Investigations in vivo of the effects of carbogen breathing on 5-fluorouracil pharmacokinetics and physiology of solid rodent tumours

Abstract

Purpose: We have shown previously that carbogen (95% 0 2 , 5% CO 2 ) breathing by rodents can increase uptake of anticancer drugs into tumours. The aim of this study was to extend these observations to other rodent models using the anticancer drug 5-fluorouracil (5FU). 5FU pharmacokinetics in tumour and plasma and physiological effects on the tumour by carbogen were investigated to determine the locus of carbogen action on augmenting tumour uptake of 5FU. Methods: Two different tumour models were used, rat GH3 prolactinomas xenografted s.c. into nude mice and rat H9618a hepatomas grown s.c. in syngeneic Buffalo rats. Uptake and metabolism of 5FU in both tumour models with or without host carbogen breathing was studied non-invasively using fluorine-19 magnetic resonance spectroscopy ( 19 F-MRS), while plasma samples from Buffalo rats were used to construct a NONMEM pharmacokinetic model. Physiological effects of carbogen on tumours were studied using 31 P-MRS for energy status (NTP/Pi) and pH, and gradient-recalled echo magnetic resonance imaging (GRE-MRI) for blood flow and oxygenation. Results: In both tumour models, carbogan-induced GRE-MRI signal intensity increases of $60% consistent with an increase in tumour blood oxygenation and/or flow. In GH3 xenografts, 19 F-MRS showed that carbogen had no significant effect on 5FU uptake and metabolism by the tumours, and 31 P-MRS showed there was no change in the NTP/Pi ratio. In H9618a hepatomas, 19 F-MRS showed that carbogen had no effect on tumour 5FU uptake but significantly (p=0.0003) increased 5FU elimination from the tumour (i.e. decreased the t 1/2 ) and significantly (p=0.029) increased (53%) the rate of metabolism to cytotoxic fluoronucleotides (FNuct). The pharmacokinetic analysis showed that carbogen increased the rate of tumour uptake of 5FU from the plasma but also increased the rate of removal.31 P-MRS showed there were significant (p £ 0.02) increases in the hepatoma NTP/Pi ratio of 49% and transmembrane pH gradient of 0.11 units. Conclusions: We suggest that carbogen can transiently increase tumour blood flow, but this effect alone may not increase uptake of anticancer drugs without a secondary mechanism operating. In the case of the hepatoma, the increase in tumour energy status and pH gradient may be sufficient to augment 5FU metabolism to cytotoxic FNuct, while in the GH3 xenografts this was not the case. Thus carbogen breathing does not universally lead to increased uptake of anticancer drugs. Abbreviations AUC: Area under the concentration-time curve AE C max : Maximum value AE DHFU: Dihydrofluorouracil AE 5FU: 5-Fluorouracil AE FTP: 5-Fluorotryptophan AE FBal: 5-Fluoro-b-alanine AE FUPA: 5-Fluoro-b-ureidopropionic acid AE FNuct: 5-Fluoronucleotides AE FCat: Fluorocatabolites AE GRE: Gradient recalled-echo AE MRS: Magnetic resonance spectroscopy AE NaF: Sodium fluoride AE DpH: pH gradient across the plasma membrane AE t 1/2 : 5FU elimination half-life AE V 1 : 5FU in the body AE V 2 : 5FU in the tumour AE CL 10 : 5FU elimination from th...

Investigating the Vascular Phenotype of Subcutaneously and Orthotopically Propagated PC3 Prostate Cancer Xenografts Using Combined Carbogen Ultrasmall Superparamagnetic Iron Oxide MRI

“…Efficient tumour plasma perfusion is a key determinant of drug delivery, so a clear understanding on the extent, patency and spatial distribution of functional tumour vasculature in vivo provided by techniques such as CUSPIO imaging is imperative for appropriate tumour model selection when designing pre-clinical therapy trials. Carbogen inhalation has been used both clinically and pre-clinically to increase drug uptake, in solid tumours through hypercapnia-induced vasodilation (39–43). The potential to use CUSPIO imaging to non-invasively assess the degree and heterogeneity of vascular functionality, tumour oxygenation and vascular shutdown will impact on both chemotherapy and radiotherapy, which generally exhibit higher efficacy in well oxygenated tumour tissue (44).…”

MR evaluation of response to targeted treatment in cancer cells

“…151. These studies opened up the way to several in vivo investigations in which 5‐FU uptake and pHe could be monitored simultaneously by 19 F MRS 153–156, and uptake of the weakly acidic drug could be enhanced by pHe acidification.…”

Magnetic resonance spectroscopy (MRS) in the investigation of cancer at The Royal Marsden Hospital and The Institute of Cancer Research

“…Further experiments in cells confirmed the effect of the pH gradient on 5FU uptake (Ojugo et al 1998). Tumour uptake can be modulated by carbogen (McSheehy et al 2005) and bafilomycin (McSheehy et al 2003), which both affect the intra-, extra-cellular pH gradient. 19F MRS can also be used to assess the metabolism of pro-drugs of 5FU, such as capcitebine, showing that conversion depends on the level of thymidine phosphorylase in the tumour (Chung et al 2004).…”