ALK / ROS1

Class

Third-generation ALK/ROS1 tyrosine kinase inhibitor (FDA-approved, marketed as Lorbrena; formerly PF-06463922)

Pathway

inhibits ALK and ROS1 fusion kinases, including many resistance mutations that arise after earlier-generation ALK inhibitors, with CNS penetration

ALK (anaplastic lymphoma kinase) and ROS1 are receptor tyrosine kinases that, in a subset of cancers, become abnormally fused to unrelated genes through chromosomal rearrangements. These fusion proteins lose their normal regulation and signal continuously, driving uncontrolled cell division through downstream pathways such as RAS-MAPK and PI3K-AKT. Because ALK and ROS1 share a closely related kinase domain structure, a single small molecule can often inhibit both, which is useful since some tumors harbor either fusion type and testing may not always distinguish them cleanly. Earlier-generation inhibitors targeting these fusions were effective initially, but tumors frequently acquired mutations within the kinase domain that reduced drug binding, allowing signaling to resume. Third-generation ALK/ROS1 inhibitors are engineered to retain activity against many of these resistance mutations, extending the duration of disease control. A further design consideration is penetration of the blood-brain barrier, since ALK- and ROS1-driven cancers, particularly non-small cell lung cancer, have a strong tendency to spread to the central nervous system. This combination of resistance-mutation coverage and brain penetration broadly matters wherever fusion-driven lung and other solid tumors relapse after initial kinase-inhibitor therapy.