Estrogen-regulated gene expression predicts response to endocrine therapy in patients with ovarian cancer

OBJECTIVE

To explore the predictive value of estrogen-regulated gene changes as indicators of sensitivity in ovarian cancer patients treated with the aromatase inhibitor Letrozole.

METHODS

Expression of a range of proteins was assessed by semi-quantitative immunohistochemistry in tissue sections from the tumors of patients treated with Letrozole. Expression was correlated with clinical response to Letrozole. Corresponding mRNA in ovarian cancer cell lines treated with 17beta-estradiol (E2) was measured by quantitative RT-PCR.

RESULTS

In an estrogen receptor (ER)-positive ovarian cancer cell line, quantitative RT-PCR analysis demonstrated that PLAU, VIM, BIGH3, CDH6, FN1, CASP4, KRT4, KRT7, KRT13, TRAM and NGAL were down-regulated and TFF1, TFF3, TRAP1, TFAP4, MYC, CTSD, IL17BR, TOP2A, CCNB1, CCNB2, PDZK1 and UBE2C were up-regulated by E2. The E2 modulation of these genes was reversed by the anti-estrogen tamoxifen and was ERalpha-dependent. For ovarian cancer patients treated with Letrozole, we tested the predictive value of the majority of these genes in paraffin sections from their primary tumors by semi-quantitative immunohistochemistry. Significant differences in expression levels of TFF1, TFF3, BIGH3, TRAP1, VIM, TOP2A, PLAU and UBE2C were observed between tumors from CA125 responsive/stable patients as opposed to tumors from patients whose disease progressed, using serum levels of CA125 as an indicator of response. Aromatase expression in the ovarian cancers also differed between these 2 groups of patients.

CONCLUSION

These results suggest that expression levels of certain proteins in ovarian cancers are estrogen-regulated and could help identify patients who would benefit from endocrine therapy.

Comparison of strategies targeting Raf-1 mRNA in ovarian cancer

In this study, we characterize the uptake and specificity of a first-generation Raf-1 antisense oligonucleotide (ASO) (ISIS 5132) and compare it with a second-generation ASO (ISIS 13650) and an RNA interference approach. All three approaches resulted in inhibition of both Raf-1 expression and cellular growth. Specificity of the Raf-1 ASOs was confirmed by comparison with ASOs targeted against another Raf isoform (B-Raf) as well as mismatch sequences. Cellular uptake studies with FAM-labelled ISIS 5132 revealed that whilst the majority of cells treated at a low-intermediate plating density were labelled within 3 hr, cells treated at high density demonstrated neither Raf-1 protein knockout nor significant growth inhibition, following similar treatment. This lack of response at high cell densities was associated with reduced pERK and Raf-1 inhibition. Cell cycle analysis revealed that whilst SKOV-3 cells both accumulated in the S-phase of the cell cycle and showed enhanced annexin V levels, following Raf-1 ASO treatment; these effects were also demonstrated with first-generation but not second-generation mismatch oligonucleotides. Bromodeoxyuridine incorporation analysis suggested that these effects may indeed be partly attributable to sequence nonspecific effects. Finally, the combination of ISIS 5132 with either carboplatin or taxol showed enhanced growth inhibition, supporting the view that such ASOs may have a more effective clinical role when used in combination with cytotoxic agents.

Insulin-like growth factor binding proteins IGFBP3, IGFBP4, and IGFBP5 predict endocrine responsiveness in patients with ovarian cancer

PURPOSE

This study sought to explore the predictive value of the insulin-like growth factor (IGF) binding proteins (IGFBP) as markers of response in ovarian cancer patients treated with the aromatase inhibitor letrozole.

EXPERIMENTAL DESIGN

IGFBP mRNA expression in cell lines was measured by quantitative reverse transcription-PCR and IGFBP protein expression measured in sections from primary tumors of patients treated with letrozole by semiquantitative immunohistochemistry.

