Phase II trial of veliparib and temozolomide in metastatic breast cancer patients with and without BRCA1/2 mutations

PARP inhibitors: enhancing efficacy through rational combinations

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

Mechanisms of PARP-Inhibitor-Resistance in BRCA-Mutated Breast Cancer and New Therapeutic Approaches

The recent success of Poly (ADP-ribose) polymerase (PARP) inhibitors has led to the approval of four different PARP inhibitors for the treatment of BRCA1/2-mutant breast and ovarian cancers. About 40-50% of BRCA1/2-mutated patients do not respond to PARP inhibitors due to a preexisting innate or intrinsic resistance; the majority of patients who initially respond to the therapy inevitably develop acquired resistance. However, subsets of patients experience a long-term response (>2 years) to treatment with PARP inhibitors. Poly (ADP-ribose) polymerase 1 (PARP1) is an enzyme that plays an important role in the recognition and repair of DNA damage. PARP inhibitors induce "synthetic lethality" in patients with tumors with a homologous-recombination-deficiency (HRD). Several molecular mechanisms have been identified as causing PARP-inhibitor-resistance. In this review, we focus on the molecular mechanisms underlying the PARP-inhibitor-resistance in BRCA-mutated breast cancer and summarize potential therapeutic strategies to overcome the resistance mechanisms.

Enhancing the anti-tumor response by combining DNA damage repair inhibitors in the treatment of solid tumors

The anti-cancer efficacy of anti-malignancy therapies is related to DNA damage. However, DNA damage-response mechanisms can repair DNA damage, failing anti-tumor therapy. The resistance to chemotherapy, radiotherapy, and immunotherapy remains a clinical challenge. Thus, new strategies to overcome these therapeutic resistance mechanisms are needed. DNA damage repair inhibitors (DDRis) continue to be investigated, with polyadenosine diphosphate ribose polymerase inhibitors being the most studied inhibitors. Evidence of their clinical benefits and therapeutic potential in preclinical studies is growing. In addition to their potential as a monotherapy, DDRis may play an important synergistic role with other anti-cancer therapies or in reversing acquired treatment resistance. Here we review the impact of DDRis on solid tumors and the potential value of combinations of different treatment modalities with DDRis for solid tumors.

Immunotherapy in glioblastoma treatment: Current state and future prospects

Glioblastoma remains as the most common and aggressive malignant brain tumor, standing with a poor prognosis and treatment prospective. Despite the aggressive standard care, such as surgical resection and chemoradiation, median survival rates are low. In this regard, immunotherapeutic strategies aim to become more attractive for glioblastoma, considering its recent advances and approaches. In this review, we provide an overview of the current status and progress in immunotherapy for glioblastoma, going through the fundamental knowledge on immune targeting to promising strategies, such as Chimeric antigen receptor T-Cell therapy, immune checkpoint inhibitors, cytokine-based treatment, oncolytic virus and vaccine-based techniques. At last, it is discussed innovative methods to overcome diverse challenges, and future perspectives in this area.

Folate receptor targeted nanoparticles containing niraparib and doxorubicin as a potential candidate for the treatment of high grade serous ovarian cancer

Combination chemotherapy is an established approach used to manage toxicities while eliciting an enhanced therapeutic response. Delivery of drug combinations at specific molar ratios has been considered a means to achieve synergistic effects resulting in improvements in efficacy while minimizing dose related adverse drug reactions. The benefits of this approach have been realized with the FDA approval of Vyxeos®, the first liposome formulation to deliver a synergistic drug combination leading to improved overall survival against standard of care. In the current study, we demonstrate the synergistic potential of the PARP inhibitor niraparib and doxorubicin for the treatment of ovarian cancer. Through in vitro screening in a panel of ovarian cancer cell lines, we find that niraparib and doxorubicin demonstrate consistent synergy/additivity at the majority of evaluated molar ratio combinations. Further to these findings, we report formulation of a nanoparticle encapsulating our identified synergistic combination. We describe a rational design process to achieve highly stable liposomes that are targeted with folate to folate-receptor-alpha, which is known to be overexpressed on the surface of ovarian cancer cells. With this approach, we aim to achieve targeted delivery of niraparib and doxorubicin at a pre-determined synergistic molar ratio via increased receptor-mediated endocytosis.

Breast cancer heterogeneity and its implication in personalized precision therapy

Breast cancer heterogeneity determines cancer progression, treatment effects, and prognosis. However, the precise mechanism for this heterogeneity remains unknown owing to its complexity. Here, we summarize the origins of breast cancer heterogeneity and its influence on disease progression, recurrence, and therapeutic resistance. We review the possible mechanisms of heterogeneity and the research methods used to analyze it. We also highlight the importance of cell interactions for the origins of breast cancer heterogeneity, which can be further categorized into cooperative and competitive interactions. Finally, we provide new insights into precise individual treatments based on heterogeneity.

