Synthesis and evaluation of taxol-folic acid conjugates as targeted antineoplastics

Active Targeted Nanoformulations via Folate Receptors: State of the Art and Future Perspectives

In normal tissues, the expression of folate receptors is low and limited to cells that are important for embryonic development or for folate reabsorption. However, in several pathological conditions some cells, such as cancer cells and activated macrophages, overexpress folate receptors (FRs). This overexpression makes them a potential therapeutic target in the treatment of cancer and inflammatory diseases to obtain a selective delivery of drugs at altered cells level, and thus to improve the therapeutic efficacy and decrease the systemic toxicity of the pharmacological treatments. Two strategies have been used to achieve this folate receptor targeting: (i) the use of ligands with high affinity to FRs (e.g., folic acid or anti-FRs monoclonal antibodies) linked to the therapeutic agents or (ii) the use of nanocarriers whose surface is decorated with these ligands and in which the drug is encapsulated. This manuscript analyzes the use of FRs as a target to develop new therapeutic tools in the treatment of cancer and inflammatory diseases with an emphasis on the nanoformulations that have been developed for both therapeutic and imaging purposes.

Unexpected photoactivation pathways in a folate-receptor-targeted trans-diazido Pt(IV) anticancer pro-drug

A conjugate between a photoactive trans-diazido Pt(iv) pro-drug, trans,trans,trans-[Pt(N3)2(OH)2(py)2], and folic acid has been synthesized and fully characterized by high resolution ESI-MS, NMR and UV-vis spectroscopy. Photoactivation of the Pt-folate conjugate with visible light confirmed the generation of cytotoxic Pt(ii) species capable of binding to guanine nucleobases. Importantly, photoreduction of the Pt(iv) complex triggered the photodecomposition of the folate vector into a p-aminobenzoate-containing fragment and several pterin derivatives, including 6-formylpterin. Besides exhibiting high dark stability in physiological-like conditions, the Pt-folate conjugate was ca. 2× more photocytotoxic towards MCF-7 breast cancer cell line than its parent Pt(iv) complex with a high photoselectivity index (PI > 6.9). The higher photocytotoxicity of the conjugate may be a consequence of its higher cellular accumulation and of the generation of a set of different cytotoxic species, including Pt(ii) photoproducts and several pterin derivatives, which are known to generate ROS.

Tuning the pharmacokinetics and efficacy of irinotecan (IRI) loaded gelatin nanoparticles through folate conjugation

Gelatin based nanocarriers have major limitation of shorter circulation half-life (t_1/2). Present study addressed this issue by conjugating gelatin with folate followed by nanoprecipitation in presence of polysorbate 80 to form folate attached gelatin nanoparticles (GNP-F). The folic acid was conjugated with gelatin through the formation of amide linkage with a maximum conjugation yield of ~69%. Cryo-SEM analysis indicated that unconjugated gelatin nanoparticles (GNP) and GNP-F were spherical of nearly identical size of ~200 nm. The irinotecan (IRI)-loading efficiency estimated for IRI-GNP and IRI-GNP-F was 6.6 ± 0.42% and 11.2 ± 0.73% respectively and both formulations showed faster release of IRI at acidic pH (~5) than at physiological pH (~7). Further IRI-GNP-F demonstrated significantly higher cytotoxicity in folate receptor (FR)-positive HeLa cells than the unconjugated IRI-GNP nanoparticles confirming active targeting. Subsequently the antitumor activity of above formulations in FR-positive fibrosarcoma (syngeneic) tumor-bearing mice followed the order of IRI-GNP-F > IRI-GNP > free IRI. The pharmacokinetic evaluation of IRI-GNP and IRI-GNP-F revealed that encapsulation of IRI within GNP without folate improved its plasma maximum concentration (C_max). However, folate conjugation of GNP remarkably improved the t_1/2 of IRI. Taken together, folate as a targeting ligand modulates the pharmacokinetic property of IRI loaded GNP to favor active verses passive targeting.

