Mechanisms of resistance to cabazitaxel

Association between the apoptotic effect of Cabazitaxel and its pro-oxidant efficacy on the redox adaptation mechanisms in prostate cancer cells with different resistance phenotypes

Redox adaptation causes poor prognosis by adapting cancer cells to excessive oxidative stress. Previously, we introduced an oxidative stress-resistant metastatic prostate cancer (mPC) model (LNCaP-HPR) that redox adaptation reduced the effect of Cabazitaxel (Cab), the last taxane-derivative for metastatic castration-resistant PC (mCRPC). Whereas, we investigated for the first time whether there is an association between the altered apoptotic effect and pro-oxidant efficacy of Cab on the redox adaptation in PC cells with different phenotypes, including LNCaP mPC, LNCaP-HPR, C4-2 mCRPC, and RWPE-1 cells. Cab was shown pro-oxidant efficacy proportionally with the apoptotic effect, more prominent in the less aggressive LNCaP cells, by increasing the endogenous ROS, mitochondrial damage, and inhibiting nuclear ROS scavengers, p-Nrf2 and HIF-1α. However, the pro-oxidant and apoptotic effect was lower in the LNCaP-HPR and C4-2 cells, indicating that the drug sensitivity of the cells adapted to survive with more ROS was reduced via altered regulation of redox adaptation. Additionally, unlike LNCaP, Cab caused an increase in the p-NF-κB activation, suggesting that the p-NF-κB might accompany maintaining survival with the increased ROS in the aggressive PC cells. Moreover, the cytotoxic and apoptotic effects of Cab were less on RWPE-1 cells compared to LNCaP but were closer to those on the more aggressive LNCaP-HPR and C4-2 cells, except for the changing pro-oxidant effect of Cab. Consequently, this study indicates the variable pro-oxidant effects of Cab on redox-sensitive proteins, which could be a target for improving Cab's apoptotic effect more in aggressive PC cells.

Key genes and molecular mechanisms related to Paclitaxel Resistance

Paclitaxel is commonly used to treat breast, ovarian, lung, esophageal, gastric, pancreatic cancer, and neck cancer cells. Cancer recurrence is observed in patients treated with paclitaxel due to paclitaxel resistance emergence. Resistant mechanisms are observed in cancer cells treated with paclitaxel, docetaxel, and cabazitaxel including changes in the target molecule β-tubulin of mitosis, molecular mechanisms that activate efflux drug out of the cells, and alterations in regulatory proteins of apoptosis. This review discusses new molecular mechanisms of taxane resistance, such as overexpression of genes like the multidrug resistance genes and EDIL3, ABCB1, MRP1, and TRAG-3/CSAG2 genes. Moreover, significant lncRNAs are detected in paclitaxel resistance, such as lncRNA H19 and cross-resistance between taxanes. This review contributed to discovering new treatment strategies for taxane resistance and increasing the responsiveness of cancer cells toward chemotherapeutic drugs.

Oncostatin M reverses ABCG2-mediated mitoxantrone resistance

Mitoxantrone resistant variant of SW620 line was developed, characterized and subsequently used as a model system to determine oncostatin M ability to modulate MDR phenomenon. The selection regimen allowed for overexpression of ABCG2 and ABCB1 both at the RNA and protein level, which was further confirmed by functional assays. Oncostatin M supplementation resulted in partial reversal of MDR phenotype by decreasing overexpression of ABCG2 demonstrating for the first time the ability of this cytokine for selective down-regulation of one of MDR proteins.

Deciphering the molecular landscape: integrating single-cell transcriptomics to unravel myofibroblast dynamics and therapeutic targets in clear cell renal cell carcinomas

Background

Clear cell renal cell carcinomas (ccRCCs) epitomize the most formidable clinical subtype among renal neoplasms. While the impact of tumor-associated fibroblasts on ccRCC progression is duly acknowledged, a paucity of literature exists elucidating the intricate mechanisms and signaling pathways operative at the individual cellular level.

Methods

Employing single-cell transcriptomic analysis, we meticulously curated UMAP profiles spanning substantial ccRCC populations, delving into the composition and intrinsic signaling pathways of these cohorts. Additionally, Myofibroblasts were fastidiously categorized into discrete subpopulations, with a thorough elucidation of the temporal trajectory relationships between these subpopulations. We further probed the cellular interaction pathways connecting pivotal subpopulations with tumors. Our endeavor also encompassed the identification of prognostic genes associated with these subpopulations through Bulk RNA-seq, subsequently validated through empirical experimentation.

Results

A notable escalation in the nFeature and nCount of Myofibroblasts and EPCs within ccRCCs was observed, notably enriched in oxidation-related pathways. This phenomenon is postulated to be closely associated with the heightened metabolic activities of Myofibroblasts and EPCs. The Myofibroblasts subpopulation, denoted as C3 HMGA1+ Myofibroblasts, emerges as a pivotal subset, displaying low differentiation and positioning itself at the terminal point of the temporal trajectory. Intriguingly, these cells exhibit a high degree of interaction with tumor cells through the MPZ signaling pathway network, suggesting that Myofibroblasts may facilitate tumor progression via this pathway. Prognostic genes associated with C3 were identified, among which TUBB3 is implicated in potential resistance to tumor recurrence. Finally, experimental validation revealed that the knockout of the key gene within the MPZ pathway, MPZL1, can inhibit tumor activity, proliferation, invasion, and migration capabilities.

Conclusion

This investigation delves into the intricate mechanisms and interaction pathways between Myofibroblasts and ccRCCs at the single-cell level. We propose that targeting MPZL1 and the oxidative phosphorylation pathway could serve as potential key targets for treating the progression and recurrence of ccRCC. This discovery paves the way for new directions in the treatment and prognosis diagnosis of ccRCC in the future.

Tannic Acid and Ethyl Gallate Potentialize Paclitaxel Effect on Microtubule Dynamics in Hep3B Cells

Among broad-spectrum anticancer agents, paclitaxel (PTX) has proven to be one of the most effective against solid tumors for which more specific treatments are lacking. However, drawbacks such as neurotoxicity and the development of resistance reduce its therapeutic efficacy. Therefore, there is a need for compounds able to improve its activity by synergizing with it or potentiating its effect, thus reducing the doses required. We investigated the interaction between PTX and tannins, other compounds with anticancer activity known to act as repressors of several proteins involved in oncological pathways. We found that both tannic acid (TA) and ethyl gallate (EG) strongly potentiate the toxicity of PTX in Hep3B cells, suggesting their utility in combination therapy. We also found that AT and EG promote tubulin polymerization and enhance the effect of PTX on tubulin, suggesting a direct interaction with tubulin. Biochemical experiments confirmed that TA, but not EG, binds tubulin and potentiates the apparent binding affinity of PTX for the tubulin binding site. Furthermore, the molecular docking of TA to tubulin suggests that TA can bind to two different sites on tubulin, one at the PTX site and the second at the interface of α and β-tubulin (cluster 2). The binding of TA to cluster 2 could explain the overstabilization in the tubulin + PTX combinatorial assay. Finally, we found that EG can inhibit PTX-induced expression of pAkt and pERK defensive protein kinases, which are involved in resistance to PXT, by limiting cell death (apoptosis) and favoring cell proliferation and cell cycle progression. Our results support that tannic acid and ethyl gallate are potential chemotherapeutic agents due to their potentiating effect on paclitaxel.

