IGF-Induced Gene Profiles Are Dependent on IRS Expression and Convey Prognostic Value in Human Breast Cancer

The insulin-like growth factor (IGF) pathway mediates aberrant function during the initiation and progression of primary tumors and secondary metastases in cancer. As a result, a host of tyrosine kinase inhibitors and monoclonal antibodies directed against the type 1 IGF receptor (IGF-1R) have entered clinical trials with early positive results. However, no predictive biomarkers have yet emerged from these initial studies. We propose that expanding IGF biomarkers beyond IGF-1R alone may identify the most appropriate candidates for anti-IGF therapy. Previous work has shown that the insulin receptor substrate (IRS) proteins serve as the functional link between IGF-I-induced IGF-1R phosphorylation and downstream signaling linked to cellular behavior. Our work has demonstrated that IRS isoforms differentially mediate IGF-I action, whereby IRS-1 drives proliferation and IRS-2 triggers motility. Here we employed the T47D-YA (IRS null) breast cancer cell line and T47D-YA/IRS clones stably transfected with IRS-1 or IRS-2. In response to acute (4h) and chronic (24h) IGF-I stimulation, global gene expression patterns were assessed by Affymetrix U133 Plus 2.0 microarray analysis. Analysis revealed that IGF-1R activation alone was insufficient to affect gene expression as no genes were regulated by IGF-I in T47D-YA cells. Conversely, ligand stimulation of IRS-1 and IRS-2 clones induced or repressed hundreds of transcripts in both overlapping and distinct fashions. Direct comparison of IRS-1 to IRS-2 clones revealed a number of early (4h) IRS-2 genes linked to metastasis and late (24h) IRS-1 proliferative genes. Interestingly, a 10-fold upregulation in the transforming growth factor beta 2 (TGFβ2) gene by IGF-I in IRS-2 cells suggested a link between the IRS-derived gene signatures and the TGFβ pathway known to regulate breast cancer metastasis. We then compared our arrays with published IGF-I (MCF-7) and TGFβ-derived (MCF10A, MDA-231, HaCaT, HPL1) microarrays to find a list of commonly regulated genes and performed cluster analysis to reveal consistent patterns of gene expression (Creighton el al 2008 & Padua et al 2008). We found 75 genes that were regulated in common between these signatures. To explore the clinical relevance of the signatures we developed, we examined the NKI-295 dataset used to establish the 70-gene profile of prognosis and found 71 genes regulated in common between all four datasets (van de Vijver et al 2002). Strikingly, we discovered that patient survival was heavily influenced by the degree to which tumor expression correlated to the conserved signatures. A high degree of correlation resulted in the poorest disease free survival and an inverse correlation resulted in an improved disease free survival. Our data suggest that IGF stimulation of breast cancer cells results in distinct profiles of gene expression that are dependent on IRS adaptor protein expression. In addition, some of the “IRS-regulated” genes are shared in common with other gene signatures of poor prognosis. With the use of anti-IGF therapies in breast cancer, attention should focus on the use of these profiles as prognostic and predictive biomarkers.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3031.

A Type I Insulin-Like Growth Factor Receptor Kinase Inhibitor (PQIP) Enhances the Cytotoxicity of Doxorubicin in Human Cancer Cell Lines

The type-I insulin like growth factor (IGF-IR) is either activated and/or overexpressed in a wide range of tumor types and contributes to tumorigenicity, proliferation, survival, metastasis and drug resistance. Disruption of IGF-IR signaling alone or in combination with other cytotoxic agents has emerged as an important strategy in cancer therapy. Our laboratory has shown that sequentially combining doxorubicin with anti-IGF-IR antibodies significantly enhances the response of chemotherapy, while the opposite sequence causes cells resistant to chemotherapy. Here, we show that a novel small-molecule IGF-IR kinase inhibitor, cis-3-[3-(4-methyl-piperazin-l-yl)-cyclobutyl]-1-(2-phenyl-quinolin-7-yl)-imidazo[1,5-a]pyrazin-8-ylamine (PQIP) inhibited IGF-IR and insulin receptor (IR) kinase activity and proliferation in MCF-7 and MDA435/LCC6 cell lines. Moreover, PQIP treatment blocked both IGF-I and insulin stimulated activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinase in both cell lines. At doses that inhibited monolayer cell growth, the compound also inhibited cell motility, blocked IGF-I stimulated S-phase progression and induced autophage; at higher doses, it also caused PARP cleavage. Combining PQIP with doxorubicin significantly enhanced cytotoxicity but did not further enhance doxorubicin-induced PARP cleavage in monolayer cell growth. Furthermore, our sequencing studies showed that combining PQIP with doxorubicin simultaneously or doxorubicin followed by PQIP significantly inhibited the anchorage-independent growth in both MCF-7 and MDA435/LCC6 cells. In contrast, pre-treatment with PQIP followed by doxorubicin did not enhance the cytotoxicity of doxorubicin in anchorage-independent growth, which is similar as anti-IGF-IR antibodies in combination with doxorubicin. In summary, these results suggest that the IGF-IR tyrosine kinase inhibitor PQIP can be used alone or in combination with chemotherapy to enhance cytotoxicity of human tumor cell lines, and the timing of IGF-IR inhibition may affect responses to doxorubicin.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6110.

