Defining the localization and molecular characteristic of minor salivary gland label-retaining cells.

Adult stem cells (SCs) are important to maintain homeostasis of tissues including several mini-organs like hair follicles and sweat glands. However, the existence of stem cells in minor salivary glands (SGs) is largely unexplored. In vivo histone2B green fluorescent protein pulse chase strategy has allowed us to identify slow-cycling, label-retaining cells (LRCs) of minor SGs that preferentially localize in the basal layer of the lower excretory duct with a few in the acini. Engraftment of isolated SG LRC in vivo demonstrated their potential to differentiate into keratin 5 (basal layer marker) and keratin 8 (luminal layer marker)-positive structures. Transcriptional analysis revealed activation of TGFß1 target genes in SG LRC and BMP signaling in SG progenitors. We also provide evidence that minor SGSCs are sensitive to tobacco-derived tumor-inducing agent and give rise to tumors resembling low grade adenoma. Our data highlight for the first time the existence of minor SG LRCs with stem cells characteristic and emphasize the role of transforming growth factor beta (TGFß) pathway in their maintenance.

Gold nanorod-sphingosine kinase siRNA nanocomplexes: a novel therapeutic tool for potent radiosensitization of head and neck cancer.

Radiation therapy (RT) is an important treatment modality used against a number of human cancers, including head and neck squamous cell carcinoma (HNSCC). However, most of these cancers have an inherent anti-apoptotic mechanism that makes them resistant to radiation therapy. This radioresistance of cancer cells necessitates the irradiation of tumor areas with extremely high doses of radiation to achieve effective therapy, resulting in damage to normal tissues and leading to several treatment related side effects. These side effects significantly impair the quality of life of treated patients, and preclude the possibility of repeat radiation treatment in patients with tumor recurrence. Our previous research has correlated the upregulation of the anti-apoptotic sphingosine kinase (SphK1) gene in HNSCC cells with their radioresistance properties. In the current study, we hypothesized that by downregulating the SphK1 gene using nanotechnology mediated gene silencing, we can render these cells more vulnerable to radiation therapy by enabling apoptosis at lower radiation doses. We have employed biocompatible gold nanorods (GNRs) as carriers of short interfering RNA (siRNA) targeting the SphK1 gene. GNRs play a critical role in protecting the siRNA molecules against physiological degradation, as well as delivering them inside target cells. Following their synthesis and characterization, these nanoplexes were applied to HNSCC cells in culture, resulting in the radiosensitization of the treated cells. Furthermore, the GNR-siRNA nanoplexes were injected intratumorally into subcutaneous HNSCC tumors grown in mice, prior to the initiation of radiation therapy in vivo. Subsequent exposure of GNR-SphK1siRNA nanoplex-treated tumors to radiation (GNR-SphK1siRNA + IRRA) resulted in over 50% tumor regression compared to control GNR-GFPsiRNA nanoplex and radiation treated tumors (GNR-GFPsiRNA + IRRA). In addition, we were able to induce this tumor regression in nanoplex treated tumors with radiation doses much lower than those commonly required in clinical RT. These experiments lay the foundation for the development of a nanotechnology-mediated gene silencing tool for more potent radiation therapy of a number of human cancers, with minimal, if any, toxic side effects.