Inhibition of p300/CBP Overcomes BTK Inhibitor Resistance in MCL By Counteracting IL-6/JAK/STAT3 Signaling

Introduction: Although Bruton's tyrosine kinase inhibitors (BTKi) are effective against relapsed refractory mantle cell lymphoma (MCL), their limited efficacy and resistance remain clinical issues. Previously, we conducted CRISPR/Cas9 screening and found that p300/CBP, lysine acetyltransferases, are the genes responsible for one mechanism of BTKi resistance. A p300/CBP inhibitor A-485 with ibrutinib synergistically induced apoptosis and cell cycle arrest in ibrutinib-resistant MCL cells.

Methods: To elucidate the synergistic mechanism, we conducted RNA sequencing using an ibrutinib-resistant MCL cell line, Granta519, and compared the transcriptomic profiles of Granta519, treated with ibrutinib, A-485, or both.

Results: Genes related to the G2M checkpoint were upregulated when treated with the combination therapy. Pathway enrichment analysis revealed that the combination therapy downregulated pathways including Myc targets, TNF-α signaling via NF-κB, E2F targets, mTORC1 signaling, and IL-2/STAT5 signaling activation. Moreover, we observed that addition of A-485 restored the efficiency of ibrutinib to suppress downstream BCR signaling in Granta519 cells. We also detected IL6/JAK/STAT3 signaling activation by ibrutinib monotherapy, and the addition of A-485 significantly counteracted IL6/JAK/STAT3 signaling activation, suggesting that IL6/JAK/STAT3 signaling contributes to ibrutinib resistance.

Pathway analysis showed that Myc was the most suppressed target by the combination therapy, reducing Myc mRNA levels by 90%. Using the MTS assay, we confirmed that Myc overexpression impaired the therapeutic effect of A-485 and significantly reduced the synergistic therapeutic effect of the combination therapy. This impairment suggests that the combination therapy achieves therapeutic effects by attenuating Myc function. We next focused on IL6/JAK/STAT3 signaling and tested ruxolitinib to inhibit JAK1/2. Interestingly, the IC50 value of ruxolitinib was lower in ibrutinib-resistant cells than ibrutinib-sensitive cells. To confirm that A-485 suppresses IL6/JAK/STAT3 signaling, we also confirmed that A-485 inhibited the nuclear translocation of STAT3 and the acetylation of STAT3 by Western blotting.

Conclusion: p300/CBP inhibition overcomes BTKi resistance in MCL through IL-6/JAK/STAT3 signaling inhibition and attenuation of Myc transcription. Thus, p300/CBP inhibition could be a novel strategy for treating BTKi-resistant MCL.

Arima:Verastem, Inc: Other. Takaori-Kondo:Gilead Sciences: Honoraria; AstraZeneca K.K.: Honoraria; Megakaryon Co., Ltd.: Consultancy, Honoraria; Otsuka Pharmaceutical Co., Ltd.: Honoraria; Janssen Pharmaceutical K.K.: Honoraria; Bristol Myers Squibb: Honoraria; Japanese Society of Hematology: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Shionogi & Co., Ltd.: Research Funding; Kyowa Kirin Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Eisai Co., Ltd: Research Funding; AbbVie Inc.: Honoraria, Research Funding; ASAHI KASEI PHARMA CORPORATION: Research Funding; PhamaEssentia Japan: Research Funding; Dai-ichi Kogyo Seiyaku Co., Ltd.: Research Funding; ONO PHARMACEUTICAL CO., LTD.: Research Funding.