The ATP Competitor INNO-406 (NS-187) Inhibits Proliferation and Survival of Mouse Cells Expressing Several Immatinib Mesylate Resistant Bcr/Abl Mutants and Cells from CML Patients.

Imatinib mesylate (IM) resistance during the therapy of chronic myeloid leukemia (CML) patients is associated with point mutations in the Bcr/Abl kinase, which strongly interferes with IM binding to Abl kinase domain. INNO-406 (NS-187) is reported to be a new specific inhibitor of the Bcr/Abl and Lyn kinase, and is a candidate for treatment of IM resistant CML patients (

The MTT results showed 32Dp210 wt and four of the six Bcr/Abl mutants were sensitive to INNO-406, with the IC₅₀ values of 0.6 nM (wild type), 15 nM (L387M ), 35 nM (H396R), 0.8 nM (Q252R) and 8.2 nM (F311L). The IC₅₀ values of those four cell lines treated with IM were much higher than with INNO-406 treatment. The IC₅₀ values for IM were: 100 nM (wild type), 500 nM (L387M), 1220 nM (H396R), 100 nM (Q252R) and 100 nM (F311L). But neither INNO-406 nor IM exhibited inhibitory effects on the proliferation of T315I and Y253H mutants (IC₅₀ > 10000 nM). These results indicated that INNO-406 suppressed the growth of Bcr/Abl mouse leukemia cell lines expressing wt Bcr/Abl and Bcr/Abl mutants except T315I and Y253H. We note that the Y253F mutant was sensitive to INNO-406 (IC₅₀ 64 nM, Nippon Shinyaku Co. Ltd.). Annexin V/PI apoptosis assays were conducted on cells from CML patient samples after 72 hours treatment with various concentrations of INNO-406. Flow cytometry results showed that INNO-406 (10–20 nM) induced apoptosis in blood/marrow cells from two blast crisis patients, one of which had the G250E mutation. INNO-406 also induced apoptosis in marrow cells from two patients in IM induced remission. One of these samples with a Bcr/Abl mutation at M244V showed a weak response to IM but a strong apoptosis with INNO-406 (20 nM), indicating that NS-187 worked more efficiently in the M244V mutant. Based on these results, INNO-406 (NS-187) appears to be a candidate for the treatment of some forms of imatinib resistant CML. A phase I study of INNO-406 has been initiated in patients with CML who have failed prior imatinib therapy and the first cohort has been safely treated.