Histochemistry of therapeutically relevant enzymes in human tumours transplanted into severe combined immunodeficient (SCID) mice: nitric oxide synthase-associated diaphorase, beta-D-glucuronidase and non-specific alkaline phosphatase.

Human breast (MCF-7, HBL 100, T47D, BT20, HS578T), colon (HT29, CACO2, SW620, SW480, COLO320DM) and small cell lung cancer (NCI-N417, OH3, SW2) cell lines were transplanted subcutaneously into severe combined immunodeficient (SCID) mice. When sizeable tumours developed, the mice were sacrificed and the following enzyme activities were detected histochemically: presumed nitric oxide synthase-associated diaphorase (NOSaD), beta-D-glucuronidase (beta-Gluc) and non-specific alkaline phosphatase (alP). Except for HT29 and MCF-7 presumed NOSaD activity was not detected in the tumour itself or in the neo-vasculature of the tumours. beta-Gluc activity was found in all tumour cells (except N417 and COLO 320), in the necrotic parts of the tumours and in stromal cells of the tumour bed. AlP activity was present in all tumours including their necrotic areas. However, the activities of beta-Gluc and alP varied considerably even within one tumour, ranging from very weak to very strong. Principally the results show that the human/SCID mouse tumour model is well suited to test modern applications of tumour therapy involving the enzymes NOSaD, beta-Gluc and alP. In particular, antibody directed enzyme prodrug therapy concepts and activation of prodrugs by enzymes released from tumour cells into the necrotic areas of the tumour can be evaluated in this in vivo model.