DNA Damage Response Inhibitors Research Articles

Discovery of KPT-6566 as STAG1/2 Inhibitor sensitizing PARP and NHEJ Inhibitors to suppress tumor cells growth in vitro

Stromal antigen 1 and 2 (STAG1 and STAG2) are two mutually exclusive components of the cohesin complex that is crucial for centromeric and telomeric cohesion. Beyond its structural role, STAG2 also plays a pivotal role in homologous recombination (HR) repair and has emerged as a promising therapeutic target in cancer treatment. Here, we employed a fluorescence polarization (FP)-based high-throughput screening and identified KPT-6566 as a dual inhibitor of STAG1 and STAG2. Biochemical and biophysical analyses demonstrated that KPT-6566 directly binds to STAG1 and STAG2, disrupting their interactions with SCC1 and double-stranded DNA. A metaphase chromosome spread assay showed that KPT-6566 causes premature chromosome separation and induces chromosome damages in HeLa cells. Furthermore, KPT-6566 also impairs DNA damage repair, leading to the accumulation of double-strand breaks and cell apoptosis. Finally, KPT-6566 can sensitize HeLa and HepG2 cells to PARP inhibitor Olaparib and the NHEJ inhibitor UMI-77, exhibiting a synergistic effect in suppressing cell proliferation. Our findings highlight the potential of STAG1/2 as promising therapeutic targets in cancer treatment, particularly when they are targeted in combination with other DNA damage response inhibitors.

Ion channel modulator DPI-201-106 significantly enhances anti-tumour activity of DNA damage response inhibitors in glioblastoma

Abstract Background Glioblastoma, a lethal high-grade glioma, has not seen improvements in clinical outcomes in nearly 30 years. Ion channels are increasingly associated with tumourigenesis, and there are hundreds of brain-penetrant drugs that inhibit ion channels, representing an untapped therapeutic resource. The aim of this exploratory drug study was to screen an ion channel drug library against patient-derived glioblastoma cells to identify new treatments for brain cancer. Methods 72 ion channel inhibitors were screened in patient-derived glioblastoma cells, and cell viability was determined using the ViaLight Assay. Cell cycle and apoptosis analysis was determined with flow cytometry using PI and Annexin V staining, respectively. Protein and phosphoprotein expression was determined using mass spectrometry and analysed by gene set enrichment analysis. Kaplan-Meier survival analyses were performed using intracranial xenograft models of GBM6 and WK1 cells. Results The voltage-gated sodium channel modulator, DPI-201-106, was revealed to reduce glioblastoma cell viability in vitro by inducing cell cycle arrest and apoptosis. Phosphoproteomics indicated that DPI-201-106 may impact DNA damage response pathways. Combination treatment of DPI-201-106 with the CHK1 inhibitor prexasertib or the PARP inhibitor niraparib demonstrated synergistic effects in multiple patient-derived glioblastoma cells both in vitro and in intracranial xenograft mouse models, extending survival of glioblastoma-bearing mice. Conclusion DPI-201-106 enhances the efficacy of DNA damage response inhibitors to reduce glioblastoma growth. As these drugs have already been clinically tested in humans, repurposing DPI-201-106 in novel combinatorial approaches will allow for rapid translation into the clinic.

DNA damage response inhibitors in cancer therapy: lessons from the past, current status and future implications.

The DNA damage response (DDR) is a network of proteins that coordinate DNA repair and cell-cycle checkpoints to prevent damage being transmitted to daughter cells. DDR defects lead to genomic instability, which enables tumour development, but they also create vulnerabilities that can be used for cancer therapy. Historically, this vulnerability has been taken advantage of using DNA-damaging cytotoxic drugs and radiotherapy, which are more toxic to tumour cells than to normal tissues. However, the discovery of the unique sensitivity of tumours defective in the homologous recombination DNA repair pathway to PARP inhibition led to the approval of six PARP inhibitors worldwide and to a focus on making use of DDR defects through the development of other DDR-targeting drugs. Here, we analyse the lessons learnt from PARP inhibitor development and how these may be applied to new targets to maximize success. We explore why, despite so much research, no other DDR inhibitor class has been approved, and only a handful have advanced to later-stage clinical trials. We discuss why more reliable predictive biomarkers are needed, explore study design from past and current trials, and suggest alternative models for monotherapy and combination studies. Targeting multiple DDR pathways simultaneously and potential combinations with anti-angiogenic agents or immune checkpoint inhibitors are also discussed.

