Development of novel bisphosphonate prodrugs of doxorubicin for targeting bone metastases that are cleaved pH dependently or by cathepsin B: synthesis, cleavage properties, and binding properties to hydroxyapatite as well as bone matrix

Rh(iii)-Catalyzed directed C–H carbenoid coupling reveals aromatic bisphosphonates inhibiting metallo- and Serine-β-lactamases

The C–H coupling of arenes with diazo-methylene-diphosphonates enables efficient synthesis of new diphosphonates, which exhibit dual MBL and SBL inhibition.

Impact of cathepsin B-sensitive triggers and hydrophilic linkers onin vitroefficacy of novel site-specific antibody–drug conjugates

Promising anti-HER2 site-specific ADCs with anin vitroefficacy equivalent to Kadcyla®.

Bifunctional Platinum(II) Complexes with Bisphosphonates Substituted Diamine Derivatives: Synthesis and In vitro Cytotoxicity

A series of N,N'-dibisphosphonate-containing 1,3-propanediamine derivatives (L1 - L6) and their corresponding dichloridoplatinum(II) complexes (1 - 6) have been synthesized and characterized by elemental analysis, ¹ H-NMR, ¹³ C-NMR, ³¹ P-NMR and HR-MS spectra. The in vitro antitumor activities of compounds L1 - L6 and 1 - 6 were tested by WST-8 assay with Cell Counting Kit-8, indicating that platinum-based complexes 1 - 6 showed higher cytotoxicity than corresponding ligands L1 - L6 against A549 and MG-63, especially complex 2 which displayed comparable cytotoxicity to those of cisplatin and zoledronate after 48 h incubation. In addition, complexes 1 - 6 were more active in vitro on osteosarcoma cell line MG-63 than normal osteoblast cell line hFOB 1.19. The structure-activity relationship has been summarized based on the in vitro cytotoxicity of three series of platinum complexes from this and our previous studies. The in vitro bone affinity of platinum complexes was also tested by hydroxyapatite (HAP) chromatography in terms of capacity factor K'. Besides, in this paper, representative complex 2, which has been proved to be a promising antitumor agent with high cytotoxicity and bone HAP binding property, was investigated for its mechanism of action producing cell death against MG-63.

Development and Properties of Valine-Alanine based Antibody-Drug Conjugates with Monomethyl Auristatin E as the Potent Payload

Antibody-drug conjugates (ADCs), designed to selectively deliver cytotoxic agents to antigen-bearing cells, are poised to become an important class of cancer therapeutics. Human epithelial growth factor receptor (HER2) is considered an effective target for cancer treatment, and a HER2-targeting ADC has shown promising results. Most ADCs undergoing clinical evaluation contain linkers that have a lysosomal protease-cleavable dipeptide, of which the most common is valine-citrulline (VC). However, valine-alanine (VA), another dipeptide comprising two human essential amino acids, has been used in next generation ADCs loading new toxins, but the druggable properties of ADCs loaded the most popular monomethyl auristatin E (MMAE) remain to be further explored. In this study, we generated VA-based ADCs that connected MMAE to an anti-HER2 antibody. We studied the differences in the preparation process, in vitro stability, cathepsin B activity and in vitro cytotoxicity of VA-based ADC compared to the ADC of VC. VA had comparable performance to VC, which preliminarily displays its practicability. Additional efficacy and safety studies in a xenograft model indicate this novel ADC exerted potent anti-tumor activity and negligible toxicity. The results of this study show the application potential of VA-based ADC with MMAE as the payload.

