Biomedical subjects

Rita Nahta

Publications and source records attributed to Rita Nahta.

At least 19 recordsLinked to original sources

PubMed2007

Adenovirus type 5 E1A gene therapy for ovarian clear cell carcinoma: a potential treatment strategy.

Resistance of ovarian clear cell carcinoma (CCC) to platinum-based chemotherapy is associated with poor prognosis, and an effective treatment for advanced disease is urgently needed. HER2/neu is up-regulated more often in CCC than in other histologic types of epithelial ovarian cancer. The purpose of this study was to assess possible treatment for ovarian CCC with the anti-HER2 antibody trastuzumab or human adenovirus type 5 E1A. We treated 10 CCC cell lines with trastuzumab or E1A and assessed cell viability, proliferation, and colony formation and the expression of HER2 and wild-type p53 proteins and molecules downstream of those signaling pathways. HER2 protein was detected at various levels in all 10 cell lines by Western blotting and in 5 CCC cell lines by immunohistochemical staining; HER2 gene amplification was detected (by fluorescence in situ hybridization) in only one cell line (RMG-I). Trastuzumab did not inhibit proliferation in any of the four CCC cell lines tested (RMG-I, SKOV-2, OVTOKO, and OVSAYO). However, transfection with E1A (as compared with control vectors) reduced colony formation in all 10 CCC cell lines regardless of HER2 expression level. Infection of RMG-I and SMOV-2 cells with an adenoviral vector encoding E1A led to significant (P < 0.05) suppression of proliferation and enhancement of cell death; this effect required stabilization of p53 (but not p73) protein and was associated with the up-regulation of Bax and the cleavage of caspase-9. Other mechanisms, such as p53-independent apoptosis, may also be involved in E1A-mediated cell death in CCC. Finally, treatment with E1A prolonged survival in a CCC xenograft model (P < 0.001). E1A gene therapy, because of its ability to stabilize wild-type p53, is worth exploring as a treatment modality for women with ovarian CCC, which typically expresses wild-type p53.

Adenocarcinoma, Clear Cell↗

PubMed2006

Herceptin: mechanisms of action and resistance.

HER-2 is overexpressed in 20-25% of invasive breast cancers and is associated with an aggressive tumor phenotype and reduced survival rate. The HER-2 status of a tumor is the critical determinant of response to the HER-2-targeted antibody Herceptin. Thus, accurate assessment of HER-2 expression levels is essential for identifying breast cancer patients who will benefit from HER-2-targeted therapy. Herceptin combined with chemotherapy increases response rates, time to disease progression, and survival. However, the majority of cancers that initially respond to Herceptin begin to progress again within 1 year. This review describes mechanisms by which Herceptin inhibits cell growth in breast cancers that overexpress HER-2 and highlights possible mechanisms contributing to Herceptin resistance.

Angiogenesis Inhibitors↗

PubMed2006

Mechanisms of disease: understanding resistance to HER2-targeted therapy in human breast cancer.

Trastuzumab is a monoclonal antibody targeted against the human epidermal growth factor receptor (HER) 2 tyrosine kinase receptor, which is overexpressed in approximately 25% of invasive breast cancers. The majority of patients with metastatic breast cancer who initially respond to trastuzumab, however, demonstrate disease progression within 1 year of treatment initiation. Preclinical studies have indicated several molecular mechanisms that could contribute to the development of trastuzumab resistance. Increased signaling via the phosphatidylinositol 3-kinase/Akt pathway could contribute to trastuzumab resistance because of activation of multiple receptor pathways that include HER2-related receptors or non-HER receptors such as the insulin-like growth factor 1 receptor, which appears to be involved in a cross-talk with HER2 in resistant cells. Additionally, loss of function of the tumor suppressor PTEN gene, the negative regulator of Akt, results in heightened Akt signaling that leads to decreased sensitivity to trastuzumab. Decreased interaction between trastuzumab and its target receptor HER2, which is due to steric hindrance of HER2 by cell surface proteins such as mucin-4 (MUC4), may block the inhibitory actions of trastuzumab. Novel therapies targeted against these aberrant molecular pathways offer hope that the effectiveness and duration of response to trastuzumab can be greatly improved.

Antibodies, Monoclonal↗

PubMed2006

B cell translocation gene 1 contributes to antisense Bcl-2-mediated apoptosis in breast cancer cells.

