Lucia Cicchillitti

Paclitaxel Directly Binds to Bcl-2 and Functionally Mimics Activity of Nur77

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 beta-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 beta-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.

The seco-taxane IDN5390 is able to target class III beta-tubulin and to overcome paclitaxel resistance.

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.

Proteomic characterization of cytoskeletal and mitochondrial class III β-tubulin

Class III β-tubulin (TUBB3) has been discovered as a marker of drug resistance in human cancer. To get insights into the mechanisms by which this protein is involved in drug resistance, we analyzed TUBB3 in a panel of drug-sensitive and drug-resistant cell lines. We identified two main different isoforms of TUBB3 having a specific electrophoretic profile. We showed that the apparently higher molecular weight isoform is glycosylated and phosphorylated and it is localized in the cytoskeleton. The apparently lower molecular weight isoform is instead found exclusively in mitochondria. We observed that levels of phosphorylation and glycosylation of TUBB3 are associated with the resistant phenotype and compartmentalization into cytoskeleton. By two-dimensional nonreduced/reduced SDS-PAGE analysis, we also found that TUBB3 protein in vivo forms protein complexes through intermolecular disulfide bridges. Through TUBB3 immunoprecipitation, we isolated protein species able to interact with TUBB3. Following trypsin digestion, these proteins were characterized by mass spectrometry analysis. Functional analysis revealed that these proteins are involved in adaptation to oxidative stress and glucose deprivation, thereby suggesting that TUBB3 is a survival factor able to directly contribute to drug resistance. Moreover, glycosylation of TUBB3 could represent an attractive pathway whose inhibition could hamper cytoskeletal compartmentalization and TUBB3 function. [Mol Cancer Ther 2008;7(7):2070–9]

Microsatellite Instability Is an Independent Indicator of Recurrence in Sporadic Stage I-II Endometrial Adenocarcinoma

PURPOSE The aim of this study was to define the prognostic role of microsatellite status in 65 stage I-II primary sporadic endometrioid endometrial adenocarcinoma (EEA) patients. PATIENTS AND METHODS Familiarity for neoplasia was ascertained in all patients on the basis of a questionnaire. Microsatellite status was assessed by matching normal and tumoral DNA probed for five dinucleotide repeats and one mononucleotide repeat marker. Microsatellite status was analyzed in relation to clinicopathologic characteristics of the patients and length of disease-free survival (DFS). RESULTS Eleven tumors (17%) of 65 had instability at two or more loci and were considered as unstable or microsatellite instability (MI). Tumors with no instability or instability at one locus were classified as microsatellite stable (MS). The percentage of MI was significantly higher in poorly than in well to moderately differentiated tumors (50% v 9%; P =.003). The 5-year DFS rate of MI patients was 63% (95% confidence interval [CI], 35% to 91%) versus 96% (95% CI, 91% to 101%) of MS patients (P =.0004). In multivariate analysis, only the presence of MI, stage II of disease, and depth of myometrial invasion greater than 50% retained independent prognostic roles. CONCLUSION The assessment of microsatellite status may provide useful information for preoperative prognostic characterization of stage I-II primary sporadic EEA patients in which more individualized treatment options can be attempted.

A proteomic approach to paclitaxel chemoresistance in ovarian cancer cell lines.

Ovarian cancer is the leading cause of gynaecological cancer mortality. Paclitaxel is used in the first line treatment of ovarian cancer, but acquired resistance represents the most important clinical problem and a major obstacle to a successful therapy. Several mechanisms have been implicated in paclitaxel resistance, however this process has not yet been fully explained. To better understand molecular resistance mechanisms, a comparative proteomic approach was undertaken on the human epithelial ovarian cancer cell lines A2780 (paclitaxel sensitive), A2780TC1 and OVCAR3 (acquired and inherently resistant). Proteins associated with chemoresistance process were identified by DIGE coupled with mass spectrometry (MALDI-TOF and LC-MS/MS). Out of the 172 differentially expressed proteins in pairwise comparisons among the three cell lines, 151 were identified and grouped into ten main functional classes. Most of the proteins were related to the category of stress response (24%), metabolism (22%), protein biosynthesis (15%) and cell cycle and apoptosis (11%), suggesting that alterations of those processes might be involved in paclitaxel resistance mechanisms. This is the first direct proteomic comparison of paclitaxel sensitive and resistant ovarian cancer cells and may be useful for further studies of resistance mechanisms and screening of resistance biomarkers for the development of tailored therapeutic strategies.

Looking at Drug Resistance Mechanisms for Microtubule Interacting Drugs: Does TUBB3 Work?

Vinca alkaloids and taxanes represent the mainstay of medical treatment of hematological and solid tumors. Unfortunately, a major clinical problem with these agents is drug resistance. Although a plethora of mechanisms of drug resistance have been described, only a few of them have been validated in clinical trials. Among these, the one involving the protein TUBB3 seems to represent a promising target for studying drug resistance. In fact, it seems that this protein is a factor promoting cell survival and represents an endogenous element of an inherent drug-resistance program built into cells to counteract the activity of microtubule-interacting drugs. Its pivotal role has been ascertained in clinical trials in lung, breast, and ovarian cancer, three diseases that can be successfully treated with microtubule-interacting drugs. Although TUBB3 is probably not a unique factor in drug resistance, the hope is that direct targeting of this protein will increase the response to microtubule-interacting drugs, thereby overcoming an important element in the growth of drug resistance.

