TRI-611, a development stage molecular glue degrader of ALK, promotes the degradation of TKI-resistant ALK fusion proteins and leads to regression of ALK TKI-refractory tumors

TRI-611 is a potent, brain-penetrant molecular glue degrader (MGD) of anaplastic lymphoma kinase (ALK) that represents the first development stage MGD of an oncogenic fusion protein. By engaging ALK via a novel degron that is distal from the orthosteric tyrosine kinase inhibitor (TKI) binding site, TRI-611 has the potential to promote the degradation of ALK proteins that are either wild-type or mutant in the kinase domain, the latter of which are an important mechanism of disease progression in patients treated with ALK TKIs. Here we show through in vitro biochemical and biophysical studies that TRI-611 is equally effective at promoting the interaction of CRBN with wild-type ALK and the ALK L1196M/G1202R compound mutant protein, as well as subsequent poly-ubiquitination. Through the use of Ba/F3 cells engineered to express 30 distinct alleles of EML4-ALK, we show that TRI-611 effectively targets all tested EML4-ALK mutant proteins in cells, including those that are refractory to ALK TKIs. The broad phenotypic activity of TRI-611 is further highlighted by potent anti-proliferation of cell line and patient-derived ALK+ NSCLC models with multiple ALK TKI resistance alleles. In mouse efficacy studies, TRI-611 leads to the regression of subcutaneous xenografts of CRISPR engineered EML4-ALK-mutant NCI-H3122 cells that do not respond to ALK TKIs. Finally, we show that TRI-611 leads to the regression of an EML4-ALK mutant primary patient-derived xenograft isolated from a patient that had progressed on prior alectinib and lorlatinib. These data demonstrate the potential of TRI-611 to address a key liability of ALK TKIs that all target the same site on ALK and support the development of TRI-611 in all ALK+ NSCLC patients, including patients with wild-type ALK kinase domain and those with acquired TKI resistance mutations.