Kantima Leelahavanichkul

mTOR Inhibition Prevents Epithelial Stem Cell Senescence and Protects from Radiation-Induced Mucositis

The integrity of the epidermis and mucosal epithelia is highly dependent on resident self-renewing stem cells, which makes them vulnerable to physical and chemical insults compromising the repopulating capacity of the epithelial stem cell compartment. This is frequently the case in cancer patients receiving radiation or chemotherapy, many of whom develop mucositis, a debilitating condition involving painful and deep mucosal ulcerations. Here, we show that inhibiting the mammalian target of rapamycin (mTOR) with rapamycin increases the clonogenic capacity of primary human oral keratinocytes and their resident self-renewing cells by preventing stem cell senescence. This protective effect of rapamycin is mediated by the increase in expression of mitochondrial superoxide dismutase (MnSOD), and the consequent inhibition of ROS formation and oxidative stress. mTOR inhibition also protects from the loss of proliferative basal epithelial stem cells upon ionizing radiation in vivo, thereby preserving the integrity of the oral mucosa and protecting from radiation-induced mucositis.

Rac1 Is Required for Epithelial Stem Cell Function during Dermal and Oral Mucosal Wound Healing but Not for Tissue Homeostasis in Mice

Background The regenerative capacity of the skin, including the continuous replacement of exfoliated cells and healing of injuries relies on the epidermal stem cells and their immediate cell descendants. The relative contribution of the hair follicle stem cells and the interfollicular stem cells to dermal wound healing is an area of active investigation. Recent studies have revealed that the small GTPase Rac1, which regulates cell migration and nuclear gene expression, is required for hair follicle stem function but not for the normal homeostasis of the interfollicular skin. Methodology/Principal Findings Here we explored whether Rac1 contributes to wound healing in the skin and in the oral mucosa, the latter an anatomical site that presents similar architecture to that of the skin but is devoid of any hair follicle structures, and hence lacks hair follicle stem cells. Epidermal Rac1 gene excision led to the clearly delayed closure of cutaneous wounds. Remarkably, genetic ablation of Rac1 from the oral mucosa resulted in the complete inability of oral wounds to heal. We present evidence that the lack of oral mucosal re-epithelization may result from the reduced migratory capacity of cells lacking Rac1 together with altered expression of injury-induced proliferative and cellular stress-related expression programs. Conclusions/Significance Together, these observations support that while the normal development and homeostasis of the interfollicular skin and oral mucosa do not require Rac1 function, the interfollicular and oral epithelial stem cells may require a Rac1-dependent program to orchestrate the tissue response to injury and ultimate for wound closure. Ultimately, these findings may enable the molecular characterization of the acute tissue regenerative response of these stem cell populations, thus facilitating the identification of novel molecular-targeted strategies aimed at accelerating wound closure.

A Retroinhibition Approach Reveals a Tumor Cell–Autonomous Response to Rapamycin in Head and Neck Cancer

Emerging evidence supporting the activation of the Akt-mammalian target of rapamycin (mTOR) signaling network in head and neck squamous cell carcinoma (HNSCC) progression has provided the rationale for exploring the therapeutic potential of inhibiting this pathway for HNSCC treatment. Indeed, rapamycin, a clinically relevant mTOR inhibitor, promotes the rapid regression of HNSCC-tumor xenografts in mice. However, rapamycin does not affect the growth of HNSCC cells in vitro, thus raising the possibility that, as for other cancer types, rapamycin may not target cancer cells directly but may instead act on a component of the tumor microenvironment, such as tumor-associated vasculature. Here, we used a retroinhibition approach to assess the contribution of cancer cell-autonomous actions of rapamycin to its antitumor activity in HNSCC. A rapamycin-resistant form of mTOR (mTOR-RR) was expressed in HNSCC cells while retaining the wild-type (rapamycin-sensitive) mTOR (mTOR-WT) alleles in host-derived endothelial and stromal cells. Expression of mTOR-RR prevented the decrease in phospho-S6 levels caused by rapamycin through mTOR in HNSCC cells but not in stromal cells, and rendered HNSCC xenografts completely resistant to the antitumoral activity of rapamycin. This reverse pharmacology strategy also enabled monitoring the direct consequences of inhibiting mTOR in cancer cells within the complex tumor microenvironment, which revealed that mTOR controls the accumulation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) and the consequent expression of vascular endothelial growth factor and a glucose transporter, Glut-1, in HNSCC cells. These findings indicate that HNSCC cells are the primary target of rapamycin in vivo, and provide evidence that its antiangiogenic effects may represent a downstream consequence of mTOR inhibition in HNSCC cells.

