Trastuzumab is the only HER2/neu-directed therapy to have received Food and Drug Administration approval for the treatment of patients with metastatic breast cancer. The efficacy of trastuzumab depends on the HER2/neu status of the tumour and the patient's prior treatment, but even when patients are selected on the basis of HER2/neu gene amplification, the single-agent response rate ranges from 12 to 30% and few patients respond to trastuzumab monotherapy. Here, we propose PTEN as a predictive biomarker for trastuzumab efficacy. Human breast cancer SKBR3 and drug-resistant SKBR3/R cells were investigated. We also examined clinical samples from patients who had been treated with trastuzumab and analysed the relationship between trastuzumab efficacy and PTEN level. The PI3K/Akt signalling pathway was observed to be highly active in the drug-resistant cells, and their level of PTEN was low. Delivery of antisense PTEN duplex siRNA significantly decreased the trastuzumab chemosensitivity of parental SKBR3 cells, and marked activation of Akt signalling pathway was also recognised. Moreover, immunohistochemical investigation revealed that trastuzumab treatment was remarkably successful in cells with elevated PTEN expression. Along with the immune-system-associated cytotoxic mechanism, several mechanisms have been proposed for the effect of trastuzumab. PTEN activity might play an important and major role in its HER2/PI3K/Akt-mediated antitumour effect, and could be a useful biomarker for predicting the efficacy of trastuzumab in the treatment of breast cancer.

High expression of epidermal growth factor receptor (EGFR) is thought to be correlated with cell proliferation, invasion, metastasis, resistance to chemoradiotherapy, and poor prognosis in various kinds of human cancers. Blockade of EGFR signal transduction can be a promising strategy for cancer therapy. Approximately 40-70% of esophageal squamous cell carcinomas (ESCCs) show high expression of EGFR. In this study, we examined the antitumor effect of gefitinib, an EGFR tyrosine kinase inhibitor, against ESCC cells in vitro and in vivo. In three ESCC cell lines (TE8, T.T and T.Tn), cell proliferation had been inhibited in a dose-dependent manner and IC(50) values (respectively, 8.49, 18.9 and 17.3muM). Gefitinib inhibited EGF-induced autophosphorylation of EGFR and its downstream signaling pathways, Ras/Raf/MAPK and PI3K/Akt, and caused G(1) arrest of cell cycle and apoptosis confirmed with flow cytometry. We examined the effect of gefitinib on nude mice bearing established TE8 and T.T xenografts. Gefitinib (100 or 200mg/kg once-daily, p.o.) showed antitumor activity in a dose-dependent manner, resulting in a significantly improved survival of treated mice as compared with untreated mice. Immunohistochemical examination of the harvested tumor was performed to examine the status of phosphorylated EGFR, PCNA, Factor VIII and apoptosis. We found inhibition of EGFR phosphorylation, cell cycle arrest (by PCNA staining), decrease of microvessel density (Factor VIII) and induction of apoptosis by TUNEL staining. In conclusion, our findings demonstrate that gefitinib is effective for growth inhibition of ESCC cell lines in vitro and in vivo and suggest that gefitinib may be one of the new therapeutic options for ESSC.

Some kinds of breast cancer cell lines, similar to several types of solid tumors, express epidermal growth factor receptor (EGFR). However, gefitinib, an EGFR tyrosine kinase inhibitor, is not effective for all these cell lines. Similarly, taxane is effective for many of the cell lines, although some, such as the multidrug-resistant MCF7/ADR cell line, show taxane-resistance. Here, we examined the growth inhibitory effect of combination treatment with gefitinib and taxane on the breast cancer cell lines MDA-MB-231 (EGFR-positive) and MCF7/ADR (EGFR-and HER2-positive). To estimate the combined effect, a Combination Index was calculated for each cell line. The combination of gefitinib and taxane showed a strong synergistic effect on MCF7/ADR cells, but an in vitro additive-antagonistic effect on MDA-MB-231 cells. Similarly, the combination treatment showed a significantly increased tumor inhibitory effect on MCF7/ADR xenografts, but not on MDA-MB-231 xenografts. Regarding the mechanism of the synergistic effect, Western blotting analysis revealed that taxane activated the EGFR-Akt pathway in MCF7/ADR cells but not in MDA-MB-231. To determine the optimal sequential administration of gefitinib and taxane for MCF7/ADR cells, we used flow cytometry to analyze the cell cycle and apoptosis; finding that taxane treatment followed by gefitinib produced a higher rate of G2 arrest and apoptosis than gefitinib treatment followed by taxane. These results suggest gefitinib overcomes the drug-resistance of these cells, thereby increasing the effects of taxane on MCF7/ADR cells. Further, activation of the EGFR-Akt pathway by taxane is related to this synergistic effect. ' 2006 Wiley-Liss, Inc.

Sixty-three cases of benign and malignant canine mammary tumors were analyzed to define the alteration of exons 5-8 for the p53 tumor suppressor gene using polymerase chain reaction direct sequence analysis with paraffin-embedded tissues. Four missense mutations were found in 38 benign mammary tumors (11%), and five missense (one tumor had two missense mutations) and one nonsense mutations were found in 25 mammary carcinomas (20%). These data suggest that the p53 gene alterations might be initiated at an early stage of canine mammary carcinogenesis and p53 mutations might be associated with malignancy. However, there was no evidence of any relationship between the p53 alterations and the histologic types of tumors or breeds of dogs.

Numerous signaling pathways were reported to be involved in the resistance for conventional cytotoxic drugs, although one of the main reasons is the overexpression of P-glycoprotein (P-gp) in multidrug resistant cancer cells. The overexpression of P-gp has been associated with the resistance to a wide range of anticancer drugs. Doxorubicin and paclitaxel are substrates of this transporter system and have an important role for the various human malignancies. In the present study, drug-sensitive MCF7 and multidrug resistant MCF7/ADR (characterized by overexpression of P-gp) human breast cancer cell lines were used as an experimental model. We have found that PS341 and MG132, proteasome inhibitors, reduced the degree of the multidrug resistance (MDR) in MCF7/ADR cells. This phenomenon was accompanied by a decrease in the IC50 value of doxorubicin and paclitaxel from 55.9 6 3.46 to 0.60 6 0.08 lM, and from 17.61 6 1.77 to 0.59 6 0.12 lM, respectively. The IC50 values of sensitive cells for doxorubicin and paclitaxel were about 0.42 and 0.83 lM, respectively. The effect of PS341 and MG132 on MCF7/ADR cells was associated with a significant decrease in both protein and gene levels of P-gp expression. Moreover, with regard to the expression of possible signal transduction pathways of mitogen-activated protein kinase (MAPK) related to the activation of mdr1, proteasome inhibitors did significantly influence the activation of these proteins. Western blot analysis revealed that 24 hr exposure of multidrug resistant MCF7/ADR cells with proteasome inhibitors did change the levels of DNA binding activity of nuclear factor-kappaB (NFkappaB), pERK1/2, c-Jun, and p-c-Jun. In conclusion, we could remark that proteasome inhibitors (especially PS341) attenuate the resistance of MCF7/ADR cells for P-gp substrate drugs of doxorubicin and paclitaxel. Several proteins are supposed to be associated with the resensitization of the cells to conventional cytotoxic drugs, although decreased activity of P-gp is at least involved in the proteasome inhibitor-related resensitization. And influence with MAPK pathways, which have been reported to be associated with the regulation of P-gp, might be contributed to the resensitization brought by proteasome inhibitors. ' 2005 Wiley-Liss, Inc.