On June 15, 2018 Aptose Biosciences Inc. (NASDAQ:APTO) (TSX:APS) reported the presentation of preclinical data demonstrating that CG-806, a highly potent pan-FLT3/pan-BTK inhibitor, exhibits a distinct mechanism of action and greater potency on patient-derived hematologic cancer cells than ibrutinib, a BTK inhibitor approved for the treatment of certain hematologic malignancies (Press release, Aptose Biosciences, JUN 15, 2018, View Source;p=RssLanding&cat=news&id=2354764 [SID1234527344]). The data were presented in a poster on Friday, June 15, at the 23rd Congress of the European Hematology Association (EHA) (Free EHA Whitepaper), taking place June 14-17, 2018 in Stockholm, Sweden.
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CG-806 is an oral small molecule pan-FLT3/pan-BTK inhibitor being developed by Aptose for acute myeloid leukemia (AML) and B-cell malignancies. It is a highly potent, reversible (non-covalent) inhibitor of the wild type and mutant forms of the Bruton’s tyrosine kinase (BTK) enzymes. Ibrutinib, a covalent BTK inhibitor approved for chronic lymphocytic leukemia (CLL) and certain B-cell malignancies, is limited by acquired resistance, as well as refractory disease and tolerance challenges.
The poster, entitled CG’806, A NON-COVALENT PAN-FLT3/PAN-BTK INHIBITOR, EXHIBITS UNIQUE BINDING TO WILD TYPE AND C481S MUTANT BTK AND GREATER POTENCY THAN IBRUTINIB AGAINST MALIGNANT B CELLS, compared CG-806 and ibrutinib with respect to BTK binding mode, kinase inhibition profiles and cytotoxic activity against patient-derived and cultured malignant B-cells. Kinase profiling revealed that CG-806 most potently inhibits kinases from the BTK, FLT3, TRK, and AURK clusters and had similar potency against BTK-WT (IC50 = 8.4 nM) and C481S mutant (IC50 = 2.5 nM), as opposed to ibrutinib that was >60-fold less potent against the C481S mutant. CG-806 did not inhibit TEC, EGFR or ERBB2/4, which are related to ibrutinib’s side effects; CG-806 also demonstrated a favorable safety profile. CG-806 inhibited cell proliferation 2-6,000 times more potently than ibrutinib in 14 tested malignant B-cell lines; it also had greater activity on primary CLL samples than ibrutinib.
"A safe and potent agent that inhibits all forms of BTK and other key rescue pathways (including AKT/PI3K, ERK and NFƙB) is needed for patients intolerant, refractory and resistant to ibrutinib," said William G. Rice, Ph.D., Chairman, President and Chief Executive Officer. "These data strongly support the clinical development of CG-806 to address the limitations and challenges of ibrutinib. CG-806 is being readied for the clinic and we look forward to reporting on its development."
The EHA (Free EHA Whitepaper) poster can be accessed here or at the Publications & Presentations section of the Aptose website, www.aptose.com.
About CG-806
CG-806 is an oral, first-in-class pan-FLT3/pan-BTK multi-kinase inhibitor. This small molecule demonstrates potent inhibition of wild type and mutant forms of FLT3 (including internal tandem duplication, or ITD, and mutations of the receptor tyrosine kinase domain and gatekeeper region), eliminates acute myeloid leukemia (AML) tumors in the absence of toxicity in murine xenograft models, and represents a potential best-in-class therapeutic for patients with AML. Likewise, CG-806 demonstrates potent, non-covalent inhibition of the wild type and Cys481Ser mutant forms of the BTK enzyme, as well as other oncogenic kinase pathways operative in B cell malignancies, suggesting CG-806 may be developed for various B cell malignancy patients (including CLL, MCL, DLBCL and others) that are resistant/refractory/intolerant to covalent BTK inhibitors.