Synthesis and Study of Alendronate Derivatives as Potential Prodrugs of Alendronate Sodium for the Treatment of Low Bone Density and Osteoporosis

Research progress of bone-targeted drug delivery system on metastatic bone tumors

Bone metastases are common in malignant tumors and the effect of conventional treatment is limited. How to effectively inhibit tumor bone metastasis and deliver the drug to the bone has become an urgent issue to be solved. While bone targeting drug delivery systems have obvious advantages in the treatment of bone tumors. The research on bone-targeted anti-tumor therapy has made significant progress in recent years. We introduced the related tumor pathways of bone metastases. The tumor microenvironment plays an important role in metastatic bone tumors. We introduce a drug-loading systems based on different environment-responsive nanocomposites for anti-tumor and anti-metastatic research. According to the process of bone metastases and the structure of bone tissue, we summarized the information on bone-targeting molecules. Bisphosphate has become the first choice of bone-targeted drug delivery carrier because of its affinity with hydroxyapatite in bone. Therefore, we sought to summarize the bone-targeting molecule of bisphosphate to identify the modification effect on bone-targeting. And this paper discusses the relationship between bisphosphate bone targeting molecular structure and drug delivery carriers, to provide some new ideas for the research and development of bone-targeting drug delivery carriers. Targeted therapy will make a more outstanding contribution to the treatment of tumors.

Prodrugs of pyrophosphates and bisphosphonates: disguising phosphorus oxyanions

Pyrophosphates have important functions in living systems and thus pyrophosphate-containing molecules and their more stable bisphosphonate analogues have the potential to be used as drugs for treating many diseases including cancer and viral infections. Both pyrophosphates and bisphosphonates are polyanionic at physiological pH and, whilst this is essential for their biological activity, it also limits their use as therapeutic agents. In particular, the high negative charge density of these compounds prohibits cell entry other than by endocytosis, prevents transcellular oral absorption and causes sequestration to bone. Therefore, prodrug strategies have been developed to temporarily disguise the charges of these compounds. This review examines the various systems that have been used to mask the phosphorus-containing moieties of pyrophosphates and bisphosphonates and also illustrates the utility of such prodrugs.

Platinum Nanoparticles in Biomedicine: Preparation, Anti-Cancer Activity, and Drug Delivery Vehicles

Cancer is the main cause of morbidity and mortality worldwide, excluding infectious disease. Because of their lack of specificity in chemotherapy agents are used for cancer treatment, these agents have severe systemic side effects, and gradually lose their therapeutic effects because most cancers become multidrug resistant. Platinum nanoparticles (PtNPs) are relatively new agents that are being tested in cancer therapy. This review covers the various methods for the preparation and physicochemical characterization of PtNPs. PtNPs have been shown to possess some intrinsic anticancer activity, probably due to their antioxidant action, which slows tumor growth. Targeting ligands can be attached to functionalized metal PtNPs to improve their tumor targeting ability. PtNPs-based therapeutic systems can enable the controlled release of drugs, to improve the efficiency and reduce the side effects of cancer therapy. Pt-based materials play a key role in clinical research. Thus, the diagnostic and medical industries are exploring the possibility of using PtNPs as a next-generation anticancer therapeutic agent. Although, biologically prepared nanomaterials exhibit high efficacy with low concentrations, several factors still need to be considered for clinical use of PtNPs such as the source of raw materials, stability, solubility, the method of production, biodistribution, accumulation, controlled release, cell-specific targeting, and toxicological issues to human beings. The development of PtNPs as an anticancer agent is one of the most valuable approaches for cancer treatment. The future of PtNPs in biomedical applications holds great promise, especially in the area of disease diagnosis, early detection, cellular and deep tissue imaging, drug/gene delivery, as well as multifunctional therapeutics.

Bisphosphonates, Old Friends of Bones and New Trends in Clinics

Bisphosphonates, used for a long time in osteoporosis management, are currently the target of intensive research, from pre-formulation studies to more advanced stages of clinical practice. This review presents an overview of the contributions of this family of compounds to human health, starting with the chemistry and clinical uses of bisphosphonates. Following this, their pharmacology is described, highlighting administration-borne handicaps and undesirable effects. The last three sections of the review describe the research efforts that seek to curb delivery-related issues and expand bisphosphonate use. Innovative routes and strategies of administration, such as nano-encapsulation for oral intake or injectable cements for local or in-bone delivery are presented, as well as the latest results of case studies or preclinical studies proposing new therapeutic indications for the clinically approved bisphosphonates. Finally, a selection of anti-infectious bisphosphonate new drug candidates is shown, with focus on the molecules reported in the last two decades.