Potential Benefit of an Agonistic Anti IGFIR Antibody (scFv-Fc) as an Effective Breast Cancer Therapy

Multiple monoclonal antibodies targeting the type-1 insulin-like growth factor receptor (IGFIR) are currently in different phases of clinical trials. All the reported antibodies inhibit biochemical activation of IGFIR and block cell proliferation. In contrast, we have reported an agonistic anti-IGFIR antibody scFv-Fc that stimulates IGFIR and its downstream signaling of PI3K and MAPK pathways to promote cell proliferation in vitro. Like the purely antagonistic antibodies, our previous work has shown that scFv-Fc can down regulate IGFIR levels, partially inhibit xenograft growth of MCF-7 cells in athymic mice, and render MCF-7 cells refractory to the mitogenic effects of IGF-I after the initial wave of agonistic activity. MCF-7 cells maintained long term in scFv-Fc have low levels of IGFIR expression, yet the remaining receptor is activated and inhibited by an IGFIR tyrosine kinase inhibitor (TKI) AEW541. In this study, we have further explored the future potential of using this antibody as breast cancer therapy. The common characteristic effect of anti-IGFIR antibodies is to down regulate IGFIR. Since scFv-Fc can activate IGFIR signaling in a manner different than the natural ligand IGF-I, we examined if this antibody could render cells more sensitive to TKI. In MCF-7 cells, IC50 of the IGF1R tyrosine kinase inhibitor AEW541 was decreased 5 to 10 fold when cultured in scFv-Fc. ER negative MDA-MB-231 cells are insensitive to both inhibitory antibody (AVE1642) and TKI (AEW541) in the presence or absence of IGF-I, which may due to the very low levels of IGF1R that are weakly activated by IGF-I. MDA-MB-231 cells were not affected by AEW541 in monolayer growth assays. After chronic treatment of MDA-MB-231 with scFv-Fc for 2 months, AEW541 significantly inhibited monolayer cell growth by 30% in the presence or absence of IGF-I. We also examined the effect of scFv-Fc's effect on AEW541 inhibition of cell motility in MDA-MB-231 cells. Both acute and chronic treatment of scFv-Fc dramatically inhibited cell migration by 90%.Inhibitory antibodies AVE 1642 and MK 0646 had no effect on cell migration. Both IGF-I and excess amounts of AVE 1642/MK 0646 did not reverse scFv-Fc inhibition on cell migration, suggesting other cell signaling system may be involved. In MDA231-BO, a metastatic variant of MDA-MB-231, scFv-Fc had less inhibitory effect on basal cell migration, but in combination of AEW541 treatment, cell migration was significantly decreased by 70%. In conclusion, our data suggests an antibody with agonistic activity may have different properties than purely inhibitory antibodies. Specifically, initiating biochemical signaling followed by inhibition of tyrosine kinase activity and receptor downregulation may be a potent way to disrupt IGF mediated breast cancer cell biology.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3125.

The type I insulin-like growth factor receptor regulates cancer metastasis independently of primary tumor growth by promoting invasion and survival

