유방암에서 EGFR/HER2 Tyrosine Kinase 억제제인 Lapatinib에 대한 반응 및 내성에 관한 연구

Abstract

Lapatinib is a dual tyrosine kinase inhibitor of EGFR and HER2. Lapatinib plus capecitabine is an effective treatment option in trastuzumab-refractory HER2-Positive (+) metastatic breast cancer. However, not all patients benefit from the treatment and patients who benefit eventually develop acquired resistance to the treatment. In order to identify optimal patients for the treatment and elucidate mechanism of resistance, 1) tumor specimen for biomarker identification predicting treatment outcome, and 2) in vitro acquired resistance model were investigated. Total HER2 (H2T), p95HER2 (p95), and total HER3 (H3T) expression were quantified in formalin-fixed paraffin-embedded samples using the VeraTag assay and correlations with treatment outcomes of lapatinib and capecitabine in HER2+, trastuzumab-refractory metastatic breast cancer patients were analyzed. SK-BR-3 cell line, which is a HER2-positive lapatinib-sensitive breast cancer cell line, was continuously exposed to lapatinib and lapatinib-resistant (LR) cell line was generated. Various representative targeted agents of key signaling pathways were tested in addition to lapatinib to test inhibition of which pathway could restore the sensitivity to lapatinib in the LR cell line. A total of 52 patients were evaluable for protein expression and clinical outcome. H2T level was significantly higher in responders (median 93.49 in partial response, 47.66 in stable disease, and 17.27 in progressive disease p = 0.020). Longer time-to-progression (TTP) was observed in patients with high H2T [p = 0.018, median 5.2 months in high (>14.95) vs. 1.8 in low (<14.95)] and high H3T [p = 0.017, median 5.0 months in high (>0.605) vs. 2.2 in low (<0.605)]. Patients having both high H2T and high H3T had significantly longer TTP [adjusted hazard ratio (HR) 0.38 (95% CI 0.20 – 0.73), p = 0.004] and overall survival [adjusted HR 0.46 (95% CI 0.24 – 0.89), p = 0.020]. No significant association between p95 and response or survival was observed. SK-BR-3 cell line, which is a HER2-positive lapatinib-sensitive breast cancer cell line, was continuously exposed to lapatinib. The IC50 value of lapatinib in the LR cells was 3.03 uM compared to 0.13 of the parental cells. Lapatinib was unable to inhibit p-STAT3 expression and p-Akt expression was only partly inhibited in the LR cell line. Among the various agents tested, NVP-BEZ235, a dual inhibitor of PI3K and mTOR, inhibited the persistent PI3K/Akt/mTOR pathway activation in the LR cell line and restored sensitivity to lapatinib. In conclusion, overexpression of HER2 and HER3 is associated with sensitivity to lapatinib, whereas persistent PI3K/Akt/mTOR pathway activation can lead to acquired resistance.