RESULTS

Quantitative reverse transcription-PCR analysis showed that IGFBP3 and IGFBP5 were down-regulated and IGFBP4 was up-regulated by 17beta-estradiol (E(2)) in an estrogen receptor (ER)-positive ovarian cancer cell line. Expressions of IGFBP1, IGFBP2, and IGFBP6 were unaffected by E(2). The E(2) modulation of these genes was reversed by tamoxifen. Using ERalpha-specific (propyl pyrazole triol) and ERbeta-specific (diarylpropionitrile) agonists, the gene expression modulations produced by E(2) could be replicated by propyl pyrazole triol but not by diarylpropionitrile. For ovarian cancer patients being treated with letrozole, we tested the predictive value of the IGFBPs in paraffin-fixed sections from their primary tumors by semiquantitative immunohistochemistry. Using serum CA125 as an indicator of progression/response, significant differences in expression levels of IGFBPs were observed between tumors from CA125 responding/stable patients compared with tumors from progressing patients. Mean immunoscores for IGFBP3 and IGFBP5 were significantly lower, and mean expression of IGFBP4 was significantly higher in tumors from patients demonstrating CA125 response or stabilization compared with CA125 progression.

CONCLUSION

These results indicate that expression levels of certain IGFBP family members in ovarian cancers are estrogen regulated and can, thus, help identify patients who could benefit from endocrine therapy.

Sensitivity to pertuzumab (2C4) in ovarian cancer models: cross-talk with estrogen receptor signaling

Pertuzumab (Omnitarg, rhuMab 2C4) is a humanized monoclonal antibody, which inhibits HER2 dimerization. Because it has shown some clinical activity in ovarian cancer, this study sought to identify predictors of response to this agent in a model of ovarian cancer. A panel of 13 ovarian cancer cell lines was treated with heregulin beta1 (HRGbeta1) or transforming growth factor-alpha, and cell proliferation was assessed. Both agents increased cell number in the majority of cell lines studied, the response to both being similar (r = 0.83; P = 0.0004, Pearson test). HRGbeta1 stimulation could be partially reversed by pertuzumab in 6 of 13 cell lines, with complete reversal in PE04 and PE06 cells. Addition of pertuzumab to transforming growth factor-alpha-stimulated cells produced growth inhibition in 3 of 13 cell lines (PE01, PE04, and PE06). The magnitude of HRGbeta1-driven growth stimulation correlated significantly with an increase in extracellular signal-regulated kinase 2 (P = 0.037) but not Akt (P = 0.99) phosphorylation. Such HRGbeta1-driven phosphorylation of extracellular signal-regulated kinase 1/2 and Akt could be reduced with pertuzumab, accompanied by changes in cell cycle distribution. In cell lines responsive to pertuzumab, HRGbeta1-enhanced phosphorylation of HER2 (Tyr(877)) was reduced. Estrogen-stimulated changes in growth, cell cycle distribution, and signaling were reversed by pertuzumab, indicating cross-talk between HER2 and estrogen signaling. These data indicate that there is a subset of ovarian cancer cell lines sensitive to pertuzumab and suggest possible predictors of response to identify patients who could benefit from this therapy. Furthermore, we have identified an interaction between HER2 and estrogen signaling in this disease.

Endocrine therapy resistance can be associated with high estrogen receptor alpha (ERalpha) expression and reduced ERalpha phosphorylation in breast cancer models

Hormone-dependent estrogen receptor (ER)-positive breast cancer cells may adapt to low estrogen environments such as produced by aromatase inhibitors. In many instances, cells become insensitive to the effects of estrogen but may still retain dependence on ER. We have investigated the expression, function, and activation of ERalpha in two endocrine-resistant MCF-7 models to identify mechanisms that could contribute to resistance. While MCF-7/LCC1 cells are partially estrogen dependent, MCF-7/LCC9 cells are fully estrogen insensitive and fulvestrant and tamoxifen resistant. In both MCF-7/LCC1 and MCF-7/LCC9 cell lines, high expression of ERalpha was associated with enhanced binding to the trefoil factor 1 (TFF1) promoter in the absence of estrogen and increased transcription of TFF1 and progesterone receptor. In contrast to the observations derived from hypersensitive and supersensitive models, these cells were truly estrogen independent; nevertheless, removal of ERalpha by siRNA, or fulvestrant, a specific ER downregulator, inhibited growth indicating dependence on ERalpha. In the absence of estrogen, neither ERalpha Ser118 nor Ser167 were phosphorylated as frequently found in other ligand-independent cell line models. Addition of estrogen activated ERalpha Ser118 in MCF-7 and LCC1 cells but not in LCC9 cells. We suggest that the estrogen-independent growth within these cell lines is accounted for by high levels of ERalpha expression driving transcription and full estrogen independence explained by lack of ERalpha activation through Ser118.