Acidity constant and DFT-based modelling of pH-responsive alendronate loading and releasing on propylamine-modified silica surface

A computational methodology that couples the acidity (K_a) and density functional theory (DFT) calculations has been developed to explain the pH-dependent drug loading on and releasing from mesoporous silica nanoparticles.

Drug-Eluting Biodegradable Implants for the Sustained Release of Bisphosphonates

Despite being one of the first-line treatments for osteoporosis, the bisphosphonate drug class exhibits an extremely low oral bioavailability (<1%) due to poor absorption from the gastrointestinal tract. To overcome this, and to explore the potential for sustained drug release, bioerodible poly(lactic acid) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) implants loaded with the bisphosphonate alendronate sodium (ALN) were prepared via hot-melt extrusion. The rate of drug release in vitro was modulated by tailoring the ratio of lactide to glycolide in the polymer and by altering the ALN-loading of the implants. All investigated implants exhibited sustained ALN release in vitro between 25 to 130 days, where implants of greater glycolide composition and higher ALN-loadings released ALN more rapidly. All PLGA implants demonstrated a sigmoidal release profile, characterised by an initial surface dissolution phase, followed by a period of zero-order drug diffusion, then relaxation or erosion of the polymer chains that caused accelerated release over the subsequent days. Contrastingly, the PLA implants demonstrated a logarithmic release profile, characterised by a gradual decrease in ALN release over time.

Preparation, Characterization, and Radiolabeling of [68Ga]Ga-NODAGA-Pamidronic Acid: A Potential PET Bone Imaging Agent

Early diagnosis of bone metastases is crucial to prevent skeletal-related events, and for that, the non-invasive techniques to diagnose bone metastases that make use of image-guided radiopharmaceuticals are being employed as an alternative to traditional biopsies. Hence, in the present work, we tested the efficacy of a gallium-68 (⁶⁸Ga)-based compound as a radiopharmaceutical agent towards the bone imaging in positron emitting tomography (PET). For that, we prepared, thoroughly characterized, and radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid radiopharmaceutical, a ⁶⁸Ga precursor for PET bone cancer imaging applications. The preparation of NODAGA-pamidronic acid was performed via the N-Hydroxysuccinimide (NHS) ester strategy and was characterized using liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MSⁿ). The unreacted NODAGA chelator was separated using the ion-suppression reverse phase-high performance liquid chromatography (RP-HPLC) method, and the freeze-dried NODAGA-pamidronic acid was radiolabeled with ⁶⁸Ga. The radiolabeling condition was found to be most optimum at a pH ranging from 4 to 4.5 and a temperature of above 60 °C. From previous work, we found that the pamidronic acid itself has a good bone binding affinity. Moreover, from the analysis of the results, the ionic structure of radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid has the ability to improve the blood clearance and may exert good renal excretion, enhance the bone-to-background ratio, and consequently the final image quality. This was reflected by both the in vitro bone binding assay and in vivo animal biodistribution presented in this research.

Synthesis and biological activities of drugs for the treatment of osteoporosis

Osteoporosis is an asymptomatic progressive disease. With the improvement of people's living standard and the aging of population, osteoporosis and its fracture have become one of the main diseases threatening the aging society. The serious medical and social burden caused by this has aroused wide public concern. Osteoporosis is listed as one of the three major diseases of the elderly. At present, the drugs for osteoporosis include bone resorption inhibitors and bone formation promoters. The purpose of these anti-osteoporosis drugs is to balance osteoblast bone formation and osteoclast bone resorption. With the development of anti-osteoporosis drugs, new anti osteoporosis drugs have been designed and synthesized. There are many kinds of new compounds with anti osteoporosis activity, but most of them are concentrated on the original drugs with anti osteoporosis activity, or the natural products with anti-osteoporosis activity are extracted from the natural products for structural modification to obtain the corresponding derivatives or analogues. These target compounds showed good ALP activity in vitro and in vivo, promoted osteoblast differentiation and mineralization, or had anti TRAP activity, inhibited osteoclast absorption. This work attempts to systematically review the studies on the synthesis and bioactivity of anti-osteoporosis drugs in the past 10 years. The structure-activity relationship was discussed, which provided a reasonable idea for the design and development of new anti-osteoporosis drugs.

