A Novel Class of Bifunctional Immunotherapeutic That Exploit a Universal Antibody Binding Terminus (uABT) to Recruit Endogenous Antibodies to Cells Expressing CD38 Demonstrates Anti-Multiple Myeloma Activity in Vitro and Ex Vivo against Patient Tumor Cells

Background: Antibody recruiting molecules (ARM) are novel, immunotherapeutic bifunctional molecules composed of two active termini connected by a linker. One of the termini binds to a target molecule on a cancer cell. The other terminus, called universal antibody binding terminus (uABT), recruit all endogenous IgG antibodies independent of their antigen binding specificity. As a result, the target cell is “opsonized” by antibodies which then bring the immune effector cells to eliminate the target through various antibody-dependent destruction mechanisms. Kleo Pharmaceuticals has developed a series of CD38-ARM mlecules which target human CD38 highly expressed by multiple myeloma cells. CD38-ARM compounds are able to mediate ADCC without depleting CD38 expressing immune effector cells like existing therapeutic antibodies such as Daratumumab. Methods: Cyclized peptides containing natural and non-natural amino-acid that selectively bind to human CD38 were identified using Peptidream Flexizyme-based, cell free Peptide Discovery Translation System. These peptides were linked to uABT antibody binder via a linker to generate the final CD38-ARM molecules Binding of CD38-ARM was tested by ternary complex formation between CD38 expressing cells, CD38-ARM and labelled human IgG1. To confirm the activity of CD38-ARM, surrogate CD16a binding and signaling assays were performed using the NFAT Promega system. Antibody dependent cellular cytotoxicity (ADCC) assays using purified NK cells from multiple donors with polymorphism variants (V/V, F/F, and V/F) of CD16a were performed to confirm activity. Live cell imaging was utilized to assess the dynamics of NK-RAJI cell interactions mediated by CD38-ARM +/- IgG. We evaluated the ability of compounds to mediate complement dependent cytotoxicity (CDC). We tested the effect of CD38-ARM on human immune cell populations within PBMC and whole bone marrow (WBM) by flow cytometry. Lastly, ex vivo samples from WBM of MM patients at diagnosis or relapse were used to evaluate CD38-ARM anti-tumor activity as well as off-target effects, without the addition of external source of IgG, through multiparametric flow-cytometry (CD45, CD19, CD38, CD138, CD56, CD27, CD8, CD117). Results: The CD38-ARM were shown to have the ability to bind to CD38 with a 7nM affinity and to human IgG1 and IgG2 with affinity of 15nM and 11nM by SPR. Activity of KP compounds was observed in all assays except for CDC. In ternary assay, KP-6 had an apparent EC50 of 1