostic information for use in treatment selection.

Citation Format: Hope S. Rugo, Erica Mayer, Anna Maria Storniolo, Claudine Isaacs, Ingrid Mayer, Vered Stearns, Rita Nanda, Julie Nangia, Michelle Melisko, Chiara Wabl, Alona Muzikansky, Bose Kochupurakkal, Ben H. Park, Antonio Wolff, Geoffrey Shapiro. Palbociclib in combination with fulvestrant or tamoxifen as treatment for hormone receptor positive metastatic breast cancer with prior chemotherapy for advanced disease (TBCRC 035): A Phase II study with pharmacodynamic markers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT128.

Abstract 368A: Functional assessment of DNA damage repair defects and the anti-tumor immune response in high grade serous ovarian cancers using patient-derived organoids

Patients with high grade serous ovarian cancer (HGSC) have limited additional therapeutic options beyond traditional carboplatin and paclitaxel. Immuno-oncologic (IO) agents have had limited effect, and despite the fact that 50% of HGSCs have genomic alterations in DNA damage repair genes, we still have no means of predicting which of these tumors actually harbor repair defects and will respond to these agents. Using patient-derived organoids which contain patient immune cells, we have developed functional assays to test the DNA damage repair capacity, anti-tumor immune response, and therapeutic vulnerability of HGSCs. These assays include testing for defects in the two key DNA damage repair pathways, homologous recombination (HR) and stalled replication fork protection, testing for activity and specificity of the immune cells in the cultures against the tumor cells when exacerbated by specific therapeutic combinations, and testing for therapeutic sensitivity to targeted and traditional chemotherapy agents and IO agents either alone or in rational combinations. In parallel, many of the tumors and organoids have undergone genomic and RNA sequencing, searching for relevant alterations to explain detected defects. Flow cytometry analysis of the parent tumors and short term (7-10 day) organoids reveal that organoids contain an immune milieu with IO receptor expression levels similar to the parent tumors. Upon treatment with IO agents alone or in combination with chemotherapeutic agents, we have found that specific IO receptor expression is altered, certain combinations lead to induction of cytokine expression that may repress an anti-tumor response, and that some combinations do not induce the expected cytotoxicity. The DNA damage repair functional assays have revealed that in HGSC, stalled fork protection defects are more common than HR defects, regardless of the repair gene mutational status of the tumors. Importantly, there is a wider array of therapies available to target these defects. For instance, organoids with unstable replication forks are more sensitive to ATR and CHK1 inhibitors. Organoids with stable forks are more sensitive to combinations of drugs which confer replication stress, such as the combination of a CHK1 inhibitor plus gemcitabine. Overall, the repair assays will allow for a better understanding of the types and mechanisms of repair defects present in tumors and a more accurate prediction of sensitivity to targeted agents. The immune functional assays will allow for a better mechanistic understanding of what response specific agents actually induce in immune and tumor cells and allow for better rational therapeutic pairings. Through assessment of a larger number of patients, we hope to demonstrate that these functional assays can have a clinical impact in rapidly predicting patient response.

Citation Format: Sarah J. Hill, Patrick Lizotte, Neil S. Horowitz, Michael G. Muto, Michael J. Worley, Colleen M. Feltmate, Bose Kochupurakkal, Khanh T. Do, Panagiotis Konstantinopoulos, Marisa R. Nucci, Joyce F. Liu, Ursula A. Matulonis, Geoffrey I. Shapiro, Ross S. Berkowitz, Christopher P. Crum, Alan D. D'Andrea. Functional assessment of DNA damage repair defects and the anti-tumor immune response in high grade serous ovarian cancers using patient-derived organoids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 368A.

