Alterations of β‐tubulin isotypes in breast cancer cells resistant to docetaxel

βIII-Tubulin Gene Regulation in Health and Disease

Microtubule proteins form a dynamic component of the cytoskeleton, and play key roles in cellular processes, such as vesicular transport, cell motility and mitosis. Expression of microtubule proteins are often dysregulated in cancer. In particular, the microtubule protein βIII-tubulin, encoded by the TUBB3 gene, is aberrantly expressed in a range of epithelial tumours and is associated with drug resistance and aggressive disease. In normal cells, TUBB3 expression is tightly restricted, and is found almost exclusively in neuronal and testicular tissues. Understanding the mechanisms that control TUBB3 expression, both in cancer, mature and developing tissues will help to unravel the basic biology of the protein, its role in cancer, and may ultimately lead to the development of new therapeutic approaches to target this protein. This review is devoted to the transcriptional and posttranscriptional regulation of TUBB3 in normal and cancerous tissue.

Therapeutic strategies to overcome taxane resistance in cancer

One of the primary causes of attenuated or loss of efficacy of cancer chemotherapy is the emergence of multidrug resistance (MDR). Numerous studies have been published regarding potential approaches to reverse resistance to taxanes, including paclitaxel (PTX) and docetaxel, which represent one of the most important classes of anticancer drugs. Since 1984, following the FDA approval of paclitaxel for the treatment of advanced ovarian carcinoma, taxanes have been extensively used as drugs that target tumor microtubules. Taxanes, have been shown to affect an array of oncogenic signaling pathways and have potent cytotoxic efficacy. However, the clinical success of these drugs has been restricted by the emergence of cancer cell resistance, primarily caused by the overexpression of MDR efflux transporters or by microtubule alterations. In vitro and in vivo studies indicate that the mechanisms underlying the resistance to PTX and docetaxel are primarily due to alterations in α-tubulin and β-tubulin. Moreover, resistance to PTX and docetaxel results from: 1) alterations in microtubule-protein interactions, including microtubule-associated protein 4, stathmin, centriole, cilia, spindle-associated protein, and kinesins; 2) alterations in the expression and activity of multidrug efflux transporters of the ABC superfamily including P-glycoprotein (P-gp/ABCB1); 3) overexpression of anti-apoptotic proteins or inhibition of apoptotic proteins and tumor-suppressor proteins, as well as 4) modulation of signal transduction pathways associated with the activity of several cytokines, chemokines and transcription factors. In this review, we discuss the abovementioned molecular mechanisms and their role in mediating cancer chemoresistance to PTX and docetaxel. We provide a detailed analysis of both in vitro and in vivo experimental data and describe the application of these findings to therapeutic practice. The current review also discusses the efficacy of different pharmacological modulations to achieve reversal of PTX resistance. The therapeutic roles of several novel compounds, as well as herbal formulations, are also discussed. Among them, many structural derivatives had efficacy against the MDR phenotype by either suppressing MDR or increasing the cytotoxic efficacy compared to the parental drugs, or both. Natural products functioning as MDR chemosensitizers offer novel treatment strategies in patients with chemoresistant cancers by attenuating MDR and increasing chemotherapy efficacy. We broadly discuss the roles of inhibitors of P-gp and other efflux pumps, in the reversal of PTX and docetaxel resistance in cancer cells and the significance of using a nanomedicine delivery system in this context. Thus, a better understanding of the molecular mechanisms mediating the reversal of drug resistance, combined with drug efficacy and the application of target-based inhibition or specific drug delivery, could signal a new era in modern medicine that would limit the pathological consequences of MDR in cancer patients.

Taxane resistance in prostate cancer is mediated by decreased drug-target engagement

Despite widespread use of taxanes, mechanisms of action and resistance in vivo remain to be established, and there is no way of predicting who will respond to therapy. This study examined prostate cancer (PCa) xenografts and patient samples to identify in vivo mechanisms of taxane action and resistance. Docetaxel drug-target engagement was assessed by confocal anti-tubulin immunofluorescence to quantify microtubule bundling in interphase cells and aberrant mitoses. Tumor biopsies from metastatic PCa patients obtained 2 to 5 days after their first dose of docetaxel or cabazitaxel were processed to assess microtubule bundling, which correlated with clinical response. Microtubule bundling was evident in PCa xenografts 2 to 3 days after docetaxel treatment but was decreased or lost with acquired resistance. Biopsies after treatment with leuprolide plus docetaxel showed extensive microtubule bundling as did biopsies obtained 2 to 3 days after initiation of docetaxel or cabazitaxel in 2 patients with castration-resistant PCa with clinical responses. In contrast, microtubule bundling in biopsies 2 to 3 days after the first dose of docetaxel was markedly lower in 4 nonresponding patients. These findings indicate that taxanes target both mitotic and interphase cells in vivo and that resistance is through mechanisms that impair drug-target engagement. Moreover, the findings suggest that microtubule bundling after initial taxane treatment may be a predictive biomarker for clinical response.

Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Since 1984, when paclitaxel was approved by the FDA for the treatment of advanced ovarian carcinoma, taxanes have been widely used as microtubule-targeting antitumor agents. However, their historic classification as antimitotics does not describe all their functions. Indeed, taxanes act in a complex manner, altering multiple cellular oncogenic processes including mitosis, angiogenesis, apoptosis, inflammatory response, and ROS production. On the one hand, identification of the diverse effects of taxanes on oncogenic signaling pathways provides opportunities to apply these cytotoxic drugs in a more rational manner. On the other hand, this may facilitate the development of novel treatment modalities to surmount anticancer drug resistance. In the latter respect, chemoresistance remains a major impediment which limits the efficacy of antitumor chemotherapy. Taxanes have shown impact on key molecular mechanisms including disruption of mitotic spindle, mitosis slippage and inhibition of angiogenesis. Furthermore, there is an emerging contribution of cellular processes including autophagy, oxidative stress, epigenetic alterations and microRNAs deregulation to the acquisition of taxane resistance. Hence, these two lines of findings are currently promoting a more rational and efficacious taxane application as well as development of novel molecular strategies to enhance the efficacy of taxane-based cancer treatment while overcoming drug resistance. This review provides a general and comprehensive picture on the use of taxanes in cancer treatment. In particular, we describe the history of application of taxanes in anticancer therapeutics, the synthesis of the different drugs belonging to this class of cytotoxic compounds, their features and the differences between them. We further dissect the molecular mechanisms of action of taxanes and the molecular basis underlying the onset of taxane resistance. We further delineate the possible modalities to overcome chemoresistance to taxanes, such as increasing drug solubility, delivery and pharmacokinetics, overcoming microtubule alterations or mitotic slippage, inhibiting drug efflux pumps or drug metabolism, targeting redox metabolism, immune response, and other cellular functions.

Intrinsic and Extrinsic Factors Affecting Microtubule Dynamics in Normal and Cancer Cells

Microtubules (MTs), highly dynamic structures composed of α- and β-tubulin heterodimers, are involved in cell movement and intracellular traffic and are essential for cell division. Within the cell, MTs are not uniform as they can be composed of different tubulin isotypes that are post-translationally modified and interact with different microtubule-associated proteins (MAPs). These diverse intrinsic factors influence the dynamics of MTs. Extrinsic factors such as microtubule-targeting agents (MTAs) can also affect MT dynamics. MTAs can be divided into two main categories: microtubule-stabilizing agents (MSAs) and microtubule-destabilizing agents (MDAs). Thus, the MT skeleton is an important target for anticancer therapy. This review discusses factors that determine the microtubule dynamics in normal and cancer cells and describes microtubule-MTA interactions, highlighting the importance of tubulin isoform diversity and post-translational modifications in MTA responses and the consequences of such a phenomenon, including drug resistance development.

