BRCA-mutated Triple-negative Breast Cancer Research Articles

Discovery of dual-targeted molecules based on Olaparib and Rigosertib for triple-negative breast cancer with wild-type BRCA

PARP inhibitors (PARPis) demonstrate significant potential efficacy in the clinical treatment of BRCA-mutated triple-negative breast cancer (TNBC). However, a majority of patients with TNBC do not possess BRCA mutations, and therefore cannot benefit from PARPis. Previous studies on multi-targeted molecules derived from PARPis or disruptors of RAF-RAF pathway have offered an alternative approach to develop novel anti-TNBC agents. Hence, to broaden the application of PARP inhibitors for TNBC patients with wild-type BRCA, a series of dual-targeted molecules were constructed via integrating the key pharmacophores of Olaparib (Ola) and Rigosertib into a single entity. Subsequent studies exhibited that the resulting compounds 13a–14c obtained potential anti-proliferative activity against BRCA-defected or wild-type TNBC cells. Among them, an optimal compound 13b showed good inhibitory activity toward PARP-1, displayed approximately 34-fold higher inhibitory activity than that of Ola in MDA-MB-231 cells, and exerted multi-functional mechanisms to induce apoptosis. Moreover, 13b displayed superior antitumor efficacy (TGI, 61.3 %) than the single administration of Ola (TGI, 38.5 %), 11b (TGI, 51.8 %) or even their combined administration (TGI, 56.7 %), but did not show significant systematic toxicity. These findings suggest that 13b may serve as a potential candidate for BRCA wild-type TNBC.

Shifting Paradigms in TNBC Treatment: Emerging Alternatives to Capecitabine in the Post-Neoadjuvant Setting.

Triple-negative breast cancer (TNBC) remains a clinically challenging subtype due to its aggressive nature and limited treatment options post-neoadjuvant failure. Historically, capecitabine has been the cornerstone of adjuvant therapy for TNBC patients not achieving a pathological complete response (pCR). However, the integration of new modalities such as immunotherapy and PARP inhibitors has prompted a re-evaluation of traditional post-neoadjuvant approaches. This review synthesizes data from pivotal clinical trials and meta-analyses to evaluate the efficacy of emerging therapies in the post-neoadjuvant setting. We focus on the role of immune checkpoint inhibitors (ICIs), PARP inhibitors (PARPis), and antibody-drug conjugates (ADCs) alongside or in place of capecitabine in TNBC treatment paradigms. The addition of ICIs like pembrolizumab to neoadjuvant regimens has shown increased pCR rates and improved event-free survival, posing new questions about optimal post-neoadjuvant therapies. Similarly, PARPis have demonstrated efficacy in BRCA-mutated TNBC populations, with significant improvements in disease-free survival (DFS) and overall survival (OS). Emerging studies on ADCs further complicate the adjuvant landscape, offering potentially efficacious alternatives to capecitabine, especially in patients with residual disease after neoadjuvant therapy. The challenge remains to integrate these new treatments into clinical practice effectively, considering factors such as drug resistance, patient-specific characteristics, and socio-economic barriers. This review discusses the implications of these therapies and suggests a future direction focused on personalized medicine approaches in TNBC. As the treatment landscape for TNBC evolves, the role of capecitabine is being critically examined. While it remains a viable option for certain patient groups, the introduction of ICIs, PARPis, and ADCs offers promising alternatives that could redefine adjuvant therapy standards. Ongoing and future trials will be pivotal in determining the optimal therapeutic strategies for TNBC patients with residual disease post-neoadjuvant therapy.

Stage IV Triple-negative breast cancer with brain and visceral metastasis has a complete response to sacituzumab govitecan: A Case Report

Background: Triple-negative breast cancer (TNBC) is a particularly aggressive subtype of cancer, characterized by its high propensity for metastasis. Patients who experience the development of brain metastases (BMs) and visceral metastasis face a challenging prognosis, as effective systemic treatment options for this specific condition are limited. Case presentation: This case report describes the journey of a 42-year-old female patient diagnosed with left-sided triple-negative breast cancer with metastasis to the lymph nodes, bone, and brain. The patient underwent a combination of chemotherapy, immunotherapy, and targeted therapy, showing an initial response but subsequent disease progression. Multiple treatment modalities, including surgery, radiotherapy, including stereotactic radiotherapy, were employed to manage the metastases. The patient experienced complications such as anemia and hypocalcemia and received supportive care. Serial imaging, including positron emission tomography and MRI, were utilized for monitoring treatment response and disease progression documented. Conclusion: The findings of this case report provide support for considering sacituzumab govitecan as a potential treatment option for recurrent and even BRCA-mutant triple-negative breast cancer (TNBC). Notably, sacituzumab govitecan demonstrated high activity in the presence of active bone and brain metastases.