CTIM-32. PHASE I/II STUDY OF STEREOTACTIC RADIOSURGERY WITH CONCURRENT OLAPARIB FOLLOWED BY ADJUVANT DURVALUMAB AND PHYSICIAN’S CHOICE SYSTEMIC THERAPY IN SUBJECTS WITH BREAST CANCER BRAIN METASTASES (SOLARA)

Abstract BACKGROUND Despite progress in the treatment of brain metastasis for HER2+ breast cancer, outcomes for patients with HER2-negative breast cancer brain metastases remain poor. Preclinical studies show inhibitors of poly(ADP-ribose) polymerase (PARP) are effective in combination with radiation therapy as a DNA damage response inhibitor. Triple-negative breast cancer (TNBC) has higher rates of homologous recombination deficiency compared to other subtypes, and together with HER2-negative, BRCA-mutated breast cancer would be particularly sensitive to PARP inhibition. PARP inhibition has also demonstrated promising efficacy combined with immunotherapy in patients with germline BRCA-mutant and metastatic TNBC in clinical trials. In addition, immunotherapy with stereotactic radiosurgery (SRS) is associated with favorable intracranial control and survival in patients with brain metastases. We hypothesize that this biologically-driven combination will enhance local control of SRS-treated brain metastases through synergy with PARP inhibition, while controlling micrometastatic disease via potentiation of the immune response. METHODS We are conducting a multi-institution, Phase I/II trial of SRS plus olaparib, followed by durvalumab (with physician’s choice systemic therapy), for patients with TNBC (any BRCA status) or HER2-negative with BRCA-mutated (germline or somatic) breast cancer brain metastases [NCT04711824]. A total of 41 patients are planned for enrollment at 8 sites. The primary objectives are to evaluate safety and tolerability (Phase I) and determine intracranial disease control at 6 months (Phase II). Secondary objectives include assessing intracranial and global progression-free survival, overall survival, and intracranial and extracranial response rate. Exploratory objectives will assess potential biomarkers of treatment response, including changes in circulating tumor cells and DNA in blood and cerebrospinal fluid, germline and tumor mutations in DNA repair pathway genes, and PD-L1 expression, as well as quality of life and patient-reported outcomes. As of May 2024, phase I has been completed without dose-limiting toxicity, and phase II is currently enrolling. Funding/drug provision from AstraZeneca.

Recent advances in immunotherapy for small cell lung cancer.

This review aims to provide an overview of recent advances in immunotherapy for small cell lung cancer (SCLC), with a focus on the current status of immune checkpoint inhibitors (ICIs), novel combination strategies, and key biomarkers. The integration of ICIs into standard chemotherapy has established them as the first-line treatment for extensive-stage SCLC (ES-SCLC). The ADRIATIC trial further demonstrated the efficacy of ICI maintenance therapy in limited-stage SCLC. Additionally, combining radiotherapy with ICIs has shown promising synergistic effects, including the abscopal and radscopal effects. Ongoing investigations into the combination of ICIs with targeted therapies, such as antiangiogenic agents and DNA damage response inhibitors, have yielded encouraging preliminary results. Notably, the novel therapeutic agent tarlatamab, the first bispecific DLL3-directed CD3 T-cell engager, has recently received FDA approval for second-line treatment of ES-SCLC. Advances in omics technologies have shed light on the intra-tumor and inter-tumor heterogeneity of SCLC, leading to the identification of new molecular subtypes and biomarkers, thereby paving the way for precision medicine. Despite the improved outcomes associated with immunotherapy in SCLC, the overall clinical benefit remains modest. Further preclinical and clinical studies are essential to identify optimal treatment regimens and enhance therapeutic efficacy.

Ni(II) Cylinders Damage DNA in Cancer Cells and Preferentially Bind Y-Shaped DNA Three-Way Junctions Blocking DNA Synthesis.

