Silibinin causes cell cycle arrest and apoptosis in human bladder transitional cell carcinoma cells by regulating CDKI-CDK-cyclin cascade, and caspase 3 and PARP cleavages

Abstract

Bladder cancer is the fourth and eighth most common cancer in men and women in the USA, respectively. Flavonoid phytochemicals are being studied for both prevention and therapy of various human malignancies including bladder cancer. One such naturally occurring flavonoid is silibinin isolated from milk thistle. Here, we assessed the effect of silibinin on human bladder transitional cell carcinoma (TCC) cell growth, cell cycle modulation and apoptosis induction, and associated molecular alterations, employing two different cell lines representing high-grade invasive tumor (TCC-SUP) and high-grade TCC (T-24) human bladder cancer. Silibinin treatment of these cells resulted in a significant dose- and time-dependent growth inhibition together with a G(1) arrest only at lower doses in TCC-SUP cells but at both lower and higher doses in T-24 cells; higher silibinin dose showed a G(2)/M arrest in TCC-SUP cells. In other studies, silibinin treatment strongly induced the expression of Cip1/p21 and Kip1/p27, but resulted in a decrease in cyclin-dependent kinases (CDKs) and cyclins involved in G(1) progression. Silibinin treatment also showed an increased interaction between cyclin-dependent kinase inhibitors (CDKIs)-CDKs and a decreased CDK kinase activity. Further, the G(2)/M arrest by silibinin in TCC-SUP cells was associated with a decrease in pCdc25c (Ser216), Cdc25c, pCdc2 (Tyr15), Cdc2 and cyclin B1 protein levels. In additional studies, silibinin showed a dose- and a time-dependent apoptotic death only in TCC-SUP cells that was associated with cleaved forms of caspase 3 and poly(ADP-ribose) polymerase. Together, these results suggest that silibinin modulates CDKI-CDK-cyclin cascade and activates caspase 3 causing growth inhibition and apoptotic death of human TCC cells, providing a strong rationale for future studies evaluating preventive and/or intervention strategies for silibinin in bladder cancer pre-clinical models.

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

“…Likewise, silibinin-fed SCID mice injected with SN12K1 cells exhibited a reduction in tumor size (54). Consistent with these results, several studies have shown that silibinin inhibits growth as well as induces apoptosis in several urinary bladder cancer cell lines which were associated with an increase in p53 expression, downregulation of survivin, cyclin D1, ERK1/2 phosphorylation and nuclear phospho-p65, cleavage of caspases, PARP, and Cip1/p21, and mitochondrial release of cytochrome c, Omi/HtrA2, and apoptosis-inducing factor (55)(56)(57)(58)(59)(60). This silibinin-mediated inhibition was also observed in rat models of urinary bladder cancer reducing lesions (60).…”

Silibinin Inhibits Proliferation, Induces Apoptosis and Causes Cell Cycle Arrest in Human Gastric Cancer MGC803 Cells Via STAT3 Pathway Inhibition

“…Exposure to silibinin resulted in a G1 arrest in human bladder transitional cell carcinoma cells (McDonald et al, 2000) and human prostate cancer DU145 cells (Owa et al., 2001). Silibinin treatment aslo inhibited human nonsmall cell lung cancer (NSCLC) cells growth and targeted cell-cycle progressing causing a prominent G1 arrest in dose-and time-dependent manner (Tyagi et al, 2004), but combinations with histone deacetylase inhibitors (HDACi) exhibited a significant G 2/M arrest of the NSCLC cells . Silibinin caused G1 and G2/M cell cycle arrest in human prostate cancer PC3 cells (Mateen et al, 2010).…”

Chemopreventive and Chemotherapeutic Effects of Intravesical Silibinin against Bladder Cancer by Acting on Mitochondria

“…1A). Accumulating evidence indicates that silibinin has anticancer activity in various tumor cells, including cancers of prostate (5)(6)(7)(8)(9), breast (10,11), skin (12), colon (13), lung (14), kidney (15,16), and bladder (17)(18)(19)(20). There is increasing interest in elucidating the mechanisms of action for silibinin as an effective agent for chemoprevention and chemotherapy against various types of cancers.…”