Glycoproteomics of paclitaxel resistance in human epithelial ovarian cancer cell lines: towards the identification of putative biomarkers.

Glycosylation, one of the most common post translational modifications (PTMs) of proteins, is often associated with carcinogenesis and tumor malignancy. Ovarian cancer is the sixth cause of cancer-related death in Western countries. Currently, it is treated by debulking surgery followed by chemotherapy based on paclitaxel, alone or in combination with other drugs. However, chemoresistance represents a major obstacle to positive clinical outcome. We used two approaches, Multiplexed Proteomics (MP) technology and Multilectin Affinity Chromatography (MAC) to characterize the glycoproteome of the human ovarian cancer cell line A2780 and its paclitaxel resistant counterpart A2780TC1. Furthermore proteins were separated by traditional 2DE or DIGE and identified by MS (MALDI TOF or LC MS/MS). Seventy glycoproteins were successfully identified in ovarian cancer cells and 10 were found to be differentially expressed between sensitive and resistant cell lines. We focused on four glycoproteins (tumor rejection antigen (gp96) 1, triose phosphate isomerase, palmitoyl-protein thioesterase 1 precursor and ER-associated DNAJ) which were remarkably upregulated in A2780TC1 compared to A2780 cell line and which may represent biomarkers for paclitaxel resistance in ovarian cancer.

Comparative study on the induction of cytostasis and apoptosis by ICI 182,780 and tamoxifen in an estrogen receptor-negative ovarian cancer cell line

We have compared the effects of a broad range of clinically relevant concentrations (0.1 to 10 μM) of the steroidal pure anti‐estrogen ICI 182,780 and the non‐steroidal partial anti‐estrogen tamoxifen (TAM) on cell proliferation and induction of apoptosis in the estrogen receptor (ER)‐negative ovarian carcinoma cell line A2780. Cell proliferation was assessed by evaluating the number of viable cells, changes in cell‐cycle distribution and cell replication rate; while apoptosis induction was assessed by examining nuclear morphological changes associated with apoptotic death and DNA cleavage into 300 and 50 kbp units (large DNA fragmentation) and into 180 bp units (internucleosomal DNA fragmentation). We provide evidence that 0.1 to 10 μM ICI 182,780 and TAM significantly inhibit the growth of A2780 cells in a dose‐dependent fashion. Cytokinetic analysis revealed that only 10 μM TAM caused a significant blockade in G1 and a diminished replication rate. Conversely, we show that 0.1 to 10 μM ICI 182,780 and TAM induce apoptosis in a dose‐dependent fashion. The earliest recognizable apoptotic change induced by treating the cells with these 2 drugs was DNA cleavage into 300 and 50 kbp units. This started to be visible in adherent cells, implying that apoptosis induction by ICI 182,780 and TAM was not determined by the loss of cell–substrate interaction. A further degradation of 300 and 50 kbp DNA fragments occurred in cells that had lost their adhesion to the culture plate. We observed the ladder pattern typical of internucleosomal DNA cleavage by treating A2780 cells with the highest dose (10 μM) of ICI 182,780 and TAM. Lower concentrations of these 2 drugs (0.1 to 1 μM) did not produce such a pattern of DNA fragmentation. Typical features of apoptotic nuclei were detectable after both drug treatments. However, cells undergoing apoptosis induced by ICI 182,780 showed hyper‐aggregation of chromatin, whereas TAM‐treated cells preferentially exhibited chromatin clumping. Int. J. Cancer 76:47–54, 1998.© 1998 Wiley‐Liss, Inc.

From plasma membrane to cytoskeleton: a novel function for semaphorin 6A

Class III β-tubulin (TUBB3) overexpression has been reported in ovary, lung, breast, and gastric cancer patients. Currently, no clinical drugs are available for a specific targeting of TUBB3, whereas the investigational drug IDN5390 specifically interacts with TUBB3. To gain insight into the pathways leading to TUBB3 up-regulation, we did a human genome microarray analysis in A2780 cells made resistant to IDN5390 to identify selected pathways specifically disrupted in resistant cells. Using this approach, we discovered that semaphorin 6A (SEMA6A) is down-regulated not only in IDN5390-resistant cells but also in cells made resistant to cisplatin, topotecan, and doxorubicin, whereas no changes were noticed in paclitaxel- and gemcitabine-resistant cells. Acute treatment with IDN5390 was able to down-regulate SEMA6A in cells unselected for drug resistance. TUBB3 expression was assessed in A2780 clones with stable overexpression of SEMA6A and in a panel of clones in which silencing of the protein was obtained. Quantitative PCR was then used to check the modulation of SEMA6A as well as to assess the expression of TUBB3. TUBB3 was increased (median value, 5.4) and reduced (median value, 0.47) in cells with overexpression and silencing of SEMA6A, respectively. Thus, the findings indicate a correlation between the expression of SEMA6A and TUBB3. Then, we found that a form of 83 kDa of SEMA6A is expressed in the cytoskeleton in association with β-actin. These findings suggest for SEMA6A a novel function in the cytoskeleton and a role in modulating tubulin isotype composition and microtubule dynamics. [Mol Cancer Ther 2008;7(1):233–41]