The type I insulin-like growth factor receptor (IGF1R) regulates multiple aspects of malignancy and is the target of several drugs currently in clinical trials. While IGF1R’s role in proliferation and survival is well-studied, the regulation of metastasis by IGF1R is not as clearly delineated. Previous work showed that disruption of IGF1R signaling via overexpression of a dominant negative IGF1R inhibited metastasis. To establish a clinically applicable approach to inhibition of metastasis by targeting IGF1R, the effect of an inhibitory antibody against IGF1R, EM164 and its humanized version, AVE1642 on metastasis of cancer cells was examined. EM164 and AVE1642 did not affect primary tumor growth of MDA-435A/LCC6 cells but inhibited metastasis of these cells. Consistent with this inhibition in the formation of metastatic nodules, disruption of IGF1R also resulted in a decreased number of circulating tumor cells in blood of tumor-bearing mice. Disruption of IGF1R with a dominant negative construct or antibody inhibited invasion across Matrigel in vitro. When tumor cells were directly injected into the circulation via the lateral tail vein of mice, IGF1R disruption also resulted in significant reduction of pulmonary nodules, suggesting that regulation of invasion is not the only function of IGF1R signaling. Further, disruption of IGF1R rendered cells more susceptible to anoikis. Thus, IGF1R regulated metastasis independently of tumor growth. The multiple phenotypes regulated by IGF1R must be considered during development of this therapeutic strategy as inhibition of metastasis independent of inhibition of tumor growth is not easily assessed in phase II clinical trials.

Feasibility of single-voxel MRS measurement of apparent diffusion coefficient of water in breast tumors

We report initial results with single voxel spectroscopy (SVS) using diffusion weighting and localization by adiabatic selective refocusing (LASER) in breast tumors to measure the apparent diffusion coefficient of water (ADCw). This is a quick (30 s) and relatively easy method to implement compared with image-based diffusion measurements, and is insensitive to lipid signal contamination. The ADCw and concentration of total choline containing compounds [tCho] were evaluated for associations with each other and final pathologic diagnosis in 25 subjects. The average (+/- SD) ADCw in benign and malignant lesions was 1.96 +/- 0.47 mm(2)/s and 1.26 +/- 0.29 x 10(-3) mm(2)/s, respectively, P< 0.001. Receiver operating characteristic curve analysis showed an area under the curve of 0.92. Analysis of the single voxel (SV) ADCw and [tCho] showed significant correlation with a R(2) of 0.56, P< 0.001. Compared with more commonly used image-based methods of measuring water ADC, SV-ADCw is faster, more robust, insensitive to fat, and potentially easier to implement on standard clinical systems.

Locally advanced prostate cancer: A population-based study of treatment patterns and predictors

6606

Background: Treatment of locally advanced prostate cancer (LA PCa) is controversial, but recent trial results demonstrate superior outcomes for combination therapy compared to monotherapy. We aimed to identify treatment patterns, predictors, and trends in a population-based cohort of men with LA PCa. Methods: From Surveillance, Epidemiology and End Results (SEER) cancer registry records linked with Medicare claims, we identified men age 65 and older diagnosed with clinical stage T3 and T4 nonmetastatic PCa from1995 through 2002. Using Medicare claims, we classified treatments (radical prostatectomy (RP), radiation therapy (RT), or androgen deprivation (AD)) received within 6 and 24 months of PCa diagnosis. We assessed trends over time and used multivariable logistic regression to assess sociodemographic and clinical predictors of treatment. Results: The Table shows the distribution of treatments given within 6 months following diagnosis among 3,412 men with LA PCa. Approximately one third of patients were treated with a combination of RT and AD (31%), 46% received monotherapy, and 17% received no active treatment. Between 1995 and 2002, the most notable change was an increase in use of the combination of RT and AD as primary therapy. The percent of patients who received RT and AD rose from 16% in 1995 to 39% in 2002. Significant predictors of receiving combination therapy over the study period were age, race, urban residence, marital status, clinical stage, year of diagnosis, and Charlson comorbidity score. All results were similar when we examined treatments received within 24 months of diagnosis. Conclusions: Patterns of treatment for locally advanced prostate cancer shifted during the study period, with the combination of RT and AD becoming the most common treatment modality. This movement toward combination therapy for LA PCA is encouraging, given recent evidence of the superiority of such therapy in these patients. Future efforts should focus on further increasing the use of multimodality therapy in LA PCa.

[Table: see text]

No significant financial relationships to disclose.

Do ACE-I protect against the development of doxorubicin cardiac toxicity?

