[Abstract unavailable

Poor chemosensitivity and the development of chemoresistance remain major obstacles to successful chemotherapy of malignant gliomas. GRP78 is a key regulator of the unfolded protein response (UPR). As a Ca 2+ -binding molecular chaperone in the endoplasmic reticulum (ER), GRP78 maintains ER homeostasis, suppresses stress-induced apoptosis, and controls UPR signaling. We report here that GRP78 is expressed at low levels in normal adult brain, but is significantly elevated in malignant glioma specimens and human malignant glioma cell lines, correlating with their rate of proliferation. Down-regulation of GRP78 by small interfering RNA leads to a slowdown in glioma cell growth. Our studies further reveal that temozolomide, the chemotherapeutic agent of choice for treatment of malignant gliomas, leads to induction of CHOP, a major proapoptotic arm of the UPR. Knockdown of GRP78 in glioblastoma cell lines induces CHOP and activates caspase-7 in temozolomide-treated cells. Colony survival assays further establish that knockdown of GRP78 lowers resistance of glioma cells to temozolomide, and, conversely, overexpression of GRP78 confers higher resistance. Knockdown of GRP78 also sensitizes glioma cells to 5-fluorouracil and CPT-11. Treatment of glioma cells with (À)-epigallocatechin gallate, which targets the ATP-binding domain of GRP78 and blocks its protective function, sensitizes glioma cells to temozolomide. These results identify a novel chemoresistance mechanism in malignant gliomas and show that combination of drugs capable of suppressing GRP78 with conventional agents such as temozolomide might represent a novel approach to eliminate residual tumor cells after surgery and increase the effectiveness of malignant glioma chemotherapy. [Cancer Res 2007;67(20):9809-16]

The endoplasmic reticulum (ER) is a multifunctional organelle required for lipid biosynthesis, calcium storage, and protein folding and processing. A number of physiological and pathological conditions, as well as a variety of pharmacological agents, are able to disturb proper ER function and thereby cause ER stress, which severely impairs protein folding and therefore poses the risk of proteotoxicity. Specific triggers for ER stress include, for example, particular intracellular alterations (e.g., calcium or redox imbalances), certain microenvironmental conditions (e.g., hypoglycemia, hypoxia, and acidosis), high-fat and high-sugar diet, a variety of natural compounds (e.g., thapsigargin, tunicamycin, and geldanamycin), and several prescription drugs (e.g., bortezomib/Velcade, celecoxib/Celebrex, and nelfinavir/Viracept). The cell reacts to ER stress by initiating a defensive process, called the unfolded protein response (UPR), which is comprised of cellular mechanisms aimed at adaptation and safeguarding cellular survival or, in cases of excessively severe stress, at initiation of apoptosis and elimination of the faulty cell. In recent years, this dichotomic stress response system has been linked to several human diseases, and efforts are underway to develop approaches to exploit ER stress mechanisms for therapy. For example, obesity and type 2 diabetes have been linked to ER stress-induced failure of insulin-producing pancreatic beta cells, and current research efforts are aimed at developing drugs that ameliorate cellular stress and thereby protect beta cell function. Other studies seek to pharmacologically aggravate chronic ER stress in cancer cells in order to enhance apoptosis and achieve tumor cell death. In the following, these principles will be presented and discussed.

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The anticancer potency of green tea and its individual components is being intensely investigated, and some cancer patients already self-medicate with this "miracle herb" in hopes of augmenting the anticancer outcome of their chemotherapy. Bortezomib (BZM) is a proteasome inhibitor in clinical use for multiple myeloma. Here, we investigated whether the combination of these compounds would yield increased antitumor efficacy in multiple myeloma and glioblastoma cell lines in vitro and in vivo. Unexpectedly, we discovered that various green tea constituents, in particular (-)-epigallocatechin gallate (EGCG) and other polyphenols with 1,2-benzenediol moieties, effectively prevented tumor cell death induced by BZM in vitro and in vivo. This pronounced antagonistic function of EGCG was evident only with boronic acid-based proteasome inhibitors (BZM, MG-262, PS-IX), but not with several nonboronic acid proteasome inhibitors (MG-132, PS-I, nelfinavir). EGCG directly reacted with BZM and blocked its proteasome inhibitory function; as a consequence, BZM could not trigger endoplasmic reticulum stress or caspase-7 activation, and did not induce tumor cell death. Taken together, our results indicate that green tea polyphenols may have the potential to negate the therapeutic efficacy of BZM and suggest that consumption of green tea products may be contraindicated during cancer therapy with BZM. (Blood. 2009;113:5927-5937) IntroductionHerbal supplements are commonly perceived as "innocent" or "holistic" and have become hugely popular as unrestrictedly available, over-the-counter, cure-all remedies. Cancer patients in particular may be tempted to self-medicate with such supplements in hopes to delay the progression of their disease and/or reduce the side effects associated with conventional chemotherapy, 1-3 and they may do this unbeknownst to their health care providers. 2,3 One very popular herb is green tea, brewed from the leaves of the plant Camellia sinensis, which appears to be an ideal alternative medicine because it is nontoxic and shown to have cardioprotective, neuroprotective, anti-infective, and antitumoral properties. [4][5][6][7][8][9][10] Green tea products are also available as highly concentrated extracts, which can be easily accessed by the public at local grocery, pharmacy, and health food stores throughout the United States.Green tea is a heterogeneous product that contains several antioxidant compounds, known as polyphenols. (-)-Epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), (-)-epigallate catechin (EGC), and (-)-epicatechin (EC) are some of the polyphenol compounds found in green tea. 9 EGCG, the most bioactive green tea polyphenol, was demonstrated to be a multipotent chemopreventive and anticancer agent in several animal models, including leukemia, lung, prostate, colon, and breast cancer. 9,[11][12][13][14][15] It was shown to interact with numerous protein targets and to disrupt biologic/biochemical reactions involved in cancer progression. The EGCG compound can vary its chemical conf...

