Enzyme-mediated depletion of l-cyst(e)ine synergizes with thioredoxin reductase inhibition for suppression of pancreatic tumor growth

Sabin Kshattry,John DiGiovanni,Achinto Saha,Everett Stone,Paul Gries,George Georgiou,Stefano Tiziani

doi:10.1038/s41698-019-0088-z

Abstract

Perturbing redox homeostasis potentially constitutes a selective cancer-killing strategy. An engineered human enzyme, cyst(e)inase that degrades extracellular cysteine (l-Cys) and cystine (CSSC) leading to depletion of intracellular l-Cys and glutathione (GSH) was evaluated for its effects on pancreatic cancer cell lines. Cyst(e)inase caused oxidative stress and apoptosis in only Panc1 cells, whereas MIA-PaCa2 and BxPC3 cells demonstrated survival under conditions of cyst(e)inase-mediated l-Cys depletion through maintenance of mitochondrial metabolism and lower levels of reactive oxygen species (ROS). A correlation was also observed between thioredoxin 1 protein levels and resistance to cyst(e)inase treatment. Notably, cyst(e)inase in combination with auranofin, a thioredoxin reductase inhibitor, caused a synergistic increase in mitochondrial ROS and apoptosis and inhibition of mitophagy in the more resistant cells. In addition, auranofin treatment sensitized the more resistant pancreatic cancer xenografts to cyst(e)inase without systemic toxicity. These data provide strong rationale to further investigate therapeutic strategies that target multiple antioxidant pathways for treatment of pancreatic ductal adenocarcinoma.

Highlights

Pancreatic ductal adenocarcinoma (PDAC) has a dismal 5-year survival rate at 8%1 despite our increased understanding of the underlying cancer biology and improved ability to perform complex surgical procedures.[2]
Differential sensitivity of PDAC cell lines to L-Cys/CSSC deprivation Treatment of three pancreatic cancer cell lines, BxPC3 (KrasWT), MIA-PaCa2 (KrasG12C), and Panc[1] (KrasG12D), with cyst(e)inase caused a dose-dependent inhibition of cell survival to different extents (Panc1 >> MIA-PaCa2 > BxPC3) (Fig. 1a)
Oxidative stress signaling via JNK and ataxia-telangiectasia mutated (ATM), and apoptosis signaling following cyst(e)inase treatment

Summary

Introduction

Pancreatic ductal adenocarcinoma (PDAC) has a dismal 5-year survival rate at 8%1 despite our increased understanding of the underlying cancer biology and improved ability to perform complex surgical procedures.[2]. I Cellular growth assay of Panc[1], MIA-PaCa2, and BxPC3 cells (n = 3 cultures for each time point) with cyst(e)inase treatment.

Results

Conclusion