Sagopilone, an optimized fully synthetic
epothilone, is a microtubule-stabilizing compound that has shown high in vitro and in vivo activity against a broad range of human
tumor models. We analyzed the differential mechanism of action of
sagopilone in
non-small cell lung cancer cell lines in vitro.
Sagopilone inhibited proliferation of
non-small cell lung cancer cell lines at lower nanomolar concentration. The treatment with
sagopilone caused strong disturbances of cellular cytoskeletal organization. Two concentration-dependent phenotypes were observed. At 2.5 nM
sagopilone or 4 nM
paclitaxel an
aneuploid phenotype occur whereas a mitotic arrest phenotype was induced by 40 nM
sagopilone or
paclitaxel. Interestingly, treatment with 2.5 nM of
sagopilone effectively inhibited cell proliferation, but--compared to high concentrations (40 nM)--only marginally induced apoptosis. Treatment with a high versus a low concentration of
sagopilone or
paclitaxel regulates a non-overlapping set of genes, indicating that both phenotypes substantially differ from each other. Genes involved in G2/M phase transition and the spindle assembly checkpoint, like
Cyclin B1 and BUBR1 were upregulated by treatment with 40 nM
sagopilone. Unexpectedly, also genes involved in DNA damage response were upregulated under that treatment. In contrast, treatment of A549 cells with a low concentration of
sagopilone revealed an upregulation of direct transcriptional target genes of TP53, like CDKN1A, MDM2, GADD45A, FAS. Knockdown of TP53, which inhibited the transcriptional induction of TP53 target genes, led to a significant increase in apoptosis induction in A549 cells when treated with a low concentration of
sagopilone. The results indicate that activation of TP53 and its downstream effectors like CDKN1A by low concentrations of
sagopilone is responsible for the relative apoptosis resistance of A549 cells and might represent a mechanism of resistance to
sagopilone.