Discovery of imidazo[1,2-a]pyridine-thiophene derivatives as FLT3 and FLT3 mutants inhibitors for acute myeloid leukemia through structure-based optimization of an NEK2 inhibitor

Abstract

FMS-like tyrosine kinase 3 (FLT3) with an internal tandem duplication (ITD) mutation has been validated as a driver lesion and a therapeutic target for acute myeloid leukemia (AML). Currently, several potent small-molecule FLT3 kinase inhibitors are being evaluated or have completed evaluation in clinical trials. However, many of these inhibitors are challenged by the secondary mutations on kinase domain, especially the point mutations at the activation loop (D835) and gatekeeper residue (F691). To overcome the resistance challenge, we identified a novel series of imidazo[1,2-a]pyridine-thiophene derivatives from a NIMA-related kinase 2 (NEK2) kinase inhibitor CMP3a, which retained inhibitory activities on FTL3-ITD^D835V and FLT3-ITD^F691L. Through this study, we identified the imidazo[1,2-a]pyridine-thiophene derivatives as type-I inhibitors of FLT3. Moreover, we observed compound 5o as an inhibitor displaying equal anti-proliferative activities against FLT3-ITD, FTL3-ITD^D835Y and FLT3-ITD^F691L driven acute myeloid leukemia (AML) cell lines. Meanwhile, the apoptotic effects of compound supported its mechanism of anti-proliferative action. These results indicate that the imidazo[1,2-a]pyridine-thiophene scaffold is promising for targeting acquired resistance caused by FLT3 secondary mutations and compound 5o is an interesting lead in this direction.

Keywords: AML; FLT3; Imidazole pyridine; Mutants.

Fig. 1.

Structure modification of CMP3a to imidazo[1,2-a]pyridine thiophene.

Fig 2.

(A) Binding pose of 5e in FLT3 model. (B) and (C): Binding pose of 6b in FLT3. Panel (B) Surface representation of the protein shows that pyrazole group is significantly solvent exposed. Panel (C) depicts the close proximity of N-methyl group to Asp698 and Asn701. Hydrogen bonds are depicted in dark blue and aromatic- bond in cyan.

Fig. 3.

Inhibition kinetic study of compounds 5e and 5g.

Fig. 4.

Apoptosis analysis of compound 5o on MOLM14 cell lines.

Scheme 1.

Reagents and conditions: (a). 2-chlorocetaldehyde, n-butanol, 130 °C; (b)boronic acid, Na₂CO₃, Pd(PPh₃)₄, 1,4-dioxane/water, 120 °C; (c) 2,5-dichlorothiophene, K₂CO₃, Pd(PPh₃)₄, Pd(OAc)₂, 1,4-dioxane/water, 120 °C; (d) boronic acid, Na₂CO₃, Pd(PPh₃)₄, 1,4-dioxane/methanol, microwave irradiation, 130 °C.

Scheme 2.

Reagents and conditions: (a). 2-chlorocetaldehyde, n-butanol, 130 °C; (b) 2,5-dichlorothiophene, K₂CO₃, Pd(PPh₃)₄, Pd(OAc)₂, 1,4-dioxane/water, 120 °C; (c) boronic acid, Na₂CO₃, Pd(PPh₃)₄, 1,4-dioxane/methanol, microwave irradiation, 130 °C.