Abstract 5551: Targeted nanoparticles co-delivering PARP inhibitor and other immune modulators overcome the immunosuppressive tumor microenvironment

Abstract Several mutations have been identified that are associated with an increased risk of triple-negative breast cancer (TNBC), including those that are deleterious in the BRCA gene. TNBC is associated with the worst prognosis and the highest incidence of brain metastasis (30%) among all subtypes of BC. Despite objective responses to poly (ADP-ribose) polymerase (PARP) inhibition and improvements in progression-free survival (PFS) compared to standard chemotherapy in patients with BRCA-mutated TNBC, benefits are transitory. Furthermore, our understanding of the effect of PARP inhibitors (PARPi) in treating breast cancer brain metastasis (BCBM) and modulating its tumor microenvironment (TME) is still lacking. To this end, we analyzed the brain TME of BRCA-mutated BCBM in the absence or presence of treatment with PARPi. Interestingly, we found that the immune TME of the brain hinder the antitumor activity of PARPi by upregulating multiple immunosuppressive molecules, including PD-L1. Furthermore, we found that BCBM overexpress P-selectin through its interaction with the tumor-associated microglia, bone marrow-derived macrophages and endothelial cells in the TME. Thus, we designed a novel nanoparticle (NP) targeting P-selectin to serve as a brain-penetrant delivery system for the treatment of BCBM. In order to target BRCA-mutated BCBM, we harnessed our novel P-selectin-targeted NPs to entrap PARPi and other immune modulators that we found to exert synergistic activity when combined. To evaluate the antitumor activity of our P-selectin-targeted NPs, we established 3-dimensional (3D) ex vivo and in vivo BRCA-mutated BCBM models. Importantly, we saw favorable effects of the P-selectin-targeted NPs in comparison to the combination of the free drugs, suggesting that out targeted-NPs overcome the TME-mediated resistance to PARPi through the modulation of the immunosuppressive microenvironment of the brain. Citation Format: Rami Khoury, Ron Kleiner, Eilam Yeini, Daniel Rodriguez Ajamil, Sahar Israeli Dangoor, Tamer Sanalla, Iris Barshack, Roni Satchi-Fainaro. Targeted nanoparticles co-delivering PARP inhibitor and other immune modulators overcome the immunosuppressive tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5551.

State-of-the-art management of HER2-negative early breast cancer: Treatment patterns among healthcare professionals and concordance with expert recommendations.

553 Background: The management of high-risk HER2-negative early-stage breast cancer (EBC) has recently evolved with the addition of newer agents including abemaciclib, olaparib, and pembrolizumab as (neo)adjuvant therapy options for appropriate patients. To aid healthcare professionals (HCPs) in the recommended implementation of these agents, we developed an online treatment decision support tool providing case-specific treatment guidance from 5 breast cancer experts. Here, we report an analysis of cases entered into the tool by HCPs, comparing their planned treatment with expert recommendations. Methods: Expert therapy recommendations for 10 case scenarios in high-risk HER2-negative EBC based on 3 pivotal clinical trials (KEYNOTE-522, OlympiA, and monarchE) were obtained in March 2022. Patient and disease characteristics included hormone receptor (HR) status, BRCA mutational status, lymph node positivity, presence of residual disease after resection, and additional criteria based on the 3 practice-changing trials. HCPs entered specific patient and disease factors into the tool along with their intended treatment plan and were shown 5 individual expert treatment recommendations for the unique case scenario. Results: From June 2022 to January 2023, 547 HCPs entered 982 patient case scenarios into the tool. A comparison of treatment recommendations by experts and HCPs showed divergence for several case scenarios. For patients with high-risk HR-positive/HER2-negative EBC and no BRCA mutation, all 5 experts recommended adjuvant abemaciclib plus endocrine therapy. By contrast, 64% of HCPs’ therapy choices were discordant with the experts, with 49% choosing chemotherapy followed by endocrine therapy. For patients with triple-negative breast cancer (TNBC) who received neoadjuvant chemotherapy and have no residual disease, all 5 experts recommended observation, whereas 36% of HCPs recommended additional adjuvant therapy. In the setting of BRCA-mutated TNBC with residual disease after neoadjuvant pembrolizumab plus chemotherapy, 4 of 5 experts recommended adjuvant pembrolizumab plus olaparib, but just 33% of HCPs chose this combination. One third of HCPs who initially selected treatment options that diverged from expert recommendations or who were uncertain about treatment choice intend to change their therapy selection to align with the experts. Conclusions: Analysis of data from this tool suggests differences in clinical practice between experts and HCPs for multiple case scenarios of high-risk EBC, including examples of potential overtreatment. Moreover, our data demonstrate that this decision support tool may lead to better alignment of HCP treatment choices with experts, with the potential to improve clinical management of patients.

Novel combination treatment of CDK 4/6 inhibitors with PARP inhibitors in triple negative breast cancer cells.

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors provide promising results for treating hormone receptor-positive breast cancer. However, the efficacy of CDK4/6 inhibitors remains uncertain in triple negative breast cancer (TNBC) patients with particularly carrying RB-deficient tumors. Poly-(ADP-ribose) polymerase (PARP) inhibitors offer a therapeutic strategy for the treatment of BRCA-mutated TNBC patients. However, the acquired drug resistance, changes in the cell cycle regulation, and DNA damage repair have demonstrated the necessity for developing new combination strategies. This preclinical study assessed a combinatory treatment of the CDK4/6 inhibitor abemaciclib with PARP inhibitors talazoparib (TAL) in HCC1937 BRCA-mutated RB-deficient TNBC cells and TAL-resistant HCC1937-R cells through WST-1 analysis, annexin V, cell cycle, acridine orange/propidium iodide staining, RT-PCR, and apoptosis array. Our findings revealed that abemaciclib and TAL combination synergistically suppressed the growth of TNBC cells and overcame TAL resistance through G0/G1 arrest and the activity of both intrinsic and extrinsic apoptotic pathways. These preliminary results suggest that the combination of abemaciclib and TAL could expand the use of these inhibitors in BRCA mutated and RB deficient TNBC patients and potentially overcomes PARP inhibitors resistance.

