AMAM - Ambrx stock surges 45% as prostate cancer drug shows promise in phase 1 trial

Ambrx Biopharma ( NYSE: AMAM ) stock rose ~45% on Thursday after reporting initial data from an ongoing phase 1 trial of ARX517 to treat patients with advanced prostate cancer whose tumors have progressed on at least two prior FDA-approved treatments.

To date, 22 patients have been dosed across 7 dose level cohorts starting from 0.32 mg/kg to 2.4 mg/kg in the study, dubbed APEX-01.

Ambrx said that in group 6 (2.0 mg/kg dose), 3 of 3 patients experienced a greater than 50% reduction in prostate-specific antigen (PSA) levels from baseline. Two out of 3 patients experienced a greater than 90% reduction of PSA levels. One of three patients had soft tissue measurable disease and experienced a RECIST v1.1 partial response at the first on-treatment scan.

The company added that PSA reductions of >30% were seen in groups 2-5, beginning at the second to lowest dose, 0.64 mg/kg.

Of the 22 patients evaluable for safety, no drug-related severe adverse events (SAEs) or grade ?3 treatment-related AEs were seen. ARX517 was well-tolerated with grade 1 or 2 treatment-related adverse events (TRAEs) being reported, according to the company.

The maximum tolerated dose (MTD) has not yet been reached, the company noted.

Ambrx added that three patients have been dosed in group 7 with no dose limiting toxicities (DLTs).

The company plans to report further information on ARX517 and the study at its upcoming Analyst and Investor Day scheduled for Feb. 24.

ARX517 is an antibody-drug conjugate composed of a fully humanized anti-PSMA mAb linked to AS269, a Ambrx proprietary potent microtubule inhibitor, as per the company.

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