Expression of class III beta tubulin in cervical cancer patients administered preoperative radiochemotherapy: correlation with response to treatment and clinical outcome

Expression of ERCC1 and TUBB3 in Locally Advanced Cervical Squamous Cell Cancer and its Correlation with Different Therapeutic Regimens

Background

Several studies in solid tumors have shown that expression of excision repair cross-complementation group 1 (ERCC1) and class III β-tubulin (TUBB3) can predict response to chemoradiotherapy and might be prognostic factors. We assessed the role of ERCC1 and TUBB3 expressions as predictive and prognostic factors in locally advanced cervical squamous cell carcinoma (LACSCC) patients treated with different neoadjuvant regimens.

Methods

ERCC1 and TUBB3 were detected in 88 patients with LACSCC by immunohistochemical analysis. Sixty-two patients were included in 3 different prospective trials and grouped as follows: vinorelbine or docetaxel (group A, n = 44) and ifosfamide-vinorelbine-cisplatin (group B, n = 18). Both groups were compared with standard cisplatin chemoradiotherapy (group C, n = 26). Clinical data at baseline, disease-free survival (DFS) and overall survival (OS) were also collected. Univariate and multivariate Cox models were used to analyze the risk factors.

Results

Thirty-five patients (39.8%) and 18 (20.5%) had high ERCC1 and TUBB3 expression, respectively. Both proteins were overexpressed in tumors with unfavorable characteristics. High ERCC1 was associated with advanced FIGO stage (p = 0.034) and progressive disease (49% vs. 28%). Poor DFS (p = 0.021) and OS (p = 0.005) were observed in group C patients with high ERCC1 expression. Multivariate analysis showed that ERCC1 expression, FIGO stage and pretreatment hemoglobin level were significant prognostic factors (p = 0.002, p = 0.008 and p = 0.005, respectively).

Conclusions

ERCC1 expression could be a predictive and prognostic factor in LACSCC patients who receive cisplatin monotherapy. Conversely, TUBB3 had no impact on survival in patients treated with antimicrotubule agents.

Prevalence of βIII-tubulin (TUBB3) expression in human normal tissues and cancers

Microtubules are multifunctional cytoskeletal proteins that are involved in crucial cellular roles including maintenance of cell shape, intracellular transport, meiosis, and mitosis. Class III beta-tubulin (βIII-tubulin, also known as TUBB3) is a microtubule protein, normally expressed in cells of neuronal origin. Its expression was also reported in various other tumor types, such as several types of lung cancer, ovarian cancer, and esophageal cancer. TUBB3 is of clinical relevance as overexpression has been linked to poor response to microtubule-targeting anti-cancer drugs such as taxanes. To systematically investigate the epidemiology of TUBB3 expression in normal and neoplastic tissues, we used tissue microarrays for analyzing the immunohistochemically detectable expression of TUBB3 in 3911 tissue samples from 100 different tumor categories and 76 different normal tissue types. At least 1 tumor with weak expression could be found in 93 of 100 (93%) different tumor types, and all these 93 entities also had at least 1 tumor with strong positivity. In normal tissues, a particularly strong expression was found in neurons of the brain, endothelium of blood vessels, fibroblasts, spermatogenic cells, stroma cells, endocrine cells, and acidophilic cells of the pituitary gland. In tumors, strong TUBB3 expression was most frequently found in various brain tumors (85%-100%), lung cancer (35%-80%), pancreatic adenocarcinoma (50%), renal cell carcinoma (15%-80%), and malignant melanoma (77%). In summary, these results identify a broad spectrum of cancers that can at least sporadically express TUBB3. Testing of TUBB3 in cancer types eligible for taxane-based therapies could be helpful to identify patients who might best benefit from this treatment.

Prognostic and predictive factors in patients with metastatic or recurrent cervical cancer treated with platinum-based chemotherapy

BACKGROUND

Recognizing resistance or susceptibility to the current standard cisplatin and paclitaxel treatment could improve therapeutic outcomes of metastatic or recurrent cervical cancer.

METHODS

Forty-five tissue samples from patients participating in a phase II trial of cisplatin and ifosfamide, with or without paclitaxel were collected for retrograde analysis. Immunohistochemistry and genotyping was performed to test ERCC1, III β-tubulin, COX-2, CD4, CD8 and ERCC1 (C8092A and N118 N) and MDR1 (C3435T and G2677 T) gene polymorphisms, as possible predictive and prognostic markers. Results were statistically analyzed and correlated with patient characteristics and outcomes.

