Summary BRD4, a bromodomain and extraterminal domain (BET) family member, is an attractive target in multiple pathological settings, particularly cancer. While BRD4 inhibitors have shown some promise in MYC-driven malignancies such as Burkitt’s Lymphoma (BL), we show that BRD4 inhibitors lead to robust BRD4 protein accumulation, which may account for their limited suppression of MYC expression, modest anti-proliferative activity and lack of apoptotic induction. To address these limitations, we designed ARV-825, a heterobifunctional PROTAC (Proteolysis Targeting Chimera) that recruits BRD4 to the E3 ubiquitin ligase cereblon leading to fast, efficient, and prolonged degradation of BRD4 in all BL cell lines tested. Consequently, ARV-825 more effectively suppresses c-MYC levels and downstream signaling than small molecule BRD4 inhibitors resulting in more effective cell proliferation inhibition and apoptosis induction in BL. Our findings provide strong evidence that cereblon-based PROTACs provide a better and more efficient strategy in targeting BRD4 than traditional small molecule inhibitors.

Prostate cancer has the second highest incidence among cancers in men worldwide and is the second leading cause of cancer deaths of men in the United States. Although androgen deprivation can initially lead to remission, the disease often progresses to castration-resistant prostate cancer (CRPC), which is still reliant on androgen receptor (AR) signaling and is associated with a poor prognosis. Some success against CRPC has been achieved by drugs that target AR signaling, but secondary resistance invariably emerges, and new therapies are urgently needed. Recently, inhibitors of bromodomain and extraterminal (BET) family proteins have shown growth-inhibitory activity in preclinical models of CRPC. Here, we demonstrate that ARV-771, a small-molecule pan-BET degrader based on proteolysis-targeting chimera (PROTAC) technology, demonstrates dramatically improved efficacy in cellular models of CRPC as compared with BET inhibition. Unlike BET inhibitors, ARV-771 results in suppression of both AR signaling and AR levels and leads to tumor regression in a CRPC mouse xenograft model. This study is, to our knowledge, the first to demonstrate efficacy with a small-molecule BET degrader in a solid-tumor malignancy and potentially represents an important therapeutic advance in the treatment of CRPC.BET | BRD4 | protein degradation | prostate | PROTAC

Angiogenesis is the growth of new blood vessels from existing ones. It is an important aspect of new tissue development, growth, and tissue repair. It is also a component of many diseases including cancer, blindness, and chronic inflammation such as rheumatoid arthritis (RA) and psoriasis. There is considerable evidence to suggest that angiogenesis and chronic inflammation are codependent; recent studies have begun to reveal the nature of this link, which involves both augmentation of cellular infiltration and proliferation and overlapping roles of regulatory growth factors and cytokines. Through these studies, we have begun to understand the codependence of chronic inflammation and angiogenesis, the potential benefits of targeting angiogenesis in the treatment of chronic inflammation, and of targeting chronic inflammation to affect angiogenesis.

Purpose: The Ras-Raf-mitogen-activated protein kinase kinase (MEK) pathway is overactive in many human cancers and is thus a target for novel therapeutics. We have developed a highly potent and selective inhibitor of MEK1/2. The purpose of these studies has been to show the biological efficacy of ARRY-142886 (AZD6244) in enzymatic, cellular, and animal models. Experimental Design: The ability of ARRY-142886 to inhibit purified MEK1 as well as other kinases was evaluated. Its effects on extracellular signal-regulated kinase (ERK) phosphorylation and proliferation in several cell lines were also determined. Finally, the inhibitor was tested in HT-29 (colorectal) and BxPC3 (pancreatic) xenograft tumor models. Results: The IC 50 of ARRY-142886 was determined to be 14 nmol/L against purified MEK1. This activity is not competitive with ATP, which is consistent with the high specificity of compound for MEK1/2. Basal and epidermal growth factor^induced ERK1/2 phosphorylation was inhibited in several cell lines as well as 12-O-tetradecanoylphorbol-13-acetate^induced ERK1/2 phosphorylation in isolated peripheral blood mononuclear cells.Treatment with ARRY-142886 resulted in the growth inhibition of several cell lines containing B-Raf and Ras mutations but had no effect on a normal fibroblast cell line.When dosed orally, ARRY-142886 was capable of inhibiting both ERK1/ 2 phosphorylation and growth of HT-29 xenograft tumors in nude mice. Tumor regressions were also seen in a BxPC3 xenograft model. In addition, tumors remained responsive to growth inhibition after a 7-day dosing holiday. Conclusions: ARRY-142886 is a potent and selective MEK1/2 inhibitor that is highly active in both in vitro and in vivo tumor models. This compound is currently being investigated in clinical studies.Excessive growth factor signaling leads to unregulated growth that can contribute to the pathogenesis of human cancer. The signaling cascade is initiated by the binding of peptide growth factors to their tyrosine kinase receptors at the plasma membrane. The receptor kinases are activated and through the recruitment of the growth factor receptor binding protein 2/son of sevenless complex to autophosphorylated sites on the receptors, the G protein Ras is induced to its active GTP-bound state. Ras recruits the serine/threonine kinase Raf to the plasma membrane, where it is then able to phosphorylate and activate mitogen-activated protein kinase kinases (MEK) 1 and 2, which are dual specificity protein kinases that phosphorylate serine/ threonine and tyrosine residues. The MEK kinases in turn phosphorylate and activate their only currently known substrates, extracellular signal-regulated kinases (ERK) 1 and 2. ERK1/2 proteins translocate to the nucleus where they phosphorylate and activate effector proteins and transcription factors, resulting in diverse cellular responses, including proliferation.The overexpression and/or mutation of epidermal growth factor (EGF) receptor (EGFR), erbB2, platelet-derived growth factor receptor, RET, and othe...

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