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

Pincer-Type Pt(II)-NHC Antibody-Drug Conjugate for HER-2-Targeted Chemoimmunotherapy

Platinum-based chemotherapy drugs play an indispensable role in clinical cancer treatment, but exhibit considerable side effects due to their non-specific mechanism of killing cancer cells and normal cells. In this regard, the use of antibodies conjugated to anti-cancer platinum complexes will enable better differentiation of cancer cells from normal cells. Here, six pincer-platinum(II) NHC (N-heterocyclic carbene) complexes are reported, one of which has an amino group on the N-alkyl group of the NHC ligand. This platinum(II) complex is used as the payload for platinum(II)-based antibody-drug conjugate (ADC) targeting human epidermal growth factor receptor 2 (HER-2). Notably, this ADC can specifically bind to the HER-2 antigen, distinguish target cells from non-target cells, and exhibit good anti-tumor activity in vitro and in vivo.

Discovery of novel dual tubulin and MMPs inhibitors for the treatment of lung cancer and overcoming drug resistance

Nowadays, hybrid molecule with dual targets activity or effect is regarded as an effective strategy for combating the drug resistance development in cancer therapy. Herein, novel of bifunctional conjugates targeting tubulin and MMPs inhibitors were synthesized. Among them, 15j exhibited robust anticancer activity in vitro and in vivo, with IC50 values of 0.154-0.296 μM against four human cancer cells and a 74.7 % (@20 mg/kg) tumor growth inhibition in vivo without obvious systemic toxicity. Mechanistic studies indicated that 15j exerted inhibitory effects on both tubulin polymerization, MMP-2 and MMP-9 activity. Moreover, 15j remarkably inhibited cell proliferation, migration and invasion, and accordingly disrupted the NF-κB signaling transduction. Furthermore, 15j effectively initiated mitochondria-dependent apoptotic pathway by causing mitochondrial dysfunction, promoting the accumulation of reactive oxygen species, and inducing DNA damage. Collectively, these results demonstrated that 15j, as a tubulin/MMPs dual-targeting inhibitor, has exhibited significant potential for the lung cancer therapy.

Design and evaluation of a multi-responsive dual-modality bone-targeted drug delivery vehicle for the treatment of osteosarcoma

The combination of chemotherapy and photothermal therapy not only improves the therapeutic effect but also limits the side effects of drugs. Herein, a multi-responsive dual-modality bone-targeted drug delivery vehicle for the treatment of osteosarcoma was designed by utilizing alendronate sodium as a bone-targeting ligand for the targeted delivery of doxorubicin (DOX) loaded polydopamine nanoparticles (PDA NPs) coated with γ-polyglutamic acid (APC@PDA/DOX NPs). The average size of spherical NPs was 140.0 nm with a zeta potential of -25.63 mV. The drug loading and encapsulation efficiency were 11.63 % and 96.44 %, respectively. The constructed NPs were responsive to acidic pH, redox conditions, and near-infrared light as the drug release rate of the system reached 70 %. Cell experiments showed that APC@PDA/DOX NPs significantly enhanced cytotoxicity in mouse K7M2 osteosarcoma cells due to PDA-induced hyperthermia and DOX-induced cytotoxicity. Compared with the free DOX solution, the area under the curve of APC@PDA/DOX NPs increased by 8.52 times, iterating the significantly prolonged circulation time of NPs in vivo that manifested in higher bioavailability. The biodistribution study showed that APC@PDA/DOX NPs enacted excellent bone targeting and tumor tissue localization. In general, APC@PDA/DOX NPs may offer a feasible and effective strategy for osteosarcoma-targeted therapy.

Generation of BT-Amide, a Bone-Targeted Pyk2 Inhibitor, Effective via Oral Administration, for the Prevention of Glucocorticoid-Induced Bone Loss

Glucocorticoid-induced osteoporosis (GIOP) is the leading cause of iatrogenic osteoporosis due to the widespread clinical use of glucocorticoids (GC) as immunosuppressants. Previous research identified the proline-rich tyrosine kinase 2, Pyk2, as a critical mediator of GC-induced bone loss, and that blocking Pyk2 could protect the skeleton from adverse GC actions. However, systemic administration of current Pyk2 inhibitors causes harmful side effects, such as skin lesions. To address this, we developed bone-targeted (BT) Pyk2 inhibitors by conjugating them with bisphosphonates (BP), ensuring adherence to the bone matrix and reducing impact on noncalcified tissues. We synthesized BT-Amide by linking a derivative of TAE-226, a Pyk2 inhibitor, with alendronic acid. Oral administration (gavage) of BT-Amide prevented GC-induced bone loss in mice without causing skin lesions, or elevation of any organ toxicity markers. These findings introduce BT-Amide as the first orally effective bone-targeted Pyk2 inhibitor for preventing GC-induced bone loss while minimizing off-target effects.

Design, Synthesis, and Characterization of HBP-Vectorized Methotrexate Prodrug Molecule 1102-39: Evaluation of In Vitro Cytotoxicity Activity in Cell Culture Models, Preliminary In Vivo Safety and Efficacy Results in Rodents

A novel bone-targeted prodrug, 1102-39, is discussed with the aim of enhancing the therapeutic effects of methotrexate (MTX) within bone tissues while minimizing systemic toxicity. Within the 1102-39 molecule, the central linker part forms a cleavable ester group, with MTX being also linked by a stable imine bond to the specially designed hydroxybisphosphonic (HBP) vector. Synthesized through a convergent approach starting from MTX, this prodrug advantageously modulates MTX's activity by selective esterification of its α-carboxyl group. In vitro tests revealed a 10-fold reduction in cytotoxicity compared to standard MTX, in alignment with prodrug behavior and correlated with gradual MTX release. In vivo in rodents, 1102-39 displayed preliminary encouraging antitumor effects on orthotopic osteosarcoma. Furthermore, various aspects of designing molecules for selective therapy in bone tissue based on bisphosphonate molecules as vectors for delivering active compounds to the bone are discussed. The 1102-39 molecule exhibits strong affinity for hydroxyapatite and a progressive release of MTX in aqueous environments, enhancing the safety and efficacy of bone-specific treatments and enabling sustained activity within bone and bone joints in the therapy of tumor and inflammation.

