Identification of a targetable JAK-STAT enriched androgen receptor and androgen receptor splice variant positive triple-negative breast cancer subtype.

Triple-negative breast cancer (TNBC) is an aggressive subtype with no targeted therapeutics. The luminal androgen receptor (LAR) subtype constitutes 15% of TNBC and is enriched for androgen receptor (AR) and AR target genes. Here, we show that a cohort of TNBC not only expresses AR at a much higher rate (∼80%) but also expresses AR splice variants (AR-SVs) (∼20%), further subclassifying LAR-TNBC. Higher AR and AR-SV expression and corresponding aggressive phenotypes are observed predominantly in specimens obtained from African American women. LAR TNBC specimens are enriched for interferon, Janus kinase (JAK)-signal activator and transducer (STAT), and androgen signaling pathways, which are exclusive to AR-expressing epithelial cancer cells. AR- and AR-SV-expressing TNBC cell proliferation and xenograft and patient-tumor explant growth are inhibited by AR N-terminal domain-binding selective AR degrader or by a JAK inhibitor. Biochemical analysis suggests that STAT1 is an AR coactivator. Collectively, our work identifies pharmacologically targetable TNBC subtypes and identifies growth-promoting interaction between AR and JAK-STAT signaling.

Inhibiting androgen receptor splice variants with cysteine-selective irreversible covalent inhibitors to treat prostate cancer.

Androgen receptor (AR) and its splice variants (AR-SVs) promote prostate cancer (PCa) growth by orchestrating transcriptional reprogramming. Mechanisms by which the low complexity and intrinsically disordered primary transactivation domain (AF-1) of AR and AR-SVs regulate transcriptional programming in PCa remains poorly defined. Using omics, live and fixed fluorescent microscopy of cells, and purified AF-1 and AR-V7 recombinant proteins we show here that AF-1 and the AR-V7 splice variant form molecular condensates by liquid-liquid phase separation (LLPS) that exhibit disorder characteristics such as rapid intracellular mobility, coactivator interaction, and euchromatin induction. The LLPS and other disorder characteristics were reversed by a class of small-molecule-selective AR-irreversible covalent antagonists (SARICA) represented herein by UT-143 that covalently and selectively bind to C406 and C327 in the AF-1 region. Interfering with LLPS formation with UT-143 or mutagenesis resulted in chromatin condensation and dissociation of AR-V7 interactome, all culminating in a transcriptionally incompetent complex. Biochemical studies suggest that C327 and C406 in the AF-1 region are critical for condensate formation, AR-V7 function, and UT-143's irreversible AR inhibition. Therapeutically, UT-143 possesses drug-like pharmacokinetics and metabolism properties and inhibits PCa cell proliferation and tumor growth. Our work provides critical information suggesting that clinically important AR-V7 forms transcriptionally competent molecular condensates and covalently engaging C327 and C406 in AF-1, dissolves the condensates, and inhibits its function. The work also identifies a library of AF-1-binding AR and AR-SV-selective covalent inhibitors for the treatment of PCa.

Reciprocal interplay between OTULIN-LUBAC determines genotoxic and inflammatory NF-κB signal responses.

Targeting nuclear factor-kappa B (NF-κB) represents a highly viable strategy against chemoresistance in cancers as well as cell death. Ubiquitination, including linear ubiquitination mediated by the linear ubiquitin chain assembly complex (LUBAC), is emerging as a crucial mechanism of overactivated NF-κB signaling. Ovarian tumor family deubiquitinase OTULIN is the only linear linkage-specific deubiquitinase; however, the molecular mechanisms of how it counteracts LUBAC-mediated NF-κB activation have been largely unknown. Here, we identify Lys64/66 of OTULIN for linear ubiquitination facilitated in a LUBAC-dependent manner as a necessary event required for OTULIN-LUBAC interaction under unstressed conditions, which becomes deubiquitinated by OTULIN itself in response to genotoxic stress. Furthermore, this self-deubiquitination of OTULIN occurs intermolecularly, mediated by OTULIN dimerization, resulting in the subsequent dissociation of OTULIN from the LUBAC complex and NF-κB overactivation. Oxidative stress induces OTULIN dimerization via cysteine-mediated covalent disulfide bonds. Our study reveals that the status of the physical interaction between OTULIN and LUBAC is a crucial determining factor for the genotoxic NF-κB signaling, as measured by cell survival and proliferation, while OTULIN loss of function resulting from its dimerization and deubiquitination leads to a dissociation of OTULIN from the LUBAC complex. Of note, similar molecular mechanisms apply to the inflammatory NF-κB signaling in response to tumor necrosis factor α. Hence, a fuller understanding of the detailed molecular mechanisms underlying the disruption of the OTULIN-LUBAC interaction will be instrumental for developing future therapeutic strategies against cancer chemoresistance and necroptotic processes pertinent to numerous human diseases.