Reversion and non-reversion mechanisms of resistance (MoR) to PARP inhibitor (PARPi) or platinum chemotherapy (chemotx) in patients (pts) with BRCA1/2-mutant metastatic breast cancer (MBC)

1085

Background: Little is known about MoR to PARPi and platinum chemotx in MBC pts with BRCA1/2 mutations. Biomarkers predictive of response/resistance have not been identified, but could have clinical utility. Methods: We obtained 8 BRCA-mutant metastatic tumor biopsies from MBC pts with acquired resistance to DNA-damaging tx (PARPi/platinum) on a prospective tissue collection protocol. In 7/8 patients, we also obtained pre-tx biopsies. Whole exome sequencing (WES) was performed on each tumor and on germline DNA from blood. We performed immunohistochemical (IHC) staining for RAD51 foci for functional assessment of intact homologous recombination (HR). Results: 4/7 pts with complete WES analysis acquired a somatic reversion mutation likely to result in functional BRCA1/2 protein in the post-tx tumor specimen after platinum (2 pts) or PARPi (2 pts; Table). 4/7 pts had plausible non-reversion MoR identified by WES, including alterations in genes involved in replication fork protection and DNA end resection. As expected, in all pts with genomic reversion, RAD51 foci were acquired in the post-resistance tumor, consistent with reconstitution of HR. In 2 pts without reversion, presence of RAD51 foci post-resistance was mixed. Reversion mutations occurred both with and without other alterations that could possibly lead to fork protection, suggesting > 1 MoR could occur in the same tumor. 3 pts whose tumors demonstrated RAD51 foci post-resistance were later re-exposed to DNA-damaging tx, to which all had intrinsic resistance. Conclusions: BRCA1/2 reversion was identified as a MoR in the majority of pts. WES identified potential novel MoR in fork protection and end resection genes. The presence of RAD51 foci by IHC was consistent with BRCA protein functional status from genomic data and predicted response to later DNA-damaging tx, suggesting RAD51 IHC may be a clinically useful biomarker. [Table: see text]

Olaparib and α-specific PI3K inhibitor alpelisib for patients with epithelial ovarian cancer: a dose-escalation and dose-expansion phase 1b trial

BACKGROUND

Based on preclinical work, we found that combination of poly (ADP-ribose) polymerase (PARP) inhibitors with drugs that inhibit the homologous recombination repair (HRR) pathway (such as PI3K inhibitors) might sensitise HRR-proficient epithelial ovarian cancers to PARP inhibitors. We aimed to assess the safety and identify the recommended phase 2 dose of the PARP inhibitor olaparib in combination with the PI3K inhibitor alpelisib in patients with epithelial ovarian cancer and in patients with breast cancer.

METHODS

In this multicentre, open-label, phase 1b trial following a 3 + 3 dose-escalation design, we recruited patients aged 18 years or older with the following key eligibility criteria: confirmed diagnosis of either recurrent ovarian, fallopian tube, or primary peritoneal cancer of high-grade serous histology; confirmed diagnosis of either recurrent ovarian, fallopian tube, or primary peritoneal cancer of any histology with known germline BRCA mutations; confirmed diagnosis of recurrent breast cancer of triple-negative histology; or confirmed diagnosis of recurrent breast cancer of any histology with known germline BRCA mutations. Additional patients with epithelial ovarian cancer were enrolled in a dose-expansion cohort. Four dose levels were planned: the starting dose level of alpelisib 250 mg once a day plus olaparib 100 mg twice a day (dose level 0); alpelisib 250 mg once a day plus olaparib 200 mg twice a day (dose level 1); alpelisib 300 mg once a day plus olaparib 200 mg twice a day (dose level 2); and alpelisib 200 mg once a day plus olaparib 200 mg twice a day (dose level 3). Both drugs were administered orally, in tablet formulation. The primary objective was to identify the maximum tolerated dose and the recommended phase 2 dose of the combination of alpelisib and olaparib for patients with epithelial ovarian cancer and patients with breast cancer. Analyses included all patients who received at least one dose of the study drugs. The trial is active, but closed to enrolment; follow-up for patients who completed treatment is ongoing. This trial is registered with ClinicalTrials.gov, number NCT01623349.

