Vascular disrupting agents in clinical development

Growth of human tumours depends on the supply of oxygen and nutrients via the surrounding vasculature. Therefore tumour vasculature is an attractive target for anticancer therapy. Apart from angiogenesis inhibitors that compromise the formation of new blood vessels, a second class of specific anticancer drugs has been developed. These so-called vascular disrupting agents (VDAs) target the established tumour vasculature and cause an acute and pronounced shutdown of blood vessels resulting in an almost complete stop of blood flow, ultimately leading to selective tumour necrosis. As a number of VDAs are now being tested in clinical studies, we will discuss their mechanism of action and the results obtained in preclinical studies. Also data from clinical studies will be reviewed and some considerations with regard to the future development are given.

Two course illuminating scheme improves aminolevulinic acid photodynamic therapy in cell cultures

Photodynamic therapy with the pro-drug 5-aminolaevulinic acid (ALA-PDT) is being used for the treatment of Barrett's oesophagus. We postulated that a first early course of ALA-PDT would increase protoporphyrin IX (PPIX) accumulation and thus the efficacy of a second course of ALA-PDT, by manipulating ferrochelatase (FC) and porphobilinogen deaminase (PBG-d) activity. Human EBV-transformed lymphoblastoid cells were used as a model of human tumour cells for the ability to form haem is present in all cells. After a single course of illumination (633 nm, 100 mW/cm2) the FC activity decreased significantly whereas the PBG-d activity did not change. During continued incubation with ALA following the first illumination, cells accumulated up to four times more PPIX than non-illuminated controls [220% +/- 30% versus (vs) 55% +/- 5%; p<0.001]. Two illuminations resulted in more cell death than one illumination (97% +/- 1% vs 80% +/- 2%; p<0.001). Since a second course of ALA-PDT within 3 hr after the first course resulted in a four fold increase in PPIX accumulation and significantly more cell death, we propose that a two course ALA-PDT scheme might improve the efficacy of this treatment for Barrett's oesophagus.

Porphyrin biosynthesis in human Barrett's oesophagus and adenocarcinoma after ingestion of 5-aminolaevulinic acid

5-Aminolaevulinic acid (ALA)-induced porphyrin biosynthesis, which is used for ALA-based photodynamic therapy (ALA-PDT), was studied in tissues of 10 patients with Barrett's oesophagus (BE) and adenocarcinoma of the oesophagus (AC) undergoing oesophagectomy at a mean time interval of 6.7 h after the ingestion of ALA (60 mg kg(-1)). In BE, AC, squamous epithelium (SQ) and gastric cardia, the activities of the haem biosynthetic enzymes porphobilinogen deaminase (PBG-D) and ferrochelatase (FC) and the PDT power index--the ratio between PBG-D and FC in BE and AC in comparison with SQ--were determined before ALA ingestion. Following ALA administration, ALA, porphobilinogen, uroporphyrin I and PPIX were determined in tissues and plasma. The PDT power index did not predict the level of intracellular accumulation of PPIX found at 6.7 h. In BE, there was no selectivity of PPIX accumulation compared to SQ, whereas in half of patients with AC selectivity was found. Higher haem biosynthetic enzyme activities (i.e. PBG-D) and lower PPIX precursor concentrations were found in BE and AC compared to SQ. It is therefore possible that PPIX levels will peak at earlier time intervals in BE and AC compared to SQ.

Acrylate yellow filters in operating lights protect against photosensitization tissue damage

BACKGROUND

Photosensitized patients are exposed to bright lights when undergoing intraoperative photodynamic therapy or fluorescence measurements. Acrylate yellow filters might reduce unwanted tissue damage.

METHODS

To investigate the protective value of these filters, the spectral power distribution of the operating lights and light energy densities with and without an acrylate yellow filter were measured. Subsequently the effects of light exposure on the survival of a human hepatocellular carcinoma cell line and the photodamage induced in pig tissues after the administration of 5-aminolaevulinic acid were also studied.

RESULTS

The light energy density in the ultraviolet and blue region of the light spectrum emitted by the operating light was reduced up to 50 per cent by the acrylate yellow filter. The survival of photosensitized cells was longer and photodamage induced in pig tissues was less when exposed to filtered light.

CONCLUSION

Photodamage induced by operating lights can be reduced by filtering out ultraviolet and blue light by means of acrylate yellow filters.

[Endoscopic treatment of Barrett esophagus]

The purpose of the treatment of Barrett epithelium in the distal oesophagus is to reduce or even eliminate the increased risk of malignant degeneration in it. This can be achieved by removing the Barrett epithelium, whether or not dysplastic, and to have it replaced by normal squamous epithelium. Drug treatment or surgical antireflux treatment of Barrett epithelium has hardly any effect on the length of the Barrett epithelium or on the occurrence of malignancy. Various forms of endoscopic ablative therapy (laser coagulation, multipolar electrocoagulation, photodynamic therapy and argon plasma coagulation), in combination with antireflux treatment enable removal of the Barrett epithelium with regeneration of squamous epithelium. However, islets of Barrett epithelium may be found beneath the regenerated squamous epithelium and there is also the possibility of malignant potential of pluripotent stem cells left behind in the oesophagus. Future studies will have to afford insight into long-term results, the costs, the side effects of the various methods of treatment and the quality of life of patients during and after treatment of the Barrett oesophagus.

Biochemical basis of 5-aminolaevulinic acid-induced protoporphyrin IX accumulation: a study in patients with (pre)malignant lesions of the oesophagus

Administration of 5-aminolaevulinic acid (ALA) leads to porphyrin accumulation in malignant and premalignant tissues, and ALA is used as a prodrug in photodynamic therapy (PDT). To understand the mechanism of porphyrin accumulation after the administration of ALA and to investigate whether ALA-induced protoporphyrin IX might be a suitable photosensitizer in Barrett's oesophagus and adenocarcinoma, we determined the activities of porphobilinogen deaminase (PBG-D) and ferrochelatase (FC) in various malignant and premalignant as well as in normal tissues of the human oesophagus. A PDT power index for ALA-induced porphyrin accumulation, the ratio of PBG-D to FC normalized for the normal squamous epithelium of the oesophagus, was calculated to evaluate intertissue variation in the ability to accumulate porphyrins. In malignant and premalignant tissue a twofold increased PBG-D activity and a marginally increased FC activity was seen compared with normal squamous epithelium. A significantly increased PDT power index in Barrett's epithelium and adenocarcinoma was found. Our results suggest that, after the administration of ALA, porphyrins will accumulate in a greater amount in Barrett's epithelium and adenocarcinoma of the oesophagus because of an imbalance between PBG-D and FC activities. The PDT power index here defined might be a useful indicative parameter for predicting the susceptibility of these tissues to ALA-PDT.