Unraveling MCL biology to understand resistance and identify vulnerabilities.

Mantle cell lymphoma (MCL) is a rare (5-7%), aggressive B-cell non-Hodgkin's lymphoma with well-defined hallmarks (e.g. Cyclin D1, SOX11), and whose expansion is highly dependent on the tumor microenvironment (TME). Parallel drastic progresses in the understanding of the lymphomagenesis and improved treatments led to paradigm shift in this B-cell malignancy with now prolonged disease-free survival after intensive chemotherapy and anti-CD20 based maintenance. However, this toxic strategy is not applicable in frail or elderly patients and a small but significant part of the cases will present a refractory disease representing unmet medical needs. Importantly, the field has recently seen the rapid emergence of targeted and immune-based strategies with effective combinations relying on biological rationales to overcome malignant plasticity and intratumor heterogeneity. In this review, we expose how unraveling the biology of MCL allows to better understand the therapeutic resistances and to identify neo-vulnerabilities of tumors, which are essential to offer efficient novel strategies for high-risk patients. We first highlight the tumor intrinsic resistance mechanisms, and associated Achilles heels within various pathways such as NFkB, mitochondrial apoptosis, DNA repair or epigenetic regulators. We then place the tumor in its complex ecosystem to decipher the dialog with the multiple TME components and show how the resulting protumoral signals could be disrupted with innovative therapeutics strategies. Finally, we discuss how these progresses could be integrated in a personalized approach in MCL.

Cyclin dependent kinase 4/6 inhibitor palbociclib synergizes with BCL2 inhibitor venetoclax in experimental models of mantle cell lymphoma without RB1 deletion.

BACKGROUND: Mantle cell lymphoma (MCL) is a chronically relapsing malignancy with deregulated cell cycle progression. We analyzed efficacy, mode of action, and predictive markers of susceptibility to palbociclib, an approved CDK 4/6 inhibitor, and its combination with venetoclax, a BCL2 inhibitor. METHODS: A panel of nine MCL cell lines were used for in vitro experiments. Four patient derived xenografts (PDX) obtained from patients with chemotherapy and ibrutinib-refractory MCL were used for in vivo proof-of-concept studies. Changes of the mitochondrial membrane potential, energy-metabolic pathways, AKT activity, and pro-apoptotic priming of MCL cells were evaluated by JC-1 staining, Seahorse XF analyser, genetically encoded fluorescent AKT reporter, and BH3 profiling, respectively. MCL clones with gene knockout or transgenic (over)expression of CDKN2A, MYC, CDK4, and RB1 were used to estimate impact of these aberrations on sensitivity to palbociclib, and venetoclax. RESULTS: Co-targeting MCL cells with palbociclib and venetoclax induced cytotoxic synergy in vitro and in vivo. Molecular mechanisms responsible for the observed synthetic lethality comprised palbociclib-mediated downregulation of anti-apoptotic MCL1, increased levels of proapoptotic BIM bound on both BCL2, and BCL-XL and increased pro-apoptotic priming of MCL cells mediated by BCL2-independent mechanisms, predominantly palbociclib-triggered metabolic and mitochondrial stress. Loss of RB1 resulted in palbociclib resistance, while deletion of CDKN2A or overexpression of CDK4, and MYC genes did not change sensitivity to palbociclib. CONCLUSIONS: Our data strongly support investigation of the chemotherapy-free palbociclib and venetoclax combination as an innovative treatment strategy for post-ibrutinib MCL patients without RB1 deletion.

Selective pharmacologic targeting of CTPS1 shows single-agent activity and synergizes with BCL2 inhibition in aggressive mantle cell lymphoma.

