Accompanying protein alterations in malignant cells with a microtubule-polymerizing drug-resistance phenotype and a primary resistance mechanism

Deciphering the Molecular Mechanisms behind Drug Resistance in Ovarian Cancer to Unlock Efficient Treatment Options

Ovarian cancer is a highly lethal form of gynecological cancer. This disease often goes undetected until advanced stages, resulting in high morbidity and mortality rates. Unfortunately, many patients experience relapse and succumb to the disease due to the emergence of drug resistance that significantly limits the effectiveness of currently available oncological treatments. Here, we discuss the molecular mechanisms responsible for resistance to carboplatin, paclitaxel, polyadenosine diphosphate ribose polymerase inhibitors, and bevacizumab in ovarian cancer. We present a detailed analysis of the most extensively investigated resistance mechanisms, including drug inactivation, drug target alterations, enhanced drug efflux pumps, increased DNA damage repair capacity, and reduced drug absorption/accumulation. The in-depth understanding of the molecular mechanisms associated with drug resistance is crucial to unveil new biomarkers capable of predicting and monitoring the kinetics during disease progression and discovering new therapeutic targets.

Tubulin Complexity in Cancer and Metastasis

Tubulin plays a fundamental role in cellular function and as the subject for microtubule-active agents in the treatment of ovarian cancer. Microtubule-binding proteins (e.g., tau, MAP1/2/4, EB1, CLIP, TOG, survivin, stathmin) and posttranslational modifications (e.g., tyrosination, deglutamylation, acetylation, glycation, phosphorylation, polyamination) further diversify tubulin functionality and may permit additional opportunities to understand microtubule behavior in disease and to develop microtubule-modifying approaches to combat ovarian cancer. Tubulin-based structures that project from suspended ovarian cancer cells known as microtentacles may contribute to metastatic potential of ovarian cancer cells and could represent an exciting novel therapeutic target.

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.

Expression of Syk and MAP4 proteins in ovarian cancer

Purpose

We have previously reported on the prognostic importance of the calpain family of proteins in ovarian cancer, especially calpain-2. Spleen tyrosine kinase (Syk) phosphorylates a variety of cytoskeletal proteins with studies suggesting potential interactions between Syk and conventional calpains. Microtubule-associated protein 4 (MAP4) has been reported to be regulated by Syk.

Methods

The current study assessed Syk and MAP4 protein expression, by immunohistochemistry on a tissue microarray comprised of cores from primary ovarian carcinomas (n = 575), to evaluate associations with patient clinical outcomes and other clinicopathological factors and sought to determine whether there were any correlations between the expression of Syk, MAP4 and the calpain system.

Results

MAP4 expression was significantly associated with ovarian cancer histological subtype (P < 0.001), stage (P = 0.001), grade (P < 0.001) and residual tumour (P = 0.005). Despite this finding, we found no significant association existing between MAP4 expression and overall survival. Syk expression was also found significantly associated with histological subtype (P < 0.001). Syk seems to play a contradictory role with respect to tumour progression: low cytoplasmic Syk expression was significantly associated with low stage (P = 0.013), and low nuclear Syk expression with chemo-resistance in patients treated with taxane-containing therapy (P = 0.006). Interestingly, despite the lack of association in the whole cohort, high nuclear Syk expression was significantly associated with better overall survival in certain subgroups (P = 0.001).

Conclusions

The current study indicates a lack of correlation between calpain-2 expression and Syk and MAP4. Syk, MAP4 and calpain-1 appeared to significantly correlate with each other in the whole cohort, with calpain-1 being more highly associated with MAP4 and Syk in mucinous carcinomas. Overall, the current results suggest that Syk, MAP4, and calpain-1 expression are correlated with each other and these proteins may be involved in early stages of tumour spread.

Electronic supplementary material

The online version of this article (10.1007/s00432-019-02856-9) contains supplementary material, which is available to authorized users.

Vinca alkaloids and analogues as anti-cancer agents: Looking back, peering ahead

Cancer still represents a "nightmare" worldwide, causing annually millions of victims. Several antiproliferative molecules are currently used as drugs market and offer a pharmaceutical opportunity for attenuating and treating tumor manifestations. In this context, natural sources have a relevant role, since they provide the 60% of currently-used anticancer agents. Among the numerous natural products, acting via different mechanisms of action, microtubule-targeting agents (MTAs) have a high therapeutic potential, since they disrupt the abnormal cancer cell growth, interfering with the continuous mitotic division. Vinca alkaloids (VAs) are the earliest developed MTAs and approved for clinical use (Vincristine, Vinblastine, Vinorelbine, Vindesine, and Vinflunine) as agents in the treatment of hematological and lymphatic neoplasms. Here, we review the state-of-art of VAs, discussing their mechanism of action and pharmacokinetic properties and highlighting their therapeutic relevance and toxicological profile. Additionally, we briefly disclosed the technological approaches faced so far to ameliorate the pharmacological properties, as well as to avoid the drug resistance. Lastly, we introduced the recent advances in the discovery of new derivatives.

Microtubule-Associated Protein 4 Is a Prognostic Factor and Promotes Tumor Progression in Lung Adenocarcinoma

Microtubule-associated protein 4 (MAP4) plays an important role in microtubule assembly and stabilization. The purpose of this study was to investigate the level of expression of MAP4 in lung adenocarcinoma (LADC) samples and to evaluate its prognostic value and the influence on cancer progression in LADC patients. The expression of MAP4 protein was analyzed using immunohistochemistry. The clinical significance and the prognostic significance of MAP4 expression were assessed by Kaplan-Meier analysis and Cox regression analysis. The roles of MAP4 in the migration and invasion of LADC cells were detected by wound-healing assays and transwell assays, respectively. We found the expression levels of MAP4 protein in LADC tissues to be significantly higher than those in noncancerous tissues. MAP4 expression was significantly correlated with differentiation, pathological T stage, and TNM stage. Kaplan-Meier survival analysis indicated that patients with high MAP4 expression had significantly poorer overall survival (OS). Cox regression analysis revealed that MAP4 expression level was an independent prognostic factor for OS. Functionally, in vitro studies showed that MAP4 knockdown efficiently suppressed the migration and invasion of LADC cells. Our data indicated that MAP4 protein may represent a novel prognostic biomarker and a potential therapeutic target for LADC.

