Background: Profiling protein signaling activation in cancer is critical as these proteins represent targets for new molecular therapeutics. The I-SPY TRIAL (CALGB 150007/150012, ACRIN 6657) is a trial of neoadjuvant anthracycline- and taxane- based chemotherapy that longitudinally collected biopsy specimens and molecular and clinical/pathological characterization.
Methods: Tumor epithelium was procured by Laser Capture Microdissection from 149 pretreatment frozen biopsy specimens (T1) and 102 frozen biopsy specimens (T2, 1–4 days post-chemotherapy). Reverse Phase Protein Microarray technology was used to quantitatively measure the activation of 39 and 100 key signaling proteins in the T1 and T2 biopsies, respectively, including numerous drug targets for Phase I-III and FDA-cleared therapeutics. Associations between protein activation and response to chemotherapy (RCB 0/1 vs 2/3) and relapse-free survival (RFS) were evaluated for the HR+/HER2− patient population at each time point and for changes between T1 and T2. Significance thresholds for response and RFS were as follows: Wilcoxon rank sum test p < 0.05; Cox proportional hazard model, likelihood ratio p < 0.05.
Results: We focused our analysis on protein changes in patients who had poor clinical outcomes (Table 1)
We observed systemic activation of HER family signaling and downstream AKT activation in tumors from patients who do not respond (RCB2/3) and/or whom recurred. Increased ERBB2 and ERBB4 levels were observed at T1 and T2, respectively, from patients who did not respond to neoadjuvant therapy. Dynamic changes in ERBB3 and AKT phosphorylation/activation were revealed between the T1 and T2 time points, which were associated with recurrence. Increased phosphorylation of MARCKS, a known PKC substrate, was seen in the T1 biopsy in the non-response cohort.
Conclusions: Our analysis revealed activation/increased expression of HER family proteins along with downstream AKT activation in HR+/HER2− patients who have poor clinical response. These events, if validated, point to potential treatment options that could be rationally considered for non-responding HR+/HER2− patients with a number of investigational agents that target ERBB3 and AKT signaling in the clinic today. Increasing HER2 protein expression in a HER2− cohort may appear contradictory, however these findings may point to important subtle increases in HER2 that have important clinical considerations. Given the known clinical benefit from HER2 directed therapy in HER2− patients seen in other studies, our findings may have clinical relevance if validated. Further validation is required to explore the significance of these ongoing findings with the hope that the analysis could lead to molecularly rationalized therapies for patients with HR+/HER2− tumors.