Inhibition of HER-2 by three independent targeting strategies increases paclitaxel resistance of SKOV-3 ovarian carcinoma cells

Abstract

Current treatment options for ovarian cancer, which is one of the most widespread gynecological malignancies, are limited, mainly because patients with advanced-stage disease often develop resistance to chemotherapeutics. In breast cancer cells, several studies suggest that overexpression of the human epidermal growth factor receptor-2 (HER-2) leads to increased resistance against certain, but not all cytotoxic drugs. In ovarian carcinoma, conflicting data on the correlation of HER-2 expression and tumor cell sensitivity exist. In this paper, we explore the role of HER-2 expression and signaling levels pertaining to paclitaxel (Taxol) chemoresistance by applying three different and independent strategies in SKOV-3 ovarian carcinoma cells. Firstly, we show that treatment with the HER-2 inhibitory antibody trastuzumab (Herceptin), which is well established in tumor therapy, results in markedly increased, rather than decreased, cellular paclitaxel resistance. Next, we present two newly developed low molecular weight inhibitors of HER-2 tyrosine kinase activity, D-69491 and D-70166. With both drugs, the decrease in cellular paclitaxel sensitivity upon HER-2 inhibition is confirmed. Finally, for more detailed analysis we stably downregulate HER-2 expression by ribozyme-targeting. Using clonal ribozyme-transfected SKOV-3 cells with different residual HER-2 levels, we establish a 'HER-2 gene dose effect' of paclitaxel cytotoxicity. We show that this effect is due to differential induction of apoptosis and differential cell cycle inhibition by paclitaxel. Finally, paclitaxel- or HER-2-mediated alterations in the phosphorylation of MAP kinases p42/44, Stress-activated protein kinase/Jun-terminal kinase (SAPK/JNK), and p38, and effects on the activation of caspase-3, caspase-7, and bcl-2 are discussed. We conclude that paclitaxel cytotoxicity in SKOV-3 cells is 'HER-2 dose-dependent' and identify cell proliferation as one underlying cellular event of this effect.

Sequencing of Type I Insulin-Like Growth Factor Receptor Inhibition Affects Chemotherapy Response In vitro and In vivo

“…A large cooperative group trial demonstrated an estimated disease-free survival advantage of 18% for sequential rather than concurrent chemotherapy and tamoxifen treatment when given in the adjuvant setting (18). In addition, inhibition of HER2 by trastuzumab first, but not in the reverse order, increased paclitaxel resistance of ovarian cancer cells (19). Since several anti-IGF1R antibodies are being evaluated in phase I /II/III clinical trials, some in combination with cytotoxic chemotherapy, it is be important to determine the optimal schedule for the antibodies in combination with chemotherapy.…”

Naturally occurring resistance of bone marrow mononuclear and metastatic cancer cells to anticancer agents

“…In addition, the haematological cancer cells obtained from bone marrow had a much lower proliferation rate than the metastatic cancer cells obtained from ascites or pleural fluids. The effectiveness of various chemotherapeutic agents, including doxorubicin [20], paclitaxel [13,21] and cisplatin [13,22], may depend on cell proliferation to a certain extent.…”

Targeting HER2 in ovarian and uterine cancers: Challenges and future directions

“…Dual antibody therapy was the most potent resulting in a significant reduction in tumor volume by day four [19]. The relationship between HER2 status and chemotherapy resistance in ovarian cancer has also been examined; sensitivity to paclitaxel was increased approximately 70-fold in SKOV3 ovarian cancer cells expressing high levels of HER2 and, in a later study, treatment with trastuzumab resulted in increased resistance to paclitaxel [20,21].…”