Targeting mitotic pathways for endocrine-related cancer therapeutics

A colossal amount of basic research over the past few decades has provided unprecedented insights into the highly complex process of cell division. There is an ever-expanding catalog of proteins that orchestrate, participate and coordinate in the exquisite processes of spindle formation, chromosome dynamics and the formation and regulation of kinetochore microtubule attachments. Use of classical microtubule poisons has still been widely and often successfully used to combat a variety of cancers, but their non-selective interference in other crucial physiologic processes necessitate the identification of novel druggable components specific to the cell cycle/division pathway. Considering cell cycle deregulation, unscheduled proliferation, genomic instability and chromosomal instability as a hallmark of tumor cells, there lies an enormous untapped terrain that needs to be unearthed before a drug can pave its way from bench to bedside. This review attempts to systematically summarize the advances made in this context so far with an emphasis on endocrine-related cancers and the avenues for future progress to target mitotic mechanisms in an effort to combat these dreadful cancers.

Protein Regulator of Cytokinesis PRC1 Confers Chemoresistance and Predicts an Unfavorable Postoperative Survival of Hepatocellular Carcinoma Patients

Background: PRC1, a microtubules(MTs)-associated protein, is essential in the mitosis and cell cycle regulation. It has been recently linked to chemoresistance and tumorigenesis. The current study sought to explore the role of PRC1 on chemoresistance and postoperative prognosis of hepatocellular carcinoma(HCC). Methods: PRC1 was transfected into HCC cells to detect its effects of chemoresistance to 5-fluorouracil in vitro and in vivo. This study also investigated the impact of PRC1 on 5-FU-induced G2/M phase arrest and the potential molecular mechanism. Surgical specimens from HCC patients were examined immunohistochemically for PRC1 expression. Results: Ectopic expression of PRC1 significantly increased the chemoresistance, promoted the tumor growth and abrogated 5-FU-induced G2/M phase arrest via p21/p27-pRBs pathway. In clinical specimens, high expression of PRC1(immunostaining score≥3) in HCC cells predicted an unfavorable postoperative survival of HCC patients(P=0.019), especially for whom received postoperative chemotherapy(P=0.002). In multivariate Cox analyses, high PRC1 expression significantly predicted an unfavorable postoperative prognosis, not dependent of TNM stage. Conclusion: High PRC1 expression in HCC cells increased chemoresistance, attenuated 5-FU-induced apoptosis, abrogated 5-FU-induced G2/M phase arrest, and predicts an unfavorable survival, especially for the patients who received chemotherapy. PRC1 might be a novel prognostic and predictive marker and therapeutic target for HCC patients.

Synthesis, Evaluation, and Mechanism Study of Novel Indole-Chalcone Derivatives Exerting Effective Antitumor Activity Through Microtubule Destabilization in Vitro and in Vivo

Twenty-nine novel indole-chalcone derivatives were synthesized and evaluated for antiproliferative activity. Among them, 14k exhibited most potent activity, with IC50 values of 3-9 nM against six cancer cells, which displayed a 3.8-8.7-fold increase in activity when compare with compound 2. Further investigation revealed 14k was a novel tubulin polymerization inhibitor binding to the colchicine site. Its low cytotoxicity toward normal human cells and nearly equally potent activity against drug-resistant cells revealed the possibility for cancer therapy. Cellular mechanism studies elucidated 14k arrests cell cycle at G2/M phase and induces apoptosis along with the decrease of mitochondrial membrane potential. Furthermore, good metabolic stability of 14k was observed in mouse liver microsomes. Importantly, 14k and its phosphate salt 14k-P inhibited tumor growth in xenograft models in vivo without apparent toxicity, which was better than the reference compound CA-4P and 2. In summary, 14k deserves consideration for cancer therapy.

Spleen Tyrosine Kinase Confers Paclitaxel Resistance in Ovarian Cancer

Adaptive chemoresistance and consequent tumor recurrence present major obstacles to the improvement of the prognosis and quality-of-life of patients with advanced-stage ovarian cancer. In this issue of Cancer Cell, Yu and colleagues describe the critical role of spleen tyrosine kinase (SYK) in paclitaxel resistance by modulating the stability of microtubules.

Exploitation of the Androgen Receptor to Overcome Taxane Resistance in Advanced Prostate Cancer

Prostate cancer is a tumor addicted to androgen receptor (AR) signaling, even in its castration resistant state, and recently developed antiandrogen therapies including Abiraterone acetate and enzalutamide effectively target the androgen signaling axis, but there is ultimately recurrence to lethal disease. Development of advanced castration-resistant prostate cancer (CRPC) is a biological consequence of lack of an apoptotic response of prostate tumor cells to androgen ablation. Taxanes represent the major clinically relevant chemotherapy for the treatment of patients with metastatic CRPC; unfortunately, they do not deliver a cure but an extension of overall survival. First-generation taxane chemotherapies, Docetaxel (Taxotere), effectively target the cytoskeleton by stabilizing the interaction of β-tubulin subunits of microtubules preventing depolymerization, inducing G2M arrest and apoptosis. Shifting the current paradigm is a growing evidence to indicate that Docetaxel can effectively target the AR signaling axis by blocking its nuclear translocation and transcriptional activity in androgen-sensitive and castration-resistant prostate cancer cells, implicating a new mechanism of cross-resistance between microtubule-targeting chemotherapy and antiandrogen therapies. More recently, Cabazitaxel has emerged as a second-line taxane chemotherapy capable of conferring additional survival benefit to patients with CRPC previously treated with Docetaxel or in combination with antiandrogens. Similar to Docetaxel, Cabazitaxel induces apoptosis and G2M arrest; in contrast to Docetaxel, it sustains AR nuclear accumulation although it reduces the overall AR levels and FOXO1 expression. Cabazitaxel treatment also leads to downregulation of the microtubule-depolymerizing mitotic kinesins, MCAK, and HSET, preventing their ability to depolymerize microtubules and thus enhancing sensitivity to taxane treatment. The molecular mechanisms underlying taxane resistance involve mutational alterations in the tubulin subunits, microtubule dynamics, phenotyping programming of the epithelial-to-mesenchymal transition landscape, and the status of AR activity. This chapter discusses the mechanisms driving the therapeutic resistance of taxanes and antiandrogen therapies in CRPC, and the role of AR in potential interventions toward overcoming such resistance in patients with advanced metastatic disease.

