Tumor-targeting drug delivery of new-generation taxoids

Biotin-functionalized nanoparticles: an overview of recent trends in cancer detection

Electrochemical bio-sensing is a potent and efficient method for converting various biological recognition events into voltage, current, and impedance electrical signals. Biochemical sensors are now a common part of medical applications, such as detecting blood glucose levels, detecting food pathogens, and detecting specific cancers. As an exciting feature, bio-affinity couples, such as proteins with aptamers, ligands, paired nucleotides, and antibodies with antigens, are commonly used as bio-sensitive elements in electrochemical biosensors. Biotin-avidin interactions have been utilized for various purposes in recent years, such as targeting drugs, diagnosing clinically, labeling immunologically, biotechnology, biomedical engineering, and separating or purifying biomolecular compounds. The interaction between biotin and avidin is widely regarded as one of the most robust and reliable noncovalent interactions due to its high bi-affinity and ability to remain selective and accurate under various reaction conditions and bio-molecular attachments. More recently, there have been numerous attempts to develop electrochemical sensors to sense circulating cancer cells and the measurement of intracellular levels of protein thiols, formaldehyde, vitamin-targeted polymers, huwentoxin-I, anti-human antibodies, and a variety of tumor markers (including alpha-fetoprotein, epidermal growth factor receptor, prostate-specific Ag, carcinoembryonic Ag, cancer antigen 125, cancer antigen 15-3, etc.). Still, the non-specific binding of biotin to endogenous biotin-binding proteins present in biological samples can result in false-positive signals and hinder the accurate detection of cancer biomarkers. This review summarizes various categories of biotin-functional nanoparticles designed to detect such biomarkers and highlights some challenges in using them as diagnostic tools.

Interactions of Mn complexes with DNA: the relevance of therapeutic applications towards cancer treatment

Manganese (Mn) is one of the most significant bio-metals that helps the body to form connective tissue, bones, blood clotting factors, and sex hormones. It is necessary for fat and carbohydrate metabolism, calcium absorption, blood sugar regulation, and normal brain and nerve functions. It accelerates the synthesis of proteins, vitamin C, and vitamin B. It is also involved in the catalysis of hematopoiesis, regulation of the endocrine level, and improvement of immune function. Again, Mn metalloenzymes like arginase, glutamine synthetase, phosphoenolpyruvate decarboxylase, and Mn superoxide dismutase (MnSOD) contribute to the metabolism processes and reduce oxidative stress against free radicals. Recent investigations have revealed that synthetic Mn-complexes act as antibacterial and antifungal agents. As a result, chemists and biologists have been actively involved in developing Mn-based drugs for the treatment of various diseases including cancer. Therefore, any therapeutic drugs based on manganese complexes would be invaluable for the treatment of cancer/infectious diseases and could be a better substitute for cisplatin and other related platinum based chemotherapeutic drugs. From this perspective, attempts have been made to discuss the interactions and nuclease activities of Mn(II/III/IV) complexes with DNA through which one can evaluate their therapeutic applications.

Orange-Peel-Derived Nanobiochar for Targeted Cancer Therapy

Cancer-targeted drug delivery systems (DDS) based on carbon nanostructures have shown great promise in cancer therapy due to their ability to selectively recognize specific receptors overexpressed in cancer cells. In this paper, we have explored a green route to synthesize nanobiochar (NBC) endowed with graphene structure from the hydrothermal carbonization (HTC) of orange peels and evaluated the suitability of this nanomaterial as a nanoplatform for cancer therapy. In order to compare the cancer-targeting ability of different widely used targeting ligands (TL), we have conjugated NBC with biotin, riboflavin, folic acid and hyaluronic acid and have tested, in vitro, their biocompatibility and uptake ability towards a human alveolar cancer cell line (A549 cells). The nanosystems which showed the best biological performances-namely, the biotin- and riboflavin- conjugated systems-have been loaded with the poorly water-soluble drug DHF (5,5-dimethyl-6a-phenyl-3-(trimethylsilyl)-6,6a-dihydrofuro[3,2-b]furan-2(5H)-one) and tested for their anticancer activity. The in vitro biological tests demonstrated the ability of both systems to internalize the drug in A549 cells. In particular, the biotin-functionalized NBC caused cell death percentages to more than double with respect to the drug alone. The reported results also highlight the positive effect of the presence of oxygen-containing functional groups, present on the NBC surface, to improve the water dispersion stability of the DDS and thus make the approach of using this nanomaterial as nanocarrier for poorly water-soluble drugs effective.

