Cyclohexa-2,5-diene-1,4-dione-based antiproliferative agents: design, synthesis, and cytotoxic evaluation

Abstract

Background: Tumors are diseases characterized by uncontrolled cell growth and, in spite of the progress of medicine over the years, continue to represent a major threat to the health, requiring new therapies. Several synthetic compounds, such as those derived from natural sources, have been identified as anticancer drugs; among these compounds quinone represent the second largest class of anticancer agents in use. Several studies have shown that these act on tumor cells through several mechanisms. An important objective of this work is to develop quinoidscompounds showing antitumor activity, but with fewer side effects. The parachinone cannabinol HU-331, is a small molecule that with its core 4-hydroxy-1,4-benzoquinone, exhibits a potent and selective cytotoxic activity on different tumor cell lines. A series of derivatives 3-hydroxy-1,4-benzochinoni were thus developed through HU-331 chemical modifications. The purpose of the work is to test the ability of the compounds to induce proliferative inhibition and study the mechanisms of cell death.

Methods: The antitumor activities were evaluated in vitro by examining their cytotoxic effects against different human cancer cell lines. All cell lines tested were plated in 96-multiwell and treated with HU-100-V at different concentrations and cell viability was evaluated byMTT assay. Subsequently via flow cytometry (FACS) it was possible to assess apoptosis by the system of double labeling with PI and Annexin-V, and the effect of the compounds on ROS formation by measuring the dichlorofluorescein fluorescence.

Results: The substitution by n-hexyl chain considerably enhanced the bioactivity of the compounds. In details, 2-hexyl-5-hydroxycyclohexa-2,5-diene-1,4-dione (V), 2,5-Dimethoxy-3-hexyl-2,5-cyclohexadiene-1,4-dione (XII) and 2-hydroxy-5-methoxy-3-hexyl-cyclohexa-2,5-diene-1,4-dione (XIII) showed most prominent cytotoxicity against almost human tumour cell lines. Compound V was further subjected to downstream apoptotic analysis, demostrating a time-dependent pro-apoptotic activity on human melanoma M14 cell line mediated by caspases activation and poly-(ADP-ribose)-polymerase (PARP) protein cleavage.

Conclusions: These findings indicate that 2-hexyl-5-idrossicicloesa-2,5-diene-1,4-dione can be a promising compound for the design of a new class of antineoplastic derivatives.Carmen Petronzi, Michela Festa, Antonella Peduto and Maria Castellano: equally contributed equally to this work.

Figure 1

Development of compounds of general formula A and B.

Figure 2

Dose–response curves from the treatment of different cell lines with the molecule HU-100-V with an IC50 between more less than 20 μM.

Figure 3

Effects of HU compounds on apoptosis of human melanoma M14 cells. Analysis of the % of apoptotic cells was performed using PI cell permeabilization staining. M14 cells were treated with different concentrations of HU-331 and V (1–10 μM) for 24–72 h. Cells were then collected and % of hypodiploid nuclei was analyzed by flow cytometry (*** P < 0.001 vs 72 h control cells; ° P < 0.05, °°° P < 0.001 vs 24 h control cells). Results are expressed as mean ± SEM of three experiments performed in triplicate.

Figure 4

Effects of the caspase inhibitor Z-VAD-FMK on apoptosis induced by HU331 and V in human melanoma M14 cells. Z-VAD-FMK (30 μM) was administered 30 min before incubation with HU-331 and V (10 μM) for 72 h and the % of apoptotic cell was evaluated by flow cytometry (mean ± SEM of three experiment performed in triplicate; ***P < 0.001 vs control cells, §§§ P < 0.001 HU331 vs V treated cells.

Figure 5

Effect of HU compounds on intracellular ROS generation at early time points in M14 cells. Cells were treated with V and HU331 for 30 min and then intensity of fluorescence of positive cells to DCFH-DA was analyzed by flow cytometry (FL-1channel). Results are representative of three experiments performed in triplicate. MFI:mean fluorescence intensity.

Figure 6

Western blotting analysis of PARP cleavage and XIAP protein expression after incubation with HU-331 and V(10 μM) for 24 hours. Blots are representative of three different experiments.