Tosedostat is a proprietary orally bioavailable inhibitor of the M1 family of aminopeptidases with potential antineoplastic activity. Tosedostat is converted intracellularly into a poorly membrane-permeable active metabolite (CHR-79888) which inhibits the M1 family of aminopeptidases, particularly puromycin-sensitive aminopeptidase (PuSA), and leukotriene A4 (LTA4) hydrolase; inhibition of these aminopeptidases in tumor cells may result in amino acid deprivation, inhibition of protein synthesis due to a decrease in the intracellular free amino acid pool, an increase in the level of the proapoptotic protein Noxa, and cell death. There are several ongoing Phase 2 cooperative group-sponsored trials and investigator-sponsored trials evaluating the clinical activity of Tosedostat in combination with standard agents in patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS).

MK-5108 is a small molecule inhibitor of AuroraA kinase with high selectivity versus Aurora-B and C. It was tested in phase I study against advanced or refractory solid tumors both as a monotherapy or in combination with docetaxel, but this study was terminated early due to toxicities at MK-5108 doses below the anticipated PK exposure target.