Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands. Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands. Department of Nanomedicine and Theranostics, Institute for Experimental Molecular Imaging, University Clinic and Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Aachen, Germany.
Nanotechnology. 2019 Jun 28;30(26):264001. doi: 10.1088/1361-6528/ab0ce6. Epub 2019 Mar 5.
Hypoxia is a characteristic feature of solid tumors and an important cause of resistance to radiotherapy. Hypoxic cell radiosensitizers have been shown to increase radiotherapy efficacy, but dose-limiting side effects prevent their widespread use in the clinic. We propose the encapsulation of hypoxic cell radiosensitizers in temperature-sensitive liposomes (TSL) to target the radiosensitizers specifically to tumors and to avoid unwanted accumulation in healthy tissues. The main objective of the present study is to develop and characterize TSL loaded with the radiosensitizer pimonidazole (PMZ) and to evaluate the in vitro efficacy of free PMZ and PMZ encapsulated in TSL in combination with hyperthermia and radiotherapy. PMZ was actively loaded into TSL at different drug/lipid ratios, and the physicochemical characteristics and the stability of the resulting TSL-PMZ were evaluated. PMZ release was determined at 37 °C and 42 °C in HEPES buffer saline and fetal bovine serum. The concentration-dependent radiosensitizing effect of PMZ was investigated by exposing FaDu cells to different PMZ concentrations under hypoxic conditions followed by exposure to ionizing irradiation. The efficacy of TSL-PMZ in combination with hyperthermia and radiotherapy was determined in vitro, assessing cell survival and DNA damage by means of the clonogenic assay and histone H2AX phosphorylation, respectively. All TSL-PMZ formulations showed high encapsulation efficiencies and were stable for 30 d upon storage at 4 °C and 20 °C. Fast PMZ release was observed at 42 °C, regardless of the drug/lipid ratio. Increasing the PMZ concentration significantly enhanced the effect of ionizing irradiation. Pre-heated TSL-PMZ in combination with radiotherapy caused a 14.3-fold increase in cell death as compared to radiotherapy treatment alone. In conclusion, our results indicate that TSL-PMZ in combination with hyperthermia can assist in improving the efficacy of radiotherapy under hypoxic conditions.
缺氧是实体肿瘤的一个特征，也是放疗抵抗的一个重要原因。已经证明，缺氧细胞放射增敏剂可以提高放疗的疗效，但由于剂量限制的副作用，它们在临床上无法广泛应用。我们建议将缺氧细胞放射增敏剂包封在温度敏感脂质体（TSL）中，以将放射增敏剂特异性靶向肿瘤，并避免在健康组织中不必要的积累。本研究的主要目的是开发和表征负载放射增敏剂匹莫硝唑（PMZ）的 TSL，并评估游离 PMZ 和负载 PMZ 的 TSL 与热疗和放疗联合应用的体外疗效。PMZ 以不同的药物/脂质比主动载入 TSL，评估所得 TSL-PMZ 的理化特性和稳定性。在 HEPES 缓冲盐溶液和胎牛血清中，在 37°C 和 42°C 下测定 PMZ 的释放情况。在缺氧条件下，将 FaDu 细胞暴露于不同的 PMZ 浓度下，然后进行电离照射，研究 PMZ 的浓度依赖性放射增敏作用。通过集落形成实验评估细胞存活率，通过组蛋白 H2AX 磷酸化评估 DNA 损伤，从而确定 TSL-PMZ 与热疗和放疗联合应用的体外疗效。所有 TSL-PMZ 制剂的包封效率均较高，在 4°C 和 20°C 下储存 30 天稳定。在 42°C 下，无论药物/脂质比如何，都观察到 PMZ 的快速释放。PMZ 浓度的增加显著增强了电离照射的效果。与单独放疗相比，加热的 TSL-PMZ 与放疗联合使用可使细胞死亡增加 14.3 倍。总之，我们的结果表明，TSL-PMZ 联合热疗可以辅助改善缺氧条件下放疗的疗效。
