Abstract 2965: GADD45B as a mechanism for enhanced treatment response with the combination of copanlisib and romidepsin in colorectal cancer

Abstract Background: Treatment options for molecular subtypes of colorectal cancer (CRC) are urgently needed, including for PIK3CA mutant CRC. Previous work in our lab demonstrated enhanced activity of copanlisib in combination with romidepsin in PIK3CA mutant CRC models. Here we investigate the induction of GADD45B as a mechanism of the enhanced induction of apoptosis seen with this treatment strategy. Methods: RNA sequencing was done on the CRC 2D cell line, SW48PK (Horizon Discovery, SW48 PIK3CAH1047R/+ mutation) as well as PIK3CA mutant and wild-type patient derived cancer organoids (PDCOs) through the UW Biotechnology Center. All lines were treated with copanlisib, romidepsin, or combination and were compared with untreated controls. GADD45B gene expression was also confirmed on SW48PK, PIK3CA mutant, wild type, and PIK3CA and KRAS mutant PDCOs using RT-qPCR. Results: RNA sequencing determined that there was an increase of GADD45B expression in the SW48PK 2D cell line as well as in PIK3CA mutant and wild-type PDCOs treated with the combination compared to untreated controls (average log2 fold change= 1. 83). A significant increase in GADD45B expression was seen in the SW48PK combination treatment group compared to the control group at 6 hours (combination median fold change= 2. 7, p= 0. 045) and 24 hours (4. 1, p 0. 001). For PIK3CA mutant PDCOs treated with the combination, there was significant increase in GADD45B expression at 6 hours (9. 45, p= 0. 005) and 24 hours (14. 7, p= 0. 002) compared to untreated control. In wild type PDCOs, there was a significant increase in GADD45B expression in the combination compared to untreated control at 6 hours (32. 95, p=0. 004) but not after 24 hours (2. 6, p= 0. 42). For KRAS mutant PDCOs, there was a significant increase in GADD45B expression in combination treated cells at 6 (9. 9, p= 0. 001) and 24 hours (3. 3, p= 0. 047), however, this increase was less than PIK3CA mutant PDCOs at 24 hours (3. 3 vs 14. 7). Conclusions: Copanlisib in combination with romidepsin increases GADD45B expression in PDCOs and SW48PK. Further studies will determine if GADD45B is required for this treatment response. Citation Format: Kennedy Maduscha, Alexa Schmitz, Rebecca DeStefanis, Cheri Pasch, Dustin Deming. GADD45B as a mechanism for enhanced treatment response with the combination of copanlisib and romidepsin in colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2965.