Taxanes: Old drugs, new oral formulations

Oral Bioavailability Enhancement of Anti-Cancer Drugs Through Lipid Polymer Hybrid Nanoparticles

Cancer is considered as the second leading cause of death worldwide. Chemotherapy, radiotherapy, immunotherapy, and targeted drug delivery are the main treatment options for treating cancers. Chemotherapy drugs are either available for oral or parenteral use. Oral chemotherapy, also known as chemotherapy at home, is more likely to improve patient compliance and convenience. Oral anti-cancer drugs have bioavailability issues associated with lower aqueous solubility, first-pass metabolism, poor intestinal permeability and drug absorption, and degradation of the drug throughout its journey in the gastrointestinal tract. A highly developed carrier system known as lipid polymer hybrid nanoparticles (LPHNs) has been introduced. These nanocarriers enhance drug stability, solubility, and absorption, and reduce first-pass metabolism. Consequently, this will have a positive impact on oral bioavailability enhancement. This article provides an in-depth analysis of LPHNs as a novel drug delivery system for anti-cancer agents. It discusses an overview of the limited bioavailability of anti-cancer drugs, their reasons and consequences, LPHNs based anti-cancer drug delivery, conventional and modern preparation methods as well as their drug loading and entrapment efficiencies. In addition, this article also gives an insight into the mechanistic approach to oral bioavailability enhancement, potential applications in anti-cancer drug delivery, limitations, and future prospects of LPHNs in anti-cancer drug delivery.

Low-Dose Docetaxel Is Effective in Reducing Atherogenic Lipids and Atherosclerosis

High-density lipoprotein (HDL) particles form during cellular cholesterol removal, positioning HDL biogenesis as a potential strategy to combat atherosclerosis. We identified desmocollin 1 (DSC1) as a negative regulator of HDL biogenesis and discovered that docetaxel (DTX) effectively inhibits DSC1 activity. This study assessed the efficacy of DTX in reducing atherosclerosis in ApoE-/- mice. After two weeks on a high-fat diet, mice were divided into baseline, vehicle-treated, and DTX-treated groups. Baseline mice were sacrificed at the end of the two weeks, while the other groups received a vehicle or DTX (1 μg/μL) via subcutaneously implanted osmotic pumps delivering 0.15 μL/h for six weeks, with the high-fat diet continued. The controlled drug delivery system maintained stable DTX blood concentrations (2.7-4.3 nM) over six weeks without hematologic toxicity. DTX treatment significantly reduced circulating atherogenic lipids, including triglycerides, non-esterified fatty acids, low-density lipoprotein cholesterol, and total cholesterol, while increasing the HDL cholesterol/total cholesterol ratio. These improvements were associated with significant reductions in atherosclerotic lesions in the aortic sinus and arch. Notably, these effects occurred without altering circulating inflammatory cytokine levels. These results demonstrate that DTX effectively reduces dyslipidemia-induced atherosclerosis. Its HDL-biogenic and anti-atherosclerotic effects establish DTX as a promising candidate for developing HDL-directed therapies for atherosclerosis.

18F-Labeled dihydropyridines via Hantzsch reaction for positron emission tomography of P-glycoprotein dysfunction

Despite the availability of various 11C-labeled positron emission tomography (PET) tracers for assessing P-glycoprotein (P-gp) function, there are still limitations related to complex metabolism, high lipophilicity, and low baseline uptake. This study aimed to address these issues by exploring a series of customized dihydropyridines (DHPs) with enhanced stability and reduced lipophilicity as alternative PET tracers for P-gp dysfunction. Compared with verapamil and the rest DHPs, dimethyl 4-(4-fluorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (1) exhibited superior cellular uptake differences between the human gastric cancer cell line SGC7901 and its drug-resistant counterpart. [18F]1 is successfully synthesized using a novel "hot-Hantzsch" approach in 22.1 ± 0.1 % radiochemical yields. MicroPET/CT imaging demonstrated that the uptake of [18F]1 in the brains of P-gp blocked mice increased by > 3 times compared to the control group. Additionally, [18F]1 displayed favorable lipophilicity (log D = 2.3) and excellent clearance characteristics, making it a promising tracer candidate with low background noise and high contrast.

Chemotherapeutic properties and side-effects associated with the clinical practice of terpene alkaloids: paclitaxel, docetaxel, and cabazitaxel

Over the years, many biological and synthetic agents have been explored and tested in attempts to halt the spread of cancer and/or cure it. Currently, several natural compounds have and are being considered in this regard. For example, paclitaxel is a potent anticancer drug that originates from the tree Taxus brevifolia. Paclitaxel has several derivatives, namely, docetaxel and cabazitaxel. These agents work by disrupting microtubule assembling dynamics and inducing cell cycle arrest at the G2/M phase of the cell cycle, ultimately triggering apoptosis. Such features have helped to establish paclitaxel as an authoritative therapeutic compound against neoplastic disorders. After the completion of compound (hemi) synthesis, this drug received approval for the treatment of solid tumors either alone or in combination with other agents. In this review, we explore the mechanisms of action of paclitaxel and its derivatives, the different formulations available, as well as the molecular pathways of cancer resistance, potential risks, and other therapeutic applications. In addition, the role of paclitaxel in hematological malignancies is explored, and potential limitations in the therapeutic use of paclitaxel at the clinical level are examined. Furthermore, paclitaxel is known to cause increased antigen presentation. The immunomodulatory potential of taxanes, alone or in combination with other pharmacologic agents, is explored. Despite terpene-alkaloids derivatives' anti-mitotic potential, the impact of this class of drugs on other oncogenic pathways, such as epithelial-to-mesenchymal transition and the epigenetic modulation of the transcription profile of cancer cells, is also analyzed, shedding light on potential future chemotherapeutic approaches to cancer.