Synthesis, characterization, kinetic drug release and anticancer activity of bisphosphonates multi-walled carbon nanotube conjugates

The statistical proof that most forms of cancer metastasize to bone tissue has redirected research focus to the development of efficient secondary bone cancer treatment regimens. Bisphosphonates (BPs) have been earmarked as a drug of choice for bone metastasis. However, they have a shortcoming of being released before reaching targeted sites due to their low molecular weight. In haste to attain increased efficacy, there is a tendency for drug overdose to occur, resulting in systemic toxicity. One way to curb this is by employing drug delivery systems for targeted and controlled release of the drugs. Having been explored as versatile and innovative drug carriers, multi-walled carbon nanotubes (MWCNTs) have emerged as potential drug delivery systems. Hence, in the present study, alendronate, neridronate and pamidronate are three classes of bisphosphonates that were conjugated onto multi-walled carbon nanotubes. Conjugation was confirmed by characterization techniques including SEM, TEM, EDX, FTIR, Raman and TGA. Drug release studies were also conducted at pH 1.2, 5.5 and 7.4 to study the mechanism of release for neridronate. Results obtained were fitted into Zero order (42.6%), Higuchi (26%) and Korsmeyer-Peppas (22%). The best models describing the release of neridronate from MWCNTs were Zero order, Higuchi and Korsmeyer-Peppas at pH 1.2, 5.5 and 7.4, respectively. A tetrazolium cell viability assay was performed to assess the anticancer activity of the MWCNTs conjugated BPs.

Chemical approaches to inhibitors of isoprenoid biosynthesis: targeting farnesyl and geranylgeranyl pyrophosphate synthases

The chemical synthesis of farnesyl and geranylgeranyl pyrophosphate synthase inhibitors are surveyed.

Magnetic resonance imaging of osteosarcoma using a bis(alendronate)-based bone-targeted contrast agent

Magnetic resonance (MR) is currently used for diagnosis of osteosarcoma but not well even though contrast agents are administered. Here, we report a novel bone-targeted MR imaging contrast agent, Gd₂-diethylenetriaminepentaacetate-bis(alendronate) (Gd₂-DTPA-BA) for the diagnosis of osteosarcoma. It is the conjugate of a bone cell-seeking molecule (i.e., alendronate) and an MR imaging contrast agent (i.e., Gd-DTPA). Its physicochemical parameters were measured, including pK_a, complex constant, and T₁ relaxivity. Its bone cell-seeking ability was evaluated by measuring its adsorption on hydroxyapatite. Hemolysis was investigated. MR imaging and biodistribution of Gd₂-DTPA-BA and Gd-DTPA were studied on healthy and osteosarcoma-bearing nude mice. Gd₂-DTPA-BA showed high adsorption on hydroxyapatite, the high MR relaxivity (r₁) of 7.613mM^-1s^-1 (2.6 folds of Gd-DTPA), and no hemolysis. The MR contrast effect of Gd₂-DTPA-BA was much higher than that of Gd-DTPA after intravenous injection to the mice. More importantly, the MR imaging of osteosarcoma was significantly improved by Gd₂-DTPA-BA. The signal intensity of Gd₂-DTPA-BA reached 120.3% at 50min, equal to three folds of Gd-DTPA. The bone targeting index (bone/blood) of Gd₂-DTPA-BA in the osteosarcoma-bearing mice was very high to 130 at 180min. Furthermore, the contrast enhancement could also be found in the lung due to metastasis of osteosarcoma. Gd₂-DTPA-BA plays a promising role in the diagnoses of osteosacomas, including the primary bone tumors and metastases.

Bone targeting compounds for radiotherapy and imaging: *Me(III)-DOTA conjugates of bisphosphonic acid, pamidronic acid and zoledronic acid

Background

Bisphosphonates have a high adsorption on calcified tissues and are commonly used in the treatment of bone disorder diseases. Conjugates of bisphosphonates with macrocyclic chelators open new possibilities in bone targeted radionuclide imaging and therapy. Subsequent to positron emission tomography (PET) examinations utilizing ⁶⁸Ga-labelled analogues, endoradiotheraphy with ¹⁷⁷Lu-labelled macrocyclic bisphosphonates may have a great potential in the treatment of painful skeletal metastases.

