Murine leukemia P388 vinorelbine-resistant cell lines are sensitive to vinflunine

Phase II study of intravenous vinflunine after failure of first-line vinorelbine based regimen for advanced breast cancer

PURPOSE

This open label phase II study evaluated the safety and efficacy of vinflunine in patients with breast cancer previously treated with a vinorelbine-based regimen and who progressed during or within 6 months of completing this chemotherapy.

PATIENTS AND METHODS

Thirty eight patients received vinflunine 320 mg/m(2) once every 3 weeks. The primary efficacy endpoint was overall response rate (ORR). Secondary endpoints included disease control rate (DCR), progression-free survival (PFS), overall survival (OS) and safety.

RESULTS

ORR was 8.3% (95% CI: 1.75-22.4) and DCR was 75% (95% CI: 57.8-87.9). PFS was 4.0 months (95% CI: 2.5-6.1) and OS was 13.6 months (95% CI: 8.7-18.9). Toxicities not hampering dose intensity were as expected neutropenia (75.6% of patients), fatigue (44.7%), constipation (28.9%) and abdominal pain (26.3%).

CONCLUSION

Vinflunine demonstrated antitumour activity and can be safely administered in breast cancer patients refractory/resistant to vinorelbine.

Regulation of β-tubulin isotypes by micro-RNA 100 in MCF7 breast cancer cells

Antimitotic drugs are key components of combination chemotherapy protocols for hematological and solid tumors. The taxanes (e.g., paclitaxel) bind to the β subunit of the tubulin heterodimer and reduce microtubule dynamics, leading to cell cycle arrest in G2/M. The effectiveness of combination chemotherapy is limited by tumor resistance to drugs initially or as a cumulative effect after several cycles of treatment. Because changes in the drug receptor may be linked to drug resistance, we investigated changes in β-tubulin isotypes in response to paclitaxel treatment in MCF7 breast cancer cells. We found that paclitaxel induced a 2-3 fold increase in mRNA for β-tubulin IIA and III genes, TUBB2A, and TUBB3. β-Tubulin class III protein increased; however, β-tubulin class II protein was not detected in these cells. Paclitaxel treatment following pretreatment with actinomycin D showed that the change in β-tubulin class III was due to increased transcription and linked to G2/M arrest. The increase in β-tubulin IIA mRNA was due to both enhanced stability and increased transcription, unassociated with G2/M arrest. We used micro-RNA superarrays to look for changes in families of micro-RNAs that might be linked to drug-induced changes in β-tubulin isotype mRNA and/or protein. We found a significant decrease in the tumor suppressor, miR-100, in MCF7 cells in response to paclitaxel treatment. Transfection of MCF7 cells with miR-100 significantly reduced β-tubulin I, IIA, IIB and V mRNA and prevented paclitaxel-induced increases in β-tubulin isotypes. This is the first report of a micro-RNA that regulates these specific β-tubulin isotype mRNAs.

Applying linear interaction energy method for binding affinity calculations of podophyllotoxin analogues with tubulin using continuum solvent model and prediction of cytotoxic activity

Podophyllotoxin and its analogues have important therapeutic value in the treatment of cancer, due to their ability to induce apoptosis in cancer cells in a proliferation-independent manner. These ligands bind to colchicine binding site of tubulin near the alpha- and beta-tubulin interface and interfere with tubulin polymerization. The binding free energies of podophyllotoxin-based inhibitors of tubulin were computed using a linear interaction energy (LIE) method with a surface generalized Born (SGB) continuum solvation model. A training set of 76 podophyllotoxin analogues was used to build a binding affinity model for estimating the free energy of binding for 36 inhibitors (test set) with diverse structural modifications. The average root mean square error (RMSE) between the experimental and predicted binding free energy values was 0.56kcal/mol which is comparable to the level of accuracy achieved by the most accurate methods, such as free energy perturbation (FEP) or thermodynamic integration (TI). The squared correlation coefficient between experimental and SGB-LIE estimates for the free energy for the test set compounds is also significant (R(2)=0.733). On the basis of the analysis of the binding energy, we propose that the three-dimensional conformation of the A, B, C and D rings is important for interaction with tubulin. On the basis of this insight, 12 analogues of varying ring modification were taken, tested with LIE methodology and then validated with their experimental potencies of tubulin polymerization inhibition. Low levels of RMSE for the majority of inhibitors establish the structure-based LIE method as an efficient tool for generating more potent and specific inhibitors of tubulin by testing rationally designed lead compounds based on podophyllotoxin derivatization.