Acid-sensitive prodrugs; a promising approach for site-specific and targeted drug release

Drugs administered through conventional formulations are devoid of targeting and often spread to various undesired sites, leading to sub-lethal concentrations at the site of action and the emergence of undesired effects. Hence, therapeutic agents should be delivered in a controlled manner at target sites. Currently, stimuli-based drug delivery systems have demonstrated a remarkable potential for the site-specific delivery of therapeutic moieties. pH is one of the widely exploited stimuli for drug delivery as several pathogenic conditions such as tumor cells, infectious and inflammatory sites are characterized by a low pH environment. This review article aims to demonstrate various strategies employed in the design of acid-sensitive prodrugs, providing an overview of commercially available acid-sensitive prodrugs. Furthermore, we have compiled the progress made for the development of new acid-sensitive prodrugs currently undergoing clinical trials. These prodrugs include albumin-binding prodrugs (Aldoxorubicin and DK049), polymeric micelle (NC-6300), polymer conjugates (ProLindac™), and an immunoconjugate (IMMU-110). The article encompasses a broad spectrum of studies focused on the development of acid-sensitive prodrugs for anticancer, antibacterial, and anti-inflammatory agents. Finally, the challenges associated with the acid-sensitive prodrug strategy are discussed, along with future directions.

Bone targeted nano-drug and nano-delivery

There are currently no targeted delivery systems to satisfactorily treat bone-related disorders. Many clinical drugs consisting of small organic molecules have a short circulation half-life and do not effectively reach the diseased tissue site. This coupled with repeatedly high dose usage that leads to severe side effects. With the advance in nanotechnology, drugs contained within a nano-delivery device or drugs aggregated into nanoparticles (nano-drugs) have shown promises in targeted drug delivery. The ability to design nanoparticles to target bone has attracted many researchers to develop new systems for treating bone related diseases and even repurposing current drug therapies. In this review, we shall summarise the latest progress in this area and present a perspective for future development in the field. We will focus on calcium-based nanoparticle systems that modulate calcium metabolism and consequently, the bone microenvironment to inhibit disease progression (including cancer). We shall also review the bone affinity drug family, bisphosphonates, as both a nano-drug and nano-delivery system for bone targeted therapy. The ability to target and release the drug in a controlled manner at the disease site represents a promising safe therapy to treat bone diseases in the future.

Cysteinylprolyl ester-mediated drug release from a lipid-drug conjugate

For small-molecule drugs, lipidation via a cleavable linkage can extend half-life in circulation through interaction with albumin. Here we modified the cysteinylprolyl ester (CPE) system used in peptide thioester synthesis, which normally requires basic conditions, for use as an self-immolative linker and release device for a lipid-gemcitabine conjugate. To improve release under physiological conditions for medical application, a methyl group at the α-position of cysteine on the CPE unit was incorporated in anticipation of the Thorpe-Ingold effect. As a result, Ac-Gly-(α-Me)Cys(SH)-Pro-gemcitabine 11 drastically promoted the release of gemcitabine in comparison with Ac-Gly-Cys(SH)-Pro-gemcitabine 10. Furthermore, in the presence of bovine serum albumin and/or 2-mercaptoethanesulfonic acid, the gentle and continuous release of gemcitabine from the lipid-gemcitabine conjugate 16 was achieved. In addition to gemcitabine, this method could allow high clearance drugs, including nucleic acid and prostacyclin derivatives, to maintain their biological activity long enough to become effective.

Engineering small-molecule and protein drugs for targeting bone tumors

Bone cancer is common and severe. Both primary (e.g., osteosarcoma, Ewing sarcoma) and secondary (e.g., metastatic) bone cancers lead to significant health problems and death. Currently, treatments such as chemotherapy, hormone therapy, and radiation therapy are used to treat bone cancer, but they often only shrink or slow tumor growth and do not eliminate cancer completely. The bone microenvironment contributes unique signals that influence cancer growth, immunogenicity, and metastasis. Traditional cancer therapies have limited effectiveness due to off-target effects and poor distribution on bones. As a result, therapies with improved specificity and efficacy for treating bone tumors are highly needed. One of the most promising strategies involves the targeted delivery of pharmaceutical agents to the site of bone cancer by introduction of bone-targeting moieties, such as bisphosphonates or oligopeptides. These moieties have high affinities to the bone hydroxyapatite matrix, a structure found exclusively in skeletal tissue, and can enhance the targeting ability and efficacy of anticancer drugs when combating bone tumors. This review focuses on the engineering of small molecules and proteins with bone-targeting moieties for the treatment of bone tumors.

Liver-targeted polymeric prodrugs delivered subcutaneously improve tafenoquine therapeutic window for malaria radical cure

Approximately 3.3 billion people live with the threat of Plasmodium vivax malaria. Infection can result in liver-localized hypnozoites, which when reactivated cause relapsing malaria. This work demonstrates that an enzyme-cleavable polymeric prodrug of tafenoquine addresses key requirements for a mass administration, eradication campaign: excellent subcutaneous bioavailability, complete parasite control after a single dose, improved therapeutic window compared to the parent oral drug, and low cost of goods sold (COGS) at less than $1.50 per dose. Liver targeting and subcutaneous dosing resulted in improved liver:plasma exposure profiles, with increased efficacy and reduced glucose 6-phosphate dehydrogenase-dependent hemotoxicity in validated preclinical models. A COGS and manufacturability analysis demonstrated global scalability, affordability, and the ability to redesign this fully synthetic polymeric prodrug specifically to increase global equity and access. Together, this polymer prodrug platform is a candidate for evaluation in human patients and shows potential for P. vivax eradication campaigns.