DNA three-way junctions are critical in various biological processes and hold significant potential for disease treatment and therapeutic applications. In this study, it is demonstrated that triple-stranded dinuclear [Ni2L3]4+ cylinders (L = C25H20N4) exhibit a preferential binding affinity for Y-shaped DNA three-way junctions (3WJs), even in the presence of an excess of competing DNA structures, including G-quadruplexes. Notably, the investigated Ni(II) cylinders are capable of halting DNA synthesis catalyzed by DNA polymerase by stabilizing the 3WJ on the template strand. Using an extended 1D nanoarchitecture model, it is further established the high affinity and selectivity of the cylinders for DNA 3WJs and explored their potential application in stabilizing short-armed 3WJs for constructing DNA nanomaterials. The combined use of Ni(II) cylinders and DNA damage response inhibitors also revealed that the cylinders promote DNA damage, leading to the formation of double-strand breaks. This effect is likely associated with i) the binding of cylinders to 3WJs and ii) the cytotoxic activity of the cylinders in cancer cells.

Factors Influencing the Central Nervous System (CNS) Distribution of the Ataxia Telangiectasia Mutated and Rad3-Related Inhibitor Elimusertib (BAY1895344): Implications for the Treatment of CNS Tumors.

Glioblastoma (GBM) is a disease of the whole brain, with infiltrative tumor cells protected by an intact blood-brain barrier (BBB). GBM has a poor prognosis despite aggressive treatment, in part due to the lack of adequate drug permeability at the BBB. Standard of care GBM therapies include radiation and cytotoxic chemotherapy that lead to DNA damage. Subsequent activation of DNA damage response (DDR) pathways can induce resistance. Various DDR inhibitors, targeting the key regulators of these pathways such as ataxia telangiectasia mutated and Rad3-related (ATR), are being explored as radio- and chemosensitizers. Elimusertib, a novel ATR kinase inhibitor, can prevent repair of damaged DNA, increasing efficacy of DNA-damaging cytotoxic therapies. Robust synergy was observed in vitro when elimusertib was combined with the DNA-damaging agent temozolomide; however, we did not observe improvement with this combination in in vivo efficacy studies in GBM orthotopic tumor-bearing mice. This in vitro-in vivo disconnect was explored to understand factors influencing central nervous system (CNS) distribution of elimusertib and reasons for lack of efficacy. We observed that elimusertib is rapidly cleared from systemic circulation in mice and would not maintain adequate exposure in the CNS for efficacious combination therapy with temozolomide. CNS distribution of elimusertib is partially limited by P-glycoprotein efflux at the BBB, and high binding to CNS tissues leads to low levels of pharmacologically active (unbound) drug in the brain. Acknowledging the potential for interspecies differences in pharmacokinetics, these data suggest that clinical translation of elimusertib in combination with temozolomide for treatment of GBM may be limited. SIGNIFICANCE STATEMENT: This study examined the disconnect between the in vitro synergy and in vivo efficacy of elimusertib/temozolomide combination therapy by exploring systemic and central nervous system (CNS) distributional pharmacokinetics. Results indicate that the lack of improvement in in vivo efficacy in glioblastoma (GBM) patient-derived xenograft (PDX) models could be attributed to inadequate exposure of pharmacologically active drug concentrations in the CNS. These observations can guide further exploration of elimusertib for the treatment of GBM or other CNS tumors.

Impact of DNA Repair Deficiency in the Evolving Treatment Landscape of Bladder Cancer.

This review explores the current landscape of treatments which target the DNA damage response (DDR) in metastatic and muscle-invasive bladder cancer. It emphasizes recent clinical trials which integrate DDR inhibitors with standard chemotherapy and immunotherapy. Noteworthy findings include the ATLANTIS trial, which demonstrated prolonged progression-free survival (PFS) in DDR biomarker-selected patients using PARP inhibitors as maintenance after standard chemotherapy. Trials such as BAYOU, which combined immunotherapy with PARP inhibition, similarly suggested a potential therapeutic benefit in DDR biomarker-selected patients with bladder cancer. Efforts to develop bladder-sparing treatment regimens based on DDR-associated mutational profiles, such as the RETAIN and HCRN 16-257 trials, have had mixed outcomes to date. There are now ongoing efforts to combine DDR inhibitors with the newest bladder cancer therapies, such as antibody-drug conjugates. This review highlights the most recent advances in targeting DNA repair deficiency in the evolving treatment landscape of bladder cancer.

