Alligator Bioscience and Aptevo Report 60% Stable Disease in Phase 1 Solid Tumor Trial

LUND, Sweden I September 16, 2024 I Alligator Bioscience AB (“Alligator”) (Nasdaq Stockholm:ATORX) and Aptevo Therapeutics (“Aptevo”) (Nasdaq: APVO) have revealed promising interim data from the dose escalation phase of their Phase 1 trial of ALG.APV-527. This trial aims to treat solid tumors that likely express the tumor antigen 5T4. The findings, including clinical activity, safety and tolerability outcomes, as well as pharmacokinetics and pharmacodynamics data, were showcased in a poster session on September 14, 2024, at the European Society for Medical Oncology (ESMO) Annual Congress in Barcelona, Spain.

ALG.APV-527 is a pioneering bispecific antibody designed to target 4-1BB and the tumor antigen 5T4. The ongoing multi-center dose escalation trial involves 18 patients who are part of the safety analysis. These patients have undergone several previous treatments for various solid tumor types. The trial is nearing full enrollment, and interim results include:

- **Clinical Activity/Efficacy**
- **Safety and Tolerability**
- **Positive pharmacokinetics and biological activity of ALG.APV-527**

Historically, 4-1BB has been an attractive target for cancer therapy despite its toxicity concerns. Novel bispecific approaches like ALG.APV-527 are designed to activate anti-tumor immunity while minimizing systemic toxicity. The Phase 1 interim data are encouraging, showing that ALG.APV-527 has a good safety profile with 60% of evaluable patients experiencing stable disease. Among these patients, one with breast cancer has been treated with monotherapy and maintained stable disease for over 11 months. This demonstrates ALG.APV-527's potential benefits for patients with solid tumors, supported by its favorable safety and tolerability profile.

Thomas Marron, MD, PhD, a Professor in Immunology & Immunotherapy and in Medicine, Hematology and Medical Oncology at Icahn School of Medicine at Mount Sinai and a participating investigator in the trial, expressed optimism about the results. He highlighted the potential of ALG.APV-527 to benefit patients with solid tumors due to its positive safety and clinical activity signals.

The ALG.APV-527 Phase 1 trial is a multi-center, multi-cohort, open-label dose-escalation trial. It involves administering ALG.APV-527 at up to six escalating dose levels in a 3+3 design. The trial includes adult patients with multiple solid tumor types likely to express the 5T4 antigen. ALG.APV-527 is administered intravenously every two weeks, and the trial is evaluating the drug's safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity.

ALG.APV-527 is a bispecific conditional 4-1BB agonist activated only upon binding to both 4-1BB and 5T4. This dual binding is significant as 4-1BB can stimulate immune cells involved in tumor control, making it a compelling target for cancer immunotherapy. The 5T4 antigen is commonly overexpressed in various solid tumors, including non-small-cell lung carcinoma, breast, head and neck, cervical, renal, gastric, and colorectal cancers. Preclinical studies have shown that ALG.APV-527's design minimizes systemic immune activation while allowing potent tumor-specific responses.

Alligator Bioscience AB is a clinical-stage biotechnology company specializing in immuno-oncology antibody drugs. Its drug portfolio includes several promising candidates, with the CD40 agonist mitazalimab being a key asset. Alligator is co-developing ALG.APV-527 with Aptevo Therapeutics Inc. and is working on several undisclosed molecules and novel candidates based on its proprietary platforms. Alligator Bioscience is listed on Nasdaq Stockholm and is headquartered in Lund, Sweden.

Aptevo Therapeutics Inc. is a clinical-stage biotechnology company focused on developing novel bispecific immunotherapies for cancer treatment. The company aims to improve treatment outcomes and transform the lives of cancer patients.