P5-06-09: Acquired Sensitivity to TRAIL Mediated Apoptosis in Lapatinib Resistant SKBR3 Cells

Introduction Lapatinib, a dual EGFR/HER2 tyrosine kinase inhibitor is approved for the treatment of trastuzumab-refractory HER2 positive metastatic breast cancer. However, not all HER2 positive tumors respond to lapatinib and patients who initially respond frequently relapse. Understanding the molecular alterations associated with acquisition of lapatinib resistance may lead to the identification of targets to overcome resistance. Thus, the aim of this study was to examine changes in apoptosis in a model of acquired lapatinib resistance.

Methods SKBR3 cells were treated with 250 nM lapatinib twice weekly for 6 months to establish the lapatinib resistant cell line SKBR3-L. The effects of TNF-related apoptosis-inducing ligand (TRAIL) and tumour necrosis factor-α (TNF-α) on cell survival and apoptosis induction were examined in SKBR3 and SKBR3-L cells, using the acid phosphatase proliferation assay and the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. Cleavage of poly ADP ribose polymerase (PARP) was used to confirm apoptosis. TRAIL-1 and TRAIL-2 receptor expression were measured by flow cytometry (FACS).

Results In SKBR3-L cells, TRAIL treatment (25 ng/ml) significantly inhibited cell survival (94.0 ± 12.0 %) compared to the SKBR3 cells (11.0 ± 2.2%). Treatment with TNF-α (0.5 ng/ml) also resulted in significant inhibition of cell survival (68.2 ± 10.1 %) in SKBR3-L cells compared to SKBR3 cells (9.4 ± 9.0 %). TRAIL (25 ng/ml) induced a low level of apoptosis in SKBR3 cells (7.0 ± 4.0%), whereas in SKBR3-L cells, TRAIL (25 ng/ml) induced significant apoptosis (54.8 ± 2.6%, p < 0.001), as determined by the TUNEL assay. We confirmed by western blotting that TRAIL treatment for 72 hours resulted in higher levels of PARP cleavage in SKBR3-L cells compared to SKBR3 cells. Both western blotting and FACS analysis of TRAIL receptor expression showed that neither TRAIL-1 nor TRAIL-2 receptor expression was significantly elevated in SKBR3-L cells compared to SKBR3 cells.

Conclusions SKBR3-L cells, a model of acquired lapatinib resistance, display significant sensitivity to TRAIL induced apoptosis compared to the parental cell line SKBR3. Thus, targeting TRAIL may represent a novel therapeutic strategy to overcome acquired lapatinib resistance.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-06-09.

P1-17-05: Preliminary Results of a Randomized Phase 2 Study of PD 0332991, a Cyclin-Dependent Kinase (CDK) 4/6 Inhibitor, in Combination with Letrozole for First-Line Treatment of Patients (pts) with Post-Menopausal, ER+, HER2−Negative (HER2–) Advanced Breast Cancer

Background: PD 0332991 is an orally bioavailable selective inhibitor of CDK 4/6 and prevents cellular DNA synthesis by prohibiting progression of the cell cycle from G1 into the S phase. Preclinical evaluations suggest that reduction in CDKN2A (p16) expression and cyclin D1 (CCND1) overexpression confer susceptibility to PD 0332991 (Finn 2009). In addition, PD 0332991 was synergistic in combination with tamoxifen in vitro in ER+ human breast cancer cell lines. Based on these observations, a phase 1/2 study in combination with letrozole as first-line therapy for advanced ER+ post-menopausal breast cancer was initiated. The phase 1 part of the study (completed) determined the recommended phase 2 dose to be PD 0332991 125 mg QD on Schedule 3/1 (3 weeks on treatment followed by 1-week off treatment) in combination with letrozole 2.5 mg QD. The combination was generally well tolerated and encouraging antitumor activity was observed. We present preliminary data from the randomized Phase 2 portion comparing letrozole alone to letrozole plus PD 0332991.

