Luciferase Bioluminescence Research Articles

Role of connexin43 hemichannels in mechanical stress-induced ATP release in human periodontal ligament cells

Our previous studies showed that mechanical stress could induce ATP release in human periodontal ligament (HPDL) cells. By signaling through P2 purinergic receptors, ATP increased the expression and the synthesis of osteopontin and RANKL. In this study, the mechanism of stress-induced ATP release was investigated. Continuous compressive forces were applied on cultured HPDL cells. The ATP released was measured using luciferin-luciferase bioluminescence. The expression of gap-junction proteins was examined using RT-PCR and western blot analysis. The opening of hemichannels was demonstrated by cellular uptake of a fluorescent dye, 5(6)-carboxyfluorescein, which is known to penetrate hemichannels. Intracellular signal transduction was investigated using inhibitors and antagonists. Mechanical stress induced the release of ATP into the culture medium, which was attenuated by carbenoxolone, a nonspecific gap-junction inhibitor. Addition of meclofenamic acid sodium salt, a connexin43 inhibitor, inhibited ATP release by mechanical stress. Knockdown of connexin43 expression by small interfering RNA reduced the amount of ATP released by mechanical stress, suggesting the role of connexin43 hemichannels. In addition, intracellular Ca(2+) blockers could also inhibit mechanical stress-induced ATP release and the opening of the gap junction. Our study demonstrated the involvement of gap-junction hemichannels, especially connexin43, in the stress-induced ATP-release mechanism. Furthermore, this mechanism may be regulated by the intracellular Ca(2+) signaling pathway. These results suggest an important role of gap-junction hemichannels in the function and behavior of HPDL cells.

Abstract 656: Antitumor activity of combined therapy with the class I BRAF inhibitor PLX4032 and immunotherapy

Abstract PLX4032 is a potent inhibitor of V600E BRAF with response rates of up to 80% in patients with metastatic melanoma. However, drug resistance develops in most of patients leading to response durations of only several months. Immunotherapy for melanoma has induced low frequency, but highly durable tumor responses, which may last years. Therefore, the concept of a combined approach of BRAF inhibition and immunotherapy is very attractive. We have established a novel animal model which allows the testing of this concept in fully immunocompetent mice. An implantable murine melanoma cell line driven by the V600E BRAF oncogene (SM1) was established from a spontaneously arising murine melanoma in transgenic mice backcrossed to C57BL/6 and harboring the V600E BRAF mutation under the control of tyrosinase promoter. The in vitro IC50 of PLX4032 against SM1 was 14μM, which indicates partial resistance to the drug and therefore useful as a model for combined therapy. In vitro assays indicated that SM1 cells undergo apoptosis and cell cycle arrest at G1 phase in the presence of the PLX4032. Mice implanted with tumors responded significantly with daily i.p. injection of PLX4032, confirming its efficacy in vivo, though there was no complete eradication of the tumor. Cultured primary murine T lymphocytes exposed to PLX4032 at different time points (24, 48 and 72h) with a broad range of concentration (0.1 to up to 100 μM) showed no evidence of cytotoxicity. In vivo real-time T cell tracking by luciferase bioluminescence imaging, as well as PET/CT, confirmed that PLX4032 did not adversarially affect the viability, engraftment or tumor infiltration of T cells in mice. We then tested the combination of PLX4032 and immunotherapy in vivo using two models of adoptive cell transfer (ACT) therapy. SM1 cells stably expressing the chicken ovalbumin (OVA) model antigen were implanted in C57BL6 mice. Daily i.p. PLX4032 combined with ACT of OVA-specific TCR transgenic cells (OTI) generated by retroviral transduction demonstrated superior effects of the combined treatment (tumor size at day 14 after ACT plus PLX4032: 114.9±23.6 mm2, PLX4032: 203.2±6.2, OTI ACT: 192.5±6.2, and vehicle control 241.3±3.1, p<0.05). We also attested this combination in the pmel-1 model, which is based on the ACT of TCR transgenic cells against the relevant melanoma antigen gp100, which is endogenously expressed by SM1. The combined treatment PLX4032 plus ACT of pmel-1 transgenic T cells also resulted in a superior tumor shrinkage (124.7±1.7 mm2) compared to PLX4032 alone (157.4±7.4), pmel-1 T cell ACT alone (203.8±2.1) or vehicle control (250.8±3.8), p<0.05. In conclusion, our data derived from two independent models combining BRAF targeted therapy and immunotherapy support the testing of such combinations in patients with V600E BRAF mutant metastatic melanoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 656. doi:10.1158/1538-7445.AM2011-656