Methods

Based on the established pharmaceuticals pamidronate and zoledronate two new DOTA-α-OH-bisphosphonates, DOTA^PAM and DOTA^ZOL(MM1.MZ) were successfully synthesized. The ligands were labelled with the positron emitting nuclide ⁶⁸Ga and the β^- emitting nuclide ¹⁷⁷Lu and compared in in vitro studies and in ex vivo biodistribution studies together with small animal PET and single photon emission computed tomography (SPECT) studies against [¹⁸F]NaF and a known DOTA-α-H-bisphosphonate conjugate (BPAPD) in healthy Wistar rats.

Results

The new DOTA-bisphosphonates can be labelled in high yield of 80 to 95 % in 15 min with post-processed ⁶⁸Ga and >98 % with ¹⁷⁷Lu. The tracers showed very low uptake in soft tissue, a fast renal clearance and a high accumulation on bone. The best compound was [⁶⁸Ga]DOTA^ZOL (SUV _Femur = 5.4 ± 0.6) followed by [¹⁸F]NaF (SUV _Femur = 4.8 ± 0.2), [⁶⁸Ga]DOTA^PAM (SUV _Femur = 4.5 ± 0.2) and [⁶⁸Ga]BPAPD (SUV _Femur = 3.2 ± 0.3). [¹⁷⁷Lu]DOTA^ZOL showed a similar distribution as the diagnostic ⁶⁸Ga complex.

Conclusion

The ⁶⁸Ga labelled compounds showed a promising pharmacokinetics, with similar uptake profile and distribution kinetics. Bone accumulation was highest for [⁶⁸Ga]DOTA^ZOL, which makes this compound probably an interesting bone targeting agent for a therapeutic approach with ¹⁷⁷Lu. The therapeutic compound [¹⁷⁷Lu]DOTA^ZOL showed a high target-to-background ratio. SPECT experiments showed concordance to the PET scans in healthy rats. [⁶⁸Ga/¹⁷⁷Lu]DOTA^ZOL appears to be a potential theranostic combination in the management of disseminated bone metastases.

Electronic supplementary material

The online version of this article (doi:10.1186/s41181-016-0017-1) contains supplementary material, which is available to authorized users.

Nanoprobes for Multimodal Visualization of Bone Mineral Phase in Magnetic Resonance and Near-Infrared Optical Imaging

Imaging agents with affinity for bone can enable early detection of changes to bone mineral density, which is a hallmark of many bone-associated pathologies such as Paget's disease and osteoporosis. Here, we report the development of a polymer nanoparticle (NP)-based multimodal imaging probe that enables visualization of bone mineral phase in near-infrared (NIR) optical tomography and detection in T₂-weighted magnetic resonance imaging (MRI). Ultrasmall superparamagnetic iron oxide was first encapsulated in NPs derived by blending poly(dl-lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) with N-hydroxysuccinimide functionalized-PLGA (NHS-PLGA). Postmodification of NHS surface functionality on the NPs with alendronic acid (Aln), a bone-targeting ligand, yielded stable ultrasmall superparamagnetic iron oxide nanoparticles (USPIONs) containing NPs that exhibit good serum stability and favorable cytocompatibility. These post-Aln-modified NPs exhibit 8- to 10-fold higher affinity for synthetic and biogenic hydroxyapatite in comparison to NPs where Aln was introduced before NP formation and shorten the T₂ relaxation times in both agarose phantoms and fresh spongy bone, thus enabling the interrogation of bone mineral phase in T₂-MRI. Finally, by introducing an NIR-dye-modified PLGA during the NP formation step, NP probes that enable the visualization of bone mineral phase in both NIR optical tomography and MRI have been realized. The system presented herein meets many of the criteria for clinical translation and therefore opens new opportunities for bone imaging and targeted therapeutics.

Bisphosphonate metal complexes as selective inhibitors of Trypanosoma cruzi farnesyl diphosphate synthase