Hybrids of Sterically Hindered Phenols and Diaryl Ureas: Synthesis, Switch from Antioxidant Activity to ROS Generation and Induction of Apoptosis

The utility of sterically hindered phenols (SHPs) in drug design is based on their chameleonic ability to switch from an antioxidant that can protect healthy tissues to highly cytotoxic species that can target tumor cells. This work explores the biological activity of a family of 45 new hybrid molecules that combine SHPs equipped with an activating phosphonate moiety at the benzylic position with additional urea/thiourea fragments. The target compounds were synthesized by reaction of iso(thio)cyanates with C-arylphosphorylated phenols containing pendant 2,6-diaminopyridine and 1,3-diaminobenzene moieties. The SHP/urea hybrids display cytotoxic activity against a number of tumor lines. Mechanistic studies confirm the paradoxical nature of these substances which combine pronounced antioxidant properties in radical trapping assays with increased reactive oxygen species generation in tumor cells. Moreover, the most cytotoxic compounds inhibited the process of glycolysis in SH-SY5Y cells and caused pronounced dissipation of the mitochondrial membrane of isolated rat liver mitochondria. Molecular docking of the most active compounds identified the activator allosteric center of pyruvate kinase M2 as one of the possible targets. For the most promising compounds, 11b and 17b, this combination of properties results in the ability to induce apoptosis in HuTu 80 cells along the intrinsic mitochondrial pathway. Cyclic voltammetry studies reveal complex redox behavior which can be simplified by addition of a large excess of acid that can protect some of the oxidizable groups by protonations. Interestingly, the re-reduction behavior of the oxidized species shows considerable variations, indicating different degrees of reversibility. Such reversibility (or quasi-reversibility) suggests that the shift of the phenol-quinone equilibrium toward the original phenol at the lower pH may be associated with lower cytotoxicity.

Technetium-99m labeled core shell hyaluronate nanoparticles as tumor responsive, metastatic skeletal lesion targeted combinatorial theranostics

Achieving target specific delivery of chemotherapeutics in metastatic skeletal lesions remains a major challenge. Towards this, a dual drug loaded, radiolabeled multi-trigger responsive nanoparticles having partially oxidized hyaluronate (HADA) conjugated to alendronate shell and palmitic acid core were developed. While the hydrophobic drug, celecoxib was encapsulated in the palmitic acid core, the hydrophilic drug, doxorubicin hydrochloride was linked to the shell via a pH responsive imine linkage. Hydroxyapatite binding studies showed affinity of alendronate conjugated HADA nanoparticles to bones. Enhanced cellular uptake of the nanoparticles was achieved via HADA-CD44 receptor binding. HADA nanoparticles demonstrated trigger responsive release of encapsulated drugs in the presence of hyaluronidase, pH and glucose, present in excess in the tumor microenvironment. Efficacy of the nanoparticles for combination chemotherapy was established by >10-fold reduction in IC₅₀ of drug loaded particles with a combination index of 0.453, as compared to free drugs in MDA-MB-231 cells. The nanoparticles could be radiolabeled with the gamma emitting radioisotope technetium-99m (^99mTc) through a simple, 'chelator free', procedure with excellent radiochemical purity (RCP) (>90 %) and in vitro stability. ^99mTc-labeled drug loaded nanoparticles reported herein constitutes a promising theranostic agent to target metastatic bone lesions. STATEMENT OF HYPOTHESES: Technetium-99m labeled, alendronate conjugated, dual targeting, tumor responsive, hyaluronate nanoparticle for tumor specific drug release and enhanced therapeutic effect, with real-time in vivo monitoring.

Diverse Biological Activity of Benzofuroxan/Sterically Hindered Phenols Hybrids

Combining two pharmacophores in a molecule can lead to useful synergistic effects. Herein, we show hybrid systems that combine sterically hindered phenols with dinitrobenzofuroxan fragments exhibit a broad range of biological activities. The modular assembly of such phenol/benzofuroxan hybrids allows variations in the phenol/benzofuroxan ratio. Interestingly, the antimicrobial activity only appears when at least two benzofuroxan moieties are introduced per phenol. The most potent of the synthesized compounds exhibit high cytotoxicity against human duodenal adenocarcinoma (HuTu 80), human breast adenocarcinoma (MCF-7), and human cervical carcinoma cell lines. This toxicity is associated with the induction of apoptosis via the internal mitochondrial pathway and an increase in ROS production. Encouragingly, the index of selectivity relative to healthy tissues exceeds that for the reference drugs Doxorubicin and Sorafenib. The biostability of the leading compounds in whole mice blood is sufficiently high for their future quantification in biological matrices.

Brief review: Applications of nanocomposite in electrochemical sensor and drugs delivery

The recent advancement of nanoparticles (NPs) holds significant potential for treating various ailments. NPs are employed as drug carriers for diseases like cancer because of their small size and increased stability. In addition, they have several desirable properties that make them ideal for treating bone cancer, including high stability, specificity, higher sensitivity, and efficacy. Furthermore, they might be taken into account to permit the precise drug release from the matrix. Drug delivery systems for cancer treatment have progressed to include nanocomposites, metallic NPs, dendrimers, and liposomes. Materials’ mechanical strength, hardness, electrical and thermal conductivity, and electrochemical sensors are significantly improved using nanoparticles (NPs). New sensing devices, drug delivery systems, electrochemical sensors, and biosensors can all benefit considerably from the NPs’ exceptional physical and chemical capabilities. Nanotechnology is discussed in this article from a variety of angles, including its recent applications in the medical sciences for the effective treatment of bone cancers and its potential as a promising option for treating other complex health anomalies via the use of anti-tumour therapy, radiotherapy, the delivery of proteins, antibiotics, and vaccines, and other methods. This also brings to light the role that model simulations can play in diagnosing and treating bone cancer, an area where Nanomedicine has recently been formulated. There has been a recent uptick in using nanotechnology to treat conditions affecting the skeleton. Consequently, it will pave the door for more effective utilization of cutting-edge technology, including electrochemical sensors and biosensors, and improved therapeutic outcomes.

