Immunocytochemical detection of deoxycytidine kinase in haematological malignancies and solid tumours

Background: Deoxycytidine kinase (dCK) is responsible for the activation of several clinically important deoxynucleoside analogues used for the treatment of haematological and solid malignancies. Aim: To measure dCK expression in tumour cells from different origins. Method: A rabbit antihuman dCK antibody was used for the immunocytochemical detection of dCK expression in three leukaemic cell lines (HL60, U937, and CCRF-CEM) and 97 patient samples (paediatric acute myeloid leukaemia (AML) and lymphoid leukaemia (ALL), retinoblastoma, paediatric brain tumours, and adult non-small cell lung cancer (NSCLC)). Results: CCRF-CEM, U937, and HL60 cells stained positively for dCK and the degree of expression correlated with dCK activity. dCK expression varied between tumour types and between individual patients within one tumour type. dCK was located predominantly in the cytoplasm. The staining intensity was scored as negative (0), low (1+), intermediate (2+), or high (3+). Expression of dCK was high in AML blasts. In contrast, brain tumour samples expressed low amounts of dCK. dCK staining ranged from low (1+) to high (3+) in ALL blasts, retinoblastoma, and NSCLC tissue samples. Staining was consistent (interobserver variability, 88%; κ = 0.83) and specific. Western blotting detected the dCK protein appropriately at 30 kDa, without additional bands. Conclusions: Immunocytochemistry is an effective and reliable method for determining the expression of dCK in patient samples and requires little tumour material. This method enables large scale screening of dCK expression in tumour samples.