Antineoplastic effect of erbstatin on human mammary and esophageal tumors in athymic nude mice

Recent Advances in the Development of Anticancer Drugs that Act against Signalling Pathways

Cancer can be considered a disease of deranged intracellular signalling. The intracellular signalling pathways that mediate the effects of oncogenes on cell growth and transformation present attractive targets for the development of new classes of drugs for the prevention and treatment of cancer. This is a new approach to developing anticancer drugs and the potential, as well as some of the problems, inherent in the approach are discussed. Anticancer drugs that produce their effects by disrupting signalling pathways are already in clinical trial. Some properties of these drugs, as well as other inhibitors of signalling pathways under development as potential anticancer drugs, are reviewed.

Genistein potentiates the effect of 17-beta estradiol on human hepatocellular carcinoma cell line

Background:

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors. This cancer may be due to a multistep process with an accumulation of epigenetic alterations in tumor suppressor genes (TSGs), leading to hypermethylation of the genes. Hypermethylation of TSGs is associated with silencing and inactivation of them. It is well-known that DNA hypomethylation is the initial epigenetic abnormality recognized in human tumors. Estrogen receptor alpha (ERα) is one of the TSGs which modulates gene transcription and its hypermethylation is because of overactivity of DNA methyltransferases. Fortunately, epigenetic changes especially hypermethylation can be reversed by pharmacological compounds such as genistein (GE) and 17-beta estradiol (E2) which involve in preventing the development of certain cancers by maintaining a protective DNA methylation. The aim of the present study was to analyze the effects of GE on ERα and DNMT1 genes expression and also apoptotic and antiproliferative effects of GE and E2 on HCC.

Materials and Methods:

Cells were treated with various concentrations of GE and E2 and the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay was used. Furthermore, cells were treated with single dose of GE and E2 (25 μM) and flow cytometry assay was performed. The expression level of the genes was determined by quantitative real-time reverse transcription polymerase chain reaction.

Results:

GE increased ERα and decreased DNMT1 genes expression, GE and E2 inhibited cell viability and induced apoptosis significantly.

Conclusion:

GE can epigenetically increase ERα expression by inhibition of DNMT1 expression which in turn increases apoptotic effect of E2. Furthermore, a combination of GE and E2 can induce apoptosis more significantly.

Esophageal Cancer: Insights From Mouse Models

Esophageal cancer is the eighth leading cause of cancer and the sixth most common cause of cancer-related death worldwide. Despite recent advances in the development of surgical techniques in combination with the use of radiotherapy and chemotherapy, the prognosis for esophageal cancer remains poor. The cellular and molecular mechanisms that drive the pathogenesis of esophageal cancer are still poorly understood. Hence, understanding these mechanisms is crucial to improving outcomes for patients with esophageal cancer. Mouse models constitute valuable tools for modeling human cancers and for the preclinical testing of therapeutic strategies in a manner not possible in human subjects. Mice are excellent models for studying human cancers because they are similar to humans at the physiological and molecular levels and because they have a shorter gestation time and life cycle. Moreover, a wide range of well-developed technologies for introducing genetic modifications into mice are currently available. In this review, we describe how different mouse models are used to study esophageal cancer.

Genistein inhibits invasive potential of human hepatocellular carcinoma by altering cell cycle, apoptosis, and angiogenesis

AIM: To study the in vitro and in vivo inhibitory effects of genistein on invasive potential of Bel 7402 hepatocellular carcinoma (HCC) cells and to explore the underlying mechanism.

METHODS: Bel 7402 HCC cells were exposed to genistein. The invasive activity of tumor cells was assayed in transwell cell culture chamber. p125^FAK expression and cell cycle were evaluated by a functional assay. Cell apoptosis analysis was performed with TUNEL method. In addition, bilateral subrenal capsule xenograft transplantation of HCC was performed in 10 nude mice. Genistein was injected and the invasion of HCC into the renal parenchyma was observed. Microvessels with immunohistochemical staining were detected.

