CTEN and LKB1: Novel tumor biomarkers that give insight into resistance and response to tyrosine kinase inhibitor (TKI)-based therapies.

B1

Background: The hyper-expression and activation of the erbB family of receptor tyrosine kinases plays a significant role in the development of many cancer types. The complexities and heterogeneity of tumor types necessitates the ongoing search for additional biomarkers to better classify a particular patient’s tumor profile for successful individualized treatment. Here we show that the reciprocal change in expression of Tensin3 and CTEN, proteins involved in Actin fiber binding, induces increased motility in EGFR- and HER-2-driven tumors and that down-regulation of CTEN was observed upon TKI treatment. Furthermore, we show that the presence of LKB1, a master regulator of cellular metabolism and activator of AMP-activated protein kinase (AMPK), is necessary for effective TKI-therapy.
 Methods: Western blot and IHC: EGFR, pEGFR, HER-2, pHER-2, pNFkB, pAMPK, pACC, peEF2, p53, LKB1, and Actin (Cell Signaling); and CTEN (Y. Yarden). Cells: AU565 IBC and A549 lung carcinoma cell lines were grown in RPMI 1640 media supplemented in 10% FBS. Treatments: EGF and GW2974 (Sigma); TNF-alpha (R&D Systems), Herceptin (Genentech).
 Results: Our results show that EGF treatment down-regulates Tensin 3 and up-regulates CTEN in EGFR- and HER-2-driven tumor cell lines and tumors resulting in increased cellular motility. Furthermore, while the expression of CTEN correlates with high EGFR and HER-2 expression in breast cancer, treatment of breast cancer patients with a dual EGFR/HER-2 inhibitor resulted in a significant down-regulation of CTEN. In addition, the intact LKB1/pAMPK/pACC pathway correlated with TKI response while LKB1-deficient cells lines that are unable to activate the AMPK pathway are non-responsive to TKI therapies. This was shown by the inability of AMPK to activate the downstream effector proteins pACC and peEF2 in the context of LKB1 mutation/deletion. Furthermore, even in the presence of an intact LKB1-AMPK pathway, response is further contingent on wild type p53. IHC staining of a responding EGFR-positive, HER-2 over-expressing, ER-negative breast cancer patients to TKI therapy demonstrates that the presence of LKB1, pACC, CTEN, and wild-type p53 are strong biomarkers to predict a positive response to TKI-based therapy.
 Conclusion: Our findings support the incorporation of CTEN, LKB1, pAMPK, pACC and p53 as additional biomarkers to aid in the targeted therapy choices for cancer patients. By combining these biomarkers to the well-documented list of traditional erbB-related biomarkers, EGFR- and HER-2-driven cancer patients can benefit from the most efficacious personalized treatment possible.