Impact of Docetaxel on blood-brain barrier function and formation of breast cancer brain metastases

BACKGROUND

Breast cancer (BC) is the most frequent malignant tumor in females and the 2nd most common cause of brain metastasis (BM), that are associated with a fatal prognosis. The increasing incidence from 10% up to 40% is due to more effective treatments of extracerebral sites with improved prognosis and increasing use of MRI in diagnostics. A frequently administered, potent chemotherapeutic group of drugs for BC treatment are taxanes usually used in the adjuvant and metastatic setting, which, however, have been suspected to be associated with a higher incidence of BM. The aim of our study was to experimentally analyze the impact of the taxane docetaxel (DTX) on brain metastasis formation, and to elucidate the underlying molecular mechanism.

METHODS

A monocentric patient cohort was analyzed to determine the association of taxane treatment and BM formation. To identify the specific impact of DTX, a murine brain metastatic model upon intracardial injection of breast cancer cells was conducted. To approach the functional mechanism, dynamic contrast-enhanced MRI and electron microscopy of mice as well as in-vitro transendothelial electrical resistance (TEER) and tracer permeability assays using brain endothelial cells (EC) were carried out. PCR-based, immunohistochemical and immunoblotting analyses with additional RNA sequencing of murine and human ECs were performed to explore the molecular mechanisms by DTX treatment.

RESULTS

Taxane treatment was associated with an increased rate of BM formation in the patient cohort and the murine metastatic model. Functional studies did not show unequivocal alterations of blood-brain barrier properties upon DTX treatment in-vivo, but in-vitro assays revealed a temporary DTX-related barrier disruption. We found disturbance of tubulin structure and upregulation of tight junction marker claudin-5 in ECs. Furthermore, upregulation of several members of the tubulin family and downregulation of tetraspanin-2 in both, murine and human ECs, was induced.

CONCLUSION

In summary, a higher incidence of BM was associated with prior taxane treatment in both a patient cohort and a murine mouse model. We could identify tubulin family members and tetraspanin-2 as potential contributors for the destabilization of the blood-brain barrier. Further analyses are needed to decipher the exact role of those alterations on tumor metastatic processes in the brain.

Class III β-tubulin expression as a predictor of docetaxel-resistance in metastatic castration-resistant prostate cancer

About half of the patients treated with docetaxel in the setting of metastatic castration-resistant prostate cancer (CRPC) are non-responders. Therefore, a marker of response would be beneficial for clinical decision-making. We evaluated class III β-tubulin (βIII-tubulin) expression as a predictor of resistance in this setting, which previously has been correlated with lack of response to taxanes in other cancers. Patients with CRPC were included if they were treated with at least 3 cycles of docetaxel between 1990 and 2011. βIII-tubulin expression was assessed by immunostaining, which was performed in tissue samples obtained either via biopsy or prostatectomy at the time of diagnosis. Rates of prostate-specific antigen (PSA) response and overall survival (OS) following docetaxel treatment were compared between patients with high (2+ or 3+ staining) vs. low (0 or 1+ staining) βIII-tubulin expression. Of 73 patients, 26 (35%) had a high expression of βIII-tubulin. A PSA decline of 10% or greater occurred in 65% of patients with a high βIII-tubulin expression vs. 89% with a low βIII-tubulin expression (p = 0.0267). The median OS for patients with a high βIII-tubulin expression was 17.4 (95% CI 8.7–21.0) months vs. 19.8 (95% CI 16.6–23.6) months for patients with a low expression (p = 0.039). Our results show that a high βIII-tubulin expression is a negative prognostic factor in metastatic CRPC patients treated with docetaxel.

Tubulin heterogeneity regulates functions and dynamics of microtubules and plays a role in the development of drug resistance in cancer

Microtubules, composed of αβ-tubulin heterodimers, exhibit diverse structural and functional properties in different cell types. The diversity in the microtubule structure originates from tubulin heterogeneities, namely tubulin isotypes and their post-translational modifications (PTMs). These heterogeneities confer differential stability to microtubules and provide spatial cues for the functioning of the cell. Furthermore, the altered expressions of tubulin isotypes and PTMs are prominent factors for the development of resistance against some cancer drugs. In this review, we summarize our current knowledge of the tubulin isotypes and PTMs and how, together, they control the cellular functions of the microtubules. We also describe how cancer cells use this tubulin heterogeneity to acquire resistance against clinical agents and discuss existing attempts to counter the developed resistance.

Therapeutic efficacy of a novel βIII/βIV-tubulin inhibitor (VERU-111) in pancreatic cancer

Background

The management of pancreatic cancer (PanCa) is exceptionally difficult due to poor response to available therapeutic modalities. Tubulins play a major role in cell dynamics, thus are important molecular targets for cancer therapy. Among various tubulins, βIII and βIV-tubulin isoforms have been primarily implicated in PanCa progression, metastasis and chemo-resistance. However, specific inhibitors of these isoforms that have potent anti-cancer activity with low toxicity are not readily available.

Methods

We determined anti-cancer molecular mechanisms and therapeutic efficacy of a novel small molecule inhibitor (VERU-111) using in vitro (MTS, wound healing, Boyden chamber and real-time xCELLigence assays) and in vivo (xenograft studies) models of PanCa. The effects of VERU-111 treatment on the expression of β-tubulin isoforms, apoptosis, cancer markers and microRNAs were determined by Western blot, immunohistochemistry (IHC), confocal microscopy, qRT-PCR and in situ hybridization (ISH) analyses.

Results

We have identified a novel small molecule inhibitor (VERU-111), which preferentially represses clinically important, βIII and βIV tubulin isoforms via restoring the expression of miR-200c. As a result, VERU-111 efficiently inhibited tumorigenic and metastatic characteristics of PanCa cells. VERU-111 arrested the cell cycle in the G2/M phase and induced apoptosis in PanCa cell lines via modulation of cell cycle regulatory (Cdc2, Cdc25c, and Cyclin B1) and apoptosis - associated (Bax, Bad, Bcl-2, and Bcl-xl) proteins. VERU-111 treatment also inhibited tumor growth (P < 0.01) in a PanCa xenograft mouse model.

Conclusions

This study has identified an inhibitor of βIII/βIV tubulins, which appears to have excellent potential as monotherapy or in combination with conventional therapeutic regimens for PanCa treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-1009-7) contains supplementary material, which is available to authorized users.

The regulatory effect of Tau protein on polymerization of MCF7 microtubules in vitro

Growing evidence continues to point toward the critical role of beta tubulin isotypes in regulating some intracellular functions. Changes that were observed in the microtubules’ intrinsic dynamics, the way they interact with some chemotherapeutic agents, or differences on translocation specifications of some molecular motors along microtubules, were associated to their structural uniqueness in terms of beta tubulin isotype distributions. These findings suggest that the effects of microtubule associated proteins (MAPs) may also vary on structurally different microtubules. Among different microtubule associated proteins, Tau proteins, which are known as neuronal MAPs, bind to beta tubulin, stabilize microtubules, and consequently promote their polymerizations.

In this study, in a set of well controlled experiments, the direct effect of Tau proteins on the polymerization of two structurally different microtubules, porcine brain and breast cancer (MCF7), were tested and compared. Remarkably, we found that in contrast with the promoted effect of Tau proteins on brain microtubules’ polymerization, MCF7 expressed a demoted polymerization while interacting with Tau proteins. This finding can potentially be a novel insight into the mechanism of drug resistance in some breast cancer cells.

