Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy

Michael G. Nichols; Thomas H. Foster

doi:10.1117/12.179983

Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy

Michael G. Nichols, Thomas H. Foster

Research output: Contribution to journal › Conference article

7 Scopus citations

Abstract

We have previously reported results of experiments in which EMT6/Ro spheroids were subjected to Photofrin®-PDT consisting of a fixed incident fluence (60 J-cm^-2) delivered at 200, 50, and 25 mW-cm^-2. Surviving fractions from treated spheroids decreased as the incident fluence rate was lowered over this range. We have interpreted these data using a model wherein the cells comprising the surviving fractions are assumed to originate from within a therapy-induced anoxic volume resulting from Type-il photochemistry. In this paper, we demonstrate direct measurements of the phenomenon in individual photosensitized EMT6 spheroids. Steadystate measurements of ³O₂ gradients in and around metabolizing spheroids allow determination of the ³O₂ diffusion constant and the rate of metabolic ³O₂ consumption within a spheroid. Timedependent measurements obtained at a single spatial location during laser irradiation are fit to numerical solutions of a pair of time-dependent diffusion with consumption equations. Fits allow a determination of the rate of PDT-induced ³O₂ consumption. Based on these fits, it is possible to calculate the spatial and temporal distributions of oxygen within a spheroid undergoing PDT.

Original language	English (US)
Pages (from-to)	260-271
Number of pages	12
Journal	Proceedings of SPIE - The International Society for Optical Engineering
Volume	2133
DOIs	https://doi.org/10.1117/12.179983
State	Published - Jul 19 1994
Externally published	Yes
Event	Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy III 1994 - Los Angeles, United States Duration: Jan 23 1994 → Jan 29 1994

All Science Journal Classification (ASJC) codes

Electronic, Optical and Magnetic Materials
Condensed Matter Physics
Computer Science Applications
Applied Mathematics
Electrical and Electronic Engineering

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10.1117/12.179983

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Nichols, M. G., & Foster, T. H. (1994). Microelectrode measurements of photochemical oxygen depletion in multicell tumor spheroids during photodynamic therapy. Proceedings of SPIE - The International Society for Optical Engineering, 2133, 260-271. https://doi.org/10.1117/12.179983

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abstract = "We have previously reported results of experiments in which EMT6/Ro spheroids were subjected to Photofrin{\textregistered}-PDT consisting of a fixed incident fluence (60 J-cm-2) delivered at 200, 50, and 25 mW-cm-2. Surviving fractions from treated spheroids decreased as the incident fluence rate was lowered over this range. We have interpreted these data using a model wherein the cells comprising the surviving fractions are assumed to originate from within a therapy-induced anoxic volume resulting from Type-il photochemistry. In this paper, we demonstrate direct measurements of the phenomenon in individual photosensitized EMT6 spheroids. Steadystate measurements of 3O2 gradients in and around metabolizing spheroids allow determination of the 3O2 diffusion constant and the rate of metabolic 3O2 consumption within a spheroid. Timedependent measurements obtained at a single spatial location during laser irradiation are fit to numerical solutions of a pair of time-dependent diffusion with consumption equations. Fits allow a determination of the rate of PDT-induced 3O2 consumption. Based on these fits, it is possible to calculate the spatial and temporal distributions of oxygen within a spheroid undergoing PDT.",

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AU - Foster, Thomas H.

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N2 - We have previously reported results of experiments in which EMT6/Ro spheroids were subjected to Photofrin®-PDT consisting of a fixed incident fluence (60 J-cm-2) delivered at 200, 50, and 25 mW-cm-2. Surviving fractions from treated spheroids decreased as the incident fluence rate was lowered over this range. We have interpreted these data using a model wherein the cells comprising the surviving fractions are assumed to originate from within a therapy-induced anoxic volume resulting from Type-il photochemistry. In this paper, we demonstrate direct measurements of the phenomenon in individual photosensitized EMT6 spheroids. Steadystate measurements of 3O2 gradients in and around metabolizing spheroids allow determination of the 3O2 diffusion constant and the rate of metabolic 3O2 consumption within a spheroid. Timedependent measurements obtained at a single spatial location during laser irradiation are fit to numerical solutions of a pair of time-dependent diffusion with consumption equations. Fits allow a determination of the rate of PDT-induced 3O2 consumption. Based on these fits, it is possible to calculate the spatial and temporal distributions of oxygen within a spheroid undergoing PDT.

AB - We have previously reported results of experiments in which EMT6/Ro spheroids were subjected to Photofrin®-PDT consisting of a fixed incident fluence (60 J-cm-2) delivered at 200, 50, and 25 mW-cm-2. Surviving fractions from treated spheroids decreased as the incident fluence rate was lowered over this range. We have interpreted these data using a model wherein the cells comprising the surviving fractions are assumed to originate from within a therapy-induced anoxic volume resulting from Type-il photochemistry. In this paper, we demonstrate direct measurements of the phenomenon in individual photosensitized EMT6 spheroids. Steadystate measurements of 3O2 gradients in and around metabolizing spheroids allow determination of the 3O2 diffusion constant and the rate of metabolic 3O2 consumption within a spheroid. Timedependent measurements obtained at a single spatial location during laser irradiation are fit to numerical solutions of a pair of time-dependent diffusion with consumption equations. Fits allow a determination of the rate of PDT-induced 3O2 consumption. Based on these fits, it is possible to calculate the spatial and temporal distributions of oxygen within a spheroid undergoing PDT.

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