Biotinylated chitosan macromolecule based nanosystems: A review from chemical design to biological targets

World Health Organization estimates that 30-50% of cancers are preventable by healthy lifestyle choices, early detection and adequate therapy. When the conventional therapeutic strategies are still regulated by the lack of selectivity, multidrug resistance and severe toxic side effects, nanotechnology grants a new frontier for cancer management since it targets cancer cells and spares healthy tissues. This review highlights recent studies using biotin molecule combined with functional nanomaterials used in biomedical applications, with a particular attention on biotinylated chitosan-based nanosystems. Succinctly, this review focuses on five areas of recent advances in biotin engineering: (a) biotin features, (b) biotinylation approaches, (c) biotin functionalized chitosan based nanosystems for drug and gene delivery functions, (d) diagnostic and theranostic perspectives, and (e) author's inputs to the biotin-chitosan based tumour-targeting drug delivery structures. Precisely engineered biotinylated-chitosan macromolecules shaped into nanosystems are anticipated to emerge as next-generation platforms for treatment and molecular imaging modalities applications.

Targeting Strategies for Enhancing Paclitaxel Specificity in Chemotherapy

Paclitaxel (PTX) has been used for cancer treatment for decades and has become one of the most successful chemotherapeutics in the clinic and financially. However, serious problems with its use still exist, owing to its poor solubility and non-selective toxicity. With respect to these issues, recent advances have addressed the water solubility and tumor specificity related to PTX application. Many measures have been proposed to remedy these limitations by enhancing tumor recognition via ligand-receptor-mediated targeting as well as other associated strategies. In this review, we investigated various kinds of ligands that have emerged as PTX tumor-targeting tools. In particular, this article highlights small molecule-, protein-, and aptamer-functionalized conjugates and nanoparticles (NPs), providing a promising approach for PTX-based individualized treatment prospects.

Current Perspectives on Taxanes: Focus on Their Bioactivity, Delivery and Combination Therapy

Taxanes, mainly paclitaxel and docetaxel, the microtubule stabilizers, have been well known for being the first-line therapy for breast cancer for more than the last thirty years. Moreover, they have been also used for the treatment of ovarian, hormone-refractory prostate, head and neck, and non-small cell lung carcinomas. Even though paclitaxel and docetaxel significantly enhance the overall survival rate of cancer patients, there are some limitations of their use, such as very poor water solubility and the occurrence of severe side effects. However, this is what pushes the research on these microtubule-stabilizing agents further and yields novel taxane derivatives with significantly improved properties. Therefore, this review article brings recent advances reported in taxane research mainly in the last two years. We focused especially on recent methods of taxane isolation, their mechanism of action, development of their novel derivatives, formulations, and improved tumor-targeted drug delivery. Since cancer cell chemoresistance can be an unsurpassable hurdle in taxane administration, a significant part of this review article has been also devoted to combination therapy of taxanes in cancer treatment. Last but not least, we summarize ongoing clinical trials on these compounds and bring a perspective of advancements in this field.

Single- versus Dual-Targeted Nanoparticles with Folic Acid and Biotin for Anticancer Drug Delivery

Cancer is one of the major causes of death worldwide and its treatment remains very challenging. The effectiveness of cancer therapy significantly depends upon tumour-specific delivery of the drug. Nanoparticle drug delivery systems have been developed to avoid the side effects of the conventional chemotherapy. However, according to the most recent recommendations, future nanomedicine should be focused mainly on active targeting of nanocarriers based on ligand-receptor recognition, which may show better efficacy than passive targeting in human cancer therapy. Nevertheless, the efficacy of single-ligand nanomedicines is still limited due to the complexity of the tumour microenvironment. Thus, the NPs are improved toward an additional functionality, e.g., pH-sensitivity (advanced single-targeted NPs). Moreover, dual-targeted nanoparticles which contain two different types of targeting agents on the same drug delivery system are developed. The advanced single-targeted NPs and dual-targeted nanocarriers present superior properties related to cell selectivity, cellular uptake and cytotoxicity toward cancer cells than conventional drug, non-targeted systems and single-targeted systems without additional functionality. Folic acid and biotin are used as targeting ligands for cancer chemotherapy, since they are available, inexpensive, nontoxic, nonimmunogenic and easy to modify. These ligands are used in both, single- and dual-targeted systems although the latter are still a novel approach. This review presents the recent achievements in the development of single- or dual-targeted nanoparticles for anticancer drug delivery.

Exosome-mediated delivery of RNA and DNA for gene therapy

Gene therapy promises to revolutionize biomedicine and personalized medicine by modulating or compensating the expression of abnormal genes. The biggest obstacle for clinical application is the lack of an effective, non-immunogenic delivery system. We show that bovine colostrum exosomes and polyethyleneimine matrix (EPM) delivers short interfering RNA (siRNA) or plasmid DNA (pDNA) for effective gene therapy. KRAS, a therapeutic focus for many cancers, was targeted by EPM-delivered KRAS siRNA (siKRAS) and inhibited lung tumor growth (>70%) and reduced KRAS expression (50%-80%). Aberrant p53 is another therapeutic focus for many cancers. EPM-mediated introduction of wild-type (WT) p53 pDNA (pcDNA-p53) resulted in p53 expression in p53-null H1299 cells in culture, subcutaneous lung tumor, and tissues of p53-knockout mice. Additionally, chemo-sensitizing effects of paclitaxel were restored by exogenous WT p53 in lung cancer cells. Together, this novel EPM technology represents an effective 'platform' for delivery of therapeutic nucleic acids to treat human disease.