Dinoflagellate Bioluminescence: Cloning and Sequence Analysis of Luciferase from Pyrocystis fusiformis

Pyrocystis fusiformis is a protozoan species, approximately forty micrometers in length, that is closely related to plants and algae. These dinoflagellates are photosynthetic and also utilize a luciferase bioluminescence system. Luciferases are a class of enzymes that are responsible for luminescence by catalyzing the oxidation of a substrate molecule, luciferin, in a reaction that produces light at 475 nm. In an effort to discover the structural biology of the luciferase contained within Pyrocystis fusiformis, long‐term research is focused on cloning the genes that code luciferase and purifying luciferin. Alignments of the sequence of this luciferase with other characterized dinoflagellate luciferase allowed the identification of a catalytic core and related fragments for later studies. Extraction and purification of chromosomal DNA from Pyrocystis fusiformis was performed for the purposes of PCR cloning. Dinoflagellates are thecate, meaning that their cellular membranes are interlaced with polysaccharide deposits that form rigid plates making it incredibly difficult to lyse, short of homogenization. Several DNA extraction methods and combinations were tested in order to determine the most effective protocol for preparation of genomic DNA for PCR.

Sequential bioluminescence resonance energy transfer–fluorescence resonance energy transfer-based ratiometric protease assays with fusion proteins of firefly luciferase and red fluorescent protein

We report here the preparation of ratiometric luminescent probes that contain two well-separated emission peaks produced by a sequential bioluminescence resonance energy transfer (BRET)–fluorescence resonance energy transfer (FRET) process. The probes are single soluble fusion proteins consisting of a thermostable firefly luciferase variant that catalyze yellow-green (560 nm maximum) bioluminescence and a red fluorescent protein covalently labeled with a near-infrared fluorescent dye. The two proteins are connected by a decapeptide containing a protease recognition site specific for factor Xa, thrombin, or caspase 3. The rates of protease cleavage of the fusion protein substrates were monitored by recording emission spectra and plotting the change in peak ratios over time. Detection limits of 0.41 nM for caspase 3, 1.0 nM for thrombin, and 58 nM for factor Xa were realized with a scanning fluorometer. Our results demonstrate for the first time that an efficient sequential BRET–FRET energy transfer process based on firefly luciferase bioluminescence can be employed to assay physiologically important protease activities.

Effect of glutathione depletion, hyperthermia, and a 100‐mT static magnetic field on an hsp70/luc reporter system

Heat shock proteins, in particular hsp70, are induced under conditions of cellular stress. It has been reported that environmental stimuli such as hyperthermia, oxidative stress, and exposure to magnetic fields increase levels of hsp70. It has also been reported that hyperthermia in combination with magnetic field exposure results in a synergistic increase in hsp70 production. We tested the hypothesis that oxidative stress induced by glutathione (GSH) depletion in combination with static magnetic field (SMF) exposure will produce a similar synergistic increase in hsp70 production. We exposed cells to heat, SMF, and diethylmaleate (DEM), which depletes GSH levels alone and in combination with each other, and measured hsp70 production using an hsp70/luciferase reporter and mRNA levels using PCR. We found that treatment with DEM significantly reduced the rate of luciferase bioluminescence production, particularly in the presence of heat. There was no significant effect of a 100-mT SMF exposure either alone or in combination with heat, DEM, or both on bioluminescence, however there was a significant interaction between SMF and DEM on hsp70 mRNA levels. Therefore, under our exposure conditions, GSH depletion reduced hsp70 levels but a synergistic effect of combining this stress with other external stimuli was only observed at the level of mRNA.

Non-invasive Bioluminescence Imaging of Myoblast-Mediated Hypoxia-Inducible Factor-1 Alpha Gene Transfer

We tested a novel imaging strategy, in which both the survival of transplanted myoblasts and their therapeutic transgene expression, a recombinant hypoxia-inducible factor-1α (HIF-1α-VP2), can be monitored using firefly luciferase (fluc) and Renilla luciferase (hrl) bioluminescence reporter genes, respectively. The plasmid pUbi-hrl-pUbi-HIF-1α-VP2, which expresses both hrl and HIF-1α-VP2 using two ubiquitin promoters, was characterized in vitro. C2c12 myoblasts stably expressing fluc and transiently transfected with pUbi-hrl-pUbi-HIF-1α-VP2 were injected into the mouse hindlimb. Both hrl and fluc expression were monitored using bioluminescence imaging (BLI). Strong correlations existed between the expression of hRL and each of HIF-1α-VP2, VEGF, and PlGF (r(2) > 0.83, r(2) > 0.82, and r(2) > 0.97, respectively). In vivo, both transplanted cells and HIF-1α-VP2 transgene expression were successfully imaged using BLI. An objective evaluation of myoblast-mediated gene transfer in living mice can be performed by monitoring both the survival and the transgene expression of transplanted myoblasts using the techniques developed herein.