Enriched variations in TEKT4 and breast cancer resistance to paclitaxel

Among chemotherapeutic agents, paclitaxel has shown great efficacy against breast cancer. Prediction of paclitaxel response may improve patient outcomes. Here we show, using exome sequencing, that in comparison with pre-treatment biopsies, two TEKT4 germline variations are enriched in post-treatment tumours. We find TEKT4 variations in ~ 10% of an independent cohort of 84 pairs of samples. Tektin4 (encoded by TEKT4) associates closely with tubulin in doublet microtubules and helps stabilize these structures. These two TEKT4 germline variations in a high cis linkage are biologically relevant, as the ectopic expression of variant TEKT4 deregulates the microtubule stability, antagonizes the paclitaxel-induced stabilizing effect of microtubules and increases paclitaxel resistance. Furthermore, TEKT4 germline variations are associated with reduced disease-free survival and overall survival compared with wild-type TEKT4 in patients undergoing paclitaxel-based chemotherapy. Taken together, we reveal a potential mechanism of resistance to paclitaxel through the acquisition of germline variations in breast cancer.

Drug delivery design for intravenous route with integrated physicochemistry, pharmacokinetics and pharmacodynamics: illustration with the case of taxane therapeutics

This review is aimed at combining the published data on taxane formulations into a generalized Drug Delivery approach, starting from the physicochemistry and assessing its relationships with the pharmacokinetics, the biodistribution and the pharmacodynamics. Owing to the number and variety of taxane formulation designs, we considered this class of cytotoxic anticancer agents of particular interest to illustrate the concepts attached to this approach. According to the history of taxane development, we propose a classification as (i) "surfactant-based formulations" first generation, (ii) "surfactant-free formulations" second generation and (iii) "modulated pharmacokinetics drug delivery systems" third generation. Since our objective was to make the link between (i) the physicochemistry of the drug and carrier and (ii) the efficacy and safety of the drug in preclinical animal models and (iii) in human, we focused on the drug delivery technologies that were tested in clinic.

Activation of cyclic AMP/PKA pathway inhibits bladder cancer cell invasion by targeting MAP4-dependent microtubule dynamics

OBJECTIVE

With the notorious reputation of the vicious invasion, the bladder cancer is the most common malignant tumor of the urinary system. Inhibiting invasion through microtubule dynamics interruption has emerged as an important treatment of bladder cancer. Here we investigated the role of the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway in human bladder cancer cells invasion.

MATERIALS AND METHODS

With or without the treatment of various cAMP elevators, we assessed invasive and migrated capabilities of T24 and UM-UC-3, two high-grade invasive bladder cancer cell lines, using matrigel transwell inserts assay and scratch wound healing assay. The microtubule (MT) dynamics were examined by immunofluorescence and immunoblotting. Microtubule-Associated Protein 4 (MAP4) was silenced to investigate its role in tumor invasion. We also analyzed gene expression of MAP4 in 34 patients with bladder cancer using immunohistochemical staining assay. The interaction between PKA and MAP4 was examined by co-immunoprecipitation.

RESULTS

We used cAMP elevators and small interfering RNA of MAP4 here, found that both of them can potently inhibit the invasion and the migration of bladder cancer cells by disrupting microtubule (MT) cytoskeleton. Consistently, the bladder cancer grade is positively correlated with the protein level of MAP4. Furthermore, we found that cAMP/PKA signaling can disrupt MT cytoskeleton by the phosphorylation of MAP4.

CONCLUSION

Our results indicated that the cAMP/PKA signaling pathway might inhibit bladder cancer cell invasion by targeting MAP4-dependent microtubule dynamics, which could be exploited for the therapy of invasive bladder cancer.

MiR-106a targets Mcl-1 to suppress cisplatin resistance of ovarian cancer A2780 cells

Resistance to chemotherapy is a major obstacle for the effective treatment of advanced ovarian cancer. The mechanism of chemoresistance is still poorly understood. Recently, more and more evidence showed microRNAs (miRNAs) modulated many key molecules and pathways involved in chemotherapy. microRNA-106a (miR-106a) has been implicated in many cancers, but its role in ovarian cancer and drug resistance still remains unexplored. This study was to investigate whether miR-106a mediated resistance of the ovarian cancer cell line A2780 to the chemotherapeutic agent cisplatin (DDP). The different levels of miR-106a in A2780 cells and their resistant variant A2780/DDP cells were identified by using real-time PCR. MTT assay and flow cytometry were used to analyze the effect of miR-106a on cisplatin resistance of these paired cells. Real-time PCR, Western blotting and luciferase reporter assay were applied to explore whether Mcl-1 was a target of miR-106a. As compared to A2780 cells, the expression of miR-106a was down-regulated in the cisplatin resistant cell line A2780/DDP. Moreover, knockdown of miR-106a dramatically decreased antiproliferative effects and apoptosis induced by cisplatin in A2780 cells, while overexpression of miR-106a significantly increased antiproliferative effects and apoptosis induced by cisplatin in A2780/DDP cells. Furthermore, miR-106a inhibited cell survival and cisplatin resistance through downregulating the expression of Mcl-1. Mcl-1 was a direct target of miR-106a. These results suggest that miR-106a may provide a novel mechanism for understanding cisplatin resistance in ovarian cancer by modulating Mcl-1.

4-oxo-N-(4-hydroxyphenyl)retinamide: two independent ways to kill cancer cells

Background

The retinoid 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) is a polar metabolite of fenretinide (4-HPR) very effective in killing cancer cells of different histotypes, able to inhibit 4-HPR-resistant cell growth and to act synergistically in combination with the parent drug. Unlike 4-HPR and other retinoids, 4-oxo-4-HPR inhibits tubulin polymerization, leading to multipolar spindle formation and mitotic arrest. Here we investigated whether 4-oxo-4-HPR, like 4-HPR, triggered cell death also via reactive oxygen species (ROS) generation and whether its antimicrotubule activity was related to a ROS-dependent mechanism in ovarian (A2780), breast (T47D), cervical (HeLa) and neuroblastoma (SK-N-BE) cancer cell lines.