Innovative therapeutic strategies have emerged over the past decade to improve outcomes for most lymphoma patients. Nevertheless, the aggressive presentation seen in high-risk mantle cell lymphoma (MCL) patients remains an unmet medical need. The highly proliferative cells that characterize these tumors depend on nucleotide synthesis to ensure high DNA replication and RNA synthesis. To take advantage of this vulnerability, STP-B, a clinically available small molecule selectively targeting CTP synthase 1 (CTPS1) has been recently developed. CTPS1 is a key enzyme of the pyrimidine synthesis pathway mediated through its unique ability to provide enough CTP in highly proliferating cells. Herein, we demonstrated that CTPS1 was expressed in all MCL cells, and that its high expression was associated with unfavorable outcomes for patients treated with chemotherapy. Using aggressive MCL models characterized by blastoid morphology, TP53 mutation or polyresistance to targeted therapies, we showed that STP-B was highly effective at nanomolar concentrations in vitro and in vivo, irrespective of these high-risk features. Inhibition of CTPS1 rapidly leads to cell cycle arrest in early S-phase accompanied by inhibition of translation, including of the anti-apoptotic protein MCL1. Consequently, CTPS1 inhibition induced synergistic cell death in combination with the selective BCL2 inhibitor venetoclax, both in vitro and in vivo. Overall, our study identified CTPS1 as a promising target for MCL patients and provided a mechanism-based combination with the BCL2 inhibitor venetoclax for the design of future chemotherapy-free treatment regimens to overcome resistance.

A p53 score derived from TP53 CRISPR/Cas9 HMCLs predicts survival and reveals a major role of BAX in the response to BH3 mimetics.

ABSTRACT: To establish a strict p53-dependent gene-expression profile, TP53-/- clones were derived from TP53+/+ and TP53-/mut t(4;14) human myeloma cell lines (HMCLs) using CRISPR/Cas9 technology. From the 17 dysregulated genes shared between the TP53-/- clones from TP53+/+ HMCLs, we established a functional p53 score, involving 13 genes specifically downregulated upon p53 silencing. This functional score segregated clones and myeloma cell lines as well as other cancer cell lines according to their TP53 status. The score efficiently identified samples from patients with myeloma with biallelic TP53 inactivation and was predictive of overall survival in Multiple Myeloma Research Foundation-coMMpass and CASSIOPEA cohorts. At the functional level, we showed that among the 13 genes, p53-regulated BAX expression correlated with and directly affected the MCL1 BH3 mimetic S63845 sensitivity of myeloma cells by decreasing MCL1-BAX complexes. However, resistance to S63845 was overcome by combining MCL1 and BCL2 BH3 mimetics, which displayed synergistic efficacy. The combination of BH3 mimetics was effective in 97% of patient samples with or without del17p. Nevertheless, single-cell RNA sequencing analysis showed that myeloma cells surviving the combination had lower p53 score, showing that myeloma cells with higher p53 score were more sensitive to BH3 mimetics. Taken together, we established a functional p53 score that identifies myeloma cells with biallelic TP53 invalidation, demonstrated that p53-regulated BAX is critical for optimal cell response to BH3 mimetics, and showed that MCL1 and BCL2 BH3 mimetics in combination may be of greater effectiveness for patients with biallelic TP53 invalidation, for whom there is still an unmet medical need.

CARD11 gain of function upregulates BCL2A1 expression and promotes resistance to targeted therapies combination in B-cell lymphoma.

A strategy combining targeted therapies is effective in B-cell lymphomas (BCL), such as mantle cell lymphoma (MCL), but acquired resistances remain a recurrent issue. In this study, we performed integrative longitudinal genomic and single-cell RNA-sequencing analyses of patients with MCL who were treated with targeted therapies against CD20, BCL2, and Bruton tyrosine kinase (OAsIs trial). We revealed the emergence of subclones with a selective advantage against OAsIs combination in vivo and showed that resistant cells were characterized by B-cell receptor (BCR)-independent overexpression of NF-κB1 target genes, especially owing to CARD11 mutations. Functional studies demonstrated that CARD11 gain of function not only resulted in BCR independence but also directly increased the transcription of the antiapoptotic BCL2A1, leading to resistance against venetoclax and OAsIs combination. Based on the transcriptional profile of OAsIs-resistant subclones, we designed a 16-gene resistance signature that was also predictive for patients with MCL who were treated with conventional chemotherapy, underlying a common escape mechanism. Among druggable strategies to inhibit CARD11-dependent NF-κB1 transduction, we evaluated the selective inhibition of its essential partner MALT1. We demonstrated that MALT1 protease inhibition led to a reduction in the expression of genes involved in OAsIs resistance, including BCL2A1. Consequently, MALT1 inhibition induced synergistic cell death in combination with BCL2 inhibition, irrespective of CARD11 mutational status, both in vitro and in vivo. Taken together, our study identified mechanisms of resistance to targeted therapies and provided a novel strategy to overcome resistance in aggressive BCL. The OAsIs trial was registered at www.clinicaltrials.gov #NCT02558816.

