Presence of classical multidrug resistance and P-glycoprotein expression in human neuroblastoma cells

The role of P-glycoprotein (Pgp) associated multidrug resistance for neuroblastoma patients is controversial. Therefore we asked whether at all the typical functional features of the multidrug resistance phenotype could be found in neuroblastoma cells and studied the prognostic relevance of Pgp expression.

Tumor touch preparations and tumor cell infiltrated bone marrow smears of 62 neuroblastoma patients were investigated. The expression of Pgp was determined by a highly sensitive immunosandwich technique. Drug resistance studies were performed by exposing cells to Pgp-dependent cytostatic drugs in tissue cultures. Intracellular drug accumulation was examined by rhodamine-123 fluorescence microscopy.

Pgp expression was demonstrable for the SK-N-SH cell line, but not detectable in CHP-100 and ten other neuroblastoma cell lines by immunocytochemistry. In tissue cultures, SK-N-SH cells showed a relative resistance to vincristine and adriamycin (45.1 and 12.7-fold resp.) and reduced intracellular accumulation of rhodamine-123 which could be normalized by the Pgp blocker verapamil. Pgp expression was detected by immunocytochemistry in 14 out of 62 tumors (22.6%). No correlation was found to the stage of the disease (P = 0.33), histopathological grading (P = 0.82), N-myc oncoprotein expression (P = 0.76) or N-myc oncogene amplification (P = 0.20). Kaplan-Meier analysis of event free survival for stage 4 tumors revealed a weak trend of inferior survival for patients with Pgp positive tumors (log-rank analysis: P = 0.069).

Though Pgp expression is detectable and functional in neuroblastoma cells, but its presence does not provide much information to the complex phenomenon of chemotherapy resistance in patients.