We reported previously that Bcl-2 is paradoxically down-regulated in paclitaxel-resistant cancer cells. We reveal here that paclitaxel directly targets Bcl-2 in the loop domain, thereby facilitating the initiation of apoptosis. Molecular modeling revealed an extraordinary similarity between the paclitaxel binding sites in Bcl-2 and β-tubulin, leading us to speculate that paclitaxel could be mimetic of an endogenous peptide ligand, which binds both proteins. We tested the hypothesis that paclitaxel mimics Nur77, which, like paclitaxel, changes the function of Bcl-2. This premise was confirmed by Nur77 interacting with both paclitaxel targets (Bcl-2 and β-tubulin) and a peptide sequence mimicking the Nur77 structural region, thus reproducing the paclitaxel-like effects of tubulin polymerization and opening the permeability transition pore channel in mitochondria. This discovery could help in the development of novel anticancer agents with nontaxane skeleton as well as in identifying the clinical subsets responsive to paclitaxel-based therapy. [Cancer Res 2009;69(17):6906–14]

Purpose: Cancer stem cells represent an attractive therapeutic target for tumor eradication. The present study aimed to determine whether CD133 expression may identify cells with characteristics of cancer stem/progenitor cells in human endometrial tumors.

Taxanes act by inhibiting microtubule dynamics; in this study, we have investigated mitochondria as an additional target of taxanes. We incubated isolated mitochondria in the presence of taxanes with or without stimulation of the mitochondrial respiratory state. Results showed that they rapidly induced the loss of ΔΨ_m after stimulation of the respiratory state. To evaluate the binding of [¹⁴C]paclitaxel to isolated mitochondria, mitochondrial proteins were precipitated yielding 18.6 ± 2.1 cpm/μg of protein. After stimulation of the respiratory state, binding of [¹⁴C]paclitaxel increased up to 163.2 ± 46.7 cpm/μg of protein. CPM values after Bcl-2 immunoprecipitation was 62.8-fold higher than those of the control antibody, thereby indicating the involvement of Bcl-2 in paclitaxel binding. Then, we established a panel of A2780 cell lines resistant to increasing doses of paclitaxel alone or to high doses of paclitaxel/cyclosporin A (A2780 TC cells). In both cases, Bcl-2 expression was consistently down-regulated, whereas levels of other members of the Bcl-2 family, such as Bax and Bcl-x, did not change in paclitaxel-resistant cell lines. When A2780TC cells were stably transfected with a Bcl-2 construct, paclitaxel sensitivity was partially restored, thereby supporting a direct role of Bcl-2 down-regulation in the maintenance of drug-resistance. Finally, we examined Bcl-2 by immunohistochemistry in a small subset of ovarian cancer paclitaxel-resistant patients and we noticed that the protein is down-regulated in this clinical setting with respect to the expression levels found in drug-sensitive tumors. These findings demonstrate that Bcl-2 is an additional intracellular target of taxanes and that its down-regulation is involved in taxane resistance.

The advent of Precision Medicine has globally revolutionized the approach of translational research suggesting a patient-centric vision with therapeutic choices driven by the identification of specific predictive biomarkers of response to avoid ineffective therapies and reduce adverse effects. The spread of “multi-omics” analysis and the use of sensors, together with the ability to acquire clinical, behavioral, and environmental information on a large scale, will allow the digitization of the state of health or disease of each person, and the creation of a global health management system capable of generating real-time knowledge and new opportunities for prevention and therapy in the individual person (high-definition medicine). Real world data-based translational applications represent a promising alternative to the traditional evidence-based medicine (EBM) approaches that are based on the use of randomized clinical trials to test the selected hypothesis. Multi-modality data integration is necessary for example in precision oncology where an Avatar interface allows several simulations in order to define the best therapeutic scheme for each cancer patient.

A prominent mechanism of drug resistance to taxanes is the overexpression of class III β-tubulin. The seco-taxane IDN5390 was chosen for its selective activity in paclitaxel-resistant cells with an overexpression of class III β-tubulin. Moreover, the combined treatment paclitaxel/IDN5390 yielded a strong synergism, which was also evident in cell-free tubulin polymerization assays. In the presence of an anti-class III β-tubulin as a blocking antibody, tubulin polymerization induced by paclitaxel and IDN5390 was enhanced and not affected, respectively, whereas synergism was abolished, thereby indicating that IDN5390 activity is not modulated by class III β-tubulin levels. Such properties can be explained by taking into consideration the composition of class III β-tubulin paclitaxel binding site; in fact, Ser²⁷⁷ interacting with paclitaxel C group in class I is replaced by an Arginine in class III. IDN5390 that has an open and flexible C ring and an acidic α-unsaturated enol-keton moiety better fits with class III β-tubulin than paclitaxel at the binding site. Taking altogether, these findings indicate that the concomitant treatment IDN5390/paclitaxel is able to successfully target class I and III β-tubulin and the combined use of two taxanes with diverse spectrum activity against tubulin isotypes could represent a novel approach to overcome paclitaxel resistance.