For treating cancer, drugs based on molecules known as tyrosine kinase inhibitors are sometimes used. One such tyrosine kinase inhibitor, called osimertinib, has been used to treat EGFR-mutated lung cancer with a certain degree of efficacy. However, in some patients, intrinsic resistance and inadequate response to osimertinib has been seen to occur. Researchers have now discovered that a particular protein known as AXL causes the resistance to osimertinib and the emergence of osimertinib-tolerant cells.

The researchers first showed that in vitro, osimertinib activated AXL in EGFR-mutated lung cancer cells. Then, they demonstrated an inverse correlation between AXL and susceptibility to tyrosine kinase inhibitors; AXL expression correlated with a poor response to treatment with osimertinib and with early tumor relapse.

The authors checked whether drug-tolerant cells (cells with significantly reduced sensitivity to drugs) exhibited higher levels of AXL. Indeed, tolerant cells were found to display a higher expression of AXL compared to parental cells. Application of an AXL inhibitor called NPS1034 led to a decrease in survival of the drug-tolerant cells.

The scientists then investigated the effect of the AXL inhibitor combined with osimertinib in a mouse model. Treatment with only NPS1034 had no effect on the tumors. Treament with only osimertinib initially led to tumor regression, but tumor regrowth was observed within 7 weeks. Simultaneous treatment with NSP1034 and osimertinib led to tumor regression within a week, and the size of the tumors being stable for 10 weeks. No adverse effects, such as weight loss, were observed during treatment.

The findings of researchers provide important insights into the molecular mechanisms causing the tolerance to osimertinib in EGFR-mutated lung cancer cells and, particularly, into the role of AXL -- and the effect of inhibiting its activity. Quoting the scientists: "these results suggest that treatment during the initial phase with a combination of osimertinib and an AXL inhibitor may prevent the development of intrinsic resistance to osimertinib and the emergence of drug-tolerant cells in EGFT-mutated lung cancer overexpressing AXL."

https://www.kanazawa-u.ac.jp/latest-research/64770

https://www.nature.com/articles/s41467-018-08074-0