Synthesis of Poly[N-(2-hydroxypropyl)methacrylamide] Conjugates of Inhibitors of the ABC Transporter That Overcome Multidrug Resistance in Doxorubicin-Resistant P388 Cells in Vitro

Abstract

The effects of novel polymeric therapeutics based on water-soluble N-(2-hydroxypropyl)methacrylamide copolymers (P(HPMA)) bearing the anticancer drug doxorubicin (Dox), an inhibitor of ABC transporters, or both, on the viability and the proliferation of the murine monocytic leukemia cell line P388 (parental cell line) and its doxorubicin-resistant subline P388/MDR were studied in vitro. The inhibitor derivatives 5-methyl-4-oxohexanoyl reversin 121 (MeOHe-R121) and 5-methyl-4-oxohexanoyl ritonavir ester (MeOHe-RIT), showing the highest inhibitory activities, were conjugated to the P(HPMA) via the biodegradable pH-sensitive hydrazone bond, and the ability of these conjugates to block the ATP driven P-glycoprotein (P-gp) efflux pump was tested. The P(HPMA) conjugate P-Ahx-NH-N═MeOHe-R121 showed a dose-dependent increase in the ability to sensitize the P388/MDR cells to Dox from 1.5 to 24 μM, and achieved an approximately 50-fold increase in sensitization at 24 μM. The P(HPMA) conjugate P-Ahx-NH-N═MeOHe-RIT showed moderate activity at 6 μM (∼10 times higher sensitization) and increased sensitization by 50-fold at 12 μM. The cytostatic activity of the P(HPMA) conjugate P-Ahx-NH-N═MeOHe-R121(Dox) containing Dox and the P-gp inhibitor MeOHe-R121, both bound via hydrazone bonds to the P(HPMA) carrier, was almost 30 times higher than that of the conjugate P-Ahx-NH-N═Dox toward the P388/MDR cells in vitro. A similar result was observed for P-Ahx-NH-N═MeOHe-RIT(Dox), which exhibited almost 10 times higher cytostatic activity than P-Ahx-NH-N═Dox.

HPMA Copolymer–Drug Conjugates with Controlled Tumor‐Specific Drug Release

“…Several other drugs, i.e . , the anticancer agents paclitaxel or docetaxel, mitomycin C, acridine, and ellipticinium; the anti‐inflammatory drug Dex; and the multidrug resistance inhibitors such as reversin 121, reversin 205, and ritonavir, were bound to polymer carriers by a hydrazone bond using oxoacid spacers, e.g., 4‐oxopentanoic acid, 4‐(2‐oxopropyl)benzoic acid, and 5‐methyl‐4‐oxohexanoic acid ( Figure 4 ). Here, the active agents were not free drugs, but their ester or amide derivatives tailored to maintain the activity of the original drugs and enable conjugation with the carrier via a hydrazone bond.…”

Controlling and Monitoring Intracellular Delivery of Anticancer Polymer Nanomedicines

“…Both linear poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA) as well as poly(amidoamine) (PAMAM) dendrimers modified with hydrazide groups have been used to couple Dox via hydrazone linkers. [32,[55][56][57][58][59][60][61][62][63] HPMA polymers bearing hydrazone linkages have also been explored for the delivery of other anticancer drugs such as paclitaxel and docetaxel. [64] The hydrazone motif has also been used to prepare micelles and nanoparticles that allow pH-dependent release of Figure 1.…”

Micelle-forming HPMA copolymer conjugates of ritonavir bound via a pH-sensitive spacer with improved cellular uptake designed for enhanced tumor accumulation

“…Ritonavir 5-methyl-4-oxohexanoate (Rit) and all the polymer-Rit conjugates prepared by conjugation of the copolymer precursor with Rit, forming the pH-sensitive hydrazone bond, were prepared according to the literature. 12 The polymer conjugates were isolated by gel filtration on a Sephadex LH-20 column in methanol, followed by precipitation with ethyl acetate. The content of Rit in the polymer conjugates was determined using HPLC after acid hydrolysis as previously described.…”

“…We have recently reported that a ritonavir derivative, ritonavir 5-methyl-4-oxohexanoate (Rit), has a similar biological activity to the parent drug. 12 In this work, we have bound Rit to HPMA copolymers via a pH-sensitive hydrazone bond that is relatively stable at neutral pH (in the blood) and hydrolyzed in a slightly acidic environment, such as that of the tumor tissue or inside tumor cells, thus enabling the release of free, active Rit from the carrier.…”

“…We expected that the conjugates of the diblock copolymers with Rit were sensitive to the pH changes of aqueous solutions and that the micelles formed by the self-assembly of the copolymers were stable at physiological pH (7.4) and disintegrated relatively quickly upon a drop in pH in a mildly acidic region (pH 5-6) corresponding to the pH of the intracellular environment. After the release of the highly hydrophobic Rit from the polymer carrier, which is a prerequisite for its biological activity, 12 the polymer chains will become less hydrophobic, resulting in the disruption of the supramolecular organization and the formation of the soluble and excretable polymer fragments.…”