Aptevo Therapeutics (APVO), Alligator Bioscience Report Bispecific 4-1BBx5T4 Antibody ALG.APV-527 Advances into Phase 1 Clinical Development

Aptevo Therapeutics Inc. (NASDAQ: APVO) and Alligator Bioscience today provided an update on ALG.APV-527, a novel immunotherapeutic bispecific candidate intended for the treatment of multiple solid tumors expressing 5T4, a tumor-restricted antigen.

Aptevo and Alligator are advancing ALG.APV-527 into Phase 1 clinical development in a co-development 50/50 partnership. The companies anticipate filing a Clinical Trial Authorization during the first half of 2021 to initiate Phase 1 clinical development in multiple sites in the European Union. Aptevo and Alligator will continue to explore licensing opportunities as ALG.APV-527 moves into clinical development.

"We are very excited about taking ALG.APV-527 into the clinic now, as recent APVO436 complete remission data in two patients in cohort 6 of that Phase 1 clinical trial speaks to the potential of our ADAPTIR platform. As a potential first-in-class molecule, ALG.APV-527 showcases the versatility of our ADAPTIR platform in generating bispecific antibodies with unique mechanisms of action and a therapeutic profile that is more consistent with traditional antibodies, including an extended half-life, desirable antibody-like manufacturing characteristics and optimized for potency and stability," said Mr. Marvin White, President and CEO of Aptevo.

"Our collaboration with Alligator Bioscience continues to yield encouraging data supporting the potential advantages of this novel pathway for targeted immunotherapy of cancer. For these reasons, and given recent improvements in our financial position, we are excited to advance this asset into the clinic with the desire to enable potential additional value creation for shareholders as we develop the asset," concluded Mr. White.

"Aptevo's clinical candidate APVO436 is based on the same ADAPTIR platform as ALG.APV-527. It is my belief that the response data observed in the APVO436 Phase 1 trial validates the bispecific format of ALG.APV-527, and strengthens our view that it has the potential to become a successful cancer therapy," said Per Norl�n, CEO of Alligator Bioscience.

ALG.APV-527 is designed to simultaneously target 5T4 and the co-stimulatory receptor 4-1BB (CD137) to promote potent, tumor-directed immune T-cell activation. 5T4 is a well-defined tumor antigen expressed on many different types of malignancies including, non-small cell lung, renal, pancreatic, prostate, breast, colorectal, gastric, ovarian and cervical cancers and mesothelioma. Conversely, 5T4 has limited expression on adult normal tissues, making it an attractive target for cancer immunotherapy.

Presentation at the SITC 35th Annual Meeting

As announced on Monday, November 9, Aptevo is presenting two new posters at the Society for Immunotherapy of Cancer's (SITC) 35^th Virtual Annual Meeting, including one on ALG.APV-527. The poster will present preclinical data demonstrating that ALG.APV-527 has a potentially favorable safety profile with no indication of systemic immune activation or liver toxicity in NHP or murine models. ALG.APV-527 induces robust in vitro killing of tumors that is dependent on 5T4 engagement. In vivo, ALG.APV-527 augmented anti-tumor responses and promoted tumor-specific memory.

Details of the Poster Presentation are as follows:

ALG.APV-527: Potent tumor-directed T cell activation and in vivo tumor inhibition induced by a 4-1BB x 5T4 ADAPTIR bispecific antibody

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