Evaluation of AZD8931, an Equipotent Inhibitor of erbB1, erbB2, and erbB3 Receptor Signaling, on Ligand Stimulated Breast Cancer Cell Lines with Differing Levels of erbB2 Expression

Background: Further treatment options for patients whose breast cancers do not overexpress erbB2 are required. AZD8931, an equipotent, reversible inhibitor of erbB1 (HER1, EGFR), erbB2 (HER2), and erbB3 (HER3) receptor signaling may be useful in this setting and may lead to inhibition of tumor cell proliferation, invasion, metastasis, angiogenesis and tumor cell survival.Objectives: To compare the activity of AZD8931 with other erbB inhibitors (gefitinib [G] and lapatinib [L]) in breast cancer cell lines stimulated with erbB ligands.Methods: A panel of 9 breast cancer cell lines with differing erbB2 expression levels were used: erbB2+/ER+ (BT474c; MDA-MB-361); erbB2+/ER- (MDA-MB-453; SKBR-3); erbB2-/ER+ (MCF7; T47D; ZR75-1); or erbB2-/ER- (MDA-MB-231; MDA-MB-468). Following overnight serum starvation, cells were incubated with AZD8931, G or L (0-10 µM) for 90 min and then stimulated with erbB ligands (50 ng/ml; EGF, TGFα, amphiregulin, epiregulin, betacellulin, neuregulin1, or HBEGF) for 5 min before lysis. Levels of phosphorylated erbB1, erbB2, and erbB3 were analyzed by ELISA. For IC50 determination, mean basal phosphorylation was subtracted. Geometric mean IC50s were calculated from triplicate assays and 2-sided unequal variance t-tests compared logIC50s.Results: AZD8931 demonstrated potent inhibitory activity (IC50s ≤10610 nM) when phosphorylation of erbB1, erbB2 or erbB3 receptors was driven by any erbB ligand. G demonstrated potent inhibitory activity (IC50s ≤20 nM) when the phosphorylation of erbB1 and erbB2 was driven by any erbB ligand. L more strongly inhibited the phosphorylation of erbB2 (IC50s ≤10 nM) than erbB1 (IC50s <400 nM) and showed a ligand and cell-dependant range of activities against erbB3 phosphorylation. AZD8931 was particularly differentiated from G and L in the inhibition of neuregulin1-driven erbB3 phosphorylation: IC50s were lower for AZD8931 (1-5 nM) than for G (1-120 nM) or L (20-80 nM) in the majority of the cell lines tested. Inhibition of erbB1 phosphorylation driven by EGF (IC50s ≤ vs >20 nM), TGFα (≤5 vs >20 nM), HB-EGF (≤ vs >25 nM), or betacellulin (≤6 vs 10-118 nM) also indicated more potent inhibitory activity for AZD8931 over L in cell lines that respond to ligand stimulation. No phosphorylation response to amphiregulin was seen in any of the cell lines.Conclusion: This study demonstrates that in a range of breast cell lines with varying levels of erbB2 expression, AZD8931 is a potent and balanced inhibitor of erbB1, erbB2, and erbB3 signaling. The pharmacological profile of AZD8931 is thus distinct from G and L and suggests that AZD8931 offers an agent to test the hypothesis that combined, balanced inhibition of erbB signaling could provide clinical benefit. AZD8931 may be particularly useful in the treatment of solid tumors that do not overexpress erbB2 including trastuzumab-ineligible breast cancer, an area of unmet medical need. AZD8931 is being evaluated in a Phase I clinical trial.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5059.

Exploratory subset analysis according to prior endocrine treatment of two randomized phase II trials comparing gefitinib (G) with placebo (P) in combination with tamoxifen (T) or anastrozole (A) in hormone receptor-positive (HR+) metastatic breast cancer (MBC)

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Background: Preclinical and clinical data suggest that increased EGFR and HER-2 activity contribute to acquired resistance to endocrine therapy. Strata of two clinical trials recently showed that the addition of G to T or A in HR+ MBC prolonged progression free-survival (PFS). Certain preclinical data also suggested that G should be combined with T or A from the start of endocrine therapy rather than waiting for resistance to develop. To examine this clinically a post hoc analysis compared the subsets of patients (pts) who had received prior endocrine therapy (may have already upregulated HER receptors) to those that were endocrine therapy naïve (not yet upregulated HER receptors). Methods: One trial evaluated G (250 mg/day orally) + A (1 mg/day orally) versus A+P ( NCT00077025 ) and one trial evaluated G (250 mg/day orally) + T (20 mg/day orally) versus T+P ( NCT00229697 ). Post hoc analysis of PFS was performed in two pt subgroups; previously treated with endocrine therapy (ET) and endocrine naïve (EN). The PFS HR and associated 95% CI and p-value for G relative to P were estimated using the Cox proportional hazards model along with interaction test for treatment by subset. Results: In the ET subgroup of the G+A versus A+P study, 31 PFS events were reobserved in 51 pts (hazard ratio [HR] 0.65 95% CI 0.32, 1.33; median PFS: G+A 11.2 mo, A+P 7.1 mo). In the EN subgroup, 23 PFS events were reobserved in 42 pts (HR 0.39, 95% CI 0.16, 0.97; median PFS: G+A 20.2 mo, A+P 8.4 mo). The interaction test p-value was 0.28. In the ET subgroup of the G+T versus T+P study, 95 PFS events were reobserved in 131 pts (HR 1.22, 95% CI 0.81, 1.86; median PFS: G+T 9.4 mo, T+P 10.9 mo). In the EN subgroup, 106 PFS events were reobserved in 158 patients (HR 0.78, 95% CI 0.52, 1.15; median PFS: G+T 12.1 mo, T+P 8.9 mo). The interaction test p-value was 0.13. Conclusions: The EN pt subgroups of both trials demonstrated prolonged PFS when G was combined with A or with T compared with A or T alone, respectively. A further prospective clinical trial of EGFR inhibition combined with endocrine therapy in EN pts with HR+ MBC is warranted on the basis of these findings.