Selective degradation of PARP2 by PROTACs via recruiting DCAF16 for triple-negative breast cancer

Triple negative breast cancer (TNBC) is a complex and heterogeneous neoplasm, and till now no effective therapies are available. PARP inhibitors, which target DNA repair, are lethal to those cells that have impaired homologous recombination (HR) pathway. So, PARP inhibitors might exert promising results in the treatment of BRCA-mutated TNBC, but show compromised effect to those wild-type TNBC. Herein, we describe a novel PROTACs C8, which was obtained by conjugating PARP1/2 inhibitor Olaparib to KB02, can induce potent and specific degradation of PARP2 by recruiting DCAF16 E3 ligase for treatment of wild-type TNBC. Moreover, C8 exhibits therapeutic potential in TNBC cell lines MDA-MB-231 both in vitro and in vivo. These studies demonstrated that the DCAF16 E3 ligases can be used in PARP2 PROTACs design, and C8, as a novel PARP2 selective DCAF16 based PROTACs, might be a promising lead compound for the treatment of BRCA-wild-type TNBC.

Impact of different sequencing strategies of talazoparib and carboplatin combination upon efficacy and toxicity in BRCA-wild type and BRCA-mutant triple-negative breast cancer models.

586 Background: PARP inhibitors (PARPi) such as talazoparib and olaparib, have demonstrated an improvement in progression-free survival (PFS) amongst metastatic HER2-negative breast cancer patients with germline mutations in BRCA1/2 (BRCA-MUT). Clinical trials have evaluated PARPi in combination with carboplatin, but with mixed results. Earlier trials studied the combination of carboplatin and a low-dose PARPi of low potency, veliparib. The concomitant combination of carboplatin and talazoparib, a higher-potency PARPi, was also evaluated in solid tumors, using a heavily pre-treated population. Here, we perform a comparative evaluation of different sequencing strategies of talazoparib and carboplatin to determine efficacy and toxicity in BRCA-MUT and BRCA wild-type (WT) TNBC models. Methods: We used three orthotopic xenograft models in NSG (NOD scid gamma) mice, with 7-14 mice in each treatment group: MDAMB231 (BRCA-WT), HCC1806 (BRCA-WT), and MX1 (BRCA-MUT). We treated mice with carboplatin (C) (35 mg/kg intraperitoneally) in combination with talazoparib (T) (0.33 mg/kg oral gavage) using 2 dosing strategies: a) concomitant administration of C + T; and b) T first, followed by C three days later, each compared to vehicle control. We evaluated primary tumor inhibition and hematologic toxicity. Kruskal-Wallis test and Dunn’s multiple comparison test was used to assess statistical significance. Results: Using the MDAMB231 xenograft, we found the T-first approach led to a 66.7% (P < 0.0001), and the concomitant approach resulted in a 51.4% decrease in primary tumor volume, (P = 0.08), in comparison to control. In HCC1806, the T-first approach resulted in a 62.0% decrease in tumor volume (P < 0.0001), whereas the concomitant combination showed a 54.4% decrease (P = 0.002). In MX1, the T-first and concomitant approaches resulted in 72.7% (P < 0.0001) and 81.4% (P < 0.0001) decrease in tumor volume, respectively. With regards to neutrophil counts, T-first approach decreased neutrophils by 66.2% and 43.0% in MDAMB231 and HCC1806 xenografts respectively, similar to the trend with concomitant T + C: 61.4% and 38.0%. In the MX1 cohort, the T-first approach resulted in a 66.2% decrease in neutrophils (P = 0.001), and the concomitant approach led to a 77.5% decrease in neutrophils (P = 0.006). Conclusions: Our results demonstrate that the talazoparib-first approach is effective in two BRCA-WT models with no statistically significant neutropenia. While the concomitant combination approach demonstrated greater tumor inhibition in the BRCA-MUT model, this was also associated with significant neutropenia. This is suggestive that sequencing of talazoparib and carboplatin may have differential effect in BRCA-WT and BRCA-MUT tumors and may play an important role in improving efficacy in BRCA-WT tumors.

