Over the past two decades, the natural history of multiple myeloma (MM) has evolved dramatically, owing primarily to novel agents targeting MM in the bone marrow microenvironment (BMM) pathways. However, the mechanisms of resistance acquisition remain a mystery and are poorly understood. Autophagy and apoptosis are tightly controlled processes and play a critical role in the cell growth, development, and survival of MM. Genetic instability and abnormalities are two hallmarks of MM. During MM progression, plasma malignant cells become genetically unstable and activate various signaling pathways, resulting in the overexpression of abnormal proteins that disrupt autophagy and apoptosis biological processes. Thus, achieving a better understanding of the autophagy and apoptosis processes and the proteins that crosslinked both pathways, could provide new insights for the MM treatment and improve the development of novel therapeutic strategies to overcome resistance. This review presents a sufficient overview of the roles of autophagy and apoptosis and how they crosslink and control MM progression and drug resistance. Potential combination targeting of both pathways for improving outcomes in MM patients also has been addressed.

Acute myeloid leukemia (AML) is the most common leukemia in adult patients, with a 5-year survival rate of less than 30 percent. Therefore, more effective therapeutic strategies are required to prolong the survival of AML patients. Importantly, anti-apoptotic proteins, especially B-cell lymphoma 2 (Bcl-2), overexpression in AML is associated with uncontrolled growth as well as chemoresistance. Unsurprisingly, Bruton’s tyrosine kinase (BTK) overexpresses in AML and associated with poor prognosis and chemoresistance. The FDA-approved BTK inhibitor, ibrutinib, has been successful in treating other hematologic malignancies, but a proportion of patients relapse mainly because of acquired mutations at Cys481Ser (C481S) in the kinase domain of BTK. If we are to develop effective BTK-based therapeutic regimens, it is critical that we account for these likely mutations and avoid agents that target the kinase domain. To develop a more selective and effective BTK inhibitor, we modified our first-generation BTK inhibitor to avoid the C481S mutation in the BTK kinase domain. This advance allowed us to develop a second-generation BTK inhibitor, KS151, that shows in vitro potency against C481S mutants. Because BTK and Bcl-2 are critical in chemoresistance and poor prognosis, combination therapy targeting BTK and Bcl-2 is a more viable option for AML patients to achieve better therapeutic outcomes. We propose the combination of KS151 with venetoclax (ABT-199) or ABT-737 in resistant AML cells. We employed a panel of three AML cell lines: Kusami-1, U937, and THP-1. Remarkably, KS151 was able to induce AML cell death with an average IC50 of 4 μM. Furthermore, KS151 showed a significant increase in both venetoclax and ABT-737 efficacy against AML cells. Western blot analysis demonstrated that Kusami-1 cells have the highest expression of both BTK and Bcl-2 proteins. Taken further, flow cytometry (Annexin V staining) demonstrated that KS151 combined with inhibition of Bcl-2 by venetoclax synergistically induced apoptosis (approximately 95%) of Kusami-1 cells. Collectively, the combination therapy showed promising and synergistic in vitro anti-leukemic activity against AML cell lines and represents a new viable treatment for AML patients. Future studies will apply the combination strategies in AML-resistant cell lines and include assessment in patient samples and in vivo studies. Citation Format: Nicole K. Schmalbach, Omar S. Al-Odat, Weam Othman Elbezanti, Gabriella Yao, Daniel A. Guirguis, Krishne Gowda, Shantu G Amin, Tulin Budak-Alpdogan, Subash C. Jonnalagadda, Manoj K. Pandey. Development of a novel BTK inhibitor against resistant acute myeloid leukemia [abstract]. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr A01.

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