The antiapoptotic protein Bcl-2 is overexpressed in a majority of breast cancers, and is associated with a diminished apoptotic response and resistance to various antitumor agents. Bcl-2 inhibition is currently being explored as a possible strategy for sensitizing breast cancer cells to standard chemotherapeutic agents. Antisense Bcl-2 oligonucleotides represent one method for blocking the antiapoptotic effects of Bcl-2. In this study, we show that antisense Bcl-2 efficiently blocks Bcl-2 expression, resulting in the apoptosis of breast cancer cells. Antisense Bcl-2-mediated cytotoxicity was associated with the induction of the B cell translocation gene 1 (BTG1). Importantly, knockdown of BTG1 reduced antisense Bcl-2-mediated cytotoxicity in breast cancer cells. Furthermore, BTG1 expression seems to be negatively regulated by Bcl-2, and exogenous expression of BTG1 induced apoptosis. These results suggest that BTG1 is a Bcl-2-regulated mediator of apoptosis in breast cancer cells, and that its induction contributes to antisense Bcl-2-mediated cytotoxic effects.

Apoptosis↗

PubMed2006

HER2 therapy: molecular mechanisms of trastuzumab resistance.

Trastuzumab is a monoclonal antibody targeted against the HER2 tyrosine kinase receptor. The majority of patients with metastatic breast cancer who initially respond to trastuzumab develop resistance within one year of treatment initiation, and in the adjuvant setting 15% of patients still relapse despite trastuzumab-based therapy. In this review, we discuss potential mechanisms of antitumor activity by trastuzumab, and how these mechanisms become altered to promote therapeutic resistance. We also discuss novel therapies that may improve the efficacy of trastuzumab, and that offer hope that the survival of breast cancer patients with HER2-overexpressing tumors can be vastly improved.

Antibodies, Monoclonal↗

PubMed2005

Insulin-like growth factor-I receptor/human epidermal growth factor receptor 2 heterodimerization contributes to trastuzumab resistance of breast cancer cells.

The majority of breast cancer patients who achieve an initial therapeutic response to the human epidermal growth factor receptor 2 (HER-2)-targeted antibody trastuzumab will show disease progression within 1 year. We previously reported the characterization of SKBR3-derived trastuzumab-resistant pools. In the current study, we show that HER-2 interacts with insulin-like growth factor-I receptor (IGF-IR) uniquely in these resistant cells and not in the parental trastuzumab-sensitive cells. The occurrence of cross talk between IGF-IR and HER-2 exclusively in resistant cells is evidenced by the IGF-I stimulation resulting in increased phosphorylation of HER-2 in resistant cells, but not in parental cells, and by the inhibition of IGF-IR tyrosine kinase activity leading to decreased HER-2 phosphorylation only in resistant cells. In addition, inhibition of IGF-IR tyrosine kinase activity by I-OMe-AG538 increased sensitivity of resistant cells to trastuzumab. HER-2/IGF-IR interaction was disrupted on exposure of resistant cells to the anti-IGF-IR antibody alpha-IR3 and, to a lesser extent, when exposed to the anti-HER-2 antibody pertuzumab. Heterodimer disruption by alpha-IR3 dramatically restored sensitivity to trastuzumab and resistant cells showed a slightly increased sensitivity to pertuzumab versus parental cells. Neither alpha-IR3 nor pertuzumab decreased HER-2 phosphorylation, suggesting that additional sources of phosphorylation other than IGF-IR exist when HER-2 and IGF-IR are not physically bound. Our data support a unique interaction between HER-2 and IGF-IR in trastuzumab-resistant cells such that cross talk occurs between IGF-IR and HER-2. These data suggest that the IGF-IR/HER-2 heterodimer contributes to trastuzumab resistance and justify the need for further studies examining this complex as a potential therapeutic target in breast cancers that have progressed while on trastuzumab.

Amino Acid Sequence↗

PubMed2004

P27(kip1) down-regulation is associated with trastuzumab resistance in breast cancer cells.

Trastuzumab (Herceptin) is a recombinant humanized monoclonal antibody directed against HER-2. The objective response rate to trastuzumab monotherapy is 12-34% for a median duration of 9 months, by which point most patients become resistant to treatment. We created two trastuzumab-resistant (TR) pools from the SKBR3 HER-2-overexpressing breast cancer cell line to study the mechanisms by which breast cancer cells escape trastuzumab-mediated growth inhibition. Both pools maintained her-2 gene amplification and protein overexpression. Resistant cells demonstrated a higher S-phase fraction by flow cytometry and a faster doubling time of 24-36 h compared with 72 h for parental cells. The cyclin-dependent kinase inhibitor p27(kip1) was decreased in TR cells, and cyclin-dependent kinase 2 activity was increased. Importantly, exogenous addition of p27(kip1) increased trastuzumab sensitivity. Additionally, resistant cells displayed heightened sensitivity to the proteasome inhibitor MG132, which induced p27(kip1) expression. Thus, we propose that trastuzumab resistance may be associated with decreased p27(kip1) levels and may be susceptible to treatments that induce p27(kip1) expression.