Methods: The Phase 2 portion of the study is designed as a two-part study; we present data from Part 1. In both parts, eligible patients are randomized 1:1 to letrozole 2.5 mg QD alone (control) or PD 0332991 125 mg QD on schedule 3/1 and letrozole 2.5 mg QD (treatment, tx). Part 1enrolled post-menopausal women with ER+, HER2− cancer using only ER+, HER2−as a selection criteria. Part 2 is now enrolling post-menopausal women with ER+, HER2− breast cancer with CCND1 amplification and/or loss of p16 by FISH (target N=150). The primary endpoint is progression-free survival (PFS); secondary endpoints include overall survival, response rate, safety, and correlative studies. Pts are stratified for disease site and length from prior adjuvant therapy. Pts continue assigned study treatment until disease progression, unacceptable toxicity, or consent withdrawal and are followed every 2 months to assess disease status. Tumor tissue was required for participation.

Results: 66 patients have been randomized in Part 1. At the time of data cut-off (April 2011) median duration of treatment is 20 (range 4–64) wks for control and 27 (2-59) wks for tx. Dose reductions occurred in 9 pts on the tx arm and none on the control arm. There are no complete responses. The number of partial responses for pts with measurable disease are similar between arms (4/22 control vs 5/24 in tx). The number of pts with stable disease> 24 weeks was higher in the tx arm (5 vs 8). The number of pts with best response of progressive disease is lower in the treatment arm (2 vs 6). PFS data are immature. Twelve pts remain on control vs. 21 on tx. As in the Phase I portion of the study, the most common treatment-related AEs were neutropenia and leucopenia without febrile neutropenia. Biomarker studies for CCND1 amplification, p16 loss, RB status, and Ki67 are ongoing.

Conclusion: The combination of PD 0332991 and letrozole is well tolerated as first-line treatment of ER+, HER2− post-menopausal breast cancer. Updated efficacy data and biomarker data will be presented.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-17-05.

P2-18-04: Pilot Evaluation of Bevacizumab (Bev) in Combination with Docetaxel (T) and Cyclophosphamide (C) as Adjuvant Treatment (AdjRx) for Patients (pts) with Early Stage (ES) Breast Cancer (BrCa)

Background

The combination of Bev + chemotherapy (CRx) has been shown to produce superior response rates and progression free survival compared to CRx alone, providing a rationale for the study of Bev with AdjCRx for pts with ESBrCa. As Bev can cause hypertension (HTN) and may increase the risk of cardiac failure, there is a rationale for studying a standard non-anthracycline (Anth) AdjCRx with Bev, e.g. TC (docetaxel-cyclophosphamide). We performed a pilot phase II study to evaluate the feasibility and toxicity of TC+Bev in pts with ESBrCa in preparation for participation in a random assignment trial. We have previously reported preliminary toxicity data.

Methods: Eligibility criteria included: ESBrCa which was HER-2 normal, node+ or, N- and primary tumour (T) >2 cm and receptor negative, or T >3 cm, normal left ventricle ejection fraction (LVEF), no active/uncontrolled cardiovascular disease, normal organ and marrow function. Treatment consisted of four 3-weekly cycles of docetaxel 75 mg/m2 together with cyclophosphamide 600 mg/m2. Patients commenced Bev 15 mg/kg i.v. on day 1, and then every 3 weeks to a total of 18 cycles of treatments. Pts were monitored clinically, with echocardiograms and with serial estimations of BNP and troponin.