Recent Advances in Targeted Tumor Chemotherapy Based on Smart Nanomedicines

Efficacy and safety of chemotherapeutic drugs constitute two major criteria in tumor chemotherapy. Nanomedicines with tumor-targeted properties hold great promise for improving the efficacy and safety. To design targeted nanomedicines, the pathological characteristics of tumors are extensively and deeply excavated. Here, the rationale, principles, and advantages of exploiting these pathological characteristics to develop targeted nanoplatforms for tumor chemotherapy are discussed. Homotypic targeting with the ability of self-recognition to source tumors is reviewed individually. In the meanwhile, the limitations and perspective of these targeted nanomedicines are also discussed.

A paclitaxel prodrug with bifunctional folate and albumin binding moieties for both passive and active targeted cancer therapy

Folate receptor (FR) has proven to be a valuable target for chemotherapy using folic acid (FA) conjugates. However, FA-conjugated chemotherapeutics still have low therapeutic efficacy accompanied with side effects, resulting from complications such as short circulation half-life, limited tumor delivery, as well as high kidney accumulation. Herein, we present a novel FA-conjugated paclitaxel (PTX) prodrug which was additionally conjugated with an Evans blue (EB) derivative for albumin binding. The resulting bifunctional prodrug prolonged blood circulation, enhanced tumor accumulation, and consequently improved tumor therapeutic efficacy. Methods: Fmoc-Cys(Trt)-OH was coupled onto PTX at the 7'-OH position for further synthesis of ester prodrug FA-PTX-EB. The targeting ability was investigated using confocal microscopy and flow cytometry. The pharmacokinetics of this bifunctional compound was also studied. Meanwhile, cell viability was evaluated in normal cells and three cancer cell lines by MTT assay. In vivo therapeutic effect was tested on FR-α overexpressing MDA-MB-231 tumor model. Results: Compared with free PTX, the FA-PTX, PTX-EB and FA-PTX-EB prodrugs increased circulation half-life in mice from 2.19 to 3.82, 4.41, and 7.51 h, respectively. Pharmacokinetics studies showed that the FA-PTX-EB delivered more PTX to tumors than FA-PTX and free PTX. In vitro and in vivo studies demonstrated that FA-EB-conjugated PTX induced potent antitumor activity. Conclusion: FA-PTX-EB showed prolonged blood circulation, enhanced drug accumulation in tumors, higher therapeutic index, and lower side effects than either free PTX or monofunctional FA-PTX and EB-PTX. The results support the potential of using EB for the development of long-acting therapeutics.

Targeting folate receptor alpha for cancer treatment

Promising targeted treatments and immunotherapy strategies in oncology and advancements in our understanding of molecular pathways that underpin cancer development have reignited interest in the tumor-associated antigen Folate Receptor alpha (FRα). FRα is a glycosylphosphatidylinositol (GPI)-anchored membrane protein. Its overexpression in tumors such as ovarian, breast and lung cancers, low and restricted distribution in normal tissues, alongside emerging insights into tumor-promoting functions and association of expression with patient prognosis, together render FRα an attractive therapeutic target. In this review, we summarize the role of FRα in cancer development, we consider FRα as a potential diagnostic and prognostic tool, and we discuss different targeted treatment approaches with a specific focus on monoclonal antibodies. Renewed attention to FRα may point to novel individualized treatment approaches to improve the clinical management of patient groups that do not adequately benefit from current conventional therapies.

Efficient route to pre-organized and linear polyaminopolycarboxylates: Cy-TTHA, Cy-DTPA and mono/di- reactive, tert-butyl protected TTHA/Cy-TTHA

Pre-organized polyaminopolycarboxylate chelators Cy-TTHA and Cy-DTPA were synthesized via modular five-step syntheses from commercially available starting materials in ~ 62% and 47% overall yields, respectively. Furthermore, strategies are reported for the efficient preparation of mono- and di-reactive, tert-butyl-protected TTHA/Cy-TTHA to selectively functionalize central chelators' carboxylic acids.