Metastatic Castration-Resistant Prostate Cancer: Insights on Current Therapy and Promising Experimental Drugs

The therapeutic landscape of metastatic hormone sensitive and metastatic castration-resistant prostate cancer (mCRPC) is rapidly changing. We reviewed the current treatment options for mCRPC, with insights on new available therapeutic strategies. Chemotherapy with docetaxel or cabazitaxel (for patients progressing on docetaxel), as well as treatment with androgen receptor axis targeted therapies, and Radium-223 are well-established treatment options for patients with mCRPC. The advent of theragnostic in prostate cancer established Lutetium-177 (177Lu)-PSMA-617 as a new standard of care for PSMA-positive mCRPC previously treated with ARAT and taxane-based chemotherapy. Olaparib, a poly-ADP-ribose polymerase (PARP) inhibitor, is approved for selected patients with mCRPC progressed on ARATs and in combination with abiraterone acetate as first-line treatment for mCRPC. Immunotherapy showed limited efficacy in unselected patients with mCRPC and novel immunotherapy strategies need to be explored. The search for biomarkers is a growing field of interest in mCRPC, and predictive biomarkers are needed to support the choice of treatment and the development of tailored strategies.

Crosstalk between Microtubule Stabilizing Agents and Prostate Cancer

A variety of microtubule-stabilizing cytotoxic agents (MSA) with diverse chemical scaffolds have been discovered from marine sponges, microorganisms, and plants. Two MSAs, docetaxel and cabazitaxel, are the exclusive chemotherapeutics that convey a survival benefit in patients with castration-resistant prostate cancer (CRPC). Additional MSAs have been investigated for their potential in treating prostate cancer in both clinical and preclinical settings. Independent of promoting mitotic arrest, MSAs can suppress the nuclear accumulation of androgen receptor (AR), which is the driving force for prostate cancer cell growth and progression. The alternative mechanism not only helps to better understand the clinical efficacy of docetaxel and cabazitaxel for AR-driven CRPC but also provides an avenue to seek better treatments for various forms of prostate cancer. The dual mechanisms of action enable MSAs to suppress AR-null prostate cancer cell proliferation by cell mitosis pathway and to interfere with the AR signaling pathway in AR positive cells. MSA chemotherapeutics, being administered alone or in combination with other therapeutics, may serve as the optimal therapeutic option for patients with either castration-sensitive or castration-resistant prostate cancer. This review provides an overview of the anti-prostate cancer profiles (including preclinical and clinical studies, and clinical use) of diverse MSAs, as well as the mechanism of action.

Cancer stem cell in prostate cancer progression, metastasis and therapy resistance

Prostate cancer (PCa) is the most diagnosed malignancy in the men worldwide. Cancer stem cells (CSCs) are the sub-population of cells present in the tumor which possess unique properties of self-renewal and multilineage differentiation thus thought to be major cause of therapy resistance, disease relapse, and mortality in several malignancies including PCa. CSCs have also been shown positive for the common stem cells markers such as ALDH EZH2, OCT4, SOX2, c-MYC, Nanog etc. Therefore, isolation and characterization of CSCs specific markers which may discriminate CSCs and normal stem cells are critical to selectively eliminate CSCs. Rapid advances in the field offers a theoretical explanation for many of the enduring uncertainties encompassing the etiology and an optimism for the identification of new stem-cell targets, development of reliable and efficient therapies in the future. The emerging reports have also provided unprecedented insights into CSCs plasticity, quiescence, renewal, and therapeutic response. In this review, we discuss the identification of PCa stem cells, their unique properties, stemness-driving pathways, new diagnostics, and therapeutic interventions.

Current development of cabazitaxel drug delivery systems

The second-generation taxane cabazitaxel has been clinically approved for the treatment of metastatic castration-resistant prostate cancer after docetaxel failure. Compared with the first-generation taxanes paclitaxel and docetaxel, cabazitaxel has potent anticancer activity and is less prone to drug resistance due to its lower affinity for the P-gp efflux pump. The relatively high hydrophobicity of cabazitaxel and the poor aqueous colloidal stability of the commercial formulation, following its preparation for injection, presents opportunities for new cabazitaxel formulations with improved features. This review provides an overview of cabazitaxel drug formulations and hydrophobic taxane drug delivery systems in general, and particularly focuses on emerging cabazitaxel delivery systems discovered in the past 5 years. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Factors influencing survival in metastatic castration resistant prostate cancer therapy

INTRODUCTION

The number of patients with metastatic castration resistant prostate cancer (mCRPC) is expecting to increase due to the long-life expectancy of those with advanced disease who are also more commonly diagnosed today because of stage migration. Several compounds are available for treating these patients.

AREAS COVERED

We reviewed currently available treatments for mCRPC, their mechanism of action and resistance and we explored possible predictors of treatment success useful to predict survival in mCRPC patients.

EXPERT OPINION

A combination of molecular, clinical, pathological, and imaging features is necessary to correctly estimate patients' risk of death. The combination of these biomarkers may allow clinicians to tailor treatments based on cancer history and patients' features. The search of predictive biomarkers remains an unmet medical need for most patients with mCRPC.

Targeting the Mitochondria with Pseudo-Stealthy Nanotaxanes to Impair Mitochondrial Biogenesis for Effective Cancer Treatment

The clinical success of anticancer therapy is usually limited by drug resistance and the metastatic dissemination of cancer cells. Mitochondria are essential generators of cellular energy and play a crucial role in sustaining cell survival and metastatic escape. Selective drug strategies targeting mitochondria are able to rewire mitochondrial metabolism and may provide an alternative paradigm to treat many aggressive cancers with high efficiency and low toxicity. Here, we present a pseudo-stealthy mitochondria-targeted pro-nanotaxane and test it against recurrent and metastatic tumor xenografts. The nanoparticle encapsulates a mitochondria-targetable pro-taxane agent, which can be converted into the chemically unmodified cabazitaxel drug, with further surface cloaking with a low-density lipophilic triphenylphosphonium cation. The resultant nanotaxane could be effectively taken up by cells and consequently specifically localized to the mitochondria. The in situ activated cabazitaxel causes mitochondrial dysfunction and ultimately results in potent cell apoptosis. After intravenous administration to animals, pro-nanotaxane mimics the stealthy behavior of polyethylene glycol-cloaked nanoparticles to provide a long circulation time. The antitumor efficacy of this mitochondria-targeted system was validated in multiple preclinical drug-resistant tumor models. Notably, in a patient-derived metastatic melanoma model that was initially pretreated with cabazitaxel, nanotaxane administration not only produced durable tumor reduction but also substantially suppressed metastatic recurrence. Taken together, these results demonstrate that this combination of a pseudo-stealthy platform with a rationally designed pro-drug is an attractive approach to target mitochondria and enhance drug efficacy.

