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Herein, 2,3-dioxo-1,2,3,4-tetrahydroquinoxaline was used as a bio-isosteric scaffold to the phthalazinone motif of the standard drug Olaparib to design and synthesize new derivatives of potential PARP-1 inhibitory activity using the 6-sulfonohydrazide analog <b>3</b> as the key intermediate. Although the new compounds represented the PARP-1 suppression impact of IC₅₀ values in the nanomolar range, compounds <b>8a</b>, <b>5</b> were the most promising suppressors, producing IC₅₀ values of 2.31 and 3.05 nM compared to Olaparib with IC₅₀ of 4.40 nM. Compounds <b>4</b>, <b>10b</b>, and <b>11b</b> showed a mild decrease in the potency of the IC₅₀ range of 6.35–8.73 nM. Furthermore, compounds <b>4</b>, <b>5</b>, <b>8a</b>, <b>10b</b>, and <b>11b</b> were evaluated as in vitro antiproliferative agents against the mutant BRCA1 (MDA-MB-436, breast cancer) compared to Olaparib as a positive control. Compound <b>5</b> exhibited the most significant potency of IC₅₀; 2.57 µM, whereas the IC₅₀ value of Olaparib was 8.90 µM. In addition, the examined derivatives displayed a promising safety profile against the normal WI-38 cell line. Cell cycle, apoptosis, and autophagy analyses were carried out in the MDA-MB-436 cell line for compound <b>5,</b> which exhibited cell growth arrest at the G2/M phase, in addition to induction of programmed apoptosis and an increase in the autophagic process. Molecular docking of the compounds <b>4</b>, <b>5</b>, <b>8a</b>, <b>10b</b>, and <b>11b</b> into the active site of PARP-1 was carried out to determine their modes of interaction. In addition, an in silico ADMET study was performed. The results evidenced that compound <b>5</b> could serve as a new framework for discovering new potent anticancer agents targeting the PARP-1 enzyme.