[Role of 8-allyl Garcinol in the Chemoprevention of Oral Squamous Cell Carcinoma].

Objective To evaluate the chemopreventive effects of 8-allyl garcinol on oral squamous cell carcinoma(OSCC).Methods OSCC cell line CAL27 were cultured and treated with different concentrations of garcinol or 8-allyl garcinol. Their effects on the biological behaviors of OSCC cell line CAL27 were measured by MTT assay,clony formation assay,scratch migration assay,and flow cytometry with Annexin V-FITC/PI staining assay. We established DMBA-induced hamster cheek pouch models of dysplasia. While the negative control group was not treated,the positive group was treated with 0.5% DMBA solution tropically to the left cheek pouch three times per week for three consecutive weeks. The other four groups received 0.5 mmol/L or 1.0 mmol/L garcinol or 8-allyl garcinol respectively three times within the following two weeks after DMBA treatment. Hamsters were sacrificed at the fifth week to obtain tissue samples of the left cheek pouch. The samples were examined by histopathology and BrdU immunohistochemisty.Results MTT assay showed that both garcinol and 8-allyl garcinol inhibited the proliferation of CAL27 cells in a concentration-and time-dependent manner. The half maximal inhibitory concentration(IC50)of 8-allyl garcinol[(13.13±2.55)µmol/L] was significantly lower than garcinol[(32.20±3.24)µmol/L;t=8.008,P=0.001]. Comparing the two grougs of medicine in the same concentration,the inhibiting proliferation effects 8-allyl garcinol had significantly stronger effect in inhibiting proliferation than garcinol when the same dose was applied,and the difference was largest at the concentrations of 10(24 h:t=8.012,P=0.001;48 h:t=5.939,P=0.001;72 h:t=12.551,P=0.001)and 20 µmol/L(24 h:t=8.887,P=0.001;48 h:t=9.324,P=0.002;72 h:t=5.361,P=0.002). The clone formation assay showed the clone formation rates after the treatment with 20 µmol/L garcinol and 20 µmol/L 8-allyl garcinol were(44.1±0.4)% and(23.6±0.6)%,respectively,which were significantly lower than those after treatment with 10 µmol/L garcinol[(55.6±2.8)%;t=6.894,P=0.019] and 10 µmol/L 8-allyl garcinol[(31.0±0.6)%;t=15.556,P=0.001]. The inhibiting effects of 8-allyl garcinol at the concentrations of 10 µmol/L(t=14.682,P=0.003)and 20 µmol/L(t=51.514,P=0.001)were significantly stronger than garcinol.Scratch test showed the relative cell migration rates after treatment with 10 and 20 µmol/L garcinol for 12 hours were(16.00±4.55)%(t=3.139,P=0.026)and(3.00±3.16)%(t=6.608,P=0.001),respectively,which were lower than negative control [(30.33±7.64)%]. The relative cell migration rates after treatment with 10 and 20 µmol/L 8-allyl garcinol for 12 hours were(16.25±3.86)%(t=3.245,P=0.023)and(6.00±2.65)%(t=5.214,P=0.006),respectively,which were also lower than negative control[(30.33±7.64)%]. In addition,the relative cell migration rates after treatment with 10 and 20 µmol/L garcinol for 24 hours were(23.75±4.57)%(t=4.718,P=0.005)and(5.75±1.50)%(t=10.432,P=0.001),respectively,which were lower than negative control[(45.33±7.64)%]. The relative cell migration rates after treatment with 10 and 20 µmol/L 8-allyl garcinol for 24 hours were(23.50±2.38)%(t=5.529,P=0.003)and(11.67±2.31)%(t=7.308,P=0.002),respectively,which were also lower than negative control[(45.33±7.64)%]. Furthermore,the relative cell migration rate after treatment with 20 µmol/L garcinol for 24 hours was significantly lower than after treatment with 8-allyl garcinol(t=4.151,P=0.009). The apoptosis experiments showed that the early apoptosis rate of CAL27 cells was(5.00±0.10)% after treatment with 10 µmol/L garcinol,which was significantly higher than negative control[(1.57±0.21)%;F=70.950,P=0.001]. The early and late apoptosis rates of CAL27 cells were(5.90±0.78)%(t=39.384,P=0.001)and(9.73±1.67)%(t=10.101,P=0.001),respectively,after treatment with 20 µmol/L garcinol,which were also significantly higher than negative control. The early apoptosis rate of CAL27 cells was(4.63±1.16)% after treatment with 8-allyl garcinol,which was significantly higher than negative control(t=4.511,P=0.041). The effects of 8-allyl garcinol in promoting cell apoptosis were weaker than garcinol(10 µmol/L:t=5.982,P=0.004;20 µmol/L:t=8.578,P=0.001). The histopathological test also showed that the hyperplastic areas of oral mucosal epithelium in hamsters after treatment with 0.5 mmol/L garcinol(t=2.546,P=0.031),0.5 mmol/L 8-allyl garcinol(t=3.485,P=0.008),1.0 mmol/L garcinol(t=4.556,P=0.001),and 1.0 mmol/L 8-allyl garcinol(t=5.393,P=0.001)were significantly smaller than positive control. The dysplasia areas of oral mucosal epithelium in hamsters after treatment with 0.5 mmol/L 8-allyl garcinol(t=2.130,P=0.046),1.0 mmol/L garcinol(t=3.434,P=0.010),and 1.0 mmol/L 8-allyl garcinol(t=4.518,P=0.004)were also smaller than positive control;1.0 mmol/L garcinol group(t=2.793,P=0.023)and 1.0 mmol/L 8-allyl garcinol group(t=4.997,P=0.001)were smaller than 0.5 mmol/L garcinol treatment group. Immunohistochemical staining of BrdU showed that the BrdU-labeled indicators were significantly lower in negative control group(t=7.563,P=0.001),0.5 mmol/L garcinol(t=2.862,P=0.029),0.5 mmol/L 8-allyl garcinol(t=4.693,P=0.002),1.0 mmol/L garcinol(t=5.071,P=0.002),and 1.0 mmol/L 8-allyl garcinol(t=5.133,P=0.001)when compared with the positive control. The BrdU-labeled indicators in 0.5 mmol/L 8-allyl garcinol(t=3.724,P=0.007),1.0 mmol/L garcinol(t=7.000,P=0.001),and 1.0 mmol/L 8-allyl garcinol(t=4.413,P=0.003)were also significantly lower than in 0.5 mmol/L garcinol group.Conclusions 8-allyl garcinol could inhibit the proliferation and migration of OSCC cell line CAL27 and promotes apoptosis. It also has prominent inhibitory effects on DMBA-induced hamster cheek pouch dysplasia. However,the specific effects are slightly different from garcinol.

