Inhibition of PIM Kinases in DLBCL Targets MYC Transcriptional Program and Augments the Efficacy of Anti-CD20 Antibodies

Abstract

The family of PIM serine/threonine kinases includes three highly conserved oncogenes, PIM1, PIM2, and PIM3, which regulate multiple prosurvival pathways and cooperate with other oncogenes such as MYC. Recent genomic CRISPR-Cas9 screens further highlighted oncogenic functions of PIMs in diffuse large B-cell lymphoma (DLBCL) cells, justifying the development of small-molecule PIM inhibitors and therapeutic targeting of PIM kinases in lymphomas. However, detailed consequences of PIM inhibition in DLBCL remain undefined. Using chemical and genetic PIM blockade, we comprehensively characterized PIM kinase–associated prosurvival functions in DLBCL and the mechanisms of PIM inhibition–induced toxicity. Treatment of DLBCL cells with SEL24/MEN1703, a pan-PIM inhibitor in clinical development, decreased BAD phosphorylation and cap-dependent protein translation, reduced MCL1 expression, and induced apoptosis. PIM kinases were tightly coexpressed with MYC in diagnostic DLBCL biopsies, and PIM inhibition in cell lines and patient-derived primary lymphoma cells decreased MYC levels as well as expression of multiple MYC-dependent genes, including PLK1. Chemical and genetic PIM inhibition upregulated surface CD20 levels in an MYC-dependent fashion. Consistently, MEN1703 and other clinically available pan-PIM inhibitors synergized with the anti-CD20 monoclonal antibody rituximab in vitro, increasing complement-dependent cytotoxicity and antibody-mediated phagocytosis. Combined treatment with PIM inhibitor and rituximab suppressed tumor growth in lymphoma xenografts more efficiently than either drug alone. Taken together, these results show that targeting PIM in DLBCL exhibits pleiotropic effects that combine direct cytotoxicity with potentiated susceptibility to anti-CD20 antibodies, justifying further clinical development of such combinatorial strategies. Significance: These findings demonstrate that inhibition of PIM induces DLBCL cell death via MYC-dependent and -independent mechanisms and enhances the therapeutic response to anti-CD20 antibodies by increasing CD20 expression.

MYC and therapy resistance in cancer: risks and opportunities

“…synthetic lethality with MYC and synergy with anti-CD20 immunotherapy in preclinical models of MYCdriven TNBC and DLBCL, respectively [202,203].…”

“…Furthermore, the three PIM‐family kinases proved redundant for the cooperation with oncogenic MYC [ 200 ]. Several small molecule inhibitors of PIM kinases are currently in clinical development [ 191 , 201 ] and some of them showed synthetic lethality with MYC and synergy with anti‐CD20 immunotherapy in preclinical models of MYC‐driven TNBC and DLBCL, respectively [ 202 , 203 ].…”

Molecular subtyping of CD5+ diffuse large B-cell lymphoma based on DNA-targeted sequencing and Lymph2Cx

“…It has been reported that patients with DLBCL harboring MYD88 and/or CD79B mutations are more sensitive to BTKi ( 49 , 50 ). More recently, PIMi was reported to enhance the efficacy of CD20 antibodies by targeting MYC transcription ( 51 ). Inhibitors targeting epigenetic alterations have been widely studied, and the application of HDACi was considered to be a feasible solution for treating patients with KMT2D alterations ( 52 ).…”

Activity and rational combinations of a novel, engineered chimeric, TRAIL-based ligand in diffuse large B-cell lymphoma

“…Immunoblotting was performed as previously described ( 20 , 21 ). Briefly, protein lysates were resolved by SDS-PAGE, transferred to PVDF membranes (Millipore) and immunoblotted with primary and appropriate HRP-labelled secondary antibodies (listed in Supplemental Table 1 ).…”