| The application of anti-angiogenic drug(combination)s in the clinic is hampered by the lacking of suitable methods for target validation and effectivity. We pursue the possibility to monitor (sub)populations of circulating endothelial cells/progenitors (CEC or CEP) in the peripheral blood (PB) of cancer patients. A study protocol has been set-up to establish the reliability and reproducibility of a 4-colour flow cytometry procedure for measuring the frequencies of subpopulations of circulating cells with endothelial markers, including CD34, AC133, P1H12 (CD146), CD31, CD105, in particular in combination with a newly available VEGFR2 antibody. CD45 low , CD31 bright , P1H12, VEGFR2 weakly positive subpopulations could be reproducibly measured in cancer patients (CECs). CD45 dim , CD34 bright , VEGFR2 positive cells (CEPs) appeared to be present in very low frequencies in PB. The first studies, that measure CECs and CEPs in cancer patients treated with VEGF(R)-targeted agents, bevacizumab and sunitinib are ongoing and results are currently being analysed. In vitro cultures of endothelial progenitor cells from human umbilical cord blood have been established as models for tumor(-growth promoting) endothelial cells. The effects of concurrent VEGFR and EGFR blocking agents on the proliferative, invasive and tube-forming capacity will be studied. |