Dendrimer-Functionalized Nanodiamonds as Safe and Efficient Drug Carriers for Cancer Therapy: Nucleus Penetrating Nanoparticles

Nanodiamonds (NDs) are increasingly being assessed as potential candidates for drug delivery in cancer cells and they hold great promise in overcoming the side effects of traditional chemotherapeutics. In the current work, carboxylic acid functionalized nanodiamonds (ND-COOH) were covalently modified with poly(amidoamine) dendrimer (PAMAM) to form amine-terminated nanodiamonds (NP). Unlike ND-COOH, the chemically modified nanodiamond platform NP revealed a pH-independent aqueous dispersion stability, enhancing its potential as an effective carrier. Physical encapsulation of poorly water soluble cabazitaxel (CTX) drug on NP formed ND-PAMAM-CTX (NPC) nanoconjugates and substantially reduced the size of CTX from micrometer to nanometer. CTX was localized within the pores of nanoparticle aggregates and the cavities of the PAMAM dendrimer, thus facilitating the loaded drug's controlled and sustained release. NPC's cumulative CTX release efficiency was determined to be ∼95% at pH 4 after 96 h. A high cellular uptake of NPC both within the cytoplasm and nucleus of U87 cells is confirmed, accounting for a reduced IC₅₀ value (1 nM). Both the cell cycle and Western blot analyses confirmed enhanced cell death and suppressed tubulin protein expression in NPC-treated cells. A significantly high inhibition to cell division with early apoptosis and reduced metastasis demonstrates the effective loading of CTX dosages on the nanocarrier. The present work highlights the potential of a newly designed nanocarrier NP as an efficient nanocargo for cellular delivery applications and may provide future insights to treat one of the most aggressive tumors in neuro-oncological research, glioblastoma multiforme (GBM).

An in vitro redox adaptation model for metastatic prostate cancer: Establishing, characterizing, and Cabazitaxel response evaluating

Little is known about the redox-adapted cancer cells for understanding their pharmacologically targetable features and chemotherapeutic responses. Thus, we presented the first in vitro redox adaptation model for metastatic prostate cancer (mPC), LNCaP-HPR, with enhanced oxidative stress resistance accompanying poor Cabazitaxel response. After establishing, the cells were characterized by comparing the viability, death, oxidative stress, total GSH levels, and the mRNA and protein levels of the redox-sensitive transcription factors responsible for the adaptation, Nrf-2, NF-κB, and HIF-1α. Then, the apoptotic effect of Cabazitaxel was evaluated in LNCaP mPC, LNCaP-HPR, and C4-2 metastatic castration-resistant (mCRPC) cells. In response to H₂ O₂ , viability, oxidative stress, and the total GSH levels of LNCaP-HPR cells have confirmed the oxidative stress resistance. Nrf-2, NF-κB, and HIF-1α were upregulated in LNCaP-HPR cells, not in LNCaP, confirming that resistant cells were much less affected by exogenous oxidative stress. Unlike LNCaP, LNCaP-HPR cells were less sensitive to Cabazitaxel, as closer to the response of C4-2 mCRPC cells, indicating that redox adaptation decreased Cabazitaxel response. This is the first evaluated association between redox adaptation and poor Cabazitaxel response, suggesting that in vitro Cabazitaxel efficiency is affected by PC cells' endogenous oxidative stress tolerance. This article is protected by copyright. All rights reserved.

Design, Synthesis, and Biological Evaluation of 5,6,7,8-Tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidines as Microtubule Targeting Agents

A series of eleven 4-substituted 5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidines were designed and synthesized and their biological activities were evaluated. Synthesis involved the Gewald reaction to synthesize ethyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate ring, and SNAr reactions. Compound 4 was 1.6- and ~7-fold more potent than the lead compound 1 in cell proliferation and microtubule depolymerization assays, respectively. Compounds 4, 5 and 7 showed the most potent antiproliferative effects (IC50 values < 40 nM), while compounds 6, 8, 10, 12 and 13 had lower antiproliferative potencies (IC50 values of 53-125 nM). Additionally, compounds 4-8, 10 and 12-13 circumvented Pgp and βIII-tubulin mediated drug resistance, mechanisms that diminish the clinical efficacy of paclitaxel (PTX). In the NCI-60 cell line panel, compound 4 exhibited an average GI50 of ~10 nM in the 40 most sensitive cell lines. Compound 4 demonstrated statistically significant antitumor effects in a murine MDA-MB-435 xenograft model.

Identification of biomarkers, pathways and potential therapeutic target for docetaxel resistant prostate cancer

Docetaxel has been proved to provide survival benefit for advanced prostate cancer (PCa) patients. Resistance to docetaxel further reduces the survival of these patients. Herein, we performed a comprehensive bioinformatic analysis to identify differentially expressed genes (DEGs) between docetaxel sensitive and resistant PCa (DRPC) cell based on Gene Expression Omnibus (GEO) database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were applied for functional and pathway analysis of DEGs. The STRING database, cytoscape software and plug-in 'cytoHubba' were used to construct protein-protein interaction (PPI) networks and identify hub genes. Survival analysis were performed via GEPIA database. Finally, we conducted immune infiltration analysis by TIMER. A total of 460 DEGs were identified. GO functional analysis showed that these DEGs are mainly enriched in chemotaxis, negative regulation of intracellular signal transduction, and regulation of cell adhesion, positive regulation of inflammatory response, regulation of response to cytokine stimulus. According to the results of KEGG pathway analysis, these DEGs are mainly involved in signaling by Rho GTPases, Miro GTPases and RHOBTB3; interferon Signaling; arginine biosynthesis; PI3K-Akt signaling pathway; cytokine-cytokine receptor interaction; MAPK signaling pathway. Finally, CCNB1 and EZH2 were identified as prognostic hub genes and the expression of these two genes were associated with immune infiltration. The present study may helps to improve the understanding of the molecular mechanisms of DRPC and facilitate the selection of therapeutic and prognostic biomarkers for DRPC.

Proteomic analysis of extracellular vesicles identified PI3K pathway as a potential therapeutic target for cabazitaxel-resistant prostate cancer

BACKGROUND

Cabazitaxel (CBZ) is now widely used for prostate cancer (PC) patients resistant to docetaxel (DOC), however, most patients eventually acquire resistance. It will, therefore, be of great benefit to discover novel therapeutic target for the resistance. We aimed to identify candidate therapeutic targets for CBZ-resistance by proteomic analysis of extracellular vesicles (EVs) isolated from serum of DOC-resistant PC patients who later developed CBZ-resistance as well as those harvested from culture medium of DOC- and CBZ-resistant PC cell lines.

METHODS

Using T-cell immunoglobulin domain and mucin domain-containing protein 4 (Tim4) conjugated to magnetic beads, EVs were purified from serum of PC patients with DOC-resistance that was collected before and after acquiring CBZ-resistance and conditioned medium of DOC-resistant (22Rv1DR) and CBZ-resistant (22Rv1CR) PC cell lines. Protein analysis of EVs was performed by nanoLC-MS/MS, followed by a comparative analysis of protein expression and network analysis. The cytotoxic effect of a phosphatidylinositol-3-kinase (PI3K) inhibitor, ZSTK474, was evaluated by WST-1 assay. The expression and phosphorylation of PI3K and PTEN were examined by western blot analysis.