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Characterization of AZD8931, a potent reversible small molecule inhibitor against epidermal growth factor receptor (EGFR), erythroblastic leukemia viral oncogene homolog 2 (HER2) and 3 (HER3) with a unique and balanced pharmacological profile

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Background: Successful combined pharmacological inhibition of EGFR, HER2, and HER3 signaling is currently under investigation in the clinic. HERs (erbB receptors including EGFR, erbB2, erbB3, erbB4) undergo various types of alteration and in many cancers HER ligands are produced either by the tumor cells themselves or surrounding stromal cells. These mechanisms of receptor activation all lead to constitutive proliferative and/or survival signaling driven by homo- and/or heterodimerization of the HER family. Characterization of a novel tyrosine kinase inhibitor with a potent and balanced profile against EGFR, HER2 (erbB2), and HER3 (erbB3) has been carried out. Methods: A range of assays has been developed to assess the detailed pharmacology of AZD8931 and understand how the profile of AZD8931 compares with other HER family inhibitors, such as gefitinib and lapatinib. These assays have provided unique insights into the pharmacology of these drugs that result from the varying levels of HER and their associated ligands. Results: Across a number of cell systems, AZD8931 has been shown to be a potent inhibitor of tumor cell growth. This effect is through the ability of AZD8931 to inhibit potently the phosphorylation of EGFR (0.004 μM; 95% CIR: 1.377), HER2 (0.003 μM; 95% CIR: 1.817) and HER3 (0.004 μM; 95% CIR: 1.890) in a balanced manner. Furthermore, when compared to control AZD8931 has significant and dramatic effects on the downstream signaling pathways (pAKT [p=0.002] & pMAK [NS]), apoptotic (M30 [p=0.004]), and proliferative (Ki67 [p<0.0005]) endpoints. The novel agent AZD8931 displays a distinct pharmacological profile compared to both gefitinib and lapatinib. Conclusions: Based on our data as well as published literature, the combined pharmacological inhibition of EGFR, HER2, and HER3 signaling has not yet been tested in the clinic. AZD8931 offers an agent to test the hypothesis that combined inhibition of HER signaling could provide additional clinical benefit in cancer, particularly in the majority of solid tumors that do not overexpress HER2.

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Role of EGFR but not HER2 or HER3 gene copy number in predicting sensitivity of head and neck squamous cell carcinoma (SCCHN) cell lines to EGFR tyrosine kinase inhibitors

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Background: EGFR gene copy number has previously been reported to predict for improved overall survival in NSCLC patients treated with gefitinib (IRESSA) or erlotinib compared with placebo [JCO 2006;24:5034–42 & N Engl J Med 2005;353:133–44]. The utility of EGFR gene copy number as a predictive biomarker in other tumour types such as squamous cell carcinoma of the head and neck (SCCHN) is currently under clinical investigation. The present study examined a panel of 20 SCCHN cell lines to identify potential biomarkers predicting in vitro sensitivity to EGFR tyrosine kinase inhibitors (TKIs). Methods: A panel of 20 SCCHN cell lines was screened for sensitivity to gefitinib, vandetanib or erlotinib using a viable cell number endpoint, with G150 values determined for each cell line (inhibitor concentration required to give 50% growth inhibition). Cell lines were blinded and assessed for EGFR, HER2 and HER3 protein expression by ELISA, mutation status by dye-terminator sequencing, and gene copy number by fluorescence in situ hybridisation (FISH). Results: A broad range in sensitivity was observed for all compounds across the panel of 20 SCCHN cell lines (G150 ranging from 0.001uM to =10uM). 12 cell lines were positive for EGFR genomic gain. Sensitivity (GI50 <1uM) to all EGFR TKIs was seen in 11 lines and resistance (GI50 >8uM) in 5 lines. Of the sensitive cell lines, 9 were positive for EGFR genomic gain compared with only 1 of the resistant lines. Furthermore, EGFR protein expression also had a direct association with EGFR TKI sensitivity. In contrast, only 4 cell lines were positive for HER2 or HER3 genomic gain and there was no correlation with sensitivity. The most sensitive cell line was positive for EGFR genomic gain and was the only line to have an EGFR TK mutation (S768I in exon 20). Conclusions: EGFR gene copy number and protein expression appeared to have predictive value in identifying SCCHN cell lines sensitive to EGFR TKIs.