Antibodies, Monoclonal↗

PubMed2004

The HER-2-targeting antibodies trastuzumab and pertuzumab synergistically inhibit the survival of breast cancer cells.

Trastuzumab (herceptin) and pertuzumab (Omnitarg, 2C4) are recombinant humanized monoclonal antibodies that target different extracellular regions of the HER-2 tyrosine kinase receptor. We explored combination effects of these agents in the HER-2-overexpressing BT474 breast cancer cell line. Trastuzumab and 2C4 synergistically inhibited the survival of BT474 cells, in part, because of increased apoptosis. Trastuzumab increased 2C4-mediated disruption of HER-2 dimerization with the epidermal growth factor receptor and HER-3. Combination drug treatment reduced levels of total and phosphorylated HER-2 protein and blocked receptor signaling through Akt but did not affect mitogen-activated protein kinase. These results suggest that combining HER-2-targeting agents may be a more effective therapeutic strategy in breast cancer rather than treating with a single HER-2 monoclonal antibody.

Antibodies, Monoclonal↗

PubMed2004

Prognostic significance of phosphorylated P38 mitogen-activated protein kinase and HER-2 expression in lymph node-positive breast carcinoma.

BACKGROUND: Chemotherapy-induced p38 mitogen-activated protein kinase (MAPK) phosphorylation reportedly leads to increased apoptosis in breast carcinoma cells. The goals of the current study were to assess the incidence of activated phosphorylated p38 MAPK (P-p38) expression in invasive breast carcinoma, correlate expression of P-p38 MAPK with HER-2, and estimate the prognostic value of this marker in patients with lymph node-positive breast carcinoma treated with adjuvant chemotherapy. METHODS: P-p38, HER-2, and Ki-67 were measured using immunohistochemistry (peroxidase method) in 96 patients with lymph node-positive breast carcinoma treated with adjuvant fluorouracil, doxorubicin, and cyclophosphamide chemotherapy. All markers were measured in the primary tumors, before the initiation of adjuvant chemotherapy. The median follow-up period was 11 years after initial cancer surgery. P-p38 MAPK expression was scored visually and quantified using an image analyzer. RESULTS: The rate of P-p38 MAPK expression ranged from 19-24%, depending on the scoring system used. There was a trend toward shorter progression-free survival (PFS) for patients whose tumors expressed high levels of P-p38 MAPK, although the difference was not statistically significant (P=0.39). PFS was shorter in patients whose tumors overexpressed P-p38 MAPK and had a high level of Ki-67 (P=0.04). In HER-2-negative patients, P-p38 MAPK overexpression was associated with a shorter PFS (P=0.05). CONCLUSIONS: P38 MAPK phosphorylation occurred in 20% of primary breast carcinomas and may be associated with poor outcome in patients with lymph node-positive breast carcinoma. Further studies are needed to define the interaction between P-p38 MAPK and HER-2 expression in breast carcinoma.

Aged↗

PubMed2004

TAFII70 isoform-specific growth suppression correlates with its ability to complex with the GADD45a protein.

TAFII70, a member of the basal transcription complex implicated in p53-mediated transcription, is synthesized as several alternately spliced variants. The predominant forms found in normal and neoplastic breast epithelial cells are shown to be 72 kDa (TAFII70) and 78 kDa (TAFII80). Most cancers express higher levels of the TAFII80 isoform, whereas normal breast epithelia express higher levels of the TAFII70 isoform. Expression of TAFII70, but not TAFII80, causes dramatic growth suppression of normal and transformed breast epithelial cell lines in a p53-independent manner. Growth suppression correlates with mitotic inhibition resulting from an increased number of cells in G2. Both isoforms induce expression of the G2 arrest associated gene, GADD45a, but a novel protein-protein interaction was observed between TAFII70 (not TAFII80) and GADD45a, suggesting that this interaction is important for the observed growth arrest phenotype induced by the TAFII70 isoform. GADD45a null cells are not subject to TAFII70 inhibition, further supporting the relevance of this interaction.

Amino Acid Sequence↗

PubMed2003

Jun activation domain binding protein 1 expression is associated with low p27(Kip1)levels in node-negative breast cancer.

