Combination Index (CI) values <1, =1 and >1 indicated synergism, additive effect and antagonism, respectively

Combination Index (CI) values <1, =1 and >1 indicated synergism, additive effect and antagonism, respectively. domain-containing protein-1 (CDCP1) phosphorylation and slightly suppressed Src phosphorylation in PC9 and H1975 cells. Conclusion: The results of this study indicate that pterostilbene may be used to abrogate the activated resistance pathways of single osimertinib treatment in EGFR-mutation Peucedanol positive NSCLC. Future studies should focus on in vivo translation and confirmation of these results. Keywords: Pterostilbene, NSCLC, osimertinib, therapy resistance Introduction Epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) patients were discovered in 2004 1. To date, monotherapy with EGFR tyrosine kinase inhibitors (TKIs) still leads to incomplete responses in 95% of patients 2, often due to intrinsic or Peucedanol acquired resistance. Relevant signaling network- and crosstalk changes after EGFR blockade are underappreciated, Peucedanol including hyperactivation of signal transducer and activator of transcription 3 (STAT3) 3-7. Ongoing and previously published research indicates that gefitinib, afatinib and osimertinib TKI treatments are unable to inhibit STAT3 activation, and lead to parallel compensatory activation of the Src-yes-associated protein 1 (YAP1) signaling pathway 8-10. We have previously shown that co-targeting EGFR, STAT3 and Src-YAP1 was highly synergistic in vitro and in vivo. We also found that several receptor tyrosine kinases (RTKs) and non-RTKs are upregulated at baseline or after treatment with gefitinib or osimertinib, limiting their therapeutic efficacy 8-11. The genetic or pharmacologic inhibition of Src Peucedanol family kinases (SFKs) or YAP1 diminishes the phosphorylation of the RTK AXL and the transmembrane protein CUB domain-containing protein-1 (CDCP1) 10. When overexpressed, both of these proteins are related to worse survival outcomes in patients treated with single EGFR TKIs. The combination of EGFR TKIs with a multikinase inhibitor, that inhibits janus kinase 2 (JAK2), Src and focal adhesion kinase (FAK), abrogates not only STAT3, but also YAP1 and SFKs activation and downregulates AXL and CDCP1 expression 10. Pterostilbene (3,5-dimethoxy-4′-hydroxy-trans-stilbene) is usually a stilbene of the family of phytoalexin compounds, found in in blueberries and Pterocarpus marsupium (PM) heartwood. It is structurally similar to resveratrol, a compound found in red wine that has comparable antioxidant, anti-inflammatory, and anti-carcinogenic properties. Due to the presence of two methoxyl groups, pterostilbene has increased lipophilic and oral absorption and therefore increased bioavailability compared to resveratrol 12. It has been shown that pterostilbene has apoptotic and anti-proliferative effects in solid tumors 13, including TNFAIP3 EGFR-mutation positive NSCLC 14. In triple unfavorable breast malignancy (TNBC), pterostilbene abolished the activation of Src, FAK, Paxillin and STAT3. Moreover, by altering mainly the Src-mediated signaling pathway pterostilbene suppressed the metastatic potential of TNBC cells. It was also found to decrease the levels of mesenchymal markers, amongst which MET 15. Pterostilbene also causes endoplasmic reticulum (ER) stress and consequently leads to apoptosis 14. In addition, pterostilbene was shown to be safe in patients, even at high doses 16-18. Henceforth, we posit that this combination of pterostilbene plus an EGFR TKI could Peucedanol substantially improve the outcome of single EGFR TKIs in EGFR-mutation positive NSCLC (Physique ?Figure11). In this study we explored whether pterostilbene inhibits compensatory osimertinib-induced signaling pathways, and if the combination can optimize the upfront therapy of EGFR-mutation positive NSCLC cells. Open in a separate windows Physique 1 The effects of pterostilbene1 and EGFR TKIs on RTKs and downstream components. EGFR TKIs block signaling of the EGFR receptor and its downstream pathways. Previous research has shown that this process causes hyper-activation of compensatory pathways, such as STAT3 and Src-YAP1. Consequently,.