Preparation of Dearomatized p-Coumaric Acid Derivatives as DNA Damage Response Inhibitors with Potent In Vitro Antitumor Effect.

Our research group previously identified graviquinone (1) as a promising antitumor metabolite that is formed in situ when the antioxidant methyl caffeate scavenges free radicals. Furthermore, it exerted a DNA damaging effect on cancer cells and a DNA protective effect on normal keratinocytes. To expand and explore chemical space around qraviquinone, in the current work we synthesized 9 new alkyl-substituted derivatives and tested their in vitro antitumor potential. All new compounds bypassed ABCB1-mediated multidrug resistance and showed highly different cell line specificity compared with 1. All compounds were more potent in MDA-MB-231 than on MCF-7 cells. The n-butyl-substituted derivatives 2 and 8 modulated the cell cycle and inhibited the ATR-mediated phosphorylation of checkpoint kinase-1 in MCF-7 cells. As a significant expansion of our previous findings, our results highlight the potential antitumor value of alkyl-substituted graviquinone derivatives.

Network-driven cancer cell avatars for combination discovery and biomarker identification for DNA damage response inhibitors

Combination therapy is well established as a key intervention strategy for cancer treatment, with the potential to overcome monotherapy resistance and deliver a more durable efficacy. However, given the scale of unexplored potential target space and the resulting combinatorial explosion, identifying efficacious drug combinations is a critical unmet need that is still evolving. In this paper, we demonstrate a network biology-driven, simulation-based solution, the Simulated Cell™. Integration of omics data with a curated signaling network enables the accurate and interpretable prediction of 66,348 combination-cell line pairs obtained from a large-scale combinatorial drug sensitivity screen of 684 combinations across 97 cancer cell lines (BAC = 0.62, AUC = 0.7). We highlight drug combination pairs that interact with DNA Damage Response pathways and are predicted to be synergistic, and deep network insight to identify biomarkers driving combination synergy. We demonstrate that the cancer cell ‘avatars’ capture the biological complexity of their in vitro counterparts, enabling the identification of pathway-level mechanisms of combination benefit to guide clinical translatability.

MODL-16. CRANIOSPINAL RADIOTHERAPY IN COMBINATION WITH DNA-DAMAGE RESPONSE INHIBITORS IN PATIENT-DERIVED ORTHOTOPIC XENOGRAFT MODELS OF MEDULLOBLASTOMA

Abstract BACKGROUND Despite treatment intensification, survival for high-risk subgroups of medulloblastoma (MB) such as MYC-amplified Group 3 (Gr3-II) and p53-mutant SHH (SHH-3p53mut) have remained dismal with overall survival around 40% and 20% respectively. Our previous studies have shown that the DNA-damage response inhibitors (DDRis) prexasertib and ceralasertib enhance the effects of CSI using medulloblastoma cell line-derived orthotopic mouse models. However, patient-derived orthotopic xenografts (PDOXs) are considered superior models for preclinical testing compared to immortalised cell lines. Here, we developed a CSI protocol for multiple PDOX models of high-risk medulloblastoma and tested the optimal protocol with concurrent DDRis. METHOD For our CSI optimisation studies, MED211FH (Gr3-II) or MED813FH (SHH-3p53mut) tumour-bearing mice were monitored for clinical symptoms of tumour before commencing treatment. Multiple, fractionated CSI dosing schedules using a 5-days-on, 2-days-off treatment cycle were trialled based on our lab’s previously established CSI protocols before a schedule of 10 x 0.5 Gy fractions (5.0 Gy total) proved optimal. This schedule was then used in both PDOX models plus an additional SHH-3p53mut model (MED314mCLFH), either alone or in combination with concurrent prexasertib or ceralasertib. RESULTS MED211FH and MED813FH mice treated with 5.0 Gy CSI alone resulted in significantly improved median survival compared to control mice (p<0.0001 and p<0.005 respectively) While 5.0 Gy CSI plus concurrent prexasertib or ceralasertib showed significantly improved survival when compared to CSI alone for each model used. MED211FH: p<0.01 and p<0.001 respectively, MED813FH: p<0.05 and p<0.01 respectively and MED314mCLFH: p<0.05 for both DDRi combination groups. CONCLUSION Remarkably, concurrent use of prexasertib or ceralasertib with CSI significantly improved survival in fatal Gr3-II and SHH-3p53mut models. With these results, we provide robust preclinical evidence for radiosensitising use of DDRi in paediatric high-risk MB and recommend swift clinical translation.