Tumor Microenvironment and Immunotherapy-Based Approaches in Mantle Cell Lymphoma.

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma (NHL) characterized by the translocation t(11;14) (q13;q32) and a poor response to rituximab-anthracycline-based chemotherapy. High-dose cytarabine-based regimens offer a durable response, but an important number of MCL patients are not eligible for intensive treatment and are ideal candidates for novel targeted therapies (such as BTK, proteasome or BCL2 inhibitors, Immunomodulatory Drugs (IMiDs), bispecific antibodies, or CAR-T cell therapy). On the bench side, several studies aiming to integrate the tumor within its ecosystem highlighted a critical role of the tumor microenvironment (TME) in the expansion and resistance of MCL. This led to important insights into the role of the TME in the management of MCL, including potential targets and biomarkers. Indeed, targeted agents often have a combined mechanism of action on the tumor B cell but also on the tumor microenvironment. The aim of this review is to briefly describe the current knowledge on the biology of the TME in MCL and expose the results of the different therapeutic strategies integrating the TME in this disease.

The IL32/BAFF axis supports prosurvival dialogs in the lymphoma ecosystem and is disrupted by NIK inhibition.

Aggressive B-cell malignancies, such as mantle cell lymphoma (MCL), are microenvironment-dependent tumors and a better understanding of the dialogs occurring in lymphoma-protective ecosystems will provide new perspectives to increase treatment efficiency. To identify novel molecular regulations, we performed a transcriptomic analysis based on the comparison of circulating MCL cells (n=77) versus MCL lymph nodes (n=107) together with RNA sequencing of malignant (n=8) versus normal B-cell (n=6) samples. This integrated analysis led to the discovery of microenvironment-dependent and tumor-specific secretion of interleukin-32 beta (IL32ß), whose expression was confirmed in situ within MCL lymph nodes by multiplex immunohistochemistry. Using ex vivo models of primary MCL cells (n=23), we demonstrated that, through the secretion of IL32ß, the tumor was able to polarize monocytes into specific MCL-associated macrophages, which in turn favor tumor survival. We highlighted that while IL32ß-stimulated macrophages secreted several protumoral factors, they supported tumor survival through a soluble dialog, mostly driven by BAFF. Finally, we demonstrated the efficacy of selective NIK/alternative-NFkB inhibition to counteract microenvironment-dependent induction of IL32ß and BAFF-dependent survival of MCL cells. These data uncovered the IL32ß/BAFF axis as a previously undescribed pathway involved in lymphoma-associated macrophage polarization and tumor survival, which could be counteracted through selective NIK inhibition.

Oxaliplatin before autologous transplantation in combination with high-dose cytarabine and rituximab provides longer disease control than cisplatin or carboplatin in patients with mantle-cell lymphoma: results from the LyMA prospective trial.

LyMA trial has demonstrated the benefit of rituximab maintenance after autologous stem cell transplantation (ASCT) in previously untreated mantle-cell lymphoma patients (MCL). Induction consisted of four courses of R-DHAP (rituximab, dexamethasone, high-dose cytarabine, and platinum derivative). The platinum derivative (PD) choice was free: R-DHA-cisplatin, R-DHA-carboplatin, or R-DHA-oxaliplatin. We investigated the prognostic impact of each PD. PFS and OS calculated from inclusion and investigated in an intention-to-treat (ITT) (= 298) and per-protocol analyses (PP) (n = 227). R-DHACis, R-DHACa, or R-DHAOx were used at first cycle in 184, 76, and 38 patients, respectively. Overall, 71 patients (59 in the R-DHACis) required a change in PD, mainly because of PD toxicity. In ITT-analysis, PFS in the R-DHACis and R-DHACa groups were similar (4-year PFS of 65%), while R-DHAOx had a better PFS (4-year PFS of 65% versus 86.5%, respectively, HR = 0.44, p = 0.02). The 4-year OS was 92% for R-DHAOx versus 75.9% for R-DHACis/DHACa (HR = 0.37, p = 0.03). Similar results were yielded in the PP analysis. Low MIPI and R-DHAOx were independent favorable prognostic markers for both PFS (HR = 0.44, p = 0.035) and OS (HR = 0.36, p = 0.045). In vitro and in silico analyses confirmed that oxaliplatin has an anti-MCL cytotoxic effect that differs from that of other PD. R-DHAOx before ASCT provides better outcome in transplantation eligible young MCL patients.

