Curcumin induces p73-dependent apoptosis.

<p>(A) Tu212 (left) and H1299 (right) cells were treated with curcumin and expression of p73 and p73β were measured by Western blotting. (B-C) p73 was inactivated in H1299 (B) and 041 (C) cells by dominant negative p73 and apoptosis was measured by annexin V-PE staining. (D) H1299 cells expressing empty vector or dominant negative p73 were treated with curcumin. Whole cell lysates were immunoblotted with PARP and caspase 3 antibodies. For B and C, average results from three independent experiments were plotted with standard deviation as error bars. p values were determined by student t-test. p<0.05 was considered statistically significant.</p

Inhibition of p-AKT is required for curcumin-induced apoptosis.

<p>(A) H1299, (B) Tu212 and (C) Tu686 cells were treated with the indicated concentrations of curcumin for the indicated time and expression of p-AKT, AKT and actin were measured by immunoblotting. (D) Tu212 and Tu686 cells were treated with 10 and 15 μM of curcumin, respectively. Expression of AKT mRNA was measured by qPCR. (E) CA-AKT was overexpressed in Tu686 cells and apoptosis was measured. Average results from three independent experiments were plotted with standard deviation as error bars. p value was determined by student t-test. p<0.05 was considered statistically significant.</p

IC₅₀ values of curcumin.

<p>IC₅₀ values of curcumin.</p

Curcumin Induces Apoptosis of Upper Aerodigestive Tract Cancer Cells by Targeting Multiple Pathways

<div><p>Curcumin, a natural compound isolated from the Indian spice "Haldi" or "curry powder", has been used for centuries as a traditional remedy for many ailments. Recently, the potential use of curcumin in cancer prevention and therapy urges studies to uncover the molecular mechanisms associated with its anti-tumor effects. In the current manuscript, we investigated the mechanism of curcumin-induced apoptosis in upper aerodigestive tract cancer cell lines and showed that curcumin-induced apoptosis is mediated by the modulation of multiple pathways such as induction of p73, and inhibition of p-AKT and Bcl-2. Treatment of cells with curcumin induced both p53 and the related protein p73 in head and neck and lung cancer cell lines. Inactivation of p73 by dominant negative p73 significantly protected cells from curcumin-induced apoptosis, whereas ablation of p53 by shRNA had no effect. Curcumin treatment also strongly inhibited p-AKT and Bcl-2 and overexpression of constitutively active AKT or Bcl-2 significantly inhibited curcumin-induced apoptosis. Taken together, our findings suggest that curcumin-induced apoptosis is mediated via activating tumor suppressor p73 and inhibiting p-AKT and Bcl-2.</p></div

Inhibition of Bcl-2 is required for curcumin-induced apoptosis.

<p>Tu212, A549 and H292 cells were treated with curcumin and expression of Bcl-2 was examined by immunoblotting. (B) 041 and 041 Bcl-2 overexpressing cells were treated with 10 μM of curcumin for 48 h and expression of Bcl-2 was measured. (C) 041 and 041 Bcl-2 overexpressing cells were treated with 10 μM of curcumin for 48 h and apoptosis was measured by annexin V staining. Average results from three independent experiments were plotted with standard deviation as error bars. p value was determined by student t-test. p<0.05 was considered statistically significant.</p

Curcumin dose- and time-dependently induces apoptosis of upper aerodigestive tract cancer cells.

<p>Lung cancer cell lines A549, H292, H460, H1299, and SCCHN cell lines Tu212 and 886LN were treated with the indicated concentration of curcumin for 24 and 48 h. Apoptosis was measured by annexin V-PE staining. Average apoptosis from three independent experiments is presented with standard deviation as error bars.</p

Curcumin induces mitochondria-mediated apoptosis.

<p>(A) Tu212, (B) H1299 and (C) H292 cells were treated with the indicated concentration of curcumin for the indicated times. Whole cell lysates were immunoblotted with PARP and caspase 3 (detects cleaved form only) antibodies. (D) Tu212 cells were treated with 10 μM of curcumin for the indicated times and whole cell lysates were blotted with caspase 9 antibody. (E) Tu212 cells were treated with 10 μM of curcumin for 24h. Cytoplasmic and mitochondrial fractions were separated and immunoblotted with cytochrome <i>c</i> antibody. COX4 (a mitochondrial protein) was used to show efficiency of cell fractionation. Representative data from three independent experiments are shown.</p

Honokiol Enhances Paclitaxel Efficacy in Multi-Drug Resistant Human Cancer Model through the Induction of Apoptosis

