Oral silibinin inhibits lung tumor growth in athymic nude mice and forms a novel chemocombination with doxorubicin targeting nuclear factor kappaB-mediated inducible chemoresistance

The acute and cumulative dose-related toxicity and drug resistance, mediated via nuclear factor kappaB (NFkappaB), of anthracycline anticancer drugs pose a major problem in cancer chemotherapy. Here, we report that oral silibinin (a flavanone) suppresses human non-small-cell lung carcinoma A549 xenograft growth (P = 0.003) and enhances the therapeutic response (P < 0.05) of doxorubicin in athymic BALB/c nu/nu mice together with a strong prevention of doxorubicin-caused adverse health effects. Immunohistochemical analyses of tumors showed that silibinin and doxorubicin decrease (P < 0.001) proliferation index and vasculature and increase (P < 0.001) apoptosis; these effects were further enhanced (P < 0.001) in combination treatment. Pharmacologic dose of silibinin (60 mumol/L) achieved in animal study was biologically effective (P < 0.01 to 0.001, growth inhibition and apoptosis) in vitro in A549 cell culture together with an increased efficacy (P < 0.05 to 0.001) in doxorubicin (25 nmol/L) combination. Furthermore, doxorubicin increased NFkappaB DNA binding activity as one of the possible mechanisms for chemoresistance in A549 cells, which was inhibited by silibinin in combination treatment. Consistent with this, silibinin inhibited doxorubicin-caused increased translocation of p65 and p50 from cytosol to nucleus. Silibinin also inhibited cyclooxygenase-2, an NFkappaB target, in doxorubicin combination. These findings suggest that silibinin inhibits in vivo lung tumor growth and reduces systemic toxicity of doxorubicin with an enhanced therapeutic efficacy most likely via an inhibition of doxorubicin-induced chemoresistance involving NFkappaB signaling.

In vivo suppression of hormone-refractory prostate cancer growth by inositol hexaphosphate: induction of insulin-like growth factor binding protein-3 and inhibition of vascular endothelial growth factor

PURPOSE

Diet composition is an important etiologic factor in prostate cancer (PCA) growth and has significant impact on clinical PCA appearance. Because inositol hexaphosphate (IP6) is a dietary phytochemical present in cereals, soy, legumes, and fiber-rich foods, we evaluated efficacy of IP6 against PCA growth and associated molecular events.

EXPERIMENTAL DESIGN

DU145 cells were injected into nude mice, and animals were fed normal drinking water or 1 or 2% IP6 in drinking water for 12 weeks. Body weight, diet, water consumption, and tumor sizes were monitored. Tumors were immunohistochemically analyzed for proliferating cell nuclear antigen, terminal deoxynucleotidyl transferase-mediated nick end labeling, and CD31. Tumor-secreted insulin-like growth factor binding protein (IGFBP)-3 and vascular endothelial growth factor (VEGF) were quantified in plasma by ELISA.

RESULTS

IP6 feeding resulted in suppression of hormone-refractory human prostate tumor growth without any adverse effect on body weight gain, diet, and water consumption during entire study. At the end of study, tumor growth inhibition by 1 and 2% IP6 feeding was 47 and 66% (P = 0.049-0.012) in terms of tumor volume/mouse and 40 and 66% (P = 0.08-0.003) in terms of tumor weight/mouse, respectively. Tumor xenografts from IP6-fed mice showed significantly (P < 0.001) decreased proliferating cell nuclear antigen-positive cells but increased apoptotic cells. Tumor-secreted IGFBP-3 levels were also increased up to 1.7-fold in IP6-fed groups. Additionally, IP6 strongly decreased tumor microvessel density and inhibited tumor-secreted VEGF levels.

CONCLUSIONS

IP6 suppresses hormone-refractory PCA growth accompanied by inhibition of tumor cell proliferation and angiogenesis and increased apoptosis. IP6-caused increase in IGFBP-3 and decrease in VEGF might have a role in PCA growth control.

