Here we show that the co activation of
Here, we show that the co-activation of RTKs and non-RTKs is a common trait in treatment-naïve EGFR-mutation-positive NSCLC DASA-58 receptor and patients, with AXL and CDCP1 being commonly over-expressed. The combination of gefitinib or osimertinib with the Src/FAK/Janus kinase 2 (JAK2) inhibitor TPX-0005 (Zhai et al., 2016) abrogates STAT3, YAP1 and SFKs activation and down-regulates AXL and CDCP1 expression.
Discussion Previously, we found that gefitinib or osimertinib activates STAT3 and Src-YAP1 in EGFR-mutation-positive NSCLC cells (Chaib et al., 2017). Here we find that the genetic or pharmacologic inhibition of Src or SFKs diminishes YAP1, AXL and CDCP1 phosphorylation or expression. In two cohorts of EGFR-mutation-positive NSCLC patients treated with EGFR TKI, we show that a risk-model combining AXL and CDCP1 mRNA expression was strongly associated with progression-free survival with hazard ratios of 2.95 and 2.19 and overall survival with hazard ratios of 3.56 and 2.96 between high-risk and low-risk group. In accordance with earlier findings (Yoshida et al., 2014), we show that EGFR-mutation-positive NSCLC cells co-express more than just EGFR RTKs. Non-RTKs, especially, Src, YES and FAK, are also expressed and activated. Combined EGFR TKI with TPX-0005 is more effective than EGFR TKI alone both in culture and in vivo. At the time of our work, it was reported that the AKT and the mitogen-activated protein kinase (MAPK) pathways remain active, even in the presence of osimertinib (Ichihara et al., 2017). EGFR, SFK and FAK concomitant inhibition enhances osimertinib activity and suppresses resistance (Ichihara et al., 2017). Although co-targeting EGFR and MEK (known as mitogen-activated protein kinase kinase 1, or MAP2K1) (Tricker et al., 2015) or, from our experience, AKT (Jacobsen et al., 2017), causes growth inhibition in EGFR TKI resistant NSCLC models, the combination of osimertinib with dasatinib was superior to the combination of osimertinib with MEK or phosphoinositide 3-kinase (PI3K) inhibitor inhibitors (Ichihara et al., 2017). In summary, three studies show that SFK and FAK contribute to EGFR TKI resistance (Yoshida et al., 2014; Ichihara et al., 2017; Murakami et al., 2017). Tyrosine kinase inhibitors do not induce the activation of new RTKs, rather, only increase the phosphorylation of existing RTKs to compensate the reduced phosphorylation of ERK and AKT. A combination of TKIs could completely inactivate all the RTKs and their downstream signaling molecules (Sun et al., 2016). Paradoxically, inhibition of AXL or MET led to greater Src-induced AXL and MET phosphorylation in breast and lung cancer cell lines (Baumann et al., 2017). CDCP1 overexpression triggered a cascade of tyrosine phosphorylation events, leading to the activation of signaling networks, including SFKs, to promote tumor cell growth and survival (Leroy et al., 2015). Through the combination of genomic, biological, in vivo models and clinical cohorts of patients, our findings lead to the model in Fig. 7. Our data indicate that Src-YAP1 signaling leads to further activation of AXL, CDCP1 and MET (Fig. 5E). By targeting SFK and FAK, we can obviate the need to inhibit the dominant RTKs that can be activated with the paradoxical detrimental effect of causing more activation (Baumann et al., 2017). The combination of a TKI plus SFK and FAK inhibitor has been proposed (Yoshida et al., 2014; Ichihara et al., 2017; Murakami et al., 2017). However, in our work, dasatinib induced STAT3 and FAK phosphorylation (Fig. 5F). Erlotinib plus dasatinib was not effective in a clinical trial in EGFR-mutation-positive NSCLC patients with acquired resistance to erlotinib or gefitinib (Johnson et al., 2011). Clinical trials with EGFR TKI plus SFK and FAK inhibitors, such as the Src/FAK/JAK2 inhibitor TPX-0005, deserve to be carried out. A trial is foreseen with osimertinib plus TPX-0005 and, according to our knowledge, TPX-0005 is the only compound that inhibits Src, FAK and JAK2 at a similar affinity level. Finally, we advocate customizing the therapy of EGFR-mutation-positive NSCLC patients and the use of a tool kit to optimize EGFR mutational screening by incorporating CDCP1 and AXL mRNA assessment.