Dextran-modified Quercetin-Cu(II)/hyaluronic acid nanomedicine with natural poly(ADP-ribose) polymerase inhibitor and dual targeting for programmed synthetic lethal therapy in triple-negative breast cancer

Serious side effects from chemotherapies are the main problem with cancer treatments. To solve these issues, precision cancer nanomedicine based on natural therapeutic materials is developed, which enables specifically apoptosis by interacting with genetic mutation in cancer cells, while leaving normal cells unaffected. Here, we report a novel nanomedicine (CuQDA/IO@HA) composed of hyaluronic acid (HA) / copper ion (Cu(II))-chelated dextran-aldehyde (DA)-quercetin (Q) with dual targeting for synthetic lethal therapy. The CuQDA/IO@HA prepared using a ratio of metal/Q at 0.5:1 resulted in a stable particle structure with uniform particle distribution. The CuQDA/IO@HA can specifically target and induce specific cytotoxicity in BRCA-mutant cancer cells in vitro. Combination treatment with CuQDA/IO@HA and magnetic navigation can induce poly (ADP-ribose) polymerase (PARP) inhibition and DNA damage in BRCA-mutant triple-negative breast cancer (TNBC) via CD44 targeting. The dual-targeting CuQDA/IO@HA can extend the median survival of the BRCA-mutant xenograft mice from 34 to 61 days in comparison to Q treatment alone in vivo, which is attributed to the significant increase in γH2AX, leading to significant apoptosis. More importantly, the CuQDA/IO@HA displayed biocompatibility and no obvious side-effect in normal organs. These results demonstrate the promising potential of integrating natural and metal ions into a nanomedicine that can provide precision medicine through synthetic lethality.

Abstract 4085: Blocking Fra-1 sensitises triple-negative breast cancer to olaparib

Abstract Fra-1 (FOSL1), a member of the activator protein 1 (AP-1) transcription factor complex, is overexpressed in triple-negative breast cancer (TNBC) and plays crucial roles in tumor progression and treatment resistance. We have previously identified 118 proteins that interact with endogenous chromatin-bound Fra-1 in TNBC cells in a large screen, and this included PARP1 (Poly (ADP-ribose) polymerase 1). PARP1 inhibitor olaparib is currently in use for treatment of BRCA-mutated TNBC breast cancer. Here, we corroborate that PARP1 interacts with Fra-1, and we also find that PARP1 downregulates Fra-1 and reduces AP-1 transcriptional activity. Inhibition of PARP1, on the other hand, increases Fra-1 levels and enhances AP-1 transcriptional activity. Further, we find that upon inhibition of Fra-1, TNBC cells become sensitized to olaparib treatment. By comparing the Fra-1 and PARP1 regulated transcriptomes with Fra-1 chromatin binding site, we determine that a large fraction of PARP1-regulated genes is dependent on Fra-1. Finally, we show that PARP1 protein levels significantly correlate with Fra-1 in clinical breast cancer tumors, and we identify that while high PARP1 expression is indicative of a poor clinical outcome in breast cancer patients overall, it is not in basal-like tumors. In conclusion, by exploring the functionality of the Fra-1 and PARP-1 interaction, we propose that targeting Fra-1 could serve as a therapeutic approach to improve olaparib treatment outcome for TNBC patients. Citation Format: Dandan Song, Huan He, Indranil Sinha, Linnea Pettersson, Feifei Yan, Lars-Arne Haldosen, Chunyan Zhao, Cecilia Williams. Blocking Fra-1 sensitises triple-negative breast cancer to olaparib [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4085.

Abstract 4074: Reversing acquired PARPi resistance of TNBC through combined inhibition of cMet and EGFR

Abstract Front line therapeutic failure happened to half of triple-negative breast cancer (TNBC) patients represent the effective treatment strategies for these patients are urgently needed. Poly (ADP-ribose) polymerase (PARP) is currently the most promising drug target for BRCA-mutated TNBC, and PARP inhibitors (PARPi), olaparib and talazoparib, were recently approved for the treatment of metastatic breast cancer (including TNBC) in patients with germline BRCA1/2 mutations. Despite impressive response rates of ~60%, the prolongation in median progression-free survival with a PARPi is modest, suggesting the emergence of resistance. Several studies have reported that receptor tyrosine kinases (RTKs), such as c-MET (also known as hepatocyte growth factor receptor), are involved in resistance to various anti-neoplastic agents, including PARPi. However, the mechanism by which c-MET contributes to acquired resistance to PARPi in TNBC is not fully understood. In this study, we analyzed acquired PARPi resistant TNBC cells and found c-Met is hyperactivated in these cells with PARPi treatment. We further treated these cells with talazoparib and crizotinib (a multi-kinase inhibitor that inhibits c-MET) and found synergistic inhibition effects of cell proliferation. Unexpectedly, limited effects of talazoparib sensitivity showed while depleting c-MET in PARPi-resistant cells. Interestingly, we found epidermal growth factor receptor (EGFR) is also hyperactivated and interaction of EGFR/c-Met in these cells. Notably, combination of c-MET and EGFR inhibitors increased sensitivity to talazoparib in TNBC cells with acquired resistance to PARPi. Combining EGFR and PARP inhibitors also resulted in greater inhibition of proliferation in c-MET-depleted TNBC cells. Collectively, our findings suggested a potential combination therapy of inhibiting c-MET and EGFR to overcome acquired PARPi resistance in TNBC. Citation Format: Yu Yi Chu, Clinton Yam, Mei-Kuang Chen, Li-Chuan Chan, Lei Nie, Mien-Chie Hung. Reversing acquired PARPi resistance of TNBC through combined inhibition of cMet and EGFR [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4074.

