Emch, Michael

Breast and ovarian cancer represent the most common and lethal cancers in women. Despite chemotherapy and targeted agents, recurrence is frequent and outcomes for patients with advanced disease are dismal, underscoring the need for novel therapeutic strategies. Using an unbiased approach with DepMap CRISPR screens across more than 1000 cancer cell lines, we identified six genes (CTPS1, RHOA, PRKRA, RAD9A, HUS1, and RAD1) that were essential for triple negative breast cancer (TNBC) cells, but not ERα+ breast cancer cells, that were also associated with poor outcomes. Validation of these effects by siRNA knockdown studies revealed that suppression of CTPS1 elicited the most potent inhibitory effects, characterized by S phase cell cycle arrest and apoptosis. Similar effects were also found in ovarian cancer cells which share many molecular features. CTPS1, along with CTPS2, is responsible for enzymatic conversion of UTP to CTP, an essential nucleoside triphosphate required for multiple cellular processes including DNA/RNA synthesis, phospholipid synthesis and glycosylation. CTPS1 was found to be highly expressed in tumor tissues, for both breast and ovarian cancer. RT-PCR assessment of CTPS1 expression in a panel of over 40 breast and ovarian cancer lines confirmed variable, but elevated expression relative to normal models. Notably, chemotherapy-resistant and PARP inhibitor (PARPi)-resistant models exhibited the highest levels of CTPS1 expression among all cells analyzed. In partnership with Step Pharma, which has developed a first-in-class highly selective CTPS1 inhibitor (STP938), we have demonstrated that STP938 elicits potent anti-proliferative effects at nM concentrations across many cell line and patient derived models, both in 2D and 3D culture systems. Furthermore, STP938 exhibited strong anti-cancer activity in chemotherapy- and PARPi-resistant ovarian cancer models, both as a monotherapy and in combination with standard-of-care treatments. RNA-seq analysis in cell models following STP938 treatment or CTPS1 knockdown/knockout showed significant dysregulation of DNA replication and cell cycle related genes, suggesting potential synergy with drugs targeting replication stress or DNA damage response pathways. Single-cell sequencing further revealed specific cell-cell interactions/cross talk/pathways that are disrupted by STP938 in vivo using ovarian cancer patient-derived xenograft. The first-in-human clinical trial for STP938 began in 2022 for relapsed/refractory B- and T-cell lymphomas (NCT05463263). In August 2024, a second phase I trial opened for advanced solid tumors, including an expansion cohort for CTPS2-null ovarian cancer (NCT06297525) at Mayo Clinic. These laboratory discoveries, and ongoing clinical studies, are expected to pave the way for a broader uptake of this novel therapeutic approach aimed at improving outcomes in patients with highly aggressive forms of these diseases. Citation Format: Xiyin Wang, Michael Emch, Lauren Voll, Rebecca Epp, Esther Rodman, Noa Odell, Nicole Pearson, Xiaonan Hou, Matthew Goetz, Scott Kaufmann, John Weroha, Philip Beer, John Hawse. Exploiting CTPS1 dependency for the treatment of breast and ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6388.

Abstract Ovarian cancer is the most fatal of all female reproductive cancers due to its late detection, aggressive nature, and propensity to develop resistance to current standards of care. Despite initial responses to first line platinum- and paclitaxel-based chemotherapies, >70% of ovarian cancers recur with increasingly resistant disease. Targeted therapies, including PARP-inhibitors (PARPi) and VEGF-inhibitors, are being included in the front-line setting; and while they have improved progression-free survival in a subset of patients, they have thus far failed to improve overall survival in patients without specific genetic signatures. With the broad uptake of PARPi, PARPi-resistance is becoming common. Once resistance develops, nearly all patients die of their disease and there is an obvious need to elucidate the basis for chemotherapy- and PARPi-resistance and devise novel approaches to overcome resistance. Using a small molecule drug screen, we identified lestaurtinib, a known tyrosine kinase inhibitor as a potent inhibitor of treatment naive and highly advanced models of ovarian cancer. Lestaurtinib was originally developed to target FLT3, a protein not expressed in any ovarian cancer models we’ve tested. To identify lestaurtinib targets, we preformed phospho-proteomics in parallel with RNAseq and discovered the JAK/STAT signally pathway as a top hit. We confirmed that essential components of JAK/STAT signaling are constitutively activated in chemotherapy- and PARPi-resistant cells, suggesting that induction of this pathway may drive resistance. Importantly, we found that lestaurtinib-sensitive patient-derived-xenografts (PDXs) exhibited higher expression of multiple JAK/STAT signaling pathway members compared to PDXs that did not respond to lestaurtinib. Genetic knockdown of STAT1 and STAT3 via siRNA, or knockout via CRISPR/Cas9, resulted in significant growth inhibition of sensitive and resistant models, confirming their importance in maintaining cell viability and progression. Combining lestuartinib with standard-of-care cisplatin or olaparib, a PARPi, was shown to be synergistic in multiple models, indicating that pharmacological inhibition of JAK/STAT signaling has the potential to alleviate drug resistance. Finally, we assessed a panel of JAK/STAT inhibitors that interfere at various levels of the pathway and found profound differences in their ability to block STAT-phosphorylation and inhibit cell proliferation. Thus, it is critical to further define the mechanisms by which these drugs function to selectively suppress JAK/STAT signaling in order to elucidate specific nodes of the pathway that drive ovarian cancer progression. Ongoing studies are aimed at identifying the unique roles of STAT1 and STAT3, the specific contributions of their tyrosine and serine phosphorylation, and the relevance of up-/down-stream mediators of the JAK/STAT pathway on ovarian cancer cell growth with the goal of informing future clinical trials. Citation Format: Esther Rodman, Michael Emch, Archit Bajaj, Xiaojia Tang, Xiaonan Hou, Scott Kaufmann, Krishna Kalari, John Weroha, John Hawse. Exploiting JAK/STAT signaling to inhibit highly advanced and resistant forms of ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B002.

