Synthesis of N-acyl Derivatives of Aminocombretastatin A-4 and Study of their Interaction with Tubulin and Downregulation of c-Myc

Abstract

Background: Six N-acyl derivatives of aminocombretastatin A-4 have been synthesized and evaluated according to their interaction with tubulin and as c-Myc downregulators. Aims: In search of new promising anti-cancer agents. Objective: This study is focused on the synthesis and the biological evaluation of N-acyl derivatives of aminocombretastatin A-4 (CA-4). Docking studies were carried out to find out whether the synthetic derivatives could bind to tubulin at the colchicine site in a conformation similar to that of CA- 4. The synthetic derivatives' effect on the proliferation of several cancer cells and non-cancer cells has been measured. Their effect on tubulin polymerization, cell cycle distribution, the microtubule network and c-Myc expression has also been evaluated. Method: A set of six N-acyl derivatives was achieved by means of a peptide-type coupling of aminocombretastatin A-4 and the corresponding carboxylic acid. The synthetic compounds' ability to inhibit cell proliferation was measured by MTT assay against three human carcinoma cell lines (colorectal HT-29, lung A549, and breast adenocarcinoma MCF-7) and one non-tumor cell line (HEK- 293). Turbidimetry time-course measurements evaluated the inhibition of tubulin polymerization. The action of the synthetic derivatives on cell cycle distribution was measured by flow cytometry and their effects on the microtubule network were determined by immunofluorescence microscopy. Finally, the downregulation of the synthetic derivatives on c-Myc protein was quantified by ELISA assay, while the effect on c-Myc gene was measured by RT-qPCR analysis. Results: Derivatives bearing pentanoyl (compound 2), hexanoyl (compound 3), and heptanoyl (compound 4) side chains show anti-proliferative activities on the HT-29 line in the low nanomolar range, with values similar to that exhibited by AmCA-4 but far exceeding those of CA-4. Compounds 1 (butanoyl side chain) and 2-3 inhibit tubulin polymerization in vitro in a manner similar to that of CA-4 and AmCA-4 whereas compounds 4, 5 (octanoyl side chain) and 6 (dodecanoyl side chain) may be considered as partial inhibitors of tubulin polymerization. While all derivatives are able to accumulate cells in G2/M phase, compounds with the longest acyl chains (5 and 6) are the least active ones in this particular action. Moreover, compounds 2-3 were the most active ones as c-Myc downregulators. Conclusion: Our studies show that the most active compounds in the disruption of the microtubule network are also the most potent ones in the downregulation of c-Myc expression. Other: Compounds 2 and 3 are good candidates for in vivo studies as they combine the best antimitotic and c-Myc downregulation activities at low doses.