Perfluorocarbon nanodroplets can reoxygenate hypoxic tumors in vivo without carbogen breathing

Abstract

Nanoscale perfluorocarbon (PFC) droplets have enormous potential as clinical theranostic agents. They are biocompatible and are currently used in vivo as contrast agents for a variety of medical imaging modalities, including ultrasound, computed tomography, photoacoustic and 19 F-magnetic resonance imaging. PFC nanodroplets can also carry molecular and nanoparticulate drugs and be activated in situ by ultrasound or light for targeted therapy. Recently, there has been renewed interest in using PFC nanodroplets for hypoxic tumor reoxygenation towards radiosensitization based on the high oxygen solubility of PFCs. Previous studies showed that tumor oxygenation using PFC agents only occurs in combination with enhanced oxygen breathing. However, recent studies suggest that PFC agents that accumulate in solid tumors can contribute to radiosensitization, presumably due to tumor reoxygenation without enhanced oxygen breathing. In this study, we quantify the impact of oxygenation due to PFC nanodroplet accumulation in tumors alone in comparison with other reoxygenation methodologies, in particular, carbogen breathing. Methods: Lipid-stabilized, PFC (i.e., perfluorooctyl bromide, CF 3 (CF 2 ) 7 Br, PFOB) nanoscale droplets were synthesized and evaluated in xenograft prostate (DU145) tumors in male mice. Biodistribution assessment of the nanodroplets was achieved using a fluorescent lipophilic indocarbocyanine dye label (i.e., DiI dye) on the lipid shell in combination with fluorescence imaging in mice (n≥3 per group). Hypoxia reduction in tumors was measured using PET imaging and a known hypoxia radiotracer, [ 18 F]FAZA (n≥ 3 per group). Results: Lipid-stabilized nanoscale PFOB emulsions (mean diameter of ~250 nm), accumulated in the xenograft prostate tumors in mice 24 hours post-injection. In vivo PET imaging with [ 18 F]FAZA showed that the accumulation of the PFOB nanodroplets in the tumor tissues alone significantly reduced tumor hypoxia, without enhanced oxygen (i.e., carbogen) breathing. This reoxygenation effect was found to be comparable with carbogen breathing alone. Conclusion: Accumulation of nanoscale PFOB agents in solid tumors alone successfully reoxygenated hypoxic tumors to levels comparable with carbogen breathing alone, an established tumor oxygenation method. This study confirms that PFC agents can be used to reoxygenate hypoxic tumors in addition to their current applications as multifunctional theranostic agents.

Enhanced antitumor efficacy on colon cancer using EGF functionalized PLGA nanoparticles loaded with 5-Fluorouracil and perfluorocarbon

“…In our study, dualloaded PLGA NPs encapsulating 5FU and PFC had the combinative antitumor effects on colon cancer, likely owing to that PFC in the tumor altered the diffusion status of the oxygen in tumor tissue. This was in agreement with the existing researches that PFC had great potential for enhancing intratumoral hypoxia [29,30].…”

Enhanced antitumor efficacy on colon cancer using EGF functionalized PLGA nanoparticles loaded with 5-Fluorouracil and perfluorocarbon

“…In our study, dual-loaded PLGA NPs encapsulating 5FU and PFC had the combinative antitumor effects on colon cancer, likely owing to that PFC in the tumor altered the diffusion status of the oxygen in tumor tissue. This was in agreement with the existing researches that PFC had great potential for enhancing intratumoral hypoxia [30,31].…”

Overcoming hypoxia-induced chemoresistance to cisplatin through tumor oxygenation monitored by optical imaging

“…Tumor accumulation of PN may contribute to the oxygenation but might not be substantial due to the limited amount of PN which eventually reaches tumors (in a scale of 1% of injected dose in tumors). Interestingly, a recent report has indicated little importance of carbogen breathing for tumor oxygenation [25]. In the referred report, hypoxia measurements were made 24 h post administration of PFOB droplets via PET imaging with [ 18 F]FAZA, unable to measure free oxygen levels.…”

“…For short term acute delivery of free oxygen, carbogen is recommended to promote an oxygen-rich environment for lung recharging of circulating PFOB nanodroplets, as demonstrated by the Image-iT TM tracking results which measures free oxygen. However, air breathing environment can potentially reduce hypoxia on a longer time-scale, as showcased by the referred study [25], which measured their results as a function of hypoxia state using [ 18 F]FAZA PET. The reduction of tumor hypoxia at later time-points may not necessarily correlate to current oxygenation levels expressed as a function of free, dissolved, oxygen.…”

“…Such method can greatly facilitate the development and evaluation of tumor oxygenation methods. Considerable number of reports demonstrated that supplemental hyperoxic inhalation during PFC treatment would be crucial for effective oxygen delivery to tumors, whereas some recent studies reported that inhaling room air would be effective 24 h after PFC administration [13,14,25]. In addition, oxygen-carrying capacity and circulating half-lives might be different for these formulations, thus the subsequent oxygenation efficiency may vary.…”