A Phase I/II Open-Label Study of Molibresib for the Treatment of Relapsed/Refractory Hematologic Malignancies

Catalytic inhibition of KAT6/KAT7 enhances the efficacy and overcomes primary and acquired resistance to Menin inhibitors in MLL leukaemia

Understanding the molecular pathogenesis of MLL fusion oncoprotein (MLL-FP) leukaemia has spawned epigenetic therapies that have improved clinical outcomes in this often-incurable disease. Using genetic and pharmacological approaches, we define the individual and combined contribution of KAT6A, KAT6B and KAT7, in MLL-FP leukaemia. Whilst inhibition of KAT6A/B is efficacious in some pre-clinical models, simultaneous targeting of KAT7, with the novel inhibitor PF-9363, increases the therapeutic efficacy. KAT7 interacts with Menin and the MLL complex and is co-localised at chromatin to co-regulate the MLL-FP transcriptional program. Inhibition of KAT6/KAT7 provides an orthogonal route to targeting Menin to disable the transcriptional activity of MLL-FP. Consequently, combined inhibition rapidly evicts the MLL-FP from chromatin, potently represses oncogenic transcription and overcomes primary resistance to Menin inhibitors. Moreover, PF-9363 or genetic depletion of KAT7 can also overcome acquired genetic/non-genetic resistance to Menin inhibition. These data provide the molecular rationale for rapid clinical translation of combination therapy in MLL-FP leukaemia.

Epigenetics-targeted drugs: current paradigms and future challenges

Epigenetics governs a chromatin state regulatory system through five key mechanisms: DNA modification, histone modification, RNA modification, chromatin remodeling, and non-coding RNA regulation. These mechanisms and their associated enzymes convey genetic information independently of DNA base sequences, playing essential roles in organismal development and homeostasis. Conversely, disruptions in epigenetic landscapes critically influence the pathogenesis of various human diseases. This understanding has laid a robust theoretical groundwork for developing drugs that target epigenetics-modifying enzymes in pathological conditions. Over the past two decades, a growing array of small molecule drugs targeting epigenetic enzymes such as DNA methyltransferase, histone deacetylase, isocitrate dehydrogenase, and enhancer of zeste homolog 2, have been thoroughly investigated and implemented as therapeutic options, particularly in oncology. Additionally, numerous epigenetics-targeted drugs are undergoing clinical trials, offering promising prospects for clinical benefits. This review delineates the roles of epigenetics in physiological and pathological contexts and underscores pioneering studies on the discovery and clinical implementation of epigenetics-targeted drugs. These include inhibitors, agonists, degraders, and multitarget agents, aiming to identify practical challenges and promising avenues for future research. Ultimately, this review aims to deepen the understanding of epigenetics-oriented therapeutic strategies and their further application in clinical settings.

Bromodomain proteins as potential therapeutic targets for B-cell non-Hodgkin lymphoma

BACKGROUND

B-cell non-Hodgkin lymphoma (B-NHL) is the most common type of lymphoma and is significantly heterogeneous among various subtypes. Despite of considerable advancements in treatment strategies for B-NHL, the prognosis of relapsed/refractory patients remains poor.

MAIN TEXT

It has been indicated that epigenetic dysregulation is critically associated with the pathogenesis of most hematological malignancies, resulting in the clinical targeting of epigenetic modifications. Bromodomain (BRD) proteins are essential epigenetic regulators which contain eight subfamilies, including BRD and extra-terminal domain (BET) family, histone acetyltransferases (HATs) and HAT-related proteins, transcriptional coactivators, transcriptional mediators, methyltransferases, helicases, ATP-dependent chromatin-remodeling complexes, and nuclear-scaffolding proteins. Most pre-clinical and clinical studies on B-NHL have focused predominantly on the BET family and the use of BET inhibitors as mono-treatment or co-treatment with other anti-tumor drugs. Furthermore, preclinical models of B-NHL have revealed that BET degraders are more active than BET inhibitors. Moreover, with the development of BET inhibitors and degraders, non-BET BRD protein inhibitors have also been designed and have shown antitumor activities in B-NHL preclinical models. This review summarized the mechanism of BRD proteins and the recent progress of BRD protein-related drugs in B-NHL. This study aimed to collect the most recent evidences and summarize possibility on whether BRD proteins can serve as therapeutic targets for B-NHL.