It has been reported that microtubules show destabilizing behavior in some MCF7 cells with overexpression of Tau protein when treated with a microtubules’ stabilizing agent, Taxol. This behavior has been classified by others as drug resistance, but it may instead be potentially caused by a competition between the destabilizing effect of the Tau protein and the stabilizing effect of the drug on MCF7 microtubules. Also, we quantified the polarization coefficient of MCF7 microtubules in the presence and absence of Tau proteins by the electro-orientation method and compared the values. The two significantly different values obtained can possibly be one factor considered to explain the effect of Tau proteins on the polymerization of MCF7 microtubules.

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MCF7 microtubules express slow and stable polymerization behavior.

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Tau-MCF7 microtubules express demoted polymerization behavior.

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Tau-MCF7 polymerization can possibly be explained by electrostatic specifications.

Taxane resistance in castration-resistant prostate cancer: mechanisms and therapeutic strategies

Despite its good initial response and significant survival benefit in patients with castration-resistant prostate cancer (CRPC), taxane therapy inevitably encounters drug resistance in all patients. Deep understandings of taxane resistant mechanisms can significantly facilitate the development of new therapeutic strategies to overcome taxane resistance and improve CRPC patient survival. Multiple pathways of resistance have been identified as potentially crucial areas of intervention. First, taxane resistant tumor cells typically have mutated microtubule binding sites, varying tubulin isotype expression, and upregulation of efflux transporters. These mechanisms contribute to reducing binding affinity and availability of taxanes. Second, taxane resistant tumors have increased stem cell like characteristics, indicating higher potential for further mutation in response to therapy. Third, the androgen receptor pathway is instrumental in the proliferation of CRPC and multiple hypotheses leading to this pathway reactivation have been reported. The connection of this pathway to the AKT pathway has received significant attention due to the upregulation of phosphorylated AKT in CRPC. This review highlights recent advances in elucidating taxane resistant mechanisms and summarizes potential therapeutic strategies for improved treatment of CRPC.

Multiplicity of acquired cross-resistance in paclitaxel-resistant cancer cells is associated with feedback control of TUBB3 via FOXO3a-mediated ABCB1 regulation

Acquired drug resistance is a primary obstacle for effective cancer therapy. The correlation of point mutations in class III β-tubulin (TUBB3) and the prominent overexpression of ATP-binding cassette P-glycoprotein (ABCB1), a multidrug resistance gene, have been protruding mechanisms of resistance to microtubule disruptors such as paclitaxel (PTX) for many cancers. However, the precise underlying mechanism of the rapid onset of cross-resistance to an array of structurally and functionally unrelated drugs in PTX-resistant cancers has been poorly understood. We determined that our established PTX-resistant cancer cells display ABCB1/ABCC1-associated cross-resistance to chemically different drugs such as 5-fluorouracil, docetaxel, and cisplatin. We found that feedback activation of TUBB3 can be triggered through the FOXO3a-dependent regulation of ABCB1, which resulted in the accentuation of induced PTX resistance and encouraged multiplicity in acquired cross-resistance. FOXO3a-directed regulation of P-glycoprotein (P-gp) function suggests that control of ABCB1 involves methylation-dependent activation. Consistently, transcriptional overexpression or downregulation of FOXO3a directs inhibitor-controlled protease-degradation of TUBB3. The functional PI3K/Akt signaling is tightly responsive to FOXO3a activation alongside doxorubicin treatment, which directs FOXO3a arginine hypermethylation. In addition, we found that secretome factors from PTX-resistant cancer cells with acquired cross-resistance support a P-gp-dependent association in multidrug resistance (MDR) development, which assisted the FOXO3a-mediated control of TUBB3 feedback. The direct silencing of TUBB3 reverses induced multiple cross-resistance, reduces drug-resistant tumor mass, and suppresses the impaired microtubule stability status of PTX-resistant cells with transient cross-resistance. These findings highlight the control of the TUBB3 response to ABCB1 genetic suppressors as a mechanism to reverse the profuse development of multidrug resistance in cancer.

Proteomic analysis of docetaxel resistance in human nasopharyngeal carcinoma cells using the two-dimensional gel electrophoresis method

Docetaxel-based chemotherapy has been recommended for advanced nasopharyngeal carcinoma (NPC). However, treatment failure often occurs because of acquired drug resistance. In this study, a docetaxel-resistant NPC cell line CNE-2R was established with increasing doses of docetaxel for more than 6 months. Two-dimensional gel electrophoresis and ESI-Q-TOF-MS were used to compare the differential expression of docetaxel-resistance-associated proteins between human NPC CNE-2 cells and docetaxel-resistant CNE-2R cells. As a result, 24 differentially expressed proteins were identified, including 11 proteins with increased expression and 13 proteins with decreased expression. These proteins function in diverse biological processes such as metabolism, signal transduction, calcium ion binding, immune response, proteolysis, and so on. Among these, α-enolase (ENO1), significantly upregulated in CNE-2R, was selected for detailed analysis. Inhibition of ENO1 by shRNA restored CNE-2R cells' sensitivity to docetaxel. Moreover, overexpression of ENO1 could facilitate the development of acquired resistance of docetaxel in CNE-2 cells. Western blot and reverse-transcription PCR data of clinical samples confirmed that α-enolase was upregulated in docetaxel-resistant human NPC tissues. Finding such proteins might improve interpretation of the molecular mechanisms leading to the acquisition of docetaxel chemoresistance.

Electrostatic differences: A possible source for the functional differences between MCF7 and brain microtubules

Recent studies suggested a link between diversity of beta tubulin isotypes in microtubule structures and the regulatory roles that they play not only on microtubules' intrinsic dynamic, but also on the translocation characteristics of some of the molecular motors along microtubules. Remarkably, unlike porcine brain microtubules, MCF7 microtubules are structured from a different beta tubulin distribution. These types of cancer microtubules show a relatively stable and slow dynamic. In addition, the translocation parameters of some molecular motors are distinctly different along MCF7 as compared to those parameters on brain microtubules. It is known that the diversity of beta tubulin isotypes differ predominantly in the specifications and the electric charge of their carboxy-terminal tails. A key question is to identify whether the negative electrostatic charge of tubulin isotypes and, consequently, microtubules, can potentially be considered as one of the sources of functional differences in MCF7 vs. brain microtubules. We tested this possibility experimentally by monitoring the electro-orientation of these two types of microtubules inside a uniform electric field. Through this evaluation, we quantified and compared the average normalized polarization coefficient of MCF7 vs. Porcine brain microtubules. The higher value obtained for the polarization of MCF7 microtubules, which is associated to the higher negative charge of these types of microtubules, is significant as it can further explain the slow intrinsic dynamic that has been recently reported for single MCF7 microtubules in vitro. Furthermore, it can be potentially considered as a factor that can directly impact the translocation parameters of some molecular motors along MCF7 microtubules, by altering the mutual electrostatic interactions between microtubules and molecular motors.

The Roles of β-Tubulin Mutations and Isotype Expression in Acquired Drug Resistance

The antitumor drug paclitaxel stabilizes microtubules and reduces their dynamicity, promoting mitotic arrest and eventually apoptosis. Upon assembly of the α/β-tubulin heterodimer, GTP becomes bound to both the α and β-tubulin monomers. During microtubule assembly, the GTP bound to β-tubulin is hydrolyzed to GDP, eventually reaching steady-state equilibrium between free tubulin dimers and those polymerized into microtubules. Tubulin-binding drugs such as paclitaxel interact with β-tubulin, resulting in the disruption of this equilibrium. In spite of several crystal structures of tubulin, there is little biochemical insight into the mechanism by which anti-tubulin drugs target microtubules and alter their normal behavior. The mechanism of drug action is further complicated, as the description of altered β-tubulin isotype expression and/or mutations in tubulin genes may lead to drug resistance as has been described in the literature. Because of the relationship between β-tubulin isotype expression and mutations within β-tubulin, both leading to resistance, we examined the properties of altered residues within the taxane, colchicine and Vinca binding sites. The amount of data now available, allows us to investigate common patterns that lead to microtubule disruption and may provide a guide to the rational design of novel compounds that can inhibit microtubule dynamics for specific tubulin isotypes or, indeed resistant cell lines. Because of the vast amount of data published to date, we will only provide a broad overview of the mutational results and how these correlate with differences between tubulin isotypes. We also note that clinical studies describe a number of predictive factors for the response to anti-tubulin drugs and attempt to develop an understanding of the features within tubulin that may help explain how they may affect both microtubule assembly and stability.