FINDINGS

Between Oct 3, 2014, and Dec 21, 2016, we enrolled 34 patients (28 in the dose-escalation cohort and six in the dose-expansion cohort); two in the dose-escalation cohort were ineligible at the day of scheduled study initiation. Maximum tolerated dose and recommended phase 2 dose were identified as alpelisib 200 mg once a day plus olaparib 200 mg twice a day (dose level 3). Considering all dose levels, the most common treatment-related grade 3-4 adverse events were hyperglycaemia (five [16%] of 32 patients), nausea (three [9%]), and increased alanine aminotransferase concentrations (three [9%]). No treatment-related deaths occurred. Dose-limiting toxic effects included hyperglycaemia and fever with decreased neutrophil count. Of the 28 patients with epithelial ovarian cancer, ten (36%) achieved a partial response and 14 (50%) had stable disease according to Response Evaluation Criteria in Solid Tumors 1.1.

INTERPRETATION

Combining alpelisib and olaparib is feasible with no unexpected toxic effects. The observed activity provides preliminary clinical evidence of synergism between olaparib and alpelisib, particularly in epithelial ovarian cancer, and warrants further investigation.

FUNDING

Ovarian Cancer Dream Team (Stand Up To Cancer, Ovarian Cancer Research Alliance, National Ovarian Cancer Coalition), Breast Cancer Research Foundation, Novartis.

Abstract PD2-12: Palbociclib in combination with fulvestrant or tamoxifen as treatment for hormone receptor positive (HR+) metastatic breast cancer (MBC) with prior chemotherapy for advanced disease (TBCRC 035) A phase II study with pharmacodynamics markers

Background

Addition of the cyclin dependent kinase 4/6 inhibitor (CDK4/6i) palbociclib to endocrine therapy in the first and later line settings significantly improves progression free survival (PFS) in patients with HR+ MBC. The primary toxicity is neutropenia without an increase in febrile neutropenia. TBCRC035 explored rates of neutropenia in patients who had received prior chemotherapy for MBC with 2 dose levels of palbociclib, and correlated changes in retinoblastoma protein phosphorylation (pRB) and Ki67 expression in proliferating keratinocytes and tumor with response.

Methods

TBCRC035 is a 1:1 randomized multicenter phase II study evaluating palbociclib at either 125 or 100 mg in combination with physician choice fulvestrant or tamoxifen. Eligible patients (pts) with HR+ MBC had received &gt;1 but &lt;3 lines of chemotherapy for MBC, any number of prior hormone therapies, and were naïve to CDK4/6i. The primary endpoint was grade 3/4 neutropenia; secondary endpoints included response, safety/tolerability, inhibition of pRB and change in Ki67 in skin and tumor at day 14-21 of treatment compared to baseline. FFPE sections of skin punch and tumor biopsies obtained before and on treatment were stained using antibodies to Ki67, total RB, and phospho-RB-S780 using BOND polymer red detection. Stained slides were scanned into the Aperio image analysis platform; the percentage of marker positive cells and H-score was determined.

Results

70 pts were enrolled (fully accrued); 35 randomized to 100 vs 125 mg of palbociclib respectively; data for the last 3 pts on the 125 mg arm is pending. Grade 3/4 neutropenia was more common in the 125 mg vs the 100 mg arm (56 vs 34%); dose adjustments for adverse events (AEs) occurred in 47 vs 43%, 4 vs 0 pts discontinued treatment due to AEs. Grade 3 febrile neutropenia was rare (1 patient each arm). Median duration of treatment was 5.2 vs 7.2 months. Response data and correlation with changes in pRB and Ki67 expression in skin and tumor by treatment arm will be reported.

Conclusion

In pts with prior chemotherapy for HR+ MBC, treatment with 100 mg of palbociclib in patients is associated with a lower rate of &gt; grade 3 neutropenia compared to 125 mg. Correlation of response by dose with pRB and Ki67 has the potential to inform palbociclib dosing and reduce toxicity for pts with HR+ MBC.

