Abstract
Quassinoids are a group of diterpenoids found in plants from the Simaroubaceae family. They are also the major bioactive compounds found in Eurycoma longifolia which is commonly used as traditional medicine in South East Asia to treat various ailments including sexual dysfunction and infertility. These uses are attributed to its ability to improve testosterone level in men. Chronic consumption of E. longifolia extracts has been reported to increase testosterone level in men and animal model but its effect on prostate growth remains unknown. Therefore, the present study investigates the effects of a standardized total quassinoids composition (SQ40) containing 40% of the total quassinoids found in E. longifolia on LNCaP human prostate cancer cell line. SQ40 inhibited LNCaP cell growth at IC50 value of 5.97 μg/mL while the IC50 on RWPE-1 human prostate normal cells was 59.26 μg/mL. SQ40 also inhibited 5α-dihydrotestosterone-stimulated growth in LNCaP cells dose-dependently. The inhibitory effect of SQ40 in anchorage-independent growth of LNCaP cells was also demonstrated using soft agar assay. SQ40 suppressed LNCaP cell growth via G0/G1 phase arrest which was accompanied by the down-regulation of CDK4, CDK2, Cyclin D1 and Cyclin D3 and up-regulation of p21Waf1/Cip1 protein levels. SQ40 at higher concentrations or longer treatment duration can cause G2M growth arrest leading to apoptotic cell death as demonstrated by the detection of poly(ADP-ribose) polymerase cleavage in LNCaP cells. Moreover, SQ40 also inhibited androgen receptor translocation to nucleus which is important for the transactivation of its target gene, prostate-specific antigen (PSA) and resulted in a significant reduction of PSA secretion after the treatment. In addition, intraperitoneal injection of 5 and 10 mg/kg of SQ40 also significantly suppressed the LNCaP tumor growth on mouse xenograft model. Results from the present study suggest that the standardized total quassinoids composition from E. longifolia promotes anti-prostate cancer activities in LNCaP human prostate cancer cells.
Highlights
Quassinoids are a group of diterpenoids found in plants of the family of Simaroubaceae which possess bioactivities such as anti-tumor [1,2], anti-tuberculosis [3], anti-malarial [4,5], antiulcer [6,7], insect growth regulating [8], anti-HIV [9] and anti-inflammatory [10,11]
LNCaP cells were first allowed to grow in growth medium which supplemented with 5% charcoal-stripped serum (CSS) and DHT was added to stimulate cell proliferation
P53 and caspase-9-mediated pathways were previously implicated in the cytotoxicity of E. longifolia fractions on MCF-7 and HepG2 cells [40,44], results from the present study showed that SQ40 inhibited LNCaP cell growth by arresting G0/G1 phase in a dose- and time-dependent manner
Summary
Quassinoids are a group of diterpenoids found in plants of the family of Simaroubaceae which possess bioactivities such as anti-tumor [1,2], anti-tuberculosis [3], anti-malarial [4,5], antiulcer [6,7], insect growth regulating [8], anti-HIV [9] and anti-inflammatory [10,11]. Their anti-cancer activity was extensively discussed in previous reviews [12,13]. The increased production of testosterone by E. longifolia has been attributed to the increase in human chorionic gonadotropin level [18] and the inhibition of the activity of phosphodiesterase and aromatase conversion of testosterone to oestrogen which subsequently triggers hypothalamic-pituitary-gonadal axis to increase testosterone levels [19,20]
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