Preclinical Evaluation of the Anti-Tumor Activity of Pralatrexate in High-Risk Neuroblastoma Cells

Introduction
Pralatrexate is a folate analogue inhibitor of dihydrofolate reductase exhibiting high affinity for reduced folate carrier-1 with antineoplastic and immunosuppressive activities, similar to methotrexate. Despite advances in multi-modality treatment strategies, the survival rates for children with high-risk neuroblastoma have failed to improve. Therefore, the intense research continues in order to identify the ideal novel agent or combination of chemotherapy drugs to treat high-risk neuroblastoma.

Materials and Methods
Four human neuroblastoma cell lines were used to determine IC₅₀ values of select chemotherapy agents. Antiproliferative effects of pralatrexate were assessed by adherent and non-adherent colony formation assays. Cell cycle arrest and apoptosis were measured by flow cytometry and immunoblotting. PDX tissue culture was used to assess ex vivo efficacy.

Results
Treatment with pralatrexate in all four neuroblastoma cell lines blocked cell growth in 2D and 3D culture conditions in a time-dependent manner. The potency of pralatrexate was ten-fold stronger than methotrexate, as measured by IC₅₀. Pralatrexate-induced apoptosis was confirmed by caspase-3 activation and PARP cleavage. MYCN and SLC19A1 mRNA expressions were decreased with pralatrexate in MYCN-amplified neuroblastoma cells.

Conclusions
Pralatrexate demonstrated effective inhibition of cell growth and viability. The higher potency of pralatrexate compared to methotrexate, a drug with high levels of toxicity, suggests pralatrexate may be a safer alternative to methotrexate as an effective chemotherapeutic agent in the treatment of patients with high-risk neuroblastoma.