Androgen plays a critical role in regulating the growth and differentiation of normal prostate epithelia, as well as the initial growth of prostate cancer cells. Nevertheless, prostate carcinomas eventually become androgen-unresponsive, and the cancer is refractory to hormonal therapy. To gain insight into the mechanism involved in this hormone-refractory phenomenon, we have examined the potential role of the androgen receptor (AR) in that process. We have investigated the expression of AR and two prostate-specific androgen-responsive antigens, prostatic acid phosphatase (

Overexpression of p53 causes G2 arrest, attributable in part to the loss of CDC2 activity. Transcription of cdc2 and cyclin B1, determined using reporter constructs driven by the two promoters, was suppressed in response to the induction of p53. Suppression requires the regions Ϫ287 to Ϫ123 of the cyclin B1 promoter and Ϫ104 to Ϫ74 of the cdc2 promoter. p53 did not affect the inhibitory phosphorylations of CDC2 at threonine 14 or tyrosine 15 or the activity of the cyclin-dependent kinase that activates CDC2 by phosphorylating it at threonine 161. Overexpression of p53 may also interfere with the accumulation of CDC2/cyclin B1 in the nucleus, required for cells to enter mitosis. Constitutive expression of cyclin B1, alone or in combination with the constitutively active CDC2 protein T14A Y15F, did not reverse p53-dependent G2 arrest. However, targeting cyclin B1 to the nucleus in cells also expressing CDC2 T14A Y15F did overcome this arrest. It is likely that several distinct pathways contribute to p53-dependent G2 arrest. INTRODUCTIONThe p53 tumor suppressor helps to protect mammals from developing neoplasia by blocking cell cycle progression or by inducing cell death in response to stress Levine, 1997;Agarwal et al., 1998b). p53-mediated arrest at the G1-S boundary prevents the replication of DNA damaged by ionizing or UV radiation or by chemical mutagens (Kastan et al., 1991;Gujuluva et al., 1994;Ceraline et al., 1998). G1 arrest depends on the ability of p53 to activate the transcription of specific genes (Dulic et al., 1994;Pietenpol et al., 1994). An important target, p21/waf1, inhibits cyclin-dependent kinases (CDKs) 1 2, 4, and 6, which are required to enter S phase (El-Deiry et al., 1993;Harper et al., 1993;Xiong et al., 1993). p53 also inhibits S-phase entry in response to damage to the mitotic spindle, preventing the rereplication of DNA (Cross et al., 1995), possibly by a transcription-independent mechanism (Notterman et al., 1998). p53 mediates G1 arrest in response to nucleotide deprivation, preventing DNA synthesis under conditions that would generate damaged DNA (Chernova et al., 1995;Linke et al., 1996). p53 also protects cells arrested within S phase by a lack of pyrimidine nucleotides, preventing the replication from unbalanced pools of deoxynucleoside triphosphates and consequent DNA damage (Agarwal et al., 1998a). A variety of stimuli that trigger p53-dependent cellular responses increase the ability of p53 to bind to DNA and induce the accumulation of the protein, attributable in large part to an increase in its stability (Maltzman and Czyzyk, 1984;Fritsche et al., 1993;Hupp et al., 1995). Responses to p53 vary in different types of cells and depend on the level of p53 expression. For example, thymocytes undergo p53-dependent apoptosis more readily than do fibroblasts (Lowe et al., 1993;Di Leonardo et al., 1994). In some cells, high levels of p53 induce apoptosis, whereas lower levels induce cell cycle arrest (Chen et al., 1996).p53 plays an important role in regulating the G2-M transition. ...