Ibrutinib, obinutuzumab, and venetoclax in relapsed and untreated patients with mantle cell lymphoma: a phase 1/2 trial.

Ibrutinib, obinutuzumab, and venetoclax demonstrate synergy in preclinical models of mantle cell lymphoma (MCL). OAsIs (NCT02558816), a single-arm multicenter prospective phase 1/2 trial, aimed to determine the maximum tolerated dose of venetoclax in combination with fixed doses of ibrutinib and obinutuzumab, in relapsed MCL patients. At the venetoclax MTD, extension cohorts were opened for relapsed and untreated patients. Safety and efficacy were secondary objectives. Minimal residual disease (MRD) was assessed by allele-specific oligonucleotide quantitative polymerase chain reaction. Between 14 October 2015 and 29 May 2018, 48 patients were enrolled. No dose-limiting toxicity was reported, and venetoclax at 400 mg per day was chosen for extension. Eighteen (75%) relapsed and 8 (53%) untreated patients experienced grade 3/4 adverse events. The complete response rate assessed by positron emission tomography at the end of cycle 6 was 67% in relapsed and 86.6% in untreated patients. MRD clearance for evaluable patients was seen in 71.5% of relapsed (10/14 patients) and 100% of untreated MRD-evaluable patients (n = 12) at the end of 3 cycles. The median follow-up for relapsed patients was 17 months (range, 10-35 months). The 2-year progression-free survival (PFS) was 69.5% (95% confidence interval [CI], 52.9%-91.4%) and 68.6% (95% CI, 49.5%-95.1%) for overall survival. The median follow-up was 14 months (range, 5-19) for untreated patients, the 1-year PFS was 93.3% (95% CI, 81.5%-100%). The combination of obinutuzumab, ibrutinib, and venetoclax is well tolerated and provides high response rates, including at the molecular level, in relapsed and untreated MCL patients. This trial was registered at www.clinicaltrials.gov as #NCT02558816.

Whole genome copy number analysis in search of new prognostic biomarkers in first line treatment of mantle cell lymphoma. A study by the LYSA group.

Mantle cell lymphoma (MCL) is a lymphoproliferative disorder characterized by the t(11;14)(q13;q32) CCND1/IGH translocation. This lymphoma is however extremely heterogeneous in terms of molecular alterations. Moreover, the course of the disease can vary greatly between indolent forms with slow progression and aggressive conditions rapidly pejorative. The identification of early markers allowing to predict individual patients outcome has however been unsuccessful so far. The LyMa trial treated homogeneously a cohort of young MCL patients. This appeared as a good opportunity to search for biomarkers of response to therapy. DNA extracted from diagnostic paraffin-embedded lymph node biopsies from 100 patients with newly diagnosed MCL, homogeneously treated in this prospective clinical trial, were investigated for copy number alterations and copy neutral loss of heterozygosity using the Oncoscan SNP-array scanning the whole genome. An independent confirmatory cohort was used to strengthen the possibly relevant anomalies observed. Here we describe the recurrent anomalies identified with this technique. Deletions of 17p(TP53) and 9p(CDKN2A) were more frequent in refractory or early relapsing patients (10%), but had no significant impact in univariate analysis on progression-free (PFS) or overall survival (OS). Regardless of the presence of TP53 or CDKN2A deletions, gains in 7p22 (8,5%) were associated with better PFS in univariate but not in multivariate analysis including MCL International Prognostic Index and treatment. Gains of 11q(CCDN1), suggesting gains of the CCND1/IGH fusion, were associated with worse OS and PFS in univariate and multivariate analyses. This worse prognosis impact was confirmed by FISH in an independent confirmatory cohort. This work, using a whole genome approach, confirms the broad genomic landscape of MCL and shows that gains of the CCND1/IGH fusion can be considered as a new prognostic structural variant. Genomic abnormalities of prognostic impact could be useful to strengthen or de-escalate treatment schedules or choosing targeted therapies or CART-cells.

