A Novel Class of Bifunctional Immunotherapeutic That Exploits a Universal Antibody Binding Terminus (uABT) to Recruit Endogenous Antibodies to Cell Expressing CD38 Demonstrate In Vivo efficacy in Three Distinct Animal Models
Authors: Bunin Anna , McGrath Katy , Rossi Ann Marie , Welsch Matthew , Vidal Christian , Trinh David , Spiegel David , Rastelli Luca , Alvarez Enrique 
Published: November 2019

Background:
Antibody recruiting molecules (ARM) represent a new modality in immunotherapy of cancer. These are 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 can recruit endogenous IgG antibodies independent of their antigen binding specificity representing a breakthrough improvement to previous approaches (Murelli et al.J Am Chem Soc. 2009). We named this active moiety a universal antibody binding terminus (uABT). As a result of antibody recruitment to the cell surface, the target cell is "opsonized" by antibodies which then bring in the immune effector cells to eliminate the target through various antibody-dependent destruction mechanisms.
Multiple myeloma is a neoplasm that arises from terminally differentiated immunoglobulin producing long-lived plasma cells with 32,000 new cases diagnosed each year.
Kleo Pharmaceuticals has developed a series of compounds, CD38-ARM which target human CD38 highly expressed by multiple myeloma cells. CD38 -ARM compounds are therapeutically active in three distinct in vivo models without depleting CD38 expressing immune effector cells like existing therapeutic antibodies such as Daratumumab.
Methods:
CD38-ARM compounds were tested in three independent in vivo models. In the first model, intraperitoneal Daudi xenograft in SCID mice, 20x106 fluorescently labelled Burkitt lymphoma CD38-expressing Daudi cells were injected into SCID mice and treated with 3 mg/kg of compounds. Peritoneal exudates were examined 24 hours later for percentages and absolute numbers of Daudi cells recovered. Activity of compounds was further tested in a MOLP-8 multiple myeloma cell xenograft model in nude mice. Animals received 106 MOLP8 cells subcutaneously, and were treated with a daily dose of 10 mg/kg after tumor volumes of 150 mm3 were reached. Finally, CD38-ARM efficacy was examined in hu IL-15 transgenic NOG mice that have been preconditioned with busulfan and reconstituted i.p. with 2x106human NK cells. Three weeks after reconstitution, 5x106RAJI cells expressing CD38 were implanted s.c. and treatment commenced a week later with 10 mg/kg QDx14. Mice were monitored for NK cell levels and activation status in the blood during the whole study duration by flow cytometry.
Results:
CD38-uAbt compounds are able to induce clearance of Burkitt's lymphoma Daudi cells expressing high levels of CD38 in a SCID mouse intraperitoneal model. In addition, we show efficacy of one of these compounds in a multiple myeloma xenograft model in nude mice. Using the MOLP8 subcutaneously implanted tumor model we show that administration of our lead molecule is able to induce 50% tumor growth inhibition (TGI) after a daily dosing schedule against this tumor. This activity is comparable to a pharmacologically relevant dose of Daratumumab. Finally, we demonstrate that CD38-ARM treatment shows significant efficacy in humanized mouse model, where IL-15 Tg NOG mice have been reconstituted with human NK cells prior to tumor implantation. In this model daily dosing with the CD38-ARM resulted in up to 70% TGI when compared to untreated control groups. Using this dose/schedule, the molecule did not elicit NK cell depletion as noted in the Daratumumab group.
Conclusions:
We demonstrated that CD38-ARM compounds are therapeutically active in three distinct in vivo models. Depletion of Daudi cells in a peritoneal SCID model provides strong evidence for the CD38-ARM's capacity to engage macrophage effector functions. Profound inhibition of tumor growth in the NK cell centered humanized hIL-15 Tg NOG mouse model indicates that killing of target cells is executed by human NK cells and provides a foundation to advancing our compounds towards the clinic. Overall, our results demonstrate value of CD38-ARM molecules both as stand-alone therapeutic as well as a platform to develop compounds tailored to a specific indication, by varying target binding moiety of the molecule. Our results also indicate that CD38-ARM compounds engage a variety of effector mechanisms involved in tumor clearance and tumor growth delay, indicating therapeutic potential across a wide range of clinical settings.

Disclosures
Bunin: Kleo pharmaceuticals: Employment, Equity Ownership. McGrath:Kleo pharmaceuticals: Employment, Equity Ownership. Rossi:Kleo pharmaceuticals: Employment, Equity Ownership. Welsch:Kleo pharmaceuticals: Employment, Equity Ownership. Vidal:Kleo pharmaceuticals: Employment, Equity Ownership. Trinh:Kleo pharmaceuticals: Employment, Equity Ownership. Spiegel:Kleo pharmaceuticals: Equity Ownership. Rastelli:Kleo pharmaceuticals: Employment, Equity Ownership. Alvarez:Kleo pharmaceuticals: Employment, Equity Ownership.