Inhibition of Mammalian Target of Rapamycin by Rapamycin Causes the Regression of Carcinogen-Induced Skin Tumor Lesions

Purpose: The activation of Akt/mammalian target of rapamycin (mTOR) pathway represents a frequent event in squamous cell carcinoma (SCC) progression, thus raising the possibility of using specific mTOR inhibitors for the treatment of SCC patients. In this regard, blockade of mTOR with rapamycin prevents the growth of human head and neck SCC cells when xenotransplanted into immunodeficient mice. However, therapeutic responses in xenograft tumors are not always predictive of clinical anticancer activity. Experimental Design: As genetically defined and chemically induced animal cancer models often reflect better the complexity of the clinical setting, we used here a two-step chemical carcinogenesis model to explore the effectiveness of rapamycin for the treatment of skin SCC. Results: Rapamycin exerted a remarkable anticancer activity in this chemically induced cancer model, decreasing the tumor burden of mice harboring early and advanced tumor lesions, and even recurrent skin SCCs. Immunohistochemical studies on tumor biopsies and clustering analysis revealed that rapamycin causes the rapid decrease in the phosphorylation status of mTOR targets followed by the apoptotic death of cancer cells and the reduction in the growth and metabolic activity of the surviving ones, concomitant with a decrease in the population of cancer cells expressing mutant p53. This approach enabled investigating the relationship among molecular changes caused by mTOR inhibition, thus helping identify relevant biomarkers for monitoring the effectiveness of mTOR inhibition in the clinical setting. Conclusions: Together, these findings provide a strong rationale for the early evaluation of mTOR inhibitors as a molecular targeted approach to treat SCC.

A role for p38 MAPK in head and neck cancer cell growth and tumor‐induced angiogenesis and lymphangiogenesis

We have recently gained a remarkable understanding of the mutational landscape of head and neck squamous cell carcinoma (HNSCC). However, the nature of the dysregulated signaling networks contributing to HNSCC progression is still poorly defined. Here, we have focused on the role of the family of mitogen activated kinases (MAPKs), extracellular regulated kinase (ERK), c‐Jun terminal kinase (JNK) and p38 MAPK in HNSCC. Immunohistochemical analysis of a large collection of human HNSCC tissues revealed that the levels of the phosphorylated active form of ERK1/2 and JNK were elevated in less than 33% and 16% of the cases, respectively. Strikingly, however, high levels of active phospho‐p38 were observed in most (79%) of hundreds of tissues analyzed. We explored the biological role of p38 in HNSCC cell lines using three independent approaches: treatment with a specific p38 inhibitor, SB203580; a retro‐inhibition strategy consisting in the use of SB203580 combined with the expression of an inhibitor‐insensitive mutant form of p38α; and short‐hairpin RNAs (shRNAs) targeting p38α. We found that specific blockade of p38 signaling significantly inhibited the proliferation of HNSCC cells both in vitro and in vivo. Indeed, we observed that p38 inhibition in HNSCC cancer cells reduces cancer growth in tumor xenografts and a remarkable decrease in intratumoral blood and lymphatic vessels. We conclude that p38α functions as a positive regulator of HNSCC in the context of the tumor microenvironment, controlling cancer cell growth as well as tumor‐induced angiogenesis and lymphangiogenesis.

Rab25 regulates invasion and metastasis in head and neck cancer

Purpose: Head and neck squamous cell carcinoma (HNSCC) is one of the 10 most common cancers with a 50% five-year survival rate, which has remained unchanged for the past three decades. One of the major reasons for the aggressiveness of this cancer is that HNSCCs readily metastasize to cervical lymph nodes that are abundant in the head and neck region. Hence, discovering new molecules controlling the metastatic process as well as understanding their regulation at the molecular level are essential for effective therapeutic strategies. Experimental Design: Rab25 expression level was analyzed in HNSCC tissue microarray. We used a combination of intravital microscopy in live animals and immunofluorescence in an in vitro invasion assay to study the role of Rab25 in tumor cell migration and invasion. Results: In this study, we identified the small GTPase Rab25 as a key regulator of HNSCC metastasis. We observed that Rab25 is downregulated in HNSCC patients. Next, we determined that reexpression of Rab25 in a metastatic cell line is sufficient to block invasion in a three-dimensional collagen matrix and metastasis to cervical lymph nodes in a mouse model for oral cancer. Specifically, Rab25 affects the organization of F-actin at the cell surface, rather than cell proliferation, apoptosis, or tumor angiogenesis. Conclusion: These findings suggest that Rab25 plays an important role in tumor migration and metastasis, and that understanding its function may lead to the development of new strategies to prevent metastasis in oral cancer patients. Clin Cancer Res; 19(6); 1375–88. ©2013 AACR.

