Effective therapeutics are urgently needed to counter infection and improve outcomes for patients suffering from COVID-19 and to combat this pandemic. Manipulation of epigenetic machinery to influence viral infectivity of host cells is a relatively unexplored area. The bromodomain and extraterminal (BET) family of epigenetic readers have been reported to modulate SARS-CoV-2 infection. Herein, we demonstrate apabetalone, the most clinical advanced BET inhibitor, downregulates expression of cell surface receptors involved in SARS-CoV-2 entry, including angiotensin-converting enzyme 2 (ACE2) and dipeptidyl-peptidase 4 (DPP4 or CD26) in SARS-CoV-2 permissive cells. Moreover, we show that apabetalone inhibits SARS-CoV-2 infection in vitro to levels comparable to those of antiviral agents. Taken together, our study supports further evaluation of apabetalone to treat COVID-19, either alone or in combination with emerging therapeutics.

Redundant tumor microenvironment (TME) immunosuppressive mechanisms and epigenetic maintenance of terminal T cell exhaustion greatly hinder functional antitumor immune responses in chronic lymphocytic leukemia (CLL). Bromodomain and extraterminal (BET) proteins regulate key pathways contributing to CLL pathogenesis and TME interactions, including T cell function and differentiation. Herein, we report that blocking BET protein function alleviates immunosuppressive networks in the CLL TME and repairs inherent CLL T cell defects. The pan-BET inhibitor OPN-51107 reduced exhaustion-associated cell signatures resulting in improved T cell proliferation and effector function in the Eμ-TCL1 splenic TME. Following BET inhibition (BET-i), TME T cells coexpressed significantly fewer inhibitory receptors (IRs) (e.g., PD-1, CD160, CD244, LAG3, VISTA). Complementary results were witnessed in primary CLL cultures, wherein OPN-51107 exerted proinflammatory effects on T cells, regardless of leukemic cell burden. BET-i additionally promotes a progenitor T cell phenotype through reduced expression of transcription factors that maintain terminal differentiation and increased expression of TCF-1, at least in part through altered chromatin accessibility. Moreover, direct T cell effects of BET-i were unmatched by common targeted therapies in CLL. This study demonstrates the immunomodulatory action of BET-i on CLL T cells and supports the inclusion of BET inhibitors in the management of CLL to alleviate terminal T cell dysfunction and potentially enhance tumoricidal T cell activity.

B-cell chronic lymphocytic leukemia (CLL) results from intrinsic genetic defects and complex microenvironment stimuli that fuel CLL cell growth through an array of survival signaling pathways. Novel small-molecule agents targeting the B-cell receptor pathway and anti-apoptotic proteins alone or in combination have revolutionized the management of CLL, yet combination therapy carries significant toxicity and CLL remains incurable due to residual disease and relapse. Single-molecule inhibitors that can target multiple disease-driving factors are thus an attractive approach to combat both drug resistance and combination-therapy-related toxicities. We demonstrate that SRX3305, a novel small-molecule BTK/PI3K/BRD4 inhibitor that targets three distinctive facets of CLL biology, attenuates CLL cell proliferation and promotes apoptosis in a dose-dependent fashion. SRX3305 also inhibits the activation-induced proliferation of primary CLL cells in vitro and effectively blocks microenvironment-mediated survival signals, including stromal cell contact. Furthermore, SRX3305 blocks CLL cell migration toward CXCL-12 and CXCL-13, which are major chemokines involved in CLL cell homing and retention in microenvironment niches. Importantly, SRX3305 maintains its anti-tumor effects in ibrutinib-resistant CLL cells. Collectively, this study establishes the preclinical efficacy of SRX3305 in CLL, providing significant rationale for its development as a therapeutic agent for CLL and related disorders.

