Abstract 153: Honokiol, a promising small molecular weight natural agent, activates AMP-activated protein kinase in breast cancer cells via LKB1-dependent pathway and inhibits breast carcinogenesis

Introduction: Research over the past few years have established LKB1-AMPK pathway as an important metabolic checkpoint interconnecting the signaling pathways controlling metabolism and cancer cell growth. Thus, it is of major interest to find effective therapeutic strategies to manipulate LKB1-AMPK axis to inhibit cancer growth. The importance of active constitutive agents in natural products has become increasingly apparent owing to their potential cancer preventive as well as therapeutic properties. Honokiol, a small-molecule polyphenol isolated from magnolia species, is widely known for its therapeutic potential as an anti-inflammatory, anti-thrombosis, anti-oxidant agent and more recently for its protective function in carcinogenesis. In the present study, we sought to examine the effectiveness of honokiol in modulating LKB1-AMPK axis, preventing mammary tumorigenesis and inhibiting metastasis. Methods: Clonogenicity, 3D-colony formation, matrigel invasion, scratch-migration and spheroid-migration assays were used to examine breast cancer cell growth and metastatic potential upon honokiol treatment. Western blot and immunofluorescence analysis were used to examine activation of LKB1-AMPK axis. Functional importance of AMPK and LKB1 was examined by using AMPK-null and AMPK-WT immortalized mouse embryonic fibroblasts (MEFs) and isogenic LKB1-knockdown cell line pairs. Breast cancer xenografts, immunohistochemical and western blot analysis of tumors were used. Results: Analysis of the underlying molecular mechanisms revealed that honokiol treatment increases AMP-activated protein kinase (AMPK) phosphorylation and activity as evident by increased phosphorylation of downstream target of AMPK, acetyl-coenzyme A carboxylase (ACC) and inhibition of phosphorylation of p70S6kinase (pS6K) and eukaryotic translation initiation factor 4E binding protein 1 (4EBP1). Using AMPK-null and AMPK-WT (MEFs); we found that AMPK is required for honokiol-mediated modulation of pACC-pS6K. Intriguingly, we discovered that honokiol treatment increased the expression and cytoplasmic translocation of tumor suppressor gene LKB1 in breast cancer cells. LKB1 knockdown inhibited honokiol-mediated activation of AMPK and more importantly, inhibition of migration and invasion of breast cancer cells. Furthermore, honokiol treatment resulted in inhibition of breast tumorigenesis in vivo. Analysis of tumors showed significant increase in the levels of cytoplasmic LKB1 and phospho-AMPK in honokiol-treated tumors. Conclusions: Taken together, these data providing first in vitro and in vivo evidence of the efficacy of honokiol in activating LKB1-AMPK axis resulting in effective inhibition of mammary tumorigenesis and metastasis provide impetus to determine its activity in clinical setting.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 153. doi:1538-7445.AM2012-153

Abstract 1994: Honokiol reduces drug resistance by down-regulation of survivin expression in multidrug resistant squamous cell carcinoma of the head and neck