Raf-1 is the predominant Raf isoform that mediates growth factor-stimulated growth in ovarian cancer cells

There is currently much interest in the role of the Raf family in cancer, particularly since mutated B-Raf has been shown to be oncogenic in certain disease types. In this study we have explored the expression, signaling and function of the three known Raf isoforms (Raf-1, A-Raf and B-Raf) in patients with ovarian cancer. While increased expression of Raf-1 was associated with poor survival, increased expression of B-Raf was associated with improved survival. Using a panel of ovarian cancer cell lines, all three isoforms were shown to be involved in growth factor initiated signaling. Antisense inhibition of function in ovarian cancer cell lines indicated that both Raf-1 and A-Raf, but not B-Raf, were linked to cell proliferation. Raf-1 (but not A-Raf or B-Raf) was also associated with reduced apoptosis. While individual Raf reduction by isoform-targeted antisense oligonucleotides (ODNs) produced growth inhibition in some cell lines, similar use of the MEK inhibitor UO126 produced growth inhibition in all cell lines tested. These data suggest that Raf-1 is the predominant Raf isoform responsible for regulating cellular growth in ovarian cancer cells and may be particularly important in high grade serous ovarian cancers.

Estrogen receptor-alpha mediates gene expression changes and growth response in ovarian cancer cells exposed to estrogen

Estrogens play a significant role in the development, growth, invasion and metastasis of ovarian tumors. The transcriptional program regulated by 17beta-estradiol (E(2)) in human ovarian cancer cell lines was analyzed using cDNA microarrays containing 1200 cancer-related genes. Twenty-eight transcripts had at least a threefold change in expression in E(2)-treated PEO1 ovarian carcinoma cells compared with controls. These differences were confirmed by real-time quantitative PCR and shown to be dependent upon the expression of functional estrogen receptor-alpha (ERalpha). Consistent with this, these gene expression changes were blocked by the anti-estrogen tamoxifen. The use of ERalpha- and ERbeta-specific ligands allowed molecular dissection of the E(2) response and showed that ERalpha activation was responsible for the observed changes in gene expression, whereas ERbeta played no significant role. Inhibition of de novo protein synthesis by cycloheximide was used to distinguish between primary and secondary target genes regulated by E(2). Actinomycin D was used to show that changes in gene expression levels induced by E(2) were a result of changes in transcription and not due to changes in mRNA stability. The results presented here demonstrate that estrogen-driven growth of epithelial ovarian carcinoma is mediated by activation of ERalpha-mediated, and not ERbeta-mediated, transcription.

The mechanism of action of Kahalalide F: variable cell permeability in human hepatoma cell lines

Kahalalide F (KF) is a small natural peptide that showed activity in vitro and in vivo. The dose-limiting toxicity in clinical trials was transaminitis. We investigated the cytotoxicity of KF in cell lines from breast, ovary, prostate and colon cancers, but focused on hepatoma cell lines, performing mechanistic studies in HepG2 (IC50 = 0.3 microM) and PLC/PRF/5C (IC50 = 5 microM). Following KF exposure, HepG2 cells demonstrated profound ATP depletion, associated with cell swelling and cell blebbing, and increased permeability to propidium iodide (PI), annexin V (AV) and release of lactate dehydrogenase (LDH). PLC/PRF/5C cells retained their cell structure, but were permeable to PI and, following exposure to high concentrations of KF, to AV. The pattern of cell permeability is similar to maitotoxin, another small cytotoxic peptide, but the differential effects on the cell membrane induced by KF in HepG2 and PLC/PRF/5C suggest specific interactions with membranes or proteins. This could lead to better drug design aimed at exploiting the potential for cell selectivity.