A self-microemulsion enhances oral absorption of docetaxel by inhibiting P-glycoprotein and CYP metabolism

Oral absorption of docetaxel was limited by drug efflux pump p-glycoprotein (P-gp) and cytochrome P450 enzyme (CYP 450). Therefore, co-loading agent that inhibits P-gp and CYP450 in self-nanoemulsifying drug delivery systems (SMEs) is considered a promising strategy for oral delivery of docetaxel. In this study, curcumin was selected as an inhibitor of P-gp and CYP450, and it was co-encapsuled in SMEs to improve the oral bioavailability of docetaxel. SMEs quickly dispersed in water within 20 s, and the droplet size was 32.23 ± 2.21 nm. The release rate of curcumin from DC-SMEs was higher than that of docetaxel in vitro. Compared with free docetaxel, SMEs significantly increased the permeability of docetaxel by 4.6 times. And competitive experiments showed that the increased permeability was the result of inhibition of p-gp. The half-life and oral bioavailabilty of DC-SMEs increased about 1.7 times and 1.6 times than docetaxel SMEs, which indicated that its good pharmacokinetic behavior was related to the restriction of hepatic first-pass metabolism. In conclusion, DC-SME was an ideal platform to facilitate oral delivery of docetaxel through inhibited P-gp and CYP 450.

Incorporating a Lipophilic Disulfide-Bridged Linoleic Prodrug into a Self-Microemulsifying Drug Delivery System to Facilitate Oral Absorption of Paclitaxel

The oral absorption of paclitaxel (PTX) is restricted by poor solubility in the gastrointestinal tract (GIT), low permeability, and high first-pass metabolism. Lipid carriers, such as a self-microemulsifying drug delivery system (SMEDDS), have been deemed as promising vehicles for promoting oral delivery of PTX. Herein, a lipophilic disulfide-bridged linoleic prodrug (PTX-S-S-LA) was synthesized and efficiently incorporated into SMEDDS to facilitate the oral absorption of PTX. This study mainly aims to evaluate the usefulness of the disulfide-bridged linoleic prodrug incorporated with SMEDDS and provides a new strategy for efficient oral delivery of PTX. The prodrug SMEDDS showed a markedly higher drug loading efficiency (3-fold) compared to that of parent PTX. PTX-S-S-LA SMEDDS significantly increased the drug partition (about 1.9-fold) in the intestinal micellar aqueous phase compared to PTX in the in vitro lipolysis study. Additionally, the gastrointestinal (GI) biodistribution study demonstrated that SMEDDS could enhance the GI biological adhesion and go through the lymphatic system to transport. Moreover, it was found that the reduction-sensitive prodrug (PTX-S-S-LA) has good stability in the GIT, leading to an improved antitumor efficiency without significant GI toxicity. Overall, the PTX-linoleic prodrug (PTX-S-S-LA) in combination with SMEDDS provides a promising way to enable effective oral delivery of PTX.

Factors associated with non-response to naldemedine for opioid-induced constipation in cancer patients: A subgroup analysis

BACKGROUND

Opioid-induced constipation (OIC) is one of the most common adverse events of opioid therapy and can severely reduce quality of life (QOL). Naldemedine is the orally available peripheral-acting μ-opioid receptor antagonist approved for OIC treatment. However in daily clinical practice, some cancer patients show insufficient control of OIC even while receiving naldemedine.

OBJECTIVE

To identify factors associated with non-response to naldemedine in cancer patients.

METHODS

This study retrospectively analyzed 127 cancer patients prescribed naldemedine at Seirei Hamamatsu General Hospital in Japan between November 2016 and June 2021. For the regression analysis of factors associated with OIC, variables were extracted manually from electronic medical records. Naldemedine had been prescribed by the attending physician after the presence of OIC had been defined with reference to Rome IV diagnostic criteria. Naldemedine was evaluated as "effective" in cases where the number of defecations increased at least once in the first 3 days after starting naldemedine. Multivariate logistic regression analysis was performed to identify factors associated with non-response to naldemedine. The data used were from the group of patients who received naldemedine in our previous study.

RESULTS

Factors significantly associated with non-response to naldemedine included chemotherapy with taxanes within 1 month of evaluation of naldemedine effect (odds ratio [OR] = 0.063; 95% confidence interval [CI] = 0.007-0.568), and addition of or switching to naldemedine due to insufficient efficacy of prior laxatives (OR = 0.352, 95% CI = 0.129-0.966).

CONCLUSION

The identification of factors associated with non-response to naldemedine prescribed for OIC may help improve QOL among cancer patients.

Interaction Analysis of MRP1 with Anticancer Drugs Used in Ovarian Cancer: In Silico Approach

Multidrug resistance (MDR) is one of the major therapeutic challenges that limits the efficacy of chemotherapeutic response resulting in poor prognosis of ovarian cancer (OC). The multidrug resistance protein 1 (MRP1) is a membrane-bound ABC transporter involved in cross resistance to many structurally and functionally diverse classes of anticancer drugs including doxorubicin, taxane, and platinum. In this study, we utilize homology modelling and molecular docking analysis to determine the binding affinity and the potential interaction sites of MRP1 with Carboplatin, Gemcitabine, Doxorubicin, Paclitaxel, and Topotecan. We used AutoDock Vina scores to compare the binding affinities of the anticancer drugs against MRP1. Our results depicted Carboplatin < Gemcitabine < Topotecan < Doxorubicin < Paclitaxel as the order of binding affinities. Paclitaxel has shown the highest binding affinity whereas Carboplatin displayed the lowest affinity to MRP1. Interestingly, our data showed that Carboplatin, Paclitaxel, and Topotecan bind specifically to Asn510 residue in the transmembrane domains 1 of the MRP1. Our results suggest that Carboplatin could be an appropriate therapeutic choice against MRP1 in OC as it couples weakly with Carboplatin. Further, our findings also recommend opting Carboplatin with Gemcitabine as a combinatorial chemotherapeutic approach to overcome MDR phenotype associated with recurrent OC.

