Current Cancer Drug Targets - Volume 8, Issue 3, 2008

The total expression profiles of two medulloblastoma cell lines resistant to the preactivated form of cyclophosphamide (4-hydroperoxycyclophosphamide, 4-HC) were examined using the Affymetrix GeneChip U133A array. Our primary objective was to look for possible genes, other than the well-studied aldehyde dehydrogenases (ALDH) that may be involved in cyclophosphamide (CP) resistance in medulloblastomas. We present here the lists of the most highly upregulated [30 for D341 MED (4-HCR); 20 for D283 MED (4-HCR)] and downregulated [19 for D341 MED (4-HCR); 15 for D283 MED (4-HCR)] genes which may be involved in conferring CP-resistance to the two medullobalstoma cell lines. The lists of genes from the two sublines almost had no overlap, suggesting different mechanisms of CP-resistance. One of the most noteworthy upregulated gene is TAP1 [ 90-fold increase in D341 MED (4-HCR) relative to D341 MED ]. TAP1, a protein belonging to the ABC transporter family is normally involved in major histocompatibility class I (MHC I) antigen processing. This suggests the possible role of multidrug resistance (MDR), albeit atypical (which means it does not involve the usual MDR1 and MRP glycoproteins), in medulloblastoma's CP-resistance. Apart from TAP1, a number of other genes involved in MHC1 processing were upregulated in D341 MED (4HCR). D341 MED (4-HCR) also had a 20-fold increase in the expression of the aldo-keto reductase gene, AKR1B10, which may deactivate the reactive cyclophosphamide metabolite, aldophosphamide. For D283 MED (4-HCR), the most notable increase in expression is that of ALDH1B1, a member of the aldehyde dehydrogenase (ALDH) family of proteins.

Therapeutic strategies based on the insertion of cytokine or other immunostimulatory genes into the genome of tumour cells followed by vaccination with the resulting, genetically modified, cytokine-producing vaccines represent a new potential prospect for the treatment of cancer patients. HPV 16 is the aetiological agent of more than 60 percent human cervical carcinomas (CC). At present, two prophylactic vaccines against HPV 16 are available (GlaxoSmithKline “Cervarix” and Merck “Gardasil”). These vaccines can almost completely protect the immunized individuals against both, persistent HPV 16 infection and HPV 16-related pathological findings in cervical cytology. In contrast, no clinically utilizable therapeutic vaccines against CC are available. During the last decade animal models have substantially contributed to the development of the therapeutic vaccines against HPV 16-associated tumours. It has been demonstrated that the HPV 16 E6/E7 oncoproteins can serve as tumour rejection antigens (TRA) and that the HPV 16-associated tumour cells can be genetically modified with DNA encoding immunostimulatory cytokines (IL-2, IL-12, GM-CSF) or other immunostimulatory molecules, used for vaccination, and inhibit tumour growth. To improve the HPV 16 antigen presentation in tumour-bearing individuals, dendritic cell-based vaccines loaded with HPV 16 E6/E7 DNA or hybrids of the dendritic and tumour cells have also been successfully employed. Unfortunately, when these encouraging approaches used in animal models were translated into clinical trials, the results were less optimistic. The problems that are still to be faced before the therapeutic vaccines against high-risk HPV-associated tumours can be approved for clinical purposes are discussed.

PTEN/PI3K/AKT constitutes an important pathway regulating the signaling of multiple biological processes such as apoptosis, metabolism, cell proliferation and cell growth. PTEN is a dual protein/lipid phosphatase which main substrate is the phosphatidyl-inositol,3,4,5 triphosphate (PIP3), the product of PI3K. Increase in PIP3 recruits AKT to the membrane where it is activated by other kinases also dependent on PIP3. Many components of this pathway have been described as causal forces in cancer. PTEN activity is lost by mutations, deletions or promoter methylation silencing at high frequency in many primary and metastatic human cancers. Germ line mutations of PTEN are found in several familial cancer predisposition syndromes. Activating mutations which have been reported for PI3K and AKT, in tumours are able to confer tumourigenic properties in several cellular systems. Additionally, the binding of PI3K to oncogenic ras is essential for the transforming properties of ras. In summary, the data strongly support the view of the PTEN/PI3K/AKT pathway as an important target for drug discovery.

Background: Prostate adenocarcinoma is generally characterized by slow progression although some phenotypes have a more aggressive behavior with tendency to local invasion and distant metastases, mainly to bones. Better specific care could be provided to the aggressive phenotype-group of patients if pre-surgical identification were available. Material and Methods: Correlations between pre-surgical levels of 6 blood molecules and pathological tumour staging, post-surgical Gleason score and disease-free survival have been observed. Plasma and sera from 162 men affected by prostate adenocarcinoma were analysed with ELISA to assess levels of neovascularization-related molecule (VEGF), endothelial cell adhesion molecule (VCAM), extracellular matrix destruction- related molecules (MMP-2, MMP-9), and tissue inhibitors of metalloproteinase (TIMP-1 and TIMP-2). Results: The median values of serum determinations were for VEGF 279 pg/ml, VCAM 633 ng/ml, MMP-2 206 ng/ml and MMP-9 614 ng/ml. Plasma medians (ng/ml) were 94 for TIMP-1 and 90 for TIMP-2. Patients with VCAM values > 633 ng/ml had a worse disease-free survival than patients with values <633 ng/ml with an adjusted Hazard Ratio of 2.1, significant (95% confidence interval 0.8-5.6). Patients with levels of MMP-2 < 206 ng/ml showed an increased risk of progression (adjusted HR 1.7; 95% C.I. 0.6-4.8). Conclusions: Levels of VCAM and MMP-2 should be checked in patients with prostate adenocarcinoma, because distant spread is more likely to occur in patients with high levels of VCAM and low levels of MMP-2. The scientific community should further investigate impact on prognosis of VCAM and MMP-2.

