Propolis from the Stingless Bee Trigona incisa from East Kalimantan, Indonesia, Induces In Vitro Cytotoxicity and Apoptosis in Cancer Cell lines

Background: Previously, stingless bee (Trigona spp.) products from East Kalimantan, Indonesia, weresuccessfully screened for in vitro antiproliferative activity against human cancer derived cell lines. It wasestablished that propolis from T. incisa presented the highest in vitro cytotoxicity against the SW620 coloncancer cell line (6% cell survival in 20 μg/mL). Materials and
Methods: Propolis from T. incisa was extractedwith methanol and further partitioned with n-hexane, ethyl acetate and methanol. The in vitro cytotoxicity ofthe extracts was assessed by the MTT assay against human colon (SW620), liver (Hep-G2), gastric (KATO-III),lung (Chago) and breast (BT474) cancer derived cell lines. The active fractions were further enriched by silicagel quick column, absorption and size exclusion chromatography. The purity of each fraction was checked bythin layer chromatography. Cytotoxicity in BT-474 cells induced by cardanol compared to doxorubicin wereevaluated by MTT assay, induction of cell cycle arrest and cell death by flow cytometric analysis of propidiumiodide and annexin-V stained cells.
Results: A cardol isomer was found to be the major compound in one activefraction (F45) of T. incisa propolis, with a cytotoxicity against the SW620 (IC50 of 4.51 ± 0.76 μg/mL), KATO-III(IC50 of 6.06 ± 0.39 μg/mL), Hep-G2 (IC50 of 0.71 ± 0.22 μg/mL), Chago I (IC50 of 0.81 ± 0.18 μg/mL) and BT474(IC50 of 4.28 ± 0.14 μg/mL) cell lines. Early apoptosis (programmed cell death) of SW620 cells was induced bythe cardol containing F45 fraction at the IC50 and IC80 concentrations, respectively, within 2-6 h of incubation.In addition, the F45 fraction induced cell cycle arrest at the G1 subphase.
Conclusions: Indonesian stingless bee(T. incisa) propolis had moderately potent in vitro anticancer activity on human cancer derived cell lines. Cardolor 5-pentadecyl resorcinol was identified as a major active compound and induced apoptosis in SW620 cells inan early period (≤ 6 h) and cell cycle arrest at the G1 subphase. Thus, cardol is a potential candidate for cancerchemotherapy.