Bisphosphonate-functionalized coordination polymer nanoparticles for the treatment of bone metastatic breast cancer

Bone is the most common organ affected by metastatic breast cancer. Targeting cancers within the bone remains a great challenge due to the inefficient delivery of therapeutic to bone. In this study, a polyethylene glycol (PEG) coated nanoparticles (NPs) made of a Zn²⁺ coordination polymer was linked with a bone seeking moiety, alendronate (ALN), to deliver cisplatin prodrug (DSP) to the bone. The particle sizes of this novel system, DSP-Zn@PEG-ALN NPs, were regulated by adjusting the volume ratio of water phase to oil phase in microemulsion. It was small enough (about 55nm) to extravasate through the clefts (80nm) of the bone's sinusoidal capillaries and localize into metastatic bones. DSP-Zn@PEG-ALN NPs showed much higher affinity for hydroxyapatite in vitro and bone in vivo than non-targeted DSP-Zn@PEG NPs and cisplatin. In addition, the in vivo biodistribution studies demonstrated that about 4-fold of platinum was delivered to the bone metastatic lesions than that in healthy bones by DSP-Zn@PEG-ALN NPs intravenously. Finally, DSP-Zn@PEG-ALN NPs not only inhibited the tumor growth efficiently but also reduced the osteocalastic bone destruction. Besides, DSP-Zn@PEG-ALN NPs showed significantly reduced toxicity of cisplatin. These results indicate that the DSP-Zn@PEG-ALN NPs have a great potential in enhancing chemotherapeutic efficacy for the treatment of bone metastatic breast cancer.

Protease-Cleavable Linkers Modulate the Anticancer Activity of Noninternalizing Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) represent an attractive class of biopharmaceutical agents, with the potential to selectively deliver potent cytotoxic agents to tumors. It is generally assumed that ADC products should preferably bind and internalize into cancer cells in order to liberate their toxic payload, but a growing body of evidence indicates that also ADCs based on noninternalizing antibodies may be potently active. In this Communication, we investigated dipeptide-based linkers (frequently used for internalizing ADC products) in the context of the noninternalizing F16 antibody, specific to a splice isoform of tenascin-C. Using monomethyl auristatin E (MMAE) as potent cytotoxic drug, we observed that a single amino acid substitution of the Val-Cit dipeptide linker can substantially modulate the in vivo stability of the corresponding ADC products, as well as the anticancer activity in mice bearing the human epidermoid A431 carcinoma. In these settings, the linker based on the Val-Ala dipeptide exhibited better performances, compared to Val-Cit, Val-Lys, and Val-Arg analogues. Mass spectrometric analysis revealed that the four linkers displayed not only different stability in vivo but also differences in cleavage sites. Moreover, the absence of anticancer activity for a F16-MMAE conjugate featuring a noncleavable linker indicated that drug release modalities, based on proteolytic degradation of the immunoglobulin moiety, cannot be exploited with noninternalizing antibodies. ADC products based on the noninternalizing F16 antibody may be useful for the treatment of several human malignancies, as the cognate antigen is abundantly expressed in the extracellular matrix of several tumors, while being virtually undetectable in most normal adult tissues.

Redox and pH dual sensitive bone targeting nanoparticles to treat breast cancer bone metastases and inhibit bone resorption

Bone is an especially prone metastatic site for breast cancer, and to block the vicious cycle between bone resorption and tumor growth is an important strategy for the treatment of breast cancer bone metastasis. In this paper, pH- and redox-sensitive as well as breast cancer bone metastasis-targeting nanoparticles (DOX@ALN-(HA-PASP)_CL) were prepared, and also their anti-tumor activity and anti-bone resorption effect were investigated in detail. The in vitro experimental results indicated that DOX released from DOX@ALN-(HA-PASP)_CL exhibited a GSH-, DTT- and pH-dependent manner. Moreover, in an in vitro 3D breast cancer bone metastasis model, DOX@ALN-(HA-PASP)_CL decreased bone resorption through inhibiting the proliferation of human breast cancer cells (MDA-MB-231 cells) and reducing the activity of osteoclasts. The in vivo experimental results indicated that a large amount of DOX was delivered to a breast cancer bone metastasis site after tumor-bearing mice were treated with DOX@ALN-(HA-PASP)_CL; meanwhile, DOX@ALN-(HA-PASP)_CL significantly decreased the tumor volume and bone resorption in tumor-bearing mice without causing obvious systemic toxicity. In conclusion, the in vitro and in vivo experimental results indicate that DOX@ALN-(HA-PASP)_CL has great potential in the treatment of breast cancer bone metastasis.

