Design, synthesis and anti-breast cancer activity evaluation of 6,7-dihydro-5 <i>H</i> -pyrrolo[3,4- <i>d</i> ]pyrimidine-based PARP1/ATR dual inhibitors

PARP1 inhibitors are FDA-approved for BRCA1/2-mutated breast cancer but show limited efficacy in wild-type cancers and face resistance issues. To overcome these, we designed novel 6,7-dihydro-5<i>H</i>-pyrrolo[3,4-<i>d</i>]pyrimidine-based compounds integrating PARP1 inhibitor pharmacophores with the ATR inhibitor AZD6738 scaffold. Substituent modifications influenced PARP1 and ATR selectivity, yielding dual inhibitors or selective PARP1 inhibitors. Compound <b>38a</b>, the lead candidate, exhibited potent dual inhibition (IC₅₀ < 20 nM) and strong antitumor effects in MDA-MB-231 (IC₅₀ < 0.048 μM) and MDA-MB-468 (IC₅₀: 0.01 μM) cell lines <i>in vitro</i>. Mechanistically, <b>38a</b> arrested cell cycle progression, induced apoptosis, inhibited colony formation and migration, and suppressed DNA damage repair pathways, outperforming combined Niraparib and AZD6738. These findings underscore the therapeutic potential of PARP1/ATR dual inhibitors for breast cancer and support further investigation.