Targeting of herbal bioactives through folate receptors: a novel concept to enhance intracellular drug delivery in cancer therapy

Targeted drug delivery through folate receptor (FR) has emerged as a most biocompatible, target oriented, and non-immunogenic cargoes for the delivery of anticancer drugs. FRs are highly overexpressed in many tumor cells (like ovarian, lung, breast, kidney, brain, endometrial, and colon cancer), and targeting them through conjugates bearing specific ligand with encapsulated nanodrug moiety is undoubtedly, a promising approach toward tumor targeting. Folate, being an endogenous ligand, can be exploited well to affect various cellular events occurring during the progress of tumor, in a more natural and definite way. Thus, the aim of the review lies in summarizing the advancements taken place in the drug delivery system of different therapeutics through FRs and to refine its role as an endogenous ligand, in targeting of synthetic as well as natural bioactives. The review also provides an update on the patents received on the folate-based drug delivery system.

Folate-decorated arginine-based poly(ester urea urethane) nanoparticles as carriers for gambogic acid and effect on cancer cells

Gambogic acid (GA) exhibits a broad spectrum of anticancer activity and low chemotoxicity to normal tissues. However, poor aqueous solubility and sensitivity to hydrolysis make its pharmaceutical applications a challenge. Linear and branched Arg-based poly(ester urea urethane)s (Arg-PEUUs), folate (FA)-conjugated Arg PEUUs (FA-Arg-PEUUs), and their self-assembled nanoparticles (NPs) were designed, synthesized, and studied as the potential GA carriers for cancer treatment. The average diameters of linear or branched Arg-PEUU/FA-Arg-PEUU NPs were 98-267 nm. FA-Arg-PEUU NPs adhered onto and were internalized into HeLa and A549 cells, and showed no cytotoxicity. The GA loading efficiency in the NP carriers ranged from 40 to 98%, depending on the feed weight ratio of GA to Arg-PEUU and the Arg-PEUU polymer structure (i.e., linear vs. branched). The GA at 2 µg/mL concentration delivered by the FA-Arg-PEUU NP carriers had higher cytotoxicity and induced a higher apoptosis percentage against folate receptor (FR)-overexpressed HeLa or HCT116 than Arg-PEUU NPs. When compared to the free GA treatment, the GA loaded in the FA-Arg-PEUU NP carriers also led to significant loss of the mitochondrial membrane potential in a higher percentage of the cancer cell population and more DNA fragmentation. The GA loaded in FA-Arg-PEUU NP carriers at as low as 0.6 µg/mL GA concentration led to lower MMP-2 and MMP-9 activity of cancer cells compared to free GA, suggesting that GA-loaded Arg-PEUU NPs may have greater potential to reduce cancer cell invasion and metastasis than free GA. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 475-490, 2017.

Development of a Novel Covalent Folate-Albumin-Photosensitizer Conjugate

There is considerable interest in the development of novel and more efficient delivery systems for improving the efficacy of photodynamic therapy (PDT). The authors in this highlighted issue describe the synthesis and the photobiological characterizations of two photosensitizer (PS) conjugates based on β-carboline derivatives covalently conjugated to folic acid (FA) coupled to bovine serum albumin (BSA) as a carrier system specifically targeting cancer cells overexpressing FA receptor alpha (FRα). Accordingly, only the FA-BSA-β-carboline conjugates are internalized specifically in FRα-positive cells and are proved to be phototoxic. On the other hand, albumin-β-carboline conjugates without FA or β-carboline derivatives alone are not internalized and nontoxic. This conjugate is among the first to produce a conjugate composed of a PS and FA molecules that are directly conjugated to BSA. In addition, the in vitro studies are the first evidence that directly conjugated FA-BSA can be used as carriers to selectively enhance cytotoxicity by PDT relative to unmodified PS or nontargeted BSA-PS. This strategy is a positive step forward for the covalent design and construction of a photodynamic nanomedicine for FR-positive tumors.

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.