Response of Breast Cancer Cells to PARP Inhibitors Is Independent of BRCA Status.

Poly (ADP-ribose) polymerase inhibitors (PARPi) have proven to be beneficial to patients with metastatic breast cancer with BRCA1/2 (BReast CAncer type 1 and type 2 genes) mutations. However, certain PARPi in pre-clinical studies have been shown to inhibit cell growth and promote the death of breast cancer cells lacking mutations in BRCA1/2. Here, we examined the inhibitory potency of 13 different PARPi in 12 breast cancer cell lines with and without BRCA-mutations using cell viability assays. The results showed that 5 of the 8 triple-negative breast cancer (TNBC) cell lines were susceptible to PARPi regardless of the BRCA-status. The estrogen receptor (ER) negative/ human epidermal growth factor receptor 2 (HER2) positive (ER-/HER2+) cells, SKBR3 and JIMT1, showed high sensitivity to Talazoparib. Especially JIMT1, which is known to be resistant to trastuzumab, was responsive to Talazoparib at 0.002 µM. Niraparib, Olaparib, and Rucaparib also demonstrated effective inhibitory potency in both advanced TNBC and ER-/HER2+ cells with and without BRCA-mutations. In contrast, a BRCA-mutant TNBC line, HCC1937, was less sensitive to Talazoparib, Niraparib, Rucaparib, and not responsive to Olaparib. Other PARPi such as UPF1069, NU1025, AZD2461, and PJ34HCl also showed potent inhibitory activity in specific breast cancer cells. Our data suggest that the benefit of PARPi therapy in breast cancer is beyond the BRCA-mutations, and equally effective on metastatic TNBC and ER-/HER2+ breast cancers.

Abstract P1-06-04: Small-molecule screening nominates diverse combination therapies that sensitize BRCA mutant and wild-type triple negative breast cancer to PARP inhibition

Abstract Background: Triple negative breast cancer (TNBC) remains a heterogeneous clinical phenotype with few, known therapeutic targets. PARP inhibitors (PARPi) are the first approved, targeted therapy in TNBC, limited to germline BRCA mutant (BRCAm) cancers that lack homologous recombination repair capacity. Even in this context, resistance quickly emerges via secondary mutations that restore DNA repair ability. While DNA damage repair is an intriguing target in BRCA wild type (BRCAwt) TNBC due to inherent, genomic instability, PARPi alone have been ineffective in unselected populations. Systematic approaches to define novel drugs that sensitize BRCAwt and BRCAm TNBC to PARPi would greatly improve therapeutic efficacy and durability. Methods: BRCAwt (HCC1806) and BRCAm (SUM149PT) cell lines were screened in duplicate using a 2,100-compound small molecule library. Cell lines were plated in media containing DMSO or sub-lethal doses of the PARPi, olaparib, onto Selleck Bioactive drug plates. Cell viability was assessed after 72 hours, then normalized to vehicle control. Hit cut-offs were predefined as log2 drug/DMSO of ≤ -0.7 with a viability difference greater than 20% -where stringent scoring thresholds were chosen to exceed the full range of scores observed in 816 empty control wells. Hits were sorted by target and pathway to provide mechanistic insight into the synergy of combinations. Drug combinations with the highest potential for near term translation were validated using GI50 viability assays in 9 BRCAwt and BRCAm TNBC cell lines. The most promising combination was further validated via immunoblotting, colony formation, and apoptosis assays. Results: Several drug classes affecting well-known oncogenic signaling pathways conferred sensitivity to PARPi, with more hits in the BRCAm cell line. Relevant druggable targets sensitizing cells to olaparib in BRCAm TNBC that met the predefined cut-point were inhibitors of PI3K (pan-PI3K, PI3Kα and PI3Kβ specific), VEGFR, MEK, EGFR, NF-kB, aurora kinase and several DNA damaging agents. Aurora kinase, EGFR, and NF-kB inhibition sensitized cells to olaparib, yet upon further validation, synergy was mild. The screen identified ATM inhibitors, KU-55933 and KU-60019, as sensitizers of BRCAm cells to olaparib. The potent ATM inhibitor, AZD0156, and olaparib were a highly synergistic combination validated in all 9 BRCAm and BRCAwt TNBC cell lines via cell viability, annexin V, and colony formation assays. Immunoblotting of relevant DNA damage repair proteins showed that olaparib caused upregulation of p-ATM in BRCAm and BRCAwt cells. p-ATM expression decreased in response to combination ATM and PARP inhibition. Attenuated levels of p-ATM resulted in increased levels of p- and T-γH2AX, indicating an accumulation of double stranded DNA breaks. Conclusion: In vitro, inhibition of several relevant, oncogenic pathways yielded sensitivity to PARPi in TNBC. We identified the ATM inhibitor, AZD0156, and olaparib as a potent combination regardless of BRCA status, a finding currently being evaluated in patient-derived in vivo models. Combination ATM plus PARP inhibitor therapy is a promising and feasible approach for near term translation in metastatic TNBC. Citation Format: Sammons S, Yip C, Anderson G, Force J, Marcom K, Westbrook K, Anders CK, Blackwell K, Wood K. Small-molecule screening nominates diverse combination therapies that sensitize BRCA mutant and wild-type triple negative breast cancer to PARP inhibition [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 P1-06-04.