RESULTS

Patients with higher levels of ERCC1 expression had shorter PFS and OS than patients with low ERCC1 expression (mPFS:5.1 vs 10.2 months, p = 0.027; mOS:10.5 vs. 21.4 months, p = 0.006). Patients with TT in the site of ERCC1 N118 N and GT in the site of MDR1 G2677 T polymorphisms had significantly longer PFS (p = 0.006 and p = 0.027 respectively). ERCC1 expression and the ERCC1 N118 N polymorphism remained independent predictors of PFS. Interestingly, high III beta tubulin expression was associated with chemotherapy resistance and fewer responses [5/20 (25%)] compared to lower III β-tubulin expression [15/23 (65.2%)] (p = 0.008). Finally, ΙΙΙ β-tubulin levels and chemotherapy regimen were independent predictors of response to treatment.

CONCLUSIONS

ERCC1 expression proved to be a significant prognostic factor for survival in our metastatic or recurrent cervical cancer population treated with cisplatin based chemotherapy. ERCC1 N118 N and MDR1 G2677 T polymorphism also proved of prognostic significance for disease progression, while overexpression of III β-tubulin was positively correlated with chemotherapy resistance.

Novel mutations involving βI-, βIIA-, or βIVB-tubulin isotypes with functional resemblance to βIII-tubulin in breast cancer

Tubulin is the target for very widely used anti-tumor drugs, including Vinca alkaloids, taxanes, and epothilones, which are an important component of chemotherapy in breast cancer and other malignancies. Paclitaxel and other tubulin-targeting drugs bind to the β subunit of tubulin, which is a heterodimer of α and β subunits. β-Tubulin exists in the form of multiple isotypes, which are differentially expressed in normal and neoplastic cells and differ in their ability to bind to drugs. Among them, the βIII isotype is overexpressed in many aggressive and metastatic cancers and may serve as a prognostic marker in certain types of cancer. The underpinning mechanisms accounting for the overexpression of this isotype in cancer cells are unclear. To better understand the role of β-tubulin isotypes in cancer, we analyzed over 1000 clones from 90 breast cancer patients, sequencing their β-tubulin isotypes, in search of novel mutations. We have elucidated two putative emerging molecular subgroups of invasive breast cancer, each of which involve mutations in the βI-, βIIA-, or βIVB isotypes of tubulin that increase their structural, and possibly functional, resemblance to the βIII isotype. A unifying feature of the first of the two subgroups is the mutation of the highly reactive C239 residue of βI- or βIVB-tubulin to L239, R239, Y239, or P239, culminating in probable conversion of these isotypes from ROS-sensitive to ROS-resistant species. In the second subgroup, βI, βIIA, and βIVB have up to seven mutations to the corresponding residues in βIII-tubulin. Given that βIII-tubulin has emerged as a pro-survival factor, overexpression of this isotype may confer survival advantages to certain cancer cell types. In this mini-review, we bring attention to a novel mechanism by which cancer cells may undergo adaptive mutational changes involving alternate β-tubulin isotypes to make them acquire some of the pro-survival properties of βIII-tubulin. These "hybrid" tubulins, combining the sequences and/or properties of two wild-type tubulins (βIII and either βI, βIIA, or βIVB), are novel isotypes expressed solely in cancer cells and may contribute to the molecular understanding and stratification of invasive breast cancer and provide novel molecular targets for rational drug development.

Class III β-tubulin in normal and cancer tissues

Microtubules are polymeric structures composed of tubulin subunits. Each subunit consists of a heterodimer of α- and β-tubulin. At least seven β-tubulin isotypes, or classes, have been identified in human cells, and constitutive isotype expression appears to be tissue specific. Class III β-tubulin (βIII-tubulin) expression is normally confined to testes and tissues derived from neural cristae. However, its expression can be induced in other tissues, both normal and neoplastic, subjected to a toxic microenvironment characterized by hypoxia and poor nutrient supply. In this review, we will summarize the mechanisms underlying βIII-tubulin constitutive and induced expression. We will also illustrate its capacity to serve as a biomarker of neural commitment in normal tissues and as a pure prognostic biomarker in cancer patients.

