Flavia Filippetti

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]

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]

Sox9 and Hif-2α regulate TUBB3 gene expression and affect ovarian cancer aggressiveness.

UNLABELLED SOX9 [(sex determining region Y)-box9] gene has been implicated in the development and progression of different neoplasms. This study investigated the role of Sox9 in the expression of TUBB3 gene, a marker of aggressiveness in ovarian cancer (OC), encoding βIII-tubulin protein. Gene expression was assessed by quantitative polymerase chain reaction (qPCR) in OC models. Using chromatin immunoprecipitation (ChIP) we found that Sox9 engages TUBB3 promoter at minus 980 base pairs from the transcriptional start site with transcriptional enhancing effects. Furthermore we found that Sox9 is a downstream target of Hif-2α, a transcription factor encoded by endothelial PAS domain protein-1 (EPAS1). Hypoxic microenvironment is a common feature of solid tumors associated with cancer aggressiveness. In the present work we found that knockdown of either SOX9 or EPAS1 abolished TUBB3 gene induction in hypoxia. This phenomenon was associated with a decrease in the number of cell colonies capable of growing in an anchorage-independent way. Using a nanofluidic genetic analyzer, the expression of SOX9, TUBB3 and EPAS1 was evaluated in 182 OC specimens. Double staining immunohistochemistry was employed to evaluate the expression and prognostic role of both Sox9 and βIII-tubulin. Results obtained in cellular models matched the pattern of clinical specimens. We documented a direct correlation among the expression of EPAS1, SOX9 and TUBB3 at mRNA level. Patients displaying no expression for the three genes had the best outcome. A poor prognosis significant in multivariate analysis was visible in patients featuring high expression of βIII-tubulin and nuclear Sox9. CONCLUSIONS Sox9 allows the survival of OC cells upon hypoxic condition, through the activation of βIII-tubulin expression and its aberrant activation in OC is prominent in patients with aggressive OC.

Gli family transcription factors are drivers of patupilone resistance in ovarian cancer

Epothilones constitute a novel class of antitubulin agents that are active in patients who relapse after treatment with other chemotherapeutics. This study investigated the molecular mechanisms leading to the onset of epothilone-B (patupilone) resistance in ovarian cancer. Results demonstrated that the Gli family of transcription factors was overexpressed in resistant cells and that treatment with a specific Gli1 inhibitor (GANT58) made cells more susceptible to treatment, partially reversing drug resistance. We also demonstrated that Gli1 knockdown halted growth in resistant cells that were exposed to patupilone, confirming that Gli1 is capable of directly mediating epothilone-B resistance. Another observation from our research was that patupilone-resistant cells produced HGF and acquired characteristics of a mesenchymal phenotype. However, HGF silencing alone was not capable of converting the drug-resistant phenotype to a susceptible one, and in this case we demonstrated that Gli1 overexpression led to an increase in HGF, establishing a functional link between Gli1 and HGF. These results demonstrated that Gli1 played a key role in driving resistance to patupilone, suggesting that the combination of epothilones and Gli1-targeted agents could be exploited to improve outcomes in ovarian cancer patients resistant to standard treatments.

Hormone receptor expression profile of low-grade serous ovarian cancers

OBJECTIVE Low-grade serous ovarian carcinomas (LGSOCs) are a histological subtype of epithelial ovarian tumors, accounting for fewer than 5% of all cases of ovarian carcinoma. Due to the chemoresistant nature of this subtype a search for more effective systemic therapies is actively ongoing, hormonal therapy showing some degree of activity in this clinical setting. The present study ought to investigate the hormone receptor status of LGSOCs, as a strategy to provide molecular support for patient-tailored hormonal treatments. METHODS Estrogen receptor α (ERα), ERβ isoforms (i.e. ERβ1, ERβ2 and ERβ5), progesterone and androgen receptor (PR, AR) expression was evaluated by immunohistochemistry in 25 untreated LGSOC primary tumors, 6 matched metastases and 6 micropapillary variant of serous borderline tumors (micropapillary SBOTs). In vitro cellular models were used to provide insights into clinical observations. RESULTS Our results showed prominent expression of nuclear ERα, ERβ2, ERβ5 and PR in LGSOC primary tissues, while metastatic lesions also exhibit considerable cytoplasmic ERβ2 levels. Notably, a higher expression of ERβ1 protein was determined in micropapillary SBOTs compared to LGSOCs. In vitro experiments on LGSOC cell lines (i.e. HOC-7 and VOA-1056) revealed low/absent ERα, PR and AR protein expression, whereas the three ERβ isoforms were all present. Proliferation of HOC-7 and VOA-1056 was not modulated by either the endogenous or the selective synthetic ligands. CONCLUSIONS These novel findings highlight the need of assessing relative levels of ERα and ERβ isoforms in the total receptor pool in future clinical studies investigating molecular predictors of response to hormonal therapy in LGSOC.

