ASS1 and cancer: Our studies demonstrate that SPA or LM-2I treatment significantly reduces the metabolites, such as urea, aspartic acid, CMP, UMP and TMP, while the addition of pyrimidines can rescue SPA and LM-2I -induced cancer cell death, suggesting that the antitumor activity of SPA and LM-2I is indeed through activation of ASS1, which results in reduced pyrimidine synthesis and consequently the inhibition of cancer cell proliferation.