Results: A total of 106 female pts were accrued in 9 ICORG sites between 11/2008 and 7/2010. Ages ranged from 25–75 (median 52). On 20/06/2011, 105 pts have completed study Rx, 1 will finish 7/2011. A total of 36 serious adverse events (SAEs) have been reported so far, 33 involving hospital admission, 3 serious for other reasons. In 25 (24%) pts study Rx was discontinued due to: HTN-9, intestinal perforation-2, consent withdrawl-7, infection-2, proteinuria-1, anaphylaxis-1, cancer relapse-1, arthralgia-1, anal fistula-1. The two perforations occurred at cycles 1 and 16 of Bev respectively. Neither pt with perforation had history of prior abdominal surgery. The median number of cycles achieved by the discontinued pts was 9. HTN of any grade occurred in 49 out of 103 (48%) pts who had no HTN at baseline (BL) and 42 of them required Rx. Among pts who experienced HTN on study Rx and completed Bev, 34 (81%) were still on anti-hypertensive 4 weeks after last infusion of Bev. Forty-one (39%) pts had LVEF drop >10% from BL during study Rx. In 8 (7.5%) pts LVEF declined below 50%, 6 are documented to have recovered to normal, 2 had no further LVEF measurements (1 declined, 1 unknown reason). No episodes of CCF were reported. Troponin and BNP levels were normal in all 57 pts with serial measurements. Fourteen pts required treatment for neutropenia-related infection or for abscess/fistula.

Conclusions: In this study Bev overall toxicity in ESBC pts was similar to that reported for pts with MBC, and Bev discontinuation due to toxicity was relatively frequent. Although no pt developed CCF 7.5% of decline in LVEF<50% was observed. Intestinal perforation can occur in ESBC pts in absence of prior intestinal surgery and in the post-CRx phase of Bev. Pts receiving Bev with non-Anth AdjCRx require careful monitoring for toxicity.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-18-04.

P1-12-06: The Role of MAPK and PI3K/AKT/mTOR Signaling in Innate Lapatinib Resistance

Background: Lapatinib is a tyrosine kinase inhibitor which blocks downstream MAPK and P13K/AKT/mTOR proliferation and survival signaling pathways in HER2 positive breast cancer cell lines, tumor xenografts and HER2 positive breast cancer patients. However, pre-clinical and clinical studies have shown that not all HER2 positive patients respond to lapatinib and thus innate resistance to lapatinib exists. The identification of biomarkers of lapatinib response is therefore critical and would enable individual therapeutic decisions to be based on tumor biology rather than basic histopathology data alone. The aim of this study was to examine the role of MAPK and PI3K/AKT/mTOR signaling in a panel of lapatinib sensitive and resistant HER2−amplified breast cancer cell lines to identify pharmacodynamic markers of response to lapatinib treatment.

Methods: Dose response curves were generated to determine sensitivity to lapatinib in a panel of 17 HER2−amplified breast cancer cell lines. Total and phosphorylated levels of HER2, HER3, EGFR, AKT, ERK, S6K and eEF2 were determined following 24 hours lapatinib treatment in each of the cell lines.

Results: Twelve of the cell lines were sensitive to lapatinib with IC50g < 1 μM while 5 of the cell lines were innately resistant to lapatinib with IC50g > 1 μM. Levels of pHER2 and pHER3 were decreased in response to lapatinib in all cell lines independent of sensitivity to lapatinib. This suggests that inhibition of HER2/HER3 activation is not indicative of response to lapatinib treatment. There was also no correlation between the levels of HER2, HER3, and EGFR and sensitivity to lapatinib in the cell line panel.

In lapatinib sensitive cell lines, lapatinib decreased PI3K (pAKT), mTOR (pS6K) and MAPK (pERK) signaling and increased peEF2 levels. In contrast the levels of pAKT, pS6K, peEF2 and pERK were maintained following lapatinib treatment in lapatinib resistant cells. The continued activation of these proteins in the presence of lapatinib suggests a possible feedback mechanism that warrants further investigation. These data confirm that maintained signaling through either the P13K/AKT/mTOR pathway or the MAPK pathways in the presence of lapatinib can be an early pharmacodynamic biomarker of response.

Conclusions: Maintenance of pAKT, pS6K, peEF2 and pERK levels, in response to lapatinib treatment correlates with lapatinib resistance. These data suggest that alterations in the P13K/AKT/mTOR and MAPK pathways play an important role in innate lapatinib resistance and pharmacologically targeting these pathways is a rational therapeutic approach for overcoming innate lapatinib resistance.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-12-06.

