In vitro modulation of haematoporphyrin derivative photodynamic therapy on colorectal carcinoma multicellular spheroids by verapamil

Abstract

Photodynamic therapy has possible applications in the treatment of colorectal carcinoma. The photosensitizer haematoporphyrin derivative (HpD) is selectively retained by tumours. Agents which block p-glycoprotein, an export protein expressed to increased levels in a high proportion of colorectal carcinomas, may modulate photodynamic therapy by reducing HpD efflux from cells. Multicellular spheroids derived from the colorectal cell lines HRT18 and HT29 were incubated for 24 h with 1 microgram ml-1 HpD and 0, 1, 2 and 4 microM verapamil. Bioactivity demonstrated a dose-dependent potentiation of HpD-photodynamic therapy growth retardation. Clonogenic survival of cells disaggregated from spheroids treated with HpD-photodynamic therapy was reduced when spheroids were coincubated with verapamil. The mean(s.e.m.) efflux of HpD from spheroids into fresh medium assessed by fluorimetry was greater in spheroids treated with HpD alone (93.2(18.8) arbitrary units ml-1) than in those treated with verapamil (18.1(2.8) arbitrary units ml-1), P = 0.003. Flow cytometry demonstrated increased HpD fluorescence in cells derived from spheroids coincubated with verapamil over a range of HpD incubation concentrations. Verapamil can potentiate the bioactivity of HpD-photodynamic therapy and HpD may be a substrate for p-glycoprotein.

A Light in Multidrug Resistance: Photodynamic Treatment of Multidrug-Resistant Tumors

“…In the last decade, several authors studied the photodynamic effects in MDR cells in culture, with promising results. Initially, it was shown that there was no difference in Photofrin accumulation or photosensitization between sensitive and MDR Friend leukemia cell lines [3], although the accumulation of the hematoporphyrin derivative was lower in multicellular spheroids derived from a human colorectal carcinoma cell line, a kind of tumor that usually overexpresses Pgp [39,40].…”

Three-dimensional in vitro cancer spheroid models for photodynamic therapy: strengths and opportunities

“…An interesting study exploring the interaction of haematoporphyrin derivative (HpD) with verapamil, a calcium channel blocker, observed that the small molecule improved the overall efficacy of PDT in colorectal cancer spheroids. This beneficial interaction was hypothesized to arise from verapamil's ability to hamper cellular efflux pumps, thus increasing intracellular concentrations of the photosensitizer [43].…”

Multicell tumor spheroids in photodynamic therapy

“…This, and other early studies, focused mainly on evaluating hematoporphyrin (Hpd) distributions and the effects of Hpd-PDT in a variety of MCS models [15][16][17][18][19]. In particular, fundamental studies by West [16] and West et al [19] demonstrated that human colon carcinoma spheroids were more resistant to Hpd-PDT compared to monolayers and that the sensitivity to PDT decreased with increasing spheroid size.…”