Targeting AML: The Development of Two Functionally and Mechanistically Distinct Classes of Cereblon-Mediated Protein Homeostatic Modulators

Targeting disease-relevant proteins by exploiting the cells' very own protein homeostasis machinery is the next generation drug discovery platform that has come center stage for treatment of hematological malignancies. We present our novel and unique Protein Homeostatic Modulators (PHMs^TM) - that promote ubiquitination and subsequent proteasomal degradation of known substrates as well as neosubstrates via Cereblon - as therapeutic candidates for acute myeloid leukemia (AML). Specifically, we report the discovery of two functionally and mechanistically distinct classes of Cereblon-mediated PHMs^TM from phenotypic screens of our proprietary PHM^®library. Unlike classical IMiDs, our oncology candidates, BTX508 and BTX1119 demonstrate significant cytotoxicity with IC50s in low-nanomolar range in a panel of AML cell lines. BTX508 is a purely cytotoxic compound that does not display immune modulatory activity. In contrast, BTX1119 is not only cytotoxic, but is also immunomodulatory in that it inhibits inflammatory cytokines such as IL-1β, IL-6 and TNF-α as well as induces IL-2, an indicator of T cell activation. BTX1119's immune modulatory activity is a 100-fold more potent when compared to Pomalidomide. The distinct functional activities exhibited by BTX508 and BTX1119 is a result of strategically engineered substrate degradation profiles. Importantly, BTX508 and BTX1119 exhibit a large safety window wherein the concentrations at which they target AML cells do not affect normal healthy cells such as liver epithelial cells or lung fibroblasts. To further establish BTX508 as a clinical candidate for AML, we performed in vivo efficacy studies in the MV-4-11 human AML xenograft model using athymic nude mice. A single daily dose of BTX508 results in a significant reduction in tumor volume. BTX508 exhibits significant oral bioavailability, thus making it a promising clinical candidate for treatment of AML as well as other potential hematological malignancies. With regard to BTX1119, we believe that incorporation of both the potent cytotoxic and immunomodulatory properties into a single molecule holds great therapeutic promise; however, to evaluate the synergistic potential of this combination will require use of a humanized mouse model - this work is ongoing.