Abstract IA13: Combination of DNA methyltransferase and PARP inhibitors as a novel therapy strategy for multiple cancers: Key data in AML and triple negative breast cancer

Abstract Poly (ADP-ribose) polymerase (PARP) inhibitors represent one of the most exciting recent developments in cancer therapy. While substantial efficacy has been shown with clinically available PARP inhibitors (PARPis), to date, in treatment of hereditary deletions of BRCA1/2 in breast and ovarian cancers, the high promise of these drugs has not yet been realized in sporadic cancers. We present here strong preclinical data for a novel, mechanistically based, combinatorial approach to using DNA methyltransferase inhibitors (DNMTis), such as decitabine (DAC) and 5-Azacytidine (5-AZA), with PARP inhibitors (PARPis) as a treatment strategy for acute myelogenous leukemias (AML) and triple negative breast cancer (TNBC). We have previously demonstrated that low doses of 5-AZA and DAC alone show efficacy in AML and TNBC, and propose treatment with PARPis to enhance sensitivity of cancer cells to DNMTis. The mechanistic rationale for our approach is based upon: 1) data from our group and others showing DNMT1 and PARP1 associate in a complex, and this association increases with DNA damage; 2) the fact that 5-AZA and DAC trap DNMTs led us to hypothesize that these drugs might also increase PARP trapping at DNA damage sites; and 3) the cytotoxicity of the most potent PARPis (e.g. BMN 673) appears to correlate with the degree of trapping of PARP1 in chromatin. We first find that in cultured human AML and TNBC cells, the DNMTis (5 to 20 nM DAC or 100 to 200nM 5-AZA) and PARPis (1 to 10 nM BMN 673) alone trap PARP into chromatin, and this effect is enhanced when the drugs are combined. In addition, the PARPi-DNMTi combination treatment of TNBC cell line MDA-MB-231 resulted in significantly enhanced retention of PARP1 and DNMT1 at sites of double strand breaks (DSBs) induced by laser microirradiation. Concomitant with this, the combined doses resulted in significant increases in cytotoxic DSBs, observed 4-24 hours after DSB induction, when compared to single-drug treatments. Homologous recombination (HR) DSB repair activity also appears decreased, as measured by GFP reporter assays. In keeping with these findings, colony survival assays demonstrated that the combination treatment, compared to either drug alone, strongly inhibited colony formation of TNBC cell lines (N=4). Notably non-tumorigenic MCF10A cells showed no significant differences in colony numbers with single or combination drug treatments. Similar to TNBCs, AML cell lines (N=3) as well as primary AML cells (N=8) showed dramatic decreases in colonies in combination vs single agent drug treatments. In the most important translational implications of the preliminary studies, in in vivo therapy TNBC and AML models in immune-deficient mice, our low dose combinations of DNMTis and PARPis provide for potent anti-tumor responses. Mouse xenograft experiments using BRCA mutant TNBC cell line SUM149PT demonstrated that the combination treatment has a significant (p<0.05) survival advantage compared to control (vehicle), AZA (0.5mg/kg) or BMN (0.3 mg/kg) alone. Importantly, mouse MDA-MB-231 xenografts with intact BRCA1 showed significant survival with the combined drug treatment. Likewise in AML xenografts of MOLM14 and MV411 cell lines treated with the drug combination show significantly decrease leukemia burden, as measured by luciferase imaging. Our data suggest a novel use of both DNMTis and PARPis in a compelling therapeutic strategy for TNBCs independent of BRCA mutations and poor prognosis AML; the latter will be investigated in a clinical trial to be based at the University of Maryland and funded by Van Andel-SU2C. Citation Format: Nidal Muvarak, Khadiza Chowdhury, Carine Robert, Xia Limin, Eun Yong Choi, Yi Cai, Marina Bellani, Michael Seidman, Maria R. Baer, Rena Lapidus, Stephen B. Baylin, Feyruz V. Rassool. Combination of DNA methyltransferase and PARP inhibitors as a novel therapy strategy for multiple cancers: Key data in AML and triple negative breast cancer [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr IA13.

Efficacy of anthracycline/taxane-based neo-adjuvant chemotherapy on triple-negative breast cancer inBRCA1/BRCA2mutation carriers

This study aims to estimate the pathologic complete response (pCR) rate after neo-adjuvant chemotherapy and to compare disease-free survival (DFS) and overall survival (OS) between pCR and non-pCR groups of patients with triple-negative breast cancer (TNBC) and deleterious BRCA1 or BRCA2 mutation. We carried out a retrospective analysis of 53 patients including 46 BRCA1, 6 BRCA2, and 1 combined BRCA1 and BRCA2 mutation. All patients had been diagnosed with triple-negative breast cancer (TNBC) between 1997 and 2014. Neo-adjuvant therapy consisted of regimens that were based on anthracycline or an anthracycline-taxane doublet. DFS included any relapse or second cancer. The Kaplan-Meier method and the log-rank test were used to compare pCR and non-pCR groups. A pCR was observed in 23 (42.6% [95% CI, 29.2%-56.8%]) of the TNBC included. The pCR rate was 38.3% [95% CI, 26%-55%] among BRCA1 mutation carriers, and 66% among the 6 BRCA2 mutation carriers. Median follow-up was 4.4years (range 0.62-16.2years) and did not differ between the groups (P=.25). Fifteen relapses and six second cancers were recorded during the follow-up period. Eleven deaths occurred, all of which were in the non-pCR group. DFS (P<.01) and OS (P<.01) were significantly better in the pCR group than the non-pCR group. This study shows a high pCR rate after neo-adjuvant therapy in BRCA-mutated triple-negative breast cancer, and the survival results confirm the prognostic value of pCR in this group. These outcomes should be considered as a basis of comparison to be used by future studies about new therapies in this domain.