The gut microbiome’s role in the pathogenesis of hematologic malignancies is actively being explored; yet studies on chronic lymphocytic leukemia (CLL) are limited. Using the Eμ-TCL1 murine model of CLL, we identify a unique and dysbiotic disease-associated gut microbiome that develops in mice over time. Leukemic mice show an increase in abundance of pathogenic bacteria, specifically members of the Proteobacteria phylum. We found that this dysbiotic microenvironment is associated with CLL involvement within the intestinal tract and high levels of markers indicative of altered tight junction permeability (e.g., claudin-2, soluble CD14, and zonulin). Moreover, utilizing the syngeneic model of CLL in tandem with an antibiotic-mediated microflora ablation approach, we found that leukemic mice receiving microflora-ablating antibiotics show marked changes to the gut microbiome and a delayed disease onset compared with mice receiving antibiotic-free water. Immunophenotyping of murine spleens showed that this delay in disease was accompanied by more tumor-reactive CD8+ T cells that coexpressed fewer inhibitory receptors (e.g., PD-1, LAG-3, and TIM-3). These findings confirm that a dysbiotic gut microbiome develops during CLL disease and demonstrate unique intestinal involvement and potential immune dysregulation occurring during CLL progression that may be influencing the overall microbial signature. Significance: There is a growing appreciation for the gut microbiome’s role in hematologic malignancies. Despite this, its role in CLL remains obscure. This study demonstrates a dysbiotic microbiome within CLL that may contribute to further intestinal and immune dysregulation present during CLL progression.

Background: B-cell receptor (BCR) signaling is a central driver in chronic lymphocytic leukemia (CLL), along with the activation of pro-survival pathways (e.g., NF-κB) and aberrant anti-apoptotic mechanisms (e.g., BCL2) culminating to CLL cell survival and drug resistance. Front-line targeted therapies such as ibrutinib (BTK inhibitor) and venetoclax (BCL2 inhibitor) have radically improved CLL management. Yet, persisting CLL cells lead to relapse in ~20% of patients, signifying the unmet need of inhibitor-resistant refractory CLL. SpiD3 is a novel spirocyclic dimer of analog 19 that displays NF-κB inhibitory activity and preclinical anti-cancer properties. Recently, we have shown that SpiD3 inhibits CLL cell proliferation and induces cytotoxicity by promoting futile activation of the unfolded protein response (UPR) pathway and generation of reactive oxygen species (ROS), resulting in the inhibition of protein synthesis in CLL cells. Methods: We performed RNA-sequencing using CLL cells rendered resistant to ibrutinib and venetoclax to explore potential vulnerabilities in inhibitor-resistant and SpiD3-treated CLL cells. Results: The transcriptomic analysis of ibrutinib- or venetoclax-resistant CLL cell lines revealed ferroptosis, UPR signaling, and oxidative stress to be among the top pathways modulated by SpiD3 treatment. By examining SpiD3-induced protein aggregation, ROS production, and ferroptosis in inhibitor-resistant CLL cells, our findings demonstrate cytotoxicity following SpiD3 treatment in cell lines resistant to current front-line CLL therapeutics. Conclusions: Our results substantiate the development of SpiD3 as a novel therapeutic agent for relapsed/refractory CLL disease.

Background: Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia in the Western world. Targeted therapies have made CLL manageable for many patients, but the ongoing threat of disease relapse or transformation beckons a deeper understanding of CLL pathogenesis, and thus, its durable eradication. This study identifies bile acids (BAs) as elevated in the peripheral blood of CLL patients and a murine model of CLL, in comparison to healthy controls. Elevated BA concentrations have been associated with intestinal malignancies and immunomodulation; however, their role in CLL is relatively unknown. Methods: Metabolomic analysis was performed on murine and human plasma. Flow cytometry analysis of CLL patient B-cells and healthy donor T-cells were utilized to evaluate the immunomodulatory impact of differentially abundant BAs. Results: Herein, BAs were found to be differentially abundant in CLL. Elevated BAs demonstrated minimal impact on CLL cell proliferation or CLL-associated T-cell function. Conclusions: Future studies are needed to determine the mechanistic influence of BAs on CLL pathogenesis.