PURPOSE: The purpose is to evaluate expression levels of Jun activation domain-binding protein 1 (JAB1) in breast cancer tissue and adjacent normal tissue, to determine whether JAB1 expression is associated with p27(Kip1) expression in invasive breast carcinomas, and to evaluate the prognostic significance of JAB1 and p27(Kip1) in node-negative breast cancer. EXPERIMENTAL DESIGN: JAB1 levels were measured in 10 matched pairs of invasive breast tumor tissue and adjacent normal tissue using Western blot analysis. We also investigated the immunoreactivity of JAB1 and p27(Kip1) levels in paraffin-embedded tissue specimens from 220 patients with node-negative breast cancer who had not received adjuvant systemic therapy. The median follow-up was 15 years. RESULTS: JAB1 was expressed at higher levels in invasive tumors than in adjacent normal tissue (P = 0.01). JAB1 overexpression was observed in 57% of invasive breast cancers. Low levels of p27(Kip1) were noted in 70% of the tumor specimens. We found an inverse correlation between JAB1 and p27(Kip1) expression levels (P = 0.01). JAB1 overexpression was associated with patient age of at least 50 years (P = 0.03) and tumor size of </=2 cm (P = 0.01). Elevated levels of p27(Kip1) were associated with low nuclear grade (P = 0.01). At 5 years of follow-up, neither JAB1 nor p27(Kip1) expression was related to disease-free survival. CONCLUSIONS: These data indicate that JAB1 is commonly overexpressed in invasive breast carcinomas. JAB1 overexpression is associated with low levels of p27(Kip1) in node-negative breast cancer. In this study, JAB1 and p27(Kip1) were not independent prognostic factors.

Breast Neoplasms↗

PubMed2003

In vitro effects of trastuzumab and vinorelbine in trastuzumab-resistant breast cancer cells.

PURPOSE: The majority of patients who initially respond to trastuzumab will progress within 1 year. Currently, patients who progress after trastuzumab-based therapy are often maintained on trastuzumab combined with a different chemotherapeutic agent, such as vinorelbine. However, evidence supporting the continued use of trastuzumab in these breast cancers is lacking. METHODS: We created a preclinical model of trastuzumab resistance using the SKBR3 HER-2-overexpressing breast cancer cell line. Dose-response and cell cycle alterations in response to trastuzumab and/or vinorelbine were assessed. RESULTS: In contrast to the parental SKBR3 cells, vinorelbine-mediated growth inhibition and apoptosis were not significantly enhanced by the addition of trastuzumab in the trastuzumab-resistant pools. CONCLUSIONS: These results suggest that the continued treatment of trastuzumab-resistant breast cancers with trastuzumab-containing regimens may not be effective. A randomized clinical trial of trastuzumab plus vinorelbine versus vinorelbine alone should be conducted in patients with HER-2-overexpressing breast cancer to determine the optimal duration of trastuzumab therapy upon progression.

Antibodies, Monoclonal↗

PubMed2003

HER-2-targeted therapy: lessons learned and future directions.

HER-2 is overexpressed in 20-25% of invasive breast cancers and is associated with an aggressive tumor phenotype and reduced survival rates. The HER-2 status of a tumor is the critical determinant of response to the HER-2-targeted antibody trastuzumab. Thus, accurate assessment of HER-2 expression levels is essential for identifying breast cancer patients who will benefit from HER-2-targeted therapy. Trastuzumab combined with chemotherapy increases response rates, time to progression, and survival. However, the majority of cancers that initially respond to trastuzumab begin to progress again within 1 year. This minireview describes HER-2 targeting strategies currently in use or in stages of development for the treatment of breast cancer.

Antibodies, Monoclonal↗

PubMed2003

Epidermal growth factor receptor expression is a candidate target of the synergistic combination of trastuzumab and flavopiridol in breast cancer.

ErbB2 and cyclin D1 are interacting oncogenes that are particularly important in breast cancer. We demonstrated previously synergy between two drugs that separately address each oncogene, trastuzumab and flavopiridol. Here we examine the cellular basis for this interaction. Although both drugs are thought to alter cell cycle progression, the combination of trastuzumab and flavopiridol had little effect on G(1) progression or retinoblastoma protein phosphorylation. Instead, trastuzumab-flavopiridol synergistically enhanced apoptosis. Recent data have suggested that transcription elongation mediated by Cdk9 in P-TEFb is a more sensitive flavopiridol target than Cdk4. Supporting this view, we found synergy between 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole riboside and trastuzumab, but not between inhibitors of Cdk4 and trastuzumab. Similarly, a signature set of mRNAs that included the epidermal growth factor receptor (EGFR) responded to the combination of trastuzumab-flavopiridol in a gene expression array analysis. Three lines of evidence confirmed the EGFR is a potential target of flavopiridol-trastuzumab synergy: (a) EGFR protein expression was rapidly and completely lost after combination treatment; (b) a cell line that expresses amplified levels of both erbB2 and the EGFR was resistant to the combined drugs; and (c) treatment with epidermal growth factor prevented any therapeutic effects of flavopiridol and trastuzumab, singly or in combination. Taken together, our results suggest that synergy between flavopiridol and trastuzumab can result from enhanced apoptosis, and that combination effects on EGFR expression are involved in the interaction.

