Abstract P3-14-07: Intra-cellular dsRNA receptor RIG-I: A ubiquitous novel target for treatment of chemotherapy drug resistant breast cancer
Authors: Jasani B , Navabi N , Barrett-Lee P , Thompson A , Chester J , Mason M 
Published: May 2016

INTRODUCTION: Toll-like receptor 3 (TLR3), the cell surface receptor for double stranded RNA (dsRNA), expressed in ∼40% of advanced primary breast cancers (T2/T3/N+) has been shown to be an effective therapeutic target for synthetic dsRNA poly A:U in combination with radiation and adjuvant chemotherapy, producing a significant decrease in risk of metastatic relapse (HR 1.85-2.0; 1.03-3.89; Cancer Res;71:1607).

AIM: The present pre-clinical study aimed to explore the therapeutic potential of a ubiquitously expressed intracellular dsRNA receptor, retinoic-acid-inducible gene-I (RIG-I) - a cytoplasmic pathogen recognition receptor directed at pathogen-associated molecular pattern (PAMP) motifs to differentiate viral from cellular dsRNAs. We have shown Ampligen, poly I:C12U (a synthetic dsRNA polymer designed to rapidly degrade in vivo to prevent the toxicity of long dsRNA polymers such as poly I:C) is capable of entering cells in its fragmented dsRNA oligomeric form (&lt;1–2 kb) optimal for activation of intra-cellular RIG-I (J Exp Med 2008;205:1601–1610).

METHODOLOGY & RESULTS: Preliminary experiments with Ampligen on several human breast cancer cell lines (MCF-7 & MDA-MB 453) and normal human mammary epithelial & fibroblast cell lines (HMEC & HFC) unexpectedly showed it to consistently cause a significant loss of cell viability (CellTiter-Glo Luminescent Cell Viability Assay) in p53-deficient drug resistant (5-FU/doxorubicin) MDA-MB 453 cell line in contrast to cell growth arrest (Guava cell Cycle Assay) in p53 wild type MCF-7 cancer and the two non-neoplastic cells lines. This selective effect was confirmed using syngeneic clones of MCF-7 breast cancer cells stably transfected with a dominant negative p53 construct or vector alone: p53-function blocked (DD1) vs p53-function active (EV1) MCF-7 cell lines, respectively (J Nucl Med 2006; 47:1525–1530), and shown to be associated with RIG-I specific mRNA induction (RT-PCR) and Type I interferon pathway activation both inhibited by BX795 (selective inhibitor of IRF3 activation and IFN-b production). Decitabine (DNA demethylating drug capable of intra-cellular generation of dsRNA through transcriptional activation of Alu retrotransposons - PNAS 2012; December 10: E89–E98 ) was next tested as an alternative source of intra-cellular dsRNA, and found to produce results similar to Ampligen on DD1 and EV1. Work is in progress to examine dose response and time-course relationships of the effects Ampligen or decitabine added singly or in combination with chemotherapeutic drug (e.g. doxorubicin) on DD1 and triple negative breast cancer cell lines such as MDA-MB 453 to explore potential therapeutically most effective protocols.

PROVISIONAL CONCLUSIONS: Intra-cellular dsRNA receptor RIG-I constitutively expressed in all cells offers a more ubiquitous target compared to TLR3 for the treatment of breast cancer. Ampligen and decitabine with their selective growth inhibitory effect on drug resistant p53-deficient breast cancer cell lines, merit testing as novel drugs for treatment of p53-deficient drug resistant breast cancer e.g. triple negative breast cancer frequently (∼70%) associated with drug resistance and altered p53 status.

Citation Format: Jasani B, Navabi N, Barrett-Lee P, Thompson A, Chester J, Mason M. Intra-cellular dsRNA receptor RIG-I: A ubiquitous novel target for treatment of chemotherapy drug resistant breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-14-07.