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Does tumour uptake of Foscan determine PDT efficacy?
R Veenhuizen1, H Oppelaar, M Ruevekamp
1Experimental Therapy Division, Netherlands Cancer Institute/Antoni van Leeuwenhoek Huis, Amsterdam, The Netherlands.
Abstract:
Preferential retention of photosensitizers in tumours has always been one of the major goals in the search for new photosensitizers and has determined the design of clinical trials with respect to the interval between drug administration and illumination. The purpose of this study was to investigate the importance of tumour and plasma concentrations of Foscan (mTHPC, meta-tetrahydroxyphenylchlorin) in relation to PDT effect. Both pharmacokinetic and tumour response studies were carried out in mice bearing s.c. RIF1 tumours. mTHPC was injected in 1 or 2 doses of 0.3 mg x kg-1. For distribution studies, 14C-labelled mTHPC was given 5 min to 48 hr before determination of plasma and tumour drug levels. Non-labelled sensitizer was used to determine the PDT efficacy for illumination at 5 min to 48 hr after drug administration. PDT efficacy was greatest for illumination at 1 to 3 hr, and for an interval of 48 hr there was no significant tumour-growth delay. In contrast, mTHPC tumour drug levels reached a maximum 6 hr after injection and remained high for 48 hr. A comparison of pharmacokinetics and response studies revealed no significant correlation between tumour mTHPC levels and tumour response. There was, however, a significant correlation between plasma drug levels and tumour response for time intervals of 1 to 48 hr. This association may imply that PDT protocols should use shorter drug-light intervals in combination with lower drug doses. This would increase safety and decrease the extent and duration of normal tissue photosensitization.
Insights
Photodynamic therapy (PDT) with meta-tetrahydroxyphenylchlorin (mTHPC) showed greatest efficacy when light was administered 1-3 hours after injection. Tumor response correlated with plasma mTHPC levels, not tumor levels, suggesting optimized PDT protocols.
Area of Science:
- Oncology
- Pharmacology
- Biomedical Engineering
Background:
- Preferential photosensitizer retention in tumors is crucial for effective photodynamic therapy (PDT).
- Clinical trial design often focuses on the optimal interval between photosensitizer administration and light application.
- Foscan (meta-tetrahydroxyphenylchlorin, mTHPC) is a photosensitizer used in PDT.
Purpose of the Study:
- To investigate the relationship between tumor and plasma concentrations of mTHPC and its photodynamic therapy (PDT) effect.
- To determine the optimal time interval for PDT illumination after mTHPC administration.
- To correlate pharmacokinetic data with tumor response in a preclinical model.
Main Methods:
- Pharmacokinetic and tumor response studies were conducted in mice bearing RIF1 tumors.
- 14C-labeled and non-labeled mTHPC were administered in single or double doses (0.3 mg/kg).
- Drug distribution and PDT efficacy were assessed at various time points (5 min to 48 hr) post-administration.
Main Results:
- PDT efficacy was maximal for illumination 1-3 hours after mTHPC administration; no significant tumor growth delay was observed at 48 hours.
- mTHPC tumor drug levels peaked at 6 hours and remained elevated for 48 hours.
- Tumor mTHPC levels did not correlate with tumor response, but plasma mTHPC levels showed a significant correlation for intervals of 1-48 hours.
Conclusions:
- Tumor drug concentration does not directly predict PDT efficacy for mTHPC.
- Plasma drug levels correlate with tumor response, suggesting shorter drug-light intervals may be beneficial.
- Optimizing PDT protocols with shorter intervals and lower doses could enhance safety and reduce normal tissue photosensitization.