Preclinical Comparison of the Blood-brain barrier Permeability of Osimertinib with Other EGFR TKIs.

PURPOSE

Osimertinib is a potent and selective EGFR tyrosine kinase inhibitor (EGFR-TKI) of both sensitizing and T790M resistance mutations. To treat metastatic brain disease, blood-brain barrier (BBB) permeability is considered desirable for increasing clinical efficacy.

EXPERIMENTAL DESIGN

We examined the level of brain penetration for 16 irreversible and reversible EGFR-TKIs using multiple and BBB preclinical models.

RESULTS

osimertinib was the weakest substrate for human BBB efflux transporters (efflux ratio 3.2). rat free brain to free plasma ratios (Kpuu) show osimertinib has the most BBB penetrance (0.21), compared with the other TKIs (Kpuu ≤ 0.12). PET imaging in Cynomolgus macaques demonstrated osimertinib was the only TKI among those tested to achieve significant brain penetrance ( %ID 1.5, brain/blood Kp 2.6). Desorption electrospray ionization mass spectroscopy images of brains from mouse PC9 macrometastases models showed osimertinib readily distributes across both healthy brain and tumor tissue. Comparison of osimertinib with the poorly BBB penetrant afatinib in a mouse PC9 model of subclinical brain metastases showed only osimertinib has a significant effect on rate of brain tumor growth.

CONCLUSIONS

These preclinical studies indicate that osimertinib can achieve significant exposure in the brain compared with the other EGFR-TKIs tested and supports the ongoing clinical evaluation of osimertinib for the treatment of EGFR-mutant brain metastasis. This work also demonstrates the link between low transporter efflux ratios and increased brain penetrance supporting the use of transporter assays as an early screen in drug discovery.