Restoring Apoptosis with BH3 Mimetics in Mature B-Cell Malignancies.

Apoptosis is a highly conserved mechanism enabling the removal of unwanted cells. Mitochondrial apoptosis is governed by the B-cell lymphoma (BCL-2) family, including anti-apoptotic and pro-apoptotic proteins. Apoptosis evasion by dysregulation of anti-apoptotic BCL-2 members (BCL-2, MCL-1, BCL-XL) is a common hallmark in cancers. To divert this dysregulation into vulnerability, researchers have developed BH3 mimetics, which are small molecules that restore effective apoptosis in neoplastic cells by interfering with anti-apoptotic proteins. Among them, venetoclax is a potent and selective BCL-2 inhibitor, which has demonstrated the strongest clinical activity in mature B-cell malignancies, including chronic lymphoid leukemia, mantle-cell lymphoma, and multiple myeloma. Nevertheless, mechanisms of primary and acquired resistance have been recently described and several features such as cytogenetic abnormalities, BCL-2 family expression, and ex vivo drug testing have to be considered for predicting sensitivity to BH3 mimetics and helping in the identification of patients able to respond. The medical need to overcome resistance to BH3 mimetics supports the evaluation of innovative combination strategies. Novel agents including MCL-1 targeting BH3 mimetics are currently evaluated and may represent new therapeutic options in the field. The present review summarizes the current knowledge regarding venetoclax and other BH3 mimetics for the treatment of mature B-cell malignancies.

Stabilization of ß-catenin upon B-cell receptor signaling promotes NF-kB target genes transcription in mantle cell lymphoma.

B-cell receptor (BCR) signaling pathways and interactions with the tumor microenvironment account for mantle cell lymphoma (MCL) cells survival in lymphoid organs. In several MCL cases, the WNT/ß-catenin canonical pathway is activated and ß-catenin accumulates into the nucleus. As both BCR and ß-catenin are important mediators of cell survival and interaction with the microenvironment, we investigated the crosstalk between BCR and WNT/ß-catenin signaling and analyzed their impact on cellular homeostasis as well as their targeting by specific inhibitors. ß-catenin was detected in all leukemic MCL samples and its level of expression rapidly increased upon BCR stimulation. This stabilization was hampered by the BCR-pathway inhibitor Ibrutinib, supporting ß-catenin as an effector of the BCR signaling. In parallel, MCL cells as compared with normal B cells expressed elevated levels of WNT16, a NF-κB target gene. Its expression increased further upon BCR stimulation to participate to the stabilization of ß-catenin. Upon BCR stimulation, ß-catenin translocated into the nucleus but did not induce a Wnt-like transcriptional response, i.e., TCF/LEF dependent. ß-catenin rather participated to the regulation of NF-κB transcriptional targets, such as IL6, IL8, and IL1. Oligo pull down and chromatin immunoprecipitation experiments demonstrated that ß-catenin is part of a protein complex that binds the NF-κB DNA consensus sequence, strengthening the idea of an association between the two proteins. An inhibitor targeting ß-catenin transcriptional interactions hindered both NF-κB DNA recruitment and induced primary MCL cells apoptosis. Thus, ß-catenin likely represents another player through which BCR signaling impacts on MCL cell survival.

Pannexin-1 limits the production of proinflammatory cytokines during necroptosis.

