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Rituximab combined with systemic chemotherapy significantly improves the rate of complete response in B-cell lymphomas. However, acquired rituximab resistance develops in most patients leading to relapse. The mechanisms underlying rituximab resistance are not well-understood. MDM2 and MDM4 proteins are major negative regulators of p53, but they also have p53-independent activities in mouse models of lymphomagenesis. Whether MDM2 or MDM4 is involved in rituximab resistance has not been explored. Here we report that MDM2 and MDM4 are upregulated in p53-mutant rituximab-resistant cells by transcriptional and post-transcriptional mechanisms. Knockdown of MDM2 or MDM4 significantly hindered growth of rituximab-resistant cells. To explore whether targeting the RING-domain of MDM2-MDM4 heterodimers is a viable strategy for the treatment of rituximab-resistant lymphomas, we identified MMRi36 in a high throughput small-molecule screen. Here we show that MMRi36 binds and stabilizes MDM2-MDM4 RING heterodimers and acts as an activator of the MDM2-MDM4 E3 ligase complex in vitro and promotes proteasomal degradation of MDM2/MDM4 proteins in cells. MMRi36 potently induces p53-independent apoptosis in p53-mutant lymphoma cells and it exerts non-apoptotic anti-lymphoma effect in rituximab resistant cells. The pro-apoptotic mechanisms of MMRi36 involves activation of both caspase 3 and caspase 7 associated with increased polyubiquitination and degradation of XIAP. Therefore, MMRi36 is a novel prototype small-molecule for targeting MDM2/MDM4/XIAP for degradation and induction of apoptosis in p53-mutant lymphomas. [ABSTRACT FROM AUTHOR]

Chronic lymphocytic leukemia (CLL) remains incurable and its ability to acquire resistance to front-line therapeutics has proved challenging. Bromodomain and extra-terminal proteins, particularly bromodomain-containing protein 4 (BRD4), are integral to gene expression in CLL and offer a promising therapeutic target. In this study, we examined the activity of the BRD4 inhibitor OPN-51107 alone and in combination with the BCL-2 inhibitor, venetoclax, in CLL cell lines and patient-derived CLL samples. We demonstrate that OPN-51107 induces anti-tumor activity in both CLL cell lines and patient-derived samples, including relapsed/refractory (R/R) samples and those with high-risk features (i.e. ATM and/or TP53 deletions). Importantly, the combination of OPN-51107 and venetoclax exhibited synergistic cytotoxicity in ibrutinib-resistant CLL cells and patient-derived CLL samples regardless of R/R or deletion status. This study establishes the preclinical efficacy of using OPN-51107 and venetoclax in combination in therapy-resistant and/or high-risk CLL, lending support for its further development as a combination therapy. [ABSTRACT FROM AUTHOR]

Serologic biomarker to predict clinical outcome is needed for immune checkpoint inhibitors (ICIs). We evaluated soluble intercellular adhesion molecules‐1 (sICAM‐1) as a predictor of response to ICIs treatment. Ninety‐five patients with cancer treated with ICI were studied. The serum sICAM‐1 levels of baseline, post two cycle therapy and end of therapy (EOT) were measured by enzyme‐linked immunoassay. We randomly assigned the patients into the primary cohort (n = 47) and validation cohort (n = 48). Serum sICAM‐1 post two cycle (277.7 ± 181.6 ng/mL) and EOT (403.9 ± 218.9 ng/mL) were significantly elevated compared to baseline (244.8 ± 153.8 ng/mL, p = 0.008 and p = 0.004, respectively). Early changes of sICAM‐1 (ΔsICAM‐1), deemed as sICAM‐1 after two cycles minus baseline, were assessed. Following ICI treatments, responders had significantly lower ΔsICAM‐1 compared with nonresponders in the primary cohort (p = 0.040) and the validation cohort (p = 0.026). High ΔsICAM‐1 was strongly associated with inferior progression‐free survival (PFS; (primary cohort: p = 0.001 and validation cohort: p = 0.002) and overall survival (OS; (primary cohort: p < 0.001 and validation cohort: p = 0.007). The ΔsICAM‐1 remained independently associated with worse PFS and OS in the primary cohort and the validation cohort. Subgroup analysis indicated patients whose sICAM‐1 significantly elevated had shorter PFS and OS in both anti‐PD‐1 and anti‐PD‐L1 treatment groups. Early change of serum sICAM‐1 could be used to monitor and predict clinical benefit of ICI therapy in patients with solid cancer. [ABSTRACT FROM AUTHOR]