Altered ErbB receptor signaling and gene expression in cisplatin-resistant ovarian cancer

The majority of ovarian cancer patients are treated with platinum-based chemotherapy, but the emergence of resistance to such chemotherapy severely limits its overall effectiveness. We have shown that development of resistance to this treatment can modify cell signaling responses in a model system wherein cisplatin treatment has altered cell responsiveness to ligands of the erbB receptor family. A cisplatin-resistant ovarian carcinoma cell line PE01CDDP was derived from the parent PE01 line by exposure to increasing concentrations of cisplatin, eventually obtaining a 20-fold level of resistance. Whereas PE01 cells were growth stimulated by the erbB receptor-activating ligands, such as transforming growth factor-alpha (TGFalpha), NRG1alpha, and NRG1beta, the PE01CDDP line was growth inhibited by TGFalpha and NRG1beta but unaffected by NRG1alpha. TGFalpha increased apoptosis in PE01CDDP cells but decreased apoptosis in PE01 cells. Differences in extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling were also found, which may be implicated in the altered cell response to ligands. Microarray analysis revealed 51 genes whose mRNA increased by at least 2-fold in PE01CDDP cells relative to PE01 (including FRA1, ETV4, MCM2, AXL, MT3, TRAP1, and FANCG), whereas 36 genes (including IGFBP3, TRAM1, and KRT4 and KRT19) decreased by a similar amount. Differential display reverse transcriptase-PCR identified altered mRNA expression for TCP1, SLP1, proliferating cell nuclear antigen, and ZXDA. Small interfering RNA inhibition of FRA1, TCP1, and MCM2 expression was associated with reduced growth and FRA1 inhibition with enhanced cisplatin sensitivity. Altered expression of these genes by cytotoxic exposure may provide survival advantages to cells including deregulation of signaling pathways, which may be critical in the development of drug resistance.

Inflammation-associated gene expression is altered between normal human ovarian surface epithelial cells and cell lines derived from ovarian adenocarcinomas

Ovulation is believed to contribute to the development of ovarian cancers that derive from the ovarian surface epithelium (OSE). The process of ovulation is synonymous with inflammation and inflammatory cytokines such as interleukin-1α (IL-1α) have recently been shown to induce both inflammatory and anti-inflammatory responses in human OSE (HOSE) cells. In this study we directly compared levels of IL-1α-induced gene expression by analysing the levels of 11β-hydroxysteroid dehydrogenase (11βHSD) types 1 (11βHSD-1) and 2 (11βHSD-2), cyclooxygenase-2 (COX-2), IL-1 receptor (IL-1R) and glucocorticoid receptor α (GRα) mRNA between normal HOSE cells and cell lines derived from poorly differentiated (SKOV-3, BG-1, PEO-4) and well-differentiated (PEO-14) ovarian adenocarcinoma. In HOSE cell cultures, and to a lesser extent PEO-14 cells, the basal mRNA levels of COX-2 and 11βHSD-1 were relatively high and further shown to be induced in response to IL-1α (for HOSE cells; >20-fold, P<0.05 and PEO-14 cells; >3fold, P<0.05). However, whereas HOSE cells expressed a low level of 11βHSD-2 mRNA that was only mildly responsive to IL-1α (1.3-fold, P<0.001), all cell lines exhibited a higher basal level of 11βHSD-2 mRNA that was in some cases further stimulated in PEO-4 cells (five-fold; P<0.05) or suppressed in SKOV-3 cells (two-fold; P<0.01) in response to IL-1α. All cells tested expressed IL-1R and, with the exception of BG-1, GRα. These results indicate that cell lines derived from ovarian cancers have lost the ability to respond normally to inflammatory cytokines such as IL-1α. The finding that normal OSE cells, in contrast to cell lines derived from patients with ovarian adenocarcinoma, abundantly express 11βHSD-1 mRNA but are essentially devoid of 11βHSD-2 mRNA supports the concept that the pattern of 11βHSD isoform gene expression is a defining feature of neoplastic cellular transformation, which might have particular relevance to the ovary.

Antisense oligonucleotide targeting of Raf-1: importance of raf-1 mRNA expression levels and raf-1-dependent signaling in determining growth response in ovarian cancer

PURPOSE

We sought to identify determinants of growth response to the Raf-1-targeted antisense oligonucleotide (ASO; ISIS 5132) using a large panel of ovarian cancer cell lines.

EXPERIMENTAL DESIGN

First-(ISIS 5132) and second-generation (ISIS 13650) anti-Raf 1 ASOs were compared with control oligonucleotides. Growth was assessed by cell counts; apoptosis was assessed by poly(ADP-ribose) polymerase cleavage; and cell cycle analysis was assessed by flow cytometry. Protein expression was detected by Western blot analysis, and mRNA expression was detected by quantitative reverse transcription-PCR. Raf-1 kinase activity was detected by anti-Raf-1 immunoprecipitation, followed by myelin basic protein phosphorylation.