CONCLUSION

In summary, BRD proteins are critical epigenetic regulatory factors and may be potential therapeutic targets for B-NHL.

CRISPR Dependency Screens in Primary Hematopoietic Stem Cells Identify KDM3B as a Genotype-specific Vulnerability in IDH2- and TET2-mutant Cells

Clonal hematopoiesis (CH) is a common premalignant state in the blood and confers an increased risk of blood cancers and all-cause mortality. Identification of therapeutic targets in CH has been hindered by the lack of an ex vivo platform amenable for studying primary hematopoietic stem and progenitor cells (HSPCs). Here, we utilize an ex vivo co-culture system of HSPCs with bone marrow endothelial cells to perform CRISPR/Cas9 screens in mutant HSPCs. Our data reveal that loss of the histone demethylase family members Kdm3b and Jmjd1c specifically reduces the fitness of Idh2- and Tet2-mutant HSPCs. Kdm3b loss in mutant cells leads to decreased expression of critical cytokine receptors including Mpl, rendering mutant HSPCs preferentially susceptible to inhibition of downstream JAK2 signaling. Our study nominates an epigenetic regulator and an epigenetically regulated receptor signaling pathway as genotype-specific therapeutic targets and provides a scalable platform to identify genetic dependencies in mutant HSPCs. Significance: Given the broad prevalence, comorbidities, and risk of malignant transformation associated with CH, there is an unmet need to identify therapeutic targets. We develop an ex vivo platform to perform CRISPR/Cas9 screens in primary HSPCs. We identify KDM3B and downstream signaling components as genotype-specific dependencies in CH and myeloid malignancies. See related commentary by Khabusheva and Goodell, p. 1768.

Enhancers in T Cell development and malignant lesions

Enhancers constitute a vital category of cis-regulatory elements with a Mediator complex within DNA sequences, orchestrating gene expression by activating promoters. In the development of T cells, some enhancers regulate the critical genes, which might also regulate T cell malignant lesions. This review is to comprehensively elucidate the contributions of enhancers in both normal T cell development and its malignant pathogenesis, proposing the idea that the precise subunits of the Mediator complex are the potential drug target for disrupting the specific gene enhancer for T cell malignant diseases.

Defeating MYC with drug combinations or dual-targeting drugs

Members of the MYC family of proteins are a major target for cancer drug discovery, but the development of drugs that block MYC-driven cancers has not yet been successful. Approaches to achieve success may include the development of combination therapies or dual-acting drugs that target MYC at multiple nodes. Such treatments hold the possibility of additive or synergistic activity, potentially reducing side effect profiles and the emergence of resistance. In this review, we examine the prominent MYC-related targets and highlight those that have been targeted in combination and/or dual-target approaches. Finally, we explore the challenges of combination and dual-target approaches from a drug development perspective.

A Phase I/II Study of GSK525762 Combined with Fulvestrant in Patients with Hormone Receptor-positive/HER2-negative Advanced or Metastatic Breast Cancer

PURPOSE

Endocrine-based therapy is the initial primary treatment option for hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer (mBC). However, patients eventually experience disease progression due to resistance to endocrine therapy. Molibresib (GSK525762) is a small-molecule inhibitor of bromodomain and extraterminal (BET) family proteins (BRD2, BRD3, BRD4, and BRDT). Preclinical data suggested that the combination of molibresib with endocrine therapy might overcome endocrine resistance. This study aimed to investigate the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy [objective response rate (ORR)] of molibresib combined with fulvestrant in women with HR+/HER2- mBC.

PATIENTS AND METHODS

In this phase I/II dose-escalation and dose-expansion study, patients received oral molibresib 60 or 80 mg once daily in combination with intramuscular fulvestrant. Patients enrolled had relapsed/refractory, advanced/metastatic HR+/HER2- breast cancer with disease progression on prior treatment with an aromatase inhibitor, with or without a cyclin-dependent kinase 4/6 inhibitor.