Background: Resistance to chemotherapy is a major obstacle in cancer therapy. The purpose of this study is to evaluate honokiol in combination with paclitaxel in controlling proliferation of multi-drug resistant (MDR) cancer cells. Honokiol is a small molecule purified from Magnolia officinalis. Honokiol has been shown to suppress tumor growth through apoptosis and inhibition of angiogenesis. In this study, we investigated the effects and mechanisms of those effects of honokiol on MDR squamous cell cancers of the head and neck (SCCHN) Methods: Serial MDR SCCHN lines including KB-8-5, KB-C1, and KB-V1 derived from the drug sensitive parental KB-3-1 cells were used in this study. Cytotoxic effects of honokiol alone and in combination with paclitaxel on apoptosis in drug-sensitive and -resistant cells were evaluated in vitro and in a subcutaneous KB-8-5 xenograft model, Results: The cell growth inhibition analysis revealed a wide range of IC50 values of paclitaxel from 1.66±0.09 to 6560.9 ±439.52 ng/ml in the KB serial cell lines, indicating that those cell lines have different levels of resistance to the paclitaxel treatment. In contrast, honokiol effectively inhibited proliferation and induced apoptosis in all four cell lines with IC50 values from 3.35±0.13 to 2.77±0.22 μg/ml. Mechanistic studies revealed that honokiol induced similar mitochondria-dependent apoptosis in drug resistant cell lines regardless of the differential resistance levels to paclitaxel treatment. Moreover these effects were associated with inhibition of STAT3 phosphorylation and down-regulation of STAT3 target gene expression, including survivin and Mcl-1. Combined treatment with honokiol and paclitaxel synergistically increased cytotoxicity as compared to the single drug treatment. This combination also significantly inhibited growth of xenografted tumors in nude mice. Conclusion: These results suggest that honokiol may be a promising drug in overcoming paclitaxel resistence of SCCHN. Targeting MDR SCCHN using honokiol in combination with paclitaxel, may benefit patients with SCCHN. (Supported by grants P50CA128613, GCC Distinguished Cancer Scholar to Dong M. Shin and Jonathan J Beitler)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1994. doi:1538-7445.AM2012-1994

Transgrediens pachyonychia congenita (PC): case series of a nonclassical PC presentation

BACKGROUND

Pachyonychia congenita (PC) is a rare keratin disorder that typically presents with nail dystrophy and focal plantar keratoderma. We present seven cases of PC with transgrediens involvement of the dorsal feet.

OBJECTIVES

To document the extension of their disease to the dorsum of the feet in patients with mutation-confirmed PC, to report the natural history of PC with such transgrediens involvement, to generate hypotheses regarding aetiology, and to suggest prevention and treatment modalities.

METHODS

Genetically confirmed cases of PC with transgrediens foot involvement were verified through the International Pachyonychia Congenita Research Registry (IPCRR) and characterized via telephone survey and photography.

RESULTS

Seven patients with PC in the IPCRR were confirmed to have transgrediens lesions on the dorsal feet (six KRT6A mutations; one KRT16 mutation). Six cases had pre-existing nontransgrediens keratoderma and all cases reported standing, wearing shoes, foot moisture, and/or infection as exacerbating or predisposing factors. Improvement, reported in six cases, was attributed to use of antibiotics or gentian violet, or improved footwear.

CONCLUSIONS

Transgrediens involvement of the dorsal feet is a rare manifestation of mutation-confirmed PC and may be more common in patients who carry a KRT6A mutation. Trauma, friction, infection and wound healing may exacerbate or predispose toward transgrediens lesions. It remains to be proven whether transgrediens-associated infection is causal or represents a primary or secondary process. Patients with PC who develop transgrediens lesions may benefit from fungal and bacterial cultures, followed by appropriate antimicrobial treatments. Efforts to decrease skin friction and moisture may also improve and/or prevent transgrediens spread.

Honokiol activates AMP-activated protein kinase in breast cancer cells via an LKB1-dependent pathway and inhibits breast carcinogenesis

INTRODUCTION

Honokiol, a small-molecule polyphenol isolated from magnolia species, is widely known for its therapeutic potential as an antiinflammatory, antithrombosis, and antioxidant agent, and more recently, for its protective function in the pathogenesis of carcinogenesis. In the present study, we sought to examine the effectiveness of honokiol in inhibiting migration and invasion of breast cancer cells and to elucidate the underlying molecular mechanisms.

METHODS

Clonogenicity and three-dimensional colony-formation assays were used to examine breast cancer cell growth with honokiol treatment. The effect of honokiol on invasion and migration of breast cancer cells was evaluated by using Matrigel invasion, scratch-migration, spheroid-migration, and electric cell-substrate impedance sensing (ECIS)-based migration assays. Western blot and immunofluorescence analysis were used to examine activation of the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) axis. Isogenic LKB1-knockdown breast cancer cell line pairs were developed. Functional importance of AMPK activation and LKB1 overexpression in the biologic effects of honokiol was examined by using AMPK-null and AMPK-wild type (WT) immortalized mouse embryonic fibroblasts (MEFs) and isogenic LKB1-knockdown cell line pairs. Finally, mouse xenografts, immunohistochemical and Western blot analysis of tumors were used.