6623

Background: Doxorubicin (DOX), an anthracycline, has been associated with irreversible cardiotoxicity. Recently, newer agents such as angiotensin converting enzyme (ACE-I) inhibitors have been used in small trials to prevent cardiac toxicity in patients receiving DOX. This retrospective study analyzes whether ACE-I and other medications are protective in the development of DOX cardiomyopathy. Methods: Patients receiving DOX chemotherapy at the University of Minnesota Cancer Center who had two or more multigated blood pool imaging (MUGA) scan or echocardiograms performed were identified and reviewed. Patients who had at least a 10% drop in their ejection fraction (EF) to below the lower limits of normal (50%) or had an absolute decrease in EF of 15% or greater were identified and compared with those that did not have a decline in EF. Patient variables and the use of concurrent medications were compared between these two groups using logistic regression. Results: 350 patients received DOX chemotherapy between November 2004 and 2007. Of 142 patients who had two or more MUGA scans performed during the course of their therapy, 22 (15%) had a significant drop in EF. Median age was 52 years old (range 7–88). 85 (60%) were female. Cancer diagnosis was breast (n = 26), lymphoma (n = 92), and other (n = 25). The median baseline EF of all patients was similar (62% versus 63%). A stepwise variable selection retained two predictors significant at alpha = 0.1 in a logistic regression model: Age and ACE-I (p = 0.0252 and p = 0.0940, respectively). Adjusting for Age, the odds ratio for ACE-I is 0.267, suggesting that ACE-I has a protective effect, as it reduces the probability of a drop in EF. Cumulative DOX dose, obesity, hypertension, and history of tobacco use did not appear to be associated with a decline in ejection fraction. The use of beta-blockers, aspirin or statins did not appear to be associated with a decline in ejection fraction. Conclusions: DOX chemotherapy has been associated with the development of cardiomyopathies. While this is an observational study that is limited by its retrospective nature, the study supports our hypothesis that the use of ACE-I is possibly protective when given with DOX chemotherapy and warrants further investigation.

No significant financial relationships to disclose.

IGF-IR targeted therapy for the treatment of metastatic breast cancer

Abstract #71

The type I insulin-like growth factor receptor (IGF-IR) regulates multiple aspects of malignancy and is the target of drugs currently in clinical trials. While its role in proliferation and survival is well-studied, the regulation of metastasis by IGF-IR is not as clearly delineated. Previous work showed that disruption of IGF-IR signaling via a dominant negative IGF-IR inhibited metastasis of MDA-435A/LCC6, a metastatic variant of the MDA-MB-435 cancer cells which form lung metastases when injected into the mammary fat pad of mice. To establish a clinically applicable approach to IGF-IR-mediated inhibition of metastasis, the effect of an inhibitory antibody against IGF-IR, EM164 on metastasis of cancer cells was examined.&#x2028; EM164 and AVE1642 did not inhibit primary tumor growth of LCC6 cancer cells but inhibited metastasis of these cells. Disruption of IGF-IR also resulted in a decreased number of circulating tumor cells (CTC) in blood of tumor-bearing mice. Disruption of IGF-IR inhibited invasion across Matrigel in vitro. When tumor cells were directly injected into the circulation via the tail vein of mice, IGF-IR disruption also resulted in significant reduction of pulmonary nodules, suggesting that regulation of invasion is not the only function of IGF-IR signaling. Inhibition of IGF-IR rendered cells more susceptible to anoikis. AVE1642 also inhibited metastasis of MDA-MB-231BO cells but not their primary tumor growth. Thus, IGF-IR regulated metastasis independently of tumor growth. We next examined if inhibition of IGF-IR could also be effective once micrometastases were already established since clinically many patient have micrometastases at the time of diagnosis. CTC were detected in blood of mice bearing LCC6 tumors approximately 12 days after injection of cells in the fat pad. At this time point micrometastases were not yet detected in the lungs by H&E staining. Therefore, we used presence of these CTC as an early surrogate marker of micrometastases in our model. Mice injected with LCC6 cells in the mammary fat pad were randomized to receive EM164 treatment on day 4 or day 12 after injection of cells. Treatments were administered until day 28 after injection of cells in the fat pad. There was a greater inhibition in the number of CTC in mice that received treatments on day 4 at which point CTC were not detectable, compared to mice that received EM16 beginning on day 12 when CTC were detectable. Similarly, when metastases were monitored by bioluminescence imaging of luciferase expressing LCC6 cells injected into the tail vein, mice that received EM164 starting on day 3 had greater inhibition of metastases compared to mice that received treatment starting on day 12.&#x2028; Thus, the multiple phenotypes regulated by IGF-IR must be considered and clinical trials of this therapeutic strategy may need to adjust their endpoints for assessing benefit by taking into account that inhibition of IGF-IR signaling may inhibit metastasis without affecting primary tumor growth. These results also suggest that inhibition of IGF-IR will be most beneficial to prevent metastases, but may be less successful in treating established micrometastatic disease.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 71.

