Functional nanoparticles often contain ligands including targeting molecules, fluorophores, and/or active moieties such as drugs. Characterizing the number of these ligands bound to each particle, and the distribution of nanoparticle-ligand species, is important for understanding the nanomaterial’s function. In this study, the amide coupling methods commonly used to conjugate ligands to poly(amidoamine) (PAMAM) dendrimers were examined. A skewed Poisson distribution was observed and quantified using HPLC for two sets of dendrimer-ligand samples prepared using the amine terminated form of the PAMAM dendrimer and a partially acetylated form of the PAMAM dendrimer that has been used for targeted in vivo drug delivery. The prepared samples had an average number of ligands per dendrimer ranging from 0.4 to 13. Distributions identified by HPLC are in excellent agreement with the mean ligand/dendrimer ratio, measured by 1H NMR, gel permeation chromatography (GPC), and potentiometric titration. These results provide insight into the heterogeneity of distributions that are obtained for many classes of nanomaterials to which ligands are conjugated and belie the use of simple cartoon models that present the “average” number of ligands bound as a physically meaningful representation for the material.

We report the synthesis and in vitro evaluation of folate receptor-targeted nanoconjugate that releases its therapeutic payload via a photochemical mechanism.The targeted delivery of therapeutic and imaging agents using nanoconjugates is a burgeoning field. [1][2][3][4] Strategies to develop cancer-cell specific nanoconjugates vary, but all attempts to selectively deliver therapeutics to cells use nanoscale carriers such as dendritic macromolecules, 2 liposomes, 5 polymers, 6 metal nanoparticles 3 or viruses 7 that include targeting and therapeutic agents. The desired result is less side toxicity in normal cells and more effective tumoricidal activity. Nanoconjugates also can be designed such that the therapeutic agents are released, and therefore active, only under particular conditions. The release mechanisms currently being explored are based primarily on reactions catalyzed by endogenous physiological factors such as reduction, 1 low pH, 3 and hydrolytic enzymes. 4 This communication describes a photochemical-based approach to release targeted drugs after delivery. In this scenario, the targeted drug conjugate is first placed on a surface, such as skin, or lung/gastrointestinal tract epithelium. After the exposure, the nanoconjugate drug is specifically taken up by the tumor cells and is washed away from the normal tissue; light is then applied from a laser device attached to an endoscope to specifically target the cancer cells. The strategy presented may be broadly applied to other cell targeting systems, particularly those that require time-and tissue-dependent control of drug activation.Photocaging refers to the temporary inactivation of a biologically active molecule using a protective photocleavable group. Upon UV irradiation of the photocleavable group, the active form of the caged molecule is irreversibly released. 8 Photocaging has been frequently applied in vitro towards the spatiotemporal control of biological processes 9-11 and the light-triggered payload release from nanoscale materials. 12,13 However, it has only been rarely applied in in vivo experiments 14,15 because of the low level tissue penetration and phototoxicity associated with short wavelength UV light.Recent advances in two-photon excitation 14,15 and optical fiber technology, however, have made it possible to cleave photocaged compounds by irradiation in the near-IR (720-800 nm 14 ). Because of this potential for higher level tissue penetration, we have applied the † Electronic supplementary information (ESI) available: Experimental details for synthesis and characterization of 1-9; details for photocleavage experiments of 3 and 7. See DOI: 10.1039/b927215cFax: (734) 615-0621; Tel: (734) 615-0618. NIH Public Access Author ManuscriptChem Commun (Camb). Author manuscript; available in PMC 2010 July 12. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript photocaging approach towards the targeted delivery of doxorubicin, 16 an anticancer drug that inhibits DNA replication through intercalation (Fig. 1).In ...

Our previous studies have demonstrated that a generation 5 dendrimer (G5) conjugated with both folic acid (FA) and methotrexate (MTX) has a higher chemotherapeutic index than MTX alone. Despite this, batch-to-batch inconsistencies in the number of FA and MTX molecules linked to each dendrimer led to conjugate batches with varying biological activity, especially when scaleup synthesis was attempted. Since the MTX is conjugated through an ester linkage, there were concerns that biological inconsistency could also result from serum esterase activity and differential bioavailability of the targeted conjugate. In order to resolve these problems, we undertook a novel approach to synthesize a polyvalent G5–MTXn conjugate through click chemistry, attaching the MTX to the dendrimer through an esterase-stable amide linkage. Surface plasmon resonance binding studies show that a G5–MTX10 conjugate synthesized in this manner binds to the FA receptor (FR) through polyvalent interaction showing 4300-fold higher affinity than free MTX. The conjugate inhibits dihydrofolate reductase, and induces cytotoxicity in FR-expressing KB cells through FR-specific cellular internalization. Thus, the polyvalent MTX on the dendrimer serves the dual role as a targeting molecule as well as a chemotherapeutic drug. The newly synthesized G5–MTXn conjugate may serve as a FR-targeted chemotherapeutic with potential for cancer therapy.

Vancomycin represents the preferred ligand for bacteria-targeting nanosystems. However, it is inefficient for emerging vancomycin-resistant species because of its poor affinity to the reprogrammed cell wall structure. This study demonstrates the use of a multivalent strategy as an effective way for overcoming such an affinity limitation in bacteria targeting. We designed a series of fifth generation (G5) poly(amidoamine) (PAMAM) dendrimers tethered with vancomycin at the C-terminus at different valencies. We performed surface plasmon resonance (SPR) studies to determine their binding avidity to two cell wall models, each made with either a vancomycin-susceptible (D)-Ala-(D)-Ala or vancomycin-resistant (D)-Ala-(D)-Lac cell wall precursor. These conjugates showed remarkable enhancement in avidity in the cell wall models tested, including the vancomycin-resistant model, which had an increase in avidity of four to five orders of magnitude greater than free vancomycin. The tight adsorption of the conjugate to the model surface corresponded with its ability to bind vancomycin-susceptible Staphylococcus aureus bacterial cells in vitro as imaged by confocal fluorescent microscopy. This vancomycin platform was then used to fabricate the surface of iron oxide nanoparticles by coating them with the dendrimer conjugates, and the resulting dendrimer-covered magnetic nanoparticles were demonstrated to rapidly sequester bacterial cells. In summary, this article investigates the biophysical basis of the tight, multivalent association of dendrimer-based vancomycin conjugates to the bacterial cell wall, and proposes a potential new use of this nanoplatform in targeting Gram-positive bacteria.