Relationship Between Resistance to the Tyrosine Kinase Inhibitor Osimertinib and Pharmacokinetics in Non-small Cell Lung Cancer: Toward an Individualization of the Treatment (RESISTYR)

Osimertinib is a tyrosine kinase (TKI) inhibitor targeting EGF-R (epidermal growth factor receptor) and used in the management of patients with non-small cell lung cancer (NSCLC) with oncogenic drug addiction to EGF-R. The results of the FLAURA study justifies this 3rd generation TKI as the first line TKI of choice since an increase in overall survival of several months has been observed compared to TKIs of previous generations (erlotinib, gefitinib). However, the response to osimertinib is heterogeneous and some patients are poor responder. In addition, even when an initial response to ITK is observed, the natural history of the disease inevitably leads to the appearance of resistance mutations and loss of efficacy of osimertinib after a few months of treatment.

The occurrence of resistances is a major problem since they lead to treatment failure. Identifying biomarkers predictive of the response and / or the emergence of these mutations of resistance is therefore a research challenge. Indeed, knowing risk factors molecular resistance could help to optimize the treatment.

A first approach to monitor the disease is the measurment of residual disease circulating tumor DNA in the blood of patients (ctDNA). These minimally invasive "liquid biopsies" can be performed iteratively, unlike tissue biopsies. It is a dynamic biomarker with several advantages. On the one hand, it would be a biomarker for monitoring residual disease during treatment. The ctDNA concentration and its kinetics under treatment have also been associated with the clinical outcome. Better overall survival has thus been observed with the first generation molecules in patients with low baseline ctDNA concentration or a rapid decrease in the ctDNA concentration at the start of treatment. On the other hand, the analysis of ctDNA makes it possible to characterize the nature of the acquired resistance mutations appearing during treatment.

In addition, TKI are good candidates for therapeutic drug monitoring (TDM). The objective of TDM is to assess exposure by measuring plasma concentration. TKIs are characterized by interindividual pharmacokinetic (PK) variability. Indeed, taking into account their route of administration (per os) and their metabolism (substrate for CYP450 enzymes), plasma exposure is variable from one patient to another. Thus, at the same dosage, depending on absorption and metabolic capacity, patients are not likely to be exposed to the same plasma concentrations. This PK variability is also observed for osimertinib since interindividual coefficients of variation of plasma exposure of 50 to 60% have been reported.

In the hypothesis of a concentration-effect relationship, an underexposure (an insufficient plasma concentration) to osimertinib could lead to a suboptimal response by favoring the appearance of molecular resistance. By analogy with the mechanisms of resistance to anti-infectives, the systemic concentration of TKI may have to be maintained above a certain value throughout the treatment to reach an effective concentration in the tumor, in order to to prevent the selection of resistant clones. The value of this approach for optimizing treatment with TKI has been shown for this therapeutic class. This mechanistic hypothesis has been suggested several TKIs.