Wednesday, June 10, 2015

Drugs in Clinical Pipeline: CX-6258

CX-6258 [(E)-5-chloro-3-((5-(3-(4-methyl-1,4-diazepane-1-carbonyl)phenyl)furan-2-yl)methylene)indolin-2-one] is an oral, small molecule inhibitor from a novel class of oxindole-based derivatives that selectively inhibit all three Pim (Provirus Integration site for Moloney murine leukemia virus) kinases and show robust in vivo anticancer activity in Pim kinase related xenograft models [1]. The pan-PIM inhibitory activity of CX-6258 (IC50 PIM-1, -2, -3 = 5, 25, 16 nM, respectively) is further strengthen with a good inhibition values for Flt3 kinase (IC50 = 0.134 uM). Since Flt-3 regulates the Pim kinases in leukemia, its level of inhibition is important information for the interpretation of cellular activity performed with Pim kinases inhibitors. CX-6258 was also shown to be a reversible inhibitor of Pim-1 (Ki=0.005 uM).

Cylene Pharma disclosed CX-6258 in 2011, when it was one the few pan-PIM kinase inhibitors. It was the first one with nanomolar inhibition against Pim-3 kinase. With Pim-3 isoform reported to be overexpressed in pancreatic, gastric, and colon cancer, CX-6258 could be beneficial as an anticancer agent against these malignancies.

The activity of CX-6258 is as follows:

IC50 (Pim-1 enzyme assay) = 5 nM; Ki = 5 nM
IC50 (Pim-2 enzyme assay) = 25 nM
IC50 (Pim-3 enzyme assay) = 16 nM

Common Name: CX-6258
Synonyms:  CX-6258; CX 6258; CX6258
IUPAC Name: (E)-5-chloro-3-((5-(3-(4-methyl-1,4-diazepane-1-carbonyl)phenyl)furan-2-yl)methylene)indolin-2-one
CAS Number: 1202916-90-2; 1353858-99-7 (hydrochloride hydrate)
Mechanism of Action: Kinase Inhibitor; pan-PIM Kinase Inhibitor
Indication: Various Cancers
Development Stage: Pre-Clinical
Company: Cylene Pharma

Pim kinases (Provirus Integration site for Moloney murine leukemia virus) are a family of serine/threonine kinases that regulate cell survival. This family of kinases is composed of three different isoforms (Pim-1, Pim-2, and Pim-3) that share 60-70% sequence identity in their kinase domains. The Pim kinases are tightly regulated at the level of transcription and translation,5 and their expression is mediated by the JAK/STAT signaling pathway, which is activated by various cytokines and hormones. In addition, several oncogenes, including Flt3-ITD and Bcr/Abl, were shown to upregulate the expression of Pims. The Pim kinase family members are considered oncogenes and have been implicated in tumorigenesis either alone or operating synergistically with c-Myc. Pim kinases are known to suppress apoptosis by the direct phosphorylation and inhibition of pro-apoptotic Bcl-2 antagonist of cell death (BAD). Overexpression of Pim kinases has been reported in leukemia and lymphoma tumors. They were also found to be overexpressed in solid tumors, including pancreatic cancer and prostate cancer.

To assess its selectivity profile, CX-6258 was screened against 107 kinases where using a concentration of 0.5 µM, only Pim-1, Pim-2, Pim-3, and Flt-3 were inhibited by more than 80%. The antiproliferative activity of CX-6258 was examined against a panel of cell lines derived from human solid tumors and hematological malignancies. CX-6258 demonstrated robust antiproliferative potencies against all cell lines tested. Cell lines derived from acute leukemias were the most sensitive to CX-6258.

In mechanistic cellular assays with MV-4-11 human AML cells, CX-6258 caused dose dependent inhibition of the phosphorylation of two pro-survival proteins, Bad and 4E-BP1, at the Pim kinase specific sites S112 and S65 and T37/46, respectively. Using ELISA against phospho-Flt3 (Y591), researchers demonstrated that CX-6258 does not inhibit Flt3 activity in MV-4-11 cells at relevant concentrations (IC50 greater than 10 µM) indicating that the effect of CX-6258 on phosphorylation of Bad and 4E-BP1 results from direct inhibition of Pim kinases rather than being a secondary consequence of Flt3 inhibition.

Combinations of CX-6258 with doxorubicin (10:1 molar ratio) and CX-6258 with paclitaxel (100:1 molar ratio) produced synergistic PC3 cell killing with combination index (CI50) values equal to 0.4 and 0.56, respectively. When used as single agent, the IC50 values for PC3 inhibiton were 13, doxorubicin, and paclitaxel 452 nM, 114 nM, and 2.5 nM, respectively, supporting the role of Pim kinases in modulating the chemosensitivity of cancer cells.

1. Haddach, M.; et. al. Discovery of CX-6258. A Potent, Selective, and Orally Efficacious pan-Pim Kinases Inhibitor. ACS Med Chem Lett 2011, 3(2), 135-139.