Chemical conjugation of 2-hexadecynoic acid to C5-curcumin enhances its antibacterial activity against multi-drug resistant bacteria.

The first total synthesis of a C5-curcumin-2-hexadecynoic acid (C5-Curc-2-HDA, 6) conjugate was successfully performed. Through a three-step synthetic route, conjugate 6 was obtained in 13% overall yield and tested for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) strains. Our results revealed that 6 was active against eight MRSA strains at MICs that range between 31.3 and 62.5 µg/mL. It was found that the presence of 2-hexadecynoic acid (2-HDA, 4) in conjugate 6 increased 4-8-fold its antibacterial activity against MRSA strains supporting our hypothesis that the chemical connection of 4 to C5-curcumin (2) increases the antibacterial activity of 2 against Gram-positive bacteria. Combinational index (CIn) values that range between 1.6 and 2.3 were obtained when eight MRSA strains were treated with an equimolar mixture of 2 and 4. These results demonstrated that an antagonistic effect is taking place. Finally, it was investigated whether conjugate 6 can affect the replication process of S. aureus, since this compound inhibited the supercoiling activity of the S. aureus DNA gyrase at minimum inhibitory concentrations (MIC) of 250 µg/mL (IC50=100.2±13.9 µg/mL). Moreover, it was observed that the presence of 4 in conjugate 6 improves the anti-topoisomerase activity of 2 towards S. aureus DNA gyrase, which is in agreement with results obtained from antibacterial susceptibility tests involving MRSA strains.

Synthesis of novel C5-curcuminoid-fatty acid conjugates and mechanistic investigation of their anticancer activity.

The first synthesis of C5-curcumin-fatty acid (C5-Curc-FA) conjugates was successfully performed. Through a two-step synthetic route, 10 analogs were synthesized for a structure-activity relationship (SAR) study. It was found that C5-Curc-FA conjugates containing either decanoic acid or palmitic acid moieties were cytotoxic against colorectal adenocarcinoma cell (CCL-229) at IC50s ranging from 22.5 to 56.1µg/mL, being 5c the most active C5-Curc-FA conjugate. Our results strongly suggests that a decanoic acid moiety at the meta position in C5-Curc-FA conjugates is important for their anticancer activity effect. Possible mechanisms for the anticancer activity of C5-Curc-FA conjugates were also investigated including apoptosis induction, mitochondrial damage and caspases activation. It was shown that 5c inhibited the luminescence activity of NFκB, a key signaling molecule involved in cell apoptosis and cell proliferation, at IC50=18.2µg/mL. In addition, it was demonstrated that 5c displayed significant apoptotic effect at GI50=46.0µg/mL in colorectal adenocarcinoma cell line (ATCC CCL-222), which can be explained by the significant mitochondrial membrane permeabilization and caspases 3 and 7 activation effect of 5c. Finally, it was investigated that C5-Curc-FA conjugates can affect the replication process of cancer cells, since compounds 5c, 5e, and 6c inhibited the relaxing activity of the human DNA topoisomerase I at minimum inhibitory concentrations (MICs) that range from 50 to 250µg/mL. Our results strongly support the hypothesis that the inhibition of both NFκB and DNA topoisomerase I by C5-Curc-FA conjugates is associated with their anticancer activity.