RESULTS

Among differentially regulated proteins, 77 and 61 proteins were significantly increased in EVs from CBZ-resistant PC cell line and patients, respectively. A comparison between the two datasets revealed that six proteins, fructose-bisphosphate aldolase, cytosolic nonspecific dipeptidase, CD63, CD151, myosin light chain 9, and peroxiredoxin-6 were elevated in EVs from both cell line and patients. Network analysis of the increased EV proteins identified pathways associated with CBZ-resistance including PI3K signaling pathway. ZSTK474 significantly inhibited growth of 22Rv1CR cells and improved their sensitivity to CBZ. In 22Rv1CR cells, PI3K was activated and PTEN that inhibits PI3K was deactivated.

CONCLUSIONS

Proteomic analysis of serum EVs was successfully accomplished by using Tim-4 as a tool to isolate highly purified EVs. Our results suggest that the combination use of CBZ and PI3K inhibitor could be a promising treatment option for CBZ-resistant PC patients.

MicroRNAs as Epigenetic Determinants of Treatment Response and Potential Therapeutic Targets in Prostate Cancer

Prostate cancer (PCa) is the second most common tumor in men worldwide, and the fifth leading cause of male cancer-related deaths in western countries. PC is a very heterogeneous disease, meaning that optimal clinical management of individual patients is challenging. Depending on disease grade and stage, patients can be followed in active surveillance protocols or undergo surgery, radiotherapy, hormonal therapy, and chemotherapy. Although therapeutic advancements exist in both radiatiotherapy and chemotherapy, in a considerable proportion of patients, the treatment remains unsuccessful, mainly due to tumor poor responsiveness and/or recurrence and metastasis. microRNAs (miRNAs), small noncoding RNAs that epigenetically regulate gene expression, are essential actors in multiple tumor-related processes, including apoptosis, cell growth and proliferation, autophagy, epithelial-to-mesenchymal transition, invasion, and metastasis. Given that these processes are deeply involved in cell response to anti-cancer treatments, miRNAs have been considered as key determinants of tumor treatment response. In this review, we provide an overview on main PCa-related miRNAs and describe the biological mechanisms by which specific miRNAs concur to determine PCa response to radiation and drug therapy. Additionally, we illustrate whether miRNAs can be considered novel therapeutic targets or tools on the basis of the consequences of their expression modulation in PCa experimental models.

Targeting Nrf2-antioxidant signaling reverses acquired cabazitaxel resistance in prostate cancer cells

Prostate cancer is known to have a relatively good prognosis, but long-term hormone therapy can lead to castration-resistant prostate cancer (CRPC). Cabazitaxel, a second-generation taxane, has been used for the CRPC treatment, but its tolerance is an urgent problem to be solved. In this study, to elucidate the acquisition mechanism of the cabazitaxel-resistance, we established cabazitaxel-resistant prostate cancer 22Rv1 (Cab-R) cells, which exhibited approximately 7-fold higher LD50 against cabazitaxel than the parental 22Rv1 cells. Cab-R cells showed marked increases in nuclear accumulation of NF-E2 related factor 2 (Nrf2) and expression of Nrf2-inducible antioxidant enzymes compared to 22Rv1 cells, suggesting that Nrf2 signaling is homeostatically activated in Cab-R cells. The cabazitaxel sensitivity of Cab-R cells was enhanced by silencing of Nrf2, and that of 22Rv1 cells was reduced by activation of Nrf2. Halofuginone (HF) has been recently identified as a potent Nrf2 synthetic inhibitor, and its treatment of Cab-R cells not only suppressed the Nrf2 signaling by decreasing both nuclear and cytosolic Nrf2 protein levels, but also significantly augmented the cabazitaxel sensitivity. Thus, inhibition of Nrf2 signaling may be effective in overcoming the cabazitaxel resistance in prostate cancer cells.

Balancing the stability and drug activation in adaptive nanoparticles potentiates chemotherapy in multidrug-resistant cancer

Rationale: Prodrug strategies that render the drug temporarily inactive through a cleavable linkage are able to modulate the physicochemical properties of drugs for adaptive nanoparticle (NP) formulation. Here we used cabazitaxel as a model compound to test the validity of our "balancing NP stability and specific drug activation" strategy. Methods: Cabazitaxel is conjugated to hydrophobic polylactide fragments with varying chain lengths via a self-immolation linkage, yielding polymeric prodrugs that can be reactivated by reductive agents in cells. Following a nanoprecipitation protocol, cabazitaxel prodrugs can be stably entrapped in amphiphilic polyethylene-block-polylactide matrices to form core-shell nanotherapies with augmented colloidal stability. Results: Upon cellular uptake followed by intracellular reduction, the NPs spontaneously release chemically unmodified cabazitaxel and exert high cytotoxicity. Studies with near-infrared dye-labeled NPs demonstrate that the nanodelivery of the prodrugs extends their systemic circulation, accompanied with increased drug concentrations at target tumor sites. In preclinical mouse xenograft models, including two paclitaxel-resistant xenograft models, the nanotherapy shows a remarkably higher efficacy in tumor suppression and an improved safety profile than free cabazitaxel. Conclusion: Collectively, our approach enables more effective and less toxic delivery of the cabazitaxel drug, which could be a new generalizable strategy for re-engineering other toxic and water-insoluble therapeutics.

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.

Treatment and resistance mechanisms in castration-resistant prostate cancer: new implications for clinical decision making?

Introduction: The armamentarium of treatment options in metastatic and non-metastatic CRPC is rapidly evolving. However, the question of how individual treatment decisions should be balanced by available predictive clinical parameters, pharmacogenetic and drug interaction profiles, or compound-associated molecular biomarkers is a major challenge for clinical practice.Areas covered: We discuss treatment and resistance mechanisms in PC with regard to their association to drug efficacy and tolerability. Current efforts of combination treatment and putative predictive biomarkers of available and upcoming compounds are highlighted with regard to their implication on clinical decision-making.Expert opinion: Several treatment approaches are delineated, where identification of resistance mechanisms in CRPC may guide treatment selection. To date, most of these candidate biomarkers will however be found only in a small subset of patients. While current approaches of combination treatment in CRPC are proving synergistic effects on cancer biology, higher complexity with regard to biomarker analysis and interaction profiles of the respective compounds may be expected. Among other aspects of personalized treatment, consideration of drug-drug interaction and pharmacogenetics is an underrepresented issue. However, the non-metastatic castration resistant prostate cancer situation may be an example for treatment selection based on drug interaction profiles in the future.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

Genomic stability at the coding regions of the multidrug transporter gene ABCB1: insights into the development of alternative drug resistance mechanisms in human leukemia cells

AIM

Despite considerable efforts to reverse clinical multidrug resistance (MDR), targeting the predominant multidrug transporter ABCB1/P-glycoprotein (P-gp) using small molecule inhibitors has been unsuccessful, possibly due to the emergence of alternative drug resistance mechanisms. However, the non-specific P-gp inhibitor cyclosporine (CsA) showed significant clinical benefits in patients with acute myeloid leukemia (AML), which likely represents the only proof-of-principle clinical trial using several generations of MDR inhibitors. Nevertheless, the mutational mechanisms that may underlie unsuccessful MDR modulation by CsA are not elucidated because of the absence of CsA-relevant cellular models. In this study, our aims were to establish CsA-resistant leukemia models and to examine the presence or absence of ABCB1 exonic mutations in these models as well as in diverse types of human cancer samples including AMLs.

