Measuring functional HER2-driven signaling status ex vivo to predict response to HER2 therapy: Results from a mouse breast tumor xenograft study.

Abstract

e23203 Background: Clinical trials indicate a weak correlation between HER2 expression levels and HER2 targeted therapy benefit. Other biological factors, such as HER2 signaling activity, may be important to measure when identifying patients for treatment with HER2 therapies. To measure the HER2 signaling activity of a patient’s live tumor cells, a new assay using an impedance biosensor, the CELx HER2 Signaling Function (CELx HSF) Test, was developed. In this study, we evaluated whether functional HER2 signaling status was more predictive of response to a dual-HER2 kinase inhibitor than HER2 receptor or gene amplification status, using breast tumor xenograft in vivo models. Methods: Two breast cancer cell lines were studied: HCC1954, a HER2+ cell line with normal HER2 signaling according to the CELx HSF Test, and BT483, a HER2- cell line with abnormally high HER2 signaling according to the CELx HSF Test. Thus, the HER2 receptor status of each cell line was opposite its HER2 signaling status. For each cell line, twenty 4-5 week old female NSG mice were injected with two million cells. Mice were randomly assigned to either a control group that received Captisol or a treatment group that received lapatinib at a dose of 20mg/kg daily for 16 days. Results: There was no significant difference in tumor volume between the control and lapatinib-treated groups in the mice injected with the HCC1954 (HER2+, normal HER2 signaling) cells. Average tumor sizes reached 1028.7 ± 166.9 mm3 for the control group and 893.8 ± 111.5 mm3 for the lapatinib-treated group (P = 0.285) by the end of the study. With the BT483 (HER2-, abnormal HER2 signaling) cells, lapatinib treatment significantly slowed down the increase in tumor size. Average tumor sizes reached 328.3 ± 54.9 mm3 for the control group and 192.4 ± 19.4 mm3 for the lapatinib-treated group (P = 0.0049). Conclusions: The results demonstrate that functional HER2-driven signaling status in live tumor cells is more correlative to response to lapatinib in mouse xenograft tumors than HER2 expression level. These findings provide strong evidence that HER2- breast cancer patients with abnormal HER2 signaling may respond to anti-HER2 therapies.