Citation Format: Rugo HS, Mayer EL, Storniolo AM, Isaacs C, Mayer I, Stearns V, Nanda R, Nangia J, Wabl C, Deluca A, Kochupurakkal B, Wolff AC, Shapiro GI. Palbociclib in combination with fulvestrant or tamoxifen as treatment for hormone receptor positive (HR+) metastatic breast cancer (MBC) with prior chemotherapy for advanced disease (TBCRC 035) A phase II study with pharmacodynamics markers [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD2-12.

Abstract 1620: ATR inhibition for the treatment of ATM-deficient gastric cancer

ATM and ATR are central kinases in the cellular response to DNA damage and play a crucial role in maintaining genome integrity. Inactivation of ATM has been observed in multiple tumor types and pre-clinical studies suggest that inhibition of ATR is synthetic-lethal in ATM-deficient tumors. More than 10% of gastric cancers carry potentially deleterious mutations in ATM and patients with ATM-deficient gastric cancers could potentially benefit from ATR inhibitor-based therapy. This study focuses on establishing the critical parameters for clinical development of ATR inhibitors in treating gastric cancer. First, we tested the cytotoxic response to ATR inhibition of ATM-deficient and ATM-complemented derivative of human fibroblasts. Next, we utilized a panel of gastric cancer cell lines that represent the spectrum of ATM mutations and ATM expression levels to further confirm the correlation between reduced ATM activity and the cytotoxic effects of ATR inhibition. Third, we evaluated the effect of a series of missense and truncating mutations in ATM that were identified in The Cancer Genome Atlas (TCGA) project. Finally, we developed an immunohistochemistry (IHC) assay to assess the expression level of ATM in gastric tumor samples. Our results confirmed that ATM-deficient human fibroblasts were acutely sensitive to ATR inhibition compared to ATM-complemented cells. Acute sensitivity to ATR inhibition was also observed in gastric cancer cell lines that carry deleterious mutations in ATM and in those that express very low levels of ATM. Complementation experiments with mutant versions of the ATM ORF using ATM-deficient human fibroblasts identified deleterious mutations in ATM that sensitize to ATR inhibition. The IHC assay was applied to a cohort of 208 primary gastric cancers. ATM expression was undetectable in approximately 11% of the samples; an additional 26% expressed very low levels. Our findings suggest that ATR inhibition may elicit favorable responses in gastric cancer patients with tumors harboring deleterious ATM mutations or very low levels of ATM expression. Targeted exon-sequencing methods that are used widely combined with IHC for ATM may be useful for patient selection.

Citation Format: Mu-Yan Cai, Hunter D. Reavis, Jie-Wei Chen, Chirag Ganesa, Bose Kochupurakkal, Geoffrey I. Shapiro, Alan D. D'Andrea. ATR inhibition for the treatment of ATM-deficient gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1620.

CDK12 Inhibition Reverses De Novo and Acquired PARP Inhibitor Resistance in BRCA Wild-Type and Mutated Models of Triple-Negative Breast Cancer

Although poly(ADP-ribose) polymerase (PARP) inhibitors are active in homologous recombination (HR)-deficient cancers, their utility is limited by acquired resistance after restoration of HR. Here, we report that dinaciclib, an inhibitor of cyclin-dependent kinases (CDKs) 1, 2, 5, and 9, additionally has potent activity against CDK12, a transcriptional regulator of HR. In BRCA-mutated triple-negative breast cancer (TNBC) cells and patient-derived xenografts (PDXs), dinaciclib ablates restored HR and reverses PARP inhibitor resistance. Additionally, we show that de novo resistance to PARP inhibition in BRCA1-mutated cell lines and a PDX derived from a PARP-inhibitor-naive BRCA1 carrier is mediated by residual HR and is reversed by CDK12 inhibition. Finally, dinaciclib augments the degree of response in a PARP-inhibitor-sensitive model, converting tumor growth inhibition to durable regression. These results highlight the significance of HR disruption as a therapeutic strategy and support the broad use of combined CDK12 and PARP inhibition in TNBC.