Targeting Strategies for Enhancing Paclitaxel Specificity in Chemotherapy

Paclitaxel (PTX) has been used for cancer treatment for decades and has become one of the most successful chemotherapeutics in the clinic and financially. However, serious problems with its use still exist, owing to its poor solubility and non-selective toxicity. With respect to these issues, recent advances have addressed the water solubility and tumor specificity related to PTX application. Many measures have been proposed to remedy these limitations by enhancing tumor recognition via ligand-receptor-mediated targeting as well as other associated strategies. In this review, we investigated various kinds of ligands that have emerged as PTX tumor-targeting tools. In particular, this article highlights small molecule-, protein-, and aptamer-functionalized conjugates and nanoparticles (NPs), providing a promising approach for PTX-based individualized treatment prospects.

Photocytotoxic cancer cell-targeting platinum(ii) complexes of glucose-appended curcumin and biotinylated 1,10-phenanthroline

Mixed-ligand platinum(ii) complexes, [Pt(phen)(pacac)](NO3) (1), [Pt(phen)(cur)](NO3) (2), [Pt(bt-phen)(cur)](NO3) (3) and [Pt(phen)(scur)](NO3) (4), where phen is 1,10-phenanthroline, bt-phen is 5-biotin-1,10-phenanthroline, pacac is 1,3-diphenyl-1,3-propanedioate anion, Hcur is curcumin and Hscur is diglucosylcurcumin, were prepared, characterized and their anticancer activity studied. Complexes 2-4 showed absorption bands within 410-430 nm (ε, 2.1 × 104 to 2.8 × 104 M-1 cm-1) in 10% DMSO-DPBS (Dulbecco's phosphate-buffered saline) and emission bands near 530 nm (λex = 410-430 nm) with a fluorescence quantum yield (ΦF) value of ∼0.02. The curcumin complexes showed stability over a study period of 48 h. The photocytotoxicity was studied using human cervical HeLa, human liver HepG2, human breast cancer MDA-MB 231 and human lung adenocarcinoma A549 cancer cells along with human immortalized lung epithelial HPL1D as normal cells. Complexes 2-4 showed apoptotic photo-induced cell death in light of wavelength 400-700 nm (IC50, half maximal inhibitory concentration: 6-28 μM) by reactive oxygen species (ROS), while remaining inactive in the dark (IC50: 43-95 μM). The selectivity of the complexes 3 and 4 was enhanced significantly towards the cancer cells than towards the normal cells, thus making them targeted photochemotherapeutic agents. The ROS formation and mode of cell death were studied from 2',7'-dichlorofluorescein diacetate (DCFDA) and annexin-V/FITC (fluorescein isothiocyanate)-PI assays, respectively. Preferential nuclear and mitochondrial localization was evidenced from inductively coupled plasma mass spectrometry (ICP-MS) studies.

Design, Synthesis, and Biological Evaluation of Novel Biotinylated Podophyllotoxin Derivatives as Potential Antitumor Agents

Podophyllotoxin has long been used as an active substance for cytotoxic activity. Fourteen novel biotinylated podophyllotoxin derivatives were designed, synthesized, and evaluated for cytotoxic activity for this study. The synthesized compounds were evaluated for cytotoxic activity in the following human cancer cell lines, SW480, MCF-7, A-549, SMMC-7721, and HL-60 by MTT assay. Most of them exhibited potent cytotoxic effects and compound 15 showed the highest cytotoxic activity among the five cancer cell lines tested, having its IC50 values in the range of 0.13 to 0.84 μM. Apoptosis analysis revealed that compound 15 caused obvious induction of cell apoptosis. Compound 15 significantly down-regulated the expression level of the marker proteins (caspase-3 and PARP) in H1299 and H1975 cells, activated the transcription of IRE1α, increased the expression of GRP78 and XBP-1s, and finally induced apoptosis of H1299 cells. In vivo studies showed that 15 at a dose of 20 mg/kg suppressed tumor growth of S180 cell xenografts in icr mice significantly. Further molecular docking studies suggested that compound 15 could bind well with the ATPase domain of Topoisomerase-II. These data suggest that compound 15 is a promising agent for cancer therapy deserving further research.

