Features of proliferation and in vitro drug resistance in central primitive neuro-ectodermal tumours

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%; kappa = 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.

Immunocytochemical detection of deoxycytidine kinase in pediatric malignancies in relation to in vitro cytarabine sensitivity

Deoxycytidine kinase (dCK) is essential for the phosphorylation of cytarabine (ara-C), a deoxycytidine analog active against acute leukemias. Resistance to ara-C has been linked to dCK deficiency. In this study we determined the expression of the dCK protein in pediatric malignancies, using immunocytochemistry and related the expression levels to in vitro ara-C sensitivity (measured with the MTT-assay). dCK expression was high in the AML and retinoblastoma samples, in the ALL samples dCK expression ranged from low to very high. The brain tumor samples expressed low levels of dCK. AML was significantly more sensitive in vitro to ara-C compared to ALL (p = 0.03). Retinoblastoma and brain tumor cells were extremely resistant in vitro, we were unable to detect more than 50% ara-C induced cell kill in the majority of samples. Samples were combined in groups according to dCK expression. Samples with low dCK expression were significantly more resistant to ara-C compared to samples with high dCK expression. In conclusion, dCK expression varies between individual samples and between different types of malignancies and may play a role in resistance to ara-C in particular tumor types.