Abstract 4716: Therapeutic utility of EC359 for targeting oncogenic LIFR signaling in triple negative breast cancer
Authors: Viswanadhapalli Suryavathi , Li Mengxing , Luo Yiliao , Sareddy Gangadhara R , Santhamma Bindu , Zhou Mei , Ma Shihong , Sonavane Rajni , Pratap Uday P. , Altwegg Kristin A. , Chang Annabel , Chávez-Riveros Alejandra , Dileep Kalarickal V. , Zhang Kam Y. , Bajda Marek , Raj Ganesh V. , Brenner Andrew , Manthati Vijaya , Rao Manjeet , Tekmal Rajeshwar R. , Nair Hareesh B. , Nickisch Klaus J. , Vadlamudi Ratna K. 
Published: August 2019

Abstract
Background: Leukemia inhibitory factor receptor (LIFR) and its ligand LIF play a major critical role in cancer progression, metastasis, stem cell maintenance, and therapy resistance. Recent studies in breast cancer have shown that feedback activation of LIFR limits response to histone deacetylase (HDAC) inhibitors and induce resistance. We rationally designed a small molecule (EC359) that emulates the LIF-LIFR binding site and functions as a LIFR inhibitor from a library of compounds. Here, we tested the utility of EC359 as a monotherapy and to effectively block LIF-LIFR interactions in overcoming resistance to HDAC inhibitors.
Methods: We have used multiple triple negative breast cancer (TNBC) models that represent all six types of TNBC. In vitro activity was tested using Cell-Titer Glo, MTT, invasion, and apoptosis assays. Mechanistic studies were conducted using western blot, reporter gene assays, and RNA-seq analysis. Xenograft, patient-derived xenograft (PDX), and patient-derived explant (PDeX) models were used for preclinical evaluation and toxicity.
Results: EC359 treatment exhibited anti-proliferative effects, reduced invasiveness and stemness, and promoted apoptosis in all six TNBC cell lines. The activity of EC359 is dependent on LIF and LIFR expression and CRISPR mediated knockdown of LIFR significantly abolished EC359 activity. Treatment with EC359 attenuated the activation of LIF-LIFR driven pathways including STAT3, mTOR, and AKT. EC359 significantly reduced tumor progression in TNBC xenografts, PDX models and reduced proliferation in patient derived primary TNBC explants. In MTT based cell viability assays, addition of EC359 enhanced efficacy of SAHA compared to monotherapy of SAHA. In clonogenic survival assays, EC359 significantly enhanced ability of SAHA to reduce the colony formation compared to monotherapy. Mechanistic studies using three different TNBC models using western blot analysis and reporter gene assays confirmed activation of LIFR signaling pathway upon SAHA treatment and its blockage by EC359. Treatment of TNBC PDX explants with EC359 enhanced ability of SAHA to substantially decrease the proliferation (Ki-67 positivity) compared to monotherapy treated tumors.
Conclusions: Collectively, these data support EC359 as a novel targeted therapeutic that inhibits LIFR oncogenic signaling as a monotherapy or in combination with HDAC inhibitors.
Citation Format: Suryavathi Viswanadhapalli, Mengxing Li, Yiliao Luo, Gangadhara R Sareddy, Bindu Santhamma, Mei Zhou, Shihong Ma, Rajni Sonavane, Uday P. Pratap, Kristin A. Altwegg, Annabel Chang, Alejandra Chávez-Riveros, Kalarickal V. Dileep, Kam Y. Zhang, Marek Bajda, Ganesh V. Raj, Andrew Brenner, Vijaya Manthati, Manjeet Rao, Rajeshwar R. Tekmal, Hareesh B. Nair, Klaus J. Nickisch, Ratna K. Vadlamudi. Therapeutic utility of EC359 for targeting oncogenic LIFR signaling in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4716.