Loss of
argininosuccinate synthetase 1 (ASS1), a key
enzyme for
arginine synthesis, occurs in many
cancers, making cells dependent on extracellular
arginine and targetable by the
arginine-degrading
enzyme pegylated arginine deiminase (ADI-PEG 20). We evaluated ASS1 expression and effects of ASS1 loss in
bladder cancer which, despite affecting >70,000 people in the United States annually, has limited
therapies. ASS1 loss was identified in conventional and micropapillary urothelial
carcinoma, small cell, and
squamous cell carcinoma subtypes of invasive
bladder cancer, as well as in T24, J82, and UM-UC-3 but not in 5637, RT112, and RT4 cell lines. ASS1-deficient cells showed preferential sensitivity to ADI-PEG 20, evidenced by decreased colony formation, reduced cell viability, and increased sub-G1 fractions. ADI-PEG 20 induced general control nonderepressible 2-dependent eukaryotic
initiation factor 2α phosphorylation and
activating transcription factor 4 and
C/EBP homologous protein up-regulation, associated with
caspase-independent apoptosis and autophagy. These effects were ablated with selective
siRNA silencing of these
proteins. ASS1 overexpression in UM-UC-3 or ASS1 silencing in RT112 cells reversed these effects. ADI-PEG 20 treatment of mice bearing contralateral flank UM-UC-3 and RT112 xenografts selectively arrested
tumor growth in UM-UC-3 xenografts, which had reduced
tumor size, reduced Ki-67, and increased
terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. This suggests that ASS1 loss occurs in invasive
bladder cancer and is targetable by ADI-PEG 20.