Role of the insulin receptor in IGF-system signaling and biology

Abstract #4055

The role of the type I insulin-like growth factor (IGF) receptor (IGF1R) in breast cancer has been extensively studied, and has led to the development of several IGF1R inhibitors currently in clinical trials. The closely related insulin receptor (IR) has been shown to contribute to IGF signaling through the formation of IGF1R/IR-hybrid receptors and through a homodimer of an alternatively spliced form of the IR (IR-A). Understanding the role of the IR in cancer biology will help determine which receptor(s) in the IGF system should be targeted to efficiently inhibit IGF signaling. Our previous work has shown that selective downregulation of IGF1R by siRNA resulted in enhanced sensitivity to insulin through increasing the numbers of insulin receptor homodimers. To determine how downregulation of IR affected IGF1R signaling, we used T47D cells, a breast cancer cell line expressing both the IR and IGF1R, as our model system. We transiently downregulated IR levels using siRNA and evaluated signaling. 5 nM of insulin activated downstream signaling molecules, such as insulin receptor substrate 1(IRS-1) and Akt in control cells, but this response was diminished in the IR-downregulated cells. In contrast, 5 nM of IGF-I did not result in differences in signaling between IR-downregulated cells and control cells. Using IR shRNA, we created stable clones with IR levels reduced by more than 72%. IR shRNA clones demonstrated decreased insulin binding, as measured by 125I-insulin binding assay. Additionally, clones showed decreased response to insulin signaling. 5 nM of insulin activated IRS-1 and Akt in parental T47D cells, but this response was attenuated in the IR-downregulated clones. Proliferation was also decreased in response to 5 nM insulin in the clones compared to parental cells. In contrast, IGF-I mediated signaling was not altered in clones when compared to vector control cells. Further, no change in proliferation was observed in response to IGF-I between wild-type and IR shRNA clones. We also generated stable IR shRNA clones using LCC6 cells. Insulin signaling was reduced in LCC6 clones when compared to wild-type LCC6 cells. However, in contrast to the T47D clones, IGF-I signaling was increased in LCC6 IR shRNA clones. Thus, the role of the insulin receptor in cancer biology may be dependent upon the ratio of IR, IGF1R, and the hybrid receptor. If cells contain mostly homodimers of IGF1R and IR, then downregulation of IR may affect only insulin response. However, if there are high levels of hybrid receptor, then downregulation of IR could affect, and even augment, IGF1R signaling. Our data suggest that the ratio and confirmation states of both IR and IGF1R should be understood to predict the effect of receptor downregulation.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4055.

IGF-I mediated phosphorylation of ERαS167 occurs downstream of mTOR/p70S6K1 to impact nuclear localization and chromatin interaction

Abstract #6012

Crosstalk between the insulin-like growth factor (IGF) I receptor (IGF-IR) and estrogen receptor alpha (ERα) enhances breast cancer cell growth and survival. Interaction between these receptors has been extensively characterized in numerous in vitro and in vivo cell models. Activation of the IGF-IR results in the recruitment of the serine/threonine kinase Akt/PKB, which has been shown to directly phosphorylate ERα at Serine167. These findings were demonstrated in transient transfection model systems. To study if IGF-IR activation of Akt/PKB results in ERα phosphorylation, we used the MCF-7L breast cancer cell line expressing both IGF-IR and ERα. In these cells, IGF-I-induced activation of the IGF-IR/PI3K/Akt axis resulting in the subsequent phosphorylation of ERα at serine 167 as early as 10 minutes and was seen up to 24 hours indicating that this was not a transient phenomenon. In addition, this event was site-specific for ser167, as IGF-I exposure did not result in the phosphorylation of the estradiol (E2)/mitogen activated protein kinase (MAPK) regulated serine 118 site of ERα. Contrary to prior reports, we observed that IGF-I induced ERαS167 phosphorylation was abolished by rapamycin, an inhibitor of mammalian target of rapamycin (mTOR). As expected, rapamycin failed to block E2 stimulated ERαS118 phosphorylation. These events were further confirmed in two additional strains of MCF-7 cells (MVLN & MCF-7ATCC). In an effort to confirm that the events responsible for IGF-I induced ERαS167 phosphorylation were distal to mTOR activation, we targeted multiple additional signaling molecules in the IGF-IR/PI3K/Akt/mTOR pathway. Blockade of PI3K (LY294002), mTOR (rapamycin) and the downstream mTOR kinase p70S6K1 (H89) resulted in a dose-dependent ablation of ERαS167 phosphorylation. In addition to blocking ERα phosphorylation, H89 specifically also inhibited eukaryotic initiation factor (eIF) 4B (eIF4B), a known immediate downstream target of activated p70S6K1. Phosphorylation of ERαS118 did not require MAPK activation, as the MEK inhibitor U0126 ablated MAPK activation and did not affect ERαS167 phosphorylation. Furthermore, we find that siRNA-mediated knockdown of p70S6K1 results in a concordant attenuation of IGF-mediated ERαS167 phosphorylation independent of the ERαS118 site. Thus, we find that phosphorylation of ERαS167 in MCF-7L cells is regulated downstream of IGF-IR by p70S6K1, a kinase known to initiate the translation of multiple mRNA transcripts. Since modification of ERα by serine phosphorylation has been shown to impact DNA binding, transcription, dimerization and coactivator recruitment, we hypothesize that IGF-IR/PI3K/Akt initiation induces ERαS167 phosphorylation through an PI3K/mTOR-specific pathway and may alter classical nuclear ERα function. More importantly, IGF/ERα crosstalk occurs at the level of post-translational modification of ERα and may serve to promote the malignant phenotype in breast cancer cells.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6012.