METHODS

Drug-resistant lines were established by stepwise drug co-selection and characterized by drug sensitivity assay, rhodamine-123 accumulation, [3H]-labeled drug export, ABCB1 cDNA sequencing, and RNase protection assay. The genomic stability of the ABCB1 coding regions was evaluated by exome sequencing analysis of variant allele frequencies in human populations. Moreover, the mutational spectrum of ABCB1 was further assessed in diverse types of cancer samples including AMLs in the Cancer Genome Atlas (TCGA) at the National Cancer Institute.

RESULTS

We report the development of two erythroleukemia variants, RVC and RDC, which were derived by stepwise co-selection of K562/R7 drug-resistant leukemia cells with the etoposide-CsA and doxorubicin-CsA drug combinations, respectively. Interestingly, both RVC and RDC cell lines, which retained P-gp expression, showed altered multidrug-resistant phenotypes that were resistant to CsA modulation. Strikingly, no mutations were found in the ABCB1 coding regions in these variant cells even under long-term stringent drug selection. Genomically, ABCB1 displayed relatively low variant allele frequencies in human populations when compared with several ABC superfamily members. Moreover, ABCB1 also exhibited a very low mutational frequency in AMLs compared with all types of human cancer. In addition, we found that CsA played a role in undermining the selection of highly drug-resistant cells via induction of low-level and unstable drug resistance.

CONCLUSION

Our data indicate that ABCB1 coding regions are genomically stable and relatively resistant to drug-induced mutations. Non-ABCB1 mutational mechanisms are responsible for the drug-resistant phenotypes in both RVC and RDC cell lines, which are also prevalent in clinical AML patients. Accordingly, we propose several relevant models that account for the development of alternative drug resistance mechanisms in the absence of ABCB1 mutations.

Antitumor Activity of Cabazitaxel and MSC-TRAIL Derived Extracellular Vesicles in Drug-Resistant Oral Squamous Cell Carcinoma

INTRODUCTION

TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) can induce apoptosis in a variety of cancer cells. However, drug resistance of tumor and short half-life seriously affects its clinical targeted therapy. Cabazitaxel (CTX) is a taxane drug, which can induce apoptosis or autophagy by inhibiting the phosphorylation of PI3K/Akt/mTOR and sensitive to some drug-resistant tumors. Therefore, we explored the possibility of developing a mesenchymal stem cell-derived exosomes (MSC-EXO) vector for oral squamous cell carcinoma (OSCC) to deliver CTX/TRAIL combinations.

METHODS

After ultracentrifugation and dialysis, CTX/TRAIL loaded exosomes transfected MSC (MSCT)-derived exosome (EXO) (MSCT-EXO/CTX) were isolated and purified. The expression of CD63, CD9 and TRAIL was detected by BCA to confirm the origin of EXO. High-performance liquid chromatography (HPLC) was used to determine the drug loading of VPF and draw the in vitro release profile. MTT assay, flow cytometry and Western blot were used to detect the antitumor effect of MSCT-EXO/CTX in vitro. Subsequently, the antitumor effect of MSCT-EXO/CTX in vivo was verified by mouse model.

RESULTS

The diameter of the membrane particles was about 60-150 nm. We have proved that the incorporation and release of CTX in MSCT-EXO can inhibit the activation of PI3K, Akt and mTOR, which is a possible synergistic mechanism of CTX. MSCT-EXO and CTX can induce the apoptosis of SCC25 tumor cells in a dose-dependent manner and exert a good synergistic effect in the proportion range of 10:1-5:1. The inherent activity of MSCT-EXO and the direct effect of MSCT-EXO/CTX on OSCC confirm that MSCT-EXO/CTX makes MSCT-EXO and CTX have an efficient synergistic effect and a highly effective pharmacological inhibition on cancer cells, as verified by the subsequent mouse model. MSCT-EXO/CTX showed the lowest relative tumor volume and the highest tumor inhibition rate (P<0.05) in vivo.

CONCLUSION

An MSCT-EXO-based CTX delivery system might be an effective anticancer method.

The Wnt non-canonical signaling modulates cabazitaxel sensitivity in prostate cancer cells

Background

Despite new drugs, metastatic prostate cancer remains fatal. Growing interest in the latest approved cabazitaxel taxane drug has markedly increased due to the survival benefits conferred when used at an earlier stage of the disease, its promising new therapeutic combination and formulation, and its differential toxicity. Still cabazitaxel’s mechanisms of resistance are poorly characterized. The goal of this study was thus to generate a new model of acquired resistance against cabazitaxel in order to unravel cabazitaxel’s resistance mechanisms.

Methods

Du145 cells were cultured with increasing concentrations of cabazitaxel, docetaxel/ taxane control or placebo/age-matched control. Once resistance was reached, Epithelial-to-Mesenchymal Translation (EMT) was tested by cell morphology, cell migration, and E/M markers expression profile. Cell transcriptomics were determined by RNA sequencing; related pathways were identified using IPA, PANTHER or KEGG software. The Wnt pathway was analyzed by western blotting, pharmacological and knock-down studies.

Results

While age-matched Du145 cells were sensitive to both taxane drugs, docetaxel-resistant cells were only resistant to docetaxel and cabazitaxel-resistant cells showed a partial cross-resistance to both drugs concomitant to EMT. Using RNA-sequencing, the Wnt non-canonical pathway was identified as exclusively activated in cabazitaxel resistant cells while the Wnt canonical pathway was restricted to docetaxel-resistant cells. Cabazitaxel-resistant cells showed a minimal crossover in the Wnt-pathway-related genes linked to docetaxel resistance validating our unique model of acquired resistance to cabazitaxel. Pharmacological and western blot studies confirmed these findings and suggest the implication of the Tyrosine kinase Ror2 receptor in cabazitaxel resistant cells. Variation in Ror2 expression level altered the sensitivity of prostate cancer cells to both drugs identifying a possible new target for taxane resistance.

Conclusion

Our study represents the first demonstration that while Wnt pathway seems to play an important role in taxanes resistance, Wnt effectors responsible for taxane specificity remain un-identified prompting the need for more studies.

Docetaxel-resistant prostate cancer cells become sensitive to gemcitabine due to the upregulation of ABCB1

BACKGROUND

Docetaxel is the preferred chemotherapeutic agent for hormone-refractory prostate cancer (PC) patients. However, patients eventually develop docetaxel resistance, and no effective treatment options are available for them.

OBJECTIVE

We aimed to establish docetaxel resistance in castration-resistant prostate cancer (CRPC) cell lines (DU145/TXR, PC-3/TXR, and CWR22/TXR) and characterized transcriptional changes upon acquiring resistance to the docetaxel.

METHODS

Human PC cells (DU145, PC-3, CWR22) and all docetaxel-resistant cells were maintained in Roswell Park Memorial Institute Medium (RPMI) 1640 media supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin. ABCB1 was detected by using both parental and docetaxel-resistant CRPCs prepared for flow cytometry. For the evaluation of tumor-suppressive effects under each chemotherapeutic agent, subcutaneous xenografts of DU145 or DU145/TXR were implanted at the mouse flank.