Apoptosis plays a key role in the control of rapidly renewing tissues, such as the hematopoietic system and leukemia cells invariably have abnormalities in one or more apoptotic pathways, determining a survival advantage of these cells and the development of drug resistance. These defects are also frequently associated with a low rate of response to standard chemotherapy and with a poor survival in acute myeloid leukemia (AML). The major form of apoptosis proceeds through the mitochondrial pathway, with the mitochondrial outer membrane permeabilization, leading to the release of proteins normally found in the space between the inner and outer mitochondrial membranes (cytochrome C, AIF and others). Higher levels of anti-apoptosis proteins bcl-2, bcl-xL, Mcl-1 block permeabilization of the membrane and are reported in AML patients presenting a poor outcome. On the contrary, activated pro-apoptotic bax or bad proteins allow this permeabilization and are correlated to a good prognosis in AML. Defects in the mitochondrial pathway induce multidrugresistance and confer important prognostic information in AML. High ratios of bcl-2 to bax protein confer a poor prognosis with decreased rates of complete remission and overall survival. The prognostic information from the ratio of the proteins is greater than bcl-2 levels alone. Recently, we confirmed the impressive impact of the bax/bcl-2 ratio, determined by flow cytometry, on AML prognosis (complete remission and overall survival) in 255 AML patients. Bcl-2 down regulation might lower the apoptotic threshold of leukemic cells and, through this mechanism, favor response to chemotherapy. Phase II studies of oblimersen (antisense Bcl-2), cytarabine and daunorubicin or oblimersen plus gentuzumab, a cytotoxic antibody directed against CD33+ cells in relapsed AMLs, showed promising results. Defects in apoptosome proteins, such as APAF-1, are frequent in AML and treatment with 5-aza-2'-deoxycytidine, a specific inhibitor of DNA methylation, restored APAF-1 expression in leukemic cells. In conclusion, targeted therapies that are designed to induce apoptosis in leukemic cells, are the most promising anti-leukemia strategies. The elucidation of the apoptotic machinery and of its defects in AML lays the basis for developing new drugs able to trigger apoptosis and overcome therapy resistance.

Proline directed phosphorylation is a key regulatory mechanism controlling the function of fundamental proteins involved in cell proliferation and oncogenic transformation. Recently, the identification of the phosphorylation dependent prolyl isomerase Pin1 has uncovered a distinct regulatory mechanism controlling protein function. Specifically, Pin1 controls the conversion of peptidyl proline bond conversion from cis to trans, only when the preceding serine or threonine is phosphorylated. The intrinsic inter-conversion of such bonds is rather slow and is further inhibited by phosphorylation. As a consequence catalysis by Pin1 is required to overcome this restriction. Importantly, structural evidence has now demonstrated that Pin1-catalyzed prolyl isomerization can have significant effects on the global structure of substrate proteins. Furthermore, Pin1 overexpression is found in several types of cancer where it functions to not only promote tumorigenesis induced by oncogenes such as Ras and Neu, but also to regulate molecules that facilitate persistent proliferative capacity. Consequently, Pin1-mediated phosphorylation-dependent isomerization represents a unique regulatory mechanism in cell signaling whose deregulation during tumorigenesis adds to the pro-proliferative capacity of tumor cells and therefore Pin1 represents a novel tumor marker and potential therapeutic target.

CpG are powerful drugs activating the innate immune system. In this study, the ability of their intramammary administration in impeding the devastating progression of carcinogenesis in all the mammary glands of female BALB/c mice transgenic for the rat neu transforming oncogene was assessed. Starting when in situ carcinomas were scattered over all their mammary glands (week 10), mice received CpG injections in the stroma of the fourth left gland. Local neoplastic progression was inhibited by six monthly administrations. CpG not only delayed the onset of carcinomas in the injected gland, but also hampered their progression. Extended latency was observed for tumors in glands both close to and far from the injection site. When the experiment ended (week 45), no tumors were palpable in 67% of the injected glands and a markedly impaired tumor growth was evident in the others. An impressive local infiltrate of CD11b+ cells with the morphologic features of macrophages, plasma cells, B220+ B cells, and CD4+ and CD8+ T cells was quickly recruited to the CpG-treated glands. High quantities of IFN-γ producing cells were only present in the ipsilateral axillary draining lymph nodes of the treated glands. Enhanced natural killer (NK) lytic activity was also detected in the spleens. Inhibition of progression was weaker when only four injections were given, and abolished by in vivo depletion of NK cells. CpG monotherapy is thus effective in an aggressive model of autochthonous cancer. The results strongly support the administration of CpG as a local monotherapy of multiple invasive microscopic lesions.