Novel Liver-targeted conjugates of Glycogen Phosphorylase Inhibitor PSN-357 for the Treatment of Diabetes: Design, Synthesis, Pharmacokinetic and Pharmacological Evaluations

PSN-357, an effective glycogen phosphorylase (GP) inhibitor for the treatment for type 2 diabetics, is hampered in its clinical use by the poor selectivity between the GP isoforms in liver and in skeletal muscle. In this study, by the introduction of cholic acid, 9 novel potent and liver-targeted conjugates of PSN-357 were obtained. Among these conjugates, conjugate 6 exhibited slight GP inhibitory activity (IC50 = 31.17 μM), good cellular efficacy (IC50 = 13.39 μM) and suitable stability under various conditions. The distribution and pharmacokinetic studies revealed that conjugate 6 could redistribute from plasma to liver resulting in a considerable higher exposure of PSN-357 metabolizing from 6 in liver (AUCliver/AUCplasma ratio was 18.74) vs that of PSN-357 (AUCliver/AUCplasma ratio was 10.06). In the in vivo animal study of hypoglycemia under the same dose of 50 mg/kg, conjugate 6 exhibited a small but significant hypoglycemic effects in longer-acting manners, that the hypoglycemic effects of 6 is somewhat weaker than PSN-357 from administration up to 6 h, and then became higher than PSN-357 for the rest time of the test. Those results indicate that the liver-targeted glycogen phosphorylase inhibitor may hold utility in the treatment of type 2 diabetes.

Bisphosphonate-functionalized poly(β-amino ester) network polymers

Three novel bisphosphonate-functionalized secondary diamines are synthesized and incorporated into poly(β-amino ester)s (PBAEs) to investigate the effects of bisphosphonates on biodegradation and toxicity of PBAE polymer networks. These three novel amines, BPA1, BPA2, and BPA3, were prepared from the reactions of 1,4-butanediamine, 1,6-hexanediamine, or 4,9-dioxa-1,12-dodecanediamine with tetraethyl vinylidene bisphosphonate, respectively. The PBAE macromers were obtained from the aza-Michael addition reaction of these amines to 1,6-hexane diol diacrylate (HDDA) and poly(ethylene glycol) diacrylate (PEGDA, M_n  = 575) and photopolymerized to produce biodegradable gels. These gels with different chemistries exhibited similar degradation behavior with mass loss of 53-73% within 24 h, indicating that degradation is mostly governed by the bisphosphonate group. Based on the in vitro cytotoxicity evaluation against NIH 3T3 mouse embryonic fibroblast cells, the degradation products do not exhibit significant toxicity in most cases. It was also shown that PBAE macromers can be used as cross-linkers for the synthesis of 2-hydroxyethyl methacrylate hydrogels, conferring small and customizable degradation rates upon them. The materials reported have potential to be used as nontoxic degradable biomaterials. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1412-1421, 2017.

Generation of a co-culture cell micropattern model to simulate lung cancer bone metastasis for anti-cancer drug evaluation

A549/OB co-culture micropattern was fabricated through μ-eraser strategy to mimic lung cancer bone metastasis for DOX efficacy evaluation.

Design and Biological Evaluation of Delivery Systems Containing Bisphosphonates

Bisphosphonates have found application in the treatment of reoccurrence of bone diseases, breast cancer, etc. They have also been found to exhibit antimicrobial, anticancer and antimalarial activities. However, they suffer from pharmacological deficiencies such as toxicity, poor bioavailability and low intestinal adsorption. These shortcomings have resulted in several researchers developing delivery systems that can enhance their overall therapeutic effectiveness. This review provides a detailed overview of the published studies on delivery systems designed for the delivery of bisphosphonates and the corresponding in vitro/in vivo results.

