Proposed model of PNAP-6h-mediated MCF-7 cell cycle arrest and apoptosis.

<p><b>PNAP</b>-<b>6h</b> causes cell cycle arrest at the S and G2/M phases. <b>PNAP</b>-<b>6h</b> modulates MCF-7 apoptosis via activation of the intrinsic/extrinsic pathways and the p38/ERK pathway.</p

Structure-Activity Relationship of Synthetic 2-Phenylnaphthalenes with Hydroxyl Groups that Inhibit Proliferation and Induce Apoptosis of MCF-7 Cancer Cells

<div><p>In this study, six 2-phenylnaphthalenes with hydroxyl groups were synthesized in high yields by the demethylation of the corresponding methoxy-2-phenylnaphthalenes, and one 2-phenylnaphthalene with an amino group was obtained by hydrogenation. All of the 2-phenylnaphthalene derivatives were evaluated for cytotoxicity, and the structure-activity relationship (SAR) against human breast cancer (MCF-7) cells was also determined. The SAR results revealed that cytotoxicity was markedly promoted by the hydroxyl group at the C-7 position of the naphthalene ring. The introduction of hydroxyl groups at the C-6 position of the naphthalene ring and the C-4<b>'</b> position of the phenyl ring fairly enhanced cytotoxicity, but the introduction of a hydroxyl group at the C-3<b>'</b> position of the phenyl ring slightly decreased cytotoxicity. Overall, 6,7-dihydroxy-2-(4'-hydroxyphenyl)naphthalene (<b>PNAP</b>-<b>6h</b>) exhibited the best cytotoxicity, with an IC₅₀ value of 4.8 μM against the MCF-7 cell line, and showed low toxicity toward normal human mammary epithelial cells (MCF-10A). <b>PNAP</b>-<b>6h</b> led to cell arrest at the S phase, most likely due to increasing levels of p21 and p27 and decreasing levels of cyclin D1, CDK4, cyclin E, and CDK2. In addition, <b>PNAP</b>-<b>6h</b> decreased CDK1 and cyclin B1 expression, most likely leading to G₂/M arrest, and induced morphological changes, such as nuclear shrinkage, nuclear fragmentation, and nuclear hypercondensation, as observed by Hoechst 33342 staining. <b>PNAP</b>-<b>6h</b> induced apoptosis, most likely by the promotion of Fas expression, increased PARP activity, caspase-7, caspase-8, and caspase-9 expression, the Bax/Bcl-2 ratio, and the phosphorylation of p38, and decreased the phosphorylation of ERK. This study provides the first demonstration of the cytotoxicity of PNAPs against MCF-7 cells and elucidates the mechanism underlying PNAP-induced cytotoxicity.</p></div

Expression of MAPKs in PNAP-induced apoptosis.

<p>(A) MCF-7 cells were treated with 25 μM <b>PNAP</b>-<b>1</b>, -<b>3h</b>, and -<b>6h</b> at three time points (12, 24, and 48 h). (B) MCF-7 cells were treated with <b>PNAP</b>-<b>1</b>, -<b>3h</b>, and -<b>6h</b> at three concentrations (5, 10, and 25 μM) for 48 h. ERK, p38, and JNK, as well as their respective phosphorylated forms, were then analyzed by western blot. The data are expressed as the means ± SEM from three independent assays. *P<0.05 and **P<0.01 are significantly different from the control.</p

Synthetic approaches for the production of PNAP-1–PNAP-8 and PNAP-2h–PNAP-8h.

<p>The eight 2-phenylnaphthalenes (<b>PNAP</b>-<b>1</b>–<b>PNAP</b>-<b>8</b>) were easily obtained from phenylacetonitriles and benzaldehydes through six steps. Subsequently, the six hydroxy-PNAPs (<b>PNAP</b>-<b>2h</b>−<b>PNAP</b>-<b>7h</b>) were obtained by demethylation of the corresponding methoxy-PNAPs (<b>PNAP</b>-<b>2</b>−<b>PNAP</b>-<b>7</b>). Unfortunately, attempts at the demethylation of <b>PNAP</b>-<b>8</b> under the same conditions led to complex mixtures. Another hydrophilic amino-PNAP (<b>PNAP</b>-<b>8h</b>) was produced by the reduction of nitro-PNAP (<b>PNAP</b>-<b>8</b>).</p

Effect of PNAP-1, -3h, and -6h on the expression of apoptosis-related proteins.

