Effect of Alkaline Conditions on Forming an Effective G4.0 PAMAM Complex with Doxorubicin

Abstract

In this study, special attention was paid to the correlation between the degree of ionization of the components and the effective formation of the complex under alkaline conditions. Using UV-Vis, 1H NMR, and CD, structural changes of the drug depending on the pH were monitored. In the pH range of 9.0 to 10.0, the G4.0 PAMAM dendrimer can bind 1 to 10 DOX molecules, while the efficiency increases with the concentration of the drug relative to the carrier. The binding efficiency was described by the parameters of loading content (LC = 4.80–39.20%) and encapsulation efficiency (EE = 17.21–40.16%), whose values increased twofold or even fourfold depending on the conditions. The highest efficiency was obtained for G4.0PAMAM-DOX at a molar ratio of 1:24. Nevertheless, regardless of the conditions, the DLS study indicates system aggregation. Changes in the zeta potential confirm the immobilization of an average of two drug molecules on the dendrimer’s surface. Circular dichroism spectra analysis shows a stable dendrimer-drug complex for all the systems obtained. Since the doxorubicin molecule can simultaneously act as a therapeutic and an imaging agent, the theranostic properties of the PAMAM-DOX system have been demonstrated by the high fluorescence intensity observable on fluorescence microscopy.

Dendrimer Platforms for Targeted Doxorubicin Delivery – Physicochemical Properties in Context to Biological Responses

“…The values of binding constants equal K7.5=2.07×10 6 , K9.0=9.38×10 2 , K9.5=7.01×10 2 and their values decrease with increasing pH. The determined values of binding constants at alkaline conditions are K9.0=9.38×10 2 M -1 and K9.5=7.01×10 2 M -1 and they are close to the values that we obtained in previous work using UV-vis with Hill's method (K9.0=2.39×10 2 and K9.5=2.73×10 2 ) [29]. The value of the binding constant at pH 7.5 is close to that obtained by Chanphai et al for the same system in PBS buffer at physiological pH as well (K=1.6×10 6 ) [44].…”

“…Since the PAMAM dendrimer efficiently binds doxorubicin under alkaline conditions (pH > 8.5) [29], the stability of the free drug was checked under this environment. UV-vis spectroscopy monitored the spectral changes of doxorubicin in relation to pH (pH=8.5, 9.0, 10.0) at 72h (Figure SM1).…”

“…G4.0-DOX fluorescence measurements were carried out for post-dialysis complexes with an initial G4.0-DOX molar ratio of 1:12 and 1:24 and an initial pH of 9.5. The exact methodology for preparing the complexes is described in our previous work [29]. Briefly, sufficient DOX at pH = 9.5 was added to the dendrimer at a constant concentration of 0.25 mg/mL (17.6 μM) and pH = 9.5 to give a molar ratio of the starting complexes of 1:12 and 1:24.…”

“…Release tests were performed for the G4.0-DOX complex at a molar ratio of 1:6 and pH = 9.5. The complex was prepared in accordance with a previously developed methodology [29]. The concentration of components in the final complex was cG4.0= 250 μg/mL, cDOX= 22 μg/mL (EE= 37.93%).…”

Dendrimers for Drug Delivery: Where Do We Stand in 2023?

“…They have shown that at a pH 9.0–10.0, the chemodrug and the dendrimer form stable complexes, where one dendrimer molecule can bond 1 to 10 molecules of doxorubicin. The complexes also possess high fluorescence intensity, which can be useful for theranostics [ 7 ].…”