Temporal heterogeneity in oxygen tension in human melanoma xenografts

Abstract

The spatial heterogeneity of the oxygen tension (pO 2 ) in human and experimental tumours has been studied extensively, whereas studies of the temporal heterogeneity in pO 2 are sparse. In the work reported here, pO 2 was measured continuously over periods of at least 60 min in A-07 human melanoma xenografts by using the OxyLite fibre-optic oxygen-sensing device. The main purpose of the work was to establish the usefulness of the OxyLite system in measuring the temporal heterogeneity in pO 2 in tissues and to characterise the fluctuations in tissue pO 2 in A-07 tumours. The OxyLite device was found to be suitable for studies of the temporal heterogeneity in pO 2 in tumours. However, potential pitfalls were identified, and reliable pO 2 measurements require that precautions are taken to avoid these pitfalls, that is, erroneous pO 2 readings caused by tissue trauma induced by the probe, probe movements induced by reflex actions of the host mouse and occasional probe drift. Significant fluctuations in pO 2 were detected in the majority of the 70 tumour regions subjected to measurement. The fluctuations in different regions of the same tumour were in general temporally independent, implying that they were caused primarily by redistribution of the tumour perfusion rather than fluctuations in global perfusion. Fourier analysis of the pO 2 traces showed that the pO 2 usually fluctuated at frequencies lower than 1.5 -2.0 mHz, corresponding to less than 0.1 cycle min À1 . Haemodynamic effects may cause pO 2 fluctuations in this frequency range, and hence, the redistribution of the perfusion could have been caused by morphological abnormalities of the tumour microvasculature. Moreover, acute hypoxia, that is, pO 2 fluctuations around 10 or 5 mmHg, was detected in 20 of 70 regions, that is, 29% (10 mmHg), or 27 of 70 regions, that is, 39% (5 mmHg). The median fraction of the time these regions were acutely hypoxic was 73% (10 mmHg) or 53% (5 mmHg). Consequently, if A-07 tumours are adequate models of tumours in man, acute hypoxia may be a commonly occurring phenomenon in neoplastic tissues, and hence, acute hypoxia is likely to cause resistance to radiation therapy and promote tumour aggressiveness.

Assessment of tumor oxygenation by electron paramagnetic resonance: principles and applications

“…57,58 (2) fluorescence quenching-an oxygen sensing method based on fluorescence quenching has been used in a commercial system that involves the insertion of a fiber-optic probe directly into the tissue. The system, with the brand name OxyLite 1 , [61][62][63][64][65][66][67][68][69] A limitation of the method is the impossibility to record pO 2 from the same site over days. (3) phosphorescence quenching-phosphorescence lifetime imaging has been used to evaluate changes of oxygenation of tumors during procedures to manipulate tumor oxygenation.…”

Acute Hypoxia Enhances Spontaneous Lymph Node Metastasis in an Orthotopic Murine Model of Human Cervical Carcinoma

“…The high interstitial fluid pressure, characteristic of solid tumors, may further exacerbate the situation, as suggested by recent attempts to model these temporal changes (18). The available data suggest that this blood flow instability, in the context of an already poorly organized and regulated vascular system, can produce temporal (acute) changes in oxygenation in substantial volumes of solid tumors (12,16,17).…”

“…Substantial instability in microregional blood flow and tissue oxygenation has been demonstrated to occur in animal and human tumors, using a number of techniques (11)(12)(13)(14)(15)(16)(17). These fluctuations are thought to be attributable to transient occlusion, narrowing of vessels, and arteriolar vasomotion.…”

Quantifying Transient Hypoxia in Human Tumor Xenografts by Flow Cytometry

“…Oxygen tensions have been monitored continuously in murine tumors using recessed-tip oxygen microelectrodes (17)(18)(19) and in human melanoma xenografts using Oxylite fiber-optic microprobes (20,21). These studies have provided real-time evidence that substantial yet highly heterogeneous changes in tumor blood flow and pO 2 can occur with different periodicities and magnitudes in different tumor types and in different regions of the same tumor.…”

“…A time-integrated tumor hypoxic fraction was estimated using hourly injections of pimonidazole, which could then be compared with the more "typical" hypoxic fraction determined with a single subsequent injection of CCI-103F. Importantly, the use of flow cytometry allowed quantification of transient hypoxia on a cell-by-cell basis, which provided an improvement in resolution when compared with the insertion of probes (17)(18)(19)(20)(21) or the analyses of tumor sections for changes in microregional perfusion (22)(23)(24) or hypoxia (4,28). Moreover, flow cytometry analysis provides hundreds of thousands of data points for a single tumor, while also allowing the exclusion of necrosis and host cells from the measurements.…”