Silibinin modulates UVB-induced apoptosis via mitochondrial proteins, caspases activation, and mitogen-activated protein kinase signaling in human epidermoid carcinoma A431 cells

Several recent studies by us have shown the strong chemopreventive efficacy of silibinin against both ultraviolet B (UVB) radiation and chemical carcinogen-induced tumorigenesis in mouse skin models. The molecular mechanisms underlying silibinin protective efficacy, however, are not completely known. Here, we examined the effect of silibinin on UVB-caused apoptosis in human epidermoid carcinoma A431 cells. Irradiation of cells with different doses of UVB (5-100 mJ/cm2) and different time periods (0.5-24h) resulted in a dose- and time-dependent increase in apoptosis (P < 0.05-0.001). Silibinin (100-200 microM) pre-treatment, however, resulted in an increase in UVB-induced apoptosis (P < 0.05-0.001); interestingly, its post-treatment caused a decrease in UVB-induced apoptosis (P < 0.05-0.001). A similar pattern in the activation of caspases-9, -3, and -7 was observed with these silibinin treatments. Further, silibinin treatment prior to or immediately after UVB exposure altered Bcl-2, Bax, Bak, and cytochrome c levels in mitochondria and cytosol in favor of or against apoptosis, respectively. Silibinin treatment prior to UVB also increased the activation of mitogen/stress activated protein kinases Erk1/2, JNK, and p38 kinase as compared to its post-treatment. Together, for the first time, our results demonstrate the role of mitochondrial apoptotic machinery and MAPK signaling cascade in silibinin-caused increase as well as protection in UVB-induced apoptosis in A431 cells, and suggest that similar mechanisms might be involved in preventive efficacy of silibinin against UVB-induced skin tumorigenesis.

Silibinin prevents ultraviolet radiation-caused skin damages in SKH-1 hairless mice via a decrease in thymine dimer positive cells and an up-regulation of p53-p21/Cip1 in epidermis

Non-melanoma skin cancer (NMSC) accounts for >1 million new cases each year in the US alone suggesting that more approaches are needed for its prevention and control. Earlier studies by us have shown that silymarin (a crude form of biologically active silibinin with some other isomers), isolated from milk thistle, affords strong protection against ultraviolet (UV) radiation-induced NMSC in SKH-1 hairless mice; however, the molecular mechanisms of its efficacy are not known. Here, we assessed the effect of silibinin on UV-induced DNA damage and p53-p21/Cip1 accumulation, and their roles in UV-induced cell proliferation and apoptosis in SKH-1 hairless mouse epidermis. Topical application of silibinin prior to, or immediately after, UV irradiation resulted in a very strong protective effect against UV-induced thymine dimer positive cells in epidermis accounting for 76-85% (P < 0.001) inhibition. In other studies, silibinin treatment resulted in a further up-regulation of p53 by approximately 1.6-fold (P < 0.001) together with an increase ( approximately 2-fold, P < 0.001) in p21/Cip1 protein levels. Proliferative cell nuclear antigen staining showed that silibinin pre- or post-topical application significantly inhibits (40-52 and 20-40%, respectively, P < 0.001) UV-induced epidermal cell proliferation. In addition, silibinin strongly decreased UV-caused terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive apoptotic/sunburn cell formation (P < 0.001). These findings suggest that silibinin affords strong protection against UV-induced damage in epidermis by a decrease in thymine dimer positive cells and an up-regulation of p53-p21/Cip1 possibly leading to an inhibition in both cell proliferation and apoptosis. Comparable effects of silibinin following its pre- or post-UV application suggest that mechanisms other than sunscreen effect are operational in silibinin efficacy against UV-caused skin damages.

