In vitro inhibition of human leukemia THP-1 cells by Origanum syriacum L. and Thymus vulgaris L. extracts

BACKGROUND: Natural products including, traditional medicinal plants have emerged as a tempting alternative to conventional chemotherapeutic protocols of leukemia because of their minimum side effects and less documented drug resistance. METHODS: Ethanol extracts were prepared from Thymus vulgaris L. and Origanum syriacum L. plants and investigated against the THP-1 leukemia cell line and freshly isolated peripheral blood mononuclear cells (PBMCs). The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay and the lactate dehydrogenase (LDH) assay were respectively used to determine the cellular viability and cytotoxicity in response to treatment with increasing extract concentrations. RESULTS: Both extracts exhibited a concentration dependent reduction in viability of the THP-1 cells (IC(50) = 2.126 mg/mL for O. syriacum, and 0.1569 mg/mL for T. vulgaris). O. syriacum was more potent against the PBMCs (IC(50) = 0.4247 mg/mL), while T. vulgaris was moderately selective (IC(50) = 0.3345 mg/mL with PBMCs and SI = 2.1). Only in O. syriacum the reduction in cells viability was caused by cytotoxic effect against leukemic cells (LC(50) = of 9.646 mg/mL). CONCLUSION: T. vulgaris and O. syriacum are both antileukemic in vitro. T. vulgaris represents a potential selective cytostatic and safe target for future anticancer agents’ development. O. syriacum on the other hand is cytotoxic against the leukemia cell line THP-1.