RESULTS

Analysis of the underlying molecular mechanisms revealed that honokiol treatment increases AMP-activated protein kinase (AMPK) phosphorylation and activity, as evidenced by increased phosphorylation of the downstream target of AMPK, acetyl-coenzyme A carboxylase (ACC) and inhibition of phosphorylation of p70S6kinase (pS6K) and eukaryotic translation initiation factor 4E binding protein 1 (4EBP1). By using AMPK-null and AMPK-WT (MEFs), we found that AMPK is required for honokiol-mediated modulation of pACC-pS6K. Intriguingly, we discovered that honokiol treatment increased the expression and cytoplasmic translocation of tumor-suppressor LKB1 in breast cancer cells. LKB1 knockdown inhibited honokiol-mediated activation of AMPK and, more important, inhibition of migration and invasion of breast cancer cells. Furthermore, honokiol treatment resulted in inhibition of breast tumorigenesis in vivo. Analysis of tumors showed significant increases in the levels of cytoplasmic LKB1 and phospho-AMPK in honokiol-treated tumors.

CONCLUSIONS

Taken together, these data provide the first in vitro and in vivo evidence of the integral role of the LKB1-AMPK axis in honokiol-mediated inhibition of the invasion and migration of breast cancer cells. In conclusion, honokiol treatment could potentially be a rational therapeutic strategy for breast carcinoma.

Metabotropic glutamate receptor-dependent long-term depression is impaired due to elevated ERK signaling in the ΔRG mouse model of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) and fragile X syndrome (FXS) are caused by mutations in negative regulators of translation. FXS model mice exhibit enhanced metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD). Therefore, we hypothesized that a mouse model of TSC, ΔRG transgenic mice, also would exhibit enhanced mGluR-LTD. We measured the impact of TSC2-GAP mutations on the mTORC1 and ERK signaling pathways and protein synthesis-dependent hippocampal synaptic plasticity in ΔRG transgenic mice. These mice express a dominant/negative TSC2 that binds to TSC1, but has a deletion and substitution mutation in its GAP-domain, resulting in inactivation of the complex. Consistent with previous studies of several other lines of TSC model mice, we observed elevated S6 phosphorylation in the brains of ΔRG mice, suggesting upregulated translation. Surprisingly, mGluR-LTD was not enhanced, but rather was impaired in the ΔRG transgenic mice, indicating that TSC and FXS have divergent synaptic plasticity phenotypes. Similar to patients with TSC, the ΔRG transgenic mice exhibit elevated ERK signaling. Moreover, the mGluR-LTD impairment displayed by the ΔRG transgenic mice was rescued with the MEK-ERK inhibitor U0126. Our results suggest that the mGluR-LTD impairment observed in ΔRG mice involves aberrant TSC1/2-ERK signaling.

Honokiol stimulates osteoblastogenesis by suppressing NF-κB activation

Magnolia officinalis, a component of Asian herbal teas, has long been employed in traditional Japanese and Chinese medicine to treat numerous maladies. Honokiol, a biphenolic compound, is now considered to be one of the major active ingredients of Magnolia extract, and is under intense investigation for its anti-angiogenic, anti-inflammatory, anti-tumor and neuroprotective properties. Biochemically, honokiol has been recognized to modulate the nuclear factor κ B (NF-κB) signal transduction pathway suggesting that it possesses anti-inflammatory properties. Inflammation is intimately associated with bone turnover and skeletal deterioration and consequently, anti-inflammatory drugs may hold significant promise as bone protective agents to stem bone loss in osteoporotic conditions. We and others have demonstrated that suppression of NF-κB blunts osteoclastic bone resorption, but promotes osteoblastic bone formation. Indeed previous studies have demonstrated the anti-osteoclastogenic effects of honokiol, however, activities on osteoblast differentiation and activity have yet to be investigated. In this study, we show that honokiol is a potent inducer of in vitro osteoblast differentiation by virtue of its capacity to suppress basal and tumor necrosis factor alpha (TNFα)-induced NF-κB activation and to alleviate the suppressive action of TNFα on bone morphogenetic protein (BMP)-2-induced Smad activation. Our data confirm that honokiol may have considerable promise as a dual anabolic/anti-catabolic agent for the amelioration of multiple osteoporotic diseases.

