D-501036 [2,5-bis(5-hydroxymethyl-2-selenienyl)-3-hydroxymethyl-N-methylpyrrole] is herein identified as a novel antineoplastic agent with a broad spectrum of antitumoral activity against several human cancer cells and an IC50 value in the nanomolar range. The IC50 values for D-501036 in the renal proximal tubule, normal bronchial epithelial, and fibroblast cells were > 10 μmol/L. D-501036 exhibited no cross-resistance with vincristine- and paclitaxel-resistant cell lines, whereas a low level of resistance toward the etoposide-resistant KB variant was observed. Cell cycle analysis established that D-501036 treatment resulted in a dose-dependent accumulation in S phase with concomitant loss of both the G0-G1 and G2-M phase in both Hep 3B and A-498 cells. Pulsed-field gel electrophoresis showed D-501036-induced, concentration-dependent DNA breaks in both Hep 3B and A-498 cells. These breaks did not involve interference with either topoisomerase-I and topolsomerase-II function or DNA binding. Rapid reactive oxygen species production and formation of Se-DNA adducts were evident following exposure of cells to D-501036, indicating that D-501036 - mediated DNA breaks were attributable to the induction of reactive oxygen species and DNA adduct formation. Moreover, D-501036 - induced DNA damage activated ataxia telangiectasia - mutated nuclear protein kinase, leading to hyperphosphorylation of Chk1, Chk2, and p53, decreased expression of CDC25A, and up-regulation of p2lWAF1 in both p53-proficient and p53-deficient cells. Collectively, the results indicate that D-501036-induced cell death was associated with DNA damage - mediated induction of ataxia telangiectasia - mutated activation, and p53-dependent and -independent apoptosis pathways. Notably, D-501036 shows potent activity against the growth of xenograft tumors of human renal carcinoma A-498 cells. Thus, D-501036 is a promising anticancer compound that has strong potential for the management of human cancers.