Nano-micellar Aggregates of Anticancer Cisplatin-Conjugated Poly(carboxylated 2-isopropenyl 2-oxazoline)-mPEG Copolymers

Cisplatin is an anticancer drug that can be used to treat a variety of solid tumors, where clinical use may be affected by several factors, including dose-limiting side effects and the emergence of drug resistance. Micellar-forming polymeric conjugates are a type of polymeric nanocarrier that can preferentially accumulate in tumors, thereby increasing therapeutic efficacy. In the current study, carboxylated PiPOx was synthesized first using a click reaction of 2-isopropenyl 2-oxazoline (iPOx) with thioglycolic acid (TGA) or methyl thioglycolate, followed by methyl triflate-initiated cationic ring opening polymerization (CROP). Next, different strategies were employed to prepare carboxylated PiPOx-mPEG copolymers: (a) CROP was initiated by iPOx-modified mPEG-thiol, (b) TGA-modified PiPOx were end-capped with mPEG-NH2, or (c) TGA-modified iPOx and iPOx-modified mPEG-thiol were randomly copolymerized. 1H-NMR, FT-IR, SEC, and potentiometric titration methods were used to characterize the synthesized polymers. Cisplatin-polymer conjugation was performed at three ratios of drug-to-polymer carboxyl groups (0.25, 0.5, and 1), and the conjugated cisplatin content was determined using UV-vis spectroscopy at 705 nm with O-phenylenediamine reagent. The cisplatin loading efficiencies (%) were 59.3, 26.7, and 91.0 for the respective copolymers at the chosen cisplatin/carboxyl 1:1 mol ratio. Cisplatin-conjugated PiPOx(TGA)-b-mPEG and mPEG-g-PiPOx(TGA) had mean hydrodynamic sizes of 113.3 and 178.8 nm, respectively. TEM imaging confirmed the formation of discrete and spherical particles of the cisplatin-conjugated copolymer. The MTT cytotoxicity assay demonstrated higher cytotoxicity of PiPOx(TGA)-b-mPEG compared to PiPOx(TGA)-g-mPEG polymers in both sensitive and resistant ovarian cancer cells. The IC50 values were approximately 113 mu g/ml for PiPOx(TGA)-b-mPEG and 232 mu g/ml for PiPOx(TGA)-g-mPEG in resistant tumor cells, confirming the potential application of cisplatin-conjugated copolymers in cancer chemotherapy.

Automated summary

In this study, cisplatin-polymer conjugates were prepared by synthesizing and characterizing different types of carboxylated polymers, and their potential application in cancer chemotherapy was validated through cytotoxicity assays.