Co‐targeting bromodomain and extra‐terminal proteins and MCL1 induces synergistic cell death in melanoma

Abstract

The treatment of melanoma has been markedly improved by the introduction of targeted therapies and checkpoint blockade immunotherapy. Unfortunately, resistance to these therapies remains a limitation. Novel anticancer therapeutics targeting the MCL1 anti‐apoptotic protein have shown impressive responses in haematological cancers but are yet to be evaluated in melanoma. To assess the sensitivity of melanoma to new MCL1 inhibitors, we measured the response of 51 melanoma cell lines to the novel MCL1 inhibitor, S63845. Additionally, we assessed combination of this drug with inhibitors of the bromodomain and extra‐terminal (BET) protein family of epigenetic readers, which we postulated would assist MCL1 inhibition by downregulating anti‐apoptotic targets regulated by NF‐kB such as BCLXL, BCL2A1 and XIAP, and by upregulating pro‐apoptotic proteins including BIM and NOXA. Only 14% of melanoma cell lines showed sensitivity to S63845, however, combination of S63845 and I‐BET151 induced highly synergistic apoptotic cell death in all melanoma lines tested and in an in vivo xenograft model. Cell death was dependent on caspases and BAX/BAK. Although the combination of drugs increased the BH3‐only protein, BIM, and downregulated anti‐apoptotic proteins such as BCL2A1, the importance of these proteins in inducing cell death varied between cell lines. ABT‐199 or ABT‐263 inhibitors against BCL2 or BCL2 and BCLXL, respectively, induced further cell death when combined with S63845 and I‐BET151. The combination of MCL1 and BET inhibition appears to be a promising therapeutic approach for metastatic melanoma, and presents opportunities to add further BCL2 family inhibitors to overcome treatment resistance.

Inhibition of Anti-Apoptotic Bcl-2 Proteins in Preclinical and Clinical Studies: Current Overview in Cancer

“…Several preclinical studies suggested the promising application of Mcl-1 inhibitors in combinatorial therapy: combinations of S63845 and AMG-176 (and the related compound AM8621) with inhibitors of fibroblast growth factor receptor (FGFR), MEK or BRAF showed to efficiently reduce in vitro cell proliferation and in vivo tumor growth of NSCLC [86,150], lung squamous cell carcinoma [151] and glioblastoma [152] models, while combinations of S63845 with chemotherapy or HER2-targeted therapies demonstrated to efficiently inhibit the growth of triple-, as well as HER-2-positive breast cancer [86,153]. The efficacy of combination of S63845 with selective inhibitors, such as ABT-199 or A-1331852, has been also reported in preclinical cervical cancer models [154] and pediatric solid tumors [155], while S63845 in combination with inhibitors of the bromodomain and extra-terminal proteins showed efficacy in metastatic melanoma [156].…”

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

“…Indeed, a wide range of BETi have now been tested together with various BH3mimetics, though most studies have focussed on Venetoclax where enhanced responses from combining the drugs have been seen in vitro and in vivo in many haematological malignancies including T cell lymphoma, CLL, T cell acute lymphoblastic leukaemia, and diffuse large B cell lymphoma [289][290][291][292][293][294][295][296][297], and some solid tumours such as small cell lung cancer [298]. The dual BCL-XL/BCL-2 inhibitor Navitoclax was also shown to synergise with BETi in small cell lung cancer, colorectal cancer, glioma and B-cell lymphomas [299][300][301][302], whilst BH3-mimetics targeting MCL-1 enhance BETi activity in AML and melanoma [292,303].…”

Repurposing melanoma chemotherapy to activate inflammasomes in treatment of BRAF/MAPK inhibitor resistant melanoma

“…Sample preparation, protein quantification and immunoblots were performed as described previously (Emran et al, 2021. Functional assay using lentiviral packaging and transduction were done according to our previous protocol (Tseng et al, 2020). Detailed materials and methodology are provided in the supplementary file.…”