No significant financial relationships to disclose.

Exploratory analysis of EGFR FISH criteria in Japanese non-small cell lung cancer patients treated with gefitinib

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Background: In the phase III Iressa (gefitinib) Survival Evaluation in Lung cancer (ISEL) trial, high epidermal growth factor receptor (EGFR) gene copy number was a predictor of a gefitinib effect on survival in patients (pts) with refractory advanced non-small-cell lung cancer (NSCLC) (hazard ratio 0.61 vs 1.16 for high vs low copy number; p=0.045) [JCO 2006;24:5034–42]. Although EGFR mutation status may predict response to gefitinib in Japanese pts, there is insufficient data to clarify if high EGFR gene copy number assessed by fluorescence in situ hybridization (FISH) is predictive in these pts. This analysis investigated the applicability of both published Colorado FISH criteria (Colorado Univ) and new FISH criteria to Japanese NSCLC pts. Methods: 58 tumor specimens from gefitinib-treated Japanese pts were analyzed using Vysis LSI EGFR and CEP7 (chromosome 7 control) FISH probes. Specimens were classed as FISH+ or - using Colorado and exploratory (EGFR/cell; CEP7/cell; EGFR/CEP7; % of cells with various numbers of EGFR or CEP7 signals) criteria. Results: Of the 58 pts, 17 (29%) had an objective response (OR). Using Colorado criteria, OR was 50% in the 14 FISH+ pts vs 23% in the 44 FISH- pts (2-sided Fisher's exact test p=0.089). There was a trend for an association between FISH+ status and improved survival (log rank p=0.15). Defining FISH+ as specimens with =5% cells containing >5 EGFR signals, OR was significantly better among FISH+ pts vs FISH- pts (p=0.0030; 52% of the 23 FISH+ pts responding vs 14% of the 35 FISH- pts). A survival advantage was not indicated. Defining FISH+ as =74% of cells with EGFR or CEP7 loss (<2 signals) or gain (>2 signals), OR was significantly better among FISH+ pts vs FISH- pts (p=0.043; 45% of the 22 FISH+ pts responding vs 19% of the 36 FISH- pts). Association with survival had marginal significance (log rank p=0.061). Conclusions: These preliminary data have identified loss or gain of EGFR and CEP7 abnormality as promising biomarkers for response to gefitinib in Japanese NSCLC patients. Analysis of these markers for correlation with time to progression is ongoing. Investigation of these potential markers in other cohorts of patients is worthy of further evaluation.

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Epidermal growth factor receptor (EGFR) immunohistochemistry: Comparison of antibodies (Abs) and cut points to predict benefit from gefitinib in a phase III placebo-controlled study in advanced non-small cell lung cancer (NSCLC)

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Background: Tumor tissues obtained from the ISEL phase III trial assessing the efficacy of gefitinib vs placebo in chemotherapy-pretreated NSCLC were used to evaluate two Abs (DAKO and Zymed) and assess whether different cut points of EGFR protein expression improved prediction of response and survival benefit from gefitinib. Methods: EGFR protein expression in tumor samples was assessed by immunohistochemistry using DAKO EGFR pharmDx kit (scoring percent of tumor cells with positive staining, predefined cut point of =10%) and Zymed monoclonal Ab clone 31G7 (scoring proportion of positive cells times staining intensity [scale 0–400], predefined cut point of =200). Results: Clinical characteristics of the patients (pts) assessed with DAKO (n=379) and Zymed (n=357) Abs reflected the overall study population (N=1692) with the exception of fewer never-smokers and Asians. Of the pts evaluated with DAKO/Zymed Abs, females represented 32%/31%; never-smokers, 13%/14%; Asians, 6%/4%; adenocarcinomas, 44%/42%; and 88%/88% of pts were refractory to most recent chemotherapy. With the above criteria, 70% of tumor samples were scored as positive using DAKO Ab and 68% using the Zymed Ab (agreement between assessments 76%). The objective response rates in gefitinib treated EGFR-positive pts defined with various cut points with DAKO Ab (=1% to =90%) varied between 8% and 12%, and with Zymed Ab (score =50 to =350), between 10% and 13%. Lower cut points with the DAKO Ab provided the best discrimination between EGFR positive and EGFR negative patients in terms of survival hazard ratios (HRs) comparing gefitinib to placebo, with a significant treatment/cut point interaction for the 10% cut point (p=0.049). A similar trend was noted for Zymed Ab, although the discrimination between HRs was less apparent and not significant for any cut point analyzed. Conclusion: Assessment with DAKO PharmDx kit, according to percentage of positive staining, may provide more accurate prediction of survival benefit for gefitinib-treated pts than assessment with Zymed Ab and staining index. Use of higher cut points to define positivity does not improve discrimination of the test.

No significant financial relationships to disclose.