Abstract 2077: A novel assay for PARP-DNA trapping provides insights into the mechanism of action (MoA) of clinical PARP inhibitors (PARPi)

Efficacy and Safety of BRCA-targeted Therapy (Polyadenosine Diphosphate-ribose Polymerase Inhibitors) in Treatment of BRCA-mutated Breast Cancer: A Systematic Review and Meta-analysis

Breast cancer is the second leading cause of women's cancer deaths after lung cancer. Risk factors such as environment, lifestyle, and genetics contribute to its development, including mutation in the breast cancer (BRCA) gene. Polyadenosine diphosphate-ribose polymerase inhibitors (PARPi) target these mutations, benefiting patients with advanced cancers. This review summarizes PARPi' safety and efficacy in the treatment of BRCA-mutated breast cancer. PubMed, The Cochrane Library for Clinical Trials, and Science Direct, were searched for articles from inception to April 2024. Eligible articles were analyzed, and data were extracted for meta-analysis using RevMan 5.4 software with a random-effect model. Out of 430 articles identified from online databases, only 6 randomized control trials including 3610 patients were included in the analysis. PARPi therapy improved progression-free survival (hazard ratio: 0.64; 95% CI: 0.56, 0.73; P< 0.00001) and overall survival (hazard ratio: 0.84; 95% CI: 0.73, 0.98 P = 0.02), according to the analysis. In our safety analysis, the risk of adverse events was not statistically different between PARPi versus chemotherapy (relative risk [RR]: 1.08; 95% CI: 0.44, 2.68; P = 0.86), and combined PARPi and standard chemotherapy (RR: 1.00; 95% CI: 0.93, 1.07; P = 0.80). The only statistically significant difference was observed in anemia, where PARPi increased the risk of developing anemia compared with standard chemotherapy (RR: 6.17; 95% CI: 2.44, 15.58; P = 0.0001). In BRCA-mutated breast cancer, PARPi treatment shows better overall survival and progression-free survival compared with standard chemotherapy or placebo. Furthermore, PARPi, either alone or in combination therapy, does not increase the risk of adverse events in these patients, as per the meta-analysis.

A review: FDA-approved fluorine-containing small molecules from 2015 to 2022

Fluorine-containing small molecules have occupied a special position in drug discovery research. The successful clinical use of fluorinated corticosteroids in the 1950s and fluoroquinolones in the 1980s led to an ever-increasing number of approved fluorinated compounds over the last 50 years. They have shown various biological properties such as antitumor, antimicrobial, and anti-inflammatory activities. Fluoro-pharmaceuticals have been considered a strong and practical tool in the rational drug design approach due to their benefits from potency and ADME (absorption, distribution, metabolism, and excretion) points of view. Herein, approved fluorinated drugs from 2015 to 2022 were reviewed.

Unraveling MYC's Role in Orchestrating Tumor Intrinsic and Tumor Microenvironment Interactions Driving Tumorigenesis and Drug Resistance

The transcription factor MYC plays a pivotal role in regulating various cellular processes and has been implicated in tumorigenesis across multiple cancer types. MYC has emerged as a master regulator governing tumor intrinsic and tumor microenvironment interactions, supporting tumor progression and driving drug resistance. This review paper aims to provide an overview and discussion of the intricate mechanisms through which MYC influences tumorigenesis and therapeutic resistance in cancer. We delve into the signaling pathways and molecular networks orchestrated by MYC in the context of tumor intrinsic characteristics, such as proliferation, replication stress and DNA repair. Furthermore, we explore the impact of MYC on the tumor microenvironment, including immune evasion, angiogenesis and cancer-associated fibroblast remodeling. Understanding MYC's multifaceted role in driving drug resistance and tumor progression is crucial for developing targeted therapies and combination treatments that may effectively combat this devastating disease. Through an analysis of the current literature, this review's goal is to shed light on the complexities of MYC-driven oncogenesis and its potential as a promising therapeutic target.

Preclinical Characterization of AZD5305, A Next-Generation, Highly Selective PARP1 Inhibitor and Trapper

PURPOSE

We hypothesized that inhibition and trapping of PARP1 alone would be sufficient to achieve antitumor activity. In particular, we aimed to achieve selectivity over PARP2, which has been shown to play a role in the survival of hematopoietic/stem progenitor cells in animal models. We developed AZD5305 with the aim of achieving improved clinical efficacy and wider therapeutic window. This next-generation PARP inhibitor (PARPi) could provide a paradigm shift in clinical outcomes achieved by first-generation PARPi, particularly in combination.

EXPERIMENTAL DESIGN

AZD5305 was tested in vitro for PARylation inhibition, PARP-DNA trapping, and antiproliferative abilities. In vivo efficacy was determined in mouse xenograft and PDX models. The potential for hematologic toxicity was evaluated in rat models, as monotherapy and combination.

RESULTS

AZD5305 is a highly potent and selective inhibitor of PARP1 with 500-fold selectivity for PARP1 over PARP2. AZD5305 inhibits growth in cells with deficiencies in DNA repair, with minimal/no effects in other cells. Unlike first-generation PARPi, AZD5305 has minimal effects on hematologic parameters in a rat pre-clinical model at predicted clinically efficacious exposures. Animal models treated with AZD5305 at doses ≥0.1 mg/kg once daily achieved greater depth of tumor regression compared to olaparib 100 mg/kg once daily, and longer duration of response.

CONCLUSIONS

AZD5305 potently and selectively inhibits PARP1 resulting in excellent antiproliferative activity and unprecedented selectivity for DNA repair deficient versus proficient cells. These data confirm the hypothesis that targeting only PARP1 can retain the therapeutic benefit of nonselective PARPi, while reducing potential for hematotoxicity. AZD5305 is currently in phase I trials (NCT04644068).

Combined PARP and ATR inhibition potentiates genome instability and cell death in ATM-deficient cancer cells

The poly (ADP-ribose) polymerase (PARP) inhibitor olaparib is FDA approved for the treatment of BRCA-mutated breast, ovarian and pancreatic cancers. Olaparib inhibits PARP1/2 enzymatic activity and traps PARP1 on DNA at single-strand breaks, leading to replication-induced DNA damage that requires BRCA1/2-dependent homologous recombination repair. Moreover, DNA damage response pathways mediated by the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia mutated and Rad3-related (ATR) kinases are hypothesised to be important survival pathways in response to PARP-inhibitor treatment. Here, we show that olaparib combines synergistically with the ATR-inhibitor AZD6738 (ceralasertib), in vitro, leading to selective cell death in ATM-deficient cells. We observe that 24 h olaparib treatment causes cells to accumulate in G2-M of the cell cycle, however, co-administration with AZD6738 releases the olaparib-treated cells from G2 arrest. Selectively in ATM-knockout cells, we show that combined olaparib/AZD6738 treatment induces more chromosomal aberrations and achieves this at lower concentrations and earlier treatment time-points than either monotherapy. Furthermore, single-agent olaparib efficacy in vitro requires PARP inhibition throughout multiple rounds of replication. Here, we demonstrate in several ATM-deficient cell lines that the olaparib and AZD6738 combination induces cell death within 1-2 cell divisions, suggesting that combined treatment could circumvent the need for prolonged drug exposure. Finally, we demonstrate in vivo combination activity of olaparib and AZD6738 in xenograft and PDX mouse models with complete ATM loss. Collectively, these data provide a mechanistic understanding of combined PARP and ATR inhibition in ATM-deficient models, and support the clinical development of AZD6738 in combination with olaparib.