NGAL can alternately mediate sunitinib resistance in renal cell carcinoma.

Serum NGAL is highly expressed in patients with advanced renal cancer treated with sunitinib. We investigated the role of NGAL in sunitinib resistance in renal cell carcinoma to identify potential tactics to overcome it. NGAL expression was correlated with sunitinib sensitivity. Vascular endothelial growth factor related upstream Ras, Erk1/2 and STAT1 phosphorylation activity in Caki-1 and NGAL transfected Caki-1 cells after sunitinib treatment was analyzed using Western blot. NGAL and vascular endothelial growth factor-A interaction with sunitinib therapeutic efficacy was monitored in renal cell carcinoma tumor xenografted mice by tumor growth inhibition, serum NGAL and vascular endothelial growth factor-a levels, and microscopic examination of tumor microvascular density. Sunitinib cytotoxicity in various renal cell carcinoma cell lines was reversibly related to NGAL expression. Sunitinib showed the lowest 50% inhibitory concentration (5.53 μM) in Caki-1 cells, which had the lowest NGAL expression of these renal cell carcinoma cell lines. After sunitinib treatment adding NGAL inhibited Ras and Erk1/2 phosphorylation but activated STAT1α phosphorylation in Caki-1 cells and Caki-1 cells transfected with NGAL. In a xenograft mouse model sunitinib significantly inhibited tumor growth in Caki-1 mice. NGAL transfected Caki-1 mice had higher serum NGAL and lower vascular endothelial growth factor-A than Caki-1 mice. Microvascular density was decreased in Caki-1 mice with sunitinib treatment. NGAL in tumor cells may show crosstalk with vascular endothelial growth factor-a and alternative activation in stimulating tumor growth during sunitinib treatment. It may become a therapeutic target to reverse sunitinib resistance in renal cell carcinoma.