Key Points: HCK transcription and activation is triggered by mutated MYD88, and is an important determinant of pro-survival signaling. HCK is also a target of ibrutinib, and inhibition of its kinase activity triggers apoptosis in mutated MYD88 cells.

Androgen receptor (AR) is a ligand-activated transcription factor and a key driver of prostate cancer (PCa) growth and progression. Understanding the factors influencing AR-mediated gene expression provides new opportunities for therapeutic intervention. Poly(ADP-ribose) Polymerase (PARP) is a family of enzymes, which posttranslationally modify a range of proteins and regulate many different cellular processes. PARP-1 and PARP-2 are two well-characterized PARP members, whose catalytic activity is induced by DNA-strand breaks and responsible for multiple DNA damage repair pathways. PARP inhibitors are promising therapeutic agents that show synthetic lethality against many types of cancer (including PCa) with homologous recombination (HR) DNA-repair deficiency. Here, we show that, beyond DNA damage repair function, PARP-2, but not PARP-1, is a critical component in AR transcriptional machinery through interacting with the pioneer factor FOXA1 and facilitating AR recruitment to genome-wide prostate-specific enhancer regions. Analyses of PARP-2 expression at both mRNA and protein levels show significantly higher expression of PARP-2 in primary PCa tumors than in benign prostate tissues, and even more so in castration-resistant prostate cancer (CRPC) tumors. Selective targeting of PARP-2 by genetic or pharmacological means blocks interaction between PARP-2 and FOXA1, which in turn attenuates AR-mediated gene expression and inhibits AR-positive PCa growth. Next-generation antiandrogens act through inhibiting androgen synthesis (abiraterone) or blocking ligand binding (enzalutamide). Selective targeting of PARP-2, however, may provide an alternative therapeutic approach for AR inhibition by disruption of FOXA1 function, which may be beneficial to patients, irrespective of their DNA-repair deficiency status.

BET bromodomain inhibition has contributed new insights into gene regulation and emerged as a promising therapeutic strategy in cancer. Structural analogy of early methyl-triazolo BET inhibitors has prompted a need for structurally dissimilar ligands as probes of bromodomain function. Using fluorous-tagged multicomponent reactions, we developed a focused chemical library of bromodomain inhibitors around a 3,5-dimethylisoxazole biasing element with micromolar biochemical IC₅₀. Iterative synthesis and biochemical assessment allowed optimization of novel BET bromodomain inhibitors based on an imidazo[1,2-a]pyrazine scaffold. Lead compound 32 (UMB-32) binds BRD4 with a K_d of 550 nM and 724 nM cellular potency in BRD4-dependent lines. Additionally, compound 32 shows potency against TAF1, a bromodomain-containing transcription factor previously unapproached by discovery chemistry. Compound 32 was cocrystallized with BRD4, yielding a 1.56 Å resolution crystal structure. This research showcases new applications of fluorous and multicomponent chemical synthesis for the development of novel epigenetic inhibitors.

A pot-economical synthesis involving two [3 + 2] cycloadditions for diastereoselective synthesis of novel triazolobenzodiazepine-containing polycyclic compounds.

Although combinatory antiretroviral therapy (cART) is effective to reduce HIV-1 viremia, it does not eliminate HIV-1 infection. HIV-1 remains latent with the presence of cART, impeding the cure of HIV-1/AIDS. Recently, latency-reversing agents (LRAs) have been developed to purge latent HIV-1, providing an intriguing strategy for eradication of residual, latent viral reservoirs. Our earlier studies show that the first-generation, methyl-triazolo bromodomain and extra-terminal domain inhibitor (BETi), JQ1, facilitates the reversal of HIV-1 latency. BETis have recently emerged as a new class of compounds that are promising for HIV-1 “shock and kill” eradication approach. However, due to the stochastic effcts of HIV-1 reactivation (Ho et al, Cell, 2013), JQ1 only modestly reverses HIV-1 latency as a single drug, which complicates the study of the underlining mechanisms. Thus, BETis, which are more potent, easier for synthesis, and with more structural diversity, are currently under active development. One such compound is UMB-32, a novel second-generation, 3,5-dimethylisoxazole BETi based on an imidazo[1,2-a]pyrazine scaffold. We screened 37 UMB-32 derivatives and identified that UMB-136 consistently reactivates HIV-1 in multiple cell models of HIV-1 latency with better efficiency than JQ1 and UMB-32. UMB-136 enhances HIV-1 Tat-LTR mediated transcription and increases HIV-1 viral production. Furthermore, UMB-136 enhances the latency-reversing effect of PKC agonists (prostratin, bryostatin-1) in CD8-depleted PBMCs containing HIV-1 latent reservoirs. Thus, our results illustrate that structurally improved BETis, such as UMB-136, would be useful as promising LRAs for HIV-1 eradication.