RESULTS: Genistein significantly inhibited the growth of Bel 7402 cells, the inhibitory rate of tumor cells was 26–42%. The invasive potential of Bel 7402 cells in vitro was significantly inhibited, the inhibitory rate was 11–28%. Genistein caused G2/M cell cycle arrest, S phase decreased significantly. The occurrence of apoptosis in genistein group increased significantly. The expression of p125^FAK in 5 μg/mL genistein group (15.26±0.16%) and 10 μg/mL genistein group (12.89±0.36%) was significantly lower than that in the control group (19.75±1.12%, P<0.05). Tumor growth in genistein-treated nude mice was significantly retarded in comparison to control mice, the inhibitory rate of tumor growth was about 20%. Genistein also significantly inhibited the invasion of Bel 7402 cells into the renal parenchyma of nude mice with xenograft transplant. The positive unit value of microvessels in genistein-treated group (10.422 ± 0.807) was significantly lower than that in control group (22.330 ± 5.696, P < 0.01).

CONCLUSION: Genistein can effectively inhibit the invasive potential of Bel 7402 HCC cells by altering cell cycle, apoptosis and angiogenesis, inhibition of focal adhesion kinase may play a significant role in this process.

Design of hypoxia-targeting protein tyrosine kinase inhibitor using an innovative pharmacophore 2-methylene-4-cyclopentene-1,3-dione

We review in this report our strategy and tactics for the design of 2-hydroxyarylidene-4-cyclopentene-1,3-diones as protein tyrosine kinase (PTK) inhibitors having low mitochondrial toxicities and/or hypoxia-targeting function. We based our synthetic design on an innovative pharmacophore, 2-methylene-4-cyclopentene-1,3-dione. We first showed the effectiveness of this pharmacophore in the development of 2-methylene-4-cyclopentene-1,3-dione as PTK inhibitor that have lower mitochondrial toxicity than the potent PTK inhibitor tyrphostin AG17. Our results show that the cyclopentenedione-derived TX-1123 is a more potent antitumor tyrphostin and also shows lower mitochondrial toxicity than the malononitrile-derived AG17. The O-methylation product of TX-1123 (TX-1925) retained its tyrphostin-like properties, including mitochondrial toxicity and antitumor activities. However, the methylation product of AG17 (TX-1927) retained its tyrphostin-like antitumor activities, but lost its mitochondrial toxicity. Our comprehensive evaluation of these agents with respect to PTK inhibition, mitochondrial inhibition, antitumor activity, and hepatotoxicity demonstrates that PTK inhibitors TX-1123 and TX-1925 are more promising candidates for antitumor agents than tyrphostin AG17. Secondly, as a further investigation of the promising power of this 4-cyclopentene-1,3-dione as an innovative pharmacophore, we discuss our strategy of development of hypoxia-targeting PTK inhibitor TX-1123 analogues, 2-nitroimidazole-aminomethylenecyclopentenediones, such as TX-2036, for cancer treatment, especially for pancreatic cancers, which have a high level of hypoxia.

Molecular design and biological activities of protein-tyrosine phosphatase inhibitors

Protein-tyrosine kinase (PTKase) and protein-tyrosine phosphatase (PTPase) regulate the intracellular signal transduction in various biological processes. PTPase often negatively regulates the intracellular protein-tyrosine phosphorylation. PTPases are considered to be involved in the etiology of diabetes mellitus and neural diseases, such as Alzheimer's disease and Parkinson's disease. Therefore, PTPase inhibitors should be useful tools to study the role of PTPases in these diseases and other biological phenomena, and they hopefully may be developed into chemotherapeutic agents. We first discovered a naturally occurring PTPase inhibitor, dephostatin, in 1993. Later, we developed stable and safe dephostatin analogues by a molecular design approach employing the concept of CH/pi interaction. We prepared Et-3,4-dephostatin as a stable analogue and found it to inhibit PTP-1B and SHPTP-1 PTPases selectively. Et-3,4-dephostatin increased the tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 (IRS-1), with or without insulin, in differentiated 3T3-L1 mouse adipocytes. It also increased the phosphorylation and activation of Akt. The analogue also enhanced translocation of glucose transporter 4 (GLUT4) from the cytoplasm to the membrane and 2-deoxyglucose transport. It also showed an in vivo antidiabetic effect in terms of reducing the high blood glucose level in KK-Ay mice after oral administration. Since Et-3,4-dephostatin contains a nitrosamine moiety, we designed nitrosamine-free dephostatin analogues employing the concept of CH/pi interaction. Then, we synthesized methoxime- and hexyl-methoxime-3,4-dephostatin as nitrosamine-free analogues. These analogues also showed antidiabetic activity in vivo and illustrate the utility of the CH/pi interaction molecular design approach.