Emerging microtubule targets in glioma therapy

Major advances in the genomics and epigenomics of diffuse gliomas and glioblastoma to date have not been translated into effective therapy, necessitating pursuit of alternative treatment approaches for these therapeutically challenging tumors. Current knowledge of microtubules in cancer and the development of new microtubule-based treatment strategies for high-grade gliomas are the topic in this review article. Discussed are cellular, molecular, and pharmacologic aspects of the microtubule cytoskeleton underlying mitosis and interactions with other cellular partners involved in cell cycle progression, directional cell migration, and tumor invasion. Special focus is placed on (1) the aberrant overexpression of βIII-tubulin, a survival factor associated with hypoxic tumor microenvironment and dynamic instability of microtubules; (2) the ectopic overexpression of γ-tubulin, which in addition to its conventional role as a microtubule-nucleating protein has recently emerged as a transcription factor interacting with oncogenes and kinases; (3) the microtubule-severing ATPase spastin and its emerging role in cell motility of glioblastoma cells; and (4) the modulating role of posttranslational modifications of tubulin in the context of interaction of microtubules with motor proteins. Specific antineoplastic strategies discussed include downregulation of targeted molecules aimed at achieving a sensitization effect on currently used mainstay therapies. The potential role of new classes of tubulin-binding agents and ATPase inhibitors is also examined. Understanding the cellular and molecular mechanisms underpinning the distinct behaviors of microtubules in glioma tumorigenesis and drug resistance is key to the discovery of novel molecular targets that will fundamentally change the prognostic outlook of patients with diffuse high-grade gliomas.

The marriage of quantitative genetics and cell biology: a novel screening approach reveals people have genetically encoded variation in microtubule stability

Microtubules play a central role in many essential cellular processes, including chromosome segregation, intracellular transport, and cell polarity. As these dynamic polymers are crucial components of eukaryotic cellular architecture, we were surprised by our recent discovery that a common human genetic difference leads to variation in microtubule stability in cells from different people. A single nucleotide polymorphism (SNP) near the TUBB6 gene, encoding class V β-tubulin, is associated with the expression level of this protein, which reduces microtubule stability at higher levels of expression. We discuss the novel cellular GWAS (genome-wide association study) platform that led to this discovery of natural, common variation in microtubule stability and the implications this finding may have for human health and disease, including cancer and neurological disorders. Furthermore, our generalizable approach provides a gateway for cell biologists to help interpret the functional consequences of human genetic variation.

βIII-Tubulin: biomarker of taxane resistance or drug target?

INTRODUCTION

βIII-Tubulin (TUBB3) is predominantly expressed in neurons of the central and peripheral nervous systems, while in normal non-neoplastic tissues it is barely detectable. By contrast, this cytoskeletal protein is abundant in a wide range of tumors. βIII-Tubulin is linked to dynamic instability of microtubules (MTs), weakening the effects of agents interfering with MT polymerization. Based on this principle, early studies introduced the classical theory linking βIII-tubulin with a mechanism of counteracting taxane activity and accordingly, prompted its investigation as a predictive biomarker of taxane resistance.

AREAS COVERED

We reviewed 59 translational studies, including cohorts from lung, ovarian, breast, gastric, colorectal and various miscellaneous cancers subject to different chemotherapy regimens.

EXPERT OPINION

βIII-Tubulin functions more as a prognostic factor than as a predictor of response to chemotherapy. We believe this view can be explained by βIII-tubulin's association with prosurvival pathways in the early steps of the metastatic process. Its prognostic response increases if combined with additional biomarkers that regulate its expression, since βIII-tubulin can be expressed in conditions, such as estrogen exposure, unrelated to survival mechanisms and without any predictive activity. Additional avenues for therapeutic intervention could emerge if drugs are designed to directly target βIII-tubulin and its mechanism of regulation.

Prognostic cell biological markers in cervical cancer patients primarily treated with (chemo)radiation: a systematic review

The aim of this study was to systematically review the prognostic and predictive significance of cell biological markers in cervical cancer patients primarily treated with (chemo)radiation. A PubMed, Embase, and Cochrane literature search was performed. Studies describing a relation between a cell biological marker and survival in ≥50 cervical cancer patients primarily treated with (chemo)radiation were selected. Study quality was assessed, and studies with a quality score of 4 or lower were excluded. Cell biological markers were clustered on biological function, and the prognostic and predictive significance of these markers was described. In total, 42 studies concerning 82 cell biological markers were included in this systematic review. In addition to cyclooxygenase-2 (COX-2) and serum squamous cell carcinoma antigen (SCC-ag) levels, markers associated with poor prognosis were involved in epidermal growth factor receptor (EGFR) signaling (EGFR and C-erbB-2) and in angiogenesis and hypoxia (carbonic anhydrase 9 and hypoxia-inducible factor-1α). Epidermal growth factor receptor and C-erbB-2 were also associated with poor response to (chemo)radiation. In conclusion, EGFR signaling is associated with poor prognosis and response to therapy in cervical cancer patients primarily treated with (chemo)radiation, whereas markers involved in angiogenesis and hypoxia, COX-2, and serum SCC-ag levels are associated with a poor prognosis. Therefore, targeting these pathways in combination with chemoradiation may improve survival in advanced-stage cervical cancer patients.

