Discovery of FLT3-targeting PROTACs with potent antiproliferative activity against acute myeloid leukemia cells harboring FLT3 mutations.

Acute myeloid leukemia (AML) patients harboring Fms-like tyrosine kinase 3 (FLT3) mutations often suffer from poor prognosis and relapse. Targeted protein degradation utilizing proteolysis targeting chimeras (PROTACs) is considered as a novel therapeutic strategy in drug discovery and may be a promising modality to target FLT3 mutations for the development of potent anti-AML drugs. Herein, a kind of FLT3-targeting PROTACs was rationally developed based on a FLT3 inhibitor previously reported by us. The representative compound 35 showed potent and selective antiproliferative activities against AML cells harboring FLT3 mutations. Western blot assay demonstrated that compound 35 effectively induced the degradation of FLT3-ITD and decreased the phosphorylation levels of FLT3-ITD, AKT, STAT5 and ERK in MV4-11 cells in a dose-dependent manner. Flow cytometry analysis illustrated that compound 35 strongly induced apoptosis and cell cycle arrest in MV4-11 cells in a dose-dependent manner. Moreover, compound 35 displayed favorable metabolic stability in in-vitro liver microsomes studies. Comparative molecular dynamic (MD) simulation studies further elucidated the underlying mechanism of compound 35 to stabilize the dynamic ensemble of the FLT3-compound 35-cereblon (CRBN) ternary complex. Taken together, compound 35 could serve as a lead molecule for developing FLT3 degraders against AML.

Rational discovery of dual FLT3/HDAC inhibitors as a potential AML therapy.

Acute myeloid leukemia (AML) patients often experience poor therapeutic outcomes and relapse after treatment with single-target drugs, representing the urgent need of new therapies. Simultaneous inhibition of multiple oncogenic signals is a promising strategy for tumor therapy. Previous studies have reported that concomitant inhibition of Fms-like tyrosine kinase 3 (FLT3) and histone deacetylases (HDACs) can significantly improve the therapeutic efficacy for AML. Herein, a series of novel dual FLT3/HDAC inhibitors were developed through a rational structure-based drug design strategy for the first time. Among them, multiple compounds showed potent and equivalent inhibitory activities against FLT3-ITD and HDAC1, with the representative compound 63 selectively inhibiting HDAC class I (HDAC1/2/3/8) and IIB isoforms (HDAC6) related to tumorigenesis, and intensively blocking proliferation of MV4-11 cells. The antiproliferation activity was proven to depend on the dual inhibition of FLT3 and HDAC1. Mechanism assays demonstrated that 63 prohibited both FLT3 and HDAC pathways, induced apoptosis and arrested cell cycle in MV4-11 cells in a dose-dependent manner. In summary, this study validated the therapeutic potential of a kind of dual FLT3/HDAC inhibitors for AML and provided novel compounds for further biological investigation on concomitant inhibition of FLT3/HDAC pathways. Additionally, the structure-based drug design strategy described herein may provide profound enlightenment for developing superior anti-AML drugs.

Hydrophobic tag-based protein degradation: Development, opportunity and challenge.

Targeted protein degradation (TPD) has emerged as a promising approach for drug development, particularly for undruggable targets. TPD technology has also been instrumental in overcoming drug resistance. While some TPD molecules utilizing proteolysis-targeting chimera (PROTACs) or molecular glue strategies have been approved or evaluated in clinical trials, hydrophobic tag-based protein degradation (HyT-PD) has also gained significant attention as a tool for medicinal chemists. The increasing number of reported HyT-PD molecules possessing high efficiency in degrading protein and good pharmacokinetic (PK) properties, has further fueled interest in this approach. This review aims to present the design rationale, hydrophobic tags in use, and diverse mechanisms of action of HyT-PD. Additionally, the advantages and disadvantages of HyT-PD in protein degradation are discussed. This review may help inspire the development of more HyT-PDs with superior drug-like properties for clinical evaluation.