The activation of mixed lineage kinase-like (MLKL) by receptor-interacting protein kinase-3 (RIPK3) controls the execution of necroptosis, a regulated form of necrosis that occurs in apoptosis-deficient conditions. Active oligomerized MLKL triggers the exposure of phosphatidylserine residues on the cell surface and disrupts the plasma membrane integrity by forming lytic pores. MLKL also governs endosomal trafficking and biogenesis of small extracellular vesicles as well as the production of proinflammatory cytokines during the early steps of necroptosis; however, the molecular basis continues to be elucidated. Here, we find that MLKL oligomers activate Pannexin-1 (PANX1) channels, concomitantly to the loss of phosphatidylserine asymmetry. This plasma membrane "leakiness" requires the small GTPase RAB27A and RAB27B isoforms, which regulate intracellular vesicle trafficking, docking, and fusion with the plasma membrane. Although cells in which PANX1 is silenced or inhibited normally undergo necroptotic death, they display enhanced production of cytokines such as interleukin-8, indicating that PANX1 may tamper with inflammation. These data identify a novel signaling nexus between MLKL, RAB27, and PANX1 and propose ways to interfere with inflammation associated with necroptosis.

CSF1R and BTK inhibitions as novel strategies to disrupt the dialog between mantle cell lymphoma and macrophages.

The microenvironment strongly influences mantle cell lymphoma (MCL) survival, proliferation, and chemoresistance. However, little is known regarding the molecular characterization of lymphoma niches. Here, we focused on the interplay between MCL cells and the associated monocytes/macrophages. Using circulating MCL cells (n = 58), we showed that, through the secretion of CSF1 and, to a lesser extent, IL-10, MCL polarized monocytes into specific CD163+ M2-like macrophages (MϕMCL). In turn, MϕMCL favored lymphoma survival and proliferation ex vivo. We next demonstrated that BTK inhibition abrogated CSF1 and IL-10 production in MCL cells, leading to the inhibition of macrophage polarization and consequently resulting in the suppression of microenvironment-dependent MCL expansion. In vivo, we showed that CSF1 and IL-10 plasma concentrations were higher in MCL patients than in healthy donors, and that monocytes from MCL patients overexpressed CD163. Further analyses of serial samples from ibrutinib-treated patients (n = 8) highlighted a rapid decrease of CSF1, IL-10, and CD163 in responsive patients. Finally, we showed that targeting the CSF1R abrogated MϕMCL-dependent MCL survival, irrespective of their sensitivity to ibrutinib. These data reinforced the role of the microenvironment in lymphoma and suggested that macrophages are a potential target for developing novel therapeutic strategies in MCL.

Whole-exon sequencing of human myeloma cell lines shows mutations related to myeloma patients at relapse with major hits in the DNA regulation and repair pathways.

BACKGROUND: Human myeloma cell lines (HMCLs) are widely used for their representation of primary myeloma cells because they cover patient diversity, although not fully. Their genetic background is mostly undiscovered, and no comprehensive study has ever been conducted in order to reveal those details. METHODS: We performed whole-exon sequencing of 33 HMCLs, which were established over the last 50 years in 12 laboratories. Gene expression profiling and drug testing for the 33 HMCLs are also provided and correlated to exon-sequencing findings. RESULTS: Missense mutations were the most frequent hits in genes (92%). HMCLs harbored between 307 and 916 mutations per sample, with TP53 being the most mutated gene (67%). Recurrent bi-allelic losses were found in genes involved in cell cycle regulation (RB1, CDKN2C), the NFκB pathway (TRAF3, BIRC2), and the p53 pathway (TP53, CDKN2A). Frequency of mutations/deletions in HMCLs were either similar to that of patients (e.g., DIS3, PRDM1, KRAS) or highly increased (e.g., TP53, CDKN2C, NRAS, PRKD2). MAPK was the most altered pathway (82% of HMCLs), mainly by RAS mutants. Surprisingly, HMCLs displayed alterations in epigenetic (73%) and Fanconi anemia (54%) and few alterations in apoptotic machinery. We further identified mutually exclusive and associated mutations/deletions in genes involved in the MAPK and p53 pathways as well as in chromatin regulator/modifier genes. Finally, by combining the gene expression profile, gene mutation, gene deletion, and drug response, we demonstrated that several targeted drugs overcome or bypass some mutations. CONCLUSIONS: With this work, we retrieved genomic alterations of HMCLs, highlighting that they display numerous and unprecedented abnormalities, especially in DNA regulation and repair pathways. Furthermore, we demonstrate that HMCLs are a reliable model for drug screening for refractory patients at diagnosis or at relapse.

p53 regulates CD46 expression and measles virus infection in myeloma cells.

