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

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.

Tumour necrosis factor-alpha enhances the cytolytic and cytostatic capacity of interleukin-2 activated killer cells.

The cytotoxic and cytostatic responses of peripheral blood lymphocytes from eight cancer patients and splenocytes from four patients activated with rIL2 and a combination of rIL2 and rTNF-alpha were tested against two tumour cell lines. The cytotoxic response of rIL2-activated lymphocytes did not exceed the natural killer cytotoxicity values in all patients tested. In fact the killing capacity of some PBL deteriorated after rIL2 activation. The combined use of rIL2 and rTNF-alpha reversed this detrimental effect and enhanced the cytotoxic capacity of all PBL tested. In instances where high levels of killing were already achieved by rIL2 alone additional rTNF-alpha did not induce a significant change. This indicates that the role of rTNF-alpha may be to promote the response to rIL2 of PBL which react suboptimally to this lymphokine. rTNF-alpha did not only enhance cytotoxic capacity but also conferred cytostatic capacity to rIL2-activated LAK cells which were cytotoxic but unable to inhibit the growth of the surviving target cells. Natural killer cell selected K562 target cells which were less susceptible to killing by untreated lymphocytes than the parent K562 tumour cell line were killed more aggressively by rIL2 + rTNF-alpha LAK cells than by rIL2-LAK cells. No phenotypic differences were detected in these two cultures of LAK cells which indicates that the increased cytotoxic and cytostatic capacity of rIL2 + rTNF-alpha-LAK cells may be due to a higher state of activation of these cells or due to their capacity to recognise a broader spectrum of targets than rIL2-LAK cells.