The C8 side chain is one of the key functional group of Garcinol for its anti-cancer effects.

Garcinol from the fruit rind of Garcinia indica shows anti-carcinogenic and anti-inflammatory properties, but its mechanism and key functional groups were still need to be identified. Our previous computer modeling suggested that the C8 side chain of Garcinol is so large that it may influence the bioactivity of the compound. 8-Me Garcinol, a derivative of Garcinol in which the bulky side chain at the C8 position of Garcinol is replaced with a much smaller methyl group, was synthesized through a 12-step procedure starting from 1,3-cyclohexanedione. The antitumor activity of Garcinol and 8-Me Garcinol was evaluated in vitro by MTT, cell cycle and cell apoptosis assays. The results showed that 8-Me Garcinol had weaker inhibitory activity on cells proliferation, and little effects on cell cycle and apoptosis in oral cancer cell line SCC15 cells when compared with Garcinol. All of the results indicated 8-Me Garcinol exerts weaker antitumor activity than Garcinol, and the C8 side chain might be an important active site in Garcinol. Changing the C8 side chain will affect the inhibitory effect of Garcinol.

13,14-Dihydroxy groups are critical for the anti-cancer effects of garcinol.

In the presence of K2CO3/Cs2CO3 (molar ratio 10:1), garcinol was subjected to methylation by reaction with iodomethane at room temperature to afford 13,14-dimethoxy garcinol. The methylated garcinol derivative was screened against oral cancer cell line SCC15 for cell proliferation and apoptosis. 13,14-Dimethoxy garcinol showed weaker inhibitory activity on SCC15 cell growth than garcinol, and had little effect on cell cycle and apoptosis of SCC15, whereas garcinol effectively induced cell cycle arrest and cell apoptosis. Meanwhile, the ELISA data showed that the inhibitory effect of garcinol on 5-Lox pathway was more potent than 13,14-dimethoxy garcinol (P<0.05). All these results have confirmed the important role of 13,14-dihydroxy groups for anti-cancer effects of garcinol.