Preclinical and Early Clinical Development of PTC596, a Novel Small-Molecule Tubulin-Binding Agent

PTC596 is an investigational small-molecule tubulin-binding agent. Unlike other tubulin-binding agents, PTC596 is orally bioavailable and is not a P-glycoprotein substrate. So as to characterize PTC596 to position the molecule for optimal clinical development, the interactions of PTC596 with tubulin using crystallography, its spectrum of preclinical in vitro anticancer activity, and its pharmacokinetic-pharmacodynamic relationship were investigated for efficacy in multiple preclinical mouse models of leiomyosarcomas and glioblastoma. Using X-ray crystallography, it was determined that PTC596 binds to the colchicine site of tubulin with unique key interactions. PTC596 exhibited broad-spectrum anticancer activity. PTC596 showed efficacy as monotherapy and additive or synergistic efficacy in combinations in mouse models of leiomyosarcomas and glioblastoma. PTC596 demonstrated efficacy in an orthotopic model of glioblastoma under conditions where temozolomide was inactive. In a first-in-human phase I clinical trial in patients with cancer, PTC596 monotherapy drug exposures were compared with those predicted to be efficacious based on mouse models. PTC596 is currently being tested in combination with dacarbazine in a clinical trial in adults with leiomyosarcoma and in combination with radiation in a clinical trial in children with diffuse intrinsic pontine glioma.

Resistance to Intervention: Paclitaxel in Breast Cancer

Breast cancer stands as the most prevalent cancer in women globally, and contributes to the highest percentage of mortality due to cancer-related deaths in women. Paclitaxel (PTX) is heavily relied on as a frontline chemotherapy drug in breast cancer treatment, especially in advanced metastatic cancer. Generation of resistance to PTX often derails clinical management and adversely affects patient outcomes. Understanding the molecular mechanism of PTX resistance is necessary to device methods to aid in overcoming the resistance. Recent studies exploring the mechanism of development of PTX resistance have led to unveiling of a range novel therapeutic targets. PTX resistance pathways that involve major regulatory proteins/RNAs like RNF8/Twist/ROR1, TLR, ErbB3/ErbB2, BRCA1- IRIS, MENA, LIN9, MiRNA, FoxM1 and IRAK1 have expanded the complexity of resistance mechanisms, and brought newer insights into the development of drug targets. These resistance-related targets can be dealt with synthetic/natural therapeutics in combination with PTX. The present review encompasses the recent understanding of PTX resistance mechanisms in breast cancer and possible therapeutic combinations to overcome resistance.

Oral paclitaxel with encequidar compared to intravenous paclitaxel in patients with advanced cancer: A randomised crossover pharmacokinetic study

AIMS

Paclitaxel is a widely used anti-neoplastic agent but has low oral bioavailability due to gut extrusion by P-glycoprotein (P-gp). Oral paclitaxel could be more convenient, less resource intensive, and more tolerable than intravenous administration. Encequidar (HM30181A) is a novel, minimally absorbed gut-specific P-gp inhibitor. We tested whether administration of oral paclitaxel with encequidar (oPac+E) achieved comparable AUC to intravenous paclitaxel (IVP) 80 mg/m² .

METHODS

We conducted a multi-centre randomised crossover study with two treatment periods. Patients (pts) with advanced cancer received either oral paclitaxel 615 mg/m² divided over 3 days and encequidar 15 mg orally 1 hour prior, followed by IVP 80 mg/m² , or the reverse sequence. PK blood samples were taken up to Day 9 for oPac+E and Day 5 for IVP.

RESULTS

Forty-two patients were enrolled; 35 completed both treatment periods. AUC_0-∞ was 5033.5 ± 1401.1 ng.h/mL for oPac+E and 5595.9 ± 1264.1 ng.h/mL with IVP. The geometric mean ratio (GMR) for AUC was 89.50% (90% CI 83.89-95.50). Mean absolute bioavailability of oPac+E was 12% (CV% = 23%). PK parameters did not change meaningfully after 4 weeks administration of oPac+E in an extension study. G3 treatment-emergent adverse events occurred in seven (18%) pts with oPac+E and two (5%) with IVP. Seventy-five per cent of patients preferred oPac+E over IVP.

CONCLUSIONS

GMR for AUC was within the predefined acceptable range of 80-125% for demonstrating equivalence. oPac+E is tolerable and there is no evidence of P-gp induction with repeat administration. With further study, oPac+E could be an alternative to IVP.

The Use of Real-World Evidence for Oral Chemotherapies in Breast Cancer

Almost all patients with breast cancer will eventually receive chemotherapy drugs, the majority of which are administered as IV infusions. Real-world evidence indicates that while current treatment paradigms vary considerably from guideline recommendations, there is an increasing trend towards a preference for oral oncolytics among patients with breast cancer. Recent data have shown that oral anticancer therapeutics represent 25% of the oncology drug market share and that there is a high demand for these agents. Therefore, oral formulations of chemotherapy agents such as paclitaxel are currently under development. Although oral oncolytics are associated with several advantages over conventional intravenous drugs, maintaining adherence to therapy is a major barrier in achieving improved outcomes with these agents. Advanced practitioners can facilitate improved adherence to oral oncolytics by integrating evidence into practice to support better education and communication strategies to address patient concerns, overcome key hurdles, and ultimately, empower patients.

Effect of Food on the Pharmacokinetics of the Oral Docetaxel Tablet Formulation ModraDoc006 Combined with Ritonavir (ModraDoc006/r) in Patients with Advanced Solid Tumours

INTRODUCTION

ModraDoc006 is a novel docetaxel tablet formulation that is co-administrated with the cytochrome P450 3A4 and P-glycoprotein inhibitor ritonavir (r): ModraDoc006/r.

OBJECTIVES

This study evaluated the effect of food consumed prior to administration of ModraDoc006/r on the pharmacokinetics of docetaxel and ritonavir.

METHODS

Patients with advanced solid tumours were enrolled in this randomized crossover study to receive ModraDoc006/r in a fasted state in week 1 and after a standardized high-fat meal in week 2 and vice versa. Pharmacokinetic sampling was conducted until 48 h after both study drug administrations. Docetaxel and ritonavir plasma concentrations were determined using liquid chromatography with tandem mass spectrometry. Safety was evaluated with the Common Terminology Criteria for Adverse Events, version 4.03.

RESULTS

In total, 16 patients completed the food-effect study. The geometric mean ratio (GMR) for the docetaxel area under the plasma concentration-time curve (AUC)0-48, AUC0-inf and maximum concentration (Cmax) were 1.11 (90% confidence interval [CI] 0.93-1.33), 1.19 (90% CI 1.00-1.41) and 1.07 (90% CI 0.81-1.42) in fed versus fasted conditions, respectively. For the ritonavir Cmax, the GMR was 0.79 (90% CI 0.69-0.90), whereas the AUC0-48 and AUC0-inf were bioequivalent. The most frequent treatment-related toxicities were grade ≤ 2 diarrhoea and fatigue. Hypokalaemia was the only observed treatment-related grade 3 toxicity.

