Pharmacokinetics, Tissue Distribution, Synergistic Activity, and Antitumor Activity of Two Isomeric Flavones

Flavonoids are polyphenolic secondary metabolites found in plants that have bioactive properties including antiviral, antioxidant, and anticancer. Two isomeric flavone were extracted from Gnaphalium elegans and Achyrocline bogotensis, plants used by the people from the Andean region of South America as remedies for cancer. 5,7-dihydroxy-3,6,8-trimethoxy-2-phenyl-4H-chromen-4-one (5, 7–dihydroxy- 3, 6, 8 trimethoxy flavone/ flavone A) and 3,5-dihydroxy-6,7,8-trimethoxy-2-phenyl-4H-chromen-4-one (3, 5–dihydroxy-6, 7, 8–trimethoxy flavone/ flavone B) have shown antineoplastic activity against colon cancer cell lines dependent upon their differentiation status. Pharmacokinetic studies reported herein were used to determine dosing for antitumor assays, as well as determine target tissue concentration. These included the development of methods to extract the flavones from plasma or colon tissue and reverse phase high performance liquid chromatography methods for quantification. Quantification methods were linear (r2 ≥ 0.99) with plasma calibration curves ranging from 250 - 2,500 ng/mL and 2,500 - 100,000 ng/mL for both flavones and colon calibration curves ranging from 250 – 100,000 ng/g (flavone A) and 1,000-25,000 ng/g (flavone B). Intravenous administration of a 20 mg/kg dose in rats yielded half-lives of 83.68 ± 56.61 and 107.45 ± 53.31 minutes with clearance values of 12.99 ± 13.78 and 80.79 ± 35.06 mL/min/kg for flavones A and B, respectively. Analysis of colon tissue yielded concentrations of 1639 ± 601 ng/g (flavone A) and 5975 ± 2480 ng/g (flavone B), suggesting both may be good candidate for individual or adjunct therapy for colon cancer due to distribution to the target tissue. Preliminary studies in colon cancer cells CaCo 2 and HCT 116 using either flavone in combination with 5-fluorouracil (5-FU) suggested synergistic activity of these compounds. The combination treatment increased induction of apoptosis by enhancing the DNA damaging mechanism of 5-FU. In vivo, preliminary xenograft experiments using HCT 116 cells showed smaller tumors in mice dosed with flavone B as compared to the 5-FU or combination treatment. Further experiments are warranted to confirm these observations

Quantification of Two Isomeric Flavones in Rat Colon Tissue Using Reverse Phase High Performance Liquid Chromatography

Background: Antineoplastic activity has been previously shown for two isomeric flavones, 5,7-dihydroxy-3,6,8-trimethoxy flavone (flavone A) and 3,5-dihydroxy-6,7,8-trimethoxy flavone (flavone B), against colon cancer cell lines (Thomas et al. in PLoS ONE 7:e39806, 5). Here, we present modified methods for the extraction and quantification of flavones A and B in rat colon tissue after intravenous dosing via high performance liquid chromatography, from the originally described procedure for extraction and quantification in rat plasma (Whitted et al. in J Chromatogr B Analyt Technol Biomed Life Sci 1001:150-155, 7). Results: Modifications included tissue homogenization (1 g tissue: 2 mL water), filtration of the supernatant with a PVDF membrane, and the use of only one calibration curve to determine the concentration of each flavone in colon tissue. Good separation was achieved and representative equations were linear with r 2 ≥ 0.99 for both flavones. Precision and accuracy for flavone A ranged from 0.88-24.03 and 109-116%. Precision and accuracy for flavone B ranged from 1.62-33.56 and 98-113%. Concentrations of 1639 ± 601 ng/g flavone A and 5975 ± 2480 ng/g of flavone B were detected in rat colon tissue 6 h post dosing. Conclusions: Modifications to the extraction methods for flavone A and flavone B from rat colon tissue had good separation, precision, and accuracy

Quantification of Two Isomeric Flavones in Rat Colon Tissue Using Reverse Phase High Performance Liquid Chromatography

Background: Antineoplastic activity has been previously shown for two isomeric flavones, 5,7-dihydroxy-3,6,8-trimethoxy flavone (flavone A) and 3,5-dihydroxy-6,7,8-trimethoxy flavone (flavone B), against colon cancer cell lines (Thomas et al. in PLoS ONE 7:e39806, 5). Here, we present modified methods for the extraction and quantification of flavones A and B in rat colon tissue after intravenous dosing via high performance liquid chromatography, from the originally described procedure for extraction and quantification in rat plasma (Whitted et al. in J Chromatogr B Analyt Technol Biomed Life Sci 1001:150-155, 7). Results: Modifications included tissue homogenization (1 g tissue: 2 mL water), filtration of the supernatant with a PVDF membrane, and the use of only one calibration curve to determine the concentration of each flavone in colon tissue. Good separation was achieved and representative equations were linear with r 2 ≥ 0.99 for both flavones. Precision and accuracy for flavone A ranged from 0.88-24.03 and 109-116%. Precision and accuracy for flavone B ranged from 1.62-33.56 and 98-113%. Concentrations of 1639 ± 601 ng/g flavone A and 5975 ± 2480 ng/g of flavone B were detected in rat colon tissue 6 h post dosing. Conclusions: Modifications to the extraction methods for flavone A and flavone B from rat colon tissue had good separation, precision, and accuracy

Development of reversed-phase high performance liquid chromatography methods for quantification of two isomeric flavones and the application of the methods to pharmacokinetic studies in rats

Isomers 5,7-dihydroxy-3,6,8-trimethoxy-2-phenyl-4H-chromen-4-one (5,7–dihydroxy-3,6,8 trimethoxy flavone) (flavone A) and 3,5-dihydroxy-6,7,8-trimethoxy-2-phenyl-4H-chromen-4-one (3,5-dihydroxy-6,7,8-trimethoxy flavone) (flavone B) have recently demonstrated differential antineoplastic activities against pancreatic cancer in vitro. These studies also indicated that these compounds target highly tumorigenic cells while sparing normal cells. The in vivo antitumor activities of these flavones have not been determined, and detection protocols for these compounds are needed to conduct pre-clinical assays following intravenous dosing. Here, we report methods developed using acetonitrile to extract two flavone isomers and corresponding internal standards, celecoxib and diclofenac, from rat plasma. Separation was achieved using a Shimadzu liquid chromatography system with a C18 column and mobile phase acetonitrile/water (60:40 and 70:30 for flavones A and B, respectively) containing 0.2% acetic acid and 0.05% triethylamine at a flow rate of 0.4 mL/min and detection at 245 nm. Calibration curves ranging from 250 to 2500 ng/mL and 2500 to 100,000 ng/mL for both flavones were linear (r2 ≥ 0.99) with the lower limits of quantification being 250 ng/mL. Recovery of concentrations 250, 1000, 2500, 5000, and 100,000 ng/mL ranged from 87 to 116% and 84 to 103% (n = 3) for flavone A and B, respectively. Stability of both flavones after a freezing/thawing cycle yielded a mean peak ratio ≥0.92 when compared to freshly extracted samples. Intravenous administration of a 20 mg/kg dose in rats yielded half-lives of 83.68 ± 56.61 and 107.45 ± 53.31 min with clearance values of 12.99 ± 13.78 and 80.79 ± 35.06 mL/min/kg for flavones A and B, respectively