RESULTS

A panel of 15 ovarian cancer cell lines was used to model a range of growth responses to ASOs targeting Raf-1 mRNA. Growth inhibition varied from 10% to >90% inhibition. Growth inhibition was associated with increased apoptosis and accumulation of cells in the G(2)-M and S phases of the cell cycle. Growth response was not related to level of Raf-1 protein expression, Raf-1 kinase activity, intracellular ASO uptake, or degree of Raf-1 protein inhibition. However, ASO growth response was associated with a high proportion of Raf-1 mRNA [relative to total (i.e., Raf-1 + A-Raf + B-Raf) Raf mRNA] and significantly higher Raf-1 kinase activity induction following growth factor (transforming growth factor alpha) stimulation in the cell lines consistent with dependency of these cell lines on Raf-1.

CONCLUSIONS

These data indicate that ovarian cancers demonstrate differential sensitivity to ASOs targeted against Raf-1, and target expression levels and degree of utilization of Raf-1 signaling are implicated. Clinically sensitive tumors could feasibly be identified.

Role of TGF alpha stimulation of the ERK, PI3 kinase and PLC gamma pathways in ovarian cancer growth and migration

The Epidermal Growth Factor Receptor (EGFR) and its structural relative erbB2 are frequently over-expressed in ovarian cancers and both are strongly associated with poor patient survival. To investigate the relative roles of these receptors in the regulation of cell growth and migration, a panel of ovarian carcinoma cell lines were stimulated with TGF alpha and NRG1beta. TGF alpha had a much greater influence on cell migration than NRG1beta where growth effects were equivalent. The extent of TGF alpha-stimulated migration on collagen in these assays could be associated with erbB2 expression levels. In addition, TGF alpha was found to stimulate activation of the ERK, PI3 kinase and PLC gamma pathways. Direct blockade of the TGF alpha-interacting receptor EGFR inhibited both cell growth and migration, as well as downstream signaling induced by the growth factor. Specific blockade of the downstream proteins MEK and PI3 kinase significantly affected TGF alpha-induced mitogenesis in the cell lines tested but had less impact upon migration. Conversely, inhibition of the PLC gamma pathway had little effect on cell growth but significantly decreased TGF alpha-driven migration. These results corroborate the likely importance of migration as well as growth in erbB receptor over-expressing ovarian cancers and directly implicate the roles of ERK and PI3 kinase in growth control, and PLC gamma in the regulation of migration in this disease.

Neuregulin expression, function, and signaling in human ovarian cancer cells

PURPOSE

To investigate the expression and function of neuregulin (NRG) isoforms in ovarian cancer cell lines and tumor samples.

EXPERIMENTAL DESIGN

Expression of NRG-1alpha and NRG-1beta proteins were detected by immunohistochemistry and mRNA by RT-PCR. erbB receptor levels and downstream signaling proteins were measured by Western blot analysis.

RESULTS

Expression of NRG-1alpha and NRG-1beta proteins were detected by immunohistochemistry in 46 of 53 (87%) and 41 of 53 (77%) ovarian carcinomas, respectively. Serous carcinomas express higher levels of NRG-1alpha than endometrioid carcinomas (P = 0.017). NRG mRNA was detected by RT-PCR in 20 of 24 (83%) of ovarian carcinomas and eight of nine (89%) ovarian cancer cell lines. NRG-1alpha stimulated the growth of 5 of 14 cell lines whereas NRG-1beta stimulated 7 of 14 cell lines. The magnitude of NRG growth response was significantly associated with erbB2 expression levels. NRG-1alpha and -1beta (1 nM) growth-stimulated cell lines PE01 and PE06 demonstrated increased tyrosine phosphorylation of erbB2 and elevated tyrosine phosphorylation of ERK1 and ERK2. In contrast, the SKOV-3 cell line, the growth of which was unaffected, did not show these downstream responses. An anti-erbB3 receptor antibody (clone H3.105.5) blocked NRG-1beta growth changes and signaling in these cell lines. Conversely, the anti-erbB4 antibody (clone H4.72.8) enhanced NRG-beta1 growth stimulation. Herceptin also inhibited growth.