<div><p>Resistance to chemotherapy remains a major obstacle in cancer therapy. This study aimed to evaluate the molecular mechanism and efficacy of honokiol in inducing apoptosis and enhancing paclitaxel chemotherapy in pre-clinical multi-drug resistant (MDR) cancer models, including lineage-derived human MDR (KB-8-5, KB-C1, KB-V1) and their parental drug sensitive KB-3-1 cancer cell lines. <i>In vitro</i> analyses demonstrated that honokiol effectively inhibited proliferation in KB-3-1 cells and the MDR derivatives (IC₅₀ ranging 3.35±0.13 µg/ml to 2.77±0.22 µg/ml), despite their significant differences in response to paclitaxel (IC₅₀ ranging 1.66±0.09 ng/ml to 6560.9±439.52 ng/ml). Honokiol induced mitochondria-dependent and death receptor-mediated apoptosis in MDR KB cells, which was associated with inhibition of EGFR-STAT3 signaling and downregulation of STAT3 target genes. Combined treatment with honokiol and paclitaxel synergistically augmented cytotoxicity in MDR KB cells, compared with treatment with either agent alone <i>in vitro</i>. Importantly, the combined treatment significantly inhibited <i>in vivo</i> growth of KB-8-5 tumors in a subcutaneous model. Tumor tissues from the combination group displayed a significant inhibition of Ki-67 expression and an increase in TUNEL-positive cells compared with the control group. These results suggest that targeting multidrug resistance using honokiol in combination with chemotherapy drugs may provide novel therapeutic opportunities.</p></div

Honokiol enhancement of paclitaxel induced apoptosis involves the inhibition of the EGFR-STAT3 signaling pathway.

<p>(<b>a</b>) Honokiol enhances paclitaxel induced PARP and caspase-3 cleavage in KB-8-5 cells. The cells were treated with 5 µg/ml of honokiol, 15 ng/ml of paclitaxel, or the combination of the two drugs for 24, 48, and 72 h. Full-length and cleaved PARP, cleaved caspase-3 and β-actin as a loading control were detected by immunoblotting using whole cell lysates. (<b>b</b>) Honokiol enhances paclitaxel induced release of cytochrome <i>c</i> in the cytoplasm in KB-8-5 cells. The cells were treated with 5 µg/ml of honokiol, 15 ng/ml of paclitaxel, or the combination for 48 h. Cytoplasmic and mitochondrial fractions were separated and immunoblotted with cytochrome c (Cyto C) antibody. COX4 (a mitochondrial protein) was used to show efficiency of cell fractionation. (<b>c</b>) Honokiol inhibits the EGFR-STAT3 signaling pathway and downregulates STAT3 target gene expression in KB-8-5 cells. The cells were treated with 5 µg/ml of honokiol, 15 ng/ml of paclitaxel, or the combination for 48 h. Whole cell lysates were immunoblotted for the indicated proteins. (<b>d</b>) Paclitaxel induces microtubule polymerization in KB-8-5 cells. Drug-induced stabilization of microtubules as evidenced by an increase in microtubule polymer mass resulting in bundling was observed upon treatment with both paclitaxel and the combination; however, honokiol alone was not effective in microtubule stabilization (magnification 400x). The cells were treated with 5 µg/ml of honokiol, 15 ng/ml of paclitaxel, or the combination for 24 h. All experiments were repeated at least three times, and representative data are presented.</p

Honokiol inhibits growth and induces apoptosis in multidrug-sensitive and -resistant cells.

<p>(<b>a, b</b>) Growth inhibition effect of paclitaxel and p-gp expression in KB-3-1, KB-8-5, KB-C1 and KB-V1 cells. The IC₅₀ values of paclitaxel in drug resistant KB-8-5, KB-C1 and KB-V1 cells were increased by 16-, 117-, and 4000-fold respectively when compared to parental KB-3-1 cells. (<b>c, d</b>) Growth inhibition effect of honokiol in KB-3-1, KB-8-5, KB-C1 and KB-V1 cells. The IC₅₀ values of honokiol in drug resistant KB-8-5, KB-C1 and KB-V1 cells were similar to that in parental KB-3-1 cells. (<b>e</b>) Honokiol induces apoptosis in KB cells. KB-3-1 and KB-8-5 cells were treated with 5, 10, 15 µg/ml of honokiol for 24, 48, and 72 h. KB-C1 and KB-V1 cells were treated with honokiol for 48 h. Apoptosis was measured by annexin V-phycoerythrin staining. *indicates statistically significant p values (*,versus control, p<0.05; **, versus 5 µg/ml, p<0.05).</p