Abstract A004: Radiotherapy sensitizes preclinical models to DNA damage response agents

Abstract Introduction Radiotherapy is a key treatment for various cancers, with nearly 50% of all cancer patients receiving it as part of their therapeutic plan. It can activate cytotoxic signaling pathways to promote cancer cell death but also trigger cytoprotective mechanisms that respond to cellular damage. These cytoprotective mechanisms can be inhibited by targeted anticancer agents such as DNA damage response (DDR) agents, suggesting that radiotherapy could enhance the efficacy of these drugs. This study presents data showing radiotherapy enhances the potency of DDR agents in preclinical models. Methods and experimental procedures The MDA-MB-436 breast and A549 lung cancer cell lines were utilized to establish in vitro assays and in vivo models for the study. Agents targeting DNA-PK (AZD7648) and PARP (niraparib) were used as they work on pathways crucial for the repair of radiation-induced DNA double-strand breaks. The effects on cell viability and DDR biomarkers were assessed after treatment with irradiation (IR), compound or in combination both in vitro and in vivo. Targeted X-rays were delivered using an Xstrahl CIX3 cabinet irradiator, in vivo radiotherapy was delivered to the tumor only. Data An increased sensitivity to DDR agents when combined with radiotherapy was observed in vitro in both cell lines, compared to standalone treatments. A single dose of radiotherapy significantly reduced cell viability beyond the effects of radiotherapy or compound treatment alone. The induction of biomarkers by radiotherapy as monotherapy or in combination with DDR inhibitors was assessed. Changes in biomarker expression were consistent with those observed in the in vivo xenograft models. The administration of fractionated dosing regimens for radiotherapy was well-tolerated in vivo. Combination of radiotherapy with the DDR compounds led to tumor growth delay and enhanced survival outcomes. Conclusion In summary, in vitro assays and in vivo models have been established to investigate the synergistic effects of the combination of radiotherapy and DDR agents. Radiotherapy increased sensitivity of 2 human cancer cell lines to the DDR agents in vitro, and lead to tumor growth delay in vivo. These assays can be used as preclinical tools to identify novel compounds or mechanisms that can be successfully combined with radiotherapy. Citation Format: Pablo Binder, Theoni Katopodi, Lyndsey Hanson, Charlotte R. Bell, Eimear Flanagan, Paul Farrington, Nick Moore, Emily Wright, Yin Xin Ho, Tobias Bunday, Stewart Brown, Amy Cantrell, Yael Mamane, Jon Greenall, Shannon Sharman, John Woolley, Lorraine M. Mooney, Jane Kendrew. Radiotherapy sensitizes preclinical models to DNA damage response agents [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr A004.

Olaparib, AZD1390, ceralasertib, saruparib and consolidation durvalumab (CONCORDE) phase Ib platform study of novel DNA damage response inhibitor (DDRi) agents in combination with radiotherapy in non-small cell lung cancer (NSCLC).

