Current Cancer Drug Targets - Volume 4, Issue 6, 2004

Nerve growth factor (NGF) has long been known for its effects on neuronal cell survival and differentiation. This prototypical neurotrophic factor stimulates neurons through two distinct classes of membrane receptors: the TrkA tyrosine kinase receptor, and the tumor necrosis factor receptor family member p75NTR, also known as the common neurotrophin receptor. Somewhat surprisingly, there is a growing body of evidence indicating that NGF is also a major stimulator of breast cancer cell growth. Both the survival and proliferation of breast cancer cells are strongly stimulated by NGF, mediated by TrkA and p75NTR respectively, utilising signaling pathways similar to those described for neurons. In addition, although NGF is produced by breast cancer cells, it is not in normal breast epithelial cells, giving rise to an autocrine stimulation of tumor growth. Therefore, NGF receptors and signaling are thus looking increasingly promising as potential drug targets for breast cancer.

Heparin affin regulatory peptide (HARP), also known as pleiotrophin or heparin-binding growthassociated molecule, is an 18-kDa growth factor that has a high affinity for heparin. It constitutes with midkine and retinoic acid heparin-binding protein, a family of structurally related heparin-binding growth factors. A growing body of evidence indicates that HARP is involved in the control of cellular proliferation, migration and differentiation and plays a significant role in tumor growth and angiogenesis. HARP has a well described role in physiological as well as tumor angiogenesis, and is detected in various carcinomas, such as human breast and prostate cancer, neuroblastomas, gliomas, benign meningiomas, small cell lung cancer and mammary tumors, exhibiting a proto-oncogene function. It is also constitutively expressed in tumour cell lines and is involved in tumour growth and metastasis. Therefore, HARP appears to be a potential new target for the treatment or / and diagnosis of several types of cancer.

Estrogen receptors (ERs) are proteins that mediate the action of estradiol and a series of natural and synthetic chemicals that mimic the estradiol structure. Estrogenic action was initially attributed to a single type of ER, now known as ERα, but ERβ was discovered in 1995. Tissue specific distribution and the intensity of expression of these proteins determine the first response of tissues to estrogenic compounds. Estrogens and ERs play a major role in the origin and progression of breast cancer, and antiestrogens that block ER function are useful for breast cancer prevention and treatment. Estrogen mimetics, however, do not fall into distinct categories of agonists and antagonists, since their action is regulated by tissue-specific expression of a number of auxiliary proteins called coactivators or corepressors. In addition, small molecules such as polyamines, fattyacids, and thioredoxin may modulate ER function. Estrogenic functions encompass multiple organ systems, including the reproductive, skeletal, cardiovascular, and nervous system. Estrogens are critical for bone remodeling and mineralization so that estrogen replacement therapy is proven to strengthen bone health in post-menopausal women. Ideally, selective blockade of ER function in breast epithelial cells should be accompanied by growth support on bone and cardiovascular systems. The details of estrogenic function in different organs are to be fully realized, in order to better utilize selective estrogen receptor modulators (SERMs) to fight not only breast cancer but also osteoporosis and cardiovascular diseases. Current research on SERMs points toward accomplishing this goal by exploiting ER as a versatile target against multiple diseases.

The two-domain vascular drug constructs are selective anti-cancer agents capable of specific targeting and subsequent elimination of endothelial cells lining tumor blood vessels. The destruction of existing vasculature within tumor tissue causes insufficient oxygenation of adjacent neoplastic cells and their necrotic death. The recognition (cognitive) domain of the vascular disruptive agents is responsible for recognizing markers specific for endothelial cells. This domain can be formed by variable regions of antibodies or by suitable ligands (such as those binding various integrin or growth factor receptors). The effector domain, in turn, can be constructed from proteins participating in blood clotting process, as well as from toxins, cytokines, radioactive isotopes or pro-apoptotic factors. This article outlines issues important for constructing such two-domain vascular disruptive agents and emphasizes the modularity of their assembly. Several pharmacokinetic and pharmacodynamic properties of these novel agents are discussed. Compared to known cytostatic substances exerting anti-angiogenic effects, such vascular disruptive agents can be much more effective as cytotoxic agents, especially in combination with proven anti-cancer drugs.