In the search for a pharmacological answer to treat Chagas disease, eight metal complexes with two bioactive bisphosphonates, alendronate (Ale) and pamidronate (Pam), were described. Complexes of the formula [M(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O, with M = Cu, Co, Mn, Ni, and ([CuPam]·H(2)O)(n) as well as [M(II)(Pam)(2)(H(2)O)(2)]·3H(2)O, with M = Co, Mn and Ni, were synthesized and fully characterized. Crystal structure of [Cu(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O, [Co(II)(Pam)(2)(H(2)O)(2)] and [Ni(II)(Pam)(2)(H(2)O)(2)] were solved by X-ray single crystal diffraction methods and the structures of [M(2)(II)(Ale)(4)(H(2)O)(2)]·2H(2)O complexes M = Co, Mn and Ni were studied by X-ray powder diffraction methods. All obtained complexes were active against the amastigote form of Trypanosoma cruzi (T. cruzi), etiological agent of Chagas disease. Most of them were more active than the corresponding free ligands showing no toxicity for mammalian cells. The main mechanism of the antiparasitic action of bisphosphonates, inhibition of parasitic farnesyl diphosphate synthase (TcFPPS), remains in the obtained metal complexes and an increase in the inhibiting enzyme levels was observed upon coordination. Observed enzymatic inhibition was selective for TcFPPS as the metal complexes showed no or little inhibition of human FPPS. Additionally, metal complexation might improve the bioavailability of the complexes through the hindrance of the phosphonate group's ionization at physiological pH and, eventually, through the ability of plasma proteins to work as complex transporters.

Synthesis and evaluation of a novel 68Ga-chelate-conjugated bisphosphonate as a bone-seeking agent for PET imaging

INTRODUCTION

(68)Ga is a positron-emitting nuclide that has significant imaging potential given that, unlike cyclotron-produced (18)F, the isotope can be produced on-site utilizing a (68)Ge/(68)Ga generator. We recently synthesized a novel bone-seeking agent by coupling a bisphosphonate with the (68)Ga chelator 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). This study presents a first report on the potential of this (68)Ga bone-seeking radiopharmaceutical in the detection of bone metastases.

METHODS

4-Amino-1-hydroxybutylidene-1,1-bisphosphonate was conjugated with 2-[4,7-di(carboxymethyl)-1,4,7-triazonan-1-yl]pentanedioic acid, yielding 2-[4,7-di(carboxymethyl)-1,4,7-triazonan-1-yl]-5-[(4-hydroxy-4,4-diphosphonobutyl)amino]-5-oxopentanoic acid (NOTA-BP). (68)Ga-labeled NOTA-BP ([(68)Ga]NOTA-BP) was prepared by complexation of NOTA-BP with [(68)Ga] gallium chloride and evaluated in in vitro experiments, biodistribution experiments and micro-positron emission tomography (PET) imaging experiments.

RESULTS

The labeling of NOTA-BP with (68)Ga was completed by heating for 10 min. [(68)Ga]NOTA-BP was determined to have a radiochemical purity of over 95%, a high affinity for hydroxyapatite and a high stability in plasma. In in vivo biodistribution experiments, [(68)Ga]NOTA-BP demonstrated high bone uptake potential. Compared with (99m)Tc-labeled methylene diphosphonate ([(99m)Tc]MDP) and [(18)F]fluoride, [(68)Ga]NOTA-BP exhibited faster blood clearance and a higher bone-to-blood ratio. In addition, mouse model bone metastasis was detected by micro-PET imaging at 1 h postinjection of [(68)Ga]NOTA-BP.

CONCLUSION

We have developed a novel (68)Ga-radiolabeled bone-seeking agent. This [(68)Ga]NOTA-BP complex was found to have a high bone affinity and rapid blood clearance, and may thus prove to be useful as a bone-seeking agent for clinical PET.

Investigation of alendronate-doped apatitic cements as a potential technology for the prevention of osteoporotic hip fractures: critical influence of the drug introduction mode on the in vitro cement properties

Combination of a bisphosphonate (BP) anti-osteoporotic drug, alendronate, with an apatitic calcium phosphate cement does not significantly affect the main properties of the biomaterial, in terms of injectability and setting time, provided that the BP is introduced chemisorbed onto calcium-deficient apatite, one of the components of the cement. In contrast to other modes of introducing the BP into the cement formulation, this mode allows to minimize alendronate release in the cement paste, thus limiting the setting retardant effect of the BP. An original approach based on high frequency impedance measurements is found to be a convenient method for in situ monitoring of the cement setting reaction. The release profile of the drug from a cement block under continuous flow conditions can be well described using a coupled chemistry/transport model, under simulated in vivo conditions. The results show that the released alendronate concentration is expected to be much lower than the cytotoxic concentration.