CONCLUSIONS

With NRG expression in the majority of ovarian carcinomas and cell lines, there is the potential for autocrine regulation of cell growth. Interfering with ligand-receptor interactions by receptor blocking antibodies suggests erbB3 is primarily involved in NRG-1beta-induced proliferation, with erbB4 having a more complex role.

CA125 response is associated with estrogen receptor expression in a phase II trial of letrozole in ovarian cancer: identification of an endocrine-sensitive subgroup

PURPOSE

This study was an open-label Phase II trial of the aromatase inhibitor letrozole (Femara) in patients with relapsed ovarian cancer with evaluation of possible biological markers for response.

EXPERIMENTAL DESIGN

60 patients were treated with letrozole (2.5 mg daily) at the time of CA125 relapse. Disease response was assessed by Union International Contre Cancer (UICC) criteria and by CA125 measurement. Estrogen receptor (ER), progesterone receptor, epidermal growth factor receptor, erbB2, and HSP27 were measured by immunohistochemistry in paraffin-fixed material obtained from the primary tumors at initial surgery.

RESULTS

50 patients were evaluable by UICC criteria, and although no complete or partial responses were obtained, 10 patients had stable disease on scan for at least 12 weeks. CA125 responses were evaluable in 54 patients. A partial marker response (>50% decrease) was seen in 5, and the marker remained stable in an additional 14 patients (25% increase). Tumors from the UICC stable disease group had significantly higher ER (P = 0.027) and progesterone receptor (P = 0.0066) values than the progressive disease group, and a combination of these was strongly associated with stable disease (P < 0.0001). Using CA125 criteria, comparison of the CA125 stable/responding disease with progressive disease indicated that tumors with higher ER (P = 0.013), lower erbB2 (P = 0.026), and higher epidermal growth factor receptor (P = 0.009) were associated with CA125 stable/responsive disease.

CONCLUSIONS

These results imply that letrozole treatment can produce disease stabilization and CA125 responses that in turn are linked to higher levels of ER expression. These data suggest the presence of an endocrine-sensitive group that could be targeted in future studies.

Targeting the EGF receptor in ovarian cancer with the tyrosine kinase inhibitor ZD 1839 ("Iressa")

The modulating effects of the orally active epidermal growth factor receptor-specific tyrosine kinase inhibitor ZD 1839 ("Iressa") on cell growth and signalling were evaluated in four ovarian cancer cell lines (PE01, PE04, SKOV-3, OVCAR-5) that express the epidermal growth factor receptor, and in A2780, which is epidermal growth factor receptor-negative. Transforming growth factor-alpha stimulated growth was completely inhibited by concentrations of ZD 1839 > or =0.3 microM in the epidermal growth factor receptor-expressing cell lines, as were transforming growth factor-alpha stimulated phosphorylation of the epidermal growth factor receptor and downstream components of the MAP kinase and PI-3 kinase signalling cascades. Growth inhibition in the absence of added transforming growth factor-alpha was also observed which could be consistent with suppression of action of autocrine epidermal growth factor receptor-activating ligands by ZD 1839. In support of this, transforming growth factor-alpha, EGF and amphiregulin mRNAs were detected by RT-PCR in the epidermal growth factor receptor-expressing cell lines. ZD 1839 inhibited growth of the PE04 ovarian cancer xenograft at 200 mg kg(-1)day(-1). These data lend further support to the view that targeting the epidermal growth factor receptor in ovarian cancer could have therapeutic benefit.

Association of c-Raf expression with survival and its targeting with antisense oligonucleotides in ovarian cancer

c-Raf is an essential component of the extracellular related kinase (ERK) signal transduction pathway. Immunohistochemical staining indicated that c-Raf was present in 49/53 ovarian adenocarcinomas investigated and high c-Raf expression correlated significantly with poor survival (P = 0.002). c-Raf protein was detected in 15 ovarian cancer cell lines. Antisense oligodeoxynucleotides (ODNs) (ISIS 5132 and ISIS 13650) reduced c-Raf protein levels and inhibited cell proliferation in vitro. Selectivity was demonstrated by the lack of effect of ISIS 5132 on A-Raf or ERK, while a random ODN produced only minor effects on growth and did not influence c-Raf expression. ISIS 5132 produced enhanced apoptosis and cells accumulated in S and G(2)/M phases of the cell cycle. In vivo, ISIS 5132 inhibited growth of the s.c. SKOV-3 xenograft while a mismatch ODN had no effect. These data indicate that high levels of c-Raf expression may be important in ovarian cancer and use of antisense ODNs targeted to c-Raf could provide a strategy for the treatment of this disease.

