Leaf Extracts from Dillenia philippinensis Rolfe Exhibit Cytotoxic Activity to both Drug-Sensitive and Multidrug-Resistant Cancer Cells

Abstract

Background: Cancer is one of the leading causes of illness and death worldwide. Only palliative therapeutic options are available for many types of cancers, and most anticancer drugs in clinical use exhibit significant side effects. It is therefore important to develop new anticancer drugs that are more effective and less toxic. In this study, we evaluate the bioactivity of a Philippine endemic plant, "katmon" or Dillenia philippinensis, and its potential use in cancer therapy.

Methods: The cytotoxicity of the crude leaf extract, partitions, and isocratic column chromatography fractions of Dillenia philippinensis was determined in vitro by MTT assay against drug-sensitive cancer cell lines MCF7 (human breast adenocarcinoma) and HCT 116 (human colorectal carcinoma), as well as against moderately multidrug resistant (MDR) cancer cell line HCT-15 (human colorectal carcinoma) and its highly MDR subline HCT-15/Dox. The selectivity of the extract to cancer cells was determined by computing for the selectivity index (SI) with respect to normal mouse embryonic fibroblasts (NIH/3T3) cell line. To check for a possible mechanism for overcoming cancer multiple drug resistance, Calcein-AM assay was performed to assess the activity of the extract against P-glycoprotein-activated efflux pump.

Results: Dillenia philippinensis (DP1) fraction from the hexane partition exhibited cytotoxicity (IC50< 30 µg/ml) against MCF7, HCT 116, HCT-15, and HCT-15/Dox cells. DP1 also exhibited a moderate level of selectivity against cancer cells over normal cells as supported by the SI computed from the IC50 value obtained for the normal cell line. DP1 was able to inhibit P-glycoprotein (P-gp) activity in a dose-dependent manner, suggesting its possible role in targeting cancer cells with overexpressed P-gp.

Conclusion: The present findings thus demonstrate the potential chemotherapeutic properties of D. philippinensis which can be promising for future drug development against cancer.<br />.

Keywords: Dillenia philippinensis; Multidrug Resistance; Natural products; cancer; p-glycoprotein.

Figure 1

Mean IC₅₀ values of DP1 Fraction Against HCT 116, HCT-15, HCT-15/Dox, and MCF7 Cancer Cell Lines and NIH/3T3 Non-Cancer Cell Line (a) and the corresponding selectivity index (SI) values (b). Doxorubicin serves as the positive control. Extracts with SI values >3 are considered as highly selective to cancer cells (Prayong et al., 2008; Sufian et al., 2013). Data represent three trials performed in triplicate wells. Letters signify groupings based on two-way ANOVA with Tukey’s multiple comparisons test that compared IC₅₀ across cell lines for each extract. *** signify significant difference from Doxorubicin’s IC₅₀ (p < 0.001, two-way ANOVA with Tukey’s multiple comparisons test)

Figure 2

Mean Calcein Fluorescence Values of Verapamil (Positive Control), DMSO (Negative Control), and Different Concentrations of DP1 Extract against HCT116, HCT-15, and HCT-15/Dox Cells. The data represent mean ± SD of three independent trials. Letters signify groupings based on one-way ANOVA with Tukey’s multiple comparisons test that compared calcein fluorescence across treatments for each cell line