Inhibition of Electrochemically Controlled Bioluminescence of Bacterial Luciferase by n-Alkyl Alcohols

An electrochemical system has been developed in order to assay the effect of hydrophobic molecules on the bioluminescence of bacterial luciferase (BL). The inhibition of BL luminescence by the long-chain n-alkyl alcohol has been examined using this system. The 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol and 1-dodecanol inhibited the BL reaction in a dose-dependent manner. The IC(50) value, that is, the inhibitor concentration required to decrease the luminescence intensity by half, of these alcohols decreased with increasing the alkyl chain-length of the alcohols. In contrast, the shorter chain 1-hexanol did not inhibit the BL luminescence at all in the examined concentration range. These results indicate that the molecular size and hydrophobicity of the n-alkyl alcohol are the key factors to the inhibitory potency of the BL reaction. The IC(50) values are in agreement with values obtained for the bioluminescence of the firefly luciferase system. The proposed electrochemical BL luminescence system will be used for an inhibitory assay of hydrophobic drugs, such as general anesthetics on protein functions.

Early Diagnosis of Productivity Through a Clock Gene Promoter Activity Using a Luciferase Bioluminescence Assay in Arabidopsis thaliana

A method for early diagnosis of plant productivity using a luciferase bioluminescence assay at the early stage of cultivation was developed for transgenic Arabidopsis thaliana carrying the CCA1::LUC construct, in which the promoter of the CCA1 clock gene had been fused to a modified firefly luciferase (LUC) gene. Because the intensity of luciferase bioluminescence is proportional to the CCA1 promoter activity and the expression level of LUC, the dynamics of both can be investigated by measuring the bioluminescence. In this paper, plant biomass was considered a measure of plant production andLUC protein a measure of foreign protein production. The leaf area and bioluminescence of seedlings at the early stage of cultivation were investigated as indexes for early diagnosis of productivity; leaf area was a reflection of morphological information, and bioluminescence, molecular information. Bioluminescence showed higher correlation to productivity based on biomass andLUC protein than the leaf area under various growth conditions, indicating that bioluminescence is a better index for early diagnosis. In addition, we developed a general statistical method for selecting superior seedlings based on this early diagnosis and a general theory for determining an optimal parameter set for maximizing profit. This early diagnostic methodology appears suited to enhance the quality of the products in plant factories.

Perfluorochemical Liquid-Adenovirus Suspensions Enhance Gene Delivery to the Distal Lung

We compared lung delivery methods of recombinant adenovirus (rAd): (1) rAd suspended in saline, (2) rAd suspended in saline followed by a pulse-chase of a perfluorochemical (PFC) liquid mixture, and (3) a PFC-rAd suspension. Cell uptake, distribution, and temporal expression of rAd were examined using A549 cells, a murine model using luciferase bioluminescence, and histological analyses. Relative to saline, a 4X increase in transduction efficiency was observed in A549 cells exposed to PFC-rAd for 2–4 h. rAd transgene expression was improved in alveolar epithelial cells, and the level and distribution of luciferase expression when delivered in PFC-rAd suspensions consistently peaked at 24 h. These results demonstrate that PFC-rAd suspensions improve distribution and enhance rAd-mediated gene expression which has important implications in improving lung function by gene therapy.

A microfluidic in situ analyzer for ATP quantification in ocean environments

We have developed and tested a functionally integrated in situ analyzer, the IISA-ATP system, for microbial activity assays based on a quantitative determination of the total (particulate and dissolved) ATP in ocean environments. The IISA-ATP utilizes a PDMS-glass hybrid microfluidic device as its core functional element, which can perform cell lysis and total ATP quantification by a luciferin-luciferase bioluminescence assay in situ. Transparent heaters and a temperature sensor fabricated on a glass substrate provide temperature control. As a result of the evaluation using the microfluidic device with ATP standard solutions, the bioluminescence intensity was linearly correlated with 2 × 10(-12) to 2 × 10(-8) M of ATP. A detection limit of 1.1 × 10(-11) M was determined using the completed IISA-ATP system, which includes a miniature pumping module and a control module. As a result of the evaluation using the environmental seawater sample collected from Tokyo Bay, Japan, 2.7 × 10(-10) M of total ATP was successfully determined in the laboratory by the IISA-ATP. The system was operated at a shallow submarine hot spring area in Okinawa, Japan for an in situ trial. The result shows the system was successfully operated in situ and the total ATP was determined to be 3.4 × 10(-10) M.

