Epithelial ovarian cancer is the most lethal malignancy of the female reproductive tract. A healthy ovary expresses both Estrogen Receptor α (ERα) and β (ERβ). Given that ERα is generally considered to promote cell survival and proliferation, thereby, enhancing tumor growth, while ERβ shows a protective effect against the development and progression of tumors, the activation of ERβ by its agonists could be therapeutically beneficial for ovarian cancer. Here, we demonstrate that the activation of ERβ using a newly developed ERβ agonist, OSU-ERb-12, can impede ovarian cancer cell expansion and tumor growth in an ERα-independent manner. More interestingly, we found that OSU-ERb-12 also reduces the cancer stem cell (CSC) population in ovarian cancer by compromising non-CSC-to-CSC conversion. Mechanistically, we revealed that OSU-ERb-12 decreased the expression of Snail, a master regulator of the epithelial-to-mesenchymal transition (EMT), which is associated with de novo CSC generation. Given that ERα can mediate EMT and facilitate maintenance of the CSC subpopulation and that OSU-ERb-12 can block the transactivity of ERα, we conclude that OSU-ERb-12 reduces the CSC subpopulation by inhibiting EMT in an ERα-dependent manner. Taken together, our data indicate that the ERβ agonist OSU-ERb-12 could be used to hinder tumor progression and limit the CSC subpopulation with the potential to prevent tumor relapse and metastasis in patients with ovarian cancer.

Breast cancer (BC) is the most frequent cancer and second-leading cause of cancer deaths in women in the United States. While RAS mutations are infrequent in BC, triple-negative (TN) and HER2-positive (HER2+) BC both exhibit increased RAS activity. Here, we tested the RAS effectors RALA and RALB, which are overexpressed in BC, as tractable molecular targets in these subtypes. While analysis of the breast cancer patient sample data suggests that the RALs are associated with poor outcome in both TNBC and HER2+ BC, our in vivo and in vitro experimental findings revealed the RALs to be essential in only the TNBC cell lines. While testing the response of the BC cell lines to the RAL inhibitors RBC8 and BQU57, we observed no correlation between drug efficacy and cell line dependency on RAL expression for survival, suggesting that these compounds kill via off-target effects. Finally, we report the discovery of a new small molecule inhibitor, OSURALi, which exhibits strong RAL binding, effectively inhibits RAL activation, and is significantly more toxic to RAL-dependent TNBC cells than RAL-independent HER2+ and normal cell lines. These results support the RALs as viable molecular targets in TNBC and the further investigation of OSURALi as a therapeutic agent.

Background: HOSU-53 (JBZ-001), an orally bioavailable new chemical entity, represents a highly potent dihydroorotate dehydrogenase (DHODH) inhibitor in late preclinical development for application in cancer therapy. Methods: Multiple Good Laboratory Practice (GLP) and non-GLP preclinical studies were conducted in mice, rats, and dogs. Plasma samples of HOSU-53 and dihydroorotate (DHO), the substrate of DHODH, were collected for pharmacokinetic (PK) and pharmacodynamic (PD) assessment and modeling. Two modeling approaches were utilized to understand the PK/PD properties of HOSU-53 and to recommend a first-in-human (FIH) dose. Results: A population PK/PD model was developed using a stochastic approximation of the expectation-maximization method and evaluated using graphical and numerical methods. The PK of HOSU-53 was well described by a two-compartment model with a first-order absorption and linear elimination, and the PD was described by a turnover model. No covariates were considered significant on PK/PD parameters. This model was subsequently used to predict DHO exposures in humans across a range of doses. Additionally, predicted human hepatocellular HOSU-53 concentrations were obtained from a physiologically based PK model constructed in PK-Sim. Conclusions: A first-in-human starting dose of 5 mg once daily was established from the model approaches and will be utilized in the upcoming FIH clinical study.

Pancreatic ductal adenocarcinoma (PDAC) displays profound metabolic plasticity that sustains rapid proliferation through heightened demands for nucleotide biosynthesis. Here, we characterize HOSU-53 (JBZ-001), a dihydroorotate dehydrogenase (DHODH) inhibitor demonstrating potent antitumor activity in preclinical PDAC models and define the metabolic determinants of sensitivity and resistance. In HOSU-53-sensitive PDAC cells, DHODH inhibition induces G₂/M cell cycle arrest and triggers apoptotic and ferroptotic cell death. In contrast, resistant cells evade metabolic stress by activating compensatory nucleoside transport and macropinocytosis pathways. Integrated functional and genetic analyses reveal that nucleoside salvage via the equilibrative nucleoside transporter SLC29A1 constitutes a dominant resistance mechanism, enabling uptake of extracellular nucleosides to bypass de novo pyrimidine synthesis. Unbiased metabolomic profiling demonstrates that combined inhibition of DHODH and SLC29A1 precipitates mitochondrial dysfunction, oxidative stress, lipid remodeling, and amino acid depletion, culminating in metabolic collapse and energetic failure. Consistent with these findings, dual inhibition markedly suppresses tumor growth and metastatic burden in xenograft and syngeneic orthotopic PDAC models while reprogramming the tumor microenvironment toward a pro inflammatory, immune activated state. Furthermore, co targeting DHODH and SLC29A1 synergizes with anti–PD 1 immune checkpoint blockade, enhancing immunotherapeutic efficacy. Together, these results establish dual targeting of de novo and salvage nucleotide metabolism as a compelling strategy to overcome metabolic resistance, remodel tumor–immune interactions and potentiate therapeutic responses in PDAC