Hydroxylated Single-Walled Carbon Nanotubes Inhibit Aβ42 Fibrillogenesis, Disaggregate Mature Fibrils, and Protect against Aβ42-Induced Cytotoxicity

The fibrillogenesis of amyloid-β protein (Aβ) is considered a crucial factor in the pathogenesis of Alzheimer's disease (AD). Hence, inhibiting Aβ fibrillogenesis is regarded as the primary therapeutic strategy for the prevention and treatment of AD. However, the development of effective inhibitors against Aβ fibrillogenesis has faced significant challenges. Previous studies have shown that pristine single-walled carbon nanotubes (SWNTs) can inhibit fibrillogenesis of some amyloid proteins. However, the poor dispersibility of SWNTs in an aqueous environment greatly hinders their inhibitory efficacy. Here, we examined the inhibitory activity of hydroxylated SWNTs (SWNT-OH) on the aggregation and cytotoxicity of Aβ₄₂ using thioflavin T (ThT) fluorescence, atomic force microscopy (AFM), cellular viability assays, and molecular dynamics (MD) simulations. ThT and AFM results showed that SWNT-OH inhibits Aβ₄₂ fibrillogenesis and disaggregates preformed amyloid fibrils in a dose-dependent manner. Furthermore, the ratio of hydroxyl groups in SWNT-OH is crucial for their effect against Aβ₄₂ aggregation. SWNT-OH exerted cytoprotective effects against Aβ₄₂ fibrillation-induced cytotoxicity. The results of free-energy decomposition studies based on MD simulations revealed that nonpolar interactions, and especially van der Waals forces, contributed most of the free energy of binding in the SWNT-OH-Aβ complex. Two regions of the Aβ pentamer were identified to interact with SWNT-OH, spanning H13-Q15 and V36-G38. The findings presented here will contribute to a comprehensive understanding of the inhibitory effect of hydroxylated nanoparticles against Aβ fibrillogenesis, which is critical for the search for more effective agents that can counteract amyloid-mediated pathologies.

Clathrin-mediated endocytic uptake of PUFA enriched self-nanoemulsifying lipidic systems (SNELS) of an anticancer drug against triple negative cancer and DMBA induced preclinical tumor model

The current studies envisage unravelling the underlying cellular internalisation mechanism of the systematically developed docetaxel (DTH) polyunsaturated fatty acid (PUFA) enriched self-nanoemulsifying lipidic micellar systems (SNELS). The concentration-, time- and cytotoxicity-related effects of DTH-SNELS on triple negative breast cancer (TNBC) MDA-MB-231 and non-TNBC MCF-7 cell lines were assessed through Presto-blue assay. Subsequently, rhodamine-123 (Rh-123) loaded SNELS were employed for evaluating their internalisation through flow cytometry and fluorescence microscopy, establishing it to be "clathrin-mediated" endocytic pathway. Apoptosis assay (65% cell death) and cell cycle distribution (47% inhibition at G2/M phase) further corroborated the cytotoxicity of DTH-SNELS towards cancerous cells. Biodistribution, histopathology and haematology studies indicated insignificant toxicity of the optimized formulation on vital organs. Preclinical anticancer efficacy studies using 7,12-dimethylbenzantracene (DMBA)-induced model construed significant reduction in breast tumor-volume. Overall, extensive in vitro and in vivo studies indicated the intracellular localization and cytotoxicity, suggesting DTH-SNELS as promising delivery systems for breast tumor therapeutics including TNBC.

Design, Synthesis, and Biological Evaluations of Asymmetric Bow-Tie PAMAM Dendrimer-Based Conjugates for Tumor-Targeted Drug Delivery

A unique asymmetric bow-tie poly(amidoamine) (PAMAM) dendrimer (ABTD) scaffold was designed and developed as a well-defined macromolecular carrier for tumor-targeted drug delivery. The ABTD scaffold in this study consists of a G3-half-dendron (G3-HD) unit and a G1-half-dendron (G1-HD) unit, bearing thiol moiety in each unit and a bis(maleimide) linker unit, which undergo sequential thiol-maleimide coupling to assemble the scaffold. This assembly methodology is applicable to all other combinations of different generations of PAMAM dendrimers. In the prototype ABTD in this study, 16 biotin moieties were tethered to the G3-HD unit and 4 payloads (new-generation taxoid) to the G1-HD via a self-immolative linker to form an ABTD-tumor-targeting conjugate (ABTD-TTC-1). Two other ABTD-TTCs were synthesized, wherein the G1-HD unit was tethered to a fluorescence-labeled taxoid or to a fluorescent probe. These three ABTD-TTCs were constructed by using a common key ABTD 6 bearing a terminal acetylene group in the G1-HD unit, which was fully characterized as a single molecule by high-resolution mass spectrometry and NMR despite its high molecular weight (M_w: 12 876). Then, the click reaction was employed to couple ABTD 6 with a small-molecule payload or fluorescence probe unit bearing a terminal azide moiety. ABTD-TTC-3, as a surrogate of ABTD-TTC-2, showed substantially enhanced internalization into two cancer cell lines via receptor-mediated endocytosis, attributed to multibinding effect. ABTD-TTC-1 exhibited a remarkable selectivity to cancer cells (1400-7500 times) compared to human normal cells, which demonstrates the salient feature and bright prospect of the ABTD-based tumor-targeted drug-delivery system.