Methodology/Principal Findings

We provided evidence that 4-oxo-4-HPR, besides acting as an antimicrotubule agent, induced apoptosis through a signaling cascade starting from ROS generation and involving endoplasmic reticulum (ER) stress response, Jun N-terminal Kinase (JNK) activation, and upregulation of the proapoptotic PLAcental Bone morphogenetic protein (PLAB). Through time-course analysis and inhibition of the ROS-related signaling pathway (upstream by vitamin C and downstream by PLAB silencing), we demonstrated that the antimitotic activity of 4-oxo-4-HPR was independent from the oxidative stress induced by the retinoid. In fact, ROS generation occurred earlier than mitotic arrest (within 30 minutes and 2 hours, respectively) and abrogation of the ROS-related signaling pathway did not prevent the 4-oxo-4-HPR-induced mitotic arrest.

Conclusions/Significance

These data indicate that 4-oxo-4-HPR anticancer activity is due to at least two independent mechanisms and provide an explanation of the ability of 4-oxo-4-HPR to be more potent than the parent drug and to be effective also in 4-HPR-resistant cell lines. In addition, the double mechanism of action could allow 4-oxo-4-HPR to efficiently target tumour and to eventually counteract the development of drug resistance.

Microtubule-disrupting chemotherapeutics result in enhanced proteasome-mediated degradation and disappearance of tubulin in neural cells

We sought to examine the effects of microtubule-targeting agents (MTA) on neural cells to better understand the problem of neurotoxicity, their principal side effect, and to possibly develop a model of clinical toxicity. Studies showed that microtubule-depolymerizing agents (MDA) not only disassembled microtubules in neural HCN2 cells but also led to rapid disappearance of tubulin, and that this was specific for MDAs. Tubulin levels decreased to 20% as early as 8 hours after adding vincristine, and to 1% to 30% (mean, 9.8 +/- 7.6%; median of 7%) after 100 nmol/L vincristine for 24 hours. This disappearance was reversible. An increase in both glu-terminated and acetylated tubulin, markers of stable tubulin, preceded reaccumulation of soluble tubulin, suggesting a priority for stabilizing tubulin first as microtubules before replenishing the soluble pool. Similar results were shown with other MDAs. Furthermore, microtubule reassembly did not arise from a central focus but instead appeared to involve dispersed nucleation, as evidenced by the appearance of small, stable microtubule stubs throughout the cytoplasm. In contrast, experiments with four nonneural "normal" cell lines and four cancer cell lines resulted in microtubule destabilization but only modest tubulin degradation. Evidence for proteasome-mediated degradation was obtained by demonstrating that adding a proteasome inhibitor before vincristine prevented tubulin disappearance. In summary, MDAs lead to rapid disappearance of tubulin in neural but not in other normal or cancer cells. These results underscore the fine control that occurs in neural cells and may further our understanding of neurotoxicity following MDAs.

Parkin regulates paclitaxel sensitivity in breast cancer via a microtubule-dependent mechanism

Parkin is an E3 ubiquitin ligase encoded by the Parkin gene (also called PARK2, located at 6q25.2-q27) and is involved in the pathogenesis of Parkinson's disease and the development of cancer. Recently, Parkin has been demonstrated to interact with the microtubule cytoskeleton. However, the biological implication of the Parkin-microtubule axis has been poorly explored. In this study, we report for the first time that Parkin modulates sensitivity of the chemotherapeutic agent paclitaxel in breast cancer, via a microtubule-dependent mechanism. Our data reveal that Parkin binds to the outer surface of microtubules and increases paclitaxel-microtubule interaction, resulting in enhanced paclitaxel-induced microtubule assembly and stabilization. Our data further show that Parkin promotes the activity of paclitaxel to trigger multinucleation and apoptosis, rendering breast cancer cells more sensitive to this drug. Moreover, Parkin expression correlates with the pathological response of tumours to preoperative paclitaxel-containing chemotherapy. In addition, expression of Parkin also correlates with the sensitivity of paclitaxel in primary cultures of breast cancer cells. Our results identify Parkin as a novel mediator of paclitaxel sensitivity in breast cancer. In addition, our study suggests that patients harbouring tumours with high Parkin level would be more likely to benefit from paclitaxel-containing regimens.

TP53, BCL-2 and BAX analysis in 199 ovarian cancer patients treated with taxane-platinum regimens

OBJECTIVE

In cell line studies, BCL-2 and BAX proteins interfere with cancer response to taxanes. This issue has not received much attention with regard to taxane-platinum (TP)-treated ovarian cancer patients.

METHODS

We evaluated prognostic/predictive significance of BCL-2 and BAX with regard to TP53 status. Immunohistochemical analysis was performed on 199 ovarian carcinomas FIGO stage IIB-IV treated with TP; the results were analyzed by the Cox and logistic regression models.

RESULTS

Clinicopathological parameters (residual tumor size, FIGO stage and/or tumor grade, but not patient's age) were the only or the strongest predictors of patient's outcome. Platinum highly sensitive response showed a positive association with TP53 accumulation (p=0.045). As in our previously published analysis on platinum-cyclophosphamide-treated group, complete remission showed a borderline negative (paradoxic) association with high BAX expression in the whole group (p=0.058) and with BCL-2 expression in the TP53(-) group (p=0.058).

CONCLUSION

Our results suggest that TP53, BCL-2 and BAX proteins carry some predictive potential in taxane-platinum-treated ovarian cancer patients, auxiliary to clinicopathological factors. We have confirmed on another patient group that clinical importance of BCL-2 may depend on TP53 status.

