Ambrx Provides Safety and Efficacy Data from Ongoing Phase 1/2 APEX-01 Trial of ARX517 in mCRPC at ESMO Congress - Seite 2

Abstract Highlights:

• In dose escalation patients treated via intravenous infusion every 3 weeks at putative therapeutic doses ≥2.0 mg/kg (Cohort 6 at 2.0 mg/kg, Cohort 7 at 2.4 mg/kg and Cohort 8 at 2.88 mg/kg):
  • 7 out of 9 patients experienced a ≥50% PSA reduction
    • 3 out of 3 patients in Cohort 6
    • 2 out of 3 patients in Cohort 7
    • 2 out of 3 patients in Cohort 8
  • 5 out of 5 patients experienced a ≥50% ctDNA reduction
    • 3 out of 3 patients in Cohorts 6
    • 2 out of 2 patients in Cohort 7
    • Cohort 8 data not available
• In 24 dose escalation patients treated from 0.32 mg/kg (Cohort 1) to 2.88 mg/kg (Cohort 8) ARX517 was well-tolerated at all doses
  • No treatment-related SAEs observed
  • No DLTs observed
  • Four Grade 3 treatment-related adverse events (TRAEs) were reported in Cohort 5 (1.7 mg/kg), Cohort 7 (2.4 mg/kg) and Cohort 8 (2.88 mg/kg) (two cases of lymphopenia, two cases of platelet count decrease)
    

Title: ARX517, a next generation anti-PSMA antibody drug conjugate (ADC), demonstrates notable stability and pharmacokinetic (PK) profile in the ARX517 Phase 1/2 clinical trial (APEX-01)

Abstract Highlights:

• The pharmacokinetics population consisted of 21 dose escalation patients having received ARX517 across all dose levels (0.32 to 2.4 mg/kg):
  • ARX517 exhibited virtually overlapping total antibody and ADC PK concentration-time curves at all dose levels tested indicating strong stability of the ADC with minimal premature payload release
  • A long ADC terminal half-life of ~6–10 days was observed at doses ≥ 1.4 mg/kg, thereby maximizing drug exposure over a dosing cycle of 3 weeks
  • Low concentrations of pAF-AS269 (approximately 0.02–0.2 ng/mL) were observed at all dose levels and appeared slowly in the circulation, with Cmax observed approximately 7 days after administration

“Based on the encouraging preliminary efficacy and safety results observed in the APEX-01 trial, we believe ARX517 has the potential to overcome the instability and resulting toxicity challenges of previous PSMA-targeted ADCs and may hold promise as a novel treatment modality for patients with mCRPC,” said Daniel J. O’Connor, Chief Executive Officer of Ambrx. “We look forward to sharing more results from the trial at the ESMO conference, which will include additional data from dose expansion cohorts.”