TX-1123: an antitumor 2-hydroxyarylidene-4-cyclopentene-1,3-dione as a protein tyrosine kinase inhibitor having low mitochondrial toxicity

A series of 2-hydroxyarylidene-4-cyclopentene-1,3-diones were designed, synthesized, and evaluated with respect to protein tyrosine kinase (PTK) inhibition, mitochondrial toxicity, and antitumor activity. Our results show that the cyclopentenedione-derived TX-1123 is a more potent antitumor tyrphostin and also shows lower mitochondrial toxicity than the malononitrile-derived AG17, a potent antitumor tyrphostin. The O-methylation product of TX-1123 (TX-1925) retained its tyrphostin-like properties, including mitochondrial toxicity and antitumor activities. However, the methylation product of AG17 (TX-1927) retained its tyrphostin-like antitumor activities, but lost its mitochondrial toxicity. Our comprehensive evaluation of these agents with respect to protein tyrosine kinase inhibition, mitochondrial inhibition, antitumor activity, and hepatotoxicity demonstrates that PTK inhibitors TX-1123 and TX-1925 are more promising candidates for antitumor agents than tyrphostin AG17.

Isoflavones inhibit intestinal epithelial cell proliferation and induce apoptosis in vitro

There have been many reports that high soya-based diets reduce the risk of certain types of cancer. This effect may be due to the presence of high levels of isoflavones derived from the soya bean, particularly genistein which has been shown to be a protein tyrosine kinase (PTK) inhibitor and have both oestrogenic and anti-oestrogenic properties. We have examined the effect of genistein and a number of novel synthetic analogues on both normal (IEC6, IEC18) and transformed (SW620, HT29) intestinal epithelial cell lines. Responses were compared to those elicited by oestradiol, the anti-oestrogen tamoxifen, and the tyrosine kinase inhibitor tyrphostin. Genistein and tamoxifen were potent inhibitors of cell proliferation. Of seven novel isoflavones tested, none were more potent inhibitors than genistein, and all displayed similar relative activities across the different cell lines. In addition to inhibiting cell proliferation, cell death via apoptosis was observed when the cells were exposed to the isoflavones and all but one exhibited PTK inhibitory activity. These data suggest that by reducing proliferation and inducing apoptosis, possibly due in part to PTK inhibition, isoflavones may have a role in protecting normal intestinal epithelium from tumour development (reducing the risk) and may reduce colonic tumour growth.

In vivo antitumor activity of herbimycin A, a tyrosine kinase inhibitor, targeted against BCR/ABL oncoprotein in mice bearing BCR/ABL-transfected cells

Herbimycin A, a benzoquinoid ansamycin antibiotic, has been shown to reverse the oncogenic phenotype of p60v-src transformed cells because of the inhibition of src protein tyrosine kinase. We previously demonstrated that herbimycin A displayed antitumor activity on the in vitro growth of Philadelphia chromosome-positive leukemia cells and BCR/ABL-transfected murine hematopoietic FDC-P2 cells through the inhibition of BCR/ABL protein tyrosine kinase. In this study, the transformed FDC-P2 cells were demonstrated to be tumorigenic in syngeneic DBA/2 mice. The intraperitoneal (i.p.) injection of the transformed tumor cells into DBA/2 mice induced infiltrations of abdominal organs, and then all of the mice died within time periods proportional to the cell numbers of inoculation. In mice that received an i.p. inoculation with greater than 1 x 10(5) cells, in vivo administration of herbimycin A by i.p. injection inhibited tumor formation and significantly prolonged survival time, and further, in mice inoculated with 1 x 10(4) cells, herbimycin A completely suppressed the in vivo growth of transformant FDC-P2 cells and brought about a complete remission. The present study revealed the in vivo efficacy of herbimycin A in mice bearing BCR/ABL-transfected cells.

Molecular and cellular basis of cancer invasion and metastasis: implications for treatment

In the past decade significant advances in establishing the underlying biological mechanisms of tumour invasion and metastasis have been made. Some of the triggering factors and genes relevant to metastatic spread have been identified. Advances have also been made in understanding the signal transduction pathways involved in invasion and metastasis. This increased comprehension of the malignant metastatic process has enabled new antimetastatic strategies to be devised. This review summarizes progress in these areas and discusses the implications for the treatment of metastasis.