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.

Fetoprotein Derived Short Peptide Coated Nanostructured Amphiphilic Surfaces for Targeting Mouse Breast Cancer Cells

In this work, self-assembled tumor targeting nanostructured surfaces were developed from a newly designed amphiphile by conjugating boc protected isoleucine with 2,[Formula: see text] ethylenedioxy bis ethylamine (IED). To target mouse mammary tumor cells, a short peptide sequence derived from the human alpha-fetoprotein (AFP), LSEDKLLACGEG was attached to the self-assembled nanostructures. Tumor targeting and cell proliferation were examined in the presence of nanoscale assemblies. To further obliterate mouse breast tumor cells, the chemotherapeutic drug tamoxifen was then entrapped into the nanoassemblies. Our studies indicated that the targeting systems were able to efficiently encapsulate and release tamoxifen. Cell proliferation studies showed that IED-AFP peptide loaded with tamoxifen decreased the proliferation of breast cancer cells while in the presence of the IED-AFP peptide nanoassemblies alone, the growth was relatively slower. In the presence of human dermal fibroblasts however cell proliferation continued similar to controls. Furthermore, the nanoscale assemblies were found to induce apoptosis in mouse breast cancer cells. To examine live binding interactions, SPR analysis revealed that tamoxifen encapsulated IED-AFP peptide nanoassemblies bound to the breast cancer cells more efficiently compared to unencapsulated assemblies. Thus, we have developed nanoscale assemblies that can specifically bind to and target tumor cells, with increased toxicity in the presence of a chemotherapeutic drug.

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.

Towards Engineering Novel PE-Based Immunotoxins by Targeting Them to the Nucleus

Exotoxin A (PE) from Pseudomonas aeruginosa is a bacterial ADP-ribosyltransferase, which can permanently inhibit translation in the attacked cells. Consequently, this toxin is frequently used in immunotoxins for targeted cancer therapies. In this study, we propose a novel modification to PE by incorporating the NLS sequence at its C-terminus, to make it a selective agent against fast-proliferating cancer cells, as a nucleus-accumulated toxin should be separated from its natural substrate (eEF2) in slowly dividing cells. Here, we report the cytotoxic activity and selected biochemical properties of newly designed PE mutein using two cellular models: A549 and HepG2. We also present a newly developed protocol for efficient purification of recombinant PE and its muteins with very high purity and activity. We found that furin cleavage is not critical for the activity of PE in the analyzed cell lines. Surprisingly, we observed increased toxicity of the toxin accumulated in the nucleus. This might be explained by unexpected nuclease activity of PE and its potential ability to cleave chromosomal DNA, which seems to be a putative alternative intoxication mechanism. Further experimental investigations should address this newly detected activity to identify catalytic residues and elucidate the molecular mechanism responsible for this action.

Endoplasmic reticulum targeting tumour selective photocytotoxic oxovanadium(IV) complexes having vitamin-B6 and acridinyl moieties

Oxovanadium(iv) complexes of vitamin-B6 Schiff base, viz., [VO(HL(1)/L(2)/L(3))(B)]Cl (), where B is 2,2'-bipyridine (bpy in and ), 11-(9-acridinyl)dipyrido[3,2-a:2',3'-c]phenazine (acdppz in and ), H2L(1)·HCl is 3-hydroxy-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylpyridin-1-ium chloride (in and ), HL(2) is 2-(((2-(1H-imidazol-4-yl)ethyl)imino)methyl)phenol (in ) and HL(3) is 4-(((2-(1H-imidazol-4-yl)ethyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol (in ) were synthesized, characterized and their cellular uptake, photo-activated cytotoxicity and intracellular localization were studied. Complexes , as the perchlorate salt of , and , as the hexafluorophosphate salt of , were structurally characterized. Vitamin-B6 transporting membrane carrier (VTC) mediated entry into tumour cells in preference to the normal ones seems to be responsible for the higher cellular uptake of the complexes into HeLa and MCF-7 cells over MCF-10A cells. Complexes and having acdppz as the photosensitizer exhibit remarkable photocytotoxicity in these cancer cells giving IC50 of <0.9 μM. The complexes remain non-toxic in the dark. The complexes show photo-induced apoptotic cell death via singlet oxygen ((1)O2) generation. Fluorescence microscopy reveals specific localization of complex to endoplasmic reticulum (ER) and generation of (1)O2 possibly leads to apoptotic cell death by triggering ER stress response (ERSR).