Tumoral and tissue-specific expression of the major human beta-tubulin isotypes

The beta-tubulins are microtubule components encoded by a multigene family, which produces slightly different proteins with complex expression patterns. Several widely used anticancer drugs base their activity on beta-tubulin binding, microtubule dynamics alteration, and cell division blockage. The expression of these drug targets in tumoral and normal cells could be of crucial importance for therapy outcome, unfortunately, the complex beta-tubulin expression patterns have been poorly characterized in human. In this study, we developed a quantitative RT-PCR technique that accurately determines the mRNA expression of the eight human beta-tubulin isotypes, encoding class I, IIa, IIb, III, IVa, IVb, V, and VI and applied it to 21 nontumoral tissues and 79 tumor samples belonging to seven cancer types. In the nontumoral tissues, we found that, overall, TUBB (I), TUBB2C (IVb), and TUBB6 (V) were ubiquitous, TUBB1(VI) was hematopoietic cell-specific, and TUBB2A (IIa), TUBB2B (IIb), TUBB3 (III), and TUBB4 (IVa) had high expression in brain; however, the contribution of the different isotypes to the total beta-tubulin content varied for each tissue and had a complex pattern. In tumoral tissues, most isotypes exhibited an altered expression in specific tumor types or related to tumoral characteristics. In general, TUBB3 showed a great increase in expression while TUBB6 expression was largely decreased in most tumors. Thus, normal tissues showed a complex beta-tubulin isotype distribution, which could contribute to the toxicity profile of the microtubule-binding drugs. In addition, the specific isotypes significantly altered in tumors might represent markers for drug response.

Microtubules and resistance to tubulin-binding agents

Microtubules are dynamic structures composed of alpha-beta-tubulin heterodimers that are essential in cell division and are important targets for cancer drugs. Mutations in beta-tubulin that affect microtubule polymer mass and/or drug binding are associated with resistance to tubulin-binding agents such as paclitaxel. The aberrant expression of specific beta-tubulin isotypes, in particular betaIII-tubulin, or of microtubule-regulating proteins is important clinically in tumour aggressiveness and resistance to chemotherapy. In addition, changes in actin regulation can also mediate resistance to tubulin-binding agents. Understanding the molecular mechanisms that mediate resistance to tubulin-binding agents will be vital to improve the efficacy of these agents.

Tubulin targets in the pathobiology and therapy of glioblastoma multiforme. I. Class III beta-tubulin

Glioblastoma multiforme (GBM) is the most common and deadliest form of primary brain cancer in adults. Despite advances in molecular biology and genetics of gliomas currently there is no effective treatment or promising molecularly targeted experimental therapeutic strategies for these tumors. In previous studies we have shown aberrant overexpression of the class III beta-tubulin isotype (betaIII-tubulin) in GBM and have proposed that this change may reflect perturbations in microtubule dynamics associated with glioma tumorigenesis, tumor progression and malignant transformation into GBM. This minireview focuses on microtubules and tubulin as emerging targets in potential therapy of GBM using a new class of betaIII-tubulin-targeted drugs in the light of recent developments concerning the function and potential role of this isotype in clinically aggressive tumor behavior, cancer stem cells, tumor hypoxia and chemoresistance to tubulin binding agents, principally taxanes.

Stathmin and tubulin expression and survival of ovarian cancer patients receiving platinum treatment with and without paclitaxel

BACKGROUND

Paclitaxel interacts with microtubules to exert therapeutic effects. Molecules that affect microtubule activity, such as betaIII-tubulin and stathmin, may interfere with the treatment. In this study, the authors analyzed betaIII-tubulin and stathmin expression in ovarian tumors and examined their associations with treatment response and patient survival.

METHODS

The study included 178 patients with epithelial ovarian cancer who underwent cytoreductive surgery followed by platinum-based chemotherapy; of these patients, 75 also received paclitaxel. Fresh tumor samples that were collected at surgery were analyzed for messenger RNA expression of betaIII-tubulin and stathmin using real-time polymerase chain reaction analysis. Associations of these molecules with treatment response, disease progression, and overall survival were evaluated.

