Lafever, Alex

Abstract SIAH is a new and potent anti-K-RAS drug target in human cancer. The oncogenic EGFR/HER2/K-RAS pathway activation is pivotal in driving uncontrolled tumor growth and systemic metastasis. Thus, counteracting ERBB/K-RAS hyperactivation in attempt to reverse malignant transformation and inhibit latent tumor growth is an important area for new therapy development against late-stage and metastatic cancer. Guided by Drosophila studies, we found that SIAH (Seven-In-Absentia Homologue) is the most downstream “gatekeeper” required for proper K-RAS signaling. Based on its extraordinarily evolutionary conservation, SIAH E3 ligase is well positioned to serve as an ideal drug target for developing new anti-K-RAS and anticancer therapy. We have shown that anti-SIAH-based therapy is indeed effective in inhibiting tumorigenesis and metastasis of pancreatic, lung and breast cancer cells in xenograft models. Importantly, we have shown that anti-SIAH-based anti-K-RAS strategy is effective against well-established, super-large and late-stage pancreatic and triple-negative breast tumors in a xenograft model in vivo. Through these studies, we have successfully identified a new oncogenic K-RAS "vulnerability," SIAH, in high-grade metastatic cancer. We aim to design and develop potent SIAH inhibitor, and translate these findings to the clinic to benefit more cancer patients with therapy-refractory, relapsed and metastatic diseases in the future. SIAH is a therapy-responsive and prognostic biomarker in human cancer: SIAH expression can be used to monitor tumor responses, and identify resistant tumor clones post-NST. SIAH and EGFR outperform ER, PR, HER2 and Ki67 as two robust, sensitive and prognostic biomarkers to predict survival in breast cancer patients with lymph node metastases. The prognostic power of SIAH and EGFR, alone or in combination, is comparable to the clinical gold standards of clinical predictors (LN positivity, mammary tumor size, grade, stage and molecular subtypes in combination), and imaging-guided technology. A marked reduction in SIAH/EGFR expression post-NST would indicate effective therapy and increased survival, while persistent high SIAH/EGFR expression post-NST would indicate ineffective therapy and decreased survival. The therapy-induced changes in SIAH expression are prognostic in quantifying effective/ineffective therapies, differentiating partial responders, identifying resistant tumor clones, and predicting remission/relapse in breast cancer at neoadjuvant settings. The identification of therapy-responsive and prognostic biomarkers is of paramount importance to stratify patients and guide therapies in clinical oncology and personalized medicine. By validating the RAS/SIAH pathway-centered prognostic biomarkers, we hope to guide standard therapies and improve patient survival in the future. Citation Format: Amy H. Tang, Robert E. Van Sciver, Elizaveta Svyatova, Kevin Kanda, Michael P. Lee, Caroline Dasom Lee, Lauren L. Siewertsz Van Reesema, Alex C, Lafever, Amber L. Collier, Apoorva S. Iyer, L.D. Britt, Janet S. Winston, Cynthia A. Allen, David Z. Chang, Gloria M. Petersen, Richard A. Hoefer. Conquering undruggable oncogenic K-RAS-driven incurable metastatic cancer, and delivering precision medicine at neoadjuvant settings [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 584.

Oncogenic K-RAS mutations are found in virtually all pancreatic cancers, making K-RAS one of the most targeted oncoproteins for drug development in cancer therapies. Despite intense research efforts over the past three decades, oncogenic K-RAS has remained largely “undruggable”. Rather than targeting an upstream component of the RAS signaling pathway (i.e., EGFR/HER2) and/or the midstream effector kinases (i.e., RAF/MEK/ERK/PI3K/mTOR), we propose an alternative strategy to control oncogenic K-RAS signal by targeting its most downstream signaling module, Seven-In-Absentia Homolog (SIAH). SIAH E3 ligase controls the signal output of oncogenic K-RAS hyperactivation that drives unchecked cell proliferation, uncontrolled tumor growth, and rapid cancer cell dissemination in human pancreatic cancer. Therefore, SIAH is an ideal therapeutic target as it is an extraordinarily conserved downstream signaling gatekeeper indispensable for proper RAS signaling. Guided by molecular insights and core principles obtained from developmental and evolutionary biology, we propose an anti-SIAH-centered anti-K-RAS strategy as a logical and alternative anticancer strategy to dampen uncontrolled K-RAS hyperactivation and halt tumor growth and metastasis in pancreatic cancer. The clinical utility of developing SIAH as both a tumor-specific and therapy-responsive biomarker, as well as a viable anti-K-RAS drug target, is logically simple and conceptually innovative. SIAH clearly constitutes a major tumor vulnerability and K-RAS signaling bottleneck in pancreatic ductal adenocarcinoma (PDAC). Given the high degree of evolutionary conservation in the K-RAS/SIAH signaling pathway, an anti-SIAH-based anti-PDAC therapy will synergize with covalent K-RAS inhibitors and direct K-RAS targeted initiatives to control and eradicate pancreatic cancer in the future.