Upregulation of the anti-apoptotic protein MCL-1 has been implicated in chemotherapy resistance and poor clinical outcomes in B-cell lymphoma (BCL). We report the activity of AMG176, a direct, selective MCL-1 inhibitor, in preclinical models of BCL. A panel of cell lines representing diffuse large B-cell lymphoma (DLBCL), double-hit lymphoma (DHL) and Burkitt's lymphoma (BL) was selected. AMG176 induced apoptotic cell death in a dose- and time-dependent manner in all BCL cell lines. Baseline MCL-1 expression was not predictive of response. AMG176 exhibited impressive synergy with venetoclax and chemotherapeutic agents, less so with proteasomal inhibitors, and antagonism with anti-CD20 monoclonal antibodies. The activity of AMG176 could not be confirmed in murine models of BCL. Combination therapy targeting MCL-1 and BCL-2 may provide an alternative therapeutic approach in BCL, however optimal patient selection will remain the key to obtaining high response rates and tolerability. [ABSTRACT FROM AUTHOR]

MDM2 and MDM4 proteins are key negative regulators of tumor suppressor p53. MDM2 and MDM4 interact via their RING domains and form a heterodimer polyubiquitin E3 ligase essential for p53 degradation. MDM4 also forms heterodimer E3 ligases with MDM2 isoforms that lack p53-binding domains, which regulate p53 and MDM4 stability. We are working to identify small- molecule inhibitors targeting the RING domain of MDM2-MDM4 (MMRi) that can inactivate the total oncogenic activity of MDM2-MDM4 heterodimers. Here, we describe the identification and characterization of MMRi62 as an MDM4-degrader and apoptosis inducer in leukemia cells. Biochemically, in our experiments, MMRi62 bound to preformed RING domain heterodimers altered the substrate preference toward MDM4 ubiquitination and promoted MDM2- dependent MDM4 degradation in cells. This MDM4-degrader activity of MMRi62 was found to be associated with potent apoptosis induction in leukemia cells. Interestingly, MMRi62 effectively induced apoptosis in p53 mutant, multidrug-resistant leukemia cells and patient samples in addition to p53 wild-type cells. In contrast, MMRi67 as a RING heterodimer disruptor and an enzymatic inhibitor of the MDM2-MDM4 E3 complex lacked MDM4- degrader activity and failed to induce apoptosis in these cells. In summary, this study identifies MMRi62 as a novel MDM2-MDM4-targeting agent and suggests that small molecules capable of promoting MDM4 degradation may be a viable new approach to killing leukemia cells bearing non-functional p53 by apoptosis. [ABSTRACT FROM AUTHOR]

Background: Ofatumumab is a humanized type 1 anti‐CD20 monoclonal antibody. Preclinical studies show improved complement‐mediated cytotoxicity (CMC) compared to rituximab in mantle cell lymphoma (MCL). This study evaluates the safety and efficacy of combining ofatumumab with HyperCVAD/MA (O‐HyperCVAD) in newly diagnosed MCL. Methods: In this single‐arm phase 2 study, 37 patients were treated with the combination of O‐HyperCVAD for 4 or 6 cycles, followed by high dose chemotherapy and autologous stem cell transplant. Primary objectives were overall response rate (ORR) and complete response (CR) rate at the end of therapy. Secondary objectives included minimal residual disease (MRD) negativity, progression‐free survival (PFS), and overall survival (OS). Results: Median age was 60 years; ORR was 86% and 73% achieved a CR by modified Cheson criteria. The MRD negativity rate was 78% after 2 cycles of therapy, increasing to 96% at the end of induction; median PFS and OS were 45.5 months and 56 months, respectively. Achieving a post‐induction CR by both imaging and flow cytometry was associated with improved PFS and OS. Early MRD negativity (post‐2 cycles) was also associated with an improved PFS but not OS. There were 3 deaths while on therapy, and grades 3 and 4 adverse events (AEs) were observed in 22% and 68% of the patients. Conclusion: The addition of ofatumumab to HyperCVAD/HD‐MA led to high rates of MRD negativity by flow cytometry in patients with newly diagnosed MCL. Achieving a CR post‐induction by both imaging and flow cytometry is associated with improved overall survival. Ofatumumab combined with HyperCVAD/MA results in high response rates and minimal residual disease negativity in patients with newly diagnosed mantle cell lymphoma. Achieving a post‐induction complete response by both imaging and flow cytometry was associated with improved survival rates. [ABSTRACT FROM AUTHOR]