CONCLUSIONS

The docetaxel and ritonavir exposure were not bioequivalent, as consumption of a high-fat meal prior to administration of ModraDoc006/r resulted in a slightly higher docetaxel exposure and lower ritonavir Cmax. Since docetaxel exposure is the only clinically relevant parameter in our patient population, the overall conclusion is that combined ModraDoc006 and ritonavir treatment may be slightly affected by concomitant intake of a high-fat meal. In view of the small effect, it is most likely that the intake of a light meal will not affect the systemic exposure to docetaxel. CLINICALTRIALS.

GOV IDENTIFIER

NCT03147378, date of registration: May 10 2017.

HM30181A, a potent P-glycoprotein inhibitor, potentiates the absorption and in vivo antitumor efficacy of paclitaxel in an orthotopic brain tumor model

Objective:

Delivery of chemotherapeutic drugs to the brain has remained a major obstacle in the treatment of glioma, owing to the presence of the blood-brain barrier and the activity of P-gp, which pumps its substrate back into the systemic circulation. The aim of the present study was to develop an intravenous formulation of HM30181A (HM) to inhibit P-gp in the brain to effectively deliver paclitaxel (PTX) for the treatment of malignant glioma.

Methods:

Two formulations of solubilized HM were designed on the basis of different solid dispersion strategies: i) spray-drying [polyvinlypyrrolidone (PVP)-HM] and ii) solvent evaporation [HP-β-cyclodextrin (cyclodextrin)-HM]. The P-gp inhibition of these 2 formulations was assessed on the basis of rhodamine 123 uptake in cancer cells. Blood and brain pharmacokinetic parameters were also determined, and the antitumor effect of cyclodextrin-HM with PTX was evaluated in an orthotopic glioma xenograft mouse model.

Results:

Although both PVP-HM and cyclodextrin-HM formulations showed promising P-gp inhibition activity in vitro, cyclodextrin-HM had a higher maximum tolerated dose in mice than did PVP-HM. Pharmacokinetic study of cyclodextrin-HM revealed a plasma concentration plateau at 20 mg/kg, and the mice began to lose weight at doses above this level. Cyclodextrin-HM (10 mg/kg) administered with PTX at 10 mg/kg showed optimal antitumor activity in a mouse model, according to both tumor volume measurement and survival time (P < 0.05).

Conclusions:

In a mouse orthotopic brain tumor model, the intravenous co-administration of cyclodextrin-HM with PTX showed potent antitumor effects and therefore may have potential for glioma therapy in humans.

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.

No relation between docetaxel administration route and high-grade diarrhea incidence

Oral administration of docetaxel in combination with the CYP3A4 inhibitor ritonavir is used in clinical trials to improve oral bioavailability of docetaxel. Diarrhea was the most commonly observed and dose-limiting toxicity. This study combined preclinical and clinical data and investigated incidence, severity and cause of oral docetaxel-induced diarrhea. In this study, incidence and severity of diarrhea in patients were compared to exposure to orally administered docetaxel. Intestinal toxicity after oral or intraperitoneal administration of docetaxel was further explored in mice lacking Cyp3a and mice lacking both Cyp3a and P-glycoprotein. In patients, severity of diarrhea increased significantly with an increase in AUC and Cmax (P = .035 and P = .025, respectively), but not with an increase in the orally administered dose (P = .11). Furthermore, incidence of grade 3/4 diarrhea after oral docetaxel administration was similar as reported after intravenous docetaxel administration. Intestinal toxicity in mice was only observed at high systemic exposure to docetaxel and was similar after oral and intraperitoneal administration of docetaxel. In conclusion, our data show that the onset of severe diarrhea after oral administration of docetaxel in humans is similar after oral and intravenous administration of docetaxel and is caused by the concentration of docetaxel in the systemic blood circulation. Mouse experiments confirmed that intestinal toxicity is caused by a high systemic exposure and not by local intestinal exposure. Severe diarrhea in patients after oral docetaxel is reversible and is not related to the route of administration of docetaxel.

Quantification of the pharmacokinetic-toxicodynamic relationship of oral docetaxel co-administered with ritonavir

Introduction Oral formulations of docetaxel have successfully been developed as an alternative for intravenous administration. Co-administration with the enzyme inhibitor ritonavir boosts the docetaxel plasma exposure. In dose-escalation trials, the maximum tolerated doses for two different dosing regimens were established and dose-limiting toxicities (DLTs) were recorded. The aim of current analysis was to develop a pharmacokinetic (PK)-toxicodynamic (TOX) model to quantify the relationship between docetaxel plasma exposure and DLTs. Methods A total of 85 patients was included in the current analysis, 18 patients showed a DLT in the four-week observation period. A PK-TOX model was developed and simulations based on the PK-TOX model were performed. Results The final PK-TOX model was characterized by an effect compartment representing the toxic effect of docetaxel, which was linked to the probability of developing a DLT. Simulations of once-weekly, once-daily 60 mg and once-weekly, twice-daily 30 mg followed by 20 mg of oral docetaxel suggested that 14% and 34% of patients, respectively, would have a probability >25% to develop a DLT in a four-week period. Conclusions A PK-TOX model was successfully developed. This model can be used to evaluate the probability of developing a DLT following treatment with oral docetaxel and ritonavir in different dosing regimens.

Ionically Cross-Linked Chitosan Nanoparticles for Sustained Delivery of Docetaxel: Fabrication, Post-Formulation and Acute Oral Toxicity Evaluation

Introduction

Polymeric nanoparticles are potential carriers for the efficient delivery of hydrophilic and hydrophobic drugs due to their multifaceted applications. Docetaxel is relatively less hydrophobic and twice as potent as paclitaxel. Like other taxane chemotherapeutic agents, docetaxel is not well tolerated and shows toxicity in the patients. Nanoencapsulation of potent chemotherapeutic agents has been shown to improve tolerability and therapeutic outcome. Therefore, the present study was designed to fabricate chitosan and sodium tripolyphosphate (STPP) based on ionically cross-linked nanoparticles for sustained release of docetaxel.