An Acid-Sensitive Bone Targeting Delivery System Carrying Acacetin Prevents Osteoporosis in Ovariectomized Mice

One effective treatment for postmenopausal osteoporosis is to inhibit osteoclasts and subsequent bone resorption. In our study, we demonstrated that acacetin, a flavone with potential therapeutic effects in infections, cancers, and several metabolic disorders, inhibited osteoclast differentiation and bone resorption in vitro. For improving the efficacy of acacetin in vivo, we developed an acid-sensitive bone-targeting delivery system composed of an acid-sensitive linker (N-ε-maleimidocaproic acid hydrazide, EMCH) for ensuring an effective release of acacetin at the site of action and a hydrophilic aspartic acid hexapeptide ((Asp)6, D6) as the effective bone targeting agent. Our results revealed that Acacetin-EMCH-D6 specifically bound to the bone surface once administrated in vivo, prolonged the retention time in bone and released acacetin at the osteoclastic bone resorption sites where the acidity is higher. We further demonstrated that, in ovariectomy-induced osteoporosis mice, treatment with Acacetin-EMCH-D6 inhibited osteoclast formation and increased trabecular bone mass. On the contrary, neither acacetin nor EMCH-D6 with the same dosage alone showed significant anti-osteoporosis effects in vivo. Mechanistically, targeted delivery of acacetin to the bone resorption sites by Acacetin-EMCH-D6 inhibited autophagy through activating PI3K/AKT/mTOR pathway in osteoclasts, while the activation of autophagy by rapamycin partially reversed the inhibitory effects of acacetin in vitro and in vivo. In summary, our study, for the first time, showed that the acid-sensitive bone-targeting delivery system carrying acacetin was effective for the treatment of postmenopausal osteoporosis. Thus, targeted delivery of acacetin using Acacetin-EMCH-D6 to bone resorption sites is a promising therapy for osteoporosis.

Development and Biochemical Characterization of Self-Immolative Linker Containing GnRH-III-Drug Conjugates

The human gonadotropin releasing hormone (GnRH-I) and its sea lamprey analogue GnRH-III specifically bind to GnRH receptors on cancer cells and can be used as targeting moieties for targeted tumor therapy. Considering that the selective release of drugs in cancer cells is of high relevance, we were encouraged to develop cleavable, self-immolative GnRH-III-drug conjugates which consist of a p-aminobenzyloxycarbonlyl (PABC) spacer between a cathepsin B-cleavable dipeptide (Val-Ala, Val-Cit) and the classical anticancer drugs daunorubicin (Dau) and paclitaxel (PTX). Alongside these compounds, non-cleavable GnRH-III-drug conjugates were also synthesized, and all compounds were analyzed for their antiproliferative activity. The cleavable GnRH-III bioconjugates revealed a growth inhibitory effect on GnRH receptor-expressing A2780 ovarian cancer cells, while their activity was reduced on Panc-1 pancreatic cancer cells exhibiting a lower GnRH receptor level. Moreover, the antiproliferative activity of the non-cleavable counterparts was strongly reduced. Additionally, the efficient cleavage of the Val-Ala linker and the subsequent release of the drugs could be verified by lysosomal degradation studies, while radioligand binding studies ensured that the GnRH-III-drug conjugates bound to the GnRH receptor with high affinity. Our results underline the high value of GnRH-III-based homing devices and the application of cathepsin B-cleavable linker systems for the development of small molecule drug conjugates (SMDCs).

A facile aqueous production of bisphosphonated-polyelectrolyte functionalized magnetite nanoparticles for pH-specific targeting of acidic-bone cells

Bone malignancy treatment is being hindered due to the insufficient selectivity of therapeutic nanoparticles towards malignant bone sites. Polyelectrolyte functionalized magnetic nanoparticles having dually specific pH-sensing ability and bisphosphonate moieties, can be an effective solution for selective targeting of bone malignancies. First, polyelectrolyte was prepared via N-carboxycitraconyzation of chitosan (NCCS) followed by successive functionalization with alendronic acid (AL) and fluorescein isothiocyanate (FITC). Then, Fe3O4-NCCS-FITC-AL nanoparticles were synthesized by a facile one-step microwave-assisted aqueous method via in situ surface functionalization. The formation, crystal structure, and surface conjugation of Fe3O4 nanoparticles with polyelectrolytic stabilizer were confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analyses. Synthesized Fe3O4-NCCS-FITC-AL nanoparticles were superparamagnetic, colloidally stable and highly hemocompatible under physiological conditions. Moreover, at pH 5.0, Fe3O4-NCCS-FITC-AL nanoparticles formed a precipitate due to inversion of their surface charge. This pH-dependent charge-inversion drastically changed the interactions with erythrocytes and bones. Selective membranolysis of erythrocytes occurred at pH 5.0. The designed nanoparticles showed enough potential for selective targeting of pathological bone sites in early-stage magnetofluorescent imaging and as a therapeutics carrier to treat malignant bone diseases.

Targeted Delivery of Chemotherapeutic Agents for Osteosarcoma Treatment

Since osteosarcoma (OS) is an aggressive bone cancer with unknown molecular pathways of etiology and pathophysiology, improving patient survival has long been a challenge. The conventional therapy is a complex multidisciplinary management that include radiotherapy, chemotherapy which followed by surgery and then post-operative adjuvant chemotherapy. However, they have severe side effects because the majority of the medicines used have just a minor selectivity for malignant tissue. As a result, treating tumor cells specifically without damaging healthy tissue is currently a primary goal in OS therapy. The coupling of chemotherapeutic drugs with targeting ligands is a unique therapy method for OS that, by active targeting, can overcome the aforementioned hurdles. This review focuses on advances in ligands and chemotherapeutic agents employed in targeted delivery to improve the capacity of active targeting and provide some insight into future therapeutic research for OS.

