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

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.

PIM Kinases Promote Survival and Immune Escape in Primary Mediastinal Large B-Cell Lymphoma through Modulation of JAK-STAT and NF-κB Activity.

Primary mediastinal large B-cell lymphoma (PMBL) cells depend on the constitutive activity of NF-κB and STAT transcription factors, which drive expression of multiple molecules essential for their survival. In a molecularly related B-cell malignant tumor (classic Hodgkin lymphoma), tumor Reed-Sternberg cells overexpress oncogenic (proviral integration site for Moloney murine leukemia virus (PIM) 1, 2, and 3 kinases in a NF-κB- and STAT-dependent manner and PIMs enhance survival and expression of immunomodulatory molecules. Given the multiple overlapping characteristics of Reed-Sternberg and PMBL cells, we hypothesized that PIM kinases may be overexpressed in PMBL and involved in PMBL pathogenesis. The expression of PIM kinases in PMBL diagnostic biopsy specimens was assessed and their role in survival and immune escape of the tumor cells was determined. PIMs were abundantly expressed in primary tumors and PMBL cell lines. Inhibition of PIM kinases was toxic to PMBL cells, attenuated protein translation, and down-regulated NF-κB- and STAT-dependent transcription of prosurvival factors BCL2A1, BCL2L1, and FCER2. Furthermore, PIM inhibition decreased expression of molecules engaged in shaping the immunosuppressive microenvironment, including programmed death ligand 1/2 and chemokine (C-C motif) ligand 17. Taken together, our data indicate that PIMs support PMBL cell survival and immune escape and identify PIMs as promising therapeutic targets for PMBL.

Transcriptional Profiles and Stromal Changes Reveal Bone Marrow Adaptation to Early Breast Cancer in Association with Deregulated Circulating microRNAs.

The presence of a growing tumor establishes a chronic state of inflammation that acts locally and systemically. Bone marrow responds to stress signals by expanding myeloid cells endowed with immunosuppressive functions, further fostering tumor growth and dissemination. How early in transformation the cross-talk with the bone marrow begins and becomes detectable in blood is unknown. Here, gene expression profiling of the bone marrow along disease progression in a spontaneous model of mammary carcinogenesis demonstrates that transcriptional modifications in the hematopoietic compartment occurred as early as preinvasive disease stages. The transcriptional profile showed downregulation of adaptive immunity and induction of programs related to innate immunity and response to danger signals triggered by activating transcription factor 3. Transcriptional reprogramming was paralleled by the expansion of myeloid populations at the expense of erythroid and B lymphoid fractions. Hematopoietic changes were associated with modifications of the bone marrow stromal architecture through relocalization and increased density in the interstitial area of Nestin+ mesenchymal cells expressing CXCL12 and myeloid cells expressing CXCL12 receptor CXCR4. These early events were concomitant with deregulation of circulating miRNAs, which were predicted regulators of transcripts downregulated in the bone marrow and involved in lymphoid differentiation and activation. These data provide a link between sensing of peripheral cancer initiation by the bone marrow and hematopoietic adaptation to distant noxia through transcriptional rewiring toward innate/inflammatory response programs. SIGNIFICANCE: The bone marrow senses distant tissue transformation at premalignant/preinvasive stages, suggesting that circulating messengers, intercepted in the blood, could serve as early diagnostic markers.