ENMD-981693 Is an Orally-Active Kinase Inhibitor with Activity towards Human Hematologic Cancers In Vitro and In Vivo.

The clinical success of Gleevec (imatinib) for chronic myelogenous leukemia has demonstrated that small-molecule inhibitors of specific kinases can be developed into effective oncology therapies. However, the rapid development of resistance in leukemic cells to drugs such as Gleevec and the limited therapeutic indications addressed with these molecules suggests that considerable opportunity exists for new inhibitors with a distinctive spectrum of activities against multiple kinase targets. ENMD-981693 is a novel, orally-active molecule that was discovered through a screening effort directed towards Aurora kinases, a family of serine/threonine kinases that are essential for mitotic progression. ENMD-981693 is selective for the Aurora A isoform, with an IC50 value of 25 nM, compared to an IC50 value of ~700 nM for Aurora B. The activity of ENMD-981693 was evaluated against a panel of 100 recombinant kinases, and the compound was shown to inhibit a broad range of tyrosine kinase targets including Flt3, CSF1R, Lck, JAK2, and c-Kit. ENMD-981693 inhibited the in vitro growth of human hematopoietic cancer lines including MV4;11, K562, THP-1, Jurkat, TF-1, U937, and HL-60 with IC50 values ranging from 0.04 – 21 μM. ENMD-981693 was shown to induce G2/M cell cycle arrest followed by apoptosis in U937 cells, without induction of the endo-reduplication phenotype (≥4N DNA content) associated with Aurora B-acting inhibitors such as MK-0457 (VX-680) and AZD1152. Primary cells derived from AML patients were sensitive to treatment with ENMD-981693 in vitro, resulting in IC50 values from 0.2 – 6.0 μM. Sensitivity of primary CML samples was more variable in in vitro cytotoxicity assays, with IC50s in the range of 0.1 – 40 μM. ENMD-981693 shows significant antitumor activity and is well tolerated in xenograft studies, with no weight loss or morbidity observed in administration schedules of up to 100 mg/kg bid or 200 mg/kg qd, given continuously for more than 30 days. Results from in vivo efficacy studies with ENMD-981693 using the MV4;11 xenograft model will be described. In conclusion, ENMD-981693 is a novel kinase inhibitor with potent activity towards a number of targets important in hematologic cancers.