Panhematin provides a therapeutic benefit in experimental pancreatitis

Background and aimAcute pancreatitis (AP) can result in pancreatic necrosis and inflammation, with subsequent multi-organ failure. AP is associated with increased neutrophil recruitment and a rise in pro-inflammatory cytokines such...

Dynamics studies of luciferase using elastic network model: how the sequence distribution of luciferase determines its color

Luciferase exhibits a broad range of emitting frequencies. Light emission from the bioluminescence of luciferase makes it an excellent tool for monitoring gene expression, thus the control of its bioluminescence color has great bio-analytical applications. Here I use an elastic network model to examine how the sequence distribution of luciferase is related to bioluminescence multicolor emission. Based on the open and closed forms of crystal structures for luciferase, several computational analysis tools are applied to characterize the functionally relevant dynamical features within luciferase, and probe the dynamical mechanisms underlying the interactions between luciferin (a light-emitting substrate) and luciferase. Perturbation-based correlation analysis is used to identify hot-spot residues that are dynamically coupled to the active site of luciferase, and the results show that the sequence region of subdomain B of luciferase is largely responsible for determining the emitting color of bioluminescence. Moreover, the mode decomposition analysis reveals that the lowest frequency mode is the major contributor to the dynamical couplings between the hot-spot residues and the binding site in luciferase.

NMR-derived Topology of a GFP-photoprotein Energy Transfer Complex

Förster resonance energy transfer within a protein-protein complex has previously been invoked to explain emission spectral modulation observed in several bioluminescence systems. Here we present a spatial structure of a complex of the Ca(2+)-regulated photoprotein clytin with its green-fluorescent protein (cgGFP) from the jellyfish Clytia gregaria, and show that it accounts for the bioluminescence properties of this system in vitro. We adopted an indirect approach of combining x-ray crystallography determined structures of the separate proteins, NMR spectroscopy, computational docking, and mutagenesis. Heteronuclear NMR spectroscopy using variously (15)N,(13)C,(2)H-enriched proteins enabled assignment of backbone resonances of more than 94% of the residues of both proteins. In a mixture of the two proteins at millimolar concentrations, complexation was inferred from perturbations of certain (1)H-(15)N HSQC-resonances, which could be mapped to those residues involved at the interaction site. A docking computation using HADDOCK was employed constrained by the sites of interaction, to deduce an overall spatial structure of the complex. Contacts within the clytin-cgGFP complex and electrostatic complementarity of interaction surfaces argued for a weak protein-protein complex. A weak affinity was also observed by isothermal titration calorimetry (K(D) = 0.9 mM). Mutation of clytin residues located at the interaction site reduced the degree of protein-protein association concomitant with a loss of effectiveness of cgGFP in color-shifting the bioluminescence. It is suggested that this clytin-cgGFP structure corresponds to the transient complex previously postulated to account for the energy transfer effect of GFP in the bioluminescence of aequorin or Renilla luciferase.

Evaluation of impaired β‐cell function in nonobese‐diabetic (NOD) mouse model using bioluminescence imaging

Insulin-producing pancreatic β cells are functionally impaired or destroyed in diabetes mellitus. The onset of type 1 diabetes (T1D) represents the culmination of a prolonged prediabetic phase of immune-mediated β-cell destruction. To assess the in vivo metabolic status of these cells, we used the ATP-sensitive firefly luciferase bioluminescence imaging approach, as a noninvasive probe to monitor pathological alterations in β-cell function in the nonobese-diabetic (NOD) mouse model of T1D. Hence, we generated the ToIβ-NOD transgenic mice in which doxycycline-inducible luciferase gene is selectively expressed in β cells. A sharp reduction in bioluminescence emitted in vivo from β cells at the early stages, preceded by several weeks of a limited reduction in β-cell mass. Since this decline could be due to the ongoing inflammatory process occurring in vivo, we exposed control islets to inflammatory cytokines and observed a dramatic decrease in luciferase luminescence, which appears to be due in part to a decrease in protein levels and a drop in intracellular ATP levels. This is the first evidence that selective expression of the luciferase gene represents a sensitive method for noninvasive in vivo monitoring of early β-cell dysfunction, subtle metabolic changes, such as endogenous ATP levels, indicative of a pathological condition in a tissue at the cellular level.

