On June 10, 2020 Aptevo Therapeutics Inc. (Nasdaq: APVO), a biotechnology company focused on developing novel immuno-oncology therapeutics based on its proprietary ADAPTIR bispecific technology platform, and Alligator Bioscience AB (Nasdaq Stockholm: ATORX), a biotechnology company developing antibody-based pharmaceuticals for tumor-directed immunotherapy, reported that new preclinical data for ALG.APV-527 are being presented at the PEGS Virtual Interactive Global Summit, on June 10, 2020 in an oral presentation entitled, "ALG.APV-527: Tumor-directed T-cell stimulation, in vivo tumor regression, and safety studies of a 4-1BB x 5T4 ADAPTIR bispecific antibody (Press release, Alligator Bioscience, JUN 10, 2020, View Source [SID1234560960])."

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"Our latest preclinical data for ALG.APV-527 looks very encouraging and shows that ALG.APV-527 may overcome many of the limitations observed with other 4-1BB monoclonal antibody therapeutics by improving the biodistribution, efficacy and potential safety of this novel class of immunotherapies," said Jane Gross, Ph.D., Chief Scientific Officer for Aptevo. "Since ALG.APV-527 localizes at the tumor site, immune activation depends on binding with 5T4 tumor antigen to activate via 4-1BB, therefore limiting systemic activation seen with other 4-1BB agonists. Most interestingly, our latest preclinical data show the potential for a favorable safety profile for ALG.-APV-527. In a head-to-head comparison with a urelumab analogue in preclinical studies, ALG.APV-527 did not induce systemic T-cell activity at high doses, a key differentiator from other 4-1BB therapies."

ALG.APV-527 is a novel immunotherapeutic bispecific candidate intended for the treatment of multiple solid tumors expressing 5T4, a tumor-restricted antigen. 5T4 is an antigen that is highly expressed in a large percentage of solid tumors, including, non-small cell lung cancer (NSCLC), head and neck cancer and mesothelioma. ALG.APV-527 is designed to activate anti-tumor responses by inducing signaling through the co-stimulatory receptor 4-1BB (CD137), which is an immune receptor that is upregulated on activated T cells and natural killer (NK) cells.

The preclinical data presented at the PEGS Virtual Interactive Global Summit show that ALG.APV-527 may overcome many of the limitations of competitor 4-1BB antibodies as it selectively enhances the function of activated T cells and NK cells in the presence of the tumor antigen 5T4, as shown in vitro, and potently rejects tumors in an in vivo animal model.

In a high-dose toxicity human 4-1BB knock-in murine study comparing ALG.APV-527 with a urelumab analogue, ALG.APV-527 was well tolerated at high doses with no evidence of systemic T-cell activation and no impact on body or spleen weight, whereas the urelumab analogue induced weight loss, systemic activation of T cells, and signs of ulcerative dermatitis.

In summary, the data presented at PEGS demonstrate that ALG.APV-527:

Enhances CD8+ T cell and NK function and proliferation upon 5T4-mediated engagement
Accumulates at 5T4-positive tumors in preclinical models
In an in vivo human 4-1BB knock-in model:
Induces rejection of established bladder cancer cells at low doses
Induces anti-tumor immunological memory responses
Does not induce systemic T-cell activation at high doses, which were observed in a side-by side comparison with a urelumab analogue

Is well tolerated after repeated dosing in a GLP toxicology study and displays an antibody-like half-life with a mean half-life of 8 days
"Our data supports that ALG.APV-527 has the potential to induce a strong anti-tumor immune response without systemic toxicity, which is exactly what we hoped to see," commented Christina Furebring, Ph.D., Vice President Projects at Alligator.

About ALG.APV-527
ALG.APV-527 is a bispecific antibody (4-1BB x 5T4) intended for tumor-directed treatment of solid cancers. ALG.APV-527 was built using Aptevo’s ADAPTIR bispecific platform and combines binding domains sourced from the ALLIGATOR-GOLD human scFv library. The ALG.APV-527 bispecific antibody consists of two moieties, one moiety activating tumor-specific T cells through the co-stimulatory receptor 4-1BB, the other moiety binding to the 5T4 protein displayed on the surface of tumor cells. This enables the immune-activating effect of ALG.APV-527 to be directed specifically to the tumor and not against normal tissue.