Purpose: We hypothesized that downstream effects of endogenous vascular endothelial growth factor (VEGF)/VEGF receptor signaling on acute myelogenous leukemia (AML) cell survival resulted in increased in vitro cellular drug resistance and a longer time to kill most leukemic cells in vivo upon drug exposure.
Experimental design: In primary AML cells from pediatric patients, VEGFA and VEGFC mRNA expression and in vitro cellular resistance to nine cytotoxic drugs were studied. As in vivo equivalents for in vitro drug resistance, in vivo AML blast reduction upon drug exposure, measured as blast cell reduction on day 15 in the bone marrow and as time in days from diagnosis to complete remission (CR) were used.
Results: Increased endogenous VEGFC levels significantly correlated with increased in vitro resistance for six typical AML drugs in primary AML cells from pediatric patients. Patients with >5% blasts on day 15 showed a 12.9-fold increase in the median VEGFC level compared with patients with < or =5% blasts (P = 0.002). Time to reach CR was studied using linear regression analysis with VEGFC, age at diagnosis, sex, treatment protocol, FAB type, cytogenetic risk profile, and WBC counts as variables. There was a significant positive independent association between VEGFC levels and time to CR (b = 6.02, SE = 1.58, P < or = 0.0001, n = 72).
Conclusions: These results suggest for the first time that higher endogenous VEGFC levels of AML cells are related to decreased in vitro and in vivo drug responsiveness.