Deuterium labeling improves the therapeutic index of 3,3′-diselenodipropionic acid as an anticancer agent: insights from redox reactions†

3,3′-Diselenodipropionic acid (DSePA), a selenocystine derivative, has been previously reported as an oral supplement for anticancer/radio-modulation activities. The present study is focused on devising a strategy to synthesize and characterize the deuterated derivative of DSePA and on understanding the effect of deuteration on its therapeutic index by comparing its cytotoxicity in cancerous versus non-cancerous cell types. In this context, the synthesis of 3,3′-diselenodipropionic acid-D₈ (D-DSePA) was accomplished in ∼42% yield. Further, the results clearly established that the deuteration of DSePA significantly reduced its cytotoxicity in non-cancerous cell types while retaining its cytotoxicity in cancerous cell lines. Together, D-DSePA displayed a ∼5-fold higher therapeutic index than the non-deuterated derivative for anticancer activity. The biochemical and NMR studies confirmed that the better biocompatibility of D-DSePA than its non-deuterated derivative in non-cancerous cells was due to its ability to undergo slower redox reactions and to cause lesser inhibition of intracellular redox enzymes.