Synthesis and Anti-Tumor Activities of Fluoride-Containing Gossypol Derivatives Compounds

We report herein the design and synthesis of a series of novel fluoride-containing gossypol derivatives by the condensation reaction of gossypol with fluoride-containing aromatic amine. These fluoride-containing gossypol derivatives were characterized by IR, 1H-NMR and high resolution mass spectral data, then screened as antitumor agents against three human cancer cell lines (HeLa, A-549 and BGC-823) and a normal cell line (VEC) in vitro by using MTT cell proliferation assays. Results revealed that compounds 3a, 3c and 3f exhibited superior anticancer activity against HeLa, compounds 3b,3c, 3e and 3f exhibited superior anticancer activity against A-549, compounds 3b, 3c and 3f exhibited superior anticancer activity against BGC-823 compared to gossypol. In particular, fluorine substituent at the para positions of the phenyl ring showed remarkable inhibitory effects on HeLa (3c: IC50 = 14.2 μM, 3f: IC50 = 8.34 μM), A-549(3c: IC50 = 6.32 μM, 3f: IC50 = 9.76 μM) and BGC-823 cells (3c: IC50 = 8.62 μM, 3f: IC50 = 4.36 μM). Furthermore, all the compounds 3a-3f exhibited lessened cytotoxicity against VEC compared to gossypol.

Fluorine substituents have become a widespread and important drug component.Organofluorine affects nearly all physical and adsorption, distribution, metabolism, and excretion properties of a lead compound.Its inductive effects are relatively well understood and enhancing bioavailability [25][26][27].Top-selling fluorinated pharmaceuticals include the antidepressant fluoxetine (Prozac), the cholesterol-lowering drug atorvastatin (Lipitor), and the antibacterial ciprofloxacin (Ciprobay) (Figure 2) [28].
The aforementioned findings stimulated our interest in designing and synthesizing a series of fluoride-containing gossypol Schiff base derivatives (Figure 3) which were anticipated to be a much higher anti-tumor activity yet lower systemic toxicity than gossypol.The activity of the target compounds were evaluated by three human cancer cell lines (HeLa, A-549 and BGC-823) and a normal cell line (VEC) in vitro by using MTT cell proliferation assays.To the best of our knowledge, the biological evaluation of fluoride-containing gossypol derivatives for in vitro anti-tumor activity is not reported [11].

Anti-Tumor Activities
All the fluoride-containing gossypol derivatives were screened for in vitro cytotoxicity against three human cancer cell lines (HeLa, A-549 and BGC-823) and a normal cell line (VEC) by MTT assay.In vitro, the cytotoxic activities of gossypol and fluoride-containing gossypol Schiff base derivatives were deter-Natural Science mined by the MTT cytotoxicity assay, which was performed in 96-well plates.The tumor cell line panel consisted of HeLa (human cervical carcinoma), A-549 (human lung carcinoma), BGC-823 (human gastric carcinoma), VEC (human vascular endothelial cells) (final concentration in the growth medium was (2 -4) × 10 4 /mL).MTT solution (20 μL/well) was added after cells were treated with drug for 48 h, and cells were incubated for a further 4 h at 37˚C.The purple form azan crystals were dissolved in 150 μL DMSO.After 5 min, the plates were read on an automated micro plate spectrophotometer at 570 nm.Assays were performed in triplicate in three independent experiments.The concentration required for 50% inhibition of cell viability (IC 50 ) what was calculated.In all of these experiments, three replicate wells were used to determine each point.

CONCLUSION
In summary, a series of novel fluoride-containing gossypol Schiff base derivatives were synthesized and tested for their in vitro cytotoxic activities against three human cancer cell lines(HeLa, A-549 and BGC-823) and a normal cell line (VEC) by using MTT cell proliferation assays.All the compounds exhibited lessened cytotoxicity against normal cells (VEC).Results revealed that compounds 3a, 3c and 3f exhibited superior anticancer activity against HeLa, compounds 3b, 3c, 3e and 3f exhibited superior anticancer activity against A-549, compounds 3b, 3c and 3f exhibited superior anticancer activity against BGC-823 compared to gossypol.In particular, fluorine substituent at the para positions of the phenyl ring showed remarkable inhibitory effects on HeLa (3c: IC 50 = 14.2 μM, 3f: IC 50 = 8.34 μM), A-549 (3c: IC 50 = 6.32 μM, 3f: IC 50 = 9.76 μM) and BGC-823 cells (3c: IC 50 = 8.62 μM, 3f: IC 50 = 4.36 μM).Moreover, fluoride-containing gossypol derivatives 3c and 3f exhibit good safety profiles (IC 50 > 100 μM against VEC).And thus as anti-cancer drug, fluoride-containing gossypol Schiff base derivatives has a better application prospects.Studies to determine the in vivo pharmacokinetics and efficacy of compounds 3c and 3f against some selected tumor cell lines are currently underway.

Figure 1 .
Figure 1.Chemical structure of gossypol (The highlighted aldehyde groups were supposed to be toxicity).

Table 2 .
The inhibiting effect of compounds 3a -3f to HeLa, A-549 and BGC-823 cell lines in vitro.
a IC 50 values were the means of three independent experiments run in duplicate.