RESULTS

The P-glycoprotein-encoding gene ABCB1 was distinctively upregulated in the resistant cells, and its overexpression played an essential role in docetaxel resistance in CRPC. When tested for the cytotoxicity of gemcitabine, another option for chemotherapy, the docetaxel-resistant cells were shown to become sensitive to the drug, implying additional phenotypic transformation in the docetaxel-resistant cells. Studies using xenograft animal models demonstrated that the growth of tumors composed of both docetaxel-sensitive and docetaxel-resistant cells was deterred most profoundly when docetaxel and gemcitabine were administered together.

CONCLUSION

This study suggests that when a drug develops therapeutic resistance, sensitivity tests could be another option, ultimately providing insight into a novel alternative clinical strategy.

Microtubule-targeting agents and their impact on cancer treatment

Microtubule-targeting agents (MTAs) constitute a diverse group of chemical compounds that bind to microtubules and affect their properties and function. Disruption of microtubules induces various cellular responses often leading to cell cycle arrest or cell death, the most common effect of MTAs. MTAs have found a plethora of practical applications in weed control, as fungicides and antiparasitics, and particularly in cancer treatment. Here we summarize the current knowledge of MTAs, the mechanisms of action and their role in cancer treatment. We further outline the potential use of MTAs in anti-metastatic therapy based on inhibition of cancer cell migration and invasiveness. The two main problems associated with cancer therapy by MTAs are high systemic toxicity and development of resistance. Toxic side effects of MTAs can be, at least partly, eliminated by conjugation of the drugs with various carriers. Moreover, some of the novel MTAs overcome the resistance mediated by both multidrug resistance transporters as well as overexpression of specific β-tubulin types. In anti-metastatic therapy, MTAs should be combined with other drugs to target all modes of cancer cell invasion.

Marked response to cabazitaxel in prostate cancer xenografts expressing androgen receptor variant 7 and reversion of acquired resistance by anti-androgens

BACKGROUND

Taxane treatment may be a suitable therapeutic option for patients with castration-resistant prostate cancer and high expression of constitutively active androgen receptor variants (AR-Vs). The aim of the study was to compare the effects of cabazitaxel and androgen deprivation treatments in a prostate tumor xenograft model expressing high levels of constitutively active AR-V7. Furthermore, mechanisms behind acquired cabazitaxel resistance were explored.

METHODS

Mice were subcutaneously inoculated with 22Rv1 cells and treated with surgical castration (n = 7), abiraterone (n = 9), cabazitaxel (n = 6), castration plus abiraterone (n = 8), castration plus cabazitaxel (n = 11), or vehicle and/or sham operation (n = 23). Tumor growth was followed for about 2 months or to a volume of approximately 1000 mm³ . Two cabazitaxel resistant cell lines; 22Rv1-CabR1 and 22Rv1-CabR2, were established from xenografts relapsing during cabazitaxel treatment. Differential gene expression between the cabazitaxel resistant and control 22Rv1 cells was examined by whole-genome expression array analysis followed by immunoblotting, immunohistochemistry, and functional pathway analysis.

RESULTS

Abiraterone treatment alone or in combination with surgical castration had no major effect on 22Rv1 tumor growth, while cabazitaxel significantly delayed and in some cases totally abolished 22Rv1 tumor growth on its own and in combination with surgical castration. The cabazitaxel resistant cell lines; 22Rv1-CabR1 and 22Rv1-CabR2, both showed upregulation of the ATP-binding cassette sub-family B member 1 (ABCB1) efflux pump. Treatment with ABCB1 inhibitor elacridar completely restored susceptibility to cabazitaxel, while treatment with AR-antagonists bicalutamide and enzalutamide partly restored susceptibility to cabazitaxel in both cell lines. The cholesterol biosynthesis pathway was induced in the 22Rv1-CabR2 cell line, which was confirmed by reduced sensitivity to simvastatin treatment.

CONCLUSIONS

Cabazitaxel efficiently inhibits prostate cancer growth despite the high expression of constitutively active AR-V7. Acquired cabazitaxel resistance involving overexpression of efflux transporter ABCB1 can be reverted by bicalutamide or enzalutamide treatment, indicating the great clinical potential for combined treatment with cabazitaxel and anti-androgens.

Therapeutic Targeting of MDR1 Expression by RORγ Antagonists Resensitizes Cross-Resistant CRPC to Taxane via Coordinated Induction of Cell Death Programs

Overexpression of ATP-binding cassette subfamily B member 1 (ABCB1)-encoded multidrug resistance protein 1 (MDR1) constitutes a major mechanism of cancer drug resistance including docetaxel (DTX) and cabazitaxel (CTX) resistance in castration-resistant prostate cancer (CRPC). However, no therapeutics that targets MDR1 is available at clinic for taxane sensitization. We report here that retinoic acid receptor-related orphan receptor γ (RORγ), a nuclear receptor family member, unexpectedly mediates MDR1/ABCB1 overexpression. RORγ plays an important role in controlling the functions of subsets of immune cells and has been an attractive target for autoimmune diseases. We found that its small-molecule antagonists are efficacious in resensitizing DTX and CTX cross-resistant CRPC cells and tumors to taxanes in both androgen receptor-positive and -negative models. Our mechanistic analyses revealed that combined treatment with RORγ antagonists and taxane elicited a robust synergy in killing the resistant cells, which involves a coordinated alteration of p53, Myc, and E2F-controlled programs critical for both intrinsic and extrinsic apoptosis, survival, and cell growth. Our results suggest that targeting RORγ with small-molecule inhibitors is a novel strategy for chemotherapy resensitization in tumors with MDR1 overexpression.

TUBB3 Reverses Resistance to Docetaxel and Cabazitaxel in Prostate Cancer

Recent studies have reported that TUBB3 overexpression is involved in docetaxel (DTX) resistance in prostate cancer (PCa). The aim of this study was to clarify the role of TUBB3 in DTX and cabazitaxel (CBZ) resistance, and cross-resistance between DTX and CBZ in PCa. We analyzed the effect of TUBB3 knockdown on DTX and CBZ resistance and examined the interaction between TUBB3 and PTEN. We also investigated the role of phosphoinositide 3-kinases (PI3K) inhibitor (LY294002) in DTX and CBZ resistance. TUBB3 expression was upregulated in DTX-resistant and CBZ-resistant cells. TUBB3 knockdown re-sensitized DTX-resistant cells to DTX and CBZ-resistant cells to CBZ. Additionally, TUBB3 knockdown re-sensitized DTX-resistant cell lines to CBZ, indicating that TUBB3 mediates cross-resistance between DTX and CBZ. Knockdown of TUBB3 enhanced PTEN expression, and PTEN knockout enhanced TUBB3 expression. LY294002 suppressed TUBB3 expression in DTX-resistant and CBZ-resistant cell lines. LY294002 re-sensitized DTX-resistant cell lines to DTX and CBZ-resistant cell lines to CBZ. These results suggest that TUBB3 is involved in DTX resistance and CBZ resistance. A combination of LY294002/DTX and that of LY294002/CBZ could be potential strategies for PCa treatment.

Second line chemotherapy and visceral metastases are associated with poor survival in patients with mCRPC receiving 177Lu-PSMA-617

The purpose of this study was to identify previous treatments and biomarker profile features that prognosticate overall survival (OS) in patients with mCRPC receiving ¹⁷⁷Lu-PSMA-617.