Methods

Nanoparticles were prepared by the ionic-gelation method by dropwise addition of the STPP solution into the chitosan solution in different ratios. CNPs were characterized for post-formulation parameters like size, zeta potential, scanning electron microscope (SEM), FTIR, DSC/TGA, pXRD, and in-vitro drug release, as well as for acute oral toxicity studies in Wistar rats.

Results and discussion

The optimized docetaxel loaded polymeric nanoparticles were in the size range (172.6nm–479.65 nm), and zeta potential (30.45–35.95 mV) required to achieve enhanced permeation and retention effect. In addition, scanning electron microscopy revealed rough and porous surface, whereas, FTIR revealed the compatible polymeric nanoparticles. Likewise, the thermal stability was ensured through DSC and TG analysis, and powder X-ray diffraction analysis exhibited solid-state stability of the docetaxel loaded nanoparticles. The in-vitro drug release evaluation in phosphate buffer saline (pH 7.4) showed sustained release pattern, i.e. 51.57–69.93% within 24 hrs. The data were fitted to different release kinetic models which showed Fickian diffusion as a predominant release mechanism (R²= 0.9734–0.9786, n= 0.264–0.340). Acceptable tolerability was exhibited by acute oral toxicity in rabbits and no abnormality was noted in growth, behavior, blood biochemistry or histology and function of vital organs.

Conclusion

Ionically cross-linked chitosan nanoparticles are non-toxic and biocompatible drug delivery systems for sustained release of chemotherapeutic agents, such as docetaxel.

Complex systems that incorporate cyclodextrins to get materials for some specific applications

Cyclodextrins (CDs) are a family of biodegradable cyclic hydrocarbons composed of α-(1,4) linked glucopyranose subunits, the more common containing 6, 7 or 8 glucose units are named α, β and γ-cyclodextrins respectively. Since the discovery of CDs, they have attracted interest among scientists and the first studies were about the properties of the native compounds and in particular their use as catalysts of organic reactions. Characteristics features of different types of cyclodextrins stimulated investigation in different areas of research, due to its non-toxic and non-inmunogenic properties and also to the development of an improved industrial production. In this way, many materials with important properties have been developed. This mini-review will focus on chemical systems that use cyclodextrins, whatever linked covalently or mediated by the non covalent interactions, to build complex systems developed mainly during the last five years.

Basic principles of drug delivery systems - the case of paclitaxel

Cancer is the second cause of death worldwide, exceeded only by cardiovascular diseases. The prevalent treatment currently used against metastatic cancer is chemotherapy. Among the most studied drugs that inhibit neoplastic cells from acquiring unlimited replicative ability (a hallmark of cancer) are the taxanes. They operate via a unique molecular mechanism affecting mitosis. In this review, we show this mechanism for one of them, paclitaxel, and for other (non-taxanes) anti-mitotic drugs. However, the use of paclitaxel is seriously limited (its bioavailability is <10%) due to several long-standing challenges: its poor water solubility (0.3 μg/mL), its being a substrate for the efflux multidrug transporter P-gp, and, in the case of oral delivery, its first-pass metabolism by certain enzymes. Adequate delivery methods are therefore required to enhance the anti-tumor activity of paclitaxel. Thus, we have also reviewed drug delivery strategies in light of the various physical, chemical, and enzymatic obstacles facing the (especially oral) delivery of drugs in general and paclitaxel in particular. Among the powerful and versatile platforms that have been developed and achieved unprecedented opportunities as drug carriers, microemulsions might have great potential for this aim. This is due to properties such as thermodynamic stability (leading to long shelf-life), increased drug solubilization, and ease of preparation and administration. In this review, we define microemulsions and nanoemulsions, analyze their pertinent properties, and review the results of several drug delivery carriers based on these systems.

Advancements in the oral delivery of Docetaxel: challenges, current state-of-the-art and future trends

The oral delivery of cancer chemotherapeutic drugs is challenging due to low bioavailability, gastrointestinal side effects, first-pass metabolism and P-glycoprotein efflux pumps. Thus, chemotherapeutic drugs, including Docetaxel, are administered via an intravenous route, which poses many disadvantages of its own. Recent advances in pharmaceutical research have focused on designing new and efficient drug delivery systems for site-specific targeting, thus leading to improved bioavailability and pharmacokinetics. A decent number of studies have been reported for the safe and effective oral delivery of Docetaxel. These nanocarriers, including liposomes, polymeric nanoparticles, metallic nanoparticles, hybrid nanoparticles, dendrimers and so on, have shown promising results in research papers and clinical trials. The present article comprehensively reviews the research efforts made so far in designing various advancements in the oral delivery of Docetaxel. Different strategies to improve oral bioavailability, prevent first-pass metabolism and inhibition of efflux pumping leading to improved pharmacokinetics and anticancer activity are discussed. The final portion of this review article presents key issues such as safety of nanomaterials, regulatory approval and future trends in nanomedicine research.

Safety of Polysorbate 80 in the Oncology Setting

Polysorbate 80 is a synthetic nonionic surfactant used as an excipient in drug formulation. Various products formulated with polysorbate 80 are used in the oncology setting for chemotherapy, supportive care, or prevention, including docetaxel, epoetin/darbepoetin, and fosaprepitant. However, polysorbate 80, like some other surfactants, is not an inert compound and has been implicated in a number of systemic and injection- and infusion-site adverse events (ISAEs). The current formulation of intravenous fosaprepitant has been associated with an increased risk of hypersensitivity systemic reactions (HSRs). Factors that have been associated with an increased risk of fosaprepitant-related ISAEs include the site of administration (peripheral vs. central venous), coadministration of anthracycline-based chemotherapy, number of chemotherapy cycles or fosaprepitant doses, and concentration of fosaprepitant administered. Recently, two polysorbate 80-free agents have been approved: intravenous rolapitant, which is a neurokinin 1 (NK-1) receptor antagonist formulated with the synthetic surfactant polyoxyl 15 hydroxystearate, and intravenous HTX-019, which is a novel NK-1 receptor antagonist free of synthetic surfactants. Alternative formulations will obviate the polysorbate 80-associated ISAEs and HSRs and should improve overall management of chemotherapy-induced nausea and vomiting.Funding Heron Therapeutics, Inc.

