Silibinin synergizes with mitoxantrone to inhibit cell growth and induce apoptosis in human prostate cancer cells

Abstract

The purpose of these experiments was to assess the synergistic activity of silibinin with chemotherapy agents in clinical use against prostate cancer. Silybin-phytosome, a commercially available formulation containing silibinin, has recently been studied in a phase I clinical trial. The silibinin doses used in the present study are clinically achievable based on the preliminary phase I data. DU145, PC-3 and LNCaP prostate cancer cells were seeded in 96-well plates in triplicate. Twenty-four hours later, silibinin (10, 20 and 40 lM) and either mitoxantrone or docetaxel were added to the designated wells. Seventy-two hours post-treatment, cell viability was determined with a tetrazolium-based assay. The combination index (CI) for determination of a synergistic effect was calculated, with values of <0.9 indicating synergy and values >1.1 antagonism. Apoptosis was also assessed using a luminescent assay after 72 hr of treatment with media alone, silibinin, mitoxantrone, or silibinin plus mitoxantrone. Silibinin showed a synergistic effect with mitoxantrone, as measured by reduction in cell viability. The CI values ranged from 0.413 to 2.650 for the combination of silibinin and mitoxantrone; in contrast, treatment with docetaxel and silibinin showed little or no synergy, with CI values of 0.898-4.469. In concordance with these findings, the addition of silibinin increased the level of apoptosis compared to mitoxantrone alone, particularly in the PC-3 cells. The combination of silibinin and mitoxantrone exhibits a pattern of synergy in reducing cell viability with increased apoptosis. These data are important in the planning of future clinical applications of silibinin. ' 2007 Wiley-Liss, Inc.Key words: silibinin; mitoxantrone; docetaxel; prostate cancer Prostate cancer is the most common non-skin cancer diagnosed in men. In 2005, the American Cancer Society estimates that 232,000 men were diagnosed and 30,000 died from prostate cancer in the United States. 1 Early stage or organ confined cases may be cured with surgical prostatectomy or radiation therapy, although, some low-risk patients may also choose watchful waiting. 2,3 Disease that has spread beyond the prostate is generally first treated with hormonal ablation. The addition of cytotoxic chemotherapy is used in selected hormone-refractory patients, with this approach demonstrating a small ( 2 month) survival advantage. 4,5 Milk thistle (Silybum marianum) has a long history of use in humans and is commonly used in the treatment of liver disease. 6,7 Silymarin, the name of the crude milk thistle extract, is composed of several stereoisomers including silibinin (or silybin), silychristin and silydianin. 8 Silibinin and silymarin have been shown to inhibit in vitro cell growth in several cancer models including prostate, 9-11 bladder, 12,13 colon, 14,15 breast, 16,17 cervical, 18 skin 19,20 and lung cancer. 21,22 Additional in vivo experiments have demonstrated an anti-cancer effect of silibinin and silymarin in models of prostate, 23 skin, 24,25 bladder 26 and col...

Molecular Mechanisms of Silibinin-Mediated Cancer Chemoprevention with Major Emphasis on Prostate Cancer

“…In addition, silibinin has been reported to inhibit both telomerase as well as DNA topoisomerase IIα activity in LNCaP and DU145 cells, respectively (105,122). Interestingly, both mitoxantrone and doxorubicin were found to synergize with silibinin in inhibiting prostate cancer cell proliferation (121,123), and cisplatin and carboplatin were found to synergize with silibinin in inducing G2-M arrest corresponding to potent downregulation of Cdc2, cyclin B1, and Cdc25c (124). Together, these findings suggest the potential for combinatorial treatments to arrest prostate cancer progression.…”

“…The mechanism appeared to be a consequence of decreased Bcl-2 and survivin levels, caspase activation (caspases 3, 9, and 7), subsequent cytochrome c release from mitochondria, and ultimately apoptosis (99,107,108,124). Interestingly, mitoxantrone, doxorubicin, cisplatin, and carboplatin were each found to synergize with silibinin in inducing apoptosis in prostate cancer cells (121,123,124).…”

Multitargeted therapy of cancer by silymarin

“…Similar results have also been seen in DU145 cells with inhibition of active Stat3. Silibinin synergies the growth-inhibitory effect of mitoxantrone, a topoisomerase II inhibitor in prostate carcinoma PC-3 cells by reducing cell viability with increased apoptosis [34]. Silymarin causes apoptosis in human K562 leukemia cells by inhibiting Akt activity associated with activation of caspases-9 and -3 as well as PARP cleavage [35].…”

Silibinin Inhibits Cell Growth and Induces Apoptosis through Cell-cycle Arrest in PC-3 Prostate Cancer Cells

“…Silymarin은 silibinin, siliychristin, silydianin 등의 입체 이성질체를 포함하고 있으며, 현재까지 전립선암, 폐암, 대장 암, 피부암, 방광암, 유방암 등 다양한 암세포에 대하여 항암 효과가 있다고 보고되어 있다 [1][2]6,[8][9]19,21,26,29,[30][31][33][34]. 특히 silibinin은 urokinase plasminogen activator (u-PA), matrix metalloproteinase-2 (MMP-2), mitogen-activated protein kinase (MAPK)의 활성을 조절하여 암세포의 증식, 침윤 및 전이에 영향을 미치고 [4][5], 세포주기조절 및 세포사멸 유 도에 관한 활성이 보고되어 있다 [7,11,[17][18]25,28].…”