Cellular mechanisms of resistance to anthracyclines and taxanes in cancer: intrinsic and acquired

Taxanes and anthracyclines are two of the most potent and broadly effective classes of chemotherapeutic agents. However, resistance to these agents is common and significantly limits their potential. As such, there is a great need to understand the mechanisms underlying de novo and acquired resistance to these agents. Beyond the resistance barrier lies even greater potential to significantly alter the natural course of human cancer. This review discusses what we currently understand about the mechanisms of resistance to taxanes and anthracyclines. Preclinical models suggest a role for ATP-binding cassette transporters, tubulin isoforms, microtubule-associated proteins, tubulin gene mutations, and mitotic checkpoint signaling proteins in resistance to taxanes. Preclinical models also suggest that drug transport proteins, antioxidant defenses, apoptotic signaling, and topoisomerase modulation may mediate anthracycline resistance. Many of these hypotheses remain untested in appropriately designed clinical studies, but limited clinical evidence will be reviewed. Epothilones represent a novel class of non-taxane microtubule stabilizing agents with distinct drug-resistance profiles. Potential mechanisms behind these differences and their potential role in the treatment of both taxane- and anthracycline-refractory patients are discussed.

Taxanes, microtubules and chemoresistant breast cancer

The taxanes, paclitaxel and docetaxel are microtubule-stabilizing agents that function primarily by interfering with spindle microtubule dynamics causing cell cycle arrest and apoptosis. However, the mechanisms underlying their action have yet to be fully elucidated. These agents have become widely recognized as active chemotherapeutic agents in the treatment of metastatic breast cancer and early-stage breast cancer with benefits gained in terms of overall survival (OS) and disease-free survival (DFS). However, even with response to taxane treatment the time to progression (TTP) is relatively short, prolonging life for a matter of months, with studies showing that patients treated with taxanes eventually relapse. This review focuses on chemoresistance to taxane treatment particularly in relation to the spindle assembly checkpoint (SAC) and dysfunctional regulation of apoptotic signaling. Since spindle microtubules are the primary drug targets for taxanes, important SAC proteins such as MAD2, BUBR1, Synuclein-gamma and Aurora A have emerged as potentially important predictive markers of taxane resistance, as have specific checkpoint proteins such as BRCA1. Moreover, overexpression of the drug efflux pump MDR-1/P-gp, altered expression of microtubule-associated proteins (MAPs) including tau, stathmin and MAP4 may help to identify those patients who are most at risk of recurrence and those patients most likely to benefit from taxane treatment.

Epothilones in the treatment of cancer

Epothilones are cytotoxic macrolides with a similar mechanism of action to paclitaxel but with the potential advantage of activity in taxane-resistant settings in preclinical models. The epothilones ixabepilone, patupilone, BMS-310705, KOS-862 and ZK-EPO are in early clinical trials for cancer treatment. Phase I studies have shown that dose-limiting toxicities of epothilones are generally neurotoxicity and neutropoenia although initial studies with patupilone indicated that diarrhoea was dose limiting. Neuropathy induced by ixabepilone may be schedule dependent. Over 20 Phase II studies of epothilones in cancer treatment have been reported, and significant activity in taxane-sensitive tumour types (such as breast, lung and prostate cancers) has been noted. Response rates in taxane-refractory metastatic breast cancer are relatively modest, but ixabepilone and patupilone have shown promising efficacy in hormone-refractory metastatic prostate cancer and in taxane-refractory ovarian cancer.

Identification of molecular determinants of tumor sensitivity and resistance to anticancer drugs

Resistance to drugs is a major problem in cancer chemotherapy. Various cellular mechanisms of drug resistance have been identified in cultured tumor cell lines selected for growth in the presence of sublethal concentrations of various anticancer drugs. They involve drug transport and detoxification, qualitative or quantitative alterations of the drug target, repair of drug-induced DNA lesions, and alterations in signaling or execution of apoptosis. More recently, the possibility to simultaneously analyze the expression of thousands of genes using DNA microarrays has allowed exploring the relationships between gene expression and sensitivity to several anticancer drugs. A number of studies using microarrays for identifying genes governing tumor chemosensitivity focused on tumor cell lines. Some clinical studies have also been carried out to investigate whether tumor gene expression patterns could predict clinical response to chemotherapy. Results of these studies are encouraging, indicating that individualization of drug treatment based on multigenic response-predictive markers is feasible.

Microtubule-associated proteins as targets in cancer chemotherapy

Natural and synthetic compounds that disrupt microtubule dynamics are among the most successful and widely used cancer chemotherapeutic agents. However, lack of reliable markers that predict sensitivity of cancers to these agents and development of resistance remain vexing issues. There is accumulating evidence that a family of cellular proteins that are associated with and alter the dynamics of microtubules can determine sensitivity of cancer cells to microtubule-targeting agents and play a role in tumor cell resistance to these agents. This growing family of microtubule-associated proteins (MAP) includes products of oncogenes, tumor suppressors, and apoptosis regulators, suggesting that alteration of microtubule dynamics may be one of the critical events in tumorigenesis and tumor progression. The objective of this review is to integrate the knowledge on these seemingly unrelated proteins that share a common function and examine their relevance to microtubule-targeting therapies and highlight MAPs-tubulin-drug interactions as a novel avenue for new drug discovery. Based on the available evidence, we propose that rational microtubule-targeting cancer therapeutic approaches should ideally include proteomic profiling of tumor MAPs before administration of microtubule-stabilizing/destabilizing agents preferentially in combination with agents that modulate the expression of relevant MAPs.

PD98059 triggers G1 arrest and apoptosis in human leukemic U937 cells through downregulation of Akt signal pathway

MEK/ERK pathways are frequently activated in acute myelogenous leukemia, and this signal pathway's inhibitor has made it an interesting candidate for cancer chemotherapy. Little is known, however, about the effects of cellular and molecular mechanisms on human leukemic U937 cells. In the present study, we found that treatment with PD98059 significantly arrests the G1 phase through up-regulation of cyclin-dependent kinase (Cdk) inhibitor, and produces morphological features of apoptosis in U937 cells, which were associated with poly(ADP-ribose)polymerase (PARP) cleavage and PLC-gamma1 degradation. PD98059 also decreased the Cdk-2, Cdk-4, cyclin D1, and cyclin E expression, and increased high levels of the mitotic inhibitors p16(INIa), p21(Waf1), and p27(Kip1). Also, Bcl-2's overexpression and a caspase-3 inhibitor z-DEVD-fmk significantly attenuated PD98059-induced apoptosis through the down-regulation of caspase-3 activity, but did not attenuate G1 phase arrest. Moreover, PD98059 down-regulated Akt phosphorylation and produced a synergy effect of apoptosis with LY294002 co-treatment. Thus, our results imply that PD98059-induced apoptosis is significantly involved in down-regulation of Bcl-2, caspase-3 activity, the Akt pathway, and some of the biological functions in U937 cells.

