Vol 10, No 7 (2010)

Glioblastoma (GBM) is the most common type of primary malignant brain tumor. Despite advances in surgical resection, radiotherapy and chemotherapy, prognosis remains very poor. Accordingly, recent studies have been focused on the aberrant signal transduction pathways in glioblastoma. Many patient derived primary glioblastomas and cell lines express constitutively activated signal transducers and activators of transcription 3 (STAT3). Here we focused on the recent progresses regarding to the roles of STAT3 in glioblastoma and glioblastoma stem cells (GBM-SCs), the dysregulation of STAT3 in glioblastoma, and targeting STAT3 for glioblastoma therapy.

Patients with malignant gliomas have poor prognoses, and the majority of the patients have local tumor recurrence after various treatments including surgery, radiotherapy, and chemotherapy. Thus it is mandatory to develop better therapies for treatment of these malignant brain tumors. Tetrandrine, a bisbenzylisoquinoline alkaloid, has antitumor effects against some cancers. Tetrandrine affects the cell cycle, production of reactive oxygen species, mitogen-activated protein kinase activity, and reverses multidrug resistance in various cancer cells. Since tetrandrine is a highly lipid-soluble and hydrophobic molecule with a low molecular weight, it may cross the blood brain barrier; thus, it could be used for the treatment of gliomas. Tetrandrine inhibits the large-conductance, calcium-activated potassium (BK) channels and the expression of BK channel has a positive correlation with tumor malignancy grade in human gliomas. Furthermore, tetrandrine also exerts cytotoxic effects, and induces apoptosis and radiosensitization in glioma cells by elimination of radiation-induced cell cycle perturbation. It also has anti-angiogenesis effects in gliomas, and exerts an antitumor effect on subcutaneous and intracerebral gliomas. Tetrandrine is a radiosensitizer and also a multidrug resistance reversing agent. Tetrandrine can probably be combined with radiotherapy or other chemotherapeutic agents to treat gliomas. Nonetheless, it is important to determine the balance between the safety and efficacy of tetrandrine in patients with malignant gliomas before any clinical application.

Tetracyclines have been long known for their antimicrobial role. They are one of the most widely used antibiotics in clinical practice since last 5 decades. Recently their role as matrix metalloproteinase inhibitor and in apoptosis has widely attracted attention in biological field. Of them, doxycycline is one with long duration of actions and has recently been shown to have various anti-cancer properties, especially cytotoxic and anti-proliferative activities. Here, we systematically reviewed the role of doxycycline in the mitochondrial mediated apoptosis in various tissues. MEDLINE and EMBASE databases were searched using a formal search strategy with definite inclusion and exclusion criteria. Data extraction was performed for each included study using a custom designed data extraction form. A total of 81 references were identified through MEDLINE and 5 were identified through EMBASE. 74 references from MEDLINE and all 5 in EMBASE were excluded through reading titles, abstracts and full text. In total, 7 studies fulfilled inclusion criteria. Following systematic review of these studies, we concluded that doxycycline induces apoptosis through mitochondrial mediated pathway in different tissue cells however it may be cell specific. The caspase independent apoptosis as one of the mechanisms of actions of doxycycline needs further studies for better understanding.

Mammalian target of rapamycin (mTOR) is a central controller of cell growth, proliferation, metabolism and angiogenesis. mTOR signaling is often dysregulated in various human diseases and thus attracts great interest in developing drugs that target mTOR. Currently it is known that mTOR functions as two complexes, mTOR complex 1/2 (mTORC1/2). Rapamycin and its analogs (all termed rapalogs) first form a complex with the intracellular receptor FK506 binding protein 12 (FKBP12) and then bind a domain separated from the catalytic site of mTOR, blocking mTOR function. Rapalogs are selective for mTORC1 and effective as anticancer agents in various preclinical models. In clinical trials, rapalogs have demonstrated efficacy against certain types of cancer. Recently, a new generation of mTOR inhibitors, which compete with ATP in the catalytic site of mTOR and inhibit both mTORC1 and mTORC2 with a high degree of selectivity, have been developed. Besides, some natural products, such as epigallocatechin gallate (EGCG), caffeine, curcumin and resveratrol, have been found to inhibit mTOR as well. Here, we summarize the current findings regarding mTOR signaling pathway and review the updated data about mTOR inhibitors as anticancer agents.