RESULTS

High stathmin expression was associated with worse disease progression-free and overall survival compared with low stathmin expression. This association was independent of patient age, disease stage, tumor grade, histology, and residual tumor size and was observed in patients who received platinum plus paclitaxel, but not in patients who received platinum without paclitaxel, suggesting that stathmin expression in tumor tissue may interfere with paclitaxel treatment. Similar effects were not observed for betaIII-tubulin, although high betaIII-tubulin expression was associated with disease progression among patients who received platinum without paclitaxel. No associations were observed between treatment response and tubulin or stathmin expression. Expression levels of betaIII-tubulin and stathmin were correlated significantly.

CONCLUSIONS

High stathmin expression predicted an unfavorable prognosis in patients with ovarian cancer who received paclitaxel and platinum chemotherapy. This finding supports the possibility that stathmin may interfere with paclitaxel treatment, leading to a poor prognosis for patients with ovarian cancer.

Molecular mechanisms of patupilone resistance

Patupilone is an epothilone in advanced clinical development that has shown promising efficacy in heavily pretreated patients. This study aimed at characterizing the mechanisms of patupilone activity in resistant patients. To this end, we generated patupilone-resistant cells using two cellular models, the first characterized by high chemosensitivity and low class III beta-tubulin (TUBB3) expression (A2780), and the second by low chemosensitivity and high TUBB3 expression (OVCAR-3). The obtained cell lines were named EPO3 and OVCAR-EPO, respectively. The same selection procedure was done in A2780 cells to generate a paclitaxel-resistant cell line (TAX50). Factors of resistance are expected to increase in the drug-resistant cell lines, whereas factors of drug sensitivity will be down-regulated. Using this approach, we found up-regulation of TUBB3 in TAX50, but not EPO3, cells, showing that TUBB3 mediates the resistance to paclitaxel but not to patupilone. Moreover, TUBB3 was a factor of patupilone sensitivity because OVCAR-EPO cells exhibited a dramatic reduction of TUBB3 and a concomitant sensitization to hypoxia and cisplatin-based chemotherapy. To identify the mechanisms underlying patupilone resistance, tubulin genes were sequenced, thereby revealing that a prominent mechanism of drug resistance is represented by point mutations in class I beta-tubulin. Overall, these results suggest that paclitaxel and patupilone have nonoverlapping mechanisms of resistance, thus allowing the use of patupilone for those patients relapsing after paclitaxel-based chemotherapy. Furthermore, patupilone represents a promising first-line option for the treatment of high-risk ovarian cancer patients, who exhibit high TUBB3 levels and poor response to standard paclitaxel-platin chemotherapy.

Hypoxia induces class III beta-tubulin gene expression by HIF-1alpha binding to its 3' flanking region

Class III beta-tubulin (TUBB3) overexpression represents a major mechanism of drug resistance to microtubule interacting agents such as taxanes and Vinca alkaloids. Here, we tested hypoxia as a possible inducer of TUBB3. The effects of hypoxia on TUBB3 expression were monitored at mRNA and protein level in A2780, in its paclitaxel-resistant counterpart (TC1) and in HeLa cells. Hypoxia was a strong inducer of TUBB3 in A2780, but not in TC1 and HeLa cells. In A2780 HIF-1alpha was knocked down using RNA interference and TUBB3 expression was assessed in normoxia and hypoxia. The silencing abolished the hypoxia-dependent increase of TUBB3, thereby demonstrating that HIF-1alpha mediates TUBB3 induction in hypoxia. To investigate this phenomenon, the 5' flanking region of human TUBB3 was cloned upstream GFP as a reporter. This region contained the promoter gene, but activity of the reporter was unaffected by hypoxia. Thus, we looked at the 3' flanking region and, at +168 nucleotides from the stop codon, an HIF-1alpha binding site was proven to be active in hypoxia, using a construct in which the site was cloned downstream GFP as reporter gene. Deletion of the site in the construct abolished GFP enhancement upon hypoxia. Chromatin immunoprecipitation revealed the engagement by HIF-1alpha of this site in hypoxia. Methylation analysis of this 3' enhancer showed that it was free of methylation in 70% of cells in A2780, while in less than 16% in both TC1 and HeLa cells, thereby suggesting that TUBB3 increase upon hypoxia is abolished through methylation of the 3' enhancer.