Prostate Tumor Overexpressed-1 (PTOV1) promotes docetaxel-resistance and survival of castration resistant prostate cancer cells

Metastatic prostate cancer is presently incurable. The oncogenic protein PTOV1, first described in prostate cancer, was reported as overexpressed and significantly correlated with poor survival in numerous tumors. Here, we investigated the role of PTOV1 in prostate cancer survival to docetaxel and self-renewal ability. Transduction of PTOV1 in docetaxel-sensitive Du145 and PC3 cells significantly increased cell survival after docetaxel exposure and induced docetaxel-resistance genes expression (ABCB1, CCNG2 and TUBB2B). In addition, PTOV1 induced prostatospheres formation and self-renewal genes expression (ALDH1A1, LIN28A, MYC and NANOG). In contrast, Du145 and PC3 cells knockdown for PTOV1 significantly accumulated in the G2/M phase, presented a concomitant increased subG1 peak, and cell death by apoptosis. These effects were enhanced in docetaxel-resistant cells. Analyses of tumor datasets show that PTOV1 expression significantly correlated with prostate tumor grade, drug resistance (CCNG2) and self-renewal (ALDH1A1, MYC) markers. These genes are concurrently overexpressed in most metastatic lesions. Metastases also show PTOV1 genomic amplification in significant co-occurrence with docetaxel-resistance and self-renewal genes. Our findings identify PTOV1 as a promoter of docetaxel-resistance and self-renewal characteristics for castration resistant prostate cancer. The concomitant increased expression of PTOV1, ALDH1A1 and CCNG2 in primary tumors, may predict metastasis and bad prognosis.

Chemoresistance of Lung and Breast Cancer Cells Growing Under Prolonged Periods of Serum Starvation

The efficacy of chemotherapy is hindered by both tumor heterogeneity and acquired or intrinsic multi-drug resistance caused by the contribution of multidrug resistance proteins and stemness-associated prosurvival markers. Therefore, targeting multi-drug resistant cells would be much more effective against cancer. In this study, we characterized the chemoresistance properties of adherent (anchorage-dependent) lung H460 and breast MCF-7 cancer cells growing under prolonged periods of serum starvation (PPSS). We found that under PPSS, both cell lines were highly resistant to Paclitaxel, Colchicine, Hydroxyurea, Obatoclax, Wortmannin, and LY294002. Levels of several proteins associated with increased stemness such as Sox2, MDR1, ABCG2, and Bcl-2 were found to be elevated in H460 cells but not in MCF-7 cells. While pharmacological inhibition of either MDR1, ABCG2, Bcl-2 with Verapamil, Sorafenib, or Obatoclax, respectively decreased the levels of their target proteins under routine culture conditions as expected, such inhibition did not reverse PX resistance in PPSS conditions. Paradoxically, treatment with inhibitors in serum-starved conditions produced an elevation of their respective target proteins. In addition, we found that Digitoxin, an FDA approved drug that decrease the viability of cancer cells growing under PPSS, downregulates the expression of Sox2, MDR1, phospho- AKT, Wnt5a/b, and β-catenin. Our data suggest that PPSS-induced chemoresistance is the result of extensive rewiring of intracellular signaling networks and that multi-resistance can be effectively overcome by simultaneously targeting multiple targets of the rewired network. Furthermore, our PPSS model provides a simple and useful tool to screen drugs for their ability to target multiple pathways of cancer resistance. J. Cell. Physiol. 232: 2033-2043, 2017. © 2016 Wiley Periodicals, Inc.

Enhanced stability of microtubules contributes in the development of colchicine resistance in MCF-7 cells

Understanding the mechanism of resistance to tubulin-targeted anticancer drugs is important for improved chemotherapy. In this work, a colchicine-resistant MCF-7 cell line (MCF-7_Col30) was generated by the gradual increment of colchicine treatment and the MCF-7_Col30 showed ∼8-fold resistance towards colchicine. MCF-7_Col30 cells showed ∼2.5-fold resistance against microtubule depolymerizing agents, vinblastine, and nocodazole. In contrast, it displayed more sensitivity towards paclitaxel, a microtubule-polymerizing agent. MCF-7 and MCF-7_Col30 cells showed similar sensitivity towards cisplatin. Further, the level of P-glycoprotein did not increase in MCF-7_Col30 cells. MCF-7_Col30 cells resisted the microtubule depolymerizing effects of colchicine. The time-lapse imaging of individual microtubules in live cells showed that the dynamics of microtubules in MCF-7_Col30 cells was suppressed as compared to the parent MCF-7 cells. The levels of tubulin acetylation and glutamylation increased in MCF-7_Col30 cells than the parent MCF-7 cells suggesting that microtubules are stabilized in MCF-7_Col30 cells. Interestingly, the level of βIII tubulin was increased by 2.3 folds whereas that of βII and βIV tubulin was decreased by 55 and 150%, respectively in MCF-7_Col30 cells. The results suggested that the changes in the level of β-tubulin isoforms and the post-translational modifications of microtubules altered the stability and dynamics of microtubules and contributed to the development of colchicine-resistance in MCF-7 cells.

Delineating the Role of βIV-Tubulins in Pancreatic Cancer: βIVb-Tubulin Inhibition Sensitizes Pancreatic Cancer Cells to Vinca Alkaloids

Pancreatic cancer (PC) is a lethal disease which is characterized by chemoresistance. Components of the cell cytoskeleton are therapeutic targets in cancer. βIV-tubulin is one such component that has two isotypes-βIVa and βIVb. βIVa and βIVb isotypes only differ in two amino acids at their C-terminus. Studies have implicated βIVa-tubulin or βIVb-tubulin expression with chemoresistance in prostate, breast, ovarian and lung cancer. However, no studies have examined the role of βIV-tubulin in PC or attempted to identify isotype specific roles in regulating cancer cell growth and chemosensitivity. We aimed to determine the role of βIVa- or βIVb-tubulin on PC growth and chemosensitivity. PC cells (MiaPaCa-2, HPAF-II, AsPC1) were treated with siRNA (control, βIVa-tubulin or βIVb-tubulin). The ability of PC cells to form colonies in the presence or absence of chemotherapy was measured by clonogenic assays. Inhibition of βIVa-tubulin in PC cells had no effect chemosensitivity. In contrast, inhibition of βIVb-tubulin in PC cells sensitized to vinca alkaloids (Vincristine, Vinorelbine and Vinblastine), which was accompanied by increased apoptosis and enhanced cell cycle arrest. We show for the first time that βIVb-tubulin, but not βIVa-tubulin, plays a role in regulating vinca alkaloid chemosensitivity in PC cells. The results from this study suggest βIVb-tubulin may be a novel therapeutic target and predictor of vinca alkaloid sensitivity for PC and warrants further investigation.

