Synthesis and biological evaluation of 4-(4-aminophenyl)-6-methylisoxazolo[3,4-b] pyridin-3-amine covalent inhibitors as potential agents for the treatment of acute myeloid leukemia.

Fms-like tyrosine kinase 3 (FLT3) mutation has been strongly associated with increased risk of relapse, and the irreversible covalent FLT3 inhibitors had the potential to overcome the drug-resistance. In this study, a series of simplified 4-(4-aminophenyl)-6-methylisoxazolo[3,4-b] pyridin-3-amine derivatives containing two types of Michael acceptors (vinyl sulfonamide, acrylamide) were conveniently synthesized to target FLT3 and its internal tandem duplications (ITD) mutants irreversibly. The kinase inhibitory activities showed that compound C14 displayed potent inhibition activities against FLT3 (IC50 = 256 nM) and FLT3-ITD by 73 % and 25.34 % respectively, at the concentration of 1 µM. The antitumor activities indicated that C14 had strong inhibitory activity against the human acute myeloid leukemia (AML) cell lines MOLM-13 (IC50 = 507 nM) harboring FLT3-ITD mutant, as well as MV4-11 (IC50 = 325 nM) bearing FLT3-ITD mutation. The biochemical analyses showed that these effects were related to the ability of C14 to inhibit FLT3 signal pathways, and C14 could induce apoptosis in MV4-11 cell as demonstrated by flow cytometry. Fortunately, C14 showed very weak potency against FLT3-independent human cervical cancer cell line HL-60 (IC50 > 10 µM), indicating that it might have no off-target toxic effects. In light of these data, compound C14 represents a novel covalent FLT3 kinase inhibitor for targeted therapy of AML.

Design and synthesis of selective FLT3 inhibitors via exploration of back pocket II.

Aim: The clinical benefits of FLT3 inhibitors against acute myeloid leukemia (AML) have been limited by selectivity and resistance mutations. Thus, to identify FLT3 inhibitors possessing high selectivity and potency is of necessity. Methods & results: The authors used computational methods to systematically compare pocket similarity with 269 kinases. Subsequently, based on these investigations and beginning with in-house compound 10, they synthesized a series of 6-methyl-isoxazol[3,4-b]pyridine-3-amino derivatives and identified that compound 45 (IC50: 103 nM) displayed gratifying potency in human AML cell lines with FLT3-internal tandem duplications mutation as well as FLT3-internal tandem duplications-tyrosine kinase domain-transformed BaF3 cells. Conclusion: The integrated biological activity results indicated that compound 45 deserves further development for therapeutic remedies for AML.

Medicinal Chemistry Strategies for the Development of Bruton's Tyrosine Kinase Inhibitors against Resistance.

Despite significant efficacy, one of the major limitations of small-molecule Bruton's tyrosine kinase (BTK) agents is the presence of clinically acquired resistance, which remains a major clinical challenge. This Perspective focuses on medicinal chemistry strategies for the development of BTK small-molecule inhibitors against resistance, including the structure-based design of BTK inhibitors targeting point mutations, e.g., (i) developing noncovalent inhibitors from covalent inhibitors, (ii) avoiding steric hindrance from mutated residues, (iii) making interactions with the mutated residue, (iv) modifying the solvent-accessible region, and (v) developing new scaffolds. Additionally, a comparative analysis of multi-inhibitions of BTK is presented based on cross-comparisons between 2916 unique BTK ligands and 283 other kinases that cover 7108 dual/multiple inhibitions. Finally, targeting the BTK allosteric site and uding proteolysis-targeting chimera (PROTAC) as two potential strategies are addressed briefly, while also illustrating the possibilities and challenges to find novel ligands of BTK.