Development of novel bone targeting peptide-drug conjugate of 13-aminomethyl-15-thiomatrine for osteoporosis therapy

13-Aminomethyl-15-thiomatrine (M19) previously developed by our research group was a promising candidate for novel anti-osteoporosis drug development. However, the application of M19 was limited by its unsatisfactory druggability including poor chemical stability, excessively broad pharmacological activity and some degree of cytotoxicity. To solve these problems, M19-based bone targeting and cathepsin K sensitive peptide–drug conjugates (BTM19-1, BTM19-2 and BTM19-3) were developed to realize precise drug release in the bone tissue. Subsequent studies showed a rapid drug release process via cathepsin K digestion but sufficient stability over several hours in chymotrypsin. Besides, greatly improved chemical stability and strong hydroxyapatite binding affinity were also demonstrated. In biological evaluation studies, these PDCs showed less cytotoxicity and similar osteoclast inhibitory activity compared with the prototype drug. The optimal BTM19-2 could serve as a suitable candidate for further osteoporosis therapy research.

13-Aminomethyl-15-thiomatrine (M19) previously developed by our research group was a promising candidate for novel anti-osteoporosis drug development.

New Progress in Improving the Delivery Methods of Bisphosphonates in the Treatment of Bone Tumors

Bone tumors are tumors that occur in the bone or its accessory tissues, including primary tumors and metastatic tumors. The main mechanism of bisphosphonate is to inhibit the resorption of destructive bone, inhibit the activity of osteoclasts and reduce the concentration of blood calcium. Therefore, bisphosphonates can be used for malignant hypercalcaemia, pain caused by osteolytic bone metastasis, prevention of osteolytic bone metastasis, multiple myeloma osteopathy, improving radiosensitivity and so on. However, the traditional administration of bisphosphonates can cause a series of adverse reactions. To overcome this disadvantage, it is necessary to develop novel methods to improve the delivery of bisphosphonates. In this paper, the latest research progress of new and improved bisphosphonate drug delivery methods in the treatment of bone tumors is reviewed. At present, the main design idea is to connect bisphosphonate nanoparticles, liposomes, microspheres, microcapsules, couplings, prodrugs and bone tissue engineering to targeted anti-tumors systems, and positive progress has been made in in vitro and animal experiments. However, its safety and effectiveness in human body still need to be verified by more studies.

Polyethylenimine-Bisphosphonate-Cyclodextrin Ternary Conjugates: Supramolecular Systems for the Delivery of Antineoplastic Drugs

Bisphosphonates (BPs) are bone-binding molecules that provide targeting capabilities to bone cancer cells when conjugated with drug-carrying polymers. This work reports the design, synthesis, and biological evaluation of polyethyleneimine-BP-cyclodextrin (PEI-BP-CD) ternary conjugates with supramolecular capabilities for the loading of antineoplastic drugs. A straightforward, modular, and versatile strategy based on the click aza-Michael addition reaction of vinyl sulfones (VSs) allows the grafting of BPs targeting ligands and βCD carrier appendages to the PEI polymeric scaffold. The in vitro evaluation (cytotoxicity, cellular uptake, internalization routes, and subcellular distribution) for the ternary conjugates and their doxorubicin inclusion complexes in different bone-related cancer cell lines (MC3T3-E1 osteoblasts, MG-63 sarcoma cells, and MDA-MB-231 breast cancer cells) confirmed specificity, mitochondrial targeting, and overall capability to mediate a targeted drug transport to those cells. The in vivo evaluation using xenografts of MG-63 and MDA-MB-231 cells on mice also confirmed the targeting of the conjugates.

Harnessing the power of antibodies to fight bone metastasis

Antibody-based therapies have proved to be of great value in cancer treatment. Despite the clinical success of these biopharmaceuticals, reaching targets in the bone microenvironment has proved to be difficult due to the relatively low vascularization of bone tissue and the presence of physical barriers. Here, we have used an innovative bone-targeting (BonTarg) technology to generate a first-in-class bone-targeting antibody. Our strategy involves the use of pClick antibody conjugation technology to chemically couple the bone-targeting moiety bisphosphonate to therapeutic antibodies. Bisphosphonate modification of these antibodies results in the delivery of higher conjugate concentrations to the bone metastatic niche, relative to other tissues. In xenograft mice models, this strategy provides enhanced inhibition of bone metastases and multiorgan secondary metastases that arise from bone lesions. Specific delivery of therapeutic antibodies to the bone, therefore, represents a promising strategy for the treatment of bone metastatic cancers and other bone diseases.

Drug Delivery to the Bone Microenvironment Mediated by Exosomes: An Axiom or Enigma

The increasing incidence of bone-related disorders is causing a burden on the clinical scenario. Even though bone is one of the tissues that possess tremendous regenerative potential, certain bone anomalies need therapeutic intervention through appropriate delivery of a drug. Among several nanosystems and biologics that offer the potential to contribute towards bone healing, the exosomes from the class of extracellular vesicles are outstanding. Exosomes are extracellular nanovesicles that, apart from the various advantages, are standing out of the crowd for their ability to conduct cellular communication. The internal cargo of the exosomes is leading to its potential use in therapeutics. Exosomes are being unraveled in terms of the mechanism as well as application in targeting various diseases and tissues. Through this review, we have tried to understand and review all that is already established and the gap areas that still exist in utilizing them as drug delivery vehicles targeting the bone. The review highlights the potential of the exosomes towards their contribution to the drug delivery scenario in the bone microenvironment. A comparison of the pros and cons of exosomes with other prevalent drug delivery systems is also done. A section on the patents that have been generated so far from this field is included.

Self-immolative Linkers in Prodrugs and Antibody Drug Conjugates in Cancer Treatment

BACKGROUND

The design of anti-cancer therapies with high anti-tumour efficacy and reduced toxicity continues to be challenging. Anti-cancer prodrug and antibody-drug-conjugate (ADC) strategies that can specifically and efficiently deliver cytotoxic compounds to cancer cells have been used to overcome some of the challenges. Key to the success of many of these strategies is a self-immolative linker, which after activation can release the drug payload. Various types of triggerable self-immolative linkers are used in prodrugs and ADCs to improve their efficacy and safety.