Linker stability influences the anti-tumor activity of acetazolamide-drug conjugates for the therapy of renal cell carcinoma

Small molecule-drug conjugates (SMDCs) are increasingly being considered as an alternative to antibody-drug conjugates (ADCs) for the selective delivery of anticancer agents to the tumor site, sparing normal tissues. Carbonic anhydrase IX (CAIX) is a membrane-bound enzyme, which is over-expressed in the majority of renal cell carcinomas and which can be efficiently targeted in vivo, using charged derivatives of acetazolamide, a small heteroaromatic sulfonamide. Here, we show that SMDC products, obtained by the coupling of acetazolamide with monomethyl auristatin E (MMAE) using dipeptide linkers, display a potent anti-tumoral activity in mice bearing xenografted SKRC-52 renal cell carcinomas. A comparative evaluation of four dipeptides revealed that SMDCs featuring valine-citrulline and valine-alanine linkers exhibited greater serum stability and superior therapeutic activity, compared to the counterparts with valine-lysine or valine-arginine linkers. The most active products substantially inhibited tumor growth over a prolonged period of time, in a tumor model for which sunitinib and sorafenib do not display therapeutic activity. However, complete tumor eradication was not possible even after ten intravenous injection. Macroscopic near-infrared imaging procedures confirmed that ligands had not lost the ability to selectively localize at the tumor site at the end of therapy and that the neoplastic masses continued to express CAIX. The findings are of mechanistic and of therapeutic significance, since CAIX is a non-internalizing membrane-associated antigen, which can be considered for targeted drug delivery applications in kidney cancer patients.

Local and targeted drug delivery for bone regeneration

While experimental bone regeneration approaches commonly employ cells, technological hurdles prevent translation of these therapies. Alternatively, emulating the spatiotemporal cascade of endogenous factors through controlled drug delivery may provide superior bone regenerative approaches. Surgically placed drug depots have clinical indications. Additionally, noninvasive systemic delivery can be used as needed for poorly healing bone injuries. However, a major hurdle for systemic delivery is poor bone biodistribution of drugs. Thus, peptides, aptamers, and phosphate-rich compounds with specificity toward proteins, cells, and molecules within the regenerative bone microenvironment may enable the design of targeted carriers with bone biodistribution greater than that achieved by drug alone. These carriers, combined with osteoregenerative drugs and/or stimuli-sensitive linkers, may enhance bone regeneration while minimizing off-target tissue effects.

Targeted delivery to bone and mineral deposits using bisphosphonate ligands

The high concentration of mineral present in bone and pathological calcifications is unique compared with all other tissues and thus provides opportunity for targeted delivery of pharmaceutical drugs, including radiosensitizers and imaging probes. Targeted delivery enables accumulation of a high local dose of a therapeutic or imaging contrast agent to diseased bone or pathological calcifications. Bisphosphonates (BPs) are the most widely utilized bone-targeting ligand due to exhibiting high binding affinity to hydroxyapatite mineral. BPs can be conjugated to an agent that would otherwise have little or no affinity for the sites of interest. This article summarizes the current state of knowledge and practice for the use of BPs as ligands for targeted delivery to bone and mineral deposits. The clinical history of BPs is briefly summarized to emphasize the success of these molecules as therapeutics for metabolic bone diseases. Mechanisms of binding and the relative binding affinity of various BPs to bone mineral are introduced, including common methods for measuring binding affinity in vitro and in vivo. Current research is highlighted for the use of BP ligands for targeted delivery of BP conjugates in various applications, including (1) therapeutic drug delivery for metabolic bone diseases, bone cancer, other bone diseases, and engineered drug delivery platforms; (2) imaging probes for scintigraphy, fluorescence, positron emission tomography, magnetic resonance imaging, and computed tomography; and (3) radiotherapy. Last, and perhaps most importantly, key structure-function relationships are considered for the design of drugs with BP ligands, including the tether length between the BP and drug, the size of the drug, the number of BP ligands per drug, cleavable tethers between the BP and drug, and conjugation schemes.

Design and development of an in situ synthesized layered double hydroxide structure of Fe-induced hydroxyapatite for drug carriers

Possible mechanisms: (i) formation of LDH structure of Fe-induced hydroxyapatite (HA), (ii) intercalation of Aceclofenac (AF) drug in LDH structure of FH carriers and (iii) releasing of drug via hydrolysis and/or reaction with other biomolecules.