Activity Essential Residue Analysis of Taxoid 10β-O-Acetyl Transferase for Enzymatic Synthesis of Baccatin

Taxoid 10β-O-acetyl transferase (DBAT) is a key enzyme in the biosynthesis of the famous anticancer drug paclitaxel, which catalyses the formation of baccatin III from 10-deacetylbaccatin III (10-DAB). However, the activity essential residues of the enzyme are still unknown, and the acylation mechanism from its natural substrate 10-deacetylbaccatin III and acetyl CoA to baccatin III remains unclear. In this study, the homology modelling, molecular docking, site-directed mutagenesis, and kinetic parameter determination of the enzyme were carried out. The results showed that the enzyme mutant DBAT^H162A resulted in complete loss of enzymatic activity, suggesting that the residue histidine at 162 was essential to DBAT activity. Residues D166 and R363 which were located in the pocket of the enzyme by homology modelling and molecular docking were also important for DBAT activity through the site-directed mutations. Furthermore, four amino acid residues including S31 and D34 from motif SXXD, D372 and G376 from motif DFGWG also played important roles on acylation. This was the first report of the elucidation of the activity essential residues of DBAT, making it possible for the further structural-based re-design of the enzyme for efficient biotransformation of baccatin III and paclitaxel.

Pharmacology and in vivo efficacy of pyridine-pyrimidine amides that inhibit microtubule polymerization

Microtubule-targeting agents are important tools in cancer treatment. Generating novel microtubule targeting agents with novel pharmacology could dramatically expand the utility of this class of drugs. Here we characterize the pharmacology of recently described small molecule microtubule polymerization inhibitors. Pharmacokinetic experiments show oral bioavailability through gastric absorption. In vitro assays designed to predict absorption, distribution, metabolism, and excretion (ADME) and safety reveal a scaffold that is metabolically stable, evades P-glycoprotein, does not inhibit CYP enzymes, occurs as a significant free fraction in serum, and has exceptionally high cellular permeability. Together with in vivo efficacy models, pharmacology supports further development as a treatment for solid tumors.

Inherent formulation issues of kinase inhibitors

The small molecular Kinase Inhibitor (smKI) drug class is very promising and rapidly expanding. All of these drugs are administered orally. The clear relationship between structure and function has led to drugs with a general low intrinsic solubility. The majority of the commercial pharmaceutical formulations of the smKIs are physical mixtures that are limited by the low drug solubility of a salt form. This class of drugs is therefore characterized by an impaired and variable bioavailability rendering them costly and their therapies suboptimal. New formulations are sparingly being reported in literature and patents. The presented data suggests that continued research into formulation design can help to develop more efficient and cost-effective smKI formulation. Moreover, it may also be of help in the future design of the formulations of new smKIs.

In vitro and in vivo effects of morin on the intestinal absorption and pharmacokinetics of olmesartan medoxomil solid dispersions

PURPOSE

In-situ evaluation to corroborate morin effects on the intestinal absorption and pharmacokinetic behavior of freeze-dried OLM-loaded solid dispersions with Caco-2 and in-vivo studies Methods: Intestinal transport and absorption studies were examined by Caco-2 permeability, in-situ single pass perfusion and closed-loop models along with in-vivo pharmacokinetic studies to evaluate and confirm the effect of P-gp-mediated activity of morin. We evaluated the intestinal membrane damage in the presence of morin by measuring the release of protein and lactate dehydrogenase (LDH) followed by using qualitative and quantitative morphometric analysis to describe the surface characteristics of intestinal epithelium.

RESULTS

Morin showed the highest P_eff value 13.8 ± 0.34 × 10^-6cm/s in jejunum than ileum (p < .01) at 100 µM with absorption enhancement of 1.31-fold together with enhanced (p < .01) secretory transport of 6.27 ± 0.27 × 10 ^-6cm/s in Caco-2 monolayer cells. Our findings noticed 2.37 (in-situ); 2.39 (in-vivo) and 1.43 (in-situ); 1.36 (in-vivo) fold increase in AUC_0-t with elevated C_max and shortened T_max for freeze-dried solid dispersion in the presence of morin as compared to pure OLM and freeze-dried solid dispersions without morin, respectively.

CONCLUSIONS

Our study demonstrated that increased solubilization through freeze-dried OLM-loaded solid dispersion together with efflux inhibition improved intestinal permeability to one system that might lead to novel solubilization and efflux pump inhibition as a novel alternative potential to increase oral absorption and bioavailability of OLM.

Pharmaceutical development of an oral tablet formulation containing a spray dried amorphous solid dispersion of docetaxel or paclitaxel

Previously, it was shown in Phase I clinical trials that solubility-limited oral absorption of docetaxel and paclitaxel can be drastically improved with a freeze dried solid dispersion (fdSD). These formulations, however, are unfavorable for further clinical research because of limitations in amorphicity of SD and scalability of the production process. To resolve this, a spray drying method for an SD (spSD) containing docetaxel or paclitaxel and subsequently drug products were developed. Highest saturation solubility (Smax), precipitation onset time (Tprecip), amorphicity, purity, residual solvents, yield/efficiency and powder flow of spSDs were studied. Drug products were monitored for purity/content and dissolution during 24 months at +15-25°C. Docetaxel spSD Smax was equal to that of fdSD but Tprecip was 3 times longer. Paclitaxel spSD Smax was 30% increased but Tprecip was equal to fdSD. spSDs were fully amorphous, >99% pure, <5% residual solvents, mean batch yield was 100g and 84%. spSDs had poor powder flow characteristics, which could not be resolved by changing settings, but by using 75% lactose as diluent. The drug product was a tablet with docetaxel or paclitaxel spSD and was stable for at least 24 months. Spray drying is feasible for the production of SD of docetaxel or paclitaxel for upcoming clinical trials.