OBJECTIVE

Numerous patents have reported the significance of self-immolative linkers in prodrugs and ADCs in cancer treatment. Based on the recent patent literature, we summarise methods for designing the site-specific activation of non-toxic prodrugs and ADCs in order to improve selectivity for killing cancer cells.

METHODS

In this review, an integrated view of the potential use of prodrugs and ADCs in cancer treatment are provided. This review presents recent patents and related publications over the past ten years to 2020.

RESULTS

The recent patent literature has been summarised for a wide variety of self-immolative PABC linkers, which are cleaved by factors including responding to the difference between the extracellular and intracellular environments (pH, ROS, glutathione), by over-expressed enzymes (cathepsin, plasmin, β-glucuronidase) or bioorthogonal activation. The mechanism for self-immolation involves the linker undergoing a 1,4- or 1,6-elimination (via electron cascade) or intramolecular cyclisation to release cytotoxic drug at the targeted site.

CONCLUSION

This review provides the commonly used strategies from recent patent literature in the development of prodrugs based on targeted cancer therapy and antibody-drug conjugates, which show promising results in therapeutic applications.

Drug delivery nanocarriers and recent advances ventured to improve therapeutic efficacy against osteosarcoma: an overview

BACKGROUND

Osteosarcoma (OS) is one of the key cancers affecting the bone tissues, primarily occurred in children and adolescence. Recently, chemotherapy followed by surgery and then post-operative adjuvant chemotherapy is widely used for the treatment of OS. However, the lack of selectivity and sensitivity to tumor cells, the development of multi-drug resistance (MDR), and dangerous side effects have restricted the use of chemotherapeutics.

MAIN BODY

There is an unmet need for novel drug delivery strategies for effective treatment and management of OS. Advances in nanotechnology have led to momentous progress in the design of tumor-targeted drug delivery nanocarriers (NCs) as well as functionalized smart NCs to achieve targeting and to treat OS effectively. The present review summarizes the drug delivery challenges in OS, and how organic nanoparticulate approaches are useful in overcoming barriers will be explained. The present review describes the various organic nanoparticulate approaches such as conventional nanocarriers, stimuli-responsive NCs, and ligand-based active targeting strategies tested against OS. The drug conjugates prepared with copolymer and ligand having bone affinity, and advanced promising approaches such as gene therapy, gene-directed enzyme prodrug therapy, and T cell therapy tested against OS along with their reported limitations are also briefed in this review.

CONCLUSION

The nanoparticulate drugs, drug conjugates, and advanced therapies such as gene therapy, and T cell therapy have promising and potential application in the effective treatment of OS. However, many of the above approaches are still at the preclinical stage, and there is a long transitional period before their clinical application.

Targeted nanomedicines for the treatment of bone disease and regeneration

Targeted delivery by either passive or active targeting of therapeutics to the bone is an attractive treatment for various bone related diseases such as osteoporosis, osteosarcoma, multiple myeloma, and metastatic bone tumors. Engineering novel drug delivery carriers can increase therapeutic efficacy and minimize the risk of side effects. Developmnet of nanocarrier delivery systems is an interesting field of ongoing studies with opportunities to provide more effective therapies. In addition, preclinical nanomedicine research can open new opportunities for preclinical bone-targeted drug delivery; nevertheless, further research is needed to progress these therapies towards clinical applications. In the present review, the latest advancements in targeting moieties and nanocarrier drug delivery systems for the treatment of bone diseases are summarized. We also review the regeneration capability and effective delivery of nanomedicines for orthopedic applications.

Improving the Stability of Maleimide-Thiol Conjugation for Drug Targeting

Maleimides are essential compounds for drug conjugation reactions via thiols to antibodies, peptides and other targeting units. However, one main drawback is the occurrence of thiol exchange reactions with, for example, glutathione resulting in loss of the targeting ability. A new strategy to overcome such retro-Michael exchange processes of maleimide-thiol conjugates by stabilization of the thiosuccinimide via a transcyclization reaction is presented. This reaction enables the straightforward synthesis of stable maleimide-thiol adducts essential in drug-conjugation applications.

Targeting nanoparticles for diagnosis and therapy of bone tumors: Opportunities and challenges

A variety of targeted nanoparticles were developed for the diagnosis and therapy of orthotopic and metastatic bone tumors during the past decade. This critical review will focus on principles and methods in the design of these bone-targeted nanoparticles. Ligands including bisphosphonates, aspartic acid-rich peptides and synthetic polymers were grafted on nanoparticles such as PLGA nanoparticles, liposomes, dendrimers and inorganic nanoparticles for bone targeting. Besides, other ligands such as monoclonal antibodies, peptides and aptamers targeting biomarkers on tumor/bone cells were identified for targeted diagnosis and therapy. Examples of targeted nanoparticles for the early detection of bone metastatic tumors and the ablation of cancer via chemotherapy, photothermal therapy, gene therapy and combination therapy will be intensively reviewed. The development of multifunctional nanoparticles to break down the "vicious" cycle between tumor cell proliferation and bone resorption, and the challenges and perspectives in this area will be discussed.

Phosphonopeptides containing free phosphonic groups: recent advances

Phosphonopeptides are mimetics of peptides in which phosphonic acid or related (phosphinic, phosphonous etc.) group replaces either carboxylic acid group present at C-terminus, is located in the peptidyl side chain, or phosphonamidate or phosphinic acid mimics peptide bond. Acting as inhibitors of key enzymes related to variable pathological states they display interesting and useful physiologic activities with potential applications in medicine and agriculture. Since the synthesis and biological properties of peptides containing C-terminal diaryl phosphonates and those with phosphonic fragment replacing peptide bond were comprehensively reviewed, this review concentrate on peptides holding free, unsubstituted phosphonic acid moiety. There are two groups of such mimetics: (i) peptides in which aminophosphonic acid is located at C-terminus of the peptide chain with most of them (including antibiotics isolated from bacteria and fungi) exhibiting antimicrobial activity; (ii) non-hydrolysable analogues of phosphonoamino acids, which are useful tools to study physiologic effects of phosphorylations.

