Abstract P027: Extending intratumoral therapeutic durability using a multivalent immunotherapy platform
Authors: Brier Livia W. , Mahomed Mavish , Twite Amy A. , Barnebey Adam , Jackson Wesley M. 
Published: January 2022

Abstract
Purpose: The risk of severe side effects has limited the development of immune cell activating immunotherapies. There is a critical need in immunotherapy drug development to enable focused and sustained immune cell activation within a tumor to induce a system-wide anti-tumor response. We have developed a novel immunotherapy platform that could be used to generate geographically focused cancer cell growth inhibition or immune cell activation, thereby stimulating an anti-tumor immune response against primary solid tumors that can also travel to secondary metastases.
Methods: Using published methods, we synthesized multivalent protein (MVP) conjugates by conjugating multiple copies (i.e. valency) of immune stimulating proteins (e.g. Interleukin-15) or anti-tumor antibodies (e.g. anti-Epidermal Growth Factor Receptor) to soluble, long-chain biopolymers (e.g. carboxymethylcellulose or hyaluronic acid, ~700 kDa). We verified that we can reproducibly generate MVP valencies ranging from 20-120 protein copies (±10%) per polymer backbone. We determined the binding affinity of these MVPs to their respective targets using biolayer interferometry and cell bioassays, and we measured the hydrodynamic radius of these immunotherapies using dynamic light scattering. Then, we injected flurosecently modified MVPs or their unconjugated counterparts directly into a variety of solid tumor models in mice. By taking longitudinal in vivo fuorescence measurments of the intratumoral (IT) drug signal over multiple days, we measured the IT half-life of each treatment.
Results: Based on binding affinity measurements, we found that MVP potency increased directly with their protein valency, and at high valency, the potency of MVPs were substantially greater than the unconjugated protein controls. Multivalent conjugation also increased the hydrodynamic radius of the MVPs to at least ten times larger than the unconjugated therapeutics. This large size was sufficient to slow the diffusion of MVP immunotherapies through dense tissues, such as solid tumors, as demonstrated by our in vivo studies. MVPs exhibited a higher IT drug signal with a more durable gradient within the tumor compared to the unconjugated controls, resulting in an extension of their IT half-lives by &gt;5X in mouse solid tumors.
Conclusions: The MVP platform can be used to modulate the potency and therapeutic durability for a wide range of immunotherapy targets. Further, the MVPs stay focused within the tumor after IT injection where they could generate a sustained anti-tumor immune response with minimal systemic exposure. Therefore, we expect MVP immunotherapies to have a better safety profile than IT or systemic delivery of an unconjugated therapeutic. We will continue to develop our internal MVP pipeline to finalize a candidate for IND-enabling studies. We are also seeking to collaborations for co-development of additional immunotherapies that could benefit from the extended IT exposure and potency modulation enabled by the MVP platform.
Citation Format: Livia W. Brier, Mavish Mahomed, Amy A. Twite, Adam Barnebey, Wesley M. Jackson. Extending intratumoral therapeutic durability using a multivalent immunotherapy platform [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P027.