An investigation of nitrile transforming enzymes in the chemo-enzymatic synthesis of the taxol sidechain

Paclitaxel (taxol) is an antimicrotubule agent widely used in the treatment of cancer. Taxol is prepared in a semisynthetic route by coupling the N-benzoyl-(2R,3S)-3-phenylisoserine sidechain to the baccatin III core structure. Precursors of the taxol sidechain have previously been prepared in chemoenzymatic approaches using acylases, lipases, and reductases, mostly featuring the enantioselective, enzymatic step early in the reaction pathway. Here, nitrile hydrolysing enzymes, namely nitrile hydratases and nitrilases, are investigated for the enzymatic hydrolysis of two different sidechain precursors. Both sidechain precursors, an openchain α-hydroxy-β-amino nitrile and a cyanodihydrooxazole, are suitable for coupling to baccatin III directly after the enzymatic step. An extensive set of nitrilases and nitrile hydratases was screened towards their activity and selectivity in the hydrolysis of two taxol sidechain precursors and their epimers. A number of nitrilases and nitrile hydratases converted both sidechain precursors and their epimers.

Piperlongumine for Enhancing Oral Bioavailability and Cytotoxicity of Docetaxel in Triple-Negative Breast Cancer

Very low oral bioavailability due to extensive pre-systemic metabolism and P-gp efflux has constrained the oral metronomic chemotherapy of docetaxel (DTX). There is tremendous need of compounds facilitating oral delivery of DTX. The research was aimed to investigate the effect of piperlongumine (PPL) on human liver microsomal metabolism, Caco-2 permeability, and cytotoxicity of DTX in triple-negative breast cancer cell lines. Reduction in testosterone and DTX metabolism (twofold increase in half-life) by PPL was comparable to the standard CYP3A4 inhibitor, cyclosporine A. P-gp efflux ratio of DTX across caco-2 monolayer was reduced from 2.37 to 1.52 on co-incubation with PPL. The IC50 value of DTX was reduced three to five times and combination index values in all the cell lines were below 0.6. PPL at non-cytotoxic concentration showed significant enhancement of the antimigration effect of DTX. Expression of tumor markers such as survivin, bcl2, C-myc, and cyclin D1 were downregulated to a great extent with enhanced p53 expression when treated with combination instead of individual drug. Co-treatment with PPL led to 1.68-fold enhancement in DTX bioavailability in SD rats. PPL could be a potential candidate in overcoming the obstacles associated with oral DTX delivery with synergistic anticancer activity.

Treatment regimens of classical and newer taxanes

The classical taxanes (paclitaxel, docetaxel), the newer taxane cabazitaxel and the nanoparticle-bound nab-paclitaxel are among the most widely used anticancer drugs. The taxanes share the characteristics of extensive hepatic metabolism and biliary excretion, the need for dose adaptation in patients with liver dysfunction, and a substantial pharmacokinetic variability even after taking into account known covariates. Data from clinical studies suggest that optimal scheduling of the taxanes is dependent not only on the specific taxane compound, but also on the tumor type and line of treatment. Still, the optimal dosing regimen (weekly vs 3 weekly) and optimal dose of the taxanes are controversial, as is the value of pharmacological personalization of taxane dosing. In this article, an overview is given on the pharmacological properties of the taxanes, including metabolism, pharmacokinetics-pharmacodynamics and aspects in the clinical use of taxanes. The latter includes the ongoing debate on the most active and safe regimen, the recommended initial dose and the issue of therapeutic drug dosing.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

Paclitaxel and Its Evolving Role in the Management of Ovarian Cancer

Paclitaxel, a class of taxane with microtubule stabilising ability, has remained with platinum based therapy, the standard care for primary ovarian cancer management. A deeper understanding of the immunological basis and other potential mechanisms of action together with new dosing schedules and/or routes of administration may potentiate its clinical benefit. Newer forms of taxanes, with better safety profiles and higher intratumoural cytotoxicity, have yet to demonstrate clinical superiority over the parent compound.

Paclitaxel and Its Evolving Role in the Management of Ovarian Cancer

Paclitaxel, a class of taxane with microtubule stabilising ability, has remained with platinum based therapy, the standard care for primary ovarian cancer management. A deeper understanding of the immunological basis and other potential mechanisms of action together with new dosing schedules and/or routes of administration may potentiate its clinical benefit. Newer forms of taxanes, with better safety profiles and higher intratumoural cytotoxicity, have yet to demonstrate clinical superiority over the parent compound.

Paclitaxel and Its Evolving Role in the Management of Ovarian Cancer

Paclitaxel, a class of taxane with microtubule stabilising ability, has remained with platinum based therapy, the standard care for primary ovarian cancer management. A deeper understanding of the immunological basis and other potential mechanisms of action together with new dosing schedules and/or routes of administration may potentiate its clinical benefit. Newer forms of taxanes, with better safety profiles and higher intratumoural cytotoxicity, have yet to demonstrate clinical superiority over the parent compound.

Pharmacokinetic synergy from the taxane extract of Taxus chinensis improves the bioavailability of paclitaxel

BACKGROUND

Taxus chinensis (Pilger) Rehd is widely distributed in China and the northern hemisphere, and the most popular medicinal component isolated from Taxus chinensis is paclitaxel (PTX), which has now become the first-line chemotherapeutic drug for breast cancer and ovarian cancer. Oral administration of pure PTX as a potential anti-cancer agent is compromised by low bioavailability.

HYPOTHESIS/PURPOSE

In the clinical practice of traditional Chinese medicine, drug co-administration in the form of mixtures or formula could achieve pharmacokinetic/pharmacodynamic synergies. In this study, we aimed to investigate whether there exist any 'inherent' phytochemical synergy from Taxus chinensis extract that could improve PTX bioavailability.

STUDY DESIGN

Pharmacokinetic study of PTX after oral administration of Taxus chinensis extracts or single PTX was performed. In addition, comparative cytotoxic studies were carried out on the MCF-7 breast cancer cell lines.

METHODS

The plasma concentrations of PTX were determined using a validated high performance chromatography tandem mass spectrometry method. The cytotoxicity was compared using the MTT assay.