Methods: 109 mCRPC patients treated with a median of 3 cycles of ¹⁷⁷Lu-PSMA-617 were included. Data were analyzed according to OS as well as PSA response patterns with regard to prior therapies, laboratory biomarkers and metastatic extent in univariate as well as multivariate Cox's proportional hazards models. PSA decline was assessed using the lowest PSA levels after the first cycle of therapy (initial PSA response) and during the entire observation period (best PSA response).

Results: In total, 54 patients (49.5%) died during the observation period. First and second line chemotherapy were performed in 85% and 26%, and Abiraterone and Enzalutamide were administered in 83% and 85%, respectively. Any initial PSA decline occurred in 55% while 25% showed a PSA decline of ≥50%. The median estimated OS was 9.9 months (95% CI: 7.2-12.5) for all patients. Any initial decline of PSA was associated with significantly prolonged OS (15.5 vs. 5.7 months, p = 0.002). Second line cabazitaxel chemotherapy (6.7 vs. 15.7 months, p = 0.002) and presence of visceral metastases (5.9 vs. 16.4 months, p<0.001) were associated with shorter OS. Only visceral metastases remained significant in a multivariate analysis.

Conclusion:¹⁷⁷Lu-PSMA-617 is an effective therapy for patients with mCRPC. However, the present data indicate that its beneficial effects on OS are strongly influenced by pretreatment (history of second line chemotherapy with cabazitaxel) and the presence of visceral metastases at onset of ¹⁷⁷Lu-PSMA-617 treatment.

The Syk inhibitor R406 is a modulator of P-glycoprotein (ABCB1)-mediated multidrug resistance

In a previously published study, higher levels of spleen tyrosine kinase (Syk) were observed in recurrent post-chemotherapy ovarian cancers compared to primary tumors. Syk inhibition was found to stabilize microtubules and potentiate paclitaxel activity in cellular models of taxane-resistant ovarian cancers. We further studied the effects of Syk inhibition on paclitaxel activity in Syk(+) ovarian cancer cell models and in variants selected for taxane resistance. Syk inhibition was accomplished using RNAi and by exposure to the small molecule competitive inhibitor R406, the active metabolite of fostamatinib. Exposure to R406 or to a SYK-specific pool of siRNAs did not alter taxane activity in the OVCAR-3 cell line, which has the most Syk content in our panel of nine human ovarian cancer cell lines. However, treatment with R406 sensitised the multidrug resistant (MDR) variants MES-SA/Dx5 and SK-OV-3/TR to paclitaxel in a dose-dependent manner resulting from the inhibition of the ABCB1/P-glycoprotein (P-gp) drug transporter. These observations are Syk-independent since both MDR cell models are Syk negative. R406 modulated resistance to other known P-gp substrates, and we observed orthovanadate-sensitive ATPase stimulation resulting from treatment with R406. These data indicate that the chemo-sensitizing effect of R406 in taxane-resistant cells previously reported was not associated with Syk but resulted from the modulation of P-gp-mediated MDR.

Cabazitaxel-loaded Poly(2-ethylbutyl cyanoacrylate) nanoparticles improve treatment efficacy in a patient derived breast cancer xenograft

The effect of poly(2-ethyl-butyl cyanoacrylate) nanoparticles containing the cytotoxic drug cabazitaxel was studied in three breast cancer cell lines and one basal-like patient-derived xenograft model grown in the mammary fat pad of immunodeficient mice. Nanoparticle-encapsulated cabazitaxel had a much better efficacy than similar concentrations of free drug in the basal-like patient-derived xenograft and resulted in complete remission of 6 out of 8 tumors, whereas free drug gave complete remission only with 2 out of 9 tumors. To investigate the different efficacies obtained with nanoparticle-encapsulated versus free cabazitaxel, mass spectrometry quantification of cabazitaxel was performed in mice plasma and selected tissue samples. Nanoparticle-encapsulated drug had a longer circulation time in blood. There was approximately a three times higher drug concentration in tumor tissue 24 h after injection, and two times higher 96 h after injection of nanoparticles with drug compared to the free drug. The tissue biodistribution obtained after 24 h using mass spectrometry analyses correlates well with biodistribution data obtained using IVIS® Spectrum in vivo imaging of nanoparticles labeled with the fluorescent substance NR668, indicating that these data also are representative for the nanoparticle distribution. Furthermore, immunohistochemistry was used to estimate infiltration of macrophages into the tumor tissue following injection of nanoparticle-encapsulated and free cabazitaxel. The higher infiltration of anti-tumorigenic versus pro-tumorigenic macrophages in tumors treated with the nanoparticles might also contribute to the improved effect obtained with the nanoparticle-encapsulated drug. Tumor infiltration of pro-tumorigenic macrophages was four times lower when using nanoparticles containing cabazitaxel than when using particles without drug, and we speculate that the very good therapeutic efficacy obtained with our cabazitaxel-containing particles may be due to their ability to reduce the level of pro-tumorigenic macrophages in the tumor. In summary, encapsulation of cabazitaxel in poly(2-ethyl-butyl cyanoacrylate) nanoparticles seems promising for treatment of breast cancer.

MiR-30a: A Novel Biomarker and Potential Therapeutic Target for Cancer

MicroRNAs (miRNAs) are small, highly conserved noncoding RNAs molecules, consisting of 18–25 nucleotides that regulate gene expression by binding to complementary binding sites within the 3′untranslated region (3′UTR) of target mRNAs. MiRNAs have been involved in regulating gene expression and diverse physiological and pathological processes. Several studies have reported that miR-30a, situated on chromosome 6q.13, is produced by an intronic transcriptional unit. Moreover, miR-30a has demonstrated its role in biological processes, including inhibiting proliferation and metastasis in many tumors, autophagy in chronic myelogenous leukemia, and regulating TGF-b1-induced epithelial-mesenchymal transition. However, based on the pathogenetic relationship between miR-30a and cancer in tumorigenesis, we believe that miR-30a may serve as tumor promising biomarker. Moreover, it would offer a therapeutic target for the treatment of cancer.

PEGylated lipid microspheres loaded with cabazitaxel for intravenous administration: stability, bioavailability, antitumor efficacy, and toxicity

This paper aimed to develop a novel lipid microsphere delivering cabazitaxel (CTX) using phosphatidylcholine combined with DSPE-PEG2000 as emulsifier, and evaluate its stability, pharmacokinetics, antitumor efficacy, and toxicity. The pegylated cabazitaxel-loaded lipid microspheres (CTX-PLMs) were prepared by high-pressure homogenization methods; the biological samples were analyzed by the UPLC-MS/MS method. CTX-PLMs had a drug concentration of 1.2 mg/ml and a mean particle size of 180.0 ± 51.119 nm. CTX-PLMs showed a superior physical stability as it could remain nearly intact after 1-year storage. The AUC_0-t of the CTX-PLMs was 1562.6 ± 520.1 μg h L^-1 compared with the CTX-solution of 860.734 ± 312.4 μg h L^-1. CTX-PLMs exhibited a strong antitumor efficacy against NCI-N87 and DU145 tumor models with tumor growth inhibition rates of 93.5 and 88.5%, respectively. The LD50 of CTX-PLMs in rats was 20.89 mg/kg. As for the long-term toxicity, the thymus, mesenteric lymph nodes, and bone marrow were the main toxic target organs and systemic toxicity induced by CTX-PLMs was alleviated relative to that of the CTX-solution. Safety assessment studies including hemolysis test, dermal sensitization test, systemic anaphylaxis, and vascular stimulation test indicated that CTX-PLMs is safe enough for intravenous administration. In a word, CTX-PLMs are a promising carrier for intravenous administration with satisfactory stability, stronger tumor inhibition, and superior safety profile.

