Thursday, Alligator Bioscience AB and Aptevo Therapeutics Inc ( APVO ) released interim data from the dose escalation phase of their Phase 1 trial evaluating ALG.APV-527 for solid tumors likely to express the tumor antigen 5T4.

The multi-center, dose-escalation trial is now more than 50% enrolled, and preliminary results include:

Treatment was overall well-tolerated, and a maximum tolerated dose has not yet been determined.

Dose escalation in higher-dose cohorts is ongoing.

ALG.APV-527 could be measured in all patients with plasma concentrations of ALG.APV-527, consistent with the administered dose.

Biomarker analyses indicate the expression of the targets (4-1BB and 5T4) in tumor biopsies and confirm the biological activity of ALG.APV-527.

The company says signs of clinical activity were observed for both enrolled patients with heavily pre-treated breast cancer. 

These patients demonstrated a measurable level of drug in circulation (pharmacokinetic) and reproducible elevation of serum pharmacodynamic markers with dosing, suggesting the drug is biologically active. 

One patient remained on study for seven months and a second remains on study beyond nine months. Both patients achieved best overall response of stable disease.

In its fourth-quarter 2023 earnings update, Aptevo said it did not find evidence of increased cytokine release, which can lead to potentially serious side effects, in vitro using human peripheral blood mononuclear cells or whole blood.

Price Action: APVO shares are up 18.8% at $7.60 on the last check Thursday.