A small molecule inhibitor of isoprenylcysteine carboxymethyltransferase induces autophagic cell death in PC3 prostate cancer cells.

A number of proteins involved in cell growth control, including members of the Ras family of GTPases, are modified at their C terminus by a three-step posttranslational process termed prenylation. The enzyme isoprenylcysteine carboxylmethyl-transferase (Icmt) catalyzes the last step in this process, and genetic and pharmacological suppression of Icmt activity significantly impacts on cell growth and oncogenesis. Screening of a diverse chemical library led to the identification of a specific small molecule inhibitor of Icmt, cysmethynil, that inhibited growth factor signaling and tumorigenesis in an in vitro cancer cell model (Winter-Vann, A. M., Baron, R. A., Wong, W., dela Cruz, J., York, J. D., Gooden, D. M., Bergo, M. O., Young, S. G., Toone, E. J., and Casey, P. J. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 4336-4341). To further evaluate the mechanisms through which this Icmt inhibitor impacts on cancer cells, we developed both in vitro and in vivo models utilizing PC3 prostate cancer cells. Treatment of these cells with cysmethynil resulted in both an accumulation of cells in the G(1) phase and cell death. Treatment of mice harboring PC3 cell-derived xenograft tumors with cysmethynil resulted in markedly reduced tumor size. Analysis of cell death pathways unexpectedly showed minimal impact of cysmethynil treatment on apoptosis; rather, drug treatment significantly enhanced autophagy and autophagic cell death. Cysmethynil-treated cells displayed reduced mammalian target of rapamycin (mTOR) signaling, providing a potential mechanism for the excessive autophagy as well as G(1) cell cycle arrest observed. These results identify a novel mechanism for the antitumor activity of Icmt inhibition. Further, the dual effects of cell death and cell cycle arrest by cysmethynil treatment strengthen the rationale for targeting Icmt in cancer chemotherapy.

Combinatorial-approached neuroprotection using pan-caspase inhibitor and poly (ADP-ribose) polymerase (PARP) inhibitor following experimental stroke in rats; is there additional benefit?

Energy requiring apoptosis and presumably unregulated necrosis are considered conceptually and morphologically distinct forms of cell death which have been initially identified as two exclusive pathways. However, several apoptotic characteristics have been observed in the necrotic core lesion in ischemia which led to the controversial theory that cell death advances via a number of hybrid pathways among a continuum between the two processes. ATP availability has been shown to influence the decision between apoptosis and necrosis. The aims of our study are 1) to determine if combined inhibitors administration of pan-caspase inhibitor Carbobenzoxy-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk) and non-selective poly (ADP-ribose) polymerase (PARP) inhibitor 3-aminobenzamide (3-AB) can further reduce infarct volume compared to single modality of either inhibitor following ischemic insult, 2) to ascertain the pharmacological intervention up to 24 hour post-middle cerebral artery occlusion (MCAo), and 3) to correlate intracellular ATP level with infarct volume. Single modality treatment was optimised at 3 mg/kg z-VAD-fmk and 30 mg/kg 3-AB with infarct volume measured at 24.13%+/-3.89% and 26.98%+/-2.22% respectively, while untreated control group was determined at 45.97%+/-1.86%. Combined inhibitors treatment rendered further reduction in infarct volume, measuring 7.228%+/-1.988%, 21.02%+/-1.06%, 24.40%+/-2.12% at 30 min, 6 h, 24 h post-ischemia respectively. In conclusion, the combined inhibitors administration of both z-VAD-fmk and 3-AB show further increased in infarct volume reduction with our ischemic model up to the 24 hour post-MCAo. However, in our in vivo study, no correlation between intracellular ATP level and infarct size was established.

Hypoxia inducible factor-1alpha and expression of vascular endothelial growth factor and its receptors in cerebral arteriovenous malformations.

BACKGROUND: Vascular endothelial growth factor (VEGF) and its tyrosine kinase family of receptors (VEGFR) (Flt-1, Flk-1, Flt-4) have been implicated in vascular angiogenesis and remodelling in cerebral arteriovenous malformations (CAVM). In this study, we investigate the role of hypoxia inducible factor-1 (HIF-1alpha) in CAVM and its relationship to VEGF and VEGFR. METHODS: Surgical specimens from 26 patients undergoing CAVM resection were studied for HIF-1alpha , VEGF, Flt-1, Flk-1 and Flt-4. The mean age was 34.08 +/- 14.18 years. Twenty-one patients presented with intracerebral haemorrhage. RESULTS: VEGF, Flt-1 and Flt-4 were expressed in all specimens. Flk-1 was expressed in 15 of 26 patients. HIF-1alpha was expressed in 15 of 26 patients. HIF-1alpha expression was significantly associated with VEGF, Flt-1 and Flk-1 expression (p < 0.05) CONCLUSIONS: HIF-1alpha is expressed in human CAVM. The expression of HIF-1alpha is significantly related to VEGF and VEGFR expression, suggesting a possible role for its induction and role in maintaining angiogenesis and vascular remodelling.

p53 point mutation is rare in meningiomas from Singaporean patients.

In Asian populations, meningiomas account for up to 35% of all central nervous system tumours, a significantly higher incidence than in Caucasian populations. While several studies have examined p53 both at the level of the gene and the protein in both benign and malignant meningiomas, its role remains controversial, particularly with regard to the discrepancy between p53 over-expression and gene mutation. We examined 19 benign meningiomas, all of which were known to over-express p53, and eight malignant meningiomas, of which three were known to over-express p53, for mutations in the p53 gene using polymerase chain reaction amplification and direct sequencing of exons 4 to 9, inclusive. Only one single mutation was detected in a benign meningioma, confirming that p53 over-expression in meningiomas is commonly found in the absence of gene mutations, and that despite the significantly higher incidence of meningiomas in some Asian populations, this is not associated with a significantly higher rate of p53 mutations.

