New insights in β-tubulin sequence analysis in non-small cell lung cancer

Abstract

Scarce data are available regarding the molecular mechanisms implicated in paclitaxel resistance. There is controversial data about β-tubulin mutations role in paclitaxel resistance. We have conducted this trial to address the influence of β-tubulin mutations in paclitaxel resistance in advanced non-small cell lung cancer (NSCLC). A group of 15 patients were biopsied and diagnosed of stages IIIB and IV NSCLC. Tumor specimens were used for DNA isolation and exon 4 of HM40 β-tubulin isotype was amplified and automatically sequenced, using both intronic and exonic primers. Next, the chemotherapy schedule consisted of weekly paclitaxel (100 or 150 mg/m 2×6) followed 2 weeks later by cisplatin 100 mg/m 2 on day 1, gemcitabine 1000 mg/m 2 on days 1 and 14, and vinorelbine 25 mg/m 2 on days 1 and 14, every 28 days. Using exonic primers, gene sequence alterations were found in 13/15 (87%) patients, including transitions (codons 180 and 182) and one silent transversion (codon 195). Also, three transversions (codons 231, 234, and 235) were found in all patients and controls. All alterations disappeared when sequenced with intronic primers. Our results suggest that point mutations demonstrated with exonic primers but not with intronic ones are probably due to β-tubulin pseudogenes present in advanced NSCLC specimens. Even so, when these β-tubulin pseudogenes are found there is a clear relation with clinical response. Although these changes could be relevant in paclitaxel resistance, this observation must be proven in future clinical trials to resolve “the tubulin dilemma”.