Microfluidic fabrication of alendronate-loaded chitosan nanoparticles for enhanced osteogenic differentiation of stem cells

AIMS

In this study, we used a cross-junction microfluidic device for preparation of alendronate-loaded chitosan nanoparticles with desired characteristics to introduce a suitable element for bone tissue engineering scaffolds.

MAIN METHODS

By controlling the reaction condition in microfluidic device, six types of alendronate-loaded chitosan nanoparticles were fabricated which had different physical properties. Hydrodynamic diameter of synthetized particles was evaluated by dynamic light scattering (102 to 215 nm). Nanoparticle morphology was determined by SEM and AFM images. The osteogenic effects of prepared selected nanoparticles on human adipose stem cells (hA-MSCs) were evaluated by assessment of alkaline phosphatase (ALP) activity, calcium deposition, ALP and osteopontin gene expression.

KEY FINDINGS

The highest loading efficiency percentage (%LE) was %32.42 ± 2.02. Based on MTT assessment, two samples which had no significant cytotoxicity were chosen for further studies (particle sizes and %LE were 142 ± 6.1 nm, 198 ± 16.56 nm, %16.76 ± 3.91 and %32.42 ± 2.02, respectively). In vitro release behavior of nanoparticles displayed pH responsive characteristics. Significant faster release was seen in acidic pH = 5.8 than neutral pH = 7.4. The selected nanoparticles demonstrated higher ALP activity at 14 days in comparison to selected blank sample and osteogenic differentiation media (ODM) and a downregulation at 21 days in comparison to 14 days. Calcium content assay at 21 days displayed significant differences between alendronate-loaded nanoparticles and ODM. ALP and osteopontin mRNA expression was significantly higher than the cells cultured in ODM at 14 and 21 days.

SIGNIFICANCE

We concluded that our prepared nanoparticles significantly enhanced osteogenic differentiation of hA-MSCs and can be a suitable compartment of bone tissue engineering scaffolds.

Bone-targeted PAMAM nanoparticle to treat bone metastases of lung cancer

Aim: To prepare pH-sensitive nanoparticle composed of alendronate (ALN) and poly(amidoamine) (PAMAM) to treat bone metastases of lung cancer. Methods: The solvent evaporation method was used to prepare docetaxel (DTX)-loaded ALN-PAMAM nanoparticles (DTX@ALN-PAMAM). Results: The in vitro results showed DTX@ALN-PAMAM significantly enhanced the anticancer activity of DTX and inhibited the formation of osteoclasts. DTX@ALN-PAMAM concentrated at bone metastasis site in mice, which resulted in the suppression of bone resorption, pain response and growth of bone metastases. Eventually, the therapeutic effect of DTX on bone metastases of lung cancer was obviously improved. Conclusion: ALN modified PAMAM nanoparticle could be an effective platform for the treatment of bone metastases of lung cancer.

Synthesis, mechanisms of action, and toxicity of novel aminophosphonates derivatives conjugated irinotecan in vitro and in vivo as potent antitumor agents

Twenty novel aminophosphonates derivatives (5a-5j and 6a-6j) conjugated irinotecan were synthesized through esterification reaction, and evaluated their anticancer activities using MTT assay. In vitro evaluation revealed that they displayed similar or superior cytotoxicity compared to the positive drug irinotecan against A549, MCF-7, SK-OV-3, MG-63, U2OS and multidrug-resistant (MDR) SK-OV-3/CDDP cancer cell lines. Among them, 9b displayed the most potent activity, with IC₅₀ values of 0.92-3.23 μM against five human cancer cells, which exhibited a 5.4-19.1-fold increase in activity compared to the reference drug irinotecan, respectively. Moreover, cellular mechanism studies suggested that 9b arrested cell cycle at S stage and induced cell apoptosis along with the decrease of mitochondrial membrane potential (MMP). Interestingly, 9b significantly inhibited tumor growth in SK-OV-3 xenograft models in vivo without apparent toxicity, which was better than the positive drug irinotecan. Taken together, 9b possessed potent antitumor activity and may be a promising candidate for the potential treatment of human ovarian cancer cells.

12b80 - Hydroxybisphosphonate Linked Doxorubicin: Bone Targeted Strategy for Treatment of Osteosarcoma

To reply to as yet unmet medical needs to treat osteosarcoma, a form of primary bone cancer, we conceived the 12b80 compound by covalently conjugating antineoplastic compound doxorubicin to a bone targeting hydroxybisphosphonate vector and turned it into a prodrug through a custom linker designed to specifically trigger doxorubicin release in acidic bone tumor microenvironment. Synthesis of 12b80 was thoroughly optimized to be produced at gram scale. 12b80 was evaluated in vitro for high bone support affinity, specific release of doxorubicin in acidic condition, lower cytotoxicity, and cellular uptake of the prodrug. In vivo in rodents, 12b80 displayed rapid and sustained targeting of bone tissue and tumor-associated heterotopic bone and permitted a higher doxorubicin payload in tumor bone environment compared to nonvectorized doxorubicin. Consequently, 12b80 showed much lower toxicity compared to doxorubicin, promoted strong antitumor effects on rodent orthotopic osteosarcoma, displayed a dose-response therapeutic effect, and was more potent than doxorubicin/zoledronate combination.

