Mechanisms of TKI resistance

Speaker: Luc Friboulet

Luc Friboulet discusses in depth the mechanisms of resistance to tyrosine kinase inhibitors (TKIs), provides overview of current research initiatives in the field and discuss future challenges in precision medicine posed by resistance mechanisms.

Over the past 10 years, the chemotherapeutic arsenal has been expanded to include molecular-targeted therapies based on the principle that cancer cells become addicted to a single driver oncogene. This therapeutic approach not only enables healthy cells to be spared, and hence limits toxicities, but it also, and perhaps more importantly, brings the median survival from about 10 months with conventional treatment to more than 30 months when integrating targeted agents in certain metastatic cancers (i.e. non-small cell lung cancer - NSCLC).

Unfortunately, most tumours are capable of adapting to the treatment thereby limiting the clinical benefit of these new targeted therapies. The extensive examination of the resistant tumours have enabled three main categories of resistance to be identified: 1. Acquisition of a secondary mutation within the kinase domain of the target; 2. Activation of bypass kinases; 3. The target and the downstream kinases are inhibited but the cells fail to undergo apoptosis, the resistance mechanisms here are less clear but epigenetic mechanism are highly suspected.

To identify a broad spectrum of resistance mechanisms that are highly clinically relevant the author’s group established new laboratory models of resistance directly from the patient biopsies.

This project is connected to the clinical trial "MATCH-R" (for “matching resistance”) sponsored by Gustave Roussy, allowing collection of repeat biopsies before and after resistance in patients receiving targeted therapies.

A first biopsy is used for next-generation sequencing (NGS) of RNA and exomic DNA to identify acquired genetic alterations.

Other biopsies are processed in the lab for in vitro and in vivo tumour cells culture.

Pieces of biopsy are transplanted in the renal capsule of NSG (NOD Scid Gamma) immunodeficient mice to establish patient derived xenograft (PDX).

Other pieces of biopsies undergo collagenase based enzymatic dissociation and is then maintained in vitro with the use of irradiated human fibroblasts as feeder cells to generate patient-derived tumour cell lines.

The group also collects blood samples all along the course of the treatment to monitor longitudinally the clonal evolution of cancer cells.

The sequencing of ctDNA serially collected help to appreciate the extent of tumour heterogeneity in patients, analyze the mutational process of tumour evolution and predict relapses before clinical sign.

All the data are used to adjust patient’s treatment according to the mechanism of resistance identified in order to prolong further patient’s benefit from targeted agents.