Abstract P4-01-06: LP-184, an acylfulvene class small molecule therapeutic, is synthetically lethal in HR deficient and PARP inhibitor resistant triple negative breast cancer

Abstract

Abstract Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer accounting for approximately 15% to 20% of all newly diagnosed breast cancer cases. TNBCs are defined by lack of expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER-2).Due to its special molecular phenotype, it is not sensitive to endocrine therapy or targeted therapy. Therefore, chemotherapy such as anthracyclines or taxanes is the main systemic treatment, but the efficacy of conventional postoperative adjuvant chemoradiotherapy is poor. ~35% of TNBC tumors show abnormalities in the HR pathway, making them sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) and DNA-damaging agents. Although more than 40% BRCA1/2-deficient patients fail to respond to PARPi and a substantial proportion of patients acquire PARPi resistance over time. TNBCs heterogeneous nature, poor prognosis and limited treatment options presents the urgent need of development of novel agents targeting tumor specific alterations. Lantern Pharma is advancing LP-184, an acylfulvene-derived prodrug that is specifically activated in tumors that overexpress the oxidoreductase enzyme Prostaglandin Reductase 1 (PTGR1), for the treatment of solid tumor indications including TNBC. LP-184 has multiple mechanisms of action (MOA). While It is synthetically lethal in tumors harboring DNA damage repair defects including Homologous Recombination (HR) deficiencies, it can also interrupt transcription. LP-184 efficacy was tested in a panel of breast cancer cell lines and patient derived TNBC xenografts models, both sensitive as well as resistant to PARP inhibitors and anthracyclines. LP-184 demonstrated nanomolar potency in six NCI-60 breast cancer cell lines (median IC50 = 327 nM). Subcutaneous patient-derived TNBC xenograft mouse models were used to determine tumor volume responses to LP-184 treatment in vivo. Xenograft tumors were derived from 10 treatment-naive HR deficient (HRD score > 50) primary TNBC patients with known BRCA1/2 loss of heterozygosity (LOH), 7 of which subsequently progressed on PARP inhibitor Olaparib. LP-184 (4mg/kg i.v., (q2d x 5 then 7 days off)x2) led to complete and durable regression in all 10 TNBC HRD-PDX models tested as compared to control (p < 0.0001). A tumor growth inhibition range of 107-141% was achieved across all the 10 models. For LP-184, T/C at the control group end day was 0% in 10/10 models, whereas across the same models for Olaparib, T/C was 0% in 2/10 models and ranged from 15 - 90% in 8/10 models. Terminal body weight change was only a transient weight loss < 4% with LP-184 treatment across all models. LP-184 exhibited superior potency than olaparib in TNBC PDX models that carry HRD mutations including PARP resistant models and was well tolerated in mice. As acylfulvene-induced damage is primarily repaired by transcription-coupled nucleotide-excision repair (TC-NER) and HR pathways, response to LP-184 is influenced by tumor DNA damage repair pathway status. Recent data highlight an important role of super enhancer driven core transcription regulatory circuits in the pathogenesis of TNBCs. Our results support the superior efficacy of LP-184 in TNBCs, likely linked to the multiple MOAs, and establish LP-184 as a promising new agent for future clinical testing in TNBC patients. We finally propose that LP-184 may be broadly efficacious in solid tumors with HR and/or TC-NER pathway defects, such as pancreatic, prostate, ovarian and bladder cancers. Citation Format: Aditya Kulkarni, Neha Biyani, Laura Brullé-Soumaré, Stefano Cairo, Panna Sharma, Kishor Bhatia. LP-184, an acylfulvene class small molecule therapeutic, is synthetically lethal in HR deficient and PARP inhibitor resistant triple negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-06.