TCTP as therapeutic target in cancers.

The translationally controlled tumor protein (TCTP) is a highly conserved protein present in eukaryotic organisms. This protein, located both in the cytoplasmic and the nucleus, is expressed in various tissues and is regulated in response to a wide range of extracellular stimuli. TCTP interacts with itself and other protein including MCL1 and p53. TCTP has been shown to play an important role in physiological events, such as cell proliferation, cell death and immune responses but also in stress response and tumor reversion. Moreover, TCTP expression is associated with malignancy and chemoresistance. In this review, we will evaluate pathways regulated by TCTP and current inhibitory strategy to target TCTP in cancerous diseases.

Hsp27 as a therapeutic target in cancers.

Heat shock protein 27 (Hsp27), induced by heat shock, environmental and pathophysiological stressors, is a multidimensional protein that acts as a protein chaperone and an antioxidant. This protein plays a major role in the inhibition of apoptosis and actin cytoskeletal remodeling. This stress-activated protein is up-regulated in many cancers and is associated with poor prognosis as well as treatment resistance by protecting cells from therapeutic agent that normally induces apoptosis. This review highlights the most recent findings and role of Hsp27 in cancer and the different strategies to target and inhibit Hsp27 for clinical purposes.

Adrenomedullin blockade suppresses growth of human hormone-independent prostate tumor xenograft in mice.

PURPOSE: To study the role of the adrenomedullin system [adrenomedullin and its receptors (AMR), CLR, RAMP2, and RAMP3] in prostate cancer androgen-independent growth. EXPERIMENTAL DESIGN: Androgen-dependent and -independent prostate cancer models were used to investigate the role and mechanisms of adrenomedullin in prostate cancer hormone-independent growth and tumor-associated angiogenesis and lymphangiogenesis. RESULTS: Adrenomedullin and AMR were immunohistochemically localized in the carcinomatous epithelial compartment of prostate cancer specimens of high grade (Gleason score >7), suggesting a role of the adrenomedullin system in prostate cancer growth. We used the androgen-independent Du145 cells, for which we demonstrate that adrenomedullin stimulated cell proliferation in vitro through the cAMP/CRAF/MEK/ERK pathway. The proliferation of Du145 and PC3 cells is decreased by anti-adrenomedullin antibody (αAM), supporting the fact that adrenomedullin may function as a potent autocrine/paracrine growth factor for prostate cancer androgen-independent cells. In vivo, αAM therapy inhibits the growth of Du145 androgen-independent xenografts and interestingly of LNCaP androgen-dependent xenografts only in castrated animals, suggesting strongly that adrenomedullin might play an important role in tumor regrowth following androgen ablation. Histologic examination of αAM-treated tumors showed evidence of disruption of tumor vascularity, with depletion of vascular as well as lymphatic endothelial cells and pericytes, and increased lymphatic endothelial cell apoptosis. Importantly, αAM potently blocks tumor-associated lymphangiogenesis, but does not affect established vasculature and lymphatic vessels in normal adult mice. CONCLUSIONS: We conclude that expression of adrenomedullin upon androgen ablation in prostate cancer plays an important role in hormone-independent tumor growth and in neovascularization by supplying/amplifying signals essential for pathologic neoangiogenesis and lymphangiogenesis. Clin Cancer Res; 19(22); 6138-50. ©2013 AACR.

Targeting TCTP as a new therapeutic strategy in castration-resistant prostate cancer.

Heat shock protein 27 (Hsp27) is highly overexpressed in castration-resistant prostate cancer (CRPC) and an antisense inhibitor (OGX-427) is currently in phase II clinical trials. In order to understand mechanisms of action of Hsp27 and find new therapeutic targets specific of CRPC, we screened for Hsp27 client proteins. Here, we report that translationally controlled tumor protein (TCTP) is a new Hsp27 client protein involved in Hsp27 cytoprotection. We found that TCTP expression is absent or weak in normal prostate cells, moderately expressed in 18.5% of treatment naive PC, and becomes uniformly and strongly expressed in 75% of CRPC. To define TCTP function, we developed and worldwide patented a TCTP antisense oligonucleotide (ASO). Interestingly, we found that CRPC progression correlates with TCTP overexpression and loss of P53. TCTP knockdown restored P53 expression and function, suggesting that castration-sensitivity is directly linked to P53 expression. Collectively, these findings provide a new Hsp27 cytoprotection mechanism in CRPC, and preclinical proof-of-concept that combining ASO-mediated TCTP knockdown with castration and/or docetaxel therapy could serve as a novel strategy to treat CRPC, with no or little toxicity for normal prostate cells.