Abstract Background: Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer-related death among women worldwide. Triple-negative breast cancer (TNBC) is an aggressive subtype representing 15-20% of all breast cancers. TNBC often ends with a poor clinical outcome due to high histological grade and recurrence rates with few treatment options. Chemotherapy remains the standard of care for TNBC treatment, but unfortunately, patients frequently develop resistance, and alternative treatment strategies for the chemoresistant disease remain a major unmet need. circRNAs are newly identified non-coding RNA molecules with covalently closed circular structures. Recently, an increasing number of studies have indicated that circRNAs play crucial roles in regulating tumor development and chemoresistance. However, the role of circRNAs in the process of TNBC chemotherapy resistance is not yet fully clear. Materials and methods: To study the molecular functions of circRNAs in TNBC chemoresistance, identify alternative biomarkers for chemotherapy-resistant disease, and elucidate novel therapeutic targets, doxorubicin-resistant (Doxo-R) and paclitaxel-resistant (Taxol-R) cell lines were generated using TNBC models. Results: Doxo-R and Taxol-R cells exhibited a 3- and 12-fold decrease in sensitivity to their respective chemotherapeutic agents. We identified a large spectrum of gene expression changes that were acquired in Doxo-R and Taxol-R cells. The expression of circRNAs was profiled using circRNA microarrays, and top hits were validated using RT-PCR. We identified 429 and 310 circRNAs that were differentially expressed in Doxo-R and Taxol-R resistant cells respectively compared to the parental chemosensitive cell line (|FC| ≥ 1.5; p value < 0.05). Of these, 66 were commonly differentially expressed between the two chemotherapy resistant models. Conclusions: These results revealed that Doxo-R and Taxol-R TNBC cell lines were successfully established and serve as good models for studying the mechanisms of chemotherapy resistance and the regulatory roles of circRNAs in the development of chemoresistance in TNBC. Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies and prognostic/predictive biomarkers for TNBC. Citation Format: Xiyin Wang, Michael Emch, John Hawse. The role of circular RNAs in triple-negative breast cancer and chemotherapy resistance [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-22-02.

Abstract Ovarian cancer is the 7th most common cancer in women. It is the most fatal of all female reproductive cancers, due to the 5-year overall survival of 10-30% and over half of patients being diagnosed with late-stage disease. Despite initial response to front line platinum- and taxol-based chemotherapies, over 70% of patients develop recurrent and chemotherapy resistant disease and nearly all of these women die of their disease. Recently, the use of targeted therapies such as bevacizumab and PARP inhibitors have been shown to improve progression-free survival. However, these regimens have thus far failed to improve overall survival in patients without specific genetic signatures, highlighting the urgent need for alternative therapies. We have identified lestaurtinib as a potent inhibitor of many ovarian cancer cell lines, including platinum and PARP inhibitor resistant models, and patient derived organoid models. RNA-sequencing following lestaurtinib treatment identified JAK/STAT signaling as one of the most profoundly downregulated pathways. Additionally, it was recently reported via single cell RNA sequencing of patient tumors that downstream mediators of the JAK/STAT pathway are among the most highly expressed genes in ovarian tumor cells. Further, we have discovered that STAT1 and STAT3 are constitutively activated in chemotherapy and PARP inhibitor resistant cell lines as reflected by high levels of Tyr701/705 and Ser727 phosphorylation suggesting induction of this pathway may drive resistance. Selective siRNA-mediated knockdown of STAT1/3 resulted in significant growth inhibition confirming their importance in maintaining cell viability. Surprisingly, we have identified profound differences in the ability of various JAK/STAT inhibitors to suppress ovarian cancer cell growth. For example, ruxolitinib, the only JAK/STAT inhibitor currently in clinical trials for ovarian cancer, failed to inhibit the growth sensitive, platinum resistant or PARP inhibitor resistant cell lines. Our preliminary data indicate that JAK/STAT inhibitor efficacy in preventing ovarian cancer cell growth is related to their ability to block specific phosphorylation events on STAT1/3 proteins. We believe that precise and selective inhibition of STAT1 and STAT3 signaling represents a robust, durable, and novel approach for the treatment of highly aggressive and resistant forms of ovarian cancer. Further we plan to elucidate the molecular mechanisms by which STAT1 and STAT3 function to support ovarian cancer cell viability and growth, in order to substantially advance our understanding of JAK/STAT signaling in ovarian cancer and to identify the most effective ways to pharmacologically inhibit JAK/STAT signaling in ovarian cancer cells. Outcomes from this work will have both immediate and long-term impacts for our patients and will lay the foundation for future biomarker-driven clinical trials. Citation Format: Esther Rodman, Michael Emch, Elizabeth Bruinsma, Xiaonan Hou, John Weroha, John Hawse. Interrogating JAK/STAT signaling in ovarian cancer as a potential oncogenic driver and therapeutic target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1129.