Peroxisome proliferation-associated control of reactive oxygen species sets melanocortin tone and feeding in diet-induced obesity

Previous studies have proposed roles for hypothalamic reactive oxygen species (ROS) in the modulation of circuit activity of the melanocortin system. Here we show that suppression of ROS diminishes pro-opiomelanocortin (POMC) cell activation and promotes the activity of neuropeptide Y (NPY)- and agouti-related peptide (AgRP)-co-producing (NPY/AgRP) neurons and feeding, whereas ROS-activates POMC neurons and reduces feeding. The levels of ROS in POMC neurons were positively correlated with those of leptin in lean and ob/ob mice, a relationship that was diminished in diet-induced obese (DIO) mice. High-fat feeding resulted in proliferation of peroxisomes and elevated peroxisome proliferator-activated receptor γ (PPAR-γ) mRNA levels within the hypothalamus. The proliferation of peroxisomes in POMC neurons induced by the PPAR-γ agonist rosiglitazone decreased ROS levels and increased food intake in lean mice on high-fat diet. Conversely, the suppression of peroxisome proliferation by the PPAR antagonist GW9662 increased ROS concentrations and c-fos expression in POMC neurons. Also, it reversed high-fat feeding-triggered elevated NPY/AgRP and low POMC neuronal firing, and resulted in decreased feeding of DIO mice. Finally, central administration of ROS alone increased c-fos and phosphorylated signal transducer and activator of transcription 3 (pStat3) expression in POMC neurons and reduced feeding of DIO mice. These observations unmask a previously unknown hypothalamic cellular process associated with peroxisomes and ROS in the central regulation of energy metabolism in states of leptin resistance.

A key role for NOX4 in epithelial cell death during development of lung fibrosis

The pathogenesis of pulmonary fibrosis is linked to oxidative stress, possibly generated by the reactive oxygen species (ROS) generating NADPH oxidase NOX4. Epithelial cell death is a crucial early step in the development of the disease, followed only later by the fibrotic stage. We demonstrate that in lungs of patients with idiopathic lung fibrosis, there is strong expression of NOX4 in hyperplastic alveolar type II cells.

AIM

To study a possible causative role of NOX4 in the death of alveolar cells, we have generated NOX4-deficient mice.

RESULTS

Three weeks after administration of bleomycin, wild-type (WT) mice developed massive fibrosis, whereas NOX4-deficient mice displayed almost normal lung histology, and only little Smad2 phosphorylation and accumulation of myofibroblasts. However, the protective effects of NOX4 deficiency preceded the fibrotic stage. Indeed, at day 7 after bleomycin, lungs of WT mice showed massive increase in epithelial cell apoptosis and inflammation. In NOX4-deficient mice, no increase in apoptosis was observed, whereas inflammation was comparable to WT. In vitro, NOX4-deficient primary alveolar epithelial cells exposed to transforming growth factor-β(1) did not generate ROS and were protected from apoptosis. Acute treatment with the NOX inhibitors also blunted transforming growth factor-β(1)-induced apoptosis.

CONCLUSION

ROS generation by NOX4 is a key player in epithelial cell death leading to pulmonary fibrosis.