Risedronate metal complexes potentially active against Chagas disease

In the search for new metal-based drugs for the treatment of Chagas disease, the most widespread Latin American parasitic disease, novel complexes of the bioactive ligand risedronate (Ris, (1-hydroxy-1-phosphono-2-pyridin-3-yl-ethyl)phosphonate), [M(II)(Ris)(2)]·4H(2)O, where M═Cu, Co, Mn and Ni, and [Ni(II)(Ris)(2)(H(2)O)(2)]·H(2)O were synthesized and characterized by using analytical measurements, thermogravimetric analyses, cyclic voltammetry and infrared and Raman spectroscopies. Crystal structures of [Cu(II)(Ris)(2)]·4H(2)O and [Ni(II)(Ris)(2)(H(2)O)(2)]·H(2)O were solved by single crystal X-ray diffraction methods. The complexes, as well as the free ligand, were evaluated in vitro against epimastigotes and intracellular amastigotes of the parasite Trypanosoma cruzi, causative agent of Chagas disease. Results demonstrated that the coordination of risedronate to different metal ions improved the antiproliferative effect against T. cruzi, exhibiting growth inhibition values against the intracellular amastigotes ranging the low micromolar levels. In addition, this strong activity could be related to high inhibition of farnesyl diphosphate synthase enzyme. On the other hand, protein interaction studies showed that all the complexes strongly interact with albumin thus providing a suitable means of transporting them to tissues in vivo.

Hydronium (3-oxo-1-phosphono-1,3-dihydroisobenzofuran-1-yl)phosphonate

In the title compound, H₃O⁺·C₈H₇O₈P₂⁻, the anions form inversion dimmers by way of pairs of O—H⋯O hydrogen bonds involving the phospho­nic functions and via the hydro­nium cation. Further O—H⋯O links involving the hydronium cation play a prominant part in the cohesion of the crystal structure by building bridges between bis­phospho­nate pairs, forming infinite ribbons along the b-axis direction and by cross-linking these ribbons perpendicularly along the a-axis direction, forming an infinite three-dimensional hydrogen-bond network. The benzene ring and the C=O atoms of the furan ring are disordered over two sets of positions of equal occupancy.

Electrospray tandem mass spectrometry of alendronate analogues: fingerprints for characterization of new potential prodrugs

1-hydroxymethylene-1,1-bisphosphonic acids (HMBPs) are important drugs for the treatment of a variety of bone diseases. Since these compounds have no chromophore, their detection is challenging and mass spectrometry (MS) appears to be an appropriate sensitive tool. Our work deals with the analysis by electrospray ionization tandem mass spectrometry (ESI-MSn) of the well-known nitrogen-containing HMBP alendronate and of three analogues, considered as potential prodrugs. These four molecules share a common structure with different protecting groups on the phosphonic acid and on the amine functions. We describe the dissociation mechanisms of nitrogen-containing HMBPs in positive ion mode and we compare, in negative ion mode, our results with literature data. In both modes, the dissociations are essentially losses of ROH, and of phosphorus-containing species (HPO2, ROP(OH)2 and ROPO(OH)2), where R=H, C6H5, or CH3OC6H5. These fingerprints will be of great value for differentiating alendronate from its potential prodrugs in complex biological mixtures.

Unexpected degradation of the bisphosphonate P-C-P bridge under mild conditions

Unexpected degradation of the P-C-P bridge from novel bisphosphonate derivative 1a and known etidronate trimethyl ester (1b) has been observed under mild reaction conditions. A proposed reaction mechanism for the unexpected degradation of 1a and 1b is also reported.

Novel Therapeutic Agents for Bone Resorption. Part 1. Synthesis and Protonation Thermodynamics of Poly(amido-amine)s Containing Bis-phosphonate Residues

Two poly(amido-amine)s (oligoPAM and oligoNER) containing bis-phosphonate residues were obtained by a Michael-type polyaddition of pamidronate and neridronate to 1,4-bis(acryloyl)piperazine. The SEC (size-exclusion chromatography) and the MALDI-TOF (matrix assisted laser desorption ionization) analyses were consistent with the presence of oligomeric species (2-3 kDa) and with a narrow polydispersity index. The thermodynamic results (log Ks, -DeltaH(o) , and DeltaS(o) obtained at 25 degrees C in 0.15 M NaCl) of both the oligomers and the corresponding low molecular weight precursors were in line with a cluster structure formed during the protonation of the basic nitrogen in the pamidronate. The solubility of the oligoNER with a longer aliphatic chain was improved at high pHs, allowing the evaluation of their solution properties. Preliminary biological results show that both the oligomers do not negatively affect the in vitro viability, proliferation, and cellular activity of either normal animal or human osteoblasts.