Abstract 4842: Inhibition of BPTF enhances the antitumor effects of doxorubicin through mitochondrial disfunction

Abstract Epigenetics has established itself as a hallmark of cancer having essential roles in its initiation, establishment, and progression. Because of their reversibility, epigenetics has been aggressively targeted pharmacologically to correct abnormal cancer biology in the hopes of reversing cancer phenotypes. To develop novel epigenetic based therapeutic strategies for triple negative breast cancer (TNBC) we combined loss of function approaches (shRNA - KD, CAS9 - KO, and small molecule inhibitors) to the chromatin remolding protein Bromodomain PHD-finger Transcription Factor (BPTF) with standard of care chemotherapies doxorubicin (Doxo), etoposide (Eto) and paclitaxel (Pac). Using the 4T1 and E0771-LMB mouse TNBC models we show that BPTF inhibited cells are more susceptible to the anticancer effects of Doxo, Eto and Pac. However, in tumor bearing mice sensitivity to Doxo, but not Eto or Pac is observed. A 30 color spectral flow cytometry analysis of both intratumor and splenic immune cells does not observe significant differences in immune cell populations from mice bearing BPTF inhibited tumors treated with Doxo. Using immune compromised mouse backgrounds, we observe that the in vivo sensitivity to Doxo requires NK cells, but not CD8 or CD4 T cells. Ex vivo NK cell coculturing assays discovers selectivity for NK cell killing after treatment with Doxo, but not Eto or Pac. RNA-Seq analysis of genetic and BPTF small molecule inhibited cells treated with Doxo discovers the activation of several pro-apoptotic pathways including TNF signaling, apoptosis, mitophagy, and ferroptosis. In vitro analysis shows that BPTF inhibited cells increase apoptosis selectively after exposure to Doxo over Eto and Pac, and the increase in apoptosis coincides with increased mitophagy (Mitotracker QC), but not autophagy (LC3B-GFP-RFP conversion) and is preceded by enhanced cytochrome c release. Depletion of mitophagy regulators reduces the observed enhanced apoptosis in vitro and tumor growth control in vivo with the combination of BPTF KO and Doxo exposure. Analysis of NK cell receptor binding (NKG2D, NCR1, DNAM1) to control and BPTF KD Doxo treated cells did not reveal significant differences and analysis of cytokine, and eicosanoid release with Doxo, Eto and Pac show minor significant differences with BPTF KD. However, enhanced sensitivity to select pro-apoptotic molecules produced by NK cells was observed, and this sensitivity was reduced with suppression of mitophagy. These results suggest that BPTF inhibition results in enhanced mitochondrial disfunction with Doxo exposure which results in enhanced activity of NK cell proapoptotic molecules which results in enhanced tumor growth control. Citation Format: Manjulata Singh, Nasser AlAbdulaly, Madison Isbell, Dipankar Bandyopadhyay, Mikhail Dozmorov, Rebecca Martin, Will Pomerantz, Joseph W. Landry. Inhibition of BPTF enhances the antitumor effects of doxorubicin through mitochondrial disfunction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4842.