Sequencing of type I IGF receptor (IGF1R) inhibition affects chemotherapy response in vitro and in vivo

Abstract #3122

Purpose: To determine the optimal sequence of combining anti-IGF1R antibodies with chemotherapeutic drugs in cancer cells in vitro and in vivo.&#x2028; Experimental design: MCF-7 and LCC6 cells were treated with sub-cytotoxic concentrations of doxorubicin (DOX) with or without anti-IGF1R antibodies (scFv-Fc or EM164 and its humanized version AVE1642). Treatments were given simultaneously, DOX followed by anti-IGF1R antibody, or anti-IGF1R antibody followed by DOX, with measurement of in vitro proliferation, apoptosis, and anchorage-independent growth. Effects of sequencing on LCC6 xenograft growth and metastasis were studied.&#x2028; Results: DOX followed by anti-IGF1R antibody (scFv-Fc or EM164) was the most effective combination strategy to inhibit cell monolayer growth and anchorage-independent growth. This sequential combination triggered increased Poly (ADP-ribose) polymerase (PARP) cleavage compared to other treatment sequences. The reverse sequence, antibody followed by DOX treatment, protected cells from chemotherapy by decreasing apoptosis, arresting cells in S phase, and inhibiting the level and activity of topoisomerase IIα . Finally, our in vivo data show that recovery of IGF1R prior to DOX therapy resulted in the best therapeutic responses. Low doses of AVE1642 that allowed IGF1R expression to recover at one week were more effective in combination with DOX than higher antibody doses.&#x2028; Conclusion: The timing of IGF1R inhibition affects responses to chemotherapy. The optimal sequence was DOX followed by anti-IGF1R antibody, while the opposite sequence inhibited DOX effects. Thus, short course suppression in combination with DOX might be the optimal combination and provides a rationale for the design of future clinical trials.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3122.

MCF-7 cells selected for acquired resistance to an anti IGF-IR antibody remain sensitive to fulvestrant and to an IGFIR tyrosine kinase inhibitor (TKI)

