Temporally and Spatially Heterogeneous Distribution of mTHPC in a Murine Tumor Observed by Two‐color Confocal Fluorescence Imaging and Spectroscopy in a Whole‐mount Model

Abstract

Efficient intratumor delivery of anticancer drugs and photosensitizers is an important factor in the success of chemotherapy and photodynamic therapy, respectively. Unfortunately, their adequate and uniform intratumor distribution is impeded by several physiological barriers and by binding to tissue components. Measurement of gross tumor drug accumulation is a routine method of investigating the uptake and clearance of chemotherapy agents and photosensitizers but tells little about their extravascular spatial distribution. We use whole-mount two-color confocal fluorescence imaging and imaging spectroscopy of unprocessed excised murine tumor fragments to investigate the intratumor distribution of the photosensitizer meso-tetrahydroxyphenyl chlorin (mTHPC) as a function of distance from blood vessels perfused with 0.2 mum diameter fluorescent microspheres. Significant mismatches between drug and perfused vasculature are caused by heterogeneities in tumor blood supply. We describe complex microscopic mTHPC gradients that reverse dramatically relative to the perfused vasculature with time after injection. This imaging technique can be applied to screen the dynamic intratumor distribution of other fluorescent photosensitizers and anticancer drugs.

Photodynamic therapy with conventional and PEGylated liposomal formulations of mTHPC (temoporfin): comparison of treatment efficacy and distribution characteristics in vivo

“…Along with the drug release rate, blood circulation time and the spatiotemporal uptake in the tumor are considered to be the crucial properties of the liposomal drug formulation. 15,16 The aim of this study was to compare and interlink the properties related to the drug behavior in vivo and the efficacy of PDT treatment with Foslip ® and Fospeg ® in tumor-bearing mice. The pharmacokinetics, biodistribution, drug release, stability of liposomes, and intratumoral mTHPC localization were investigated, as well as the PDT outcome at different drug-light intervals.…”

“…The vascular tumor compartment was stained as described earlier. 16 Briefly, 5 minutes prior to macroscopy observations, 40 µL of 0.2 µm of fluorescent carboxylate-modified polystyrene microspheres (F-8809; Molecular Probes ® ; Life Technologies) was injected, rendering perfused vessels highly fluorescent. An incision of the skin in the vicinity of the tumor was made without damaging the blood vessels.…”

Integration of fluorescence differential path-length spectroscopy to photodynamic therapy of the head and neck tumors is useful in monitoring clinical outcome

“…Out of 27 treated tumors eight had incomplete response or early recurrence (lesions 1,8,12,13,22,23,25,27). When the spectroscopy data was analyzed three types of possible reasons of failure were identified for four of the lesions treated (lesions 1, 8, 12, 13).…”

<italic>In vivo</italic> quantification of photosensitizer concentration using fluorescence differential path-length spectroscopy: influence of photosensitizer formulation and tissue location

“…Besides tissue specific differences in mTHPC uptake, the biodistribution of mTHPC varies greatly with time. 46,48 However, the tissue specific mTHPC distribution is bound to have some influence on optical concentration measurements.…”

“…23 Another complicating factor is significant spatial variation in mTHPC biodistribution within tumors. 48 Moreover, tumors of the oral cavity could also disrupt or change the keratin layer, and therefore influence the performance of our technique. All these aspects may lead to very different observations and very different levels of homogeneity and heterogeneity in human healthy and tumor tissues.…”