Multifunctional Water-Soluble Polymers for Drug Delivery

Preparation and characterization of biocompatible and thermoresponsive micelles based on poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) grafted on polysuccinimide for drug delivery

Biocompatible and temperature-sensitive amphiphilic polymeric micelles comprised of poly(succinimide)- g-poly( N-isopropylacrylamide- co-N, N-dimethylacrylamide) (PSI- g-poly(NIPAAm- co-DMAAm)) were synthesized to use as new drug carriers. The PSI- co-poly(PNIPAAm- co-DMAAm) polymers were prepared by nucleophilic opening of poly(succinimide) using amino-terminated poly(NIPAAm- co-DMAAm). The lower critical solution temperature of the copolymer was 40.6℃ higher than normal human body temperature. The blank polymeric micelles were observed to have a regular spherical shape, and the particle sizes were approximately 85 nm. This copolymer exhibited no significant cytotoxicity and hemolysis indicated that the micelles had good biocompatibility. In addition, these polymeric micelles encapsulated the anti-inflammatory drug, hesperetin, in the inner core with a drug loading content of approximately 20%. The release profiles of hesperetin showed a significant temperature-sensitive switching behavior. The hesperetin release response was dramatically lower at a temperature below the lower critical solution temperature as compared with a temperature above the lower critical solution temperature. The lipopolysaccharide-induced nitric oxide production inhibition experiments demonstrated that hesperetin-encapsulated micelles showed a significant reduction. In this study, the biocompatible temperature-sensitive micelles based on PSI- g-poly(NIPAAm- co-DMAAm) have great potential to act as a suitable carrier for drug delivery.

Combination chemotherapy and photodynamic therapy with fab' fragment targeted HPMA copolymer conjugates in human ovarian carcinoma cells

The biological activities of sequential combinations of anticancer drugs, SOS thiophene (SOS) and mesochlorin e₆ monoethylenediamine (Mce₆), in the form of free drugs, nontargeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer−drug conjugates, P-GFLG-Mce₆ and P-GFLG-SOS (P is the HPMA copolymer backbone and GFLG is the glycylphenylalanylleucylglycine spacer), and Fab′-targeted HPMA copolymer−drug conjugates, P-(GFLG-Mce₆)-Fab′ and P-(GFLG-SOS)-Fab′ (Fab′ from OV-TL16 antibodies complementary to CD47), were evaluated against human ovarian carcinoma OVCAR-3 cells. Mce₆, SOS, P-GFLG-Mce₆, P-GFLG-SOS, P-(GFLG-Mce₆)-Fab′, and P-(GFLG-SOS)-Fab′, when used as single agents or in binary combination, exhibited cytotoxic activities against OVCAR-3 cells, as determined using a modified MTT assay. The binding and internalization of P-(GFLG-Mce₆)-Fab′ and P-(GFLG-SOS)-Fab′ by OVCAR-3 cells were visualized by confocal microscopy and flow cytometry. The results confirmed an enhanced biorecognition by OVCAR-3 cells of Fab′-targeted HPMA copolymer conjugates over nontargeted conjugates. The median-effect analysis and the determination of the combination index (CI) were used to describe the drug interaction and quantify the synergism, antagonism, or additivity in anticancer effects. The sequential combinations of SOS+Mce₆ and P-GFLG-SOS+P-GFLG-Mce₆ displayed very strong synergism to synergism in the entire range of cell inhibition levels (f_a = 0.5 − 0.95). The P-(GFLG-SOS)-Fab′+P-(GFLG-Mce₆)-Fab′ exhibited a strong synergism for f_a values up to about 0.85, but showed synergistic effect and nearly additive effect at f_a = 0.9 and 0.95, respectively. These observations support the continuation of in vivo investigations of these conjugates for the treatment of ovarian cancer.

Stability in plasmas of various species of HPMA copolymer-PGE1 conjugates

PURPOSE

To determine the stability of HPMA copolymer-prostaglandin E(1) (PGE(1)) conjugates in plasmas of different species and to identify the enzymes responsible for the cleavage of the ester bond.

METHODS

The conjugates were incubated in human, rat, and mouse plasma at 37 degrees C in the presence and absence of specific esterase inhibitors. The released PGE(1) was analyzed using an HPLC assay. To evaluate the effect of the conformation of the conjugate on the rate of PGE(1) release, its structure was modified by the attachment of hydrophobic side chains.

RESULTS

The rate of PGE(1) release was strongly species dependent. Whereas the conjugate was stable in human plasma, the PGE(1) release in rat or mouse plasma was substantial. In rat plasma, the ester bond cleavage was mainly catalyzed by butyrylcholinesterase; in mouse plasma, in addition to butyrylcholinesterase, carboxylesterase also contributed to the cleavage. The formation of compact polymer coils stabilized the ester bond.

CONCLUSIONS

HPMA copolymer-PGE(1) conjugates are strong candidates as novel therapeutics for the treatment of osteoporosis. The observed species differences in plasma stability of ester bonds are of importance, because the ovariectomized rat model is recommended by the FDA for pre-clinical evaluation.