Abstract 3689: Targeting cell survival pathways with the combination of honokiol and resveratrol for prevention of head and neck cancer

Natural dietary agents have drawn great attention for cancer prevention because of their wide safety margin and ready availability. However, single agent intervention has failed to bring the expected outcomes in clinical trials. In the current study, we investigated a combinatorial approach using two natural compounds, honokiol (isolated from the bark of the magnolia tree) and resveratrol (a major constituent of red wines and grapes), and found that their combination at low doses (at which single agents induce minimal cell growth inhibition) strongly inhibited cell growth as measured by SRB assay. Moreover, the combination of low dose honokiol (which alone induces 10-15% apoptosis) with low dose resveratrol (also induces ∼10% apoptosis) strongly increased apoptosis (to 60-80%) in multiple head and neck cancer cell lines as evidenced by annexin V-PE staining and PARP cleavage. Interestingly, normal human fibroblasts (BJ) or immortalized normal bronchial epithelial cells (BEAS-2B) were resistant to apoptosis induced by the combination of the two compounds (less than 10% apoptosis). To understand the mechanism of apoptosis, we fractionated cytosolic and mitochondrial fractions to study the release of cytochrome c from the mitochondria to the cytosol, and found that the combination of honokiol and resveratrol more efficiently caused release of cytochrome c compared with either single agent alone. Further mechanistic studies suggested that the combination of the two agents inhibited phospho-STAT3 and phospho-AKT and reduced NF-κB protein level more efficiently than either single agent. Moreover, although single agent treatment has only minimal effect on expression of NF-κB and the STAT3 targets Bcl-2, Mcl-1 and survivin, the combination of the two agents strongly inhibited expression of these proteins, further supporting the involvement of mitochondria-mediated apoptosis. However, expression of Bcl-xL, another proapoptotic Bcl-2 protein remained unchanged after treatment with the compounds. We also found transient inhibition of phospho S6 kinase, a downstream target of p-AKT. NF-κB, phospho-STAT3 and phospho-AKT pathways are frequently over-active in head and neck cancer, suggesting that the combination of honokiol and resveratrol might be an effective strategy for the prevention of head and neck cancer and providing an important rationale for future preclinical and clinical development. (Supported by U01CA101244, R01CA112643, and P50CA128613 to DMS)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3689. doi:10.1158/1538-7445.AM2011-3689

Disruption of the mitochondrial thioredoxin system as a cell death mechanism of cationic triphenylmethanes

Alterations in mitochondrial structure and function are a hallmark of cancer cells compared to normal cells and thus targeting mitochondria has emerged as an novel approach to cancer therapy. The mitochondrial thioredoxin 2 (Trx2) system is critical for cell viability, but its role in cancer biology is not well understood. Recently some cationic triphenylmethanes such as brilliant green (BG) and gentian violet were shown to have antitumor and antiangiogenic activity with unknown mechanisms. Here we demonstrate that BG killed cells at nanomolar concentrations and targeted mitochondrial Trx2, which was oxidized and degraded. HeLa cells were more sensitive to BG than fibroblasts. In HeLa cells, Trx2 down-regulation by siRNA resulted in increased sensitivity to BG, whereas for fibroblasts, the same treatments had no effect. BG was observed to accumulate in mitochondria and cause a rapid and dramatic decrease in mitochondrial Trx2 protein. With a redox Western blot method, we found that treatment with BG caused oxidation of both Trx1 and Trx2, followed by release of cytochrome c and apoptosis-inducing factor from the mitochondria into the cytosol. Moreover, this treatment resulted in an elevation of the mRNA level of Lon protease, a protein quality control enzyme in the mitochondrial matrix, suggesting that the oxidized Trx2 may be degraded by Lon protease.

Effectiveness of gentian violet and similar products commonly used to treat pyodermas

The term pyoderma encompasses a variety of distinct entities including impetigo (bullous and nonbullous), erysipelas, cellulitis, folliculitis, and staphylococcal scalded skin syndrome. Treatment of pyodermas centers around wound care and appropriate antibiotic selection. Triphenylmethane dyes, such as gentian violet, represent a unique group of compounds that act as antiseptics and have shown clinical efficacy as antibiotics in a variety of pyodermas, including those secondary to methicillin-resistant Staphylococcus aureus. Given their low cost, ease of application, and favorable side effect profile, triphenylmethanes must be considered legitimate treatment options for pyodermas, particularly in the face of continued and emerging bacterial resistance.

