Abstract C107: INTASYL™ self-delivering RNAi therapeutic targeting BRD4 elicits on-target apoptosis of human tumor cells

Abstract Background: A wealth of preclinical data supports the therapeutic potential of targeting bromodomain and extra-terminal motif (BET) protein BRD4 as a promising strategy to treat a spectrum of cancers. However, clinical translation of BRD4 inhibitors (BRD4i) has not yet been achieved. While clinical trials for next generation small molecule BRD4i compounds are ongoing, such systemic approaches must overcome a narrow therapeutic window. Therefore, a local approach to BRD4i represents a potential strategy to realize its therapeutic potential in injectable solid tumor indications. INTASYL™ is a self-delivering RNAi platform technology that enables rapid and efficient delivery into target cells without need for specialized drug delivery systems or formulations. INTASYL compounds provide precise and durable gene silencing. In preclinical studies, INTASYL compounds provided a robust direct, abscopal and/or anti-metastatic antitumor efficacy when administered intratumorally (IT) as monotherapy, multi-targeting formulations, or in combination with current standard of care treatments. PH-894 is an INTASYL compound designed to specifically silence human BRD4 mRNA. We assessed the direct on-target antitumor effects of PH-894 across a spectrum of human tumor cell lines: HepG2 (hepatocellular carcinoma), HCC1806 (acantholytic squamous cell carcinoma), A549 (lung adenocarcinoma), U-251 MG (malignant glioblastoma), SK-MEL-5 (melanoma), HT-29 (colorectal adenocarcinoma), SK-OV-3 (ovarian adenocarcinoma), HeLa (cervical adenocarcinoma). Methods: Tumor cells were cell-cycle synchronized by serum starvation for ~18 h and treated in the presence of serum with increasing concentrations of PH-894 or a non-targeting control (NTC) INTASYL for 24 h. Apoptosis was assessed by annexin-v and 7-aminoactinomycin D (7AAD) staining/flow cytometry. On-target silencing of BRD4 mRNA by PH-894 was confirmed at 24 h by qPCR. Results: PH-894 elicited on-target apoptosis in all tumor cell lines tested in a concentration correlated manner, with variable levels of response across the various tumor cell lines. BRD4 mRNA was specifically silenced on-target in a concentration correlated manner with PH-894. Conclusions: This study demonstrates the direct cytotoxic effects of INTASYL PH-894 mediated by sequence specific silencing of BRD4 mRNA across tumor cell lines representing a broad spectrum of injectable solid tumors. Local therapy with IT PH-894 represents a potential strategy to mitigate toxicities associated with systemic BETi or BRD4i. This study supports further development of PH-894 toward unlocking the therapeutic potential of BRD4i. Citation Format: Andrew Boone, Dingxue Yan, Melissa Maxwell, Brianna Rivest, James Cardia, Benjamin Cuiffo. INTASYL™ self-delivering RNAi therapeutic targeting BRD4 elicits on-target apoptosis of human tumor cells [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C107.