Abstract #72

Monoclonal antibodies and tyrosine kinase inhibitors (TKI) targeting the type-1 Insulin-like growth factor receptor (IGFIR) are currently in clinical trials. Resistance to several targeted therapies has been observed and is not well understood. Estrogen receptor (ER) has been shown to interact with IGFIR signaling to promote cell growth. To examine acquired resistance to IGF1R monoclonal antibodies, we selected ER positive MCF7L cells in increasing concentrations of an IGFIR inhibitory antibody (scFvFc, treated over 2 years). These cells (MCF7L-scFvFc) had downregulated IGFIR levels, increased basal phosphorylation of IRS-1 with constitutive activation of Akt. MCF7L-scFvFc cells had enhanced basal growth and were no longer responsive to IGF-I and estradiol (E2). To examine the relationship between IGF1R and ER function, we used the pure steroidal anti-estrogen fulvestrant to examine effects on growth of the parent and antibody-resistance cells. In parent MCF7L cells, fulvestrant inhibited growth responses to IGF-I and E2 treatment when each ligand was given individually, but when both ligands were given together, the growth inhibition was reversed. In MCF7L-scFvFc, fulvestrant inhibited growth response to IGF-I, but cells still responded to E2 even in the presence of fulvestrant. Fulvestrant inhibition of MCF7L-scFvFc basal growth was associated with downregulation of ER and IGFIR system components. Fulvestrant treatment induced PARP cleavage in MCF7L, but not in MCF7L-scFvFc cells. IGF-I partially protected cells against fulvestrant induced PARP cleavage, and E2 treatment has full protective effects on these cells. These data suggest that MCF7L-scFvFc cells were more resistant to cell apoptosis induced by fulvestrant. Other monoclonal antibodies directed against IGF1R were ineffective in reversing the resistance in MCF7L-scFvFc cells. To determine if activated IGF1R was responsible for the behavior of MCF7L-scFvFc cells, we used the IGF1R TKI AEW541. AEW541 inhibited growth of these antibody resistant cells and a combination of fulvestrant and AEW541 completely inhibited cell growth and IGF signaling in both MCF7L and MCF7L-scFvFc cells. Thus, activated IGFIR signaling was still required for the growth of MCF7L-scFvFc cells. In conclusion, MCF7L-scFvFc had low levels of IGF1R but retained activated IGF1R signaling that was inhibited by TKI (AEW541). In addition, the ER antagonist fulvestrant also inhibited growth of these cells. In these ER-positive cells, combined blockade of ER and IGF1R could provide a more prolonged inhibition of cell growth. Moreover, cells selected for resistance to an IGF1R antibody remain sensitive to IGF1R TKIs. Thus, concurrent or sequential targeting of IGF1R and ER function should be examined in breast cancer clinical trials of ER positive breast cancer.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 72.

Disrupting IGF signaling in breast cancer as a therapeutic strategy

Abstract #ES-3

Disrupting endocrine signaling in breast cancer has long been a mainstay of therapy. Understanding that the estradiol and estrogen receptor-α (ERα) play and important role in breast cancer has led to important advances in risk reduction, adjuvant therapy, and management of metastatic disease. Similar to estrogen, the insulin-like growth factors (IGF) and their receptors have an important role in maintenance of the malignant phenotype.&#x2028; The type I IGF receptor (IGF1R) is a heterotetrameric, trannsmembrane tyrosine kinase receptor with a high degree of homology to insulin receptor. Physiologic activation of this receptor requires ligand binding. There are two circulating ligands (IGF-I and IGF-II) which are highly homologous to insulin. There is some promiscuity in the ligand-receptor interactions. For example, IGF-II has high affinity for the heterotetrameric insulin receptor. Though the potential for complex interactions are evident, the IGF system can be disrupted by several potential strategies including ligand deprivation, inhibition of ligand binding to the receptor, and inhibition of receptor tyrosine kinase function.&#x2028; To date, several anti-IGF monoclonal antibodies and tyrosine kinase inhibitors have entered clinical trial. Anti-IGF1R antibodies have activity as single agents and in combination with cytotoxic chemotherapy in sarcoma and lung cancer. While the future of these anti–IGF receptor antibodies are not clear yet it, appears that clinical activity would warrant further study.&#x2028; In breast cancer there are abundant preclinical data suggesting that IGF disruption could be an effective strategy. There are several important challenges regarding targeting the IGF system in breast cancer. First, it is uncertain which specific subtypes of breast cancer are sensitive to IGF system inhibition. Preclinical data suggests that every subtype of breast cancer (ER-positive, HER2 amplified, and triple-negative) could be IGF-driven. Second, some phenotypes driven by IGF1R do not result in an easily observable clinical outcome. For example, we have shown that disruption of IGF1R may block metastasis but does not interfere with tumor growth. Third, combining anti-IGF1R therapy with cytotoxic agents is not necessarily straightforward. We have shown that sequencing of IGF1R inhibition with administration of doxrubicin has an important effect on growth of xenograft tumors. Fourth, the role for insulin receptor in regulating breast cancer biology needs clarification. While we believe that specific anti-IGF1R therapies would be desirable, it is possible that insulin receptor could regulate breast cancer biology. Finally, there are no clear predictive factors for anti-IGF therapy. While expression of IGF1R is clearly required, receptor expression alone is not sufficient to predict response.&#x2028; Thus, it is encouraging that new therapies directed against key targets in breast cancer will soon likely become available. We will be challenged to fully elucidate IGF signaling pathways and their biological effects in order to optimize the therapeutic benefit of these new drugs.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr ES-3.