Uncovering the role of nuclear Lysyl oxidase (LOX) in advanced high grade serous ovarian cancer

OBJECTIVE Lysyl oxidase (LOX) is an enzyme that catalyzes the cross-linking of collagen and elastin in the extracellular matrix, thus controlling the tensile strength of tissues. Along with this primary function, there are evidences supporting a role for LOX in many critical biological functions, including gene expression regulation, cell growth, adhesion and migration. Accordingly, recent studies have supported a pivotal role for LOX in cancer progression and metastasis. The current study aimed at investigating the prognostic significance and the functional role of intracellular LOX in ovarian cancer. METHODS To this end, we analyzed LOX expression by immunohistochemistry in archived tumor material from advanced high grade serous ovarian cancer (HGSOC) patients (n=70) and correlated data with clinicopathological parameters and with response to chemotherapy. In vitro experiments were also used to investigate the functional consequences of LOX expression on behavioral aspects of HGSOC cells. RESULTS Our results showed that nuclear LOX expression is associated with unfavorable outcome in advanced HGSOC, being an independent prognostic factor for disease recurrence. Besides, high nuclear levels were seen to be associated with resistance to first-line chemotherapy. Through gene expression modulation experiments in HGSOC cell lines, we demonstrate that LOX positively regulates cell proliferation, migration and anchorage-independent growth. CONCLUSIONS Collectively, our data suggest that LOX functions as a tumor promoter in HGSOC and positively regulates several aspects of the metastatic cascade.

Identification and antitumor activity of a novel inhibitor of the NIMA-related kinase NEK6

The NIMA (never in mitosis, gene A)-related kinase-6 (NEK6), which is implicated in cell cycle control and plays significant roles in tumorigenesis, is an attractive target for the development of novel anti-cancer drugs. Here we describe the discovery of a potent ATP site-directed inhibitor of NEK6 identified by virtual screening, adopting both structure- and ligand-based techniques. Using a homology-built model of NEK6 as well as the pharmacophoric features of known NEK6 inhibitors we identified novel binding scaffolds. Twenty-five compounds from the top ranking hits were subjected to in vitro kinase assays. The best compound, i.e. compound 8 ((5Z)-2-hydroxy-4-methyl-6-oxo-5-[(5-phenylfuran-2-yl)methylidene]-5,6-dihydropyridine-3-carbonitrile), was able to inhibit NEK6 with low micromolar IC50 value, also displaying antiproliferative activity against a panel of human cancer cell lines. Our results suggest that the identified inhibitor can be used as lead candidate for the development of novel anti-cancer agents, thus opening the possibility of new therapeutic strategies.

Estrogen receptor β: Potential target for therapy in adult granulosa cell tumors?

OBJECTIVE Adult granulosa cell tumor (AGCT) is a rare form of sex-cord stromal ovarian tumors. Due to their origin, AGCTs secrete estrogens, and thus, estrogen receptor (ER)-mediated signaling has been considered as a possible target for therapy. The aim of the present study was to get insights into estrogen receptor status and activity in AGCTs, as a strategy to provide molecular support for personalized hormonal treatments. METHODS We evaluated by immunohistochemistry the expression of ERα, ERβ isoforms (i.e. ERβ1, ERβ2 and ERβ5), progesterone and androgen receptor (PR, AR) in 20 untreated AGCTs and 12 unmatched recurrent lesions. Thereafter, we visualized by immunofluorescence, the subcellular distribution of cytoplasmic receptors, and by the proximity ligation assays (PLA) we characterized in situ their ability to interact with other proteins involved in the apoptotic cascade. RESULTS Primary AGCTs predominantly expressed ERβ isoforms, along with PR and AR, while only 30% of patients showed ERα expression. Recurrent tumors were associated with a decrease in AR levels. From mechanistic studies it emerges that ERβ2, and to a lesser extent ERβ1 and AR, are mitochondrial components in cancer cells and that ERβ2 can act as a binding partner of proteins involved in the apoptotic cascade, in turn potentially inhibiting apoptosis. CONCLUSIONS As in other endocrine tumors, ERβ may play a role in the pathogenesis of AGCT; it is crucial to understand estrogen receptor-mediated pathways before planning hormonal treatment strategies in AGCT.