Fluorine-Containing Taxoid Anticancer Agents and Their Tumor-Targeted Drug Delivery

Strategies for the drug discovery and development of taxane anticancer therapeutics

INTRODUCTION

Paclitaxel and docetaxel have been extensively used in the clinic over the past three decades. Although the patents of these first-generation taxanes have expired, their clinical applications, particularly new formulations and combination therapies, are under active investigations. Inspired by the notable success of Abraxane and Lipusu, new formulations have been extensively developed. In parallel, to overcome multidrug resistance (MDR) and to eradicate cancer stem cells, immense efforts have been made on the discovery and development of new-generation taxanes with improved potency and superior pharmacological properties.

AREAS COVERED

This review covers (a) natural sources of advanced intermediates used for semi-synthesis of taxane API, (b) new formulations, (c) the major issues of FDA approved taxanes, (d) the design and development of next-generation taxanes, (e) new mechanisms of action, and (f) a variety of taxane-based drug delivery systems.

EXPERT OPINION

As the highly potent next-generation taxanes can eradicate cancer stem cells and overcome MDR, the priority is to develop these compounds as an integral part of cancer therapy, especially for pancreatic, colon and prostate cancers which hardly respond to checkpoint inhibitors. In order to mitigate undesirable side effects, the exploration of effective nanoformulations and tumor-targeted drug delivery systems are essential.

Updates and Original Case Studies Focused on the NMR-Linked Metabolomics Analysis of Human Oral Fluids Part II: Applications to the Diagnosis and Prognostic Monitoring of Oral and Systemic Cancers

Human saliva offers many advantages over other biofluids regarding its use and value as a bioanalytical medium for the identification and prognostic monitoring of human diseases, mainly because its collection is largely non-invasive, is relatively cheap, and does not require any major clinical supervision, nor supervisory input. Indeed, participants donating this biofluid for such purposes, including the identification, validation and quantification of surrogate biomarkers, may easily self-collect such samples in their homes following the provision of full collection details to them by researchers. In this report, the authors have focused on the applications of metabolomics technologies to the diagnosis and progressive severity monitoring of human cancer conditions, firstly oral cancers (e.g., oral cavity squamous cell carcinoma), and secondly extra-oral (systemic) cancers such as lung, breast and prostate cancers. For each publication reviewed, the authors provide a detailed evaluation and critical appraisal of the experimental design, sample size, ease of sample collection (usually but not exclusively as whole mouth saliva (WMS)), their transport, length of storage and preparation for analysis. Moreover, recommended protocols for the optimisation of NMR pulse sequences for analysis, along with the application of methods and techniques for verifying and resonance assignments and validating the quantification of biomolecules responsible, are critically considered. In view of the authors’ specialisms and research interests, the majority of these investigations were conducted using NMR-based metabolomics techniques. The extension of these studies to determinations of metabolic pathways which have been pathologically disturbed in these diseases is also assessed here and reviewed. Where available, data for the monitoring of patients’ responses to chemotherapeutic treatments, and in one case, radiotherapy, are also evaluated herein. Additionally, a novel case study featured evaluates the molecular nature, levels and diagnostic potential of ¹H NMR-detectable salivary ‘acute-phase’ glycoprotein carbohydrate side chains, and/or their monomeric saccharide derivatives, as biomarkers for cancer and inflammatory conditions.

Safe and selective anticancer agents from tetrafluorinated azobenzene-imidazolium ionic liquids: Synthesis, characterization, and cytotoxic effects