Antileukemia activity of MSFTZ–a novel flavanone analog

A newly synthesized flavanone derivative, (+/-)-(3aRS,4SR)-2-(2-chloro-4-methyl- sulfonylphenyl)-4'-chloro-3a,4-diethoxy-flavane[4,3-d]-Delta-1,2,3-thiadiazoline (MSFTZ), was investigated for its antileukemia activity and molecular mechanisms. Cytotoxicity assay confirmed the high antiproliferative efficiency of MSFTZ in six leukemia cell lines (including two drug-resistant cell lines), with 50% inhibition of cell viability values ranging from 1.0 to 9.2 micromol/l. The results of flow cytometry assay showed that the percentage of apoptotic HL-60 cells was 68.3% after 48 h treatment with MSFTZ, suggesting that the activation of the apoptosis pathway was an anticancer property of MSFTZ. Furthermore, the protein changes related to apoptosis were investigated. Exposure of HL-60 cells to MSFTZ induced pro-caspase-9 and pro-caspase-3 cleavage, X-linked inhibitor of apoptosis protein and Bcl-X(L) downregulation, and poly(ADP-ribose) polymerase degradation. Treatment of cells with MSFTZ resulted in a time-dependent reduction in phosphorylation (activation) of extracellular signal-regulated kinase 1/2 and an increase in phosphorylation (activation) of Jun N-terminal kinase. Taken together, our results demonstrated that activation of mitogen-activated protein kinase and apoptotic cascade is involved in MSFTZ-induced antileukemia activity. All data suggest that MSFTZ is a promising chemotherapy drug.

Paclitaxel-resistant cells have a mutation in the paclitaxel-binding region of beta-tubulin (Asp26Glu) and less stable microtubules

Resistance to paclitaxel-based therapy is frequently encountered in the clinic. The mechanisms of intrinsic or acquired paclitaxel resistance are not well understood. We sought to characterize the resistance mechanisms that develop upon chronic exposure of a cancer cell line to paclitaxel in the presence of the P-glycoprotein reversal agent, CL-347099. The epidermoid tumor line KB-3-1 was exposed to increasing concentrations of paclitaxel and 5 micromol/L CL-347099 for up to 1 year. Cells grown in 15 nmol/L paclitaxel plus CL-347099 (KB-15-PTX/099) developed 18-fold resistance to paclitaxel and were dependent upon paclitaxel for maximal growth. They grew well and retained resistance to paclitaxel when grown in athymic mice. Cross-resistance (3- to 5-fold) was observed in tissue culture to docetaxel, the novel taxane MAC-321, and epothilone B. Collateral sensitivity (approximately 3-fold) was observed to the depolymerizing agents vinblastine, dolastatin-10, and HTI-286. KB-15-PTX/099-resistant cells did not overexpress P-glycoprotein nor did they have an alteration of [14C]paclitaxel accumulation compared with parental cells. However, a novel point mutation (T to A) resulting in Asp26 to glutamate substitution in class I (M40) beta-tubulin was found. Based on an electron crystallography structure of Zn-stabilized tubulin sheets, the phenyl ring of C-3' NHCO-C6H5 of paclitaxel makes contact with Asp26 of beta-tubulin, suggesting a ligand-induced mutation. Optimized model complexes of paclitaxel, docetaxel, and MAC-321 in beta-tubulin show a novel hydrogen bonding pattern for the glutamate mutant and rationalize the observed resistance profiles. However, a mutation in the paclitaxel binding pocket does not explain the phenotype completely. KB-15-PTX/099 cells have impaired microtubule stability as determined by a reduced percentage of tubulin in microtubules and reflected by less acetylated tubulin. These results suggest that a mutation in tubulin might affect microtubule stability as well as drug binding and contribute to the observed resistance profile.

Microtubule targeting agents: basic mechanisms of multidrug resistance (MDR)

Multidrug resistance (MDR) results in the loss of activity of anticancer agents against cells possessing the MDR phenotype. In some cases, tumor cells are intrinsically resistant to chemotherapeutic drugs (intrinsic resistance), while in other instances cells become resistant after exposure to cytotoxic agents (acquired resistance). MDR has a significant impact on the management of patients with solid tumors, including those with breast cancer, where it has been previously correlated with a decreased response to treatment and a poor prognosis. Taxanes are among the most important components of chemotherapy regimens to treat recurrent breast cancer. In taxane-refractory cells, the two mechanisms most commonly associated with the development of MDR are the overexpression of members of the ATP-binding cassette family of transporters, of which P-glycoprotein is the best known, and alterations of tubulin, which is the cellular target of the taxanes. In vitro and in vivo models have been developed to study the development of MDR and to assess the potential clinical application of MDR modulators. However, despite promising advances using MDR modulators in preclinical models, clinical applications have met with limited success. Novel strategies are needed to circumvent the development of drug resistance. New cytotoxic agents capable of evading MDR offer hope for patients with breast cancer.

Apoptosis induced by the kinase inhibitor BAY 43-9006 in human leukemia cells involves down-regulation of Mcl-1 through inhibition of translation

BAY 43-9006 is a kinase inhibitor that induces apoptosis in a variety of tumor cells. Here we report that treatment with BAY 43-9006 results in marked cytochrome c and AIF release into the cytosol, caspase-9, -8, -7, and -3 activation, and apoptosis in human leukemia cells (U937, Jurkat, and K562). Pronounced apoptosis was also observed in blasts from patients with acute myeloid leukemia. These events were accompanied by ERK1/2 inactivation and caspase-independent down-regulation of Mcl-1. Inducible expression of a constitutively active MEK1 construct did not prevent Mcl-1 down-regulation, suggesting that this event is not related to MEK/ERK pathway inactivation. Furthermore, BAY 43-9006 did not induce major changes in Mcl-1 mRNA levels monitored by real-time PCR or Mcl-1 promoter activity demonstrated by luciferase reporter assays, but it did enhance Mcl-1 down-regulation in actinomycin D-treated cells. Inhibition of protein synthesis by cycloheximide or proteasome function with MG132 and pulse-chase studies with [35S]methionine demonstrated that BAY 43-9006 did not diminish Mcl-1 protein stability, nor did it enhance Mcl-1 ubiquitination, but instead markedly attenuated Mcl-1 translation in association with the rapid and potent dephosphorylation of the eIF4E translation initiation factor. Finally, ectopic expression of Mcl-1 in leukemic cells markedly inhibited BAY 43-9006-mediated cytochrome c cytosolic release, caspase-9, -7, and -3 activation, as well as cell death, indicating that Mcl-1 operates upstream of cytochrome c release and caspase activation. Together, these findings demonstrate that BAY 43-9006 mediates cell death in human leukemia cells, at least in part, through down-regulation of Mcl-1 via inhibition of translation.