Combining Poly (ADP-Ribose) Polymerase (PARP) Inhibitors with Chemotherapeutic Agents: Promise and Challenges

Better understanding of molecular drivers and dysregulated pathways has furthered the concept of precision oncology and rational drug development. The role of DNA damage response (DDR) pathways has been extensively studied in carcinogenesis and as potential therapeutic targets to improve response to chemotherapy or overcome resistance. Treatment with small molecule inhibitors of PARP has resulted in clinical response and conferred survival benefit to patients with ovarian cancer, BRCA-mutant breast cancer, HRD-deficient prostate cancer and BRCA-mutant pancreatic cancer, leading to US Food and Drug Administration (FDA) approvals. However, the observed clinical benefit with single agent PARP inhibitors is limited to few tumor types within the relevant genetic context. Since DDR pathways are essential for repair of damage caused by cytotoxic agents, PARP inhibitors have been evaluated in combination with various chemotherapeutic agents to broaden the therapeutic application of this class of drugs. In this chapter, we discuss the combination of PARP inhibitors with different chemotherapeutics agents, clinical experience to date, lessons learnt, and future directions for this approach.

The triple negative breast cancer drugs graveyard: a review of failed clinical trials 2017-2022

INTRODUCTION

Triple-negative breast cancer (TNBC) accounts for 15-20% of breast cancers (BC) and has the worst prognosis. It is characterized by the absence of both hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2). TNBC has more limited therapeutic options compared to other subtypes, meaning that there is still a long way to go to discover target treatments.

AREAS COVERED

Our review aims to summarize phase II/III clinical trials enrolling patients with TNBC that have been published between 2017 and 2022 but failed to reach their primary endpoint. We here try to emphasize the limitations and weaknesses noted in negative studies and to point out unexpected results which might be useful to enhance the therapeutic approach to TNBC disease.

EXPERT OPINION

A deeper understanding of the mechanisms behind TNBC heterogeneity allowed to enhance the knowledge of new prognostic and predictive biomarkers of response. However, it is also through several failed clinical trials that we were able to define new therapeutic approaches which improved TNBC patients' clinical outcomes. Nowadays, we still need to overcome several difficulties to fully recognize different intracellular and extracellular pathways that crosstalk in TNBC and the mechanisms of resistance to identify novel tailored-patients' therapies.

Targeting cancer stem cells in the tumor microenvironment: An emerging role of PARP inhibitors

Cancer stem cells (CSCs) constitute a small population of cancer cells in the tumor microenvironment (TME), which are responsible for metastasis, angiogenesis, drug resistance, and cancer relapse. Understanding the key signatures and resistance mechanisms of CSCs may help in the development of novel chemotherapeutic strategies to specifically target CSCs in the TME. PARP inhibitors (PARPi) are known to enhance the chemosensitivity of cancer cells to other chemotherapeutic agents by inhibiting the DNA repair pathways and chromatin modulation. But their effects on CSCs are still unknown. Few studies have reported that PARPi can stall replication fork progression in CSCs. PARPi also have the potential to overcome chemoresistance in CSCs and anti-angiogenic potentiality as well. Previous reports have suggested that epigenetic drugs can synergistically ameliorate the anti-cancer activities of PARPi through epigenetic modulations. In this review, we have systematically discussed the effects of PARPi on different DNA repair pathways with respect to CSCs and also how CSCs can be targeted either as monotherapy or as a part of combination therapy. We have also talked about how PARPi can help in reversal of chemoresistance of CSCs and the role of PARPi in epigenetic modifications to hinder cancer progression. We have also elaborated on the aspects of research that need to be investigated for development of successful therapeutic interventions using PARPi to specifically target CSCs in the TME.

PARP Inhibitors for Breast Cancer: Germline BRCA1/2 and Beyond

Simple Summary

Poly-adenosine diphosphate ribose polymerase (PARP) inhibitors (PARPi) are effective against tumors with mutations in DNA repair genes, most commonly in the BRCA1 and BRCA2 genes. Because these tumors are unable to repair their DNA, PARPi have been used to target DNA repair pathways and are useful in the treatment of breast cancers with some of these alterations. There are two FDA-approved PARPi for patients with breast cancer—olaparib and talazoparib. The data on olaparib and talazoparib in the treatment of breast cancer are summarized in this review, and we also explore potential future applications of PARPi beyond inherited BRCA mutations.

Abstract

Poly-adenosine diphosphate ribose polymerase (PARP) inhibitors (PARPi) are approved for BRCA1/2 carriers with HER2-negative breast cancer in the adjuvant setting with a high risk of recurrence as well as the metastatic setting. However, the indications for PARPi are broader for patients with other cancer types (e.g., prostate and ovarian cancer), involving additional biomarkers (e.g., ATM, PALB2, and CHEK) and genomic instability scores. Herein, we summarize the data on PARPi and breast cancer and discuss their use beyond BRCA carriers.

BRCA1 and Breast Cancer: Molecular Mechanisms and Therapeutic Strategies

Breast cancer susceptibility gene 1 (BRCA1) is a tumor suppressor gene, which is mainly involved in the repair of DNA damage, cell cycle regulation, maintenance of genome stability, and other important physiological processes. Mutations or defects in the BRCA1 gene significantly increase the risk of breast, ovarian, prostate, and other cancers in carriers. In this review, we summarized the molecular functions and regulation of BRCA1 and discussed recent insights into the detection and treatment of BRCA1 mutated breast cancer.