"Smart" nickel oxide based core-shell nanoparticles for combined chemo and photodynamic cancer therapy

We report "smart" nickel oxide nanoparticles (NOPs) as multimodal cancer therapy agent. Water-dispersible and light-sensitive NiO core was synthesized with folic acid (FA) connected bovine serum albumin (BSA) shell on entrapped doxorubicin (DOX). The entrapped drug from NOP-DOX@BSA-FA was released in a sustained way (64 hours, pH=5.5, dark conditions) while a robust release was found under red light exposure (in 1/2 hour under λmax=655 nm, 50 mW/cm(2), at pH=5.5). The cell viability, thiobarbituric acid reactive substances and diphenylisobenzofuran assays conducted under light and dark conditions revealed a high photodynamic therapy potential of our construct. Furthermore, we found that the combined effect of DOX and NOPs from NOP-DOX@BSA-FA resulted in cell death approximately eightfold high compared to free DOX. We propose that NOP-DOX@BSA-FA is a potential photodynamic therapy agent and a collective drug delivery system for the systemic administration of cancer chemotherapeutics resulting in combination therapy.

Taxane anticancer agents: a patent perspective

INTRODUCTION

Paclitaxel and docetaxel were two epoch-making anticancer drugs and have been successfully used in chemotherapy for a variety of cancer types. In the year 2010, a new taxane, cabazitaxel, was approved by FDA for use in combination with prednisone for the treatment of metastatic hormone-refractory prostate cancer. Albumin-bound paclitaxel (nab™-paclitaxel; abraxane) nanodroplet formulation was another notable invention (FDA approval 2005 for refractory, metastatic, or relapsed breast cancer). Abraxane in combination with gemcitabine for the treatment of pancreatic cancer was approved by FDA in 2013. Accordingly, there have been a huge number of patent applications dealing with taxane anticancer agents in the last 5 years. Thus, it is a good time to review the progress in this area and find the next wave for new developments.

AREA COVERED

This review covers the patent literature from the year 2010 to early 2015 on various aspects of taxane-based chemotherapies and drug developments.

EXPERT OPINION

Three FDA-approved taxane anticancer drugs will continue to expand their therapeutic applications, especially through drug combinations and new formulations. Inspired by the success of abraxane, new nano-formulations are emerging. Highly potent new-generation taxanes will play a key role in the development of efficacious tumor-targeted drug delivery systems.

Design, synthesis and biological evaluation of a highly-potent and cancer cell selective folate-taxoid conjugate

The folate receptor (FR) has been widely recognized as an excellent target for the tumor-selective delivery of cytotoxic agents, and four folate-drug conjugates have entered clinical evaluations for the treatment of solid tumors to date. However, most of these conjugates required structural modification of the cytotoxic warheads in order to achieve efficient drug release from the linkers. We designed and constructed a novel folate conjugate of a highly-potent next-generation taxoid, SB-T-1214, by exploiting bioorthogonal Cu-free 'click' chemistry. The synthesis was highly convergent and required no HPLC purification to obtain the final folate-taxoid conjugate 1. Conjugate 1 demonstrated highly FR-specific potency (IC₅₀ 2.1-3.5 nM) against a panel of cancer cell lines, with a >1000-fold decrease in cytotoxicity against normal human cells (IC₅₀>5000 nM). The remarkable potency and selectivity of conjugate 1 can be attributed to highly FR-specific receptor-mediated endocytosis as well as efficient release of the unmodified cytotoxic warhead using a mechanism-based self-immolative linker.

Design, Synthesis and Application of Fluorine-Labeled Taxoids as 19F NMR Probes for the Metabolic Stability Assessment of Tumor-Targeted Drug Delivery Systems

Novel tumor-targeting drug conjugates, BLT-F₂ (1) and BLT-S-F₆ (2), bearing a fluorotaxoid as the warhead, a mechanism-based self-immolative disulfide linker, and biotin as the tumor-targeting module, were designed and synthesized as ¹⁹F NMR probes. Fluorine atoms and CF₃ groups were strategically incorporated into the conjugates to investigate the mechanism of linker cleavage and factors that influence their plasma and metabolic stability by real-time monitoring with ¹⁹F NMR. Time-resolved ¹⁹F NMR study on probe 1 disclosed a stepwise mechanism for release of a fluorotaxoid, which might not have been detected by other analytical methods. Probe 2 was designed to bear two CF₃ groups in the taxoid moiety as "3-FAB" reporters for enhanced sensitivity and a polyethylene glycol oligomer insert to improve solubility. The clean analysis of the linker stability and reactivity of drug conjugates in blood plasma or cell culture media by HPLC and ¹H NMR is troublesome, due to the overlap of key signals/peaks with background arising from highly complex ingredients in biological systems. Accordingly, the use of ¹⁹F NMR would provide a practical solution to this problem. In fact, our "3-FAB" probe 2 was proven to be highly useful to investigate the stability and reactivity of the self-immolative disulfide linker system in human blood plasma by ¹⁹F NMR. It has also been revealed that the use of polysorbate 80 as excipient for the formulation of probe 2 dramatically increases the stability of the disulfide linker system. This finding further indicates that the tumor-targeting drug conjugates with polysorbate 80/EtOH/saline formulation for in vivo studies would have high stability in blood plasma, while the drug release in cancer cells proceeds smoothly.