Small heat shock proteins HSP27 (HspB1), αB-crystallin (HspB5) and HSP22 (HspB8) as regulators of cell death.

Hsp27, αB-crystallin and HSP22 are ubiquitous small heat shock proteins (sHsp) whose expression is induced in response to a wide variety of unfavorable physiological and environmental conditions. These sHsp protect cells from otherwise lethal conditions mainly by their involvement in cell death pathways such as necrosis, apoptosis or autophagy. At a molecular level, the mechanisms accounting for sHsp functions in cell death are (1) prevention of denatured proteins aggregation, (2) regulation of caspase activity, (3) regulation of the intracellular redox state, (4) function in actin polymerization and cytoskeleton integrity and (5) proteasome-mediated degradation of selected proteins. In cancer cells, these sHsp are often overexpressed and associated with increased tumorigenicity, cancer cells metastatic potential and resistance to chemotherapy. Altogether, these properties suggest that Hsp27, αB-crystallin and Hsp22 are appropriate targets for modulating cell death pathways. In the present, we briefly review recent reports showing molecular evidence of cell death regulation by these sHsp and co-chaperones. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Inactivation of PITX2 transcription factor induced apoptosis of gonadotroph tumoral cells.

Nonfunctioning pituitary adenomas (NFPA; gonadotroph derived), even not inducing hormonal hypersecretion, cause significant morbidity by compression neighboring structures. No effective and specific medical methods are available so far for treating these tumors. The pituitary homeobox 2 (PITX2) gene is a member of the bicoid-like homeobox transcription factor family, which is involved in the Wnt/Dvl/ß-catenin pathway. PITX2 is overexpressed in NFPA. PITX2 mutations are known to be responsible for Axenfield Rieger syndrome, a genetic disorder in which pituitary abnormalities have been detected. The R91P mutant identified in Axenfeld Rieger syndrome is a dominant-negative factor, which is able to block the expression of several pituitary genes activated by PITX2. To better understand the role of Pitx2 on gonadotroph tumorigenesis and to explore new approach for inhibiting tumoral growth, the R91P mutant was transferred via a lentiviral vector in tumoral gonadotroph cells of two kinds: the αT3-1 cell line and human adenoma cells. R91P mutant and small interfering RNA directed against Pitx2 both decreased the viability of αT3-1 cells via an apoptotic mechanism involving the activation of executioner caspase. Similar effects of the R91P mutant were observed on human gonadotroph cells in primary culture. Therefore, Pitx2 overexpression may play an antiapoptotic role during NFPA tumorigenesis.

Somatostatin receptor sst2 decreases cell viability and hormonal hypersecretion and reverses octreotide resistance of human pituitary adenomas.

In human somatotroph adenomas, growth hormone (GH) hypersecretion can be inhibited by somatostatin analogues such as octreotide. Unfortunately, serum GH levels reach normal values in only 60% of treated patients. The decreased sensitivity to octreotide is strongly related to a lower expression of somatostatin receptor sst2. In this present study, the sst2 gene was transferred by an adenoviral vector (Ad-sst2) in human somatotroph (n = 7) and lactotroph (n = 2) adenomas in vitro. Sst2 mRNA levels and sst2 immunostaining dramatically increased after infection. Ten days after infection at 20 multiplicity of infection (MOI), sst2 gene transfer decreased cell viability from 19% to 90% by caspase-dependent apoptosis. At low viral doses (5 MOI), Ad-sst2 decreased GH or prolactin (PRL) basal secretion and mRNA expression. Somatotroph tumors were classified in three groups according to their octreotide sensitivity. Four days after infection by 5 MOI Ad-sst2, the maximal GH suppression by octreotide increased from 31% to 57% in the octreotide partially resistant group and from 0% to 27% in the resistant ones. In the octreotide-sensitive group, EC(50) values significantly decreased from 1.3 x 10(-11) to 6.6 x 10(-13) mol/L without improving maximal GH suppression. Finally, lactotroph tumors, nonresponding to octreotide in basal conditions, became octreotide sensitive with a maximal PRL suppression of 43% at 10(-8) mol/L. Therefore, sst2 reexpression is able to improve octreotide sensitivity. Sst2 gene transfer may open new therapeutic strategies in treatment combined with somatostatin analogues.