RNAi-effecting vector construction in “obligate” anaerobic Salmonella strain YB1 as a potentially competent payload in cancer treatment

Abstract

By altering the anaerobic properties of Salmonella strains, our lab has developed an obligate anaerobic strain YB1 that confers specificity to hypoxia regions of the tumor, thereby avoiding indiscriminate targeting of these enzymes in aerobic healthy tissue and avoiding side-effects (Yu, Yang et al. 2012). In this study, we tested the efficacy of YB1 as a novel delivery system for a T7 RNA polymerase (T7 RNAP) positive feedback construct (pIT7S-shRNA), which is theoretically capable of maintaining a high level of T7 RNAP and an ensuing over-expression of the cargo gene—shRNAs against potential cancer therapeutic candidates Sphingosine Kinases (SKs). A more robust and prompt in vitro expression of T7 rnap in MDA-MB-231 cells after YB1-pIT7S treatment in comparison with chemical transfection was observed, and attested our anticipation on high delivery efficiency of YB1. Nonetheless, a counterintuitively elevated expression and absence of RNAi effect of Sphingosine Kinases drew our attention to the bacteria-host interaction and interference of transcription units within the construct. Through transcripts detection across the entire construct region, altogether with pIT7S-EGFP translation verification, we hypothesized that a read-through effect due to overly-high activity of T7 RNAP and insufficient transcriptional termination generated “super-long” transcripts and subsequently inhibited normal processing of shRNAs. While our study keeps going on optimization of the shRNA construct and adaptation of YB1 vehicle-cargo-host response axis, current findings has provided insights on how to enhance efficacy of treatment by high efficiency transfection and knockdown of SK expression, resulting in cancer cell death with the bacterial delivery system.