RESULTS

Oral administration of taxane fractions isolated from Taxus chinensis (containing 17.2% PTX) could achieve remarkably higher blood concentration and systemic exposure of PTX in rats, while the retention of PTX was significantly improved. Further tissue distribution analysis revealed that the penetration of PTX into major tissues was drastically increased compared with that of single PTX. In addition, in MCF-7 cells, the co-existing components in taxane mixtures could strengthen the inhibitory effects of PTX on tumor cell proliferation.

CONCLUSION

Together, these results support that administration of PTX in the form of taxane mixtures may become a novel approach to improve the poor bioavailability of PTX. Moreover, the inherent synergy from Taxus chinensis taxane extracts promises a novel strategy to strengthen PTX efficacy.

Inter-patient variability in docetaxel pharmacokinetics: A review

Docetaxel is a frequently used chemotherapeutic agent in the treatment of solid cancers. Because of the large inter-individual variability (IIV) in the pharmacokinetics (PK) of docetaxel, it is challenging to determine the optimal dose in individual patients in order to achieve optimal efficacy and acceptable toxicity. Despite the established correlation between systemic docetaxel exposure and efficacy, the precise factors influencing docetaxel PK are not yet completely understood. This review article highlights currently known factors that influence docetaxel PK, and focusses on those that are clinically relevant. For example, liver impairment should be taken into account when calculating docetaxel dosages as this may decrease docetaxel clearance. In addition, drug-drug interactions may be of distinct clinical importance when using docetaxel. Particularly, drugs strongly inhibiting CYP3A4 such as ketoconazole should not be concurrently administered without dose modification, as they may decrease the clearance of docetaxel. Gender, castration status, and menopausal status might be of importance as potential factors influencing docetaxel PK. The role of pharmacogenetics in predicting docetaxel PK is still limited, since no polymorphisms of clinical importance have yet been established.

Influence of multidrug resistance and drug transport proteins on chemotherapy drug metabolism

INTRODUCTION

Chemotherapy involving the use of anticancer drugs remains an important strategy in the overall management of patients with metastatic cancer. Acquisition of multidrug resistance remains a major impediment to successful chemotherapy. Drug transporters in cell membranes and intracellular drug metabolizing enzymes contribute to the resistance phenotype and determine the pharmacokinetics of anticancer drugs in the body.

AREAS COVERED

ATP-binding cassette (ABC) transporters mediate the transport of endogenous metabolites and xenobiotics including cytotoxic drugs out of cells. Solute carrier (SLC) transporters mediate the influx of cytotoxic drugs into cells. This review focuses on the substrate interaction of these transporters, on their biology and what role they play together with drug metabolizing enzymes in eliminating therapeutic drugs from cells.

EXPERT OPINION

The majority of anticancer drugs are substrates for the ABC transporter and SLC transporter families. Together, these proteins have the ability to control the influx and the efflux of structurally unrelated chemotherapeutic drugs, thereby modulating the intracellular drug concentration. These interactions have important clinical implications for chemotherapy because ultimately they determine therapeutic efficacy, disease progression/relapse and the success or failure of patient treatment.

Variability in bioavailability of small molecular tyrosine kinase inhibitors

Small molecular tyrosine kinase inhibitors (smTKIs) are in the centre of the very quickly expanding area of personalized chemotherapy and oral applicability thereof. The number of drugs in this class is rapidly growing, with twenty current approvals by both the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). The drugs are, however, generally characterized by a poor oral, and thus variable, bioavailability. This results in significant variation in plasma levels and exposure. The cause is a complex interplay of factors, including poor aqueous solubility, issued permeability, membrane transport and enzymatic metabolism. Additionally, food and drug-drug interactions can play a significant role. The issues related with an impaired bioavailability generally receive little attention. To the best of our knowledge, this article is the first to provide an overview of the factors that determine the bioavailability of the smTKIs.

Metabolism of the taxanes including nab-paclitaxel

INTRODUCTION

The classical taxanes (paclitaxel, docetaxel), the newer taxane cabazitaxel and the nanoparticle-bound nab-paclitaxel are among the most widely used anticancer drugs. Despite years of research, the optimal dosing regimen (weekly vs 3-weekly) and optimal dose is still controversial, as is the value of pharmacological personalization of taxane dosing.

AREAS COVERED

This review provides an overview of the pharmacological properties of the taxanes, including metabolism, pharmacokinetics-pharmacodynamics and aspects in the clinical use of taxanes. The latter includes the ongoing debate on the most active and safe regimen (paclitaxel, docetaxel, nab-paclitaxel), the recommended initial dose (cabazitaxel) and pharmacological dosing individualization.

EXPERT OPINION

Taxanes share the characteristics of extensive hepatic metabolism and biliary excretion, the need for dose adaptation in patients with liver dysfunction, and substantial pharmacokinetic variability even after taking into account known covariates. Data from clinical studies suggest that optimal scheduling of the taxanes is dependent not only on the specific taxane compound, but also on the tumor type and line of treatment. Finally, treating oncologists should be aware of the substantial risk for drug-drug interactions that is a direct consequence of the complex hepatic metabolism of the taxanes.

The design and discovery of water soluble 4-substituted-2,6-dimethylfuro[2,3-d]pyrimidines as multitargeted receptor tyrosine kinase inhibitors and microtubule targeting antitumor agents

The design, synthesis and biological evaluations of fourteen 4-substituted 2,6-dimethylfuro[2,3-d]pyrimidines are reported. Four compounds (11-13, 15) inhibit vascular endothelial growth factor receptor-2 (VEGFR-2), platelet-derived growth factor receptor β (PDGFR-β), and target tubulin leading to cytotoxicity. Compound 11 has nanomolar potency, comparable to sunitinib and semaxinib, against tumor cell lines overexpressing VEGFR-2 and PDGFR-β. Further, 11 binds at the colchicine site on tubulin, depolymerizes cellular microtubules and inhibits purified tubulin assembly and overcomes both βIII-tubulin and P-glycoprotein-mediated drug resistance, and initiates mitotic arrest leading to apoptosis. In vivo, its HCl salt, 21, reduced tumor size and vascularity in xenograft and allograft murine models and was superior to docetaxel and sunitinib, without overt toxicity. Thus 21 affords potential combination chemotherapy in a single agent.