Abstract CT047: Phase 1 dose-escalation study of the CDK inhibitor dinaciclib in combination with the PARP inhibitor veliparib in patients with advanced solid tumors

Background: Although PARP inhibition is effective against HR repair-deficient cancers, efficacy is limited by HR proficiency, whether present de novo or as a result of acquired resistance, prompting HR disrupting strategies to sensitize tumor cells. Inhibition of CDK1 and CDK12 compromise HR by blocking BRCA1 phosphorylation, affecting recruitment to sites of DNA damage, and by reducing HR gene expression, respectively. Dinaciclib is a pan-CDK inhibitor that inhibits both CDK1 and CDK12 at nanomolar potency. We conducted a Phase 1 study combining dinaciclib and veliparib in patients with advanced solid tumors who are not germline BRCA carriers. Methods: A 3+3 design was utilized. Veliparib was administered twice daily continuously in 28-day cycles. Dinaciclib was administered intravenously on days 8 and 22. In part 1A, escalation followed a two-dimensional schema, utilizing doses of dinaciclib between 10 - 45 mg/m2 and veliparib between 20 - 120 mg. In part 1B, veliparib was escalated between 200 mg - 400 mg with dinaciclib maintained at 30 mg/m2. PK and PD assessments were performed at baseline, after veliparib, and after the combination. Preliminary Results: Sixty-three heavily pretreated patients were enrolled in part 1A (n = 39) and 1B (n = 24). Thirty-four patients had breast or gynecologic malignancies. The MTD was 400 mg twice-daily veliparib with dinaciclib at 30 mg/m2. DLTs included G4 neutropenia &gt; 7 days (n =1), febrile neutropenia (n = 1), mucositis (n = 1) and fatigue (n = 1). Common drug-related toxicities were neutropenia (78%), nausea (75%), fatigue (67%), electrolyte abnormalities (59%), elevated liver function tests (57%), diarrhea (52%), lymphopenia (52%), anemia (43%), dehydration (37%), anorexia (30%), vomiting (29%), hypoalbuminemia (29%), dizziness (29%), headache (22%), mucositis (18%), elevated creatinine (16%), alopecia (16%), thrombocytopenia (14%), abdominal pain (13%), insomnia (13%), and dysgeusia (11%). The median number of cycles completed was 2 (r: 1 - 10). One patient with TNBC achieved complete resolution of axillary adenopathy lasting &gt; 8 months. Twenty-four patients (38%) had stable disease as the best response, with 9 progression-free &gt; 4 months (TNBC, gynecologic and thymic ca). Paired tumor biopsies from one patient demonstrated reduced Ki-67 and increased gamma-H2AX staining after combination treatment compared to after veliparib alone. Conclusions: Dinaciclib administered at doses known to produce PD effects is tolerable with full dose veliparib. Anti-tumor activity is limited in non-BRCA carriers, possibly related to intermittent administration of a CDK inhibitor with known short half-life. Additional patients are being enrolled utilizing dinaciclib in more dose-intense schedules.

Citation Format: Geoffrey I. Shapiro, Khanh T. Do, Sara M. Tolaney, John F. Hilton, James M. Cleary, Andrew Wolanski, Brian Beardslee, Faith Hassinger, Ketki Bhushan, Dongpo Cai, Elizabeth Downey, Solida Pruitt-Thompson, Suzanne M. Barry, Bose Kochupurakkal, Joseph Geradts, Christine Unitt, Alan D. D'Andrea, Alona Muzikansky, Richard Piekarz, L. Austin Doyle, Jeffrey Supko. Phase 1 dose-escalation study of the CDK inhibitor dinaciclib in combination with the PARP inhibitor veliparib in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT047. doi:10.1158/1538-7445.AM2017-CT047

NF-κB activation-induced anti-apoptosis renders HER2-positive cells drug resistant and accelerates tumor growth