Distinctions between dynamic characteristics of the single EG5 motor protein along neural vs. cancerous microtubules

The kinesin 5 motor contributes critically to mitosis, and is often upregulated in cancer. In vitro motility studies of kinesin 5 moving along bovine brain microtubules indicate that the motors have limited processivity. Cancer cells have abnormal mitotic behavior, so one might wonder whether the functional properties of kinesin 5 change in such a background. Because there could be multiple unknown changes in cancerous vs normal cells, we chose to address this question in a controlled in vitro environment. Specifically, through a series of parallel experiments along bovine brain vs. breast cancer microtubules, we quantified the in vitro motility characteristics of single Eg5 molecular motors along these two types of microtubules, combining the utilization of an optical trapping technique with a study of motion in the unloaded regime. The obtained values indicate that Eg5 processivity is 40% less along MCF7 microtubules, compared to that measured on bovine brain MTs. Interestingly, not all single-molecule properties are altered, as the velocity of the single motor doesn't show any significant changes on either track, though the binding time along MCF7 microtubules is almost 25% shorter. The current results, in conjunction with our previously reported outcomes of the evaluation of the Eg5's characteristics under external load, show that in transition from no-load to high-load regime, the Eg5 binding time has less sensitivity on MCF7 as compared to bovine brain MTs. This finding is intriguing, as it suggests that, potentially, groups of Eg5 motors function more effectively in the cancer background of a large ensemble, possibly contributing to faster mitosis in cancer cells.

11a-N-Tosyl-5-deoxi-pterocarpan, LQB-223, a novel compound with potent antineoplastic activity toward breast cancer cells with different phenotypes

Multidrug resistance is the major obstacle for successful treatment of breast cancer, prompting the investigation of novel anticancer compounds.

PURPOSE

In this study, we tested whether LQB-223, an 11a-N-Tosyl-5-deoxi-pterocarpan newly synthesized compound, could be effective toward breast cancer cells.

METHODS

Human breast cell lines MCF-7, MDA-MB-231, HB4a and MCF-7 Dox(R) were used as models for this study. Cell culture, MTT and clonogenic assay, flow cytometry and Western blotting were performed.

RESULTS

The LQB-223 decreased cell viability, inhibited colony formation and induced an expressive G2/M arrest in breast cancer cells. There was an induction in p53 and p21(Cip1) protein levels following treatment of wild-type p53 MCF-7 cells, which was not observed in the mutant p53 MDA-MB-231 cell line, providing evidence that the compound might act to modulate the cell cycle regardless of p53 status. In addition, LQB-223 resulted in decreased procaspase levels and increased annexin V staining, suggesting that the apoptotic cascade is also triggered. Importantly, LQB-223 treatment was shown to be less cytotoxic to non-neoplastic breast cells than docetaxel and doxorubicin. Strikingly, exposure of doxorubicin-resistant MCF-7-Dox(R) cells to LQB-223 resulted in suppression of cell viability and proliferation in levels comparable to MCF-7. Of note, MCF-7-Dox(R) cells have an elevated expression of the P-glycoprotein efflux pump when compared to MCF-7.

CONCLUSION

Together, these results show that LQB-223 mediates cytotoxic effects in sensitive and resistant breast cancer cells, while presenting low toxicity to non-neoplastic cells. The new compound might represent a potential strategy to induce toxicity in breast cancer cells, especially chemoresistant cells.

Effect of CH-35, a novel anti-tumor colchicine analogue, on breast cancer cells overexpressing the βIII isotype of tubulin

The subunit protein of microtubules is tubulin, which has been the target for some of the most successful and widely used anti-tumor drugs. Most of the drugs that target tubulin bind to the β subunit. There are many isotypes of β-tubulin and their distributions differ among different tissues. The βIII isotype is over-expressed in many tumors, particularly those that are aggressive, metastatic, and drug resistant. We have previously reported the design and synthesis of a series of compounds to fit the colchicine site on βIII but not on the other isotypes. In the current study, we tested the toxicity and the anti-tumor activity of one of these compounds, CH-35, on the human breast tumor MDA-MB-231 over-expressing βIII in a xenogeneic mouse model. We found that CH-35 was as toxic as Taxol® in vivo. Although the βIII-over-expressing cells developed into very fast-growing tumors, CH-35 was more effective against this tumor than was Taxol. Our results suggest that CH-35 is a promising candidate for future drug development.

Antiandrogens Inhibit ABCB1 Efflux and ATPase Activity and Reverse Docetaxel Resistance in Advanced Prostate Cancer

PURPOSE

Previous studies show that inhibition of ABCB1 expression overcomes acquired docetaxel resistance in C4-2B-TaxR cells. In this study, we examined whether antiandrogens, such as bicalutamide and enzalutamide, could inhibit ABCB1 activity and overcome resistance to docetaxel.

EXPERIMENTAL DESIGN

ABCB1 efflux activity was determined using a rhodamine efflux assay. ABCB1 ATPase activity was determined by Pgp-Glo assay systems. The effects of the antiandrogens bicalutamide and enzalutamide on docetaxel sensitivity were determined by cell growth assays and tumor growth in vivo.

RESULTS

We found that bicalutamide and enzalutamide inhibit ABCB1 ATP-binding cassette transporter activity through blocking ABCB1 efflux activity. Bicalutamide inhibited ABCB1 efflux activity by 40%, whereas enzalutamide inhibited ABCB1 efflux activity by approximately 60%. Both bicalutamide and enzalutamide inhibit ABCB1 ATPase activity. In addition, bicalutamide and enzalutamide inhibit ABCB1 efflux activity and desensitize docetaxel-resistant and androgen receptor (AR)-negative DU145 cells. Combination of bicalutamide with docetaxel had a significant antitumor effect in both AR-positive and AR-negative docetaxel-resistant xenograft models, suggesting that bicalutamide desensitizes docetaxel-resistant cells to docetaxel treatment independent of AR status.

CONCLUSIONS

We identified a novel mechanism of action for antiandrogens such as bicalutamide and enzalutamide as inhibitors of ABCB1 efflux and ATPase activity. Bicalutamide and enzalutamide desensitize docetaxel-resistant prostate cancer cells to docetaxel treatment independent of AR status. These studies may lead to the development of combinational therapies with bicalutamide/enzalutamide and docetaxel as effective regimens to treat advanced prostate cancer independent of AR status, and possibly other types of cancer.

AP-1-mediated expression of brain-specific class IVa β-tubulin in P19 embryonal carcinoma cells

Expression of brain-specific phenotypes increased in all trans retinoic acid (ATRA)-induced neural differentiation of mouse P19 embryonal carcinoma cells. Among these phenotypes, expression of class IVa β-tubulin isotype (TUBB4a) was particularly enhanced in neural differentiation. Transient transfection assays employing a reporter construct found that ATRA-mediated regulatory region of the TUBB4a gene lay in the region from −83 nt to +137 nt relative to the +1 transcription start site. Site-directed mutagenesis in the AP-1 binding site at −29/−17 suggested that the AP-1 binding site was a critical region for ATRA-mediated TUBB4a expression. Chromatin immunoprecipitation experiments suggested participation of JunD and activating transcription factor-2 (ATF2) in TUBB4a expression. Additionally, exogenous induction of the dominant-negative (dn) type of JunD canceled ATRA-induced upregulation of TUBB4a, and the dn type of ATF2 suppressed even the basal activity. Further immunoblot study revealed an ATRA-mediated increase in JunD protein, while a significant amount of ATF2 protein was constantly produced. These results suggest that differentiation-mediated activation of JunD results in enhanced TUBB4a expression.

