We investigated the use of
purinergic receptors as a new treatment modality for nonmelanoma
skin cancers.
Purinergic receptors, which bind
adenosine 5'-tri-phosphate, are expressed on human cutaneous keratinocytes. Previous work in rat and human epidermis suggested functional roles for
purinergic receptors in the regulation of proliferation, differentiation, and apoptosis. Immunohistochemical analysis of frozen sections in human
basal cell carcinomas and
squamous cell carcinomas for P2X5, P2X7, P2Y1, P2Y2, and
P2Y4 receptors was performed, accompanied by detailed analysis of archive material of
tumor subtypes in
paraffin sections. Functional studies were performed using a human cutaneous
squamous cell carcinoma cell line (A431), where
purinergic receptor subtype agonists were applied to cells and changes in cell number were quantified via a colorimetric assay. Immunostaining in
paraffin sections was essentially the same as that in frozen sections, although more detail of the subcellular composition was visible. P2X5 and
P2Y2 receptors were heavily expressed in
basal cell carcinomas and
squamous cell carcinomas. P2X7 receptors were expressed in the necrotic center of nodular
basal cell carcinomas and in apoptotic cells in superficial multifocal and infiltrative
basal cell carcinomas, and
squamous cell carcinomas.
P2Y1 receptors were only expressed in the stroma surrounding
tumors.
P2Y4 receptors were found in
basal cell carcinomas but not in
squamous cell carcinomas. P2X5 receptors appear to be associated with differentiation. The
P2X7 receptor agonist benzoylbenzoyl-
adenosine 5'-triphosphate and high concentrations of
adenosine 5'-triphosphate (1000-5000 microM) caused a significant reduction in A431 cell number (p<0.001), whereas the
P2Y2 receptor agonist
uridine 5'-triphosphate caused a significant amount of proliferation (p<0.001). We have demonstrated that non-
melanoma skin cancers express functional
purinergic receptors and that
P2X7 receptor agonists significantly reduce cell numbers in vitro.