Chemomodulatory influence of Ferula asafoetida on mammary epithelial differentiation, hepatic drug metabolizing enzymes, antioxidant profiles and N-methyl-N-nitrosourea-induced mammary carcinogenesis in rats

The present study was conducted to ascertain the modulatory influences of Ferula asafoetida L. (asafoetida, flavoring agent) on the mammary epithelial tissue differentiation, hepatic drug metabolizing enzymes, antioxidant profiles and N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis in Sprague-Dawley rats. Feeding with two doses of asafoetida (1.25 and 2.5% w/w in diet) showed a remarkable increase in the development and differentiation of ducts/ductules (p < 0.01-0.005), lobules (p < 0.005) and a decrease in terminal end buds (p < 0.05-0.005) as compared to both normal and MNU-treated control animals. To assess the biochemical parameters, effect of asafoetida on drug-metabolizing enzymes was evaluated in the liver of rats. Asafoetida treatment significantly reduced (p < 0.05) the levels of cytochrome P450 and b5. There was an enhancement in the activities of glutathione S-transferase (p < 0.05-0.005), DT-diaphorase (p < 0.05-0.01), superoxide dismutase (p < 0.01-0.005) and catalase (p < 0.05-0.005) and in the level of reduced glutathione (p < 0.05-0.005), followed by asafoetida treatment. Also, asafoetida significantly restored the level of antioxidant system, depleted by MNU-treatment. The strengthening of antioxidant system by the lower and higher doses of asafoetida in the presence and absence of MNU was further substantiated by a significant inhibition (p < 0.005) in lipid peroxidation as measured by thiobarbituric acid-reactive substances (TBARS) in the liver of rat. Further, in long-term animal studies, where MNU was used to induce mammary carcinogenesis, asafoetida treatment resulted in a significant reduction in the multiplicity (p < 0.001) and size of palpable mammary tumors (p < 0.005-0.001) and a delay in mean latency period of tumor appearance (p < 0.005). Together, these findings indicate the chemopreventive potential of asafoetida against MNU-induced mammary carcinogenesis. Thus, asafoetida needs further investigation with regard to identification and characterization of its active principle(s) and mechanism of action, for this compound to be developed as a potential chemopreventive agent for human cancers.

Dual efficacy of silibinin in protecting or enhancing ultraviolet B radiation-caused apoptosis in HaCaT human immortalized keratinocytes

An increasing incidence of human skin cancer and other adverse effects of solar ultraviolet (UV) radiation enhance the need for novel chemoprevention strategies. Here, we have studied the effect of silibinin on UVB-induced apoptosis in HaCaT cells. Silibinin strongly prevented lower doses (15 and 30 mJ/cm2) of UVB-induced apoptosis, as observed by a reversal in UVB-caused poly(ADP-ribose) polymerase (PARP) cleavage, caspase 9 activation and an increase in apoptotic cells. UVB-induced PARP cleavage was also abolished by all caspase inhibitor, suggesting that it is a caspase-dependent effect. In other studies, silibinin restored UVB-caused depletion of a protein inhibitor of apoptosis, survivin, concomitant with up-regulation of transcription factor nuclear factor kappaB DNA binding activity, without any noticeable effect on UVB-caused activated protein-1 activation. Further, silibinin treatment up-regulated UVB-induced extracellular signal regulated kinase 1/2 phosphorylation, suggesting a possible role as a survival event in the protective effect of silibinin. In other studies, silibinin caused a moderate increase in phospho-Bcl-2, without any noticeable changes in total Bcl-2 levels, and down-regulated bax levels moderately. Silibinin also caused a strong decrease in Bad heterodimerization with Bclx(L), which was consistent with an increased translocation of Bclx(L) to the mitochondria from the cytosol. Consistent with its protective effect on UVB-caused apoptosis, silibinin also increased S phase arrest, possibly providing a prolonged time for efficient DNA repair. Interestingly, the protective effects of silibinin in HaCaT cells were lost at a higher dose of UVB (120 mJ/cm2) and instead it further enhanced UVB-caused apoptosis together with a strong decrease in UVB-caused activated protein-1 activation. Together, these results clearly demonstrate the dual efficacy of silibinin in protecting or enhancing UVB-caused apoptosis in the same cellular system and suggest that silibinin possibly works as a UVB damage sensor to exert its biological action.