The Prodrug Approach: A Successful Tool for Improving Drug Solubility

Prodrug design is a widely known molecular modification strategy that aims to optimize the physicochemical and pharmacological properties of drugs to improve their solubility and pharmacokinetic features and decrease their toxicity. A lack of solubility is one of the main obstacles to drug development. This review aims to describe recent advances in the improvement of solubility via the prodrug approach. The main chemical carriers and examples of successful strategies will be discussed, highlighting the advances of this field in the last ten years.

Doxorubicin-poly (ethylene glycol)-alendronate self-assembled micelles for targeted therapy of bone metastatic cancer

In order to increase the therapeutic effect of doxorubicin (DOX) on bone metastases, a multifunctional micelle was developed by combining pH-sensitive characteristics with bone active targeting capacity. The DOX loaded micelle was self-assembled by using doxorubicin-poly (ethylene glycol)-alendronate (DOX-hyd-PEG-ALN) as an amphiphilic material. The size and drug loading of DOX loaded DOX-hyd-PEG-ALN micelle was 114 nm and 24.3%. In pH 5.0 phosphate buffer solution (PBS), the micelle released DOX significantly faster than in pH 7.4 PBS. In addition, with the increase of incubation time, more red DOX fluorescence was observed in tumor cells and trafficked from cytoplasm to nucleus. The IC₅₀ of DOX loaded DOX-hyd-PEG-ALN micelle on A549 cells was obviously lower than that of free DOX in 48 h. Furthermore, the in vivo image experimental results indicated that a larger amount of DOX was accumulated in the bone metastatic tumor tissue after DOX loaded DOX-hyd-PEG-ALN micelle was intravenously administered, which was confirmed by histological analysis. Finally, DOX loaded DOX-hyd-PEG-ALN micelle effectively delayed the tumor growth, decreased the bone loss and reduced the cardiac toxicity in tumor-bearing nude mice as compared with free DOX. In conclusion, DOX loaded DOX-hyd-PEG-ALN micelle had potential in treating bone metastatic tumor.

Activable Cell-Penetrating Peptide Conjugated Prodrug for Tumor Targeted Drug Delivery

In this paper, an activable cell-penetrating peptide (CR8G3PK6, ACPP) with a shielding group of 2,3-dimethylmaleic anhydride (DMA) was conjugated with antitumor drug doxorubicin (DOX) to construct a novel prodrug (DOX-ACPP-DMA) for tumor targeted drug delivery. The shielding group of DMA linked to the primary amines of K6 through the amide bond was used to block the cell-penetrating function of the polycationic CPP (R8) through intramolecular electrostatic attraction at physiological pH 7.4. At tumor extracellular pH 6.8, the hydrolysis of DMA led to charge reversal, activating the pristine function of CPP for improved cellular uptake by tumor cells. Confocal laser scanning microscopy (CLSM) and flow cytometry studies revealed that the cellular uptake of DOX-ACPP-DMA was significantly enhanced after acid-triggered activation in both HeLa and COS7 cells. After cell internalization, the overexpressed intracellular proteases would further trigger drug release in cells. Both in vitro and in vivo investigations showed that the peptidic prodrug exhibited significant tumor growth inhibition and demonstrated great potential for tumor therapy.

Synthesis of triple-bond-containing 1-hydroxy-1,1-bisphosphonic acid derivatives to be used as precursors in "click" chemistry: two examples

The synthesis of novel (ω-alkynyl-1-hydroxy-1,1-diyl)bisphosphonic acid tetramethyl esters (1a-c), their P,P'-dimethyl esters (2a-c), and two trimethyl ester derivatives (3a and 3b) is reported. The prepared compounds can be attached to many kinds of molecules containing azide (-N3) functionalities using a "click" chemistry approach. As an example, bisphosphonate trimethyl ester 3a and P,P'-dimethyl ester 2b were attached to triethylene glycol to form triethylene glycol-bisphosphonate conjugates 4 and 5 as model compounds for further studies in, for example, nanoparticle targeting.

