Anti-Proliferative Effects of Dendrophthoe pentandra Methanol Extract on BCR/ABL-Positive and Imatinib-Resistant Leukemia Cell Lines

Abstract

Background: Imatinib mesylate, a tyrosine kinase inhibitor specifically targeting the BCR/ABL fusion protein, induces hematological remission in patients with chronic myeloid leukemia (CML). However, the majority of CML patients treated with imatinib develop resistance with prolonged therapy. Dendrophthoe pentandra (L.) Miq. is a Malaysian mistletoe species that has been used as a traditional treatment for several ailments such as smallpox, ulcers, and cancers. Methods: We developed a resistant cell line (designated as K562R) by long-term co-culture of a BCR/ ABL positive CML cell line, K562, with imatinib mesylate. We then investigated the anti-proliferative effects of D. pentandra methanol extract on parental K562 and resistant K562R cells. Trypan blue exclusion assays were performed to determine the IC50 concentration; apoptosis and cell cycle analysis were conducted by flow cytometry. Results: D. pentandra extract had greater anti-proliferative effects towards K562R (IC50= 192 μg/mL) compared to K562 (500 μg/ mL) cells. Upon treatment with D. pentandra extract at the IC50. concentration: K562 but not K562R demonstrated increase in apoptosis and cell cycle arrest in the G2/M phase. Conclusion: D. pentandra methanol extract exerts potent anti-proliferative effect on BCR/ABL positive K562 cells.

Keywords: D. pentandra; BCR/ABL; K562; imatinib; CML.

Figure 1

Cell Viability Assay of D. pentandra Extract on K562 and K562R Cells. The effect of various concentrations of D. pentandra extract on (A) K562 and (B) K562R cells growth after 48 hours. There was a significant higher in the IC50 of extract concentration on K562 (500 µg/mL) compared to K562R cells (192 µg/mL).

Figure 2

Apoptotic Inductions of D. Pentandra Extract on K562 and K562R Cells. Flowcytometric scatterplots showing the effect of D. pentandra extract and bar graph illustrates the percentage of cell population of each cell cycle phases in (A and B) K562 and (C and D) K562R. Apoptotic induction was upon the treatment of both cell lines with cytotoxic dose (IC50) of D. pentandra extract for 48 hours. K562 cells showed a significant increase in the total apoptosis after treatment with the extract but no significant changes were shown in K562R.

Figure 3

Cell Cycle Progression of K562 and K562R Cells Treated with D. Pentandra Extract. Modfit Software results demonstrate the cell cycle analysis; (A) untreated K562, (B) treated K562, (C) untreated K562R, and (C) treated K562R cells. The DNA content at S phase for both cells were higher with D. pentandra extract, but more significant in K562 than K562R. However, cell cycle progressions of K562 and K562R were not arrested due to continuous increased and static reading of cells at G2/M phase respectively.