Application to a Cartilage Targeting Strategy:  Synthesis and in Vivo Biodistribution of ¹⁴C-Labeled Quaternary Ammonium−Glucosamine Conjugates

Abstract

As part of a cartilage targeting program based on the affinity of the quaternary ammonium (QA) moiety for cartilage, QA derivatives of D-glucosamine (DG), an antirheumatic drug exhibiting a natural tropism for cartilaginous tissues, were designed and evaluated by pharmacokinetic studies. Two QA-DG conjugates were synthesized and labeled with (14)C by cross-linking the QA entity (trimethylammonium or pyridinium) to [(14)C]DG via an amide bond in a two-step procedure. After intravenous injection to male Sprague-Dawley rats, the two (14)C-labeled conjugates exhibited similar pharmacokinetic profiles, but their behavior clearly differed from that of unconjugated DG in several ways. (i) The tissue distribution for the conjugates was more restricted, with a decreased radioactivity level for whole tissues except for kidney, cartilage, and skin. (ii) The radioactivity concentrated more rapidly and strongly in cartilage for the conjugates than for DG for the short times after injection; on the other hand, 1 h after administration, the radioactivity level in cartilage was higher for DG, this result being consistent with the tropism already observed for this compound. (iii) Both conjugates were eliminated predominantly by the urinary route (85%); the radioactivity level in urine for DG was lower (45% of the injected dose), and significant (14)CO(2) was found in expired air, indicating metabolization and utilization of DG for energy-consuming processes. (iv) Blood and plasma kinetics studies displayed an enterohepatic cycle for DG, whereas for the QA conjugates, a rapid disappearance was observed. (v) HPLC analyses of plasma and urine indicated a low degree of metabolization for the conjugates, most of the radioactivity recovered in urine and plasma corresponding to the unchanged molecule. This study demonstrates that the introduction of the QA moiety on DG modifies its biodistribution and lends it a greater specificity for cartilage, at least for short times after injection. These findings justify further work on QA derivatives of other antirheumatic agents.

Assessment of Therapeutic Tumor Response Using <SUP>99m</SUP>Tc-Ethylenedicysteine-Glucosamine

“…D-glucosamine (DG), an antirheumatic drug exhibiting a natural tropism for cartilaginous tissues, has been labeled with 14 C-DG for pharmacokinetic studies. 39 Biodistribution and autoradiogram of 14 C-DG indicated poor brain and heart uptake, which showed a similar pattern to our autoradiographic findings. In gamma scintigraphic imaging studies, compared to 99m Tc-EC (control), a tumor could be visualized by 99m Tc-EC-DG in VX-2 tumorbearing rabbits.…”

“…Poor brain uptake of radiolabeled glucosamine was also reported by others. 39 There are at least five glucose transporters. Glucose transporters 1 and 3 are localized in brain tissue.…”

Synovial fluid levels and serum pharmacokinetics in a large animal model following treatment with oral glucosamine at clinically relevant doses

“…In other investigations, a quaternary ammonium conjugate of glucosamine (35) was found to concentrate in cartilage, but its physiologic effects on tissue metabolism were not reported. For in vivo effects of glucosamine on chondrocytes (which are normally exposed to ∼5 m M glucose in vivo), the monosaccharide would have to “accumulate” in the cartilage to levels at least 500 times higher than those present in the synovial fluid.…”

Cationic contrast agents improve quantification of glycosaminoglycan (GAG) content by contrast enhanced CT imaging of cartilage

“…Even so, high concentrations inside the tissue are difficult to achieve because of the electrostatic repulsion between the anionic GAGs and the anionic agent. Cationic moieties, such as quaternary ammonium groups, can guide imaging agents31–33 and therapeutic molecules34 to cartilage through electrostatic attraction. We hypothesized that iodinated contrast agents bearing positive charges would lead to several advantages over the existing anionic contrast agents in the CECT technique.…”