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. Theseresults highlight the significance of HR disruption as a therapeutic strategy and support the broad use of combined CDK12 and PARP inhibition in TNBC.

Abstract LB-205: Combination of DNA methyltransferase and PARP inhibitors as a novel therapy strategy for poor prognosis acute myeloid leukemia and triple-negative breast cancers

Abstract Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis) have shown efficacy in treatment of breast and ovarian cancers with hereditary deletions of BRCA1/2, but the high promise of these drugs has not yet been realized in sporadic cancers. We present here strong preclinical data for a novel, mechanistically based, combinatorial approach to using DNA methyltransferase inhibitors (DNMTi’s), such as decitabine (DAC) and 5-Azacytidine (5-AZA), with PARP inhibitors (PARPi’s) as a treatment strategy for acute myelogenous leukemias (AML) and estogen-, progesterone- and HER2-receptor negative, or triple negative breast cancer (TNBC). We have previously demonstrated that low doses of 5-AZA and DAC alone show efficacy in AML and TNBC, and propose treatment with PARPi's to enhance sensitivity of cancer cells to DNMTis. The mechanistic rationale for our approach is based upon: 1) data from our group and others showing DNMT1 and PARP1 associate in a complex, and this association increases with DNA damage; 2) the fact that 5-AZA and DAC trap DNMT's led us to hypothesize that these drugs might also increase PARP trapping at DNA damage sites; and 3) the cytotoxicity of the most potent PARPi's (e.g. Talazoparib) appears to correlate with the degree of trapping of PARP1 in chromatin. We find that in cultured human AML and TNBC cells, the DNMTi's (5 to 20 nM DAC or 100 to 200nM 5-AZA) and PARPi's (1 to 10 nM Talazoparib) alone trap PARP into chromatin, and this effect is enhanced when the drugs are combined. In addition, the PARPi-DNMTi combination treatment in TNBC MDA-MB-231 and AML MOLM-14 cell lines resulted in significantly increased DNA double strand breaks (DSBs) and enhanced retention of PARP1 and DNMT1 at laser microirradiation DNA damage sites. Compared with non-tumorigenic MCF10A cells, in TNBC cell lines (N = 4), the combined doses resulted in significant (p&amp;lt;0.05) increases in colony survival, when compared to single drug treatments. Similarly, AML cell lines (N = 3) as well as primary cells (N = 8) showed dramatic decreases (p&amp;lt;0.05) in colonies in combination vs single agent drug treatments. In the most important translational implications, mouse xenograft experiments, using BRCA mutant TNBC cell line SUM149PT and MDA-MB-231 with intact BRCA1, both models demonstrated that the combination treatment has a significant (p&amp;lt;0.05) survival advantage, compared to control (vehicle), AZA (0.5mg/kg) or BMN (0.3 mg/kg) alone. Likewise in AML xenografts of MOLM14 and MV411 cell lines with poor prognosis marker, FMS-like 3 internal tandem duplication (FLT3/ITD), the drug combination show (p&amp;lt;0.05) significantly decreased leukemia burden, as measured by luciferase imaging. Our data suggest a novel use of both DNMTi's and PARPi's in a compelling therapeutic strategy for TNBCs independent of BRCA mutations and poor prognosis AML; the latter will be investigated in a clinical trial funded by Van Andel-SU2C. Citation Format: Feyruz V. Rassool, Nidal Muvarak, Khadiza Chowdury, Carine Robert, Limin Xia, Eun Yong Choi, Yi Cai, Marina Bellani, Ying Zou, Michael Seidman, Søren Bentzen, Maria Baer, Rena Lapidus, Stephen B. Baylin. Combination of DNA methyltransferase and PARP inhibitors as a novel therapy strategy for poor prognosis acute myeloid leukemia and triple-negative breast cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-205.

Triple-negative breast cancer: molecular subtypes and new targets for therapy.

