91role on tumor vascular physiology. This may have a potential impact on angiogen-
esis, as well as on tumor cell trafficking and metastasis formation, drug transport,
and tumor progression.
This hypothesis is supported by the observation that lymphoma and a mammary
adenocarcinoma cell lines genetically engineered to secrete CgA are characterized
by reduced growth rate, when implanted subcutaneously in mice, compared to non-
secreting parental cells (Veschini et al. 2011 ; Colombo et al. 2002b). Systemic
administration of CgA (1 μg) to lymphoma-bearing mice reduced TNF-induced
penetration of patent blue, a synthetic dye, in tumor tissue, pointing to a protective
effect on the endothelial barrier in tumors (Dondossola et al. 2011 ). CgA can also
inhibit the transport of chemotherapeutic drugs in tumor tissues induced by NGR-
TNF, a tumor necrosis factor-α (TNF)-based vascular targeting agent originally
developed by our group and currently tested in phase II and III clinical studies
(Dondossola et al. 2011 ; Curnis et al. 2000 , 2002 ; Corti et al. 2013 ). In particular,
studies performed in murine lymphoma and melanoma models have shown that
patho-physiologically relevant levels of circulating CgA can inhibit the NGR-
TNF−induced penetration of drugs in tumor tissues and inhibit its synergism with
doxorubicin and melphalan (Dondossola et al. 2011 ). Notably, two-fold enhance-
ment of endogenous circulating CgA, e.g. obtained by pharmacological treatment
with omeprazole, significantly reduced the NGR-TNF−induced penetration of
doxorubicin in tumors. Similar effects were obtained also by administration of
CgA1-78 to tumor-bearing mice. Interestingly, mouse mammary adenocarcinomas
genetically engineered to secrete CgA1-78 and implanted subcutaneously in mice
are characterized by reduced vascular density and more regular vessels, compared
with parental cells (Veschini et al. 2011 ). Considering that CgA1-78 can inhibit the
nuclear translocation of HIF-1α (Veschini et al. 2011 ) it is possible that this frag-
ment can inhibit hypoxia-driven endothelial cell activation and abnormal vascular-
ization, and, consequently, lead to the formation of more regular vessels.
Besides affecting the transport of drugs in tumors, CgA can also regulate the traf-
ficking of tumor cells through the endothelial barrier and, consequently, the tumor
metastatization and self-seeding processes (Dondossola et al. 2012 ). This is an
important effect, as cancer progression typically involves the seeding of malignant
cells in circulation and the colonization of distant organs, as well as the tumor rein-
filtration by aggressive circulating tumor cells. Studies in a murine model of mam-
mary adenocarcinoma showed that CgA can inhibit (i) the shedding of cancer cells
in circulation by primary tumors, (ii) the homing of circulating tumor cells to pri-
mary tumors (necessary for the self-seeding process), and (iii) the engraftment in
lungs by circulating tumor cells (another important step of the metastatic cascade)
(Dondossola et al. 2012 ). Mechanistic studies showed that CgA reduced gap forma-
tion induced by tumor cell–derived factors in endothelial cells, decreased vascular
leakage in tumors, and inhibited the transendothelial migration of cancer cells
(Dondossola et al. 2012 ). These findings point to a role for circulating CgA in the
regulation of tumor cell trafficking from tumor-to-blood and from blood-to-tumor/
normal tissues. The capability of CgA to strengthen the endothelial barrier function
in tumors and to reduce vascular leakage is also suggested by the observation that
Chromogranin A in Endothelial Homeostasis and Angiogenesis