Flow cytometric method for estimation of 5-bromo-2´-deoxyuridine content in rat serum

Elucidating the role of an immunomodulatory protein in cancer: From protein expression to functional characterization

Several fundamental discoveries made over the last two decades, in the field of cancer biology, have increased our understanding of the complex tumor micro- and macroenvironments. This has shifted the current empirical cancer therapies to more rationalized treatments targeting immunomodulatory proteins. From the point of identification, a protein target undergoes several interrogations, which are necessary to truly define its druggability. Here, we outline some basic steps that can be followed for in vitro characterization of a potential immunomodulatory protein target. We describe procedures for recombinant protein expression and purification including key annotations on protein cloning, expression systems, purification strategies and protein characterization using structural and biochemical approaches. For functional characterization, we provide detailed protocols for using flow-cytometric techniques in cell lines or primary cells to study protein expression profiles, proliferation, apoptosis and cell-cycle changes. This multilevel approach can provide valuable, in-depth understanding of any protein target with potential immunomodulatory effects.

Peroral administration of 5-bromo-2-deoxyuridine in drinking water is not a reliable method for labeling proliferating S-phase cells in rats

In rodents, peroral (p.o.) administration of 5-bromo-2'-deoxyuridine (BrdU) dissolved in drinking water is a widely used method for labeling newly formed cells over a prolonged time-period. Despite the broad applicability of this method, the pharmacokinetics of BrdU in rats or mice after p.o. administration remains unknown. Moreover, the p.o. route of administration may be limited by the relatively low amount of BrdU consumed over 24h and the characteristic drinking pattern of rats, with water intake being observed predominantly during the dark phase. Therefore, we investigated the reliability of staining proliferating S-phase cells with BrdU after p.o. administration (1mg/ml) to rats using both in vitro and in vivo conditions. Flow cytometric analysis of tumor cells co-cultivated with sera from experimental animals exposed to BrdU dissolved in drinking water or 25% orange juice revealed that the concentration of BrdU in the blood sera of rats throughout the day was below the detection limits of our assay. Ingested BrdU was only sufficient to label approximately 4.2±0.3% (water) or 4.2±0.3% (25% juice) of all S-phase cells. Analysis of data from in vivo conditions indicates that only 7.6±3.3% or 15.5±2.3% of all S-phase cells in the dentate gyrus of the hippocampus was labeled in animals administered drinking water containing BrdU during the light and dark phases of the day. In addition, the intensity of BrdU-positive nuclei in animals receiving p.o. administration of BrdU was significantly lower than in control animals intraperitoneally injected with BrdU. Our data indicate that the conventional approach of p.o. administration of BrdU in the drinking water to rats provides strongly inaccurate information about the number of proliferating cells in target tissues. Therefore other administration routes, such as osmotic mini pumps, should be considered for labeling of proliferating cells over a prolonged time-period.

Flow cytometric determination of 5-bromo-2'-deoxyuridine pharmacokinetics in blood serum after intraperitoneal administration to rats and mice

5-Bromo-2'-deoxyuridine (BrdU) is a marker that is widely used to label S-phase cells in neurobiological research in most common doses 50 or 100 mg/kg per single intraperitoneal (i.p.) injection. However, the important data regarding its pharmacokinetics in rodents are still missing. The aim of our study was to investigate the BrdU level in serum after a single i.p. injection to adult rats (doses: 50 or 100 mg/kg) and adult mice (50 mg/kg). The animals were killed at selected time-points after the BrdU injection, and proliferating tumour cells (cell lines HCT-116 and HL-60) were co-cultivated with isolated blood sera. BrdU incorporated in the DNA of the S-phase tumour cells was stained with an anti-BrdU antibody and analysed using flow cytometry. In rats, the efficacies of BrdU labelling of S-phase cells in both in vitro and in vivo conditions were compared in the 50 and 100 mg/kg groups. According to our results, BrdU was in saturated concentration to label almost all S-phase cells for 60 min in both doses and was detectable in blood serum until 120 min after the single i.p. injection. However, the 100 mg/kg dose of BrdU did not provide a prolonged staining period to offset the potentially higher toxicity in comparison with the 50 mg/kg dose. In mice, due to their faster metabolism, the concentration of BrdU in blood serum was sufficient to label the whole population of S-phase cells for only 15 min after the i.p. injection, then dropped rapidly.