Enhanced MCP-1 release by keloid CD14+ cells augments fibroblast proliferation: role of MCP-1 and Akt pathway in keloids

Keloids are fibrous overgrowth induced by cutaneous injury. The pathogenesis of keloids is poorly understood, and no convincing animal model exists. Current hypotheses of the pathogenesis classify keloids as an entity of aberrant fibrosis. Hyperactivation of the MCP-1/CCR2 axis reportedly causes fibrosis in liver cirrhosis, atherosclerosis and lung fibrosis. Circulating CD14+ monocytes are precursors of circulating fibrocytes and contribute to fibrogenesis by a MCP-1/CCR2-dependent loop. As there is an increase in monocyte lineages in keloids, the aim of this study is to determine whether peripheral CD14+ monocytes in keloid patients trigger fibroblast proliferation through MCP-1. Expressions of MCP-1 and its receptor CCR2 in keloid lesions were measured by immunohistochemistry and real-time PCR. The results revealed an increase in MCP-1 and CCR2 in the keloid tissues. Co-culture of keloid CD14+ cells and normal fibroblasts enhanced fibroblast proliferation and a parallel increase in extracellular MCP-1. We further found that MCP-1 modest enhanced fibroblast proliferation via Akt activation. Blockade of either MCP-1 or Akt signaling suppressed the mediation of fibroblast proliferation by CD14+ cells from patients. These results demonstrated that enhanced MCP-1 release by keloid CD14+ cells augments fibroblast proliferation via Akt pathway in keloids. We concluded that enhanced MCP-1 release by keloid CD14+ cells augments fibroblast proliferation, which might initiate keloid development.

Novel antiangiogenic agents in dermatology

Because angiogenesis underlies the pathogenesis of numerous conditions (cancer, psoriasis, macular degeneration), there is a pressing need for continued investigations into angiogenic signaling and potential drug targets. Antiangiogenic agents can be classified as either direct or indirect. Direct antiangiogenics act on untransformed endothelial cells to prevent differentiation and proliferation; indirect antiangiogenics act to inhibit factors involved in proangiogenic signaling. Agents currently available with dermatologic indications are few; while several established and novel biologics targeting various proangiogenic factors are currently being investigated for potential dermatologic uses, but the jury is still out on their efficacy and safety. In this review, we highlight our experience with a group of existing and novel, small molecules that combine several modes of action against angiogenesis in addition to other properties--triarylmethane dyes and fulvene derivatives.

Molecular patterns in melanoma and therapeutic targets

Malignant melanoma is one of the most lethal cancers whose treatment options are limited once it has metastasized. Recent advances in molecular technology have improved our understanding of the underlying mechanisms of melanoma pathogenesis. In this article, we highlight several pathways that have been implicated in melanoma-genesis. While a cure is not yet within grasp, the picture on the horizon is less hazy and the next decade promises to yield exciting new therapeutic discoveries.

Ulcerative granulomatous mycosis fungoides

A 42-year-old white male military recruit presented with a 2-year history of painful ulcerations on the skin of his flanks and thighs. Prior skin biopsies were nondiagnostic but raised the suspicion of an infectious etiology due to the presence ofa granulomatous infiltrate. His medical history was significant for herpes zoster and eczema, and, on review of systems, he had a 1-year history of progressive fatigue and night sweats. Examination revealed approximately one dozen 1- to 5-cm indurated, dusky violaceous plaques on his trunk and lower extremities. Several of the plaques, including one on his right flank, had overlying deep ulcerations (Figure 1A and 1B). Bilateral inguinal lymphadenopathy was present.

Honokiol inhibits epidermal growth factor receptor signaling and enhances the antitumor effects of epidermal growth factor receptor inhibitors

PURPOSE

This study aimed to investigate the utility of honokiol, a naturally occurring compound, in the treatment of head and neck squamous cell carcinoma (HNSCC) as well as its ability to target the epidermal growth factor receptor (EGFR), a critical therapeutic target in HNSCC, and to enhance the effects of other EGFR-targeting therapies.