Formulation, characterization, and evaluation of ligand-conjugated biodegradable quercetin nanoparticles for active targeting

The aim of this study was to design a targeted drug delivery system carrying a natural anticancer drug Quercetin (Qu), specifically for skin cancer. A central composite design was applied separately for each ligand, and the quadratic model was used for the process. The surface morphology was confirmed by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR), and in vitro release studies were also performed. The MTT assay was performed against two different cell lines, to measure their anticancer potentials and their targeting ability. The study thus reveals that MA-Qu-PLGA and FA-Qu-PLGA nanoparticles (NPs) can be used as effective drug delivery systems for skin cancer treatment encompassing natural drugs.

Folate receptor-β in activated macrophages: ligand binding and receptor recycling kinetics

Activated macrophages overexpress a receptor for the vitamin folic acid termed the folate receptor β (FR-β). Because conjugation of folate to low molecular weight drugs, genes, liposomes, nanoparticles, and imaging agents has minor effects on FR binding, the vitamin can be exploited to target both therapeutic and imaging agents to activated macrophages without promoting their uptake by other healthy cells. In this paper, we characterize the binding, internalization, and recycling kinetics of FR-β on activated macrophages in inflamed tissues of rats with adjuvant-induced arthritis. Our results demonstrate that saturation of macrophage FR is achieved at injection doses of ∼150-300 nmol/kg, with more rapidly perfused tissues saturating at lower doses than inflamed appendages. After binding, FR-β internalizes and recycles back to the cell surface every ∼10-20 min, providing empty receptors for additional folate conjugate uptake. Because the half-life of low molecular weight folate conjugates in the vasculature is usually <1 h, these data suggest that targeting of folate conjugates to activated macrophages in vivo can be maximized by frequent dosing at conjugate concentrations that barely saturate FR (∼150 nmol/kg), thereby minimizing nonspecific binding to receptor-negative tissues and maximizing the probability that unoccupied cell surface receptors will be exposed to folate-drug conjugate.

Novel isoprenoyl nanoassembled prodrug for paclitaxel delivery

A new paclitaxel (Ptx) prodrug was designed by coupling a single terpene unit (MIP) to the hydroxyl group in position 2' of the drug molecule. Using a squalene derivative of polyethylene glycol (SQ-PEG) as surface active agent, the resulting bioconjugate (PtxMIP) self-assembled in water leading to the formation of stable nanoparticles (PtxMIP_SQ-PEG NPs) with an impressively high drug loading (82%). In vivo, the anticancer activity of this novel Ptx nanoassembled prodrug was compared to the conventional Cremophor-containing formulation (Taxol) on a murine model of breast cancer lung metastasis induced by intravenous injection of 4T1 tumor cells, genetically modified to stably express firefly luciferase. Cell growth was assessed noninvasively by bioluminescence imaging (BLI) which enabled monitoring tumor metastatic burden in the same animals. PtxMIP_SQ-PEG nanoparticles slowed metastatic spread and were better tolerated than the Cremophor-containing formulation (i.e., free drug), thus demonstrating the potential of terpene-based nanoassembled prodrugs in the improvement of the therapeutic index of Ptx in balb/c mice.

Biotin-conjugated tumour-targeting photocytotoxic iron(III) complexes

Iron(III) complexes [FeL(B)] (1-4) of a tetradentate phenolate-based ligand (H3L) and biotin-conjugated dipyridophenazine bases (B), viz. 7-aminodipyrido [3,2-a:2',3'-c]-phenazine (dppza in 1), (N-dipyrido[3,2-a:2',3'-c]-phenazino)amidobiotin (dppzNB in 2), dipyrido [3,2-a:2',3'-c]-phenazine-11-carboxylic acid (dppzc in 3) and 2-((2-biotinamido)ethyl) amido-dipyrido[3,2-a:2',3'-c]-phenazine (dppzCB in 4) are prepared, characterized and their interaction with streptavidin and DNA and their photocytotoxicity and cellular uptake in various cells studied. The high-spin iron(III) complexes display Fe(III)/Fe(II) redox couple near -0.7 V versus saturated calomel electrode in dimethyl sulfoxide-0.1 M tetrabutylammonium perchlorate. The complexes show non-specific interaction with DNA as determined from the binding studies. Complexes with appended biotin moiety show similar binding to streptavidin as that of free biotin, suggesting biotin conjugation to dppz does not cause any loss in its binding affinity to streptavidin. The photocytotoxicity of the complexes is tested in HepG2, HeLa and HEK293 cell lines. Complex 2 shows higher photocytotoxicity in HepG2 cells than in HeLa or HEK293, forming reactive oxygen species. This effect is attributed to the presence of overexpressed sodium-dependent multi-vitamin transporters in HepG2 cells. Microscopic studies in HepG2 cells show internalization of the biotin complexes 2 and 4 essentially occurring by receptor-mediated endocytosis, which is similar to that of native biotin and biotin fluorescein isothiocyanate conjugate.