A new series of tetrafluorinated azobenzene-imidazolium salts is reported. The azobenzene and imidazolium moieties were functionalized with long alkyl chains and connected via a methylene spacer of varying lengths (n = 3-12). They were characterized using FTIR and NMR spectroscopy, and elemental microanalysis. The cytotoxic potential of these ionic dimers against neuroblastoma (SHSY-5Y), estrogen-positive breast cancer cells (MCF-7), triple-negative breast cancer cells (MDA-MB-231), cervical cancer cells (HeLa), and human skin fibroblasts (Hs27) was evaluated using the MTT assay. The cytotoxicity of these ionic liquids (ILs) was dependent on the spacer length. A cut-off effect was observed, wherein the cytotoxicity of the ILs was enhanced by increasing the nonpolar, hydrophobic spacer length up to a threshold and the potency was leveled off upon chain elongation. All ILs exhibited selective and remarkable inhibition potentials against HeLa cells in a dose-dependent manner, which was 2-22 times stronger than that of etoposide, a clinical anticancer drug. These ILs were less toxic toward skin fibroblasts as implied by much higher IC₅₀ values. The long-spacer ILs (n = 7-10) were very selective toward HeLa cells. They had a broad safety window with selectivity indices ranging between 5.6 and 11.0. The selectivity of these compounds toward HeLa cells may serve as a new strategy for the design and development of safe and effective chemotherapeutics.

Fluorine (19F) Nuclear Magnetic Resonance Spectroscopy For Real Time Maraviroc Analysis From Microparticulate Systems

Real time analysis of pharmaceuticals in controlled release nano and microsystems remains a challenge. It is hypothesized that fluorine 19 nuclear magnetic resonance (¹⁹F qNMR) can be used for real time quantification and in vitro release of maraviroc (MVC). The release of maraviroc was analyzed in simulated body fluids from spray dried sodium alginate microspheres (MS) using the ¹⁹F qNMR method. Calibration produced a linearity curve in concentration range (0.42 mg/ml - 15 mg/ml), and the limits of detection and quantification values were 0.97 mg/ml and 2.93 mg/ml, respectively. The method was confirmed to be specific, accurate, precise, and robust (%RSE > 2%). MVC was successfully microencapsulated (18% w/w) as evidenced by the FT-IR spectra and SEM images. The MS had an average diameter of 2.522 ± 0.15 μm, with a zeta potential of - 61.31 ± 2.1 mV. Overall, the ¹⁹F qNMR method enabled a direct and real time quantification of MVC for an efficient drug release kinetics. This approach could be potentially used to quantify fluorinated drug potency, purity, and stability, and evaluate in vitro release kinetic from different formulations.

An Overview of Recent Advances in Biological and Pharmaceutical Developments of Fluoro-containing Drugs

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This review article provides a brief assessment of the biological and pharmaceutical developments of fluorinated drugs. It also discusses possible impacts on the further development of new fluoro-containing pharmaceuticals. Structural aspects of new drug-candidates currently under development and their biological properties, therapeutic potential and syntheses are critically evaluated

Access to Unprotected β-Fluoroalkyl β-Amino Acids and Their α-Hydroxy Derivatives

Unprotected β-(het)aryl-β-fluoroalkyl β-amino acids and their α-hydroxy derivatives can be readily obtained using a decarboxylative Mannich-type reaction without protection/deprotection steps. This protocol utilizes lithium hexamethyldisilazide and (het)arylfluoroalkyl ketones to generate NH-ketimine intermediates. The mild reaction conditions allow the preparation of original fluorinated β-amino acids as useful building blocks in a practical and scalable manner.

Quest for Efficacious Next-Generation Taxoid Anticancer Agents and Their Tumor-Targeted Delivery

Paclitaxel and docetaxel are among the most widely used chemotherapeutic drugs against various types of cancer. However, these drugs cause undesirable side effects as well as drug resistance. Therefore, it is essential to develop next-generation taxoid anticancer agents with better pharmacological properties and improved activity especially against drug-resistant and metastatic cancers. The SAR studies by the authors have led to the development of numerous highly potent novel second- and third-generation taxoids with systematic modifications at the C-2, C-10, and C-3' positions. The third-generation taxoids showed virtually no difference in potency against drug-resistant and drug-sensitive cell lines. Some of the next-generation taxoids also exhibited excellent potency against cancer stem cells. This account summarizes concisely investigations into taxoids over 25 years based on a strong quest for the discovery and development of efficacious next-generation taxoids. Discussed herein are SAR studies on different types of taxoids, a common pharmacophore proposal for microtubule-stabilizing anticancer agents and its interesting history, the identification of the paclitaxel binding site and its bioactive conformation, characteristics of the next-generation taxoids in cancer cell biology, including new aspects of their mechanism of action, and the highly efficacious tumor-targeted drug delivery of potent next-generation taxoids.

