Endocrine Abstracts

ASA404 (Vadimezan) belongs to a class of agents with disrupting properties against tumor vasculature. Herein, putative therapeutic applicability was investigated in preclinical models for neuroendocrine tumors of the gastroenteropancreatic system (BON) and adrenocortical carcinoma (NCIh295). Upon treatment of tumor bearing mice we detected a significant disruption of microvessels, decrease in cell proliferation, increase of apoptotic cells and extensive necrosis in BON tumors while no comparable effects were detectable in those of NCIh295 origin. As TNFα-signaling had been proposed to mediate parts of ASA404 dependent effects we utilized these models based on their different responsiveness for characterization of TNFα synthesis and signaling in vitro and in vivo. While NCIh295 tumors showed higher basal TNF receptor 1 expression and a comparable increase in serum TNFα levels, a significant increase in intra-tumoral TNFα secretion as well as TNFα-specific activation of downstream NFκB and caspase 3/7 signalling was present mainly in the BON model. Furthermore, we detected high levels of Toll-like-receptor TLR4 and a significant increase in the expression of its adaptor protein MD-2 specifically in ASA404 treated BON tumors, while both was not detectable for NCIh295. As TNFα is an important downstream component of the TLR-network this could be an additional reason for intra-tumoral TNFα alterations. Moreover, we identified at RNA level several members of an inhibitory feedback loop downstream of both pathways, including TNFAIP3/A20, TNIP1 and NFKκBIA, as elevated at baseline in the adrenocortical carcinoma tumor model. Confirmation of this deregulation at protein level is ongoing and was so far succesful for TNFAIP3/A20 suggesting altogether basal inhibition of both pathways as one putative reason for the detected impairment in therapeutic response.