TPS8119 Background: Lung cancer is the leading cause of cancer mortality globally, with cases projected to exceed 62,000 by 2035. Outcomes remain poor despite advances in radiotherapy (RT) technologies. Combining novel mechanism-based agents with RT could improve the therapeutic index. DNA inhibition of cellular response to radiation-induced DNA damage can overcome intrinsic radio resistance and poses a promising strategy. Methods: CONCORDE is an open label, randomised, multi-arm, phase Ib, clinical trial opened to accrual in 11 UK hospitals designed to assess multiple DDRi in combination with radical thoracic RT (60Gy in 30 fractions over 6 weeks). Patients are randomised 3:1 to RT+/-DDRi. The study utilises an adaptive Bayesian model-based approach to dose escalation aiming to identify the recommended phase II dose for each treatment combination. Two arms will deliver up to 12 months consolidation durvalumab+/-DDRi following RT. Patients are eligible based on key criteria: not suitable for concurrent chemotherapy RT, inoperable, stage IIB/III NSCLC, performance status (KPS≥70). The dose limiting toxicity (DLT) period for treatment-related toxicities is 13.5 months post start of RT treatment, with most toxicities expected within the first 4.5 months (short DLT period). At least one patient must complete the short DLT period before dose escalation. A RT-alone calibration arm aids toxicity attribution. This trial is in progress: CONCORDE-A (olaparib (PARP inhibitor)), CONCORDE-B (AZD1390 (ATM inhibitor)), CONCORDE-C (ceralasertib (ATR inhibitor) followed by consolidation durvalumab+/-ceralasertib) and CONCORDE-E (AZD5305/saruparib (PARP1select inhibitor) followed by consolidation durvalumab) are open to accrual as of 24/11/2023. 57 of 74 registered participants have been randomised across 4 study arms. Of those 57 randomised: 55 started treatment: 20 received RT-alone, 12 received olaparib+RT, 14 received AZD1390+RT, 6 received ceralasertib+RT, 3 received AZD5305+RT and 2 withdrew. CONCORDE continues to recruit to the target sample size of 160 (40/arm) and welcomes further UK centres. A parallel multimodality translational program to identify biomarkers of treatment response, toxicity and the impact on the immune system are in development. Biomarkers of interest include plasma toxicity markers, immune cell profiling, radiomics and ctDNA. Clinical trial information: 10142971.

Beyond Chemoimmunotherapy in Advanced Non-Small Cell Lung Cancer: New Frontiers, New Challenges.

Chemoimmunotherapy is currently the preferred first-line treatment option for the majority of patients with advanced non-small cell lung cancer without driver genetic alterations. Most of these patients, however, will experience disease progression within the first year after treatment initiation and both patients and their physicians will be confronted with the dilemma of the optimal second-line treatment. Identification of molecular targets, such as KRASG12C, BRAFV600X, METexon14, and human epidermal growth factor receptor 2 mutations, and RET rearrangements offer therapeutic opportunities in pretreated patients with corresponding alterations. For those tumors that do not harbor oncogenic drivers, second-line treatment with docetaxel remains the current standard of care despite modest efficacy. Strategies to challenge docetaxel include the combination of immune checkpoint inhibitors (ICIs) with tyrosine inhibitors of multiple kinases or with DNA damage response inhibitors, antibody-drug conjugates, and locoregional treatments for oligoprogressive disease. Next-generation immunotherapy strategies, such as T-cell engagers, immune-mobilizing monoclonal T-cell receptors, chimeric antigen receptor cell therapy, tumor infiltrating lymphocytes, and T-cell receptor cell therapy are being currently investigated in the quest to reverse resistance to ICIs. Importantly, the advent of these new agents heralds a novel spectrum of toxicities that require both the physician's and the patient's education. Herein, we review current and future strategies aiming to outperform docetaxel after chemoimmunotherapy failure, and we provide practical information on how to best communicate to our patients the unique toxicity aspects associated with immunotherapy.

Enhancing genome editing in hPSCs through dual inhibition of DNA damage response and repair pathways

Precise genome editing is crucial for establishing isogenic human disease models and ex vivo stem cell therapy from the patient-derived hPSCs. Unlike Cas9-mediated knock-in, cytosine base editor and prime editor achieve the desirable gene correction without inducing DNA double strand breaks. However, hPSCs possess highly active DNA repair pathways and are particularly susceptible to p53-dependent cell death. These unique characteristics impede the efficiency of gene editing in hPSCs. Here, we demonstrate that dual inhibition of p53-mediated cell death and distinct activation of the DNA damage repair system upon DNA damage by cytosine base editor or prime editor additively enhanced editing efficiency in hPSCs. The BE4stem system comprised of p53DD, a dominant negative p53, and three UNG inhibitor, engineered to specifically diminish base excision repair, improves cytosine base editor efficiency in hPSCs. Addition of dominant negative MLH1 to inhibit mismatch repair activity and p53DD in the conventional prime editor system also significantly enhances prime editor efficiency in hPSCs. Thus, combined inhibition of the distinct cellular cascades engaged in hPSCs upon gene editing could significantly enhance precise genome editing in these cells.