Design, synthesis, and biological evaluation of theranostic vitamin-linker-taxoid conjugates

Novel tumor-targeting theranostic conjugates 1 and 2, bearing either a fluorine-labeled prosthetic as a potential (18)F-PET radiotracer (1) or a fluorescence probe (2) for internalization studies in vitro, were designed and synthesized. We confirmed efficient internalization of 2 in biotin-receptor positive (BR+) cancer cells via receptor-mediated endocytosis (RME) based on flow cytometry and confocal fluorescence microscopy (CFM) analyses, which exhibited very high specificity to BR+ cancer cells. The potency and cancer-cell selectivity of 1 were evaluated against MX-1, L1210FR and ID8 cancer cells (BR+) as well as L1210 cells and WI38 normal human lung fibroblast cells (biotin-receptor negative: BR-). In particular, we designed and performed an assay in the presence of glutathione ethyl ester (GSH-OEt) wherein only 1 molecules internalized into cells via RME in the first 24 h period exert cytotoxic effect. The observed selectivity of 1 was remarkable, with 2 orders of magnitude difference in IC50 values between BR+ cancer cells and WI38 cells, demonstrating a salient feature of this tumor-targeted drug delivery system.

The anti-cancer potency and mechanism of a novel tumor-activated fused toxin, DLM

Melittin, which acts as a membrane-disrupting lytic peptide, is not only cytotoxic to tumors, but also vital to normal cells. Melittin had low toxicity when coupled with target peptides. Despite significant research development with the fused toxin, a new fused toxin is needed which has a cleavable linker such that the fused toxin can release melittin after protease cleavage on the tumor cell surface. We describe a novel fused toxin, composed of disintegrin, uPA (urokinase-type plasminogen activator)-cleavable linker, and melittin. Disintegrin is a single strand peptide (73 aa) isolated from Gloydius Ussuriensis venom. The RGD (Arg-Gly-Asp) site of disintegrin dominates its interaction with integrins on the surface of the tumor cells. uPA is over-expressed and plays an important role in tumor cell invasiveness and metastatic progression. The DLM (disintegrin-linker-melittin) linker is uPA-cleavable, enabling DLM to release melittin. We compared binding activity of our synthesized disintegrin with native disintegrin and report that DLM had less binding activity than the native form. uPA-cleavage was evaluated in vitro and the uPA-cleavable linker released melittin. Treating tumors expressing uPA with DLM enhanced tumor cell killing as well as reduced toxicity to erythrocytes and other non-cancerous normal cells. The mechanism behind DLM tumor cell killing was tested using a DNA ladder assay, fluorescent microscopy, flow cytometry, and transmission electron microscopy. Data revealed tumor cell necrosis as the mechanism of cell death, and the fused DLM toxin with an uPA-cleavable linker enhanced tumor selectivity and killing ability.

Synthesis of enantiopure reversed structured ether lipids of the 1-O-alkyl-sn-2,3-diacylglycerol type

This report describes the synthesis of reversed structured 1-O-alkyl-2,3-diacyl-sn-glycerols (DAGEs) possessing a pure saturated even number fatty acid (C6:0-C16:0) at the sn-2 position along with a pure EPA or DHA located at the terminal sn-3 position of the glycerol backbone of chimyl, batyl and selachyl alcohols. These adducts were synthesized by a highly efficient two-step chemoenzymatic process involving an immobilized Candida antarctica lipase to introduce pure EPA and DHA activated as oxime esters exclusively to the sn-3 terminal position of enantiopure chimyl, batyl and selachyl alcohols in excellent yields. The saturated fatty acids were subsequently incorporated to the remaining sn-2 position of the resulting 3-monoacylglyceryl ethers (3-MAGEs) using EDAC coupling agent in the presence of DMAP in very high to excellent yields (85%-98%). No losses of enantiomeric composition were observed during these processes. The multiple utilities of the resulting focused library of reversed structured DAGEs are discussed including how such compounds may possibly be utilized within the pharmaceutical area.

Synthesis and characterisation of nickel Schiff base complexes containing the meso-1,2-diphenylethylenediamine moiety: selective interactions with a tetramolecular DNA quadruplex

Two nickel(ii) Schiff base complexes exhibit binding selectivity for a tetramolecular DNA quadruplex.