Understanding the Bone in Cancer Metastasis

The bone is the third most common site of metastasis for a wide range of solid tumors including lung, breast, prostate, colorectal, thyroid, gynecologic, and melanoma, with 70% of metastatic prostate and breast cancer patients harboring bone metastasis.¹ Unfortunately, once cancer spreads to the bone, it is rarely cured and is associated with a wide range of morbidities including pain, increased risk of fracture, and hypercalcemia. This fact has driven experts in the fields of bone and cancer biology to study the bone, and has revealed that there is a great deal that each can teach the other. The complexity of the bone was first described in 1889 when Stephen Paget proposed that tumor cells have a proclivity for certain organs, where they "seed" into a friendly "soil" and eventually grow into metastatic lesions. Dr. Paget went on to argue that although many study the "seed" it would be paramount to understand the "soil." Since this original work, significant advances have been made not only in understanding the cell-autonomous mechanisms that drive metastasis, but also alterations which drive changes to the "soil" that allow a tumor cell to thrive. Indeed, it is now clear that the "soil" in different metastatic sites is unique, and thus the mechanisms that allow tumor cells to remain in a dormant or growing state are specific to the organ in question. In the bone, our knowledge of the components that contribute to this fertile "soil" continues to expand, but our understanding of how they impact tumor growth in the bone remains in its infancy. Indeed, we now appreciate that the endosteal niche likely contributes to tumor cell dormancy, and that osteoclasts, osteocytes, and adipocytes can impact tumor cell growth. Here, we discuss the bone microenvironment and how it impacts cancer cell seeding, dormancy, and growth. © 2018 American Society for Bone and Mineral Research.

Bisphosphonate conjugation for bone specific drug targeting

Bones provide essential functions and are sites of unique biochemistry and specialized cells, but can also be sites of disease. The treatment of bone disorders and neoplasia has presented difficulties in the past, and improved delivery of drugs to bone remains an important goal for achieving effective treatments. Drug targeting strategies have improved drug localization to bone by taking advantage of the high mineral concentration unique to the bone hydroxyapatite matrix, as well as tissue-specific cell types. The bisphosphonate molecule class binds specifically to hydroxyapatite and inhibits osteoclast resorption of bone, providing direct treatment for degenerative bone disorders, and as emerging evidence suggests, cancer. These bone-binding molecules also provide the opportunity to deliver other drugs specifically to bone by bisphosphonate conjugation. Bisphosphonate bone-targeted therapies have been successful in treatment of osteoporosis, primary and metastatic neoplasms of the bone, and other bone disorders, as well as refining bone imaging. In this review, we focus upon the use of bisphosphonate conjugates with antineoplastic agents, and overview bisphosphonate based imaging agents, nanoparticles, and other drugs. We also discuss linker design potential and the current state of bisphosphonate conjugate research progress. Ongoing investigations continue to expand the possibilities for bone-targeted therapeutics and for extending their reach into clinical practice.

Translatable High Drug Loading Drug Delivery Systems Based on Biocompatible Polymer Nanocarriers

Most nanocarriers possess low drug loading, resulting in frequently repeated administration and thereby high cost and increased side effects. Furthermore, the characteristics of nanocarrier materials, especially the drug loading capacity, plays a vital role in the drug delivery efficacy. In this review, we focus on the readily translatable polymeric drug delivery systems with high drug loading, which are comprised of biocompatible polymers such as poly(ethylene glycol), poly( N-vinylpyrrolidone), polyoxazoline, natural proteins like albumin and casein, non-natural proteins such as recombinant elastin-like polypeptides, as well as nucleic acids. At the end of this review, applications of these polymeric nanocarriers on the delivery of proteins and gene drugs are also briefly discussed.

Targeting therapeutics to bone by conjugation with bisphosphonates

Bisphosphonates target and bind avidly to the mineral (hydroxyapatite) found in bone. This targeting ability has been exploited to design and prepare bisphosphonate conjugate prodrugs to deliver a wide variety of drug molecules selectively to bones. It is important that conjugates be stable in the blood stream and that conjugate that is not taken up by bone is eliminated rapidly. The prodrugs should release active drug at a rate appropriate so as to provide efficacy. Radiolabelling is the best method to quantify and evaluate pharmacokinetics, tissue distribution, bone uptake and release of the active drug(s). Recent reports have described bisphosphonate conjugates derived from the antiresorptive drug, alendronic acid and anabolic prostanoid drugs that effectively deliver prostaglandins and prostaglandin EP4 receptor agonists to bone and show enhanced anabolic efficacy and tolerability compared to the drugs alone. These conjugate drugs can be dosed infrequently (weekly or bimonthly) whereas the free drugs must be dosed daily.

Fluorous-tag assisted synthesis of bile acid-bisphosphonate conjugates via orthogonal click reactions: an access to potential anti-resorption bone drugs

The synthesis of a small collection of novel bile acid-bisphosphonate (BA-BP) conjugates as potential drug candidates is reported. The disclosed methodology relied on the installation of azide and thiol functionalities at the head and tail positions, respectively, of the BA scaffold and its subsequent decoration by orthogonal click reactions (copper-catalyzed azide-alkyne cycloaddition, thiol-ene or thiol-yne coupling) to introduce BP units and a fluorophore. Because of the troublesome isolation of the target conjugates by standard procedures, the methodology culminated with the functionalization of the BA scaffold with a light fluorous tag to rapidly and efficiently purify intermediates and final products by fluorous solid-phase extraction.

Bone metastasis target redox-responsive micell for the treatment of lung cancer bone metastasis and anti-bone resorption

In order to inhibit the growth of lung cancer bone metastasis and reduce the bone resorption at bone metastasis sites, a bone metastasis target micelle DOX@DBMs-ALN was prepared. The size and the zeta potential of DOX@DBNs-ALN were about 60 nm and -15 mV, respectively. DOX@DBMs-ALN exhibited high binding affinity with hydroxyapatite and released DOX in redox-responsive manner. DOX@DBMs-ALN was effectively up taken by A549 cells and delivered DOX to the nucleus of A549 cells, which resulted in strong cytotoxicity on A549 cells. The in vivo experimental results indicated that DOX@DBMs-ALN specifically delivered DOX to bone metastasis site and obviously prolonged the retention time of DOX in bone metastasis site. Moreover, DOX@DBMs-ALN not only significantly inhibited the growth of bone metastasis tumour but also obviously reduced the bone resorption at bone metastasis sites without causing marked systemic toxicity. Thus, DOX@DBMs-ALN has great potential in the treatment of lung cancer bone metastasis.