The mechanism of oncogenesis is extremely complicated and controlled by various factors, most of which are based on cell proliferation, tumor invasion, neovascularization, and inhibition of apoptosis. We have investigated the relationship between thirty three oncogenes expression and histopathological prognostic factors of endometrial carcinomas, including clinical stage, histological grade, presence of invasion to greater than one-half the myometrium, clinical outcome, and survival rate. Scoring on the basis of the percentage of positive cells indicated that Plks, EphB4, ephrin-B2, Id1, CaMKIV, c- Ets1, Elf-1, and survivin expression were significantly associated with PCNA-labeling index, clinical stage, histological grade, the presence of invasion to greater than one-half the myometrium, and clinical outcome. Survival data were available for all patients, and univariate Cox regression analysis showed that Plks, CaMKIV, Elf-1, and survivin expression were significantly associated with poor prognosis. Our results demonstrate that some oncogenes expression in endometrial carcinoma correlate with the malignant potential of these tumors. Thus, in addition to being of diagnostic value, modulation of these oncogenes activity in the tumors by chemotherapeutic agents or gene therapy may prove to be of therapeutic value. In this review, we demonstrate the biologic behavior of seven novel molecules (Plks, Eph / ephrin, Id family, CaMK, c-Ets1, Elf-1, and survivin) in the endometrial carcinoma.

TSC-22 (Transforming growth factor-β stimulated clone-22) was originally isolated as a TGF-β- inducible gene in mouse osteoblastic cells. TSC-22 encodes a putative transcriptional regulator containing a leucine zipper-like structure. Several differentiation-inducing stimuli up-regulate the TSC-22 gene. Furthermore, TSC-22 acts as an effector that integrates multiple extracellular signals during embryogenesis of Drosophila and mouse. Separately, we identified TSC-22 cDNA as an anti-cancer drug (vesnarinone)-inducible gene in a human salivary gland cancer cell line, TYS. Vesnarinone is known to have a differentiation-inducing activity in several cell types. We showed that TSC-22 negatively regulated the growth of TYS cells, and that down-regulation of TSC-22 played a major role in the salivary gland tumorigenesis. Subsequently, we found that artificial overexpression of TSC-22 enhanced chemosensitivity and radiation-sensitivity by inducing apoptosis in TYS cells. Recently, we isolated TSC-22 genomic DNA and analyzed the transcriptional and posttranscriptional regulation of the TSC-22 gene. Then, we confirmed by the luciferase reporter assay that several differentiation-inducing stimuli directly activated the promoter region of TSC-22 gene. Now we are investigating the chemical compounds, which could enhance the transcription of the TSC-22 gene. Thus, because TSC-22 is a key molecule for differentiation of several cells, it can be used as a molecular target for cancer differentiation therapy in salivary gland cancer.

Mammaglobin is a gene that is expressed almost exclusively in the normal breast epithelium and human breast cancer. It is a member of the secretoglobin gene family and forms a heterodimer with lipophilin B. We have focused on the tissue-specificity of mammaglobin as a potential mechanism for the specific killing of breast cancer cells. By elucidating the promoter region of mammaglobin, we hope to utilize this site as a method for turning on the apoptosis inducer gene, Bax, in breast cancer cells. The Bax gene will only be expressed at levels necessary to induce apoptosis in mammaglobin positive cells. This would include >80% of all breast cancer cells and some normal breast epithelium. This type of targeted killing could be conceptualized as a biochemical mastectomy; that is, genetic ablation of breast tumor cells and perhaps non-malignant breast epithelium while preserving the adipose and stromal components of the breast. Work is also being done to address the binding specificity of the secreted mammaglobin protein. There is early evidence that the mammaglobin heterodimer may in fact bind to breast and breast cancer cells. If this finding is validated, this creates the possibility that mammaglobin can be tagged with a radioisotope or a toxin, so that binding of the tagged-mammaglobin complex results in the specific killing of that breast cancer cell. Finally, mammaglobin is being explored as a target for immune-based interventions. In vitro studies have demonstrated that T cellmediated immune responses can be induced against mammaglobin-derived peptides expressed by MHC molecules on tumor cells and antigen-presenting cells. In summary, mammaglobin displays several unique features that make it a promising target for intervention.