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.

Nanoparticle Formulation Derived from Carboxymethyl Cellulose, Polyethylene Glycol, and Cabazitaxel for Chemotherapy Delivery to the Brain

Nanoparticles provide a unique opportunity to explore the benefits of selective distribution and release of cancer therapeutics at sites of disease through varying particle sizes and compositions that exploit the enhanced permeability of tumor-associated blood vessels. Though delivery of larger as opposed to smaller and/or actively transported molecules to the brain is prima facie a challenging endeavor, we wondered whether nanoparticles could improve the therapeutic index of existing drugs for use in treating brain tumors via these vascular effects. We therefore selected a family of nanoparticles composed of cabazitaxel-carboxymethyl cellulose amphiphilic polymers to investigate the potential for delivering a brain-penetrant taxane to intracranial brain tumors in mice. Among a small set of nanoparticle formulations, we found evidence for nanoparticle accumulation in the brain, and one such formulation demonstrated activity in an orthotopic model of glioma, suggesting that such nanoparticles could be useful for the treatment of glioma and brain metastases of other tumor types.

Cabazitaxel is more active than first-generation taxanes in ABCB1(+) cell lines due to its reduced affinity for P-glycoprotein

PURPOSE

The primary aim of this study was to determine cabazitaxel's affinity for the ABCB1/P-glycoprotein (P-gp) transporter compared to first-generation taxanes.

METHODS

We determined the kinetics of drug accumulation and retention using [¹⁴C]-labeled taxanes in multidrug-resistant (MDR) cells. In addition, membrane-enriched fractions isolated from doxorubicin-selected MES-SA/Dx5 cells were used to determine sodium orthovanadate-sensitive ATPase stimulation after exposure to taxanes. Custom [³H]-azido-taxane analogues were synthesized for the photoaffinity labeling of P-gp.

RESULTS

The maximum intracellular drug concentration was achieved faster with [¹⁴C]-cabazitaxel (5 min) than [¹⁴C]-docetaxel (15-30 min). MDR cells accumulated twice as much cabazitaxel than docetaxel, and these levels could be restored to parental levels in the presence of the P-gp inhibitor PSC-833 (valspodar). Efflux in drug-free medium confirmed that MDR cells retained twice as much cabazitaxel than docetaxel. There was a strong association (r² = 0.91) between the degree of taxane resistance conferred by P-gp expression and the accumulation differences observed with the two taxanes. One cell model expressing low levels of P-gp was not cross-resistant to cabazitaxel while demonstrating modest resistance to docetaxel. Furthermore, there was a 1.9 × reduction in sodium orthovanadate-sensitive ATPase stimulation resulting from treatment with cabazitaxel compared to docetaxel. We calculated a dissociation constant (Kd) value of 1.7 µM for [³H]-azido-docetaxel and ~ 7.5 µM for [³H]-azido-cabazitaxel resulting in a 4.4 × difference in P-gp labeling, and cold docetaxel was a more effective competitor than cabazitaxel.

CONCLUSION

Our studies confirm that cabazitaxel is more active in ABCB1(+) cell models due to its reduced affinity for P-gp compared to docetaxel.

Substituents at the C3' and C3'N positions are critical for taxanes to overcome acquired resistance of cancer cells to paclitaxel

We tested the role of substituents at the C3' and C3'N positions of the taxane molecule to identify taxane derivatives capable of overcoming acquired resistance to paclitaxel. Paclitaxel-resistant sublines SK-BR-3/PacR and MCF-7/PacR as well as the original paclitaxel-sensitive breast cancer cell lines SK-BR-3 and MCF-7 were used for testing. Increased expression of the ABCB1 transporter was found to be involved in the acquired resistance. We tested three groups of taxane derivatives: (1) phenyl group at both C3' and C3'N positions, (2) one phenyl at one of the C3' and C3'N positions and a non-aromatic group at the second position, (3) a non-aromatic group at both C3' and C3'N positions. We found that the presence of phenyl groups at both C3' and C3'N positions is associated with low capability of overcoming acquired paclitaxel resistance compared to taxanes containing at least one non-aromatic substituent at the C3' and C3'N positions. The increase in the ATPase activity of ABCB1 transporter after the application of taxanes from the first group was found to be somewhat higher than after the application of taxanes from the third group. Molecular docking studies demonstrated that the docking score was the lowest, i.e. the highest binding affinity, for taxanes from the first group. It was intermediate for taxanes from the second group, and the highest for taxanes from the third group. We conclude that at least one non-aromatic group at the C3' and C3'N positions of the taxane structure, resulting in reduced affinity to the ABCB1 transporter, brings about high capability of taxane to overcome acquired resistance of breast cancer cells to paclitaxel, due to less efficient transport of the taxane compound out of the cancer cells.

Heterocyclic-Fused Pyrimidines as Novel Tubulin Polymerization Inhibitors Targeting the Colchicine Binding Site: Structural Basis and Antitumor Efficacy

We report the design, synthesis, and biological evaluation of heterocyclic-fused pyrimidines as tubulin polymerization inhibitors targeting the colchicine binding site with significantly improved therapeutic index. Additionally, for the first time, we report high-resolution X-ray crystal structures for the best compounds in this scaffold, 4a, 4b, 6a, and 8b. These structures not only confirm their direct binding to the colchicine site in tubulin and reveal their detailed molecular interactions but also contrast the previously published proposed binding mode. Compounds 4a and 6a significantly inhibited tumor growth in an A375 melanoma xenograft model and were accompanied by elevated levels of apoptosis and disruption of tumor vasculature. Finally, we demonstrated that compound 4a significantly overcame clinically relevant multidrug resistance in a paclitaxel resistant PC-3/TxR prostate cancer xenograft model. Collectively, these studies provide preclinical and structural proof of concept to support the continued development of this scaffold as a new generation of tubulin inhibitors.

Inhibit or Evade Multidrug Resistance P-Glycoprotein in Cancer Treatment

Multidrug resistance (MDR) is a major cause of failure in cancer chemotherapy. P-glycoprotein (P-gp), a promiscuous drug efflux pump, has been extensively studied for its association with MDR due to overexpression in cancer cells. Several P-gp inhibitors or modulators have been investigated in clinical trials in hope of circumventing MDR, with only limited success. Alternative strategies are actively pursued, such as the modification of existing drugs, development of new drugs, or combination of novel drug delivery agents to evade P-gp-dependent efflux. Despite the importance and numerous studies, these efforts have mostly been undertaken without a priori knowledge of how drugs interact with P-gp at the molecular level. This review highlights and discusses progress toward and challenges impeding drug development for inhibiting or evading P-gp in the context of our improved understanding of the structural basis and mechanism of P-gp-mediated MDR.