The cocaine- and amphetamine-regulated transcript mediates ligand-independent activation of ERα, and is an independent prognostic factor in node-negative breast cancer

Personalized medicine requires the identification of unambiguous prognostic and predictive biomarkers to inform therapeutic decisions. Within this context, the management of lymph node-negative breast cancer is the subject of much debate with particular emphasis on the requirement for adjuvant chemotherapy. The identification of prognostic and predictive biomarkers in this group of patients is crucial. Here, we demonstrate by tissue microarray and automated image analysis that the cocaine- and amphetamine-regulated transcript (CART) is expressed in primary and metastatic breast cancer and is an independent poor prognostic factor in estrogen receptor (ER)-positive, lymph node-negative tumors in two separate breast cancer cohorts (n=690; P=0.002, 0.013). We also show that CART increases the transcriptional activity of ERα in a ligand-independent manner via the mitogen-activated protein kinase pathway and that CART stimulates an autocrine/paracrine loop within tumor cells to amplify the CART signal. Additionally, we demonstrate that CART expression in ER-positive breast cancer cell lines protects against tamoxifen-mediated cell death and that high CART expression predicts disease outcome in tamoxifen-treated patients in vivo in three independent breast cancer cohorts. We believe that CART profiling will help facilitate stratification of lymph node-negative breast cancer patients into high- and low-risk categories and allow for the personalization of therapy.

Triple negative breast cancer: proposals for a pragmatic definition and implications for patient management and trial design

In trials in triple negative breast cancer (TNBC), oestrogen and progesterone receptor negativity should be defined as < 1% positive cells. Negativity is a ratio of <2 between Her2 gene copy number and centromere of chromosome 17 or a copy number of 4 or less. In routine practice, immunohistochemistry is acceptable given stringent quality assurance. Triple negativity emerging after neoadjuvant treatment differs from primary TN and such patients should not enter TNBC trials. Patients relapsing with TN metastases should be eligible even if their primary was positive. Rare TN subtypes such as apocrine, adenoid-cystic and low-grade metaplastic tumours should be excluded. TN and basal-like (BL) signatures overlap but are not equivalent. Since the significance of basal cytokeratin or EGFR overexpression is not known and we lack validated assays, these features should not be used to subclassify TN tumours. Tissue collection in trials is mandatory so the effect on outcome of different tumour phenotypes and BRCA mutation can be explored. No prospective studies have established that TN tumours have particular sensitivity or resistance to any specific chemotherapy agent or radiation. TNBC patients should be treated according to tumour and clinical characteristics.

Abstract P3-10-24: Fibroblast Growth Factor Receptor 1 Amplification and Overexpression in Breast Cancer Tissue Microarrays Using Chromogenic In Situ Hybridization and Immunohistochemistry

Fibroblast growth factor receptors 1 (FGFR1) belongs to a subfamily of receptor tyrosine kinases (RTKs), which are involved in proliferation and apoptosis. FGFR1 amplification and mRNA overexpression occurs in ∼10% of breast cancers and has been associated with poor outcome. However, studies assessing FGFR1 amplification and protein overexpression in a large collection of breast tumors are lacking. In this prospective, we examined a series of primary breast cancers samples derived from the BCIRG trials assembled into 15 tissue microarrays. FGFR1 gene amplification was studied using chromogenic in situ hybridization (CISH) and evaluated with respect to association with level of protein expression and clinicopathological parameters. FGFR1 gene amplification was significantly associated with high protein levels as determined by immunohistochemistry (P&lt;0.0001, 3294 pts with available matched CISH and IHC records). Overall, the incidence of FGFR1 amplification found was 9.7% (160 out of 1646 pts. with available clinicopathological records) without a statistically significant difference between Her2- (78 out 720 pts., 11%) and Her2+ (82 out of 926 pts., 9%) cancers. In both cohorts, the hormone receptor-positive (ER+/PR+) cancers showed statistically significant higher levels of FGFR1 amplification compared to hormone receptor-negative tumors. In the analysis of the association of FGFR1 and the presence of PIK3CA mutations, the incidence of FGFR1 amplificationwas greatly reduced in mutant vs. wt PI3KCA tumors. In these cohorts, a clear relationship between FGFR1 amplification status and clinical outcome was not detected. Data from this large study confirms recently reported incidences of FGFR1 amplification in breast cancer and shows for the first time an association between FGFR1 gene amplification and protein overexpression. Moreover, the lower incidence of FGFR1 amplification in PIK3CA mutated cancers suggests that these are largely exclusive molecular events that could benefit from different targeted therapies.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-10-24.