Expression of the inhibitor of apoptosis protein survivin in benign meningiomas.

Survivin is a recently characterised inhibitor of apoptosis protein that has been implicated in the pathogenesis of several types of solid organ cancer. This study sought to describe the expression of survivin in a cohort of 90 benign meningiomas, together with the pattern of expression of other genes involved in the apoptotic process, namely bax and bcl2. Survivin expression was noted in 94% (85/90) of samples and was not correlated with the expression of either bax or bcl2 or with clinicopathological factors.

Expression of extracellular matrix markers in benign meningiomas.

Meningiomas have mesenchymal differentiation and studies have confirmed that meningiomas express intermediate filaments of both mesenchymal and epithelial types including vimentin and keratin. To further characterize their mesenchymal properties, particularly the role of factors requiring adhesion, extracellular matrix degradation, and migration, meningiomas were examined for a panel of extracellular matrix markers. Immunoreactivity to the matrix metalloproteinases, MMP-2 and MMP-9, and their tissue inhibitor, TIMP-1, and to an adhesion factor, galectin-3 were found in the majority of cases. The present study suggests that expression of these factors in benign meningiomas is ubiquitous and unrelated to tumor location. Therefore, these factors of the extracellular matrix may be potential targets of future therapy.

Overexpression of mdm2 and p53 and association with progesterone receptor expression in benign meningiomas.

The progesterone receptor is frequently found expressed in meningiomas at robust levels. As several studies of breast and endometrial tumors have shown an inverse correlation between progesterone receptor expression and p53 overexpression, we sought to determine if a similar relationship existed in meningiomas. As p53 may also be inactivated by the overexpression of mdm2, we examined a cohort of 90 benign meningiomas immunohistochemically for the presence of the progesterone receptor as well as overexpression of p53 and mdm2. The progesterone receptor was detected in 67% (61/90) of cases, while p53 and mdm2 overexpression were detected in 14% (13/90) and 46% (42/90) of cases, respectively. An absolute correlation was observed between the overexpression of nuclear mdm2 and overexpression of the progesterone receptor, with nuclear mdm2 overexpression being confined to progesterone receptor-positive tumors (P = 0.001). While p53 overexpression was not associated with progesterone receptor expression, a combination of mdm2 overexpression and/or p53 overexpression was significantly associated with the presence of the progesterone receptor (P = 0.025). These results suggest the existence of a novel relationship between p53 (and its regulatory control) and the presence of the progesterone receptor and, as such, may have fundamental consequences in developing progesterone receptor-targeted therapies for meningiomas.

Expression of survivin in primary glioblastomas.

PURPOSE: Studies in several tumour types have suggested that the inappropriate expression of the novel inhibitor of apoptosis protein survivin may play a key role in tumourigenesis. This study presents the first immunohistochemical examination of survivin expression in glioblastomas. METHOD: The cohort consisted of 39 ethnic Chinese patients diagnosed with primary glioblastoma multiforme. Samples were archival paraffin-embedded blocks. Concomitant with examination for survivin expression, samples were also examined for over-expression of the p53 protein as well as for evidence of apoptotic cells via the terminal deoxynucleotide transferease (TdT) mediated nick end labelling (TUNEL) technique. RESULTS: Results showed that survivin was expressed in nearly 80% (31/39) of samples. Over-expression of moderate or high levels of survivin was correlated with the absence of apoptotic cells ( P=0.03). Expression of survivin and p53 was found to be significantly related ( P=0.037), and 70% (27/39) of tumours showed co-ordinate expression of p53 and survivin. CONCLUSION: Given that p53 over-expression in primary glioblastomas is predominantly detected in the absence of mutations of the gene, and that both survivin and p53 are regulated at the level of the protein by the same ubiquitin-proteosome degradation pathway, these results suggest that primary glioblastomas may occur as a result of a failure of appropriate protein degradation regulation.

Glioblastoma multiforme in an Asian population: evidence for a distinct genetic pathway.

In Singapore astrocytic tumours occur in only 25% of patients with primary brain tumours compared to 40-60% in other series. Glioblastoma multiforme arises either de novo as a primary glioblastomas associated with epidermal growth factor receptor (EGFR) and mdm2 over-expression or as a secondary glioblastomas, through malignant progression from low-grade astrocytomas, associated with p53 mutations and PDGFR-alpha over-expression. Using immunohistochemical methods and DNA sequencing, we studied our population of glioblastomas for overexpression of EGFR, mdm2, p53, and PDGFR-alpha as well directly for mutations of the p53 gene. While levels of over-expression of EGFR and mdm2 were consistent with levels expected for primary glioblastomas, levels of p53 and PDGFR-alpha were consistent with levels documented for secondary glioblastomas. Notably 96% of the samples over-expressed p53 as detected with monoclonal antibody pAb 240. Of the 39 samples available for DNA sequencing 18% (7/39) had p53 mutations, including three mutations previously undocumented in glioblastomas. These results provide strong evidence that glioblastomas in Asian patients do not conform to currently accepted models of glioblastoma development, and that clinically defined glioblastomas in these patients show genetic changes consistent with both 'primary' and 'secondary' glioblastomas.