Synthesis of peptide radiopharmaceuticals for the therapy and diagnosis of tumor diseases

Despite the advances in molecular biology and biochemistry, the prognosis of patients suffering from tumor diseases remains poor. The limited therapeutic success can be explained by the insufficient performance of the common chemotherapeutic drugs that lack the ability to specifically target tumor tissues. Recently peptide radiopharmaceuticals have been developed that enable the concurrent imaging and therapy of tumors expressing a specific target. Here, with a special emphasis on the synthesis of the building blocks required for the complexation of metallic radioisotopes, the requirements to the design and synthesis of radiolabeled peptides for clinical applications are described.

Improving the antitumor activity of squalenoyl-paclitaxel conjugate nanoassemblies by manipulating the linker between paclitaxel and squalene

A series of new lipid prodrugs of paclitaxel, which can be formulated as nanoassemblies, are described. These prodrugs which are designed to overcome the limitations due to the systemic toxicity and low water solubility of paclitaxel consist of a squalene chain bound to the 2'-OH of paclitaxel through a 1,4-cis,cis-dienic linker. This design allows the squalene-conjugates to self-assemble as nanoparticular systems while preserving an efficient release of the free drug, thanks to the dienic spacer. The size, steric hindrance, and functional groups of the spacer have been modulated. All these prodrugs self-assemble into nanosized aggregates in aqueous solution as characterized by dynamic light scattering and transmission electron microscopy and appear stable in water for several days as determined by particle size measurement. In vitro biological assessment shows that these squalenoyl-paclitaxel nanoparticles display notable cytotoxicity on several tumor cell lines including A549 lung cell line, colon cell line HT-29, or KB 3.1 nasopharyngeal epidermoid cell line. The cis,cis-squalenyl-deca-5,8-dienoate prodrug show improved activity over simple 2'-squalenoyl-paclitaxel prodrug highlighting the favourable effect of the dienic linker. The antitumor efficacy of the nanoassemblies constructed with the more active prodrugs has been investigated on human lung (A549) carcinoma xenograft model in mice. The prodrug bearing the cis,cis-deca-5,8-dienoyl linker shows comparable antitumor efficacy to the parent drug, but reveals a much lower subacute toxicity as seen in body weight loss. Thus, nanoparticles with the incorporated squalenoyl paclitaxel prodrug may prove useful for replacement of the toxic Cremophor EL.

In vitro phototoxicity and dark-toxicity of a novel synthesized pyropheophorbide-a-paclitaxel conjugate against cancer cell lines

Synthesis of pyropheophorbide-a-paclitaxel (PPa-PTX) conjugate was performed in high yield with the aim of searching for an optimal agent for cancer treatment. After synthesis, the conjugate was confirmed to be linked through an ester bond at the 2′ position of the paclitaxel moiety using multi-nuclear magnetic resonance spectroscopy. Phototoxicity of PPa and PPa-PTX conjugate, as well as PTX, was evaluated with three human cancer cell lines (HeLa, CaSki and TC-1). The new conjugate at 0.01–0.06 μM displayed 20–40% higher phototoxicity in HeLa and CaSki cell lines than free PPa and PTX. Furthermore, cellular uptake of these bio-molecules was examined by confocal laser scanning microscopy. Although PPa-PTX showed a delayed uptake compared to PPa, it penetrated completely into cells within 24 h incubation.