Anticancer efficacy of a supramolecular complex of a 2-diethylaminoethyl-dextran-MMA graft copolymer and paclitaxel used as an artificial enzyme

The anticancer efficacy of a supramolecular complex that was used as an artificial enzyme against multi-drug-resistant cancer cells was confirmed. A complex of diethylaminoethyl-dextran-methacrylic acid methylester copolymer (DDMC)/paclitaxel (PTX), obtained with PTX as the guest and DDMC as the host, formed a nanoparticle 50-300 nm in size. This complex is considered to be useful as a drug delivery system (DDS) for anticancer compounds since it formed a stable polymeric micelle in water. The resistance of B16F10 melanoma cells to PTX was shown clearly through a maximum survival curve. Conversely, the DDMC/PTX complex showed a superior anticancer efficacy and cell killing rate, as determined through a Michaelis-Menten-type equation, which may promote an allosteric supramolecular reaction to tubulin, in the same manner as an enzymatic reaction. The DDMC/PTX complex showed significantly higher anticancer activity compared to PTX alone in mouse skin in vivo. The median survival times of the saline, PTX, DDMC/PTX4 (particle size 50 nm), and DDMC/PTX5 (particle size 290 nm) groups were 120 h (treatment (T)/control (C), 1.0), 176 h (T/C, 1.46), 328 h (T/C, 2.73), and 280 h (T/C, 2.33), respectively. The supramolecular DDMC/PTX complex showed twice the effectiveness of PTX alone (p < 0.036). Above all, the DDMC/PTX complex is not degraded in cells and acts as an intact supramolecular assembly, which adds a new species to the range of DDS.

Does androgen-ablation therapy (AAT) associated autophagy have a pro-survival effect in LNCaP human prostate cancer cells?

WHAT'S KNOWN ON THE SUBJECT? AND WHAT DOES THE STUDY ADD?: Androgen-ablation therapy (AAT) and chemotherapy are commonly used to treat incurable prostate cancer. To improve outcome, there is major on-going research to develop more effective treatments with less toxicity. Autophagy has been suggested from previous studies to play a potential role in cell survival and may be associated with resistance to chemotherapy. Autophagy is known to be upregulated by nutrient starvation or AAT in prostate cancer. However, its functional impact is not fully known. The present study describes the potential synergism between the blockade of autophagy and AAT alone or AAT combined with taxane chemotherapy. Hence, future combined treatment options are warranted to further investigate the clinical impact of autophagy suppression as a treatment strategy.

OBJECTIVE

To study the cellular effects of the anti-androgen bicalutamide on autophagy and its potential impact on response to androgen-ablation therapy (AAT) alone or combined with docetaxel chemotherapy in human prostate cancer LNCaP cells.

MATERIALS AND METHODS

LNCaP cells were treated with bicalutamide ± docetaxel, and cellular effects were assayed: lipidated LC3 (a microtubule-associated protein) for autophagy and its trafficking to fuse with lysosome; flow cytometry using propidium iodide or caspase 3 for cell death; and sulforhodamine B assay for cell growth.

RESULTS

Bicalutamide treatment enhanced autophagy in LNCaP cells with increased level of autophagosome coupled with an altered cellular morphology reminiscent of neuroendocrine differentiation. Consistent with the literature on the interaction between androgen receptor activation and taxane chemotherapy, bicalutamide diminished docetaxel mediated cytotoxicity. Significantly, pharmacological inhibition of autophagy with 3-methyladenine significantly enhanced the efficacy cell kill mediated by AAT ± docetaxel.

CONCLUSION

Autophagy associated with bicalutamide treatment in LNCaP cells may have a pro-survival effect and strategy to modulate autophagy may have a potential therapeutic value.

Evaluations of biomarkers associated with sensitivity to 5-fluorouracil and taxanes for recurrent/advanced breast cancer patients treated with capecitabine-based first-line chemotherapy

The aim of the present study was to investigate the gene expression of biomarkers associated with the sensitivity to fluoropyrimidine and taxanes in recurrent/advanced breast cancer patients treated with first-line capecitabine chemotherapy. We evaluated the clinicopathological/prognostic significance of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP), class III β-tubulin (βIII-tubulin), and stathmin-1 or oncoprotein-18 (STMN1). Formalin-fixed, paraffin-embedded tumor specimens from 42 patients were used for analysis of TS, DPD, TP, βIII-tubulin, and STMN1 expression with a real-time reverse transcription-PCR technique. Patients were classified into the high-expression and low-expression groups according to the median value of the expression level of each biomarker. There was a significantly longer time to progression (TTP) in the high-TP group (P=0.018). The multivariate analysis revealed that the TP expression (hazard ratio for the low-TP group vs. the high-TP group, 2.873; 95% confidence interval, 1.143-7.223; P=0.025) is independent of prognostic factors for TTP. In the subgroup of patients treated with capecitabine plus taxanes as first-line chemotherapy, TTP was significantly longer in the low-βIII-tubulin group (P=0.047). The gene expression of TS, DPD, and STMN1 failed to have any significant impact on the outcome. These results provide further evidence that the TP expression may be a prognostic factor in breast cancer patients treated with capecitabine-based first-line chemotherapy, and βIII-tubulin can be used to predict the outcome of capecitabine in combination with taxanes as first-line chemotherapy. Therefore, these potential biomarkers should be further evaluated.

Acquiring Metastatic Competence by Oral Squamous Cell Carcinoma Cells Is Associated with Differential Expression of α-Tubulin Isoforms

We performed comparative global proteomics analyses of patient-matched primary (686Tu) and metastatic (686Ln) OSCC cells. The metastatic OSCC 686Ln cells showed greater in vitro migratory/invasive potential and distinct cell shape from their parental primary 686Tu cells. Ettan DIGE analysis revealed 1316 proteins spots in both cell lines with >85% to be quantitatively similar (<2 folds) between the two cell lines. However, two protein spots among four serial spots were highly dominant in 686Ln cells. Mass spectrometry sequencing demonstrated all four spots to be α-tubulin isotypes. Further analysis showed no significant quantitative difference in the α-tubulin between the two cell lines either at mRNA or protein levels. Thus, two distinct isoforms of α-tubulin, probably due to posttranslational modification, were associated with metastatic 686Ln cells. Immunofluorescence demonstrated remarkable differences in the cytosolic α-tubulin distribution patterns between the two cells. In 686Tu cells, α-tubulin proteins formed a normal network composed of filaments. In contrast, α-tubulin in 686Ln cells exhibited only partial cytoskeletal distribution with the majority of the protein diffusely distributed within the cytosol. Since α-tubulin is critical for cell shape and mobility, our finding suggests a role of α-tubulin isoforms in acquisition of metastatic phenotype and represents potential target for therapeutic intervention.

Advancements in the Treatment of Metastatic Breast Cancer (MBC): The Role of Ixabepilone

Successful management of breast cancer in the metastatic setting is often confounded by resistance to chemotherapeutics, in particular anthracyclines and taxanes. The limited number of effective treatment options for patients with more aggressive biological subtypes, such as triple-negative metastatic breast cancer, is especially concerning. As such, a therapy clinically proven to be effective in this subtype would be of great value. Ixabepilone, a novel synthetic lactam analog of epothilone B, demonstrated better clinical outcomes in metastatic disease, particularly in triple-negative breast cancer. Most recently, studies have shown the activity of ixabepilone in the neoadjuvant setting, suggesting a role for this drug in primary disease. Notably, treating in the neoadjuvant setting might allow clinicians to explore the predictive value of biomarkers and response to treatment, as pharmacogenomic approaches to therapy continue to evolve. In this article, we review the efficacy and safety data of ixabepilone as a monotherapy and as a component of combination therapy for metastatic and primary breast cancer.