In vitro ultrastructural changes of MCF-7 for metastasise bone cancer and induction of apoptosis via mitochondrial cytochrome C released by CaCO3/Dox nanocrystals

Bones are the most frequent site for breast cancer cells to settle and spread (metastasise); bone metastasis is considered to have a substantial impact on the quality of patients with common cancers. However, majority of breast cancers develop insensitivity to conventional chemotherapy which provides only palliation and can induce systemic side effects. In this study we evaluated the effect of free Dox and CaCO3/Dox nanocrystal on MCF-7 breast cancer using MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide), neural red, and lactate dehydrogenase colorimetric assays while DNA fragmentation and BrdU genotoxicity were also examined. Apoptogenic protein Bax, cytochrome C, and caspase-3 protein were analysed. Morphological changes of MCF-7 were determined using contrast light microscope and scanning and transmission electron microscope (SEM and TEM). The findings of the analysis revealed higher toxicity of CaCO3/Dox nanocrystal and effective cells killing compared to free Dox, morphological changes such as formation of apoptotic bodies, membrane blebbing, and absent of microvilli as indicated by the SEM analysis while TEM revealed the presence of chromatin condensation, chromosomal DNA fragmentation, cell shrinkage, and nuclear fragmentation. Results of TUNEL assay verified that most of the cells undergoes apoptosis by internucleosomal fragmentation of genomic DNA whereas the extent of apoptotic cells was calculated using the apoptotic index (AI). Therefore, the biobased calcium carbonate nanocrystals such as Dox carriers may serve as an alternative to conventional delivery system.

Selectivity in bone targeting with multivalent dendritic polyanion dye conjugates

Targeting bone with anionic macromolecules is a potent approach for the development of novel diagnostics and therapeutics for bone related diseases. A highly efficient modular synthesis of dendritic polyglycerol (dPG) polyanion dye conjugates, namely, sulfates, sulfonates, carboxylates, phosphates, phosphonates, and bisphosphonates via click chemistry is presented. By investigating the microarchitecture of stained bone sections with confocal laser scanning microscopy, the bisphosphonate, phosphonate, and phosphate functionalized polymers are identified as strongly penetrating compounds, whereas sulfates, sulfonates, and carboxylates reveal a weaker binding to hydroxyapatite (HA) but a more pronounced affinity toward collagen. In a quantitative HA binding assay, the affinity of the dPG sulfonate, sulfate, and carboxylate toward collagen and the exceptional high HA affinity of the phosphorous containing polyelectrolytes are validated. This shows the potential of dendritic polyphosphates and phosphonates as alternatives to the commonly employed bisphosphonate modification. In cytotoxicity studies with murine fibroblasts, the conjugates have no significant effect on the cell viability at 10(-5) m. All polyanions are taken up into the cells within 24 h. The presented synthetic approach allows versatile extensions for preparing conjugates for selective bone imaging applications, tissue engineering, and drug delivery.

Bisphosphonate prodrugs: synthesis and biological evaluation in HuH7 hepatocarcinoma cells

We investigated the biological effects of new synthesized bisphosphonates (BPs) on HuH7 hepatocarcinoma cells. BPs containing p-bromophenyl (R1 = p-Br, Ph, 2) in their side chain were the more potent to inhibit HuH7 cell viability. In addition, phenyl diesterified analogues (R2 = R3 = Ph, 2a) were more potent than methyl (R2 = R3 = Me, 2b) or non-esterified BPs (2) inducing more necrosis suggesting that they better entered into cells. Phosphodiesterase inhibitor (IBMX) reversed the effect of the esterified BPs and not that of non-esterified ones suggesting role of cell phosphodiesterases to release active BPs. BP analogues inhibited HuH7 cell migration but esterified ones had no effect on invasion due to the hiding of phosphonic groups. All together, these results indicated the therapeutic interest of these new BP prodrugs.

