Early Results for ACE‑106 (ACE‑86225106): A Selective PARP1 Inhibitor for HRR‑Mutant Cancers

ACE‑106 (ACE‑86225106) is a highly selective PARP1 inhibitor designed to improve the therapeutic index compared with first‑generation pan‑PARP inhibitors, which broadly inhibit both PARP1 and PARP2 while causing substantial hematologic toxicity. The updated first‑in‑human data from the open‑label, dose‑escalation study show that ACE‑106 is well tolerated, with no dose‑limiting toxicities, no grade 4–5 treatment‑related adverse events (TRAEs), and no TRAEs leading to dose reduction or treatment discontinuation.  Critically, hematologic toxicity did not increase with dose, suggesting a dissociation between exposure and marrow toxicity—a departure from olaparib‑ and niraparib‑like profiles where cytopenias are strongly dose‑dependent.

The mean half‑life of 20.6–34.5 hours is consistent with once‑daily dosing, and drug exposure increases proportionally with dose. This indicates that even at the lower end of the dosing range, steady‑state exposures remain well above predicted efficacious levels, which may translate into durable PARP1 inhibition and reduced risk of resistance‑driven escape.

In efficacy, among 16 patients with germline or somatic HRR‑mutant tumors evaluable by RECIST v1.1, the objective response rate (ORR) was 38% (6/16), with a disease control rate (DCR) of 75% (12/16). Within the metastatic castration‑resistant prostate cancer (mCRPC) HRR‑mutant subset, ORR was 50% (4/8), and PSA50 response rate was 42% (5/12), aligning with, or exceeding, response rates seen with earlier‑generation PARP inhibitors in similar heavily pre‑treated populations. The fact that one mCRPC patient without a documented HRR mutation achieved a confirmed partial response raises the possibility of activity beyond classical HRR‑deficient contexts, though this remains anecdotal and may relate to uncharacterized genomic alterations or PARP1‑dependent vulnerabilities.

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