Natural and Semisynthetic Chalcones as Dual FLT3 and Microtubule Polymerization Inhibitors.

Activating mutations in FLT3 receptor tyrosine kinase are found in a third of acute myeloid leukemia (AML) patients and are associated with disease relapse and a poor prognosis. The majority of these mutations are internal tandem duplications (ITDs) in the juxtamembrane domain of FLT3, which have been validated as a therapeutic target. The clinical success of selective inhibitors targeting oncogenic FLT3, however, has been limited due to the acquisition of drug resistance. Herein the identification of a dual FLT3/microtubule polymerization inhibitor, chalcone 4 (2'-allyloxy-4,4'-dimethoxychalcone), is reported through screening of 15 related chalcones for differential antiproliferative activity in leukemia cell lines dependent on FLT3-ITD (MV-4-11) or BCR-ABL (K562) oncogenes and by subsequent screening for mitotic inducers in the HCT116 cell line. Three natural chalcones (1-3) were found to be differentially more potent toward the MV-4-11 (FLT3-ITD) cell line compared to the K562 (BCR-ABL) cell line. Notably, the new semisynthetic chalcone 4, which is a 2'-O-allyl analogue of the natural chalcone 3, was found to be more potent toward the FLT3-ITD+ cell line and inhibited FLT3 signaling in FLT3-dependent cells. An in vitro kinase assay confirmed that chalcone 4 directly inhibited FLT3. Moreover, chalcone 4 induced mitotic arrest in these cells and inhibited tubulin polymerization in both cellular and biochemical assays. Treatment of MV-4-11 cells with this inhibitor for 24 and 48 h resulted in apoptotic cell death. Finally, chalcone 4 was able to overcome TKD mutation-mediated acquired resistance to FLT3 inhibitors in a MOLM-13 cell line expressing FLT3-ITD with the D835Y mutation. Chalcone 4 is, therefore, a promising lead for the discovery of dual-target FLT3 inhibitors.

Synthesis and evaluation of modified chalcone based p53 stabilizing agents.

Tumor suppressor protein p53 induces cell cycle arrest and apoptotic cell death in response to various cellular stresses thereby preventing cancer development. Activation and stabilization of p53 through small organic molecules is, therefore, an attractive approach for the treatment of cancers retaining wild-type p53. In this context, a series of nineteen chalcones with various substitution patterns of functional groups including chloro, fluoro, methoxy, nitro, benzyloxy, 4-methyl benzyloxy was prepared using Claisen-Schmidt condensation. The compounds were characterized using NMR, HRMS, IR and melting points. Evaluation of synthesized compounds against human colorectal (HCT116) and breast (CAL-51) cancer cell lines revealed potent antiproliferative activities. Nine compounds displayed GI50 values in the low micromolar to submicromolar range; for example (E)-1-phenyl-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (SSE14108) showed GI50 of 0.473±0.043µM against HCT116 cells. Further analysis of these compounds revealed that (E)-3-(4-chlorophenyl)-1-phenylprop-2-en-1-one (SSE14105) and (E)-3-(4-methoxyphenyl)-1-phenylprop-2-en-1-one (SSE14106) caused rapid (4 and 8-h post-treatment) accumulation of p53 in HCT116 cells similar to its induction by positive control, Nutlin-3. Such activities were absent in 3-(4-methoxyphenyl)propiophenone (SSE14106H2) demonstrating the importance of conjugated ketone for antiproliferative and p53 stabilizing activity of the chalcones. We further evaluated p53 levels in the presence of cycloheximide (CHX) and the results showed that the p53 stabilization was regulated at post-translational level through blockage of its degradation. These chalcones can, therefore, act as fragment leads for further structure optimization to obtain more potent p53 stabilizing agents with enhanced anti-proliferative activities.

Identification and characterization of SSE15206, a microtubule depolymerizing agent that overcomes multidrug resistance.

Microtubules are highly dynamic structures that form spindle fibres during mitosis and are one of the most validated cancer targets. The success of drugs targeting microtubules, however, is often limited by the development of multidrug resistance. Here we describe the discovery and characterization of SSE15206, a pyrazolinethioamide derivative [3-phenyl-5-(3,4,5-trimethoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide] that has potent antiproliferative activities in cancer cell lines of different origins and overcomes resistance to microtubule-targeting agents. Treatment of cells with SSE15206 causes aberrant mitosis resulting in G2/M arrest due to incomplete spindle formation, a phenotype often associated with drugs that interfere with microtubule dynamics. SSE15206 inhibits microtubule polymerization both in biochemical and cellular assays by binding to colchicine site in tubulin as shown by docking and competition studies. Prolonged treatment of cells with the compound results in apoptotic cell death [increased Poly (ADP-ribose) polymerase cleavage and Annexin V/PI staining] accompanied by p53 induction. More importantly, we demonstrate that SSE15206 is able to overcome resistance to chemotherapeutic drugs in different cancer cell lines including multidrug-resistant KB-V1 and A2780-Pac-Res cell lines overexpressing MDR-1, making it a promising hit for the lead optimization studies to target multidrug resistance.

Author Correction: Identification and characterization of SSE15206, a microtubule depolymerizing agent that overcomes multidrug resistance.

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