<p>(A) MCF-7 cells were treated with <b>PNAP</b>-<b>1</b>, -<b>3h</b>, and -<b>6h</b> at three concentrations (5, 10, and 25 μM) for 48 h, and the expression of cleaved caspase-7, -8, -9 and PARP was determined by western blotting. (C) MCF-7 cells were treated with 25 μM <b>PNAP</b>-<b>1</b>, -<b>3h</b>, and -<b>6h</b> at three concentrations (5, 10, and 25 μM) for 48 h, and the Bcl-2, Bcl-xl, Bax, Bax/Bcl-2, Bid, and Fas levels were then detected by western blot. (B, D) The expression was quantified using a computerized Gel-Pro Analyzer image analysis system. The data are expressed as the means ± SEM from three independent assays. *P<0.05 and **P<0.01 are significantly different from the control.</p

Effect of 2-Phenylnaphthalenes PNAP-1−PNAP-8, Their Demethylation Derivatives PNAP-2h−PNAP-7h, and Amino PNAP-8h on the Viability of MCF-7 Cells.

<p>The MCF-7 cell line was treated with <b>PNAP</b>-<b>1</b>−<b>PNAP</b>-<b>8</b>, and <b>PNAP</b>-<b>2h</b>−<b>PNAP</b>-<b>8h</b> at eight concentrations and then incubated at 37°C for 48 h. The cell viability was examined via the MTT assay.</p><p>^a The number of viable cells remaining after PNAP treatment is expressed as a percentage of the vehicle control, which was arbitrarily assigned a value of 100.0%. The results are presented as the means ± SEM from three independent assays.</p><p>*P<0.05 and **P<0.01 compared with the control.</p><p>Effect of 2-Phenylnaphthalenes PNAP-1−PNAP-8, Their Demethylation Derivatives PNAP-2h−PNAP-7h, and Amino PNAP-8h on the Viability of MCF-7 Cells.</p

Effect of PNAP-1, -3h, and -6h on MCF-7 morphology.

<p>MCF-7 cells were treated with <b>PNAP</b>-<b>1</b>, -<b>3h</b>, and -<b>6h</b> at three concentrations (5, 10, and 25 μM) for 48 h, and then, (A–J) the morphology was observed by light microscopy (100×). The cells were stained with Hoechst 33342, and then, (K–T) the morphology was observed by fluorescence microscopy (200×). (A/K) control; (B/L) 5 μM <b>PNAP</b>-<b>1</b>; (C/M) 10 μM <b>PNAP</b>-<b>1</b>; (D/N) 25 μM <b>PNAP</b>-<b>1</b>; (E/O) 5 μM <b>PNAP</b>-<b>3h</b>; (F/P) 10 μM <b>PNAP</b>-<b>3h</b>; (G/Q) 25 μM <b>PNAP</b>-<b>3h</b>; (H/R) 5 μM <b>PNAP</b>-<b>6h</b>; (I/S) 10 μM <b>PNAP</b>-<b>6h</b>; and (J/T) 25 μM <b>PNAP</b>-<b>6h</b>.</p

Effect of PNAP-6h on the expression of caspase-7, -8, and -9 proteins.

<p>MCF-7 cells were incubated in the presence or absence of (A) the caspase-8 inhibitor z-IETD-FMK or (B) the caspase-9 inhibitor z-LEHD-FMK for 1.5 h before the addition of <b>PNAP</b>-<b>6h</b>. Western blot analyses were conducted with antibodies to caspase-7, -8, and -9, and actin. (C) MCF-7 cells were treated with <b>PNAP</b>-<b>6h</b> in the presence or absence of caspase-8 inhibitor, or caspase-9 inhibitor, and the morphology was then observed by light microscopy.</p

Effect of PNAP-1, -3h, and -6h on MCF-7 cell cycle progression.

<p>MCF-7 cells were treated with <b>PNAP</b>-<b>1</b>, -<b>3h</b>, and -<b>6h</b> at three concentrations (5, 10, and 25 μM) for 48 h, and then, (A) the cells were fixed and stained with propidium iodide to analyze the DNA content by flow cytometry. (B, C) Cell cycle-associated proteins (cyclin D1, CDK4, cyclin E, CDK2, p21, p27, cyclin B1, and CDK1) were detected and analyzed by western blot. The expression was quantified with the computerized Gel-Pro Analyzer image analysis system. The data are expressed as the means ± SEM from three independent assays. *P<0.05 and **P<0.01 are significantly different from the control.</p

Effect of withanolide on the IKK/NF-κB pathway.

<p>(A) Withanolides induce IKK degradation and inhibit NF-κB activation. MDA-MB-231 cells were treated with WA (5 µM), HW (20 µM), AA (20 µM), PH (20 µM) or GM (10 µM) for 12 h. After treatment, cells were harvested and analyzed for the proteins involved in the NF-κB pathway by Western blotting. (B) Withanolides decrease anti-apoptotic proteins that are regulated by NF-κB. Cells were treated with withanolides for 48 h. After treatment, cells were harvested and analyzed for Bcl-2, Bcl-xL, and c-FLIP by Western blotting. (C) NAC prevents IKK degradation and NF-κB inhibition by WA. Cells were treated with WA (5 µM) or GM (10 µM) in the absence or presence of NAC (2.5 mM) for 12 h. After treatment, cells were harvested and subjected to Western blotting.</p