Luciferase expression and bioluminescence does not affect tumor cell growth in vitro or in vivo

Live animal imaging is becoming an increasingly common technique for accurate and quantitative assessment of tumor burden over time. Bioluminescence imaging systems rely on a bioluminescent signal from tumor cells, typically generated from expression of the firefly luciferase gene. However, previous reports have suggested that either a high level of luciferase or the resultant light reaction produced upon addition of D-luciferin substrate can have a negative influence on tumor cell growth. To address this issue, we designed an expression vector that allows simultaneous fluorescence and luminescence imaging. Using fluorescence activated cell sorting (FACS), we generated clonal cell populations from a human breast cancer (MCF-7) and a mouse melanoma (B16-F10) cell line that stably expressed different levels of luciferase. We then compared the growth capabilities of these clones in vitro by MTT proliferation assay and in vivo by bioluminescence imaging of tumor growth in live mice. Surprisingly, we found that neither the amount of luciferase nor biophotonic activity was sufficient to inhibit tumor cell growth, in vitro or in vivo. These results suggest that luciferase toxicity is not a necessary consideration when designing bioluminescence experiments, and therefore our approach can be used to rapidly generate high levels of luciferase expression for sensitive imaging experiments.

Inhibition of the Inflammatory Cytokine TNF-α Increases Adenovirus Activity in Ovarian Cancer via Modulation of cIAP1/2 Expression

Oncolytic adenoviruses show promise as a cancer treatment. However, they generate acute inflammatory responses with production of cytokines, including tumor necrosis factor-α (TNF-α). We investigated whether inhibition of TNF-α augments efficacy of the E1A CR2-deleted adenovirus dl922-947 in ovarian cancer. dl922-947 induced transcription of TNF-α and its downstream signaling targets interleukin-6 and -8 (IL-6 and IL-8) in ovarian cancer cells. In vitro, RNAi-mediated knockdown of TNF-α reduced production of multiple inflammatory cytokines after infection and increased ovarian cancer cell sensitivity to virus cytotoxicity, as did treatment with the anti-TNF-α antibody infliximab. In vivo, stable knockdown of TNF-α in IGROV-1 xenografts increased the anticancer activity of dl922-947. In addition, inhibition of TNF-α using monoclonal antibodies also improved dl922-947 efficacy. This increased efficacy resulted from suppression of cellular inhibitor of apoptosis-1 and -2 (cIAP1 and cIAP2) transcription in malignant cells and a consequent increase in caspase-mediated apoptosis. These findings suggest that TNF-α acts as a survival factor in adenovirus-infected cells. Combining TNF-α inhibition with oncolytic adenoviruses could improve antitumor activity in clinical trials.

PET Imaging of Hypoxia-Inducible Factor-1-Active Tumor Cells with Pretargeted Oxygen-Dependent Degradable Streptavidin and a Novel 18F-Labeled Biotin Derivative

We aimed to evaluate the feasibility of using streptavidin-biotin-based pretargeting for positron emission tomography (PET) imaging of hypoxia-inducible factor (HIF)-1-active tumors. We used POS, a genetically engineered form of streptavidin that selectively stabilizes in HIF-1-active cells, and (4-(18)F-fluorobenzoyl)norbiotinamide ((18)F-FBB), a radiolabeled biotin derivative, for performing a biodistribution study and for PET imaging. The tumoral (18)F-FBB accumulation was compared to the HIF-1-dependent luciferase bioluminescence and HIF-1α immunohistochemical signal. (18)F-FBB accumulation was observed in POS-pretargeted tumors in mice (2.85 ± 0.55% injected dose per gram at 3 h), and clear PET images were obtained at the same time point. The tumoral (18)F-FBB accumulation positively correlated with luciferase bioluminescence (R = 0.72, P < 0.05), and most of the area showing (18)F-FBB accumulation corresponded to HIF-1α-positive areas. Pretargeting with POS and (18)F-FBB is an effective approach for PET imaging of HIF-1-active areas in tumors.

