Somatic chromosomal rearrangements resulting in ALK fusion oncogenes are observed
in 3-7 % of lung adenocarcinomas. ALK tyrosine kinase inhibitors (ALKi) induce initially
response, however, various resistance mechanisms limit their efficacy. Novel therapeutic
approaches are of utmost importance to tailor these targeted therapies.A synchronous
ALK-rearranged and mutated lung cancer cell line pair was established from malignant
pleural effusion (PF240-PE) and carcinosis (PF240-PC) at time of ALKi resistance.
Immunohistochemistry, FISH and sequencing were performed in pre- and post-treatment
tumors and in both cell lines. Differentiation markers were measured by immunoblot.
Viability was tested following treatment with ALKi and/or a pan-HDAC inhibitor. Additionally,
a novel treatment-naïve ALK-rearranged cell line served as control. In vivo tumorigenicity
was evaluated in subcutaneous xenografts.Two distinct resistance mutations were identified
in different carcinosis tissues at time of resistance, the previously described resistance
mutation L1152R and the hitherto uncharacterized E1161 K. Strikingly, PF240-PC cells
carried E1161 K and PF240-PE cells harbored L1152R. Immunohistochemistry and immunoblot
identified epithelial-to-mesenchymal transition markers upregulated following ALKi
resistance development both in carcinosis tissues and cell lines. While both lines
grew as xenografts, they differed in morphology, migration, in vivo growth and sensitivity
to ALKi in vitro. Strikingly, the combination of ALKi with SAHA yielded strong synergism.Using
a patient-derived ALKi resistant lung cancer model we demonstrated the synergism of
HDAC and ALK inhibition. Furthermore, our findings provide strong evidence for intratumoral
heterogeneity under targeted therapy and highlight the importance of site-specific
mutational analysis.