Inhibition of DNA topoisomerases I and II and induction of apoptosis by erbstatin and tyrphostin derivatives

Inhibitors of protein tyrosine kinases (PTK) and DNA topoisomerases are potential antitumour agents. Drugs which bind to the ATP site of PTK, such as genistein, are common inhibitors to both types of enzymes. Eleven erbstatin and tyrphostin derivatives, which inhibit epidermal growth factor receptor PTK activity by competing with both the peptide substrate and ATP were tested for their capacity to inhibit DNA topoisomerases I and II. Erbstatin, two synthetic derivatives with a modified side chain and the tyrphostin AG 786 inhibited both topoisomerases in the same range of concentrations (20-50 microM). The tyrphostin AG 213 inhibited only topoisomerase II. In this series, absence of PTK inhibitory effect was correlated with the absence of DNA topoisomerase inhibition, while the detection of PTK inhibition may or may not be associated with DNA topoisomerase inhibition. In contrast to genistein, none of these molecules induced the stabilization of the topoisomerase-DNA cleavable complex, either in vitro or in vivo. Alcaline elution analysis revealed that erbstatin did not induce the formation of protein associated DNA strand breaks. However, an extensive degradation of the cellular DNA was observed which was shown to result from an internucleosomal fragmentation. Furthermore, typical morphological modifications associated with apoptosis were observed in the erbstatin treated cells by electron microscopy. These data indicate that erbstatin induces an apoptotic cell death.

Protein tyrosine kinase inhibitors inhibit chemotaxis of vascular smooth muscle cells

The effects of protein tyrosine kinase inhibitors on platelet-derived growth factor (PDGF)-induced chemotaxis in cultured rat aortic smooth muscle cells (SMCs) were investigated to elucidate the role of tyrosine phosphorylation in the chemotaxis of vascular SMCs. Two tyrosine kinase inhibitors, methyl 2,5-dihydroxycinnamate and genistein, inhibited PDGF-induced chemotaxis, the IC50 being 5 and 150 mumol/L, respectively. Methyl cinnamate and genistein partly inhibited the adhesion of SMC to collagen-coated dishes. A chemotaxis assay using double-well culture dishes revealed that both agents also inhibited cell migration after adhesion. H-7, a C kinase inhibitor, did not inhibit either chemotaxis or SMC adhesion at 100 mumol/L. Western blot analysis using anti-phosphotyrosine revealed that the tyrosine kinase inhibitors inhibited the tyrosine phosphorylation of at least two proteins of molecular weight 85 and 95 kD under our experimental conditions. An immunocytochemical study revealed that these inhibitors eliminated tyrosine phosphorylation along the cell margins; these agents also inhibited the reorganization of microtubules and stress fibers, both of which are involved in directional cell locomotion. These findings suggest that tyrosine kinases may play an important role in SMC chemotaxis.

Signalling pathways as targets for anticancer drug development

Intracellular signalling pathways mediating the effects of oncogenes on cell growth and transformation offer novel targets for the development of anticancer drugs. With this approach, it may be sufficient to target a component of the signalling pathway activated by the oncogene rather than the oncogene product itself. In this review, the abilities of some antiproliferative drugs to inhibit signalling targets are considered. There are some anticancer drugs already in clinical trial that may act by inhibiting signalling targets, as well as drugs in preclinical development. Some problems that may be encountered in developing this new class of anticancer drugs are discussed.

Protein-tyrosine kinases: potential targets for anticancer drug development

Protein-tyrosine kinases (PTKs) were originally discovered over a decade ago as the dominant transforming components of certain tumor viruses. Since then these enzymes have become recognized as important intracellular mediators of a variety of mitogenic signaling pathways, including those associated with several growth factor receptors. The strong correlation of aberrant or over-expressed PTKs with a number of proliferative diseases has raised the possibility that PTK inhibitors may afford new approaches toward anticancer therapeutics. To address this possibility, potent and specific PTK inhibitors are needed both as pharmacological probes to study PTK-dependent signaling and as potential antiproliferative agents in their own right. De novo design of PTK inhibitors is hampered by a lack of three dimensional information regarding PTKs or the interaction of inhibitors with the enzymes. Motifs for the design of new inhibitors are therefore frequently derived by modification of structural them identified in natural-product screens. Exemplary of this process is the Laboratory of Medicinal Chemistry's program to develop PTK inhibitors based on pharmacophores present in three natural-product PTK inhibitors: lavendustin A, erbstatin and piceatannol. As summarized in this report, such efforts have led to new inhibitors with increased potency and interkinase selectivity. Whether PTK inhibitors will ultimately prove to be useful as antiproliferative therapeutics remains an open question whose answer will be heavily reliant on a cooperative partnership among natural-product and medicinal chemists, pharmacologists and clinicians.