Triple-negative breast cancer (TNBC) is a molecularly diverse disease. This heterogeneity has limited the success of targeted therapy in unselected patients to date. Recent transcriptional analysis has divided TNBC into transcriptionally similar subtypes that may have different sensitivity to neoadjuvant chemotherapy and targeted therapy. At present, chemotherapy is the mainstay of treatment for early-stage and advanced TNBC; however, several actionable targets show promise in preclinical studies. Novel therapeutic strategies are currently being tested in phase II and phase III trials and will likely require patient stratification before therapy. Examples of these tailored approaches include poly(ADP-ribose) polymerase inhibitors for BRCA-mutated TNBC, antiandrogens for androgen receptor (AR)-positive TNBC, fibroblast growth factor receptor (FGFR) inhibitors for TNBC harboring FGFR amplifications, and gamma-secretase inhibitors for TNBC with mutations in the PEST domain of NOTCH proteins. Treatment of TNBC based on molecular subsets represents a potential algorithm for the future. Well-designed clinical trials with incorporation of integrated biomarkers are necessary to advance the development of molecularly targeted therapy for different subgroups of TNBC.

Relapsed Triple-Negative Breast Cancer: Challenges and Treatment Strategies

Triple negative breast cancer (TNBC) is the most lethal form of breast cancer. Treatment options for advanced disease are limited, with a median survival from the time of developing metastases rarely exceeding 1 year. TNBC is heterogeneous, and harbours several molecular alterations. Unfortunately, up to now, clinical trials combining targeted agents and chemotherapy have failed to show substantial survival improvement; therefore, chemotherapy remains the backbone of treatment. No major advances have been made in the field of cytotoxic treatments, and hopefully ongoing trials will contribute to a more precise definition of the role of platinum salts in sporadic and BRCA-mutated TNBC. Moreover, recent gene expression data suggest that TNBC can be further segmented into smaller subgroups, characterized by different activated pathways, which may therefore warrant different targeted treatments. The lack of efficacy that has been observed for the majority of targeted agents in TNBC so far may derive from the inclusion of unselected TNBC patient populations, not enriched for patients presenting an alteration in the target. Therefore, one of the major challenges in the future is to integrate biological data into clinical trials to obtain the highest efficacy from promising targeted treatments such as anti-angiogenetic agents, poly (ADP-ribose) polymerase-1 (PARP), epidermal growth factor receptor, fibroblast growth factor receptor, androgen receptor and phosphoinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) inhibitors.

Abstract P5-19-03: Olaparib plus carboplatin in combination with vandetanib inhibited the growth of BRCA-wt triple negative breast tumors in mice: Outside BRCA-box

Abstract Introduction: PARP inhibition has emerged as one of the most exciting and promising ‘targeted’ therapeutic strategies in the treatment of advanced triple negative breast cancer (TNBC) – the intended ‘target,’ being DNA repair (Anders CK, 2010). Although olaparib is known to have antitumor activity in BRCA-related TNBC cells, a limited number of preclinical and clinical studies have shown antitumor efficacy of olaparib in non-BRCA-related BC (Shimo T, 2012). Understanding the biology of TNBC cells has identified molecular targets including RTK(s), such as EGFR. Purpose: Here we tested the combination of a PARP inhibitor, olaparib (O) (AstraZeneca) plus carboplatin (C) with the EGFR/VEGFR inhibitor, vandetanib (V) (AstraZeneca) in a BRCA-wt TNBC model. Methods: Athymic mice bearing TNBC (BRCA-wt VEGFR expressing MDA-MB231&amp; MDA-MB468 [EGFR amplified/overexpressed]) xenograft tumors (200 mm3) were treated with O plus C in combination with V (Arms: vehicle control 1, vehicle control 2, C+O, V, C+O+V). In vitro effects of V in combination with O plus C (or temozolomide) on clonogenic growth (3D on-TOP assay), proliferation (MTT and CelltiterGLO), apoptosis (Apoptosis Array), cell signaling marker(s) (Western Blot), and tumor cell phenotypes (fibronectin-directed migration, matrigel-invasion, and vascular mimicry) were investigated in a panel of five BRCA-wt and BRCA-mutated TNBC cell lines. The effects of V were tested on (a) cell signaling marker(s), (b) angiogenesis marker (HIF-1alpha), and (c) angiogenesis related phenotypes (vitronectin-directed migration, and cord formation) in HUVEC. Results: (1) O plus C in combination with V caused a regression of the in vivo growth of established tumors by 50% which was evident in both the BRCA-wt TNBC models tested. Interestingly, a marked suppression of the progression of tumor-growth was observed in the O plus C arm. (2) In vitro, V alone (10 µM) inhibited baseline as well as EGF-induced phosphorylation of AKT (S473/T308), S6RP, 4EBP1 and ERK. (3) TNBC cells exhibited higher sensitivity to V in clonogenic assays when combined with a 10 µM fixed dose of O and C/temozolomide. (4) A combination of V with O plus C increased cleaved caspase-3, PARP cleavage, and pro-apoptotic signals, while inhibiting vascular mimicry, migration, and invasion in MDA-MB231, MDA-MB468, and SUM149 cells. (5) Treatment with V blocked cord formation, migration, EGF-induced HIF-1α accumulation, and phosphorylation of AKT, 4EBP1, and ERK in HUVEC. Conclusion: A profound anti-tumor efficacy of O plus C in combination with V in BRCA-wt TNBC model can be explained by a significant anti-proliferative/pro-apoptotic and anti-migratory/anti-invasive actions of the drugs (alone or in combination), as observed both in tumor cells as well as in endothelial compartments. The combination of O plus C plus V merits further investigation in TNBC. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-19-03.