Depletion of Mutant p53 and Cytotoxicity of Histone Deacetylase Inhibitors

Mutant p53 is a cancer-specific target for pharmacologic intervention. We show that histone deacetylase inhibitors such as FR901228 and trichostatin A completely depleted mutant p53 in cancer cell lines. This depletion was preceded by induction of p53-regulated transcription. In cells with mutant p53 pretreated with histone deacetylase inhibitors, DNA damage further enhanced the p53 trans-function. Furthermore, histone deacetylase inhibitors were preferentially cytotoxic to cells with mutant p53 rather than to cells lacking wild-type p53. We suggest that, by either restoring or mimicking p53 trans-functions, histone deacetylase inhibitors initiate degradation of mutant p53. Because mutant p53 is highly expressed, a sudden restoration of p53-like functions is highly cytotoxic to cells with mutant p53. In a broader perspective, this shows how selectivity may be achieved by targeting a non-cancer-specific target, such as histone deacetylases, in the presence of a cancer-specific alteration, such as mutant p53.

Review: tubulin function, action of antitubulin drugs, and new drug development

Anticancer agents that interfere with microtubulin function are in widespread use in man and have a broad spectrum of activity against both hematological malignancies and solid tumors. The mechanisms of actions of these agents have been better defined during the past decade, indicating that there are distinct binding sites for these agents and that they interfere with microtubulin dynamics (growth and shortening of tubules) at low concentrations and only evoke microtubulin aggregation or dissociation at high concentrations. Tubulin has been recently described in the nucleus of cells and in mitochondria. Downstream events from tubulin binding are believed to be critical events for the generation of apoptosis in the malignant cell. The effects of vinca alkaloids and taxanes are distinct, suggesting that the interference with the tubulin cap by high-affinity binding of effective agents is not the only mechanism of cytotoxic effect, and the low-affinity binding of drug, which distorts microtubulin function, may also be important. The epothilones share some of the binding characteristics of the taxanes and are in clinical trials because of cytoxic activity in taxane resistant cells. Tubulin has additional target sites for anticancer drugs including interference with the binding and function of microtubule associated proteins and interference with motor proteins which are essential for the transport of substances within the cell. Because many of these microtubule associated proteins have an ATP binding site, both computer-aided design and combinatorial chemistry techniques can be used to make agents to interfere with their function analogous to imatinib mesylate (Gleevec). Agents that interfere with the motor protein kinesin are entering clinical trials.

Pharmacoproteomic approach to the study of drug mode of action, toxicity, and resistance: applications in diabetes and cancer

Proteomics is a powerful technique for investigating protein expression profiles in biological systems and their modifications in response to stimuli or to particular physiological or pathophysiological conditions. It is therefore a technique of choice for the study of drug mode of action, side-effects, toxicity and resistance. It is also a valuable approach for the discovery of new drug targets. All these proteomic applications to pharmacological issues may be called pharmacoproteomics. The pharmacoproteomic approach could be particularly useful for the identification of molecular alterations implicated in type 2 diabetes and for further characterization of existing or new drugs. In oncology, proteomics is widely used for the identification of tumour-specific protein markers, and pharmacoproteomics is used for the evaluation of chemotherapy, particularly for the characterization of drug-resistance mechanisms. The large amount of data generated by pharmacoproteomic screening requires the use of bioinformatic tools to insure a pertinent interpretation. Herein, we review the applications of pharmacoproteomics to the study of type 2 diabetes and to chemoresistance in different types of cancer and the current state of this technology in these pathologies. We also suggest a number of bioinformatic solutions for proteomic data management.

Neuronal-associated microtubule proteins class III β-tubulin and MAP2c in neuroblastoma: Role in resistance to microtubule-targeted drugs

Advanced stage neuroblastoma has a poor clinical outcome and microtubule-destabilizing agents, such as the Vinca alkaloids, are an important component in the treatment of this childhood cancer. Vinca alkaloids bind to β-tubulin on the α/β-tubulin heterodimer and disrupt microtubule dynamics, leading to cell death. To date, studies examining the contribution of microtubules and associated proteins to the efficacy of microtubule-destabilizing agents in neuroblastoma have been limited. In this study, BE(2)-C neuroblastoma cells previously selected for resistance to either vincristine (BE/VCR10) or colchicine (BE/CHCb0.2) were found to display significant decreases in neuronal-specific class III β-tubulin. Interestingly, vincristine-selected cells exhibited increased levels of polymerized tubulin that were not due to α-tubulin and class I, II, or III β-tubulin mutations. Expression levels of the microtubule-depolymerizing protein stathmin were significantly increased in BE/VCR10 cells. In contrast, levels of MAP2a and MAP2b were relatively unaltered. A marked decrease in the neuronal protein, MAP2c, was identified in the vincristine-selected cells and, to a lesser extent, in the colchicine-selected cells. This is the first report describing specific microtubule alterations in neuroblastoma cells resistant to tubulin-targeted agents. The results indicate a need to identify the factors responsible for resistance to tubulin-targeted agents in neuroblastoma so that improved and novel treatment strategies can be developed for this drug refractory disease.

