Abstract C109: INTASYL™ PH-894 self-delivering RNAi targeting BRD4 enhances the antigenicity of melanoma cells through MART-1 upregulation
Authors: Rivest Brianna , Maxwell Melissa , Boone Andrew , Cuiffo Benjamin , Yan Dingxue , Cardia James 
Published: December 2023

Background:   BRD4 is a member of the family of bromodomain and extra-terminal motif (BET) proteins that act as epigenetic readers and regulators of gene transcription. BRD4 has been shown to be significantly upregulated in cancer including melanoma, with preclinical data supporting BRD4 inhibition as a promising therapeutic target.  However, clinical translation of BRD4 inhibitors (BRD4i) has remained elusive. Current small molecule inhibitors of BET proteins are not specific to BRD4 as demonstrated by their inhibition of other members of the BET protein family. Additionally, systemic approaches must overcome a narrow therapeutic window. The INTASYL™ platform is a self-delivering RNAi technology that imparts small molecule-like properties to interfering RNAs, providing efficient delivery to target cells without need for specialized formulations or drug delivery systems. PH-894 is an INTASYL compound that silences BRD4 mRNA. PH-894 has been shown to specifically silence BRD4 mRNA and provide robust direct and abscopal antitumor efficacy in vivo when administered intratumorally (IT).  Therefore, IT PH-894 holds promise to realize the therapeutic potential of BRD4 inhibition by avoiding toxicities associated with systemic delivery of small molecule BET inhibitors.   Here, we explored the impact of PH-894 mediated BRD4 inhibition on antigenicity of melanoma tumor cells. Specifically, expression of the melanoma tumor-associated antigen MART-1 was studied following PH-894 treatment.

Methods: SK-MEL-5 melanoma cells were treated for 72 hours with PH-894 or a non-targeting control (NTC) INTASYL compound. After 72 hours (Day 3), PH-894 was washed out and cells were replated in media containing no INTAYSL compound for the duration of the experiment. Cells were collected for analysis of both BRD4 and MART-1 mRNA and protein from Day 3 through Day 7.

Results: PH-894 provided robust silencing of BRD4 mRNA and protein in SK-MEL-5 melanoma cells. Furthermore, PH-894 treatment resulted in a statistically significant upregulation of MART-1 mRNA and protein in these cells. BRD4 silencing and MART-1 upregulation persisted through at least 7 days post-treatment with PH-894.

Conclusions: This study demonstrates the ability of PH-894 to efficiently silence BRD4 and upregulate MART-1, thereby increasing the antigenicity of melanoma cells. Local treatment with PH-894 is a potential strategy to decrease BRD4 expression and increase immune response to cancer cells while reducing toxicities associated with systemic BETi. This study supports further development of PH-894 for injectable solid tumor indications such as melanoma.

Citation Format: Brianna Rivest, Melissa Maxwell, Andrew Boone, Benjamin Cuiffo, Dingxue Yan, James Cardia. INTASYL™ PH-894 self-delivering RNAi targeting BRD4 enhances the antigenicity of melanoma cells through MART-1 upregulation [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 C109.