INTRODUCTION: Bone marrow angiogenesis has increasingly been recognized as important for leukemogenesis. Identification of vascular endothelial growth factor (VEGF) mediated autocrine and paracrine loops in subsets of acute myeloid leukemia (AML) support multiple mechanisms of action for these factors. We examined whether expression of pro-angiogenic growth factors VEGF-A, VEGF-C, and angiopoietin-2 (Ang-2) correlated with marrow neovascularization (CD31 staining) and overall survival of AML patients (pts).
PATIENTS AND METHODS: Expression of VEGF-A, VEGF-C, and Ang-2 was determined in leukemia bone marrow samples at diagnosis by quantitative real-time reverse transcription polymerase chain reaction (Q-PCR) using 18s RNA controls. Expression was then analyzed for fold-differences versus normal bone marrow control samples (n=10). VEGF-A and VEGF-C protein expression in leukemia cells and CD31 protein expression in microvessels and leukemia cells was evaluated by immunohistochemistry (IHC) in the corresponding bone marrow biopsies from the same pts. A cohort of 96 AML pts (46 male, 50 female) was examined with a median age of 67.5 years (range 21–96 years). Half (n=46) achieved an initial complete remission (CR) on standard induction chemotherapy regimens. Median overall survival was 9.3 months. No pts had recurrent cytogenetic abnormalities, and 76 had normal karyotype.
RESULTS: Leukemia blast VEGF-A (median 1.77 fold increase, range 0.06–23.62) and Ang-2 (median 6.9 fold increase, range 0.07–3100) expression by Q-PCR were consistently higher than normal bone marrow controls in contrast to VEGF-C that was lower than normal controls (median 0.51, range 0.04–27.93). Using a cut-off of 1.5 fold to denote growth factor overexpression by Q-PCR, we found that prolonged pt survival correlated with low VEGF-C levels (mean 609 ± 92 n=78 vs. high VEGF-C 235 ± 46 days, n=18, p =0.056) and high Ang-2 levels (mean 581± 91, n=77 vs. low Ang-2 366 ± 98 days, n=19 vs. p=0.26) but was not statistically significant. No difference in survival was noted in low vs. high VEGF-A expressing samples (mean 545 + 171, n=26, vs. 511 + 105, n=70, p=0.96). No correlation between CD31+ microvessels and survival was noted. By IHC, most leukemic marrow biopsies were positive for VEGF-A (n=60) and negative for VEGF-C (n=87) and CD31 (n=78). Univariate analysis of overall survival using Cox proportional hazard model demonstrated that age (p=0.0008), achievement of CR (p<0.0001), karyotype (normal vs. complex/other, p=0.0210), and VEGF-A (p=0.0272), VEGF-C (p=0.0255), and CD31 positive IHC expression by AML blasts (p=0.0152) were independent prognostic factors. Multivariate analysis showed that the only factors of statistical significance were achievement of CR (hazard ratio 4.09, 95% CI 2.28–7.33, p <0.0001) and VEGF-C expression by IHC (hazard ratio 0.08, 95% CI 0.01-0.81).
CONCLUSIONS: These results show that expression of VEGF-A, VEGF-C, and CD31 (in AML blasts) by IHC in bone marrow biopsies represent prognostic factors for overall survival in AML. The importance of VEGF-C mediated angiogenic processes as an independent prognostic factor in AML outcome suggests that targeted inhibition of this factor may be of future therapeutic benefit in subsets of AML pts.
Disclosure: No relevant conflicts of interest to declare.