Granulocyte macrophage colony-stimulating factor signaling and proteasome inhibition delay neutrophil apoptosis by increasing the stability of Mcl-1

Human neutrophils normally have a very short half-life and die by apoptosis. Cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) can delay this apoptosis via increases in the cellular levels of Mcl-1, an anti-apoptotic protein of the Bcl-2 family with a rapid turnover rate. Here we have shown that inhibition of the proteasome (a) decreases the rate of Mcl-1 turnover within neutrophils and (b) significantly delays apoptosis. This led us to determine whether GM-CSF could enhance neutrophil survival by altering the rate of Mcl-1 turnover. Addition of GM-CSF to neutrophils enhanced Mcl-1 stability and delayed apoptosis by signaling pathways requiring PI3K/Akt and p44/42 Erk/Mek, because inhibitors of these pathways completely abrogated the GM-CSF-mediated effect on both Mcl-1 stability and apoptosis delay. Conversely, induction of Mcl-1 hyperphosphorylation by the phosphatase inhibitor, okadaic acid, significantly accelerated both Mcl-1 turnover and apoptosis. Neither the calpain inhibitor, carbobenzoxy-valinyl-phenylalaninal, nor the pan caspase inhibitor, benzyloxycarbonyl-VAD-fluoromethylketone, had any effect on Mcl-1 stability under these conditions. These observations indicate that profound changes in the rate of neutrophil apoptosis following cytokine signaling occur via dynamic changes in the rate of Mcl-1 turnover via the proteasome.

Drug resistance reversal--are we getting closer?

Clinical drug resistance is a major barrier to overcome before chemotherapy can become curative for most patients presenting with metastatic cancer. Rational attempts to tackle clinical drug resistance need to be based on an understanding of the mechanisms involved; these are likely to be complex and multifactorial, and may be due to inadequate drug exposure or alterations in the cancer cell itself. This article reviews a number of strategies used to tackle drug resistance, focussing on work in our institution related to the treatment of ovarian cancer and resistance to platinum and taxane-based chemotherapy. Further progress towards drug resistance reversal will require a three-pronged approach, namely: the development of novel cytotoxics which exploit selectively expressed targets; modulation of resistance to conventional agents and, most importantly, a serious attempt to understand resistance mechanisms in tumour samples taken both pre- and post-chemotherapy.

Resveratrol modifies the expression of apoptotic regulatory proteins and sensitizes non-Hodgkin's lymphoma and multiple myeloma cell lines to paclitaxel-induced apoptosis

Resveratrol (trans-3,4,5-trihydroxystilbene) has received attention for its potential chemopreventive and antitumor effects in experimental systems. Recent evidence suggests that paclitaxel, alone or in combination with other drugs, can be effectively used in the treatment of non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). This study investigated whether resveratrol can sensitize NHL and MM cell lines to paclitaxel-mediated apoptosis and to delineate the underlying molecular mechanism of sensitization. Both resveratrol and paclitaxel negatively modulated tumor cell growth by arresting the cells at the G2-M phase of the cell cycle. Low concentrations of resveratrol exerted a sensitizing effect on drug-refractory NHL and MM cells to apoptosis induced by paclitaxel. Resveratrol selectively down-regulated the expression of antiapoptotic proteins Bcl-xL and myeloid cell differentiation factor-1 (Mcl-1) and up-regulated the expression of proapoptotic proteins Bax and apoptosis protease activating factor-1 (Apaf-1). Paclitaxel down-regulated the expression of Bcl-xL, Mcl-1, and cellular inhibitor of apoptosis protein-1 antiapoptotic proteins and up-regulated Bid and Apaf-1. Combination treatment resulted in apoptosis through the formation of tBid, mitochondrial membrane depolarization, cytosolic release of cytochrome c and Smac/DIABLO, activation of the caspase cascade, and cleavage of poly(adenosine diphosphate-ribose) polymerase. Combination of resveratrol with paclitaxel had minimal cytotoxicity against quiescent and mitogenically stimulated human peripheral blood mononuclear cells. Inhibition of Bcl-xL expression by resveratrol was critical for chemosensitization and its functional impairment mimics resveratrol-mediated sensitization to paclitaxel-induced apoptosis. Inhibition of Bcl-xL expression by resveratrol was due to the inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway and diminished activator protein-1-dependent Bcl-xL expression. The findings by resveratrol were corroborated with inhibitors of the ERK1/2 pathway. This study demonstrates that in resistant NHL and MM cell lines resveratrol and paclitaxel selectively modify the expression of regulatory proteins in the apoptotic signaling pathway and the combination, via functional complementation, results in synergistic apoptotic activity.

Altered levels and regulation of stathmin in paclitaxel-resistant ovarian cancer cells

Two paclitaxel(Ptx)-resistant ovarian cancer cell lines, 1A9/Ptx-10 and 1A9/Ptx-22, isolated from the 1A9 cell line (a clone of the A2780 line) by continuous exposure to Ptx and verapamil, have point mutations in their major beta-tubulin gene and in one or both alleles of their TP53 gene. These cells were examined for alterations in cell cycle regulators and the tubulin-binding protein stathmin. Unlike parental cells, neither 1A9/Ptx-10 nor 1A9/Ptx-22 expressed detectable levels of p21(WAF1/Cip1), a putative transcriptional regulator of stathmin, but did overexpress stathmin and Bcl2. No differences were noted in the expression levels of proliferative cell nuclear antigen or tyrosine-phosphorylated p34Cdc2. Ptx treatment altered little the expression of stathmin in the parental cell line, although it increased p21(WAF1/Cip1) levels several-fold. Infection of Ptx-resistant lines with a wild-type TP53-bearing adenovirus (AdWTp53) changed cell cycle distribution and increased the levels of p21(WAF1/Cip1), but caused no changes in stathmin levels. Microtubule drug resistance in ovarian carcinoma may be associated with altered p53/21(WAF1/Cip1) regulatory pathways for stathmin expression and function.

Mechanisms of Taxol resistance related to microtubules

Since its approval by the FDA in 1992 for the treatment of ovarian cancer, the use of Taxol has dramatically increased. Although treatment with Taxol has led to improvement in the duration and quality of life for some cancer patients, the majority eventually develop progressive disease after initially responding to Taxol treatment. Drug resistance represents a major obstacle to improving the overall response and survival of cancer patients. This review focuses on mechanisms of Taxol resistance that occur directly at the microtubule, such as mutations, tubulin isotype selection and post-translational modifications, and also at the level of regulatory proteins. A review of tubulin structure, microtubule dynamics, the mechanism of action of Taxol and its binding site on the microtubule are included, so that the reader can evaluate Taxol resistance in context.