Antibodies, Monoclonal↗

PubMed2003

Bcl-2 antisense oligonucleotides: a potential novel strategy for the treatment of breast cancer.

Bcl-2 is an inhibitor of apoptosis and is overexpressed in more than half of all human cancers. Overexpression of Bcl-2 occurs in 40% to 80% of human breast tumors. Bcl-2 is not an independent prognostic marker in breast cancer patients, in part because most Bcl-2-positive breast cancers express estrogen and/or progesterone receptors. This positive association of Bcl-2 with hormone receptors in breast cancer may explain its apparent correlation with response to hormone therapy. However, diminished apoptotic response caused by Bcl-2 overexpression is associated with cellular resistance to chemotherapeutic drugs. Downregulation of bcl-2 by antisense oligonucleotides has been shown to improve the efficacy of chemotherapy in experimental models. Phase III randomized clinical trials are ongoing in patients with solid tumors. Bcl-2 antisense-based therapy represents a viable strategy for inducing apoptosis and enhancing the chemosensitivity of breast cancers.

Animals↗

PubMed2003

Novel pharmacological approaches in the treatment of breast cancer.

Breast cancer is the most common malignancy among women. Novel pharmacological agents, including hormonal, cytotoxic and biological therapies, are currently being developed and tested in clinical trials and may offer patients more treatment options and an improved chance of long-term survival. Signal transduction inhibitors that block endocrine or growth factor pathways have demonstrated exciting antitumour effects in clinical trials. In addition to new chemotherapeutic drugs, numerous biological agents including growth factor receptor-directed monoclonal antibodies and tyrosine kinase inhibitors that target specific molecular lesions are being examined as potential breast cancer treatments.

Animals↗

PubMed2003

Growth factor receptors in breast cancer: potential for therapeutic intervention.

Increased expression and activation of receptor tyrosine kinases occurs frequently in human breast carcinomas. Several therapies targeting these receptors are currently in clinical trials. Therapeutic strategies include blockade of individual receptors with monoclonal antibodies and inhibition of tyrosine kinase function. Trastuzumab is the first of these biologic therapies to be approved for patients with human epidermal growth factor receptor 2 (HER2)-overexpressing metastatic breast cancer. Novel trastuzumab-based combinations are being investigated in patients with advanced breast cancer. Large clinical trials have also been launched in the adjuvant setting. Small molecules that inhibit specific tyrosine kinases (e.g., epidermal growth factor receptor, HER2) are in phase I and phase II clinical trials. Other growth-factor-targeted drugs that have reached clinical development include STI571 and antibodies directed at the insulin-like growth factor pathway. Biologic therapies directed against these important receptors are promising. In this review we discuss challenges and opportunities for the development of growth-factor-targeted approaches for the treatment of breast cancer.

Antibodies, Monoclonal↗

PubMed2003

Signal transduction inhibitors in the treatment of breast cancer.

Signal transduction pathways are frequently altered in human breast cancer and are the targets of several novel therapies currently in clinical trials. Therapeutic strategies include extracellular blockade of tyrosine kinase receptors with the monoclonal antibodies C225 and trastuzumab. Competitive inhibitors of adenosine triphosphate binding sites on tyrosine and serine/threonine kinases are also being evaluated in phase I/II trials; these include ZD1839, OSI-774 and CI-1033. Flavopiridol and UCN-01 are nonspecific cell cycle kinase antagonists with preliminary evidence of breast cancer cell growth inhibition. Several inhibitors of mitogen-activated protein kinase and phosphatidylinositol 3-kinase signaling are also in various stages of preclinical or clinical development. Additionally, inhibitors of farnesyl transferase have demonstrated activity in breast cancer cells irrespective of ras status. Current evidence suggests that targeting of signaling molecules is a promising new approach to treatment of breast cancer.

Alkyl and Aryl Transferases↗