Investigating the role of EML4-ALK fusion proteins in mitotic progression of non-small cell lung cancer, and their sensitivity to anti-mitotic therapies

Approximately 5-8% of non-small cell lung cancers (NSCLCs) are driven by the EML4-ALK oncogenic fusion protein. This results from a gene inversion event on chromosome 2 that creates an in-frame fusion between the N-terminal microtubule binding portion of EML4 and the C-terminal catalytic domain of the tyrosine kinase ALK. Breakpoint variation within the EML4 gene result in fusions proteins of varying lengths that markedly affect patient outcome and treatment response. Several ALK kinase inhibitors are approved for clinical use but patients develop resistance. Moreover, patients with EML4-ALK variant 3 (V3, 30% incidence) respond poorly to ALK inhibitors and have lower survival rates compared to patients with other variants, such as V1 (34% incidence).

As wild-type EML4 contributes to spindle microtubule organisation and chromosome congression in mitosis, we investigated EML4-ALK fusion localisation to microtubules in mitotic cells and the impact on mitotic progression, SAC activity and cell survival. Results presented here indicate that EML4-ALK V3 protein localises to and stabilises spindle microtubules, while its expression leads to increases in mitotic defects. These include errors in chromosome congression and segregation which occur in a manner independent of ALK kinase activity. We also investigated the influence of this fusion protein on SAC integrity. We found that expression of EML4-ALK V3 led to weakened SAC activity that could be partly rescued by inhibition of ALK catalytic activity. Finally, we discovered that the NSCLC patient-derived cell line, H2228 expressing EML4-ALK V3 exhibited a synergistic response with reduced cell viability and increased apoptosis upon combination treatment with paclitaxel and ALK inhibitors.

In conclusion, mitotic defects and SAC deficiency in cells expressing EML4-ALK V3 may contribute to genomic instability and render tumour cells sensitive to combination treatments of microtubule poisons and ALK inhibitors. This suggests improved personalised treatment options for lung cancer patients with unmet clinical need.