Taxotere and vincristine inhibit the secretion of the angiogenesis-inducing vascular endothelial growth factor (VEGF) by wild-type and drug-resistanthuman leukemia T-cell lines

Recent studies have shown that angiogenesis, which is induced by VEGF, may be involved in the pathogenesis of hematopoietic malignancies. A human leuk emia model consisting of T-lymphoblastic CEM/0, 7 monoclonal refractory clo nes resistant to both cytosine arabinoside (ara-C) and L-asparaginase (ASNa se), Jurkat/E6-1 and U937, representing the leukemic blasts from relapsed p atients with leukemias was investigated for secretion of VEGF before and af ter treatment with various agents. The T-lymphoblastic cell line, Jurkat/E6 -1, was used as the negative control, which has been characterized as not e xpressing mRNA nor the VEGF protein, and did not secrete VEGF. With no teat ment, U937, the positive control, secreted the highest VEGF concentration o f 1612.7 pg/ml. The CEM/0 wild type cell line and 5 other drug-resistant cl ones secreted VEGF at levels ranging from 180.9 to 414.2 pg/ml. Two CEM dru g-resistant clones, CEM/araC/G/ASNase-0.5-1 and CEM/ara-C/G/ASNase-1-1, lac ked VEGF production. Docetaxel (Taxotere, TXR), Vincristine (VCR), ASNase, and the Flt-1/Fc chimera, a specific inhibitor of VEGF-dependent human umbi lical vein endothelial cell (HUVEC) proliferation, were tested for inhibiti on of VEGF secretion. Treatment of the leukemic cell lines with 2 mug/ml Fl t-1/Fc chimera for 24 hours completely inhibited VEGF secretion to the dete ction limit of the assay (< 10pg/ml). After 24 hours incubation with Flt-1/ Fc chimera, the leukemic cells appeared to be undergoing apoptosis, based o n microphotography examination, suggesting that VEGF could be used in an au tocrine loop to promote cell survival by the leukemic cells. Treatment with 0.5, 1, and 2 mug/ml Flt-1/FC chimera for 48 hours demonstrated a 15-25% g rowth inhibition by MTT assay. Strong inhibition of VEGF secretion in the c ulture media was observed after 10 muM TXR or 0.1 muM VCR for 24 hours in t he wild-type and drug-resistant clones, except CEM/ara-C/I, in comparison w ith controls. In contrast, treatment with 1 IU/ml ASNase, a specific T-cell protein inhibitor, in 5 cell lines for 24 hours demonstrated no inhibition of VEGF in CEM/0 3 drug-resistant clones and the myeloid U937 line. We con clude that the leukemia cell lines actively secrete VEGF, in vitro. TXR and VCR, but not ASNase, strongly inhibit the VEGF production, suggesting that inhibition of this growth factor may be a mechanism of antileukemic activi ty. Moreover, the leukemic cell lines examined here may constitute a useful model to study antiangiogenic drugs, alone or in combination with establis hed drug regimens used against refractory leukemias.