EXPERIMENTAL DESIGN

Human HNSCC cell lines and the xenograft animal model of HNSCC were used to test the effects of honokiol treatment.

RESULTS

Honokiol was found to inhibit growth in human HNSCC cell lines, with 50% effective concentration (EC(50)) values ranging from 3.3 to 7.4 micromol/L, and to induce apoptosis, as shown through Annexin V staining. These effects were associated with inhibition of EGFR signaling, including downstream inhibition of mitogen-activated protein kinase, Akt, and signal transducer and activator of transcription 3 (STAT3), and expression of STAT3 target genes, Bcl-X(L) and cyclin D1. Furthermore, honokiol enhanced the growth inhibitory and anti-invasion activity of the EGFR-targeting agent erlotinib. Although HNSCC xenograft models did not show significant inhibition of in vivo tumor growth with honokiol treatment alone, the combination of honokiol plus cetuximab, a Food and Drug Administration-approved EGFR inhibitor for this malignancy, significantly enhanced growth inhibition. Finally, HNSCC cells rendered resistant to erlotinib retained sensitivity to the growth inhibitory effects of honokiol.

CONCLUSIONS

These results suggest that honokiol may be an effective therapeutic agent in HNSCC, in which it can augment the effects of EGFR inhibitors and overcome drug resistance.

Translating cyclooxygenase signaling in patch heterozygote mice into a randomized clinical trial in basal cell carcinoma

This different perspective on Tang et al. (beginning on p. 25 in this issue of the journal) discusses the pivotal role of cyclooxygenase (COX) signaling in the pathogenesis of basal cell carcinoma (BCC). These investigators conducted elegant experiments showing increased BCC burden in patch heterozygous mice overexpressing COX-2 in the epidermis. Genetic deletion of COX-1 or COX-2 resulted in a robust decrease in BCC burden in patch heterozygote mice. They then studied pharmacologic COX inhibition in mice and humans with loss of patch, finding a trend in humans toward decreased BCC burden. This finding has implications for public health.

Tuberous sclerosis complex suppression in cerebellar development and medulloblastoma: separate regulation of mammalian target of rapamycin activity and p27 Kip1 localization

During development, proliferation of cerebellar granule neuron precursors (CGNP), candidate cells-of-origin for the pediatric brain tumor medulloblastoma, requires signaling by Sonic hedgehog (Shh) and insulin-like growth factor (IGF), the pathways of which are also implicated in medulloblastoma. One of the consequences of IGF signaling is inactivation of the mammalian target of rapamycin (mTOR)-suppressing tuberous sclerosis complex (TSC), comprised of TSC1 and TSC2, leading to increased mRNA translation. We show that mice, in which TSC function is impaired, display increased mTOR pathway activation, enhanced CGNP proliferation, glycogen synthase kinase-3 alpha/beta (GSK-3 alpha/beta) inactivation, and cytoplasmic localization of the cyclin-dependent kinase inhibitor p27(Kip1), which has been proposed to cause its inactivation or gain of oncogenic functions. We observed the same characteristics in wild-type primary cultures of CGNPs in which TSC1 and/or TSC2 were knocked down, and in mouse medulloblastomas induced by ectopic Shh pathway activation. Moreover, Shh-induced mouse medulloblastomas manifested Akt-mediated TSC2 inactivation, and the mutant TSC2 allele synergized with aberrant Shh signaling to increase medulloblastoma incidence in mice. Driving exogenous TSC2 expression in Shh-induced medulloblastoma cells corrected p27(Kip1) localization and reduced proliferation. GSK-3 alpha/beta inactivation in the tumors in vivo and in primary CGNP cultures was mTOR-dependent, whereas p27(Kip1) cytoplasmic localization was regulated upstream of mTOR by TSC2. These results indicate that a balance between Shh mitogenic signaling and TSC function regulating new protein synthesis and cyclin-dependent kinase inhibition is essential for the normal development and prevention of tumor formation or expansion.