RESULTS

The study included 123 patients. The most common treatment-related adverse events (AE) were nausea (52%), dysgeusia (49%), and fatigue (45%). At a 60-mg dosage of molibresib, >90% of patients experienced treatment-related AE. Grade 3 or 4 treatment-related AE were observed in 47% and 48% of patients treated with molibresib 60 mg and molibresib 80 mg, respectively. The ORR was 13% [95% confidence interval (CI), 8-20], not meeting the 25% threshold for proceeding to phase II. Among 82 patients with detected circulating tumor DNA and clinical outcome at study enrollment, a strong association was observed between the detection of copy-number amplification and poor progression-free survival (HR, 2.89; 95% CI, 1.73-4.83; P < 0.0001).

CONCLUSIONS

Molibresib in combination with fulvestrant did not demonstrate clinically meaningful activity in this study.

Super-enhancers and the super-enhancer reader BRD4: tumorigenic factors and therapeutic targets

Transcriptional super-enhancers and the BET bromodomain protein BRD4 are emerging as critical drivers of tumorigenesis and therapeutic targets. Characterized by substantial accumulation of histone H3 lysine 27 acetylation (H3K27ac) signals at the loci of cell identity genes and critical oncogenes, super-enhancers are recognized, bound and activated by BRD4, resulting in considerable oncogene over-expression, malignant transformation, cancer cell proliferation, survival, tumor initiation and progression. Small molecule compound BRD4 BD1 and BD2 bromodomain inhibitors block BRD4 binding to super-enhancers, suppress oncogene transcription and expression, reduce cancer cell proliferation and survival, and repress tumor progression in a variety of cancer types. Like other targeted therapy agents, BRD4 inhibitors show moderate anticancer effects on their own, and exert synergistic anticancer effects in vitro and in preclinical models, when combined with other anticancer agents including CDK7 inhibitors, CBP/p300 inhibitors and histone deacetylase inhibitors. More recently, BRD4 BD2 bromodomain selective inhibitors, proteolysis-targeting chimera (PROTAC) BRD4 protein degraders, and dual BRD4 and CBP/p300 bromodomain co-inhibitors have been developed and shown better anticancer efficacy and/or safety profile. Importantly, more than a dozen BRD4 inhibitors have entered clinical trials in patients with cancer of various organ origins. In summary, super-enhancers and their reader BRD4 are critical tumorigenic drivers, and BRD4 BD1 and BD2 bromodomain inhibitors, BRD4 BD2 bromodomain selective inhibitors, PROTAC BRD4 protein degraders, and dual BRD4 and CBP/p300 bromodomain co-inhibitors are promising novel anticancer agents for clinical translation.

Emerging synthetic drugs for the treatment of diffuse large B-cell lymphoma

INTRODUCTION

Diffuse large B-cell lymphoma (DLBCL) is the most common aggressive lymphoma. Recent advances in immunotherapy such as chimeric antigen receptor T-cell therapy have significantly improved the outcomes in patients. Despite those advances, disease still recurs in many patients after multiple lines of therapy, and they eventually die. Many novel agents are under investigation. In this review, we focus on the synthetic drugs, usually small-molecule oral agents, that target a specific tumor-cell survival pathway.

AREAS COVERED

We discuss immunomodulatory drugs, cereblon E3 ligase modulators, Bruton tyrosine kinase degraders, B-cell lymphoma-2 inhibitors, Enhancer of Zeste 2 inhibitors, IRAK4 inhibitors/IRAK4 protein degraders, bromodomain and extraterminal inhibitors, cyclin-dependent kinase 9 inhibitors, and menin inhibitors. We focus on their mechanisms of action, activities in DLBCL, and, in some cases, toxicity. We also discuss the challenges in developing synthetic drugs in DLBCL.

EXPERT OPINION

Synthetic drugs hold great potential for treating DLBCL. Many phase 1/2 trials are ongoing. To maximize their clinical benefit, a better understanding of the biology of this heterogeneous group of diseases is needed, synergic combinations need to be identified, and the sequencing of therapies needs to be considered.

