Abstract
Non-small lung cancer (NSCLC) accounts for approximately 85% of all lung cancer-related deaths worldwide. Historically, platinum-based chemotherapy regimens have been the first-line treatment for advanced NSCLC, however these are very often ineffective. The discovery of oncogenic driver mutations (a genetic mutation that drives cancer progression) in a subset of cancer patients have driven the development of targeted therapies, which are generally superior to chemotherapy. One oncogenic driver in NSCLC is the receptor tyrosine kinase Anaplastic Lymphoma Kinase (ALK). This protein has been identified as the oncogenic driver in 3 - 8% of NSCLC cases, a subtype of lung cancer frequently affecting a younger and non-smoking population.
Crizotinib is an ALK inhibitor that gained fast-tracked approval from the Food and Drug Administration (FDA) in 2011 and more than doubled progression free survival time in comparison to chemotherapy. However, resistance to crizotinib typically emerges within a year of treatment. One of the various proposed mechanisms of crizotinib resistance is through the upregulation of the Insulin-like Growth Factor Receptor 1 (IGF1R).
This study aimed to establish in vitro models of primary and acquired resistance to crizotinib and evaluate several molecular mechanisms that may underlie acquired resistance. Furthermore, we aimed to investigate whether the combination of crizotinib with the experimental IGF1R inhibitor NVP-AEW541 is more effective than monotherapy in in vitro models of primary and acquired resistance to crizotinib.
To model primary resistance, the established ALK-positive NSCLC cell line NCI-H3122, was exposed to high dose crizotinib (10 μM) for 24 hours. Following drug washout, cells were maintained for 12 days (24-H3122), allowing for the selection of a cell population with intrinsic resistance to crizotinib. The IC50 of crizotinib in a model of primary resistance increased in treated cells (0.16 μM) compared to non-treated cells (0.10 μM). Over 12 days the total protein expression of ALK decreased in conjunction with increased total IGF1R expression in comparison to control, indicating the IGF1R pathway may be a bypass pathway in this model of primary crizotinib resistance.
To develop a crizotinib-resistant cell line (C.R-H3122), NCI-H3122 cells were maintained in crizotinib (0.80 μM; the steady state plasma concentration in mice) for 114 days. Long term exposure to crizotinib led to the development of a crizotinib-resistant cell line (C.R-H3122) with an IC50 of 2.08 μM, 20.8-fold higher than control. In contrast to the 24-H3122 cells, total protein expression of ALK and IGF1R decreased over 114 days in comparison to control, suggesting the IGF1R pathway may not function as a bypass pathway in this model of acquired resistance.
Cytotoxicity testing of an IGF1R inhibitor, NVP-AEW541 resulted in a lower IC50 in the C.R-H3122 cells (2.21 μM) compared to control (2.99 μM). Importantly, the combination of crizotinib and NVP-AEW541 was more cytotoxic than monotherapy (combination indices less than 1) in both models of primary and acquired resistance, with greater synergism observed in the model of primary resistance. This supports the hypothesis that simultaneous blockade of ALK and IGF1R may be beneficial as an upfront therapy in ALK-positive NSCLC.