Abstract P5-10-17: Bevacizumab (Bev) in Combination with Docetaxel (T) and Cyclophosphamide (C) as Adjuvant Treatment (AdjRx) for Patients (pts) with Early Stage (ES) Breast Cancer (BrCa) and Normal HER-2 Status. A Pilot Evaluation

In random assignment trials, the combination of Bev+ chemotherapy has been shown to produce superior response rates and progression free survival compared to chemotherapy alone, providing a rationale for the study of Bev in the AdjRx of pts with ESBrCa. As a principal side effect of Bev is hypertension (HTN), anthracycline-containing (Anth) AdjRx may pose additional cardiovascular risks. The role of Anth in Her2 normal ESBC is uncertain. TC is a standard non-Anth AdjRx. We performed a single arm pilot study to evaluate the feasibility and toxicity of TC+Bev in pts with ESBC in preparation for participation in a random assignment trial. Methods: Eligibility criteria included: ESBC which was HER-2 normal, node-positive or &gt;2 cm and receptor negative, or &gt;3 cm and receptor positive, normal cardiac ejection fraction (EF), no active or uncontrolled cardiovascular disease, normal organ and marrow function. Treatment consisted of four 3 weekly cycles of docetaxel 75 mg/m2 together with cyclophosphamide 600 mg/m2. Patients commenced bevacizumab 15 mg/kg i.v. on day 1, and q 3 weeks to a total of 19 treatments. Pts were monitored clinically, with echocardiograms and with serial estimations of BNP and troponin.

Results: A total of 105 female pts were accrued in 9 ICORG sites between Dec 2008 and June 2010. Ages ranged from 26-86 (median 55). At June 2010, 33 have completed all phases of therapy, 54 are still on treatment. Eighteen pts have been removed from study due to: HTN -7, intestinal perforation -2, withdrew consent-4, proteinuia-1, anaphylaxis-1, infection-3. The perforations occurred at cycles 9 and 19. Neither pt. with perforation had prior abdominal surgery. The median number of cycles achieved by the discontinued pts was 9. HTN requiring Rx occurred in 25 pts. Among 12 with HTN who have completed Bev, 2 are off HTN meds, and 9 are on reducing doses. The median EF at base line was 67%, at 13 cycles (42 pts) 63%, 18 cycles (27 pts) 66%. Six pts had EF drop &gt;10%, in 3 of these EF fell below 50% as last recorded value. There were no episodes of clinical cardiac failure. Troponin and BNP levels were normal in all 57 pts with serial measurements. Thirteen pts required treatment for neutropenia-related infection or for abscess.

Conclusions: The spectrum and frequency of bevacizumab toxicity in our population of healthy adjuvant pts is similar to that reported for pts with metastatic BC and other malignancies. Hypertension is the principal cause of treatment discontinuation, but cardiac toxicity appears to be limited, with this non-anth chemotherapy +Bev. Intestinal perforation can also occur in pts with ESBC. These toxicities can occur in the post chemotherapy phase of Bev therapy. Pts enrolled on random assignment trials of Bev containing AdjRx require careful monitoring for toxicity.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-10-17.

