An in vivo model of melanoma: treatment with ATP

Abstract

Athymic mice, injected with A375 human melanoma cells, were treated daily with intraperitoneal injections of adenosine 5'-triphosphate (ATP). The tumour volume and animal weight were measured over the course of the experiment and the final tumour nodule weight was measured at the end of the experiment. Tumour volume decreased by nearly 50% by 7 weeks in treated mice. Weight loss in untreated animals was prevented by ATP. Histological examination of the excised tumour nodules showed necrosis in the ATP-treated tumours only. The presence of P2Y(1) and P2X(7) receptors, previously proposed as extracellular targets for melanoma treatment with ATP, were demonstrated in the excised specimens by immunohistochemistry. This paper provides further support for the use of ATP as a treatment for melanoma.

Fig. 1

a The weight of the untreated group of animals decreased over the six week course of the experiment from a mean of 30 g to a mean of 28.2 g. However, in the treated group, the weight of the animals increased from a mean of 30 to 31.8 g. There was a statistically significant difference in the weight of the animals over the course of the experiment (P = 0.0038). b There was a statistically significant reduction in tumour volume in the treated group compared to the untreated group (P = 0.0163). Tumours in both the treated and untreated groups continued to grow during the course of the experiment but the rate of growth of the untreated group was much higher than that of the treated group. c At the end of the experiment, the tumour nodules were excised and weighed. There was a statistically significant reduction in final tumour weight in the treated group compared to the untreated group (P = 0.0156). The tumours from the untreated group had a mean weight of 1.92 ± 0.31 g (n = 10) compared to the tumours from the treated group which had a mean weight of 1.15 ± 0.24 g (n = 10)

Fig. 2

Haematoxylin and eosin staining (a and b) and immunohistochemical staining P2Y₁ receptors (c and d) of excised tumour nodules. a Solid tumour from an untreated mouse. b Tumour from a mouse treated with ATP showing patchy necrosis, illustrated by red staining areas with no nuclear counterstain (arrows). c Scant expression of P2Y₁ receptors (pink) in a specimen of untreated melanoma with a haematoxylin nuclear counterstain (purple). b Increased P2Y₁ receptor staining in the ATP-treated group concentrated around the areas of necrosis. Haematoxylin nuclear counterstain (purple). All calibration bars = 250 µm

Fig. 3

Localisation of P2X₇ receptors and TUNEL in an excised melanoma from an ATP-treated mouse. a Red extracellular P2X₇ staining. b Green intracellular TUNEL staining. c Localisation of extracellular P2X₇ receptors and intracellular TUNEL in ATP-treated melanoma tissue undergoing apoptosis. Calibration bars = 50 μM