Analogue-based drug discovery: Contributions to medicinal chemistry principles and drug design strategies. Microtubule stabilizers as a case in point (Special Topic Article)

The benefits of utilizing marketed drugs as starting points to discover new therapeutic agents have been well documented within the IUPAC series of books that bear the title Analogue-based Drug Discovery (ABDD). Not as clearly demonstrated, however, is that ABDD also contributes to the elaboration of new basic principles and alternative drug design strategies that are useful to the field of medicinal chemistry in general. After reviewing the ABDD programs that have evolved around the area of microtubule-stabilizing chemo-therapeutic agents, the present article delineates the associated research activities that additionally contributed to general strategies that can be useful for prodrug design, identifying pharmacophores, circumventing multidrug resistance (MDR), and achieving targeted drug distribution.

Engineering folate-drug conjugates to target cancer: from chemistry to clinic

The folate receptor (FR) is a potentially useful biological target for the management of many human cancers. This membrane protein binds extracellular folates with very high affinity and, through an endocytic process, physically delivers them inside the cell for biological consumption. There are now many examples of how this physiological system can be exploited for the targeted delivery of biologically active molecules to cancer. In fact, strong preclinical as well as emerging clinical evidence exists showing how FR-positive cancers can be (i) anatomically identified using folate conjugates of radiodiagnostic imaging agents and (ii) effectively treated with companion folate-targeted chemotherapies. While the biological results are compelling, it is of equal importance to understand the conjugation chemistries that were developed to produce these active molecules. Therefore, this review will focus on the methods utilized to construct folate-based small-molecule drug conjugates (SMDCs), with particular attention focused on modular design, hydrophilic spacers, and self-immolative linkers.

Cell-specific, activatable, and theranostic prodrug for dual-targeted cancer imaging and therapy

Herein we describe the design and synthesis of a folate-doxorubicin conjugate with activatable fluorescence and activatable cytotoxicity. In this study we discovered that the cytotoxicity and fluorescence of doxorubicin are quenched (OFF) when covalently linked with folic acid. Most importantly, when the conjugate is designed with a disulfide bond linking the targeting folate unit and the cytotoxic doxorubicin, a targeted activatable prodrug is obtained that becomes activated (ON) within the cell by glutathione-mediated dissociation and nuclear translocation, showing enhanced fluorescence and cellular toxicity. In our novel design, folic acid acted as both a targeting ligand for the folate receptor as well as a quencher for doxorubicin's fluorescence.

Mechanism-based tumor-targeting drug delivery system. Validation of efficient vitamin receptor-mediated endocytosis and drug release

An efficient mechanism-based tumor-targeting drug delivery system, based on tumor-specific vitamin-receptor mediated endocytosis, has been developed. The tumor-targeting drug delivery system is a conjugate of a tumor-targeting molecule (biotin: vitamin H or vitamin B-7), a mechanism-based self-immolative linker and a second-generation taxoid (SB-T-1214) as the cytotoxic agent. This conjugate (1) is designed to be (i) specific to the vitamin receptors overexpressed on tumor cell surface and (ii) internalized efficiently through receptor-mediated endocytosis, followed by smooth drug release via glutathione-triggered self-immolation of the linker. In order to monitor and validate the sequence of events hypothesized, i.e., receptor-mediated endocytosis of the conjugate, drug release, and drug-binding to the target protein (microtubules), three fluorescent/fluorogenic molecular probes (2, 3, and 4) were designed and synthesized. The actual occurrence of these processes was unambiguously confirmed by means of confocal fluorescence microscopy (CFM) and flow cytometry using L1210FR leukemia cells, overexpressing biotin receptors. The molecular probe 4, bearing the taxoid linked to fluorescein, was also used to examine the cell specificity (i.e., efficacy of receptor-based cell targeting) for three cell lines, L1210FR (biotin receptors overexpressed), L1210 (biotin receptors not overexpressed), and WI38 (normal human lung fibroblast, biotin receptor negative). As anticipated, the molecular probe 4 exhibited high specificity only to L1210FR. To confirm the direct correlation between the cell-specific drug delivery and anticancer activity of the probe 4, its cytotoxicity against these three cell lines was also examined. The results clearly showed a good correlation between the two methods. In the same manner, excellent cell-specific cytotoxicity of the conjugate 1 (without fluorescein attachment to the taxoid) against the same three cell lines was confirmed. This mechanism-based tumor-targeting drug delivery system will find a range of applications.