Abstract PO5-20-03: Phase I/II study of stereotactic radiosurgery with concurrent olaparib followed by adjuvant durvalumab and physician’s choice systemic therapy in subjects with breast cancer brain metastases

Abstract BACKGROUND: Despite progress in the treatment of brain metastasis for HER2+ breast cancer, outcomes for patients with HER2-negative breast cancer brain metastases remain poor. Current standard of care consists of local therapies, including surgery and radiotherapy, followed by systemic therapy. Preclinical studies show inhibitors of poly(ADP-ribose) polymerase (PARP) are effective in combination with radiation therapy as a DNA damage response inhibitor. Triple-negative breast cancer (TNBC) has higher rates of homologous recombination deficiency compared to other breast cancer subtypes, and together with HER2-negative, BRCA-mutated breast cancer would be particularly sensitive to PARP inhibition. PARP inhibition has also demonstrated promising efficacy combined with immunotherapy in patients with germline BRCA-mutant and metastatic TNBC in clinical trials (MEDIOLA, TOPACIO). In addition, immunotherapy with stereotactic radiosurgery (SRS) is associated with favorable intracranial control and survival in patients with brain metastases. We hypothesize that this biologically-driven combination will enhance local control of SRS-treated brain metastases through synergy with PARP inhibition, while controlling micrometastatic disease in the brain and extracranial sites via potentiation of the immune response. METHODS: We are conducting a multi-institution, Phase I/II trial of SRS plus olaparib, followed by durvalumab (with physician’s choice systemic therapy), for patients with TNBC (any BRCA status) or HER2-negative with BRCA-mutated (germline or somatic) breast cancer brain metastases [NCT04711824]. A total of 41 patients are planned for enrollment at 8 sites. The primary objectives are to evaluate safety and tolerability (Phase I) and determine intracranial disease control at 6 months (Phase II) of this treatment combination. Secondary objectives include determining clinical activity via intracranial and global progression-free survival, overall survival, and intracranial and extracranial response rate. Exploratory objectives will assess potential biomarkers of treatment response, including changes in circulating tumor cells and DNA in blood and cerebrospinal fluid, germline and tumor mutations in DNA repair pathway genes, and PD-L1 expression, as well as quality of life and patient-reported outcomes. A surgical sub-study (n=5) will evaluate olaparib concentration/distribution in resected brain metastases. As of June 2023, cohort 2 of phase I has been completed without dose-limiting toxicity. Citation Format: Colette Shen, Yara Abdou, Linda Chen, Xianming Tan, Gaorav Gupta, Mina Lobbous, Filipa Lynce, Erica Stringer-Reasor, Carey Anders. Phase I/II study of stereotactic radiosurgery with concurrent olaparib followed by adjuvant durvalumab and physician’s choice systemic therapy in subjects with breast cancer brain metastases [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-20-03.

Abstract PO4-23-08: Estrogen therapy induces receptor-dependent DNA damage enhanced by PARP inhibition in ER+ breast cancer