βII-Tubulin and βIII-Tubulin Mediate Sensitivity to Peloruside A and Laulimalide, but not Paclitaxel or Vinblastine, in Human Ovarian Carcinoma Cells

Increased abundance of βII- and βIII-tubulin isotypes in cancer cells confers resistance to vinca and taxoid site drugs; however, the role of these isotypes in the acquired resistance of cancer cells to non-vinca or non-taxoid site binding agents has not been described. Peloruside A (PLA) and laulimalide are the only known non-taxoid site microtubule-stabilizing agents. A human ovarian cancer cell line, 1A9-L4 (L4), previously selected in high concentrations of laulimalide, has both a single point mutation in βI-tubulin and overexpression of βII- and βIII-tubulin. The cells are highly resistant to PLA as well as laulimalide but show no cross-resistance to taxoid site drugs or drugs that bind to the vinca site on β-tubulin. To understand the functional significance of the βII- and βIII-tubulin changes in this resistant cell line, isotype-specific short interfering RNA was used to knock down the expression of the βII and βIII isotypes, and the cellular effects of PLA and laulimalide were examined before and after silencing. It was found that inhibition of βII- and βIII-tubulin partially sensitized L4 cells to PLA and laulimalide, as seen by increased potency of PLA and laulimalide for inducing growth inhibition, cellular tubulin polymerization, microtubule aberrations, and G2-M arrest in the resistant cells. The sensitivity to paclitaxel, vinblastine, ixabepilone, and cisplatin was unaffected by the inhibition of isotype expression. It was concluded that the increased βII- and βIII-tubulin contributed significantly to the resistance phenotype, along with the tubulin structural mutation, and that the altered isotype effect was binding site specific. Mol Cancer Ther; 11(2); 393–404. ©2011 AACR.

Rapid decrease in delivery of chemotherapy to tumors after anti-VEGF therapy: implications for scheduling of anti-angiogenic drugs

Current strategies combining anti-angiogenic drugs with chemotherapy provide clinical benefit in cancer patients. It is assumed that anti-angiogenic drugs, such as bevacizumab, transiently normalize abnormal tumor vasculature and contribute to improved delivery of subsequent chemotherapy. To investigate this concept, a study was performed in non-small cell lung cancer (NSCLC) patients using positron emission tomography (PET) and radiolabeled docetaxel ([(11)C]docetaxel). In NSCLC, bevacizumab reduced both perfusion and net influx rate of [(11)C]docetaxel within 5 hr. These effects persisted after 4 days. The clinical relevance of these findings is notable, as there was no evidence for a substantial improvement in drug delivery to tumors. These findings highlight the importance of drug scheduling and advocate further studies to optimize scheduling of anti-angiogenic drugs.

Absolute quantification of [(11)C]docetaxel kinetics in lung cancer patients using positron emission tomography

PURPOSE

Tumor resistance to docetaxel may be associated with reduced drug concentrations in tumor tissue. Positron emission tomography (PET) allows for quantification of radiolabeled docetaxel ([(11)C]docetaxel) kinetics and might be useful for predicting response to therapy. The primary objective was to evaluate the feasibility of quantitative [(11)C]docetaxel PET scans in lung cancer patients. The secondary objective was to investigate whether [(11)C]docetaxel kinetics were associated with tumor perfusion, tumor size, and dexamethasone administration.

EXPERIMENTAL DESIGN

Thirty-four lung cancer patients underwent dynamic PET-computed tomography (CT) scans using [(11)C]docetaxel. Blood flow was measured using oxygen-15 labeled water. The first 24 patients were premedicated with dexamethasone. For quantification of [(11)C]docetaxel kinetics, the optimal tracer kinetic model was developed and a noninvasive procedure was validated.

RESULTS

Reproducible quantification of [(11)C]docetaxel kinetics in tumors was possible using a noninvasive approach (image derived input function). Thirty-two lesions (size ≥4 cm(3)) were identified, having a variable net influx rate of [(11)C]docetaxel (range, 0.0023-0.0229 mL·cm(-3)·min(-1)). [(11)C]docetaxel uptake was highly related to tumor perfusion (Spearman's ρ = 0.815;P < 0.001), but not to tumor size (Spearman's ρ = -0.140; P = 0.446). Patients pretreated with dexamethasone showed lower [(11)C]docetaxel uptake in tumors (P = 0.013). Finally, in a subgroup of patients who subsequently received docetaxel therapy, relative high [(11)C]docetaxel uptake was related with improved tumor response.

CONCLUSIONS

Quantification of [(11)C]docetaxel kinetics in lung cancer was feasible in a clinical setting. Variable [(11)C]docetaxel kinetics in tumors may reflect differential sensitivity to docetaxel therapy. Our findings warrant further studies investigating the predictive value of [(11)C]docetaxel uptake and the effects of comedication on [(11)C]docetaxel kinetics in tumors.

Specific kinesin expression profiles associated with taxane resistance in basal-like breast cancer

Breast cancer is a genetically heterogenous disease with subtypes differing in prognosis and chemosensitivity. The basal-like breast cancer (BLBC) molecular subtype is associated with poorer outcomes, but is more responsive to taxane-based chemotherapy. Kinesins are intracellular transport proteins that interact with microtubules, which are also the mechanistic target for taxanes. We investigated the relationship between taxane resistance in BLBC and kinesins using both expression and functional studies. Kinesin (KIF) expression was evaluated in three settings in relation to taxane resistance: (i) the NCI-60 cancer cell lines, (ii) pre-treatment samples from four BLBC patient cohorts receiving neoadjuvant chemotherapy regimens with and without taxanes, and (iii) post-treatment samples from residual breast cancer following neoadjuvant taxane-containing chemotherapy. We used a novel functional approach to gene modification, validation-based insertional mutagenesis, to select kinesin-overexpressing clones of BLBC cells for evaluation of related mechanisms of taxane resistance. In the NCI-60 cell line dataset, overexpression of the kinesin KIFC3 is significantly correlated with resistance to both docetaxel (P < 0.001) and paclitaxel (P < 0.001), but not to platinum-based chemotherapy, including carboplatin (P = 0.49) and cisplatin (P = 0.10). Overexpression of KIFC3 and KIF5A in pre-chemotherapy samples similarly predicted resistance to paclitaxel in the MDACC cohorts (P = 0.01); no KIF predicted resistance to fluorouracil-epirubicin-cyclophosphamide or cisplatin in BLBC patient cohorts treated without taxanes. KIF12 is the most overexpressed KIF gene in post-chemotherapy taxane-resistant residual breast cancers (2.8-fold-change). Functional studies established that overexpression of KIFC3, KIF5A, and KIF12 were specific in mediating resistance to docetaxel and not vincristine or doxorubicin. Mutation of the ATP-binding domain of a kinesin abolished its ability to mediate docetaxel resistance. Overall, kinesin overexpression correlates with specific taxane resistance in BLBC cell lines and tissues. Our results suggest a novel approach for drug development to overcome taxane resistance in breast cancer through concurrent or sequential use of kinesin inhibitors.

miRNA-34a is associated with docetaxel resistance in human breast cancer cells

Docetaxel is a chemotherapy drug to treat breast cancer, however as with many chemotherapeutic drugs resistance to docetaxel occurs in 50% of patients, and the underlying molecular mechanisms of drug resistance are not fully understood. Gene regulation through microRNAs (miRNA) has been shown to play an important role in cancer drug resistance. By directly targeting mRNA, miRNAs are able to inhibit genes that are necessary for signalling pathways or drug induced apoptosis rendering cells drug resistant. This study investigated the role of differential miRNA expression in two in vitro breast cancer cell line models (MCF-7, MDA-MB-231) of acquired docetaxel resistance. MiRNA microarray analysis identified 299 and 226 miRNAs altered in MCF-7 and MDA-MB-231 docetaxel-resistant cells, respectively. Docetaxel resistance was associated with increased expression of miR-34a and miR-141 and decreased expression of miR-7, miR-16, miR-30a, miR-125a-5p, miR-126. Computational target prediction revealed eight candidate genes targeted by these miRNAs. Quantitative PCR and western analysis confirmed decreased expression of two genes, BCL-2 and CCND1, in docetaxel-resistant cells, which are both targeted by miR-34a. Modulation of miR-34a expression was correlated with BCL-2 and cyclin D1 protein expression changes and a direct interaction of miR-34a with BCL-2 was shown by luciferase assay. Inhibition of miR-34a enhanced response to docetaxel in MCF-7 docetaxel-resistant cells, whereas overexpression of miR-34a conferred resistance in MCF-7 docetaxel-sensitive cells. This study is the first to show differences in miRNA expression, in particular, increased expression of miR-34a in an acquired model of docetaxel resistance in breast cancer. This serves as a mechanism of acquired docetaxel resistance in these cells, possibly through direct interactions with BCL-2 and CCND1, therefore presenting a potential therapeutic target for the treatment of docetaxel-resistant breast cancer.