In this study, we assessed the sensitivity of myeloma cells to the oncolytic measles virus (MV) in relation to p53 using 37 cell lines and 23 primary samples. We showed that infection and cell death were correlated with CD46 expression, which was associated with TP53 status; TP53 abn cell lines highly expressed CD46 and were preferentially infected by MV when compared with the TP53 wt cell lines (P = .046 and P = .045, respectively). Infection of myeloma cells was fully dependent on CD46 expression in both cell lines and primary cells. In the TP53 wt cell lines, but not the TP53 abn cell lines, activation of the p53 pathway with nutlin3a inhibited both CD46 expression and MV infection, while TP53 silencing reciprocally increased CD46 expression and MV infection. We showed using a p53 chromatin immunoprecipitation assay and microRNA assessment that CD46 gene expression was directly and indirectly regulated by p53. Primary myeloma cells overexpressed CD46 as compared with normal cells and were highly infected and killed by MV. CD46 expression and MV infection were inhibited by nutlin3a in primary p53-competent myeloma cells, but not in p53-deficient myeloma cells, and the latter were highly sensitive to MV infection. In summary, myeloma cells were highly sensitive to MV and infection inhibition by the p53 pathway was abrogated in p53-deficient myeloma cells. These results argue for an MV-based clinical trial for patients with p53 deficiency.

Rationale for targeting tumor cells in their microenvironment for mantle cell lymphoma treatment.

Mantle cell lymphoma (MCL) is an aggressive non-Hodgkin lymphoma associated with poor prognosis, and despite recent improvements in the therapeutic strategies for treating MCL, its management remains challenging. While improvements in next generation sequencing technology have greatly increased our understanding of the intrinsic abnormalities of MCL, the role of extrinsic signaling remains largely unknown. Recent studies have highlighted the central role of the MCL microenvironment in tumor cell survival, drug resistance and proliferation. Characterization of the diverse MCL tumoral niches and comprehension of the crosstalk between tumor cells and surrounding cells within the MCL microenvironment are needed to increase treatment efficacy. Here, we reviewed the recent findings regarding the MCL microenvironment that could be rapidly translated into new therapeutic strategies to overcome drug resistance during MCL treatment.

BCL2-Family Dysregulation in B-Cell Malignancies: From Gene Expression Regulation to a Targeted Therapy Biomarker.

BCL2-family proteins have a central role in the mitochondrial apoptosis machinery and their expression is known to be deregulated in many cancer types. Effort in the development of small molecules that selectively target anti-apoptotic members of this family i.e., Bcl-2, Bcl-xL, Mcl-1 recently opened novel therapeutic opportunities. Among these apoptosis-inducing agents, BH3-mimetics (i.e., venetoclax) led to promising preclinical and clinical activity in B cell malignancies. However, several mechanisms of intrinsic or acquired resistance have been described ex vivo therefore predictive markers of response as well as mechanism-based combinations have to be designed. In the present study, we analyzed the expression of the BCL2-family genes across 10 mature B cell malignancies through computational normalization of 21 publicly available Affimetrix datasets gathering 1,219 patient samples. To better understand the deregulation of anti- and pro-apoptotic members of the BCL2-family in hematological disorders, we first compared gene expression profiles of malignant B cells to their relative normal control (naïve B cell to plasma cells, n = 37). We further assessed BCL2-family expression according to tissue localization i.e., peripheral blood, bone marrow, and lymph node, molecular subgroups or disease status i.e., indolent to aggressive. Across all cancer types, we showed that anti-apoptotic genes are upregulated while pro-apoptotic genes are downregulated when compared to normal counterpart cells. Of interest, our analysis highlighted that, independently of the nature of malignant B cells, the pro-apoptotic BH3-only BCL2L11 and PMAIP1 are deeply repressed in tumor niches, suggesting a central role of the microenvironment in their regulation. In addition, we showed selective modulations across molecular subgroups and showed that the BCL2-family expression profile was related to tumor aggressiveness. Finally, by integrating recent data on venetoclax-monotherapy clinical activity with the expression of BCL2-family members involved in the venetoclax response, we determined that the ratio (BCL2+BCL2L11+BAX)/BCL2L1 was the strongest predictor of venetoclax response for mature B cell malignancies in vivo.