Improving thermal stability and efficacy of BCNU in treating glioma cells using PAA-functionalized graphene oxide

Yu-Jen Lu^1,2,#, Hung-Wei Yang^1,#, Sheng-Che Hung³, Chiung-Yin Huang², Shin-Ming Li⁴, Chen-Chi M Ma⁴, Pin-Yuan Chen², Hong-Chieh Tsai², Kuo-Chen Wei², Jyh-Ping Chen<sup>1

1</sup>Department of Chemical and Materials Engineering, Chang Gung University, Kwei-San, Taoyuan, Taiwan; ²Department of Neurosurgery, Chang Gung Memorial Hospital, Kwei-San, Taoyuan, Taiwan; ³Department of Radiology, Taipei Veterans General Hospital, Taipei, Taiwan; ⁴Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan

#These authors contributed equally to this work

Background: 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), a commercial chemotherapeutic drug for treating malignant brain tumors, has poor thermal stability and a short half-life. Immobilization of BCNU on a nanocarrier might increase the thermal stability of BCNU and extend its half-life.
Methods: Nanosized graphene oxide (GO) could be modified by polyacrylic acid (PAA) to improve the aqueous solubility and increase the cell penetration efficacy of the nanocarrier. PAA–GO intended as a drug carrier for BCNU was prepared and characterized in this study. The size and thickness of PAA–GO was investigated by transmission electron microscopy and atomic force microscopy, and the presence of PAA functional groups was confirmed by electron spectroscopy for chemical analysis and thermogravimetric analysis. BCNU was conjugated to PAA–GO by covalent binding for specific killing of cancer cells, which could also enhance the thermal stability of the drug.
Results: Single layer PAA–GO (about 1.9 nm) with a lateral width as small as 36 nm was successfully prepared. The optimum drug immobilization condition was by reacting 0.5 mg PAA–GO with 0.4 mg BCNU, and the drug-loading capacity and residual drug activity were 198 µg BCNU/mg PAA–GO and 70%, respectively. This nanocarrier significantly prolonged the half-life of bound BCNU from 19 to 43 hours compared with free drug and showed efficient intracellular uptake by GL261 cancer cells. The in vitro anticancer efficacy of PAA–GO–BCNU was demonstrated by a 30% increase in DNA interstrand cross-linking and a 77% decrease in the IC₅₀ value toward GL261 compared with the same dosage of free drug.
Conclusion: Nanosized PAA–GO serves as an efficient BCNU nanocarrier by covalent binding. This nanocarrier will be a promising new vehicle for an advanced drug delivery system in cancer therapy.

Keywords: graphene oxide, BCNU, glioma cells, drug delivery, thermal stability