Abstract Although clinical evidence indicates that treatment with estrogens elicits anti-cancer effects in ~30% of patients with advanced endocrine-resistant ER+ breast cancer, the underlying mechanism of action is unclear and this treatment remains under-utilized. ER+ breast cancer cells with acquired resistance to long-term estrogen deprivation (LTED) were used to model resistance to aromatase inhibitors (AIs) seen clinically. Genome-wide CRISPR/Cas9 knockout screening and transcriptomic profiling of LTED cells highlighted DNA Damage Response as a required pathway for therapeutic response to the estrogen 17b-estradiol. Tumor specimens from 2 patients with advanced ER+ breast cancer showed increased DNA damage response upon treatment with 17b-estradiol therapy compared to baseline. LTED cells treated with 17b-estradiol exhibited replication-dependent markers of DNA damage and the DNA damage response prior to apoptosis, while parental cells did not. Such DNA damage was partially driven by the formation of DNA:RNA hybrids (R-loops), and RNase H1-mediated prevention of R-loop formation abrogated 17b-estradiol-induced DNA damage. Pharmacological suppression of the DNA damage response via poly(ADP-ribose) polymerase (PARP) inhibition with olaparib enhanced 17b-estradiol-induced DNA damage. PARP inhibition synergized with 17b-estradiol to suppress growth and prevent tumor recurrence in both BRCA1/2-mutant and BRCA1/2-wild-type cell line and patient-derived xenograft models. We therefore conclude that 17b-estradiol-induced ER activity drives DNA damage and growth inhibition in endocrine-resistant breast cancer cells, and inhibition of the DNA damage response using drugs such as PARP inhibitors can exacerbate transcriptional stress and enhance therapeutic response to 17b-estradiol. This concept is being explored clinically in the PHOEBE trial testing the combination of 17b-estradiol and olaparib (NCT05900895). These findings also warrant further study of other DNA damage response inhibitors in advanced ER+ breast cancer. Moreover, these data indicate that PARP inhibitors may have applications beyond homologous recombination-deficient tumors. Citation Format: Nicole Traphagen, Gary Schwartz, Steven Tau, Alyssa Roberts, Amanda Jiang, Sarah Hosford, Jonathan Marotti, Abigail Goen, Bianca Romo, Anneka Johnson, Emily Duffy, Eugene Demidenko, Paul Heverly, Yaron Mosesson, Shannon Soucy, Fred Kolling, Todd Miller. Estrogen therapy induces receptor-dependent DNA damage enhanced by PARP inhibition in ER+ breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-23-08.

3429: Modulating innate immunity by DNA damage response inhibition

3429: Modulating innate immunity by DNA damage response inhibition

Recent Progress in DNA Damage Response-Targeting PROTAC Degraders.

DNA damage response (DDR) defects in cells play a crucial role in tumor development by promoting DNA mutations. These mutations create vulnerabilities specific to cancer cells, which can be effectively targeted through synthetic lethality-based therapies. To date, numerous small molecule DDR inhibitors have been identified, and some of them have already been approved for clinical use. However, due to the complexity of the tumor microenvironment, mutations may occur in the amino acid residues of DDR targets. These mutations can affect the efficacy of small molecule inhibitors targeting DDR pathways. Therefore, researchers have turned their attention to next-generation DNA damage repair modulators, particularly those based on PROTAC technology. From this perspective, we overviewed the recent progress on DDR-targeting PROTAC degraders for cancer therapy. In addition, we also summarized the biological functions of different DDR targets. Finally, the challenges and future directions for DDR-target PROTAC degraders are also discussed in detail.

Hierarchical cluster analysis and nonlinear mixed-effects modelling for candidate biomarker detection in preclinical models of cancer.

BackgroundPreclinical models of cancer can be of translational benefit when assessing how different biomarkers are regulated in response to particular treatments. Detection of molecular biomarkers in preclinical models of cancer is difficult due inter-animal variability in responses, combined with limited accessibility of longitudinal data. MethodsNonlinear mixed-effects modelling (NLME) was used to analyse tumour growth data based on expected tumour growth rates observed 7 days after initial doses (DD7) of Radiotherapy (RT) and Combination of RT with DNA Damage Response Inhibitors (DDRi). Cox regression was performed to confirm an association between DD7 and survival. Hierarchical Cluster Analysis (HCA) was then used to identify candidate biomarkers impacting responses to RT and RT/DDRi and these were validated using NLME. ResultsCox regression confirmed significant associations between DD7 and survival. HCA of RT treated samples, combined with NLME confirmed significant associations between DD7 and Cluster specific CD8+ Ki67 MFI, as well as DD7 and cluster specific Natural Killer cell density in RT treated mice. ConclusionApplication of NLME, as well as HCA of candidate biomarkers may provide additional avenues to assess the effect of RT in MC38 syngeneic tumour models. Additional studies would need to be conducted to confirm association between DD7 and biomarkers in RT/DDRi treated mice.