Immune checkpoint blockade reprograms systemic immune landscape and tumor microenvironment in obesity-associated breast cancer.

Immune checkpoint blockade (ICB) has improved outcomes in some cancers. A major limitation of ICB is that most patients fail to respond, which is partly attributable to immunosuppression. Obesity appears to improve immune checkpoint therapies in some cancers, but impacts on breast cancer (BC) remain unknown. In lean and obese mice, tumor progression and immune reprogramming were quantified in BC tumors treated with anti-programmed death-1 (PD-1) or control. Obesity augments tumor incidence and progression. Anti-PD-1 induces regression in lean mice and potently abrogates progression in obese mice. BC primes systemic immunity to be highly responsive to obesity, leading to greater immunosuppression, which may explain greater anti-PD-1 efficacy. Anti-PD-1 significantly reinvigorates antitumor immunity despite persistent obesity. Laminin subunit beta-2 (Lamb2), downregulated by anti-PD-1, significantly predicts patient survival. Lastly, a microbial signature associated with anti-PD-1 efficacy is identified. Thus, anti-PD-1 is highly efficacious in obese mice by reinvigorating durable antitumor immunity. VIDEO ABSTRACT.

Integrin-Linked Kinase Is a Novel Therapeutic Target in Ovarian Cancer.

OBJECTIVE: The objective of this study is to identify and validate novel therapeutic target(s) in ovarian cancer. BACKGROUND: Development of targeted therapeutics in ovarian cancer has been limited by molecular heterogeneity. Although gene expression datasets are available, most of them lack appropriate pair-matched controls to define the alterations that result in the transformation of normal ovarian cells to cancerous cells. METHODS: We used microarray to compare the gene expression of treatment-naïve ovarian cancer tissue samples to pair-matched normal adjacent ovarian tissue from 24 patients. Ingenuity Pathway Analysis (IPA) was used to identify target pathways for further analysis. Integrin-linked kinase (ILK) expression in SKOV3 and OV90 cells was determined using Western blot. ILK was knocked down using CRISPR/Cas9 constructs. Subcutaneous xenograft study to determine the effect of ILK knockdown on tumor growth was performed in NOD SCID gamma mice. RESULTS: Significant upregulation of the ILK pathway was identified in 22 of the 24 cancer specimens, identifying it as a potential player that could contribute to the transformation of normal ovarian cells to cancerous cells. Knockdown of ILK in SKOV3 cells resulted in decreased cell proliferation and tumor growth, and inhibition of downstream kinase, AKT (protein kinase B). These results were further validated using an ILK-1 chemical inhibitor, compound 22. CONCLUSION: Our initial findings validate ILK as a potential therapeutic target for molecular inhibition in ovarian cancer, which warrants further investigation.

Androgen Receptor Is a Non-canonical Inhibitor of Wild-Type and Mutant Estrogen Receptors in Hormone Receptor-Positive Breast Cancers.

Sustained treatment of estrogen receptor (ER)-positive breast cancer with ER-targeting drugs results in ER mutations and refractory unresponsive cancers. Androgen receptor (AR), which is expressed in 80%-95% of ER-positive breast cancers, could serve as an alternate therapeutic target. Although AR agonists were used in the past to treat breast cancer, their use is currently infrequent due to virilizing side effects. Discovery of tissue-selective AR modulators (SARMs) has renewed interest in using AR agonists to treat breast cancer. Using translational models, we show that AR agonist and SARM, but not antagonist, inhibit the proliferation and growth of ER-positive breast cancer cells, patient-derived tissues, and patient-derived xenografts (PDX). Ligand-activated AR inhibits wild-type and mutant ER activity by reprogramming the ER and FOXA1 cistrome and rendering tumor growth inhibition. These findings suggest that ligand-activated AR may function as a non-canonical inhibitor of ER and that AR agonists may offer a safe and effective treatment for ER-positive breast cancer.