SDF-1/CXCL12 induces directional cell migration and spontaneous metastasis via a CXCR4/Gαi/mTORC1 axis

Multiple human malignancies rely on C‐X‐C motif chemokine receptor type 4 (CXCR4) and its ligand, SDF‐1/CXCL12 (stroma cell‐derived factor 1/C‐X‐C motif chemokine 12), to metastasize. CXCR4 inhibitors promote the mobilization of bone marrow stem cells, limiting their clinical application for metastasis prevention. We investigated the CXCR4‐initiated signaling circuitry to identify new potential therapeutic targets. We used HeLa human cancer cells expressing high levels of CXCR4 endogenously. We found that CXCL12 promotes their migration in Boyden chamber assays and single cell tracking. CXCL12 activated mTOR (mechanistic target of rapamycin) potently in a pertussis‐sensitive fashion. Inhibition of mTOR complex 1 (mTORC1) by rapamycin [drug concentration causing 50% inhibition (lC50) = 5 nM] and mTORC1/mTORC2 by Torin2 (IC50 = 6 nM), or by knocking down key mTORC1/2 components, Raptor and Rictor, respectively, decreased directional cell migration toward CXCL12. We developed a CXCR4‐mediated spontaneous metastasis model by implanting HeLa cells in the tongue of SCIDNOD mice, in which 80% of the animals develop lymph node metastasis. It is surprising that mTORC1 disruption by Raptor knockdown was sufficient to reduce tumor growth by 60% and spontaneous metastasis by 72%, which were nearly abolished by rapamycin. In contrast, disrupting mTORC2 had no effect in tumor growth or metastasis compared with control short hairpin RNAs. These data suggest that mTORC 1 may represent a suitable therapeutic target in human malignancies using CXCR4 for their meta‐static spread.—Dillenburg‐Pilla, P., Patel, V., Mikelis, C. M., Zárate‐Bladés, C. R., Doçi, C. L., Amornphimoltham, P., Wang, Z., Martin, D., Leelahavanichkul, K., Dorsam, R. T., Masedunskas, A., Weigert, R., Molinolo, A. A., Gutkind, J. S., SDF‐1/CXCL12 induces directional cell migration and spontaneous metastasis via a CXCR4/Gαi/mTORC1 axis. FASEB J. 29, 1056–1068 (2015). www.fasebj.org

Oral and Pharyngeal Epithelial Keratinocyte Culture

Primary human oral epithelial cells are readily available and have been recently employed for tissue engineering. These cells are currently being widely utilized in multiple research efforts, ranging from the study of oral biology, mucosal immunity, and carcinogenesis to stem cell biology and tissue engineering. This chapter describes step-by-step protocols for the successful isolation and culture of human oral epithelial cells and fibroblasts, and techniques for their use in two-dimensional and three-dimensional culture systems. The described methods will enable to generate reconstituted tissues that resemble epithelial like structures in vitro, which can recapitulate some of the key features of the oral epithelium in vivo.

Cellular Systems for Studying Human Oral Squamous Cell Carcinomas

The human oral squamous epithelium plays an important role in maintaining a barrier function against mechanical, physical, and pathological injury. However, the self-renewing cells residing on the basement membrane of the epithelium can give rise to oral squamous cell carcinomas (OSCC), now the sixth most common cancer in the developed world, which is still associated with poor prognosis. This is due, in part, to the limited availability of well-defined culture systems for studying oral epithelial cell biology, which could advance our understanding of the molecular basis of OSCC. Here, we describe methods to successfully isolate large cultures of human oral epithelial cells and fibroblasts from small pieces of donor tissues for use in techniques such as three-dimensional cultures and animal grafts to validate genes suspected of playing a role in OSCC development and progression. Finally, the use of isolated oral epithelial cells in generating iPS cells is discussed which holds promise in the field of oral regenerative medicine.

Arachidonic Acid Metabolism and Its Implication on Head and Neck Cancer

Most of head and neck cancer (HNC) are squamous cell carcinoma. Recent advances in molecular biology have documented significant genetic differences between head and neck squamous cell carcinoma (HNSCC) cells and normal cells, leading to the development of potential new therapeutics and chemoprevention (Choi & Myers, 2008). Historically, the association between inflammation and cancer has been recognized. More recently, a number of chronic inflammatory diseases have been shown to be associated with a variety of human cancers, including HNC (Conroy et al., 2010; Fitzpatrick & Katz, 2010). The relationship between oral health and cancer has been examined for a number of specific cancer sites. Several studies have reported associations between periodontal disease or tooth loss and risk of oral, upper gastrointestinal, lung, and pancreatic cancer in different populations (Meyer et al., 2008). Cumulating evidences support the view that inflammatory mediators, some of that may downregulate DNA repair pathways directly or indirectly. Certain inflammatory mediators may affect on cell cycle checkpoints that result in the accumulation of random genetic alterations. These in turn lead to a genomically heterogenous population of expanding cells naturally selected for their ability to proliferate, invade and evade hose defenses (Colotta et al., 2009).