KEYWORDS: Tumors, Picosecond phenomena, In vivo imaging, Near infrared, Luminescence, Tissues, Optical imaging, Signal detection, Breast cancer, Cancer
Phosphatidylserine (PS), normally restricted to the inner leaflet of the plasma membrane, becomes exposed on the outer surface of viable (non-apoptotic) endothelial cells in tumor blood vessels, probably in response to oxidative stresses present in the tumor microenvironment. In the present study, we optically imaged exposed PS on tumor
vasculature in vivo using PGN635, a novel human monoclonal antibody that targets PS. PGN635 F(ab’)2 was labeled
with the near infrared (NIR) dye, IRDye 800CW. Human glioma U87 cells or breast cancer MDA-MB-231 cells were
implanted subcutaneously or orthotopically into nude mice. When the tumors reached ~5 mm in diameter, 800CW-
PGN635 was injected via a tail vein and in vivo dynamic NIR imaging was performed. For U87 gliomas, NIR imaging allowed clear detection of tumors as early as 4 h later, which improved over time to give a maximal tumor/normal ratio
(TNR = 2.9 ± 0.5) 24 h later. Similar results were observed for orthotopic MDA-MB-231 breast tumors. Localization of 800CW-PGN635 to tumors was antigen specific since 800CW-Aurexis, a control probe of irrelevant specificity, did not
localize to the tumors, and pre-administration of unlabeled PGN635 blocked the uptake of 800CW-PGN635. Fluorescence microscopy confirmed that 800CW-PGN635 was binding to PS-positive tumor vascular endothelium. Our
studies suggest that tumor vasculature can be successfully imaged in vivo to provide sensitive tumor detection.
We previously suggested that the two time constants quantified from the increase of tumor oxyhemoglobin concentration, ▵ [HbO2], during hyperoxic gas intervention are associated with two blood flow/perfusion rates in well perfused and poorly perfused regions of tumors. In this study, our hypothesis is that when cancer therapy is applied to a tumor, changes in blood perfusion will occur and be detected by the NIRS. For experiments, systemic chemotherapy, cyclophosphamide (CTX), was applied to two groups of rats bearing syngeneic 13762NF mammary adenocarcinomas: one group received a single high dose i. p. (200 mg/kg CTX) and the other group continuous low doses (20 mg/kg CTX i. p. for 10 days). Time courses of changes in tumor ▵ [HbO2] were measured at four different locations on the breast tumors non-invasively with an inhaled gas sequence of air-oxygen-air before and after CTX administration. Both rat body weight and tumor volume decreased after administration of high dose CTX, but continuous low doses showed decrease of tumor volume only. Baselines (without any therapy) intra- and inter-tumor heterogeneity of vascular oxygenation during oxygen inhalation were similar to our previous observations. After CTX treatment, significant changes in vascular hemodynamic response to oxygen inhalation were observed from both groups. By fitting the increase of ▵ [HbO2] during oxygen inhalation, we have obtained changes of vascular structure ratio and also of perfusion rate ratio before and after chemotherapy. The preliminary results suggest that cyclophosphamide has greatest effect on the well perfused tumor vasculature. Overall, our study supports our earlier hypothesis, proving that the effects of chemotherapy in tumor may be monitored non-invasively by using NIRS to detect changes of hemodynamics induced with respiratory challenges.
The effective measurement of dynamic changes of blood and tissue oxygenation of tumors could be valuable for optimizing tumor treatment plans. For this study, a near- infrared spectroscopy system and pO2 needle electrode were used to measure simultaneously changes in total hemoglobin concentration ([Hb]total), oxygenated hemoglobin concentration ([HbO2[) and local oxygen tension (pO2) in the vascular bed of prostate tumors implanted in rats in response to respiratory challenge. The inhaled gas was alternated between air and carbogen (95% oxygen, 5% CO2). Significant changes in tumor vascular oxygenation were observed with an apparent threshold for variation in [HbO2]/[HbO2]max. For comparison, a phantom study was undertaken with 1% intralipid solution and blood. The slope of [HbO2]/[HbO2[max vs. pO2 in the phantom was ten times larger than in the tumor indicating that tumor cells are relatively resistant to oxygenation. This study demonstrates that the NIR technology can provide an efficient, real-time, non-invasive approach to monitoring tumor physiology and is compatible with additional techniques.
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