Ion-Pairing with Spermine Targets Theophylline To the Lungs via the Polyamine Transport System

Abstract

Certain xenobiotics, such as paraquat, are sequestered into the lungs from the systemic circulation by the polyamine transporter system (PTS). The aim of this study was to investigate whether ion-pairing a drug (theophylline) with a PTS substrate (spermine) provides a means of using this active transport mechanism to target drug delivery to the lungs. Fourier transform infrared spectroscopy showed that two of the amine groups of spermine interact with C-N and C═O of theophylline, leaving two free amines to interact with the PTS. In A549 cells, which possess a functional PTS (spermidine K and V, 0.6 ± 0.3 μM and 1.8 ± 0.3 pmol·min per 10 cells, respectively), uptake of the theophylline-spermine ion-pair was increased 1.8-fold compared to free theophylline at 37 °C, but not at 4 °C. In an isolated perfused rat lung model (IPL) a 3.6-fold increase in lung theophylline concentration was observed after vascular administration of the ion-pair compared to free theophylline. Theophylline was cleared from the IPL with similar kinetics irrespective of whether it was delivered as the free drug or an ion-pair, although lung levels remained elevated after washout following delivery as an ion-pair. In vitro simulation of the theophylline-spermine break down demonstrated that a drop in pH from 9.6 to 7.4, such as that undergone by the ion-pair in biological matrices, induces rapid and almost complete dissociation of the ion-paired species. However, infusion of the ion-pair formulations via the vasculature provides almost immediate delivery to the pulmonary capillary bed permitting PTS-mediated active sequestering of ion-paired theophylline into the lungs.

A Cyclodextrin‐Stabilized Spermine‐Tagged Drug Triplex that Targets Theophylline to the Lungs Selectively in Respiratory Emergency

“…The same problems were not experienced with the NMR data. [17] The affinity constants of the ion-pairs were consistent with previously reported estimates for ion-pairs formed with two hydrogen bonds (affinity constants of 0.8 [6] and 1.1 [7] ).…”

“…The NMR data were in agreement with previous infrared spectroscopy studies, which also suggested the formation of 2 hydrogen bonds between theophylline and spermine. [6] The largest peak shift in the NMR spectra was observed for the theophylline C 8 -H peak and this was used to construct the theophylline-spermine association curve and derive the conditional association constant for the theophylline-spermine ionpair, pK NMR = 1.5 ± 0.02 (see Figure S1, Supporting Information). This conditional association constant was higher than the association constant generated by infrared spectroscopy, pK FTIR at 0.9 ± 0.1, reported in previous work.…”

“…These results illustrated that the theophylline ion-pair, which had previously shown remarkable physical stability both in in vitro and ex vivo models of delivery to the lung was not stable in vivo. [6] The expression of the PTS in different mammalian tissues has not been quantified, but functional studies have demonstrated a that there is a high level of PTS expression in the lungs. [3] PTS substrates such as paraquat are known to distribute and even concentrate over time in the lung tissue, but they are also found in the liver, kidney and spleen.…”

“…[14][15][16] Additionally, previous work has shown that theophylline can ion-pair with the polyamine transport system (PTS) substrate spermine. [6] In silico studies were conducted to understand the molecular structure of the triplex, in vitro studies were used to demonstrate theophylline ion-pair system uptake into A549 cells when formulated as the CD ionpair complex and in vivo studies showed how this influenced drug biodistribution.…”

“…Published work has demonstrated that ion‐pairing theophylline, a drug that is commonly used in medical emergencies such as status asthmaticus or COVID‐19 related pneumomediastinum, to the polyamine transporter substrate (PTS), with spermine, enhanced its lung uptake by 3.6‐fold in a rat isolated perfused lung model. [ 6 ] Attaching the targeting ligand to the drug through ion‐pair formation has the advantage that the dissociation rate of an ion‐paired system is controlled by the complex association strength. Therefore, the use of ion‐pairs with moderate association strength avoids any deleterious effect on drug pharmacological activity.…”