Abstract P4-01-06: The Role of the PI3K/AKT, RAS/MAPK and Novel Signaling Pathways in Resistance to HER2-Targeted Therapy

Despite the proven clinical benefits of HER2-targeted therapy, resistance to trastuzumab and lapatinib exists. Understanding the molecular mechanisms responsible for resistance is critical to improving the survival rates of patients with this aggressive subtype of breast cancer. Currently, there are no clinically validated biomarkers of resistance to therapy. To address this issue, we measured the responses of a panel of 18 HER2-amplified breast cancer cell lines to both trastuzumab and lapatinib and evaluated the activity of PI3K/AKT/mTOR and RAS/MAPK/ERK signaling in resistance. Eight of the cell lines were identified as resistant to trastuzumab and seven as resistant to lapatinib by both two and three dimensional response assays. Five of the trastuzumab resistant cell lines remained sensitive to lapatinib (IC50 &lt; 1 μM), indicating that these two agents have at least partially non-overlapping mechanisms of resistance. The combination of low PTEN or the presence of activating mutations of PI3K, and thus increased activity of PI3K/AKT signaling, is a strong predictor of resistance to trastuzumab. However, this is not the case with lapatinib, two of the cell lines with activating mutations of PI3K (MDA-361 and HCC-202) were resistant to lapatinib whereas two other PI3K mutant cells lines (SUM-190 and HCC-1954) were lapatinib sensitive, indicating that lapatinib resistance can occurindependently of increased PI3K/AKT signaling. To further investigate these mechanisms, we measured the effects of trastuzumab and lapatinib treatment on AKT/mTOR and ERK activation. Cell lines sensitive to trastuzumab or lapatinib showed a marked reduction in pAKT, pS6K and pERK in response to either agent, whereas the resistant cells maintained high pAKT, pS6K and pERK levels in the presence of trastuzumab and lapatinib. In cell lines resistant to trastuzumab yet sensitive to lapatinib, treatment with lapatinib significantly reduced the phosphorylation of AKT, S6K and ERK. Thus in a subpopulation of cell lines lapatinib can overcome trastuzumab resistance via continued deactivation of PI3K/AKT/mTOR and MAPK/ERK signaling. However, there still remains a subgroup of HER2-positive cells that are resistant to both trastuzumab and lapatinib. We used global expression analysis by both mRNA microarray and proteomic screening to identify a set of genes and proteins that are consistently altered in these innately resistant cells relative to the sensitive cell lines. In vitro validation of these targets will reveal which are playing a functional role in resistance and are thus potentially druggable targets to be used in improving the survival of patients with HER2-positive disease.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-01-06.

Inhibition of IGF1R activity enhances response to trastuzumab in HER-2-positive breast cancer cells

BACKGROUND

although trastuzumab has improved the prognosis for HER-2-positive breast cancer patients, not all HER-2-positive breast tumours respond to trastuzumab treatment and those that initially respond frequently develop resistance. Insulin-like growth factor-1 receptor (IGF1R) signalling has been previously implicated in trastuzumab resistance. We tested IGF1R inhibition to determine if dual targeting of HER-2 and IGF1R improves response in cell line models of acquired trastuzumab resistance.

MATERIALS AND METHODS

HER-2, IGF1R, phospho-HER-2, and phospho-IGF1R levels were measured by enzyme-linked immunosorbent assays in parental and trastuzumab-resistant SKBR3 and BT474 cells. IGF1R signalling was targeted in these cells using both small interfering RNA (siRNA) and the tyrosine kinase inhibitor, NVP-AEW541.

RESULTS

IGF1R levels were significantly increased in the trastuzumab-resistant model, SKBR3/Tr, compared with the parental SKBR3 cell line. In both the SKBR3/Tr and BT474/Tr cell lines, inhibition of IGF1R expression with siRNA or inhibition of tyrosine kinase activity by NVP-AEW541 significantly increased response to trastuzumab. The dual targeting approach also improved response in the parental SKBR3 cells but not in the BT474 parental cells.

CONCLUSIONS

our results confirm that IGF1R inhibition improves response to trastuzumab in HER-2-positive breast cancer cells and suggest that dual targeting of IGF1R and HER-2 may improve response in HER-2-positive tumours.