This was surprising once we followed a PIT protocol similar to that used in previous reports, which did not observe vascular occlusion. APCs induce vascular occlusion in the irradiation site. Furthermore, the level of vascular occlusion was correlated with the blood concentration of APC, not the tumor concentration. These results imply that, much like PDT, PIT can also induce non-targeted vascular occlusion and further optimization is required before widespread medical use. and after irradiation To AMG-333 analyze the effects of EpCAM-IR700 and DNP-IR700 analysis. Open in a separate window Number 3 Anti-tumor effects of each APC mechanism analysis To clarify the mechanism underlying the discrepancy between our and analyses, two experiments were carried out. First, we measured APC concentration in the tumors and serum. Our results indicate the fluorescence intensity as well as the antibody concentration were higher for EpCAM-IR700 than for DNP-IR700 in tumor cells, whereas they were almost the same in serum (Number ?(Figure4A).4A). This suggests that EpCAM-IR700 specifically accumulates in the EpCAM-positive tumor, while DNP-IR700 does not. Open in a separate windows Number 4 APC-induced vascular occlusion and study showed that EpCAM-IR700, but not DNP-IR700, specifically bound to AMG-333 EpCAM-expressing COLO 205 cells and induced cell damage after irradiation. This EpCAM specificity in focusing on cancer cells is definitely supported by additional reports demonstrating related antigen-dependent targeting by using this membrane protein [6]. In contrast to this earlier study, in our anti-tumor analyses using a mouse xenograft model, we observed significantly reduced tumor volume after irradiation in both the EpCAM-IR700-treated mice as well as the DNP-IR700-treated mice. This discrepancy between this and the previous study Rabbit Polyclonal to PLG was amazing as almost the same experimental process was conducted. Moreover, the mechanism underlying these anti-tumor effects was shown to be vascular occlusion. Consequently, these data indicate that unlike our findings, PIT by using this EpCAM-targeting APC might induce non-specific anti-cancer effects model, were different from those used in the present study and could cause the observed discrepancies. Blood vessel volume as well as blood flow in EGFR-positive cells might also be greater than that in EGFR-negative cells because EGFR signaling induces angiogenesis [16], thus increasing exposure of the cells to the APCs and allowing a greater number of EGFR-positive cells to be destroyed. With regards to the models, these previous studies used a peritoneal dissemination model and i.p. administration, which presumably mimic the conditions as APC accumulation occurs in a closed space. However, in our study, the subcutaneous transplant model used to observe the anti-tumor effects of our APC is usually highly dependent on the blood vessels. Each of these differences could have resulted in the discrepancies observed between our analyses and those previously reported for other APCs. The composition of the antibody used for the APC can also potentially affect its function. AMG-333 AMG-333 It was previously reported that a CD25-targeted APC could deplete T regulatory cells distant from the irradiation site without inducing vascular occlusion [17]. In that study, F(ab)2, which lacks the Fc domain name, was used. Notably, the Fc AMG-333 domain name binds to the neonatal Fc receptor (FcRn) in the acidic endosomes of vascular endothelial cells and can be recycled back into the blood at physiological pH [18]. Therefore, it is possible that APCs composed of an antibody fragment without this domain name could selectively eliminate the target cells without inducing vascular occlusion because it cannot bind to FcRn or be kept at low concentrations in the blood. In the present study, the concentration of EpCAM-IR700 was.