Expression of erbB-4/HER-4 growth factor receptor isoforms in ovarian cancer

Immunohistochemical expression of erbB4 protein was identified in 93% (49 of 53) of ovarian cancers using the HFR-1 antibody (targeted to the cytoplasmic domain of the erbB4 receptor) and in 89% (47 of 53) of ovarian cancers using the H4.77.16 antibody (targeted to the extracellular domain). Tumors of serous histology were more likely to express a higher level of erbB4 than endometrioid tumors, and for stage III serous tumors, long-term survival was associated with moderate to high coexpression of erbB4 and erbB2. Within ovarian cancer cell lines, high erbB4 expression was associated with cisplatin resistance. Using reverse transcription-PCR, the presence of multiple isoforms of erbB4 mRNA was identified in both ovarian primary tumors and cell lines. Splice variants in the juxtamembrane (JM-a and JM-d) and cytoplasmic (CT-a and CT-b) regions were identified in mRNA of both cell lines and primary tumors. The use of an anti-erbB4 blocking antibody suggested that erbB4 was not the mediator of the growth stimulatory effects of neuregulin in ovarian cancer cells and indeed could potentially antagonize this effect.

Ovarian cancer models : technical review

Perhaps the most fundamental question that faces the laboratory scientist is, "Which model system should I use to investigate the problem?" Failure to adequately address this issue can compromise even the most meticulous and inspired research program. If this is such a thorny issue, why use model systems at all? As with most biological systems, ovarian cancer is a complex disorder comprising tumor cells, stromal tissues, neovascularization, inflammatory responses, and other host responses to the tumor. Experimental science best progresses by controling all but a single variable and observing what occurs when that variable is modulated. Almost by definition, this requires a homogenous group of samples to work with. Using human cancer patients for research, it becomes rapidly apparent that the diverse nature of the tumors and the hosts greatly complicates such an approach, hence the development of various model systems. The problem with model systems is simple, they are models-not the true disease states, by their very nature they are less than perfect reflections of the way in which the system under investigation performs in vivo in the normal host. Model systems are essential research tools, but have to be used appropriately.

High antitumour activity of ET743 against human tumour xenografts from melanoma, non-small-cell lung and ovarian cancer

BACKGROUND

Ecteinascidin-743 (ET743) is a novel antitumour agent originating from the Caribbean tunicate Ecteinascidia turbinata. It has potent cytotoxic and antitumour activity and a potential new mechanism of action. The aim of the present study was to further explore the antitumour activity of ET743 in human tumour xenografts from melanoma, non-small-cell lung and ovarian cancer.

DESIGN

As the antitumour profile of ET743 was largely unknown a chemo-sensitive and a marginal chemo-resistant human tumour xenograft were selected for each tumour type. ET743 was administered intravenously using two administration schedules (days 0, 4, 8 and 0-2, 13-15).

RESULTS

ET743 was very active at the maximum tolerated dose (MTD) in the chemo-sensitive xenograft melanoma MEXF 989, non-small-cell lung cancer LXFL 529, and ovarian cancers HOC22 and (marginally resistant to cisplatin) HOC18. Activity was also seen at 1/2 MTD. Apart from HOC18, ET743 caused complete remissions in the responding xenografts. The compound was inactive in the chemo-resistant xenograft melanoma MEXF 514 and non-small-cell lung cancer LXFA 629. In terms of antitumour activity the days 0, 4, 8 schedule had advantages over the days 0-2, 13-15 schedule.

CONCLUSIONS

ET743 is a very effective agent in chemo-sensitive and marginal chemo-resistant xenografts, but inactive in chemo-resistant tumour xenografts. The activity of ET743 in the marginally cisplatin-resistant ovarian cancer HOC18 might indicate absence or incomplete cross-resistance against cisplatin. It is recommended to include melanoma, non-small-cell lung cancer, and ovarian cancer in phase II clinical trials and to use an intermittent schedule.