High sensitive detection of cancer cell with a folic acid-based boron-doped diamond electrode using an AC impedimetric approach

An electrochemical impedance method at a fixed frequency (10Hz) is used to detect folate receptor-rich cancer cells with the interaction between folic acid immobilized on gold nanoparticles deposited on boron-doped diamond (BDD) electrode surface and its receptor over-expressed on cancer cell membrane without additional labeling. Experimental results have shown that the BDD electrode modified with folic acid can clearly denote folate receptor-rich cancer cells, such as HeLa cells, at a concentration down to 10 cells mL(-1). The high sensitivity of BDD electrode is resulted from the change of field effect and surface charge density of BDD after cancer cells attachment. The BDD electrodes can be regenerated with 0.1M citric acid/glycine/HC1 at pH 3.0 and used seven times again. Therefore, electrochemical technique with BDD electrode has been introduced for cancer cells detection and a simple method to detect folate receptor-rich cancer cells without additional labeling has been developed.

Fluorescent silica nanoparticles for cancer imaging

In recent years, fluorescent silica nanoparticles (FSNPs) received immense interest in cancer imaging. FSNPs are a new class of engineered optical probes consisting of silica NPs loaded with fluorescent dye molecules. These probes exhibit some attractive features, such as photostability and brightness, which allow sensitive imaging of cancer cells. In general, FSNPs are chemically synthesized in solution using appropriate silane-based precursors. Fluorescent dye molecules are entrapped during the synthesis process. The synthetic process involves hydrolysis and condensation reactions of silane precursors. Stöber's sol-gel and water-in-oil (W/O) microemulsion methods are two popular chemical methods that have been used for synthesizing FSNPs. Silica matrix is capable of carrying hundreds of fluorescent dye molecules in each FSNP, resulting in bright fluorescence. In FSNPs, fluorescent molecules are somewhat protected by the surrounding silica layer, resulting in good photostability. For cancer cell imaging, surface modification of FSNPs is often necessary to obtain appropriate surface functional groups to improve NP aqueous dispersibility as well as bioconjugation capability. Using conventional bioconjugate chemistry, cancer cell-specific biomolecules are then attached to the surface-modified FSNPs. For targeting cancer cells, the FSNPs are often conjugated to specific biomolecules such as antibodies, aptamers, and folic acid. In this chapter, different approaches for the FSNP design will be discussed and some representative protocols for FSNP synthesis will be provided. We will also discuss FSNP surface modification and bioconjugation techniques that are useful for cancer cell imaging.

Folate conjugated phosphorylcholine-based polycations for specific targeting in nucleic acids delivery

Folic acid has been investigated as a targeting ligand for imaging and therapeutic agent for over a decade; however, studies on its use in targeting of nonviral gene or nucleic acids delivery systems are sparse. This study assesses potential application of a new folic acid conjugate with aminomethacrylate-phosphoryl-choline based copolymer (DMAEMA-MPC-FA) as a targeting gene delivery vector. The folate-conjugated polymers produce colloidally stable polyplexes with a particle size <200 nm and demonstrate the ability to protect DNA from enzymatic degradation to a certain extent. In cells that overexpress folate receptors (MCF-7 and KB cultures), the conjugated systems show a folate-specific association and achieved significantly enhanced transfection efficiency, compared to the nonconjugated control, with a dramatically reduced nonspecific cellular association. The transfection enhancement is achieved without a corresponding increase in cellular association, suggesting that an internal cellular trafficking of folate-conjugated system may be altered, resulting in an increased transfection efficacy. In summary, a new folate-conjugated aminomethacrylate-phosphorylcholine copolymer is capable of forming colloidal complexes with DNA, modulating their specific cell uptake and improving the level of cell transfection in folate expressing cells.