Synthesis and biological evaluation of novel steroidal 5α,8α-epidioxyandrost-6-ene-3β-ol-17-(O-phenylacetamide)oxime derivatives as potential anticancer agents

Inspired by the significant anti-cancer activity of our previously screened natural ergosterol peroxide (EP, 1), we synthesized and characterized a series of novel 5α,8α-epidioxyandrost-3β-ol-17-(O-phenylacetamide)oxime derivatives (9a-o). The anti-proliferative activity of the synthesized compounds against human hepatocellular carcinoma cells (HepG2, Sk-Hep1) and human breast cancer cells (MCF-7, MDA-MB231) were investigated. Compounds 9d, 9f, 9h, 9j and 9m displayed good anti-proliferative activity (most IC₅₀<20μM) in vitro. Furthermore, fluorescence imaging showed that the designed coumarin-9d conjugate (12) localized mainly in mitochondria, leading to enhanced anticancer activities over the parent structure.

Strategic Incorporation of Fluorine into Taxoid Anticancer Agents for Medicinal Chemistry and Chemical Biology Studies

This account exemplifies our recent progress on the strategic incorporation of fluorine and organofluorine groups to taxoid anticancer agents and their tumor-targeted drug delivery systems (TTDDSs) for medicinal chemistry and chemical biology studies. Novel 3'-difluorovinyltaxoids were strategically designed to block the metabolism by cytochrome P-450, synthesized, and evaluated for their cytotoxicity against drug-sensitive and multidrug-resistant (MDR) human cancer cell lines. 3'-Difluorovinyltaxoids exhibited impressive activities against these cancer cell lines. More significantly, a representative 3'-difluorovinyltaxoid exhibited 230-33,000 times higher potency than conventional anticancer drugs against cancer stem cell-enriched HCT-116 cell line. Studies on the mechanism of action (MOA) of these fluorotaxoids were performed by tubulin polymerization assay, morphology analysis by electron microscopy (EM) and protein binding assays. Novel ¹⁹F NMR probes, BLT-F₂ and BLT-S-F₆, were designed by strategically incorporating fluorine, CF₃ and CF₃O groups into tumor-targeting drug conjugates. These ¹⁹F-probes were designed and synthesized to investigate the mechanism of linker cleavage and factors that influence their plasma and metabolic stability by real-time ¹⁹F NMR analysis. Time-resolved ¹⁹F NMR study on probe BLT-F₂ revealed a stepwise mechanism for the release of a fluorotaxoid, which might not be detected by other analytical methods. Probe BLT-S-F₆ were very useful to study the stability and reactivity of the drug delivery system in human blood plasma by ¹⁹F NMR. The clean analysis of the linker stability and reactivity of drug conjugates in blood plasma by HPLC and ¹H NMR is very challenging, but the use of ¹⁹F NMR and suitable ¹⁹F probes can provide a practical solution to this problem.

'Dual hit' metabolic modulator LDCA selectively kills cancer cells by efficient competitive inhibition of LDH-A

Herein, we synthesize and elucidate the potential of a novel 'dual hit' molecule, LDCA, to constitutively block lactate dehydrogenase isoform-A (LDH-A) to selectively subvert apoptosis and rigorously attenuate breast tumor progression in a mouse model, comprehensively delineating the therapeutic prospectus of LDCA in the field of cancer metabolics.

Synthesis and anti-cancer evaluation of steroidal diglycoside–pyrazoline hybrids

A new series of pyrazoline-steroidal diglycoside hybrids were synthesized via catalyzed cyclocondensation of the corresponding chalcones, screened for in vitro cytotoxic activity and the SAR deduced.