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.

Cancer cells acquire mitotic drug resistance properties through beta I-tubulin mutations and alterations in the expression of beta-tubulin isotypes

BACKGROUND

Anti-mitotic compounds (microtubule de-stabilizers) such as vincristine and vinblastine have been shown clinically successful in treating various cancers. However, development of drug-resistance cells limits their efficacies in clinical situations. Therefore, experiments were performed to determine possible drug resistance mechanisms related to the application of anti-mitotic cancer therapy.

PRINCIPAL FINDINGS

A KB-derived microtubule de-stabilizer-resistant KB-L30 cancer cell line was generated for this study. KB-L30 cells showed cross-resistance to various microtubule de-stabilizers including BPR0L075, vincristine and colchicine through multiple-drug resistant (MDR)-independent mechanisms. Surprisingly, KB-L30 cells showed hyper-sensitivity to the microtubule-stabilizer, paclitaxel. Results of the RT-PCR analysis revealed that expression of both class II and III β-tubulin was down-regulated in KB-L30 cells as compared to its parental KB cancer cells. In addition, DNA sequencing analysis revealed six novel mutation sites present in exon four of the βI-tubulin gene. Computational modeling indicated that a direct relationship exists between βI-tubulin mutations and alteration in the microtubule assembly and dynamic instability in KB-L30 cells and this predicted model was supported by an increased microtubule assembly and reduced microtubule dynamic instability in KB-L30 cells, as shown by Western blot analysis.

CONCLUSIONS AND SIGNIFICANCE

Our study demonstrated that these novel mutations in exon four of the βI-tubulin induced resistance to microtubule de-stabilizers and hyper-sensitivity to microtubule stabilizer through an alteration in the microtubule assembly and dynamics in cancer cells. Importantly, the current study reveals that cancer cells may acquire drug resistance ability to anti-mitotic compounds through multiple changes in the microtubule networks. This study further provided molecular information in drug selection for patients with specific tubulin mutations.

The estrogen receptor influences microtubule-associated protein tau (MAPT) expression and the selective estrogen receptor inhibitor fulvestrant downregulates MAPT and increases the sensitivity to taxane in breast cancer cells

Introduction

Microtubule-associated protein tau (MAPT) inhibits the function of taxanes and high expression of MAPT decreases the sensitivity to taxanes. The relationship between estrogen receptor (ER) and MAPT in breast cancer is unclear. In this study, we examined the correlation of MAPT expression with the sensitivity of human breast cancer cells to taxanes, and the relationship between ER and MAPT.

Methods

The correlation between MAPT expression and sensitivity to taxanes was investigated in 12 human breast cancer cell lines. Alterations in cellular sensitivity to taxanes were evaluated after knockdown of MAPT expression. ER expression was knocked down or stimulated in MAPT- and ER-positive cell lines to examine the relationship between ER and MAPT. The cells were also treated with hormone drugs (tamoxifen and fulvestrant) and taxanes.

Results

mRNA expression of MAPT did not correlate with sensitivity to taxanes. However, expression of MAPT protein isoforms of less than 70 kDa was correlated with a low sensitivity to taxanes. Downregulation of MAPT increased cellular sensitivity to taxanes. MAPT protein expression was increased by stimulation with 17-β-estradiol or tamoxifen, but decreased by ER downregulation and by fulvestrant, an ER inhibitor. The combination of fulvestrant with taxanes had a synergistic effect, whereas tamoxifen and taxanes had an antagonistic effect.

Conclusions

Expression of MAPT protein isoforms of less than 70 kDa is correlated with a low sensitivity to taxanes in breast cancer cells. ER influences MAPT expression and fulvestrant increases the sensitivity to taxanes in MAPT- and ER-positive breast cancer cells.

Isolating tubulin from nonneural sources

Tubulin is a highly conserved, negatively charged protein that is found in essentially all eukaryotic cells. These properties ensure that isolation protocols successful in one system will likely work, with a few modifications, in most systems. Tubulin has been isolated most frequently from mammalian brain, and the main difference encountered in other systems versus brain is that tubulin is much less abundant in nearly all other sources than it is in brain. This means that attempting to purify tubulin by direct polymerization from a homogenate will often fail or be quite inefficient. However, the conservation of negative charge on tubulin means that an initial ion exchange step can be used to both purify and concentrate the protein from most systems. Polymerization-competent tubulin can usually be obtained by inducing polymerization in the salt eluate from the ion exchange step. We describe protocols for this procedure and describe its application to a number of vertebrate, fungal, protozoal, and plant sources.

Preclinical assessment of cisplatin-based therapy versus docetaxel-based therapy on a panel of human non-small-cell lung cancer xenografts

The success of treatment of advanced non-small-cell lung cancer (NSCLC) remains very poor. The aim of this study was, on a series of NSCLC xenografts, to compare the efficacy of standard cisplatin-based or docetaxel-based chemotherapy. Seven human xenografts were obtained from six patients (two xenografts were derived from primary or metastatic tumors of the same patient). Three xenografts were adenocarcinomas and four were squamous cell carcinomas. All xenografts reproduced the same histology as that of the patient's original tumor. Docetaxel, administered as single-agent chemotherapy, induced a significant response in five of the seven NSCLC xenografts (71%), without significant increase after combination with cisplatin, vinorelbine, or gemcitabine. Relative expression of genes putatively involved in drug response was also studied in all xenografts and did not explain the variability of drug sensitivity. In conclusion, this panel of human NSCLC xenografts reliably reproduces the data obtained in patient tumors and the relative sensitivity to docetaxel reported in NSCLC patients.

Stress hormones mediate drug resistance to paclitaxel in human breast cancer cells through a CDK-1-dependent pathway

Chemotherapy comprises part of successful treatment regimens for breast cancer, however, up to 50% of patients develop resistance. Stress in cancer patients can equate to poor chemotherapeutic responses. We hypothesize that drug resistance may be associated with stress hormone-induced alterations in breast cancer cells. To test this hypothesis, MDA-MB-231 cells were cultured with paclitaxel and/or cortisol, norepinephrine and epinephrine and cytotoxicity, cell cycle analyses, genomic and proteomic analyses were performed. Paclitaxel-mediated cytotoxicity and G2/M cell cycle arrest were reversed significantly by stress hormones. Genomic and proteomic analyses revealed that stress hormones modulated beta-tubulin isotypes and significantly altered genes and proteins involved in regulation of the G2/M transition, including cyclin-dependent kinase-1 (CDK-1). Inhibition of CDK-1 abrogated stress hormone-mediated reversal of paclitaxel-induced cytotoxicity, indicating that the protective effect of stress hormones act through a CDK-1-dependent mechanism. These data demonstrate that stress hormones interfere with paclitaxel efficacy and contribute significantly to drug resistance.