Circadian oscillators in the epithalamus

The habenula complex is implicated in a range of cognitive, emotional and reproductive behaviors, and recently this epithalamic structure was suggested to be a component of the brain's circadian system. Circadian timekeeping is driven in cells by the cyclical activity of core clock genes and proteins such as per2/PER2. There are currently no reports of rhythmic clock gene/protein expression in the habenula and therefore the question of whether this structure has an intrinsic molecular clock remains unresolved. Here, using videomicroscopy imaging and photon-counting of a PER2::luciferase (LUC) fusion protein together with multiunit electrophysiological recordings, we tested the endogenous circadian properties of the mouse habenula in vitro. We show that a circadian oscillator is localized primarily to the medial portion of the lateral habenula. Rhythms in PER2:: LUC bioluminescence here are visualized in single cells and oscillations continue in the presence of the sodium channel blocker, tetrodotoxin, indicating that individual cells have intrinsic timekeeping properties. Ependymal cells lining the dorsal third ventricle also express circadian oscillations of PER2. These findings establish that neurons and non-neuronal cells in the epithalamus express rhythms in cellular and molecular activities, indicating a role for circadian oscillators in the temporal regulation of habenula controlled processes and behavior.

Low generation PAMAM dendrimer and CpG free plasmids allow targeted and extended transgene expression in tumors after systemic delivery

Polyplexes consisting of a standard CMV promoter driven luciferase plasmid condensed with PAMAM starburst dendrimers (generation 4 and 5) efficiently transfected tumor cells in vitro. Tail vein injection of PAMAM polyplexes into immune competent mice bearing subcutaneous, well vascularized murine neuroblastoma tumors (Neuro2A) led to predominant luciferase reporter gene expression in the tumor, and negligible transgene expression levels in other organs. Repeated PAMAM polyplex applications were well tolerated and prolonged transgene expression in the tumor. In vivo imaging studies using polyplexes fluorescently labeled with near infrared emitting semiconductor quantum dots (quantoplexes) revealed lung accumulation for both PAMAM and linear PEI (LPEI) based polyplexes, but only LPEI polyplexes induced high luciferase expression in lung, demonstrating that biodistribution and transgene expression of polyplexes does not necessarily correlate. With a luciferase plasmid devoid of immune modulatory CpG sequences and a combination of human CMV enhancer and human elongation factor 1 alpha promoter elements, Neuro2A tumor transgene expression after a single intravenous injection of generation 5 PAMAM polyplexes was observed for up to 1 week as measured by luciferase bioluminescence imaging. Utilizing a human xenograft model (HUH7) in immune compromised nude mice, a low level of luciferase activity in the tumor area was observed after systemic PAMAM polyplex application.

Rapid detection of hypoxia-inducible factor-1-active tumours: pretargeted imaging with a protein degrading in a mechanism similar to hypoxia-inducible factor-1α

Hypoxia-inducible factor-1 (HIF-1) plays an important role in malignant tumour progression. For the imaging of HIF-1-active tumours, we previously developed a protein, POS, which is effectively delivered to and selectively stabilized in HIF-1-active cells, and a radioiodinated biotin derivative, (3-(123)I-iodobenzoyl)norbiotinamide ((123)I-IBB), which can bind to the streptavidin moiety of POS. In this study, we aimed to investigate the feasibility of the pretargeting method using POS and (123)I-IBB for rapid imaging of HIF-1-active tumours. Tumour-implanted mice were pretargeted with POS. After 24 h, (125)I-IBB was administered and subsequently, the biodistribution of radioactivity was investigated at several time points. In vivo planar imaging, comparison between (125)I-IBB accumulation and HIF-1 transcriptional activity, and autoradiography were performed at 6 h after the administration of (125)I-IBB. The same sections that were used in autoradiographic analysis were subjected to HIF-1alpha immunohistochemistry. (125)I-IBB accumulation was observed in tumours of mice pretargeted with POS (1.6%ID/g at 6 h). This result is comparable to the data derived from (125)I-IBB-conjugated POS-treated mice (1.4%ID/g at 24 h). In vivo planar imaging provided clear tumour images. The tumoral accumulation of (125)I-IBB significantly correlated with HIF-1-dependent luciferase bioluminescence (R=0.84, p<0.01). The intratumoral distribution of (125)I-IBB was heterogeneous and was significantly correlated with HIF-1alpha-positive regions (R=0.58, p<0.0001). POS pretargeting with (123)I-IBB is a useful technique in the rapid imaging and detection of HIF-1-active regions in tumours.