Insulin-like growth factor binding protein-1 (IGFBP-1) targets both the insulin-like growth factor (IGF) and integrin pathways for the inhibition of breast cancer cell motility

Abstract #402

The insulin-like growth factor (IGF) system is a relevant therapeutic target for the treatment of breast cancer. Besides receptor targeted therapies, inhibition of ligand-receptor interactions by IGF-sequestering agents such as IGF binding proteins has also proven efficacious. We have used IGF binding protein (IGFBP-1) to neutralize IGF action. This binding protein both binds IGF-I and binds integrins through a RGD sequence and blocks IGF-I induced proliferation and motility. To examine the functional motifs in IGFBP-1, we studied breast cancer cells and examined IGF-induced signaling and biology after exposure to native recombinant human IGFBP-1 (rhIGFBP-1), reduced rhIGFBP-1, and an RGD mutant (Trp-Gly-Asp, WGD) rhIGFBP-1. Native and WGD IGFBP-1 retained IGF-I binding affinity, whereas reduced IGFBP-1 lost ligand binding as confirmed by western ligand blot. Chronic (&gt;3 hour) 80nM rhIGFBP-1 treatment abrogated paxillin phosphorylation and initiated MAPK activation in an IGF-independent manner, and inhibited basal motility and adhesion to fibronectin. While 80nM native rhIGFBP-1 abolished IGF-induced IRS, PKB/Akt and ERK phosphorylation, 80nM reduced rhIGFBP-1 only inhibited IGF-induced PKB/Akt phosphorylation. rhIGFBP-1 inhibited IGF-induced motility, adhesion to fibronectin and anchorage independent growth at IC50 40-80nM. In contrast, efficacy of reduced IGFBP-1 ranged between 80-160nM. Both the IGF-binding and the integrin-binding mechanisms of action of IGFBP-1 were inhibitory to IGF-induced integrin functions. In contrast, IGF-neutralization (but not integrin effects) was required for the inhibition of biology of breast cancer cells in monolayer. Therefore, this study demonstrates that IGFBP-1 has two distinct functional motifs that contribute to the inhibition of breast cancer basal and IGF-induced functions, and that the integrin and IGF-binding motifs of IGFBP-1 cooperatively inhibit IGF-action.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 402.

Comparative breast tumor imaging to identify the expression of type I IGF receptor (IGF1R) by anti-IGF1R antibody-conjugated small molecule fluorophore or quantum dots in vivo

Abstract #6001

The type I insulin-like growth factor (IGF) receptor (IGF1R) is a transmembrane receptor tyrosine kinase involved in breast cancer proliferation, survival, and metastasis. Several antibodies against IGF1R, including some in clinical trials, downregulate the level of IGF1R both in cell line studies and in in vivo animal experiments. Thus, this downregulation is a biodynamic marker of antibody delivery to the tumor. To date, identification of IGF1R expression and its downregulation in vivo in a non-invasive way is still challenging. In this study, we sort to use two different fluorescent technologies, small molecule fluorophores, or quantum dots (QDs), to detect receptor expression and its downregulation by antibodies in vivo. Alexa 680 is a small molecule fluorophore that can be excited with a peak emission at 705 nm. QDs are nanocrystals that emit fluorescence upon excitation, and QDs with a peak emission at 705 nm was used in this study. Both Alexa 680 and QDs were conjugated with AVE-1642, a humanized anti-IGF1R antibody developed by sanofi-aventis. After conjugation, they both were able to detect the expression of IGF1R and its downregulation in in vitro cell line studies. We used mouse xenograft tumor models to examine their efficacies in vivo. AVE-1642 conjugated Alexa 680 or QDs (705 nm) was intravenously delivered to mice bearing mammary xenograft tumors that express IGF1R. After 24 hours of circulation, Alexa 680 fluorescence was shown to solely localize to the xenograft tumor, with little non-specific targeting to other tissue or organs in mice. In addition, Alexa 680 fluorescence was diminished in tumors that had downregulated IGF1R by antibody pretreatment. In contrast, conjugated QDs fluorescence was mainly localized to liver, spleen, bone marrow and lymph nodes, with very small amount of QDs in the xenograft tumors. The QDs fluorescence in xenograft tumors remained unchanged even when IGF1R was downregulated by antibody pretreatment. Furthermore, we identified that QDs were mainly localized to the hepatic sinusoids, and subsequently engulfed by Kupffer cells. Taken together, our data suggest that small molecule fluorophores, such as Alexa 680, are useful agents to detect the expression and downregulation of IGF1R in vivo. Our data provide valuable insight not only into the clinical development of anti-IGF1R antibodies, but also to other targeted therapy as well.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6001.