Antitumor effect of D-erythrose in an abdominal metastatic model of colon carcinoma

Traditional chemotherapy drugs against colorectal cancer possess little or no specificity, leading to severe intolerable side-effects. Therefore, it is necessary to develop additional specific therapeutic strategies. It has been suggested that D-erythrose may specifically inhibit the growth of tumor cells. However, the in vivo antitumor effect of D-erythrose against colorectal cancer remains unknown. Thus, the present study investigated the antitumor effect of D-erythrose in an abdominal metastatic model of colon carcinoma. Intraperitoneal (IP) colon carcinoma-bearing BALB/c mice received an IP injection of D-erythrose or normal saline (NS) daily for 15 days. The mice were weighed every three days. The tumor weights and the volume of ascites were evaluated following the treatment. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay was used to assess apoptosis in tumor tissues. The results revealed that D-erythrose significantly reduced the weight of the intraperitoneal tumor by 69.1%, markedly inhibited the development of ascites and increased tumor cell apoptosis, without any observed toxic effects. These observations suggest that D-erythrose possesses antitumor activity against colon cancer. The present study may provide a potentially effective and specific approach for colon cancer treatment.

Design, synthesis, and biological evaluations of tumor-targeting dual-warhead conjugates for a taxoid-camptothecin combination chemotherapy

Novel tumor-targeting dual-warhead conjugates, 2 (DW-1) and 3 (DW-2), which consist of a next-generation taxoid, 1 (SB-T-1214), and camptothecin as two warheads, self-immolative disulfide linkers for drug release, biotin as the tumor-targeting moiety, and 1,3,5-triazine as the tripod splitter module, were designed and synthesized. The potency of 2 was evaluated against MX-1, MCF-7, ID8, L1210FR (BR+, biotin receptor overexpressed) and WI38 (BR-, normal) cell lines in the absence and presence of glutathione (GSH), which is an endogenous thiol that triggers drug release inside the cancer cells. With the GSH and resuspension protocol, 2 exhibited IC50 values of 3.22-9.80 nM against all BR+ cancer cell lines, and 705 nM against WI38. Thus, there was a two orders of magnitude higher selectivity to cancer cells. Also, a clear cooperative effect was observed for the taxoid-camptothecin combination when two drugs were delivered to the cancer cells specifically in the form of a dual-warhead conjugate.

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

A long-standing problem of conventional chemotherapy is the lack of tumor-specific treatments. Traditional chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be killed by a cytotoxic agent. In reality, however, cytotoxic agents have very little or no specificity, which leads to systemic toxicity, causing undesirable severe side effects. Consequently, various "molecularly targeted cancer therapies" have been developed for use in specific cancers, including tumor-targeting drug delivery systems. In general, such a drug delivery system consists of a tumor recognition moiety and a cytotoxic "warhead" connected through a "smart" linker to form a conjugate. When a multi-functionalized nanomaterial is used as the vehicle, a "Trojan Horse" approach can be used for mass delivery of cytotoxic "warheads" to maximize the efficacy. Exploitation of the special properties of fluorine has proven successful in the development of new and effective biochemical tools as well as therapeutic agents. Fluorinated congeners can also serve as excellent probes for the investigation of biochemical mechanisms. ¹⁹F-NMR can provide unique and powerful tools for mechanistic investigations in chemical biology. This account presents our recent progress, in perspective, on the molecular approaches to the design and development of novel tumor-targeted drug delivery systems for new generation chemotherapy by exploiting the unique nature of fluorine.

Exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology

Over the last three decades, my engagement in "fluorine chemistry" has evolved substantially because of the multidisciplinary nature of the research programs. I began my research career as a synthetic chemist in organometallic chemistry and homogeneous catalysis directed toward organic synthesis. Then, I was brought into a very unique world of "fluorine chemistry" in the end of 1970s. I started exploring the interface of fluorine chemistry and transition metal homogeneous catalysis first, which was followed by amino acids, peptides, and peptidomimetics for medicinal chemistry. Since then, I have been exploring the interfaces of fluorine chemistry and multidisciplinary fields of research involving medicinal chemistry, chemical biology, cancer biology, and molecular imaging. This perspective intends to cover my fruitful endeavor in the exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology in a chronological order to show the evolution of my research interest and strategy.

Interview: Interview with Future Medicinal Chemistry’s US Senior Editor, Iwao Ojima

Professor Iwao Ojima studied at the University of Tokyo (Japan) before being appointed as a Senior Research Fellow and Group Leader at the Sagami Institute of Chemical Research. He is now Director of the Institute of Chemical Biology and Drug Discovery at State University of New York (USA) and has been a visiting professor in European, North American and Asian academic institutions. Professor Ojima agreed to serve as the US Senior Editor of Future Medicinal Chemistry when it launched in 2009 and continues to provide his expertise to the journal. Professor Ojima spoke to Future Medicinal Chemistry about why medicinal chemistry is such an exciting field to work in, the state of the pharmaceutical industry, and what features and issues make this journal unique.

Interview conducted by Isaac Bruce, Commissioning Editor.