In vivo imaging of bone using a deep-red fluorescent molecular probe bearing multiple iminodiacetate groups

Deep-red fluorescent molecular probes are described that have a dendritic molecular architecture with a squaraine rotaxane core scaffold and multiple peripheral iminodiacetate groups as the bone targeting units. Iminodiacetates have an inherently lower bone affinity than bisphosphonates, and a major goal of the study was to determine how many appended iminodiacetate groups are required for effective deep-red fluorescence imaging of bone in living rodents. A series of in vitro and in vivo imaging studies showed that a tetra(iminodiacetate) probe stains bones much more strongly than an analogous bis(iminodiacetate) probe. In addition, a control tetra(iminodipropionate) probe exhibited no bone targeting ability. The tetra(iminodiacetate) probe targeted the same regions of high bone turnover as the near-infrared bisphosphonate probe OsteoSense750. Longitudinal studies showed that the fluorescence image signal from living mice treated with the tetra(iminodiacetate) probe was much more stable over 19 days than the signal from OsteoSense750. The narrow emission band of the tetra(iminodiacetate) probe makes it very attractive for inclusion in multiplex imaging protocols that employ a mixture of multiple fluorescent probes in preclinical studies of bone growth or in fluorescence guided surgery. The results also suggest that molecules or nanoparticles bearing multivalent iminodiacetate groups have promise as bone targeting agents with tunable properties for various pharmaceutical applications.

Synthesis and biological evaluation of novel folic acid receptor-targeted, β-cyclodextrin-based drug complexes for cancer treatment

Drug targeting is an active area of research and nano-scaled drug delivery systems hold tremendous potential for the treatment of neoplasms. In this study, a novel cyclodextrin (CD)-based nanoparticle drug delivery system has been assembled and characterized for the therapy of folate receptor-positive [FR(+)] cancer. Water-soluble folic acid (FA)-conjugated CD carriers (FACDs) were successfully synthesized and their structures were confirmed by 1D/2D nuclear magnetic resonance (NMR), matrix-assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF-MS), high performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), and circular dichroism. Drug complexes of adamatane (Ada) and cytotoxic doxorubicin (Dox) with FACD were readily obtained by mixed solvent precipitation. The average size of FACD-Ada-Dox was 1.5–2.5 nm. The host-guest association constant K_a was 1,639 M⁻¹ as determined by induced circular dichroism and the hydrophilicity of the FACDs was greatly enhanced compared to unmodified CD. Cellular uptake and FR binding competitive experiments demonstrated an efficient and preferentially targeted delivery of Dox into FR-positive tumor cells and a sustained drug release profile was seen in vitro. The delivery of Dox into FR(+) cancer cells via endocytosis was observed by confocal microscopy and drug uptake of the targeted nanoparticles was 8-fold greater than that of non-targeted drug complexes. Our docking results suggest that FA, FACD and FACD-Ada-Dox could bind human hedgehog interacting protein that contains a FR domain. Mouse cardiomyocytes as well as fibroblast treated with FACD-Ada-Dox had significantly lower levels of reactive oxygen species, with increased content of glutathione and glutathione peroxidase activity, indicating a reduced potential for Dox-induced cardiotoxicity. These results indicate that the targeted drug complex possesses high drug association and sustained drug release properties with good biocompatibility and physiological stability. The novel FA-conjugated β-CD based drug complex might be promising as an anti-tumor treatment for FR(+) cancer.

Biomedical applications of bisphosphonates

Since their discovery over 100 years ago, bisphosphonates have been used industrially as corrosion inhibitors and complexing agents. With the discovery of their pharmacological activity in the late 1960s, implicating their high affinity for hydroxyapatite, bisphosphonates have been employed in the treatment of bone diseases and as targeting agents for colloids and drugs. They have notably been investigated for the treatment of Paget's disease, osteoporosis, bone metastases, malignancy-associated hypercalcemia, and pediatric bone diseases. Currently, they are first-line medications for several of these diseases and are taken by millions of patients worldwide, mostly postmenopausal women. A major problem associated with their use is their low oral bioavailability. Several delivery systems have been proposed to improve their absorption and to direct them to sites other than bone tissues. Beyond their important pharmacological role, the medical applications of bisphosphonates are numerous. In addition, their metal-chelating properties have been exploited to coat and stabilize implants, nanoparticulates, and contrast agents. In this contribution, we review the pharmacological and clinical uses of bisphosphonates and highlight their novel applications in the pharmaceutical and biomedical fields.