Bromodomain and extraterminal (BET) proteins: biological functions, diseases, and targeted therapy

BET proteins, which influence gene expression and contribute to the development of cancer, are epigenetic interpreters. Thus, BET inhibitors represent a novel form of epigenetic anticancer treatment. Although preliminary clinical trials have shown the anticancer potential of BET inhibitors, it appears that these drugs have limited effectiveness when used alone. Therefore, given the limited monotherapeutic activity of BET inhibitors, their use in combination with other drugs warrants attention, including the meaningful variations in pharmacodynamic activity among chosen drug combinations. In this paper, we review the function of BET proteins, the preclinical justification for BET protein targeting in cancer, recent advances in small-molecule BET inhibitors, and preliminary clinical trial findings. We elucidate BET inhibitor resistance mechanisms, shed light on the associated adverse events, investigate the potential of combining these inhibitors with diverse therapeutic agents, present a comprehensive compilation of synergistic treatments involving BET inhibitors, and provide an outlook on their future prospects as potent antitumor agents. We conclude by suggesting that combining BET inhibitors with other anticancer drugs and innovative next-generation agents holds great potential for advancing the effective targeting of BET proteins as a promising anticancer strategy.

BET Bromodomain Inhibitors: Novel Design Strategies and Therapeutic Applications

The mammalian bromodomain and extra-terminal domain (BET) family of proteins consists of four conserved members (Brd2, Brd3, Brd4, and Brdt) that regulate numerous cancer-related and immunity-associated genes. They are epigenetic readers of histone acetylation with broad specificity. BET proteins are linked to cancer progression due to their interaction with numerous cellular proteins including chromatin-modifying factors, transcription factors, and histone modification enzymes. The spectacular growth in the clinical development of small-molecule BET inhibitors underscores the interest and importance of this protein family as an anticancer target. Current approaches targeting BET proteins for cancer therapy rely on acetylation mimics to block the bromodomains from binding chromatin. However, bromodomain-targeted agents are suffering from dose-limiting toxicities because of their effects on other bromodomain-containing proteins. In this review, we provided an updated summary about the evolution of small-molecule BET inhibitors. The design of bivalent BET inhibitors, kinase and BET dual inhibitors, BET protein proteolysis-targeting chimeras (PROTACs), and Brd4-selective inhibitors are discussed. The novel strategy of targeting the unique C-terminal extra-terminal (ET) domain of BET proteins and its therapeutic significance will also be highlighted. Apart from single agent treatment alone, BET inhibitors have also been combined with other chemotherapeutic modalities for cancer treatment demonstrating favorable clinical outcomes. The investigation of specific biomarkers for predicting the efficacy and resistance of BET inhibitors is needed to fully realize their therapeutic potential in the clinical setting.

Potent bromodomain and extraterminal domain inhibitor JAB-8263 suppresses MYC expression and exerts anti-tumor activity in colorectal cancer models

BACKGROUND

The overexpression of the MYC gene plays an important role in the occurrence, development and evolution of colorectal cancer (CRC). Bromodomain and extraterminal domain (BET) inhibitors can decrease the function BET by recognizing acetylated lysine residues, thereby downregulating the expression of MYC.

AIM

To investigate the inhibitory effect and mechanism of a BET inhibitor on CRC cells.

METHODS

The effect of the BET inhibitor JAB-8263 on the proliferation of various CRC cell lines was studied by CellTiter-Glo method and colony formation assay. The effect of JAB-8263 on the cell cycle and apoptosis of CRC cells was studied by propidium iodide staining and Annexin V/propidium iodide flow assay, respectively. The effect of JAB-8263 on the expression of c-MYC, p21 and p16 in CRC cells was detected by western blotting assay. The anti-tumor effect of JAB-8263 on CRC cells in vivo and evaluation of the safety of the compound was predicted by constructing a CRC cell animal tumor model.

RESULTS

JAB-8263 dose-dependently suppressed CRC cell proliferation and colony formation in vitro. The MYC signaling pathway was dose-dependently inhibited by JAB-8263 in human CRC cell lines. JAB-8263 dose-dependently induced cell cycle arrest and apoptosis in the MC38 cell line. SW837 xenograft model was treated with JAB-8263 (0.3 mg/kg for 29 d), and the average tumor volume was significantly decreased compared to the vehicle control group (P < 0.001). The MC38 syngeneic murine model was treated with JAB-8263 (0.2 mg/kg for 29 d), and the average tumor volume was significantly decreased compared to the vehicle control group (P = 0.003).

CONCLUSION

BET could be a potential effective drug target for suppressing CRC growth, and the BET inhibitor JAB-8263 can effectively suppress c-MYC expression and exert anti-tumor activity in CRC models.