Breast cancers with HER2 overexpression are sensitive to drugs targeting the receptor or its kinase activity. HER2-targeting drugs are initially effective against HER2-positive breast cancer, but resistance inevitably occurs. We previously found that NF-κB is hyperactivated in a subset of HER2-positive breast cancer cells and tissue specimens. In this study, we report that constitutively active NF-κB rendered HER2-positive cancer cells resistant to anti-HER2 drugs and cells selected for lapatinib resistance upregulated NF-κB. In both circumstances, cells were antiapoptotic and grew rapidly as xenografts. Lapatinib-resistant cells were refractory to HER2 and NF-κB inhibitors alone but were sensitive to their combination, suggesting a novel therapeutic strategy. A subset of NF-κB-responsive genes was overexpressed in HER2-positive and triple-negative breast cancers, and patients with this NF-κB signature had poor clinical outcome. Anti-HER2 drug resistance may be a consequence of NF-κB activation, and selection for resistance results in NF-κB activation, suggesting that this transcription factor is central to oncogenesis and drug resistance. Clinically, the combined targeting of HER2 and NF-κB suggests a potential treatment paradigm for patients who relapse after anti-HER2 therapy. Patients with these cancers may be treated by simultaneously suppressing HER2 signaling and NF-κB activation.

IMPLICATIONS

The combination of an inhibitor of IκB kinase (IKK) inhibitor and anti-HER2 drugs may be a novel treatment strategy for drug-resistant human breast cancers.

Abstract LB-255: Exome mutation burden predicts clinical outcome in ovarian cancer carrying mutated BRCA1 and BRCA2 genes

Reliable biomarkers predicting resistance or sensitivity to anti-cancer therapy are critical for oncologists to select proper therapeutic drugs in individual cancer patients. Ovarian and breast cancer patients carrying germline mutations in BRCA1 or BRCA2 genes are often sensitive to DNA damaging drugs and relative to non-mutation carriers present a favorable clinical outcome following therapy. Genome sequencing studies have shown a high number of mutations in the tumor genome in patients carrying BRCA1 or BRCA2 mutations (mBRCA). The present study used exome-sequencing and SNP 6 array data of The Cancer Genome Atlas (TCGA) to correlate the total exome mutation number (Nmut) to progression-free survival (PFS) and overall survival (OS) in the patients (n = 316) with high grade serous ovarian cancer (HGSOC) after debulking surgery and platinum-based chemotherapy. HGSOC in 70 patients of this cohort had either germlines or somatic mutations of BRCA1 or BRCA2 genes. The results revealed that the Nmut was significantly lower in the chemotherapy-resistant mBRCA HGSOC defined by progression within 6 months after completion of first line platinum-based chemotherapy. We found a significant association between low Nmut and shorter PFS and OS in mBRCA HGSOC by Cox regression and Kaplan-Meier analyses. The association was also significant when the analysis was limited to germline BRCA1 or BRCA2 mutated patients with SNP array-determined loss of heterozygosity of the BRCA1 or BRCA2 locus in the tumors. In the mBRCA HGSOC tumors, Nmut was correlated with the genome fraction with loss of heterozygosity and with number of telomeric allelic imbalance, genomic measures evaluating chromosomal instability. However, no significant association between Nmut and PFS or OS was found in HGSOC carrying wild-type BRCA1 and BRCA2 genes. These results suggest that in cancers with DNA repair deficiency caused by functional BRCA loss, higher versus lower Nmut may reflect the status of deficiency or rescue by alternative mechanism(s) for DNA repair, with lower Nmut predicting for resistance to DNA-damaging drugs in mBRCA HGSOC. Our observations are consistent with the new concept that BRCA1/2 critically regulate error-free repair of nucleotide damage to suppress mutation formation, and may imply an activation of alternative repair mechanism(s) capable of bypassing the BRCA defect and restoring error-free DNA repair.

Citation Format: Nicolai Juul Birkbak, Bose Kochupurakkal, Jose MG Izarzugaza, Yang Li, Joyce Liu, Zoltan Szallasi, Ursula Matulonis, Andrea L. Richardson, J Dirk Iglehart, Zhigang C. Wang. Exome mutation burden predicts clinical outcome in ovarian cancer carrying mutated BRCA1 and BRCA2 genes. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-255. doi:10.1158/1538-7445.AM2013-LB-255