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The α-emitter 211At-labeled meta-astatobenzylguanidine (211At-MABG) has a strong antitumor effect on pheochromocytoma xenograft tumors and holds great promise as a new therapeutic option for malignant pheochromocytoma. To evaluate the acute radiation-related toxicity of 211At-MABG, we conducted biodistribution and dosimetry studies of 211At-MABG in ICR mice to estimate the doses absorbed by organs. We determined the maximum tolerated doses (MTD) of 211At-MABG on the basis of body weight loss and assessed the acute radiation-related toxicity induced by MTD administration on the basis of organ weights, histologic features, hematologic indices, and biochemical indices. The biodistribution and dosimetry studies of α-emitting 211At-MABG revealed high doses absorbed by most organs except the brain in ICR mice. The administration of 1.1, 2.2, and 3.3 MBq of 211At-MABG induced transient body weight loss, and 4.4 MBq of 211At-MABG induced unrecoverable body weight loss; thus, the MTD was 3.3 MBq for ICR mice. Although by day 5 the administration of 3.3 MBq had induced some radiation-related toxicity symptoms—such as body weight loss and leucopenia, which are generally observed in radiation therapy including β−-emitting radiopharmaceuticals—the mice had recovered by day 28. We observed no unexpected severe toxicity in ICR mice despite the high absorbed doses in most organs, especially the thyroid, heart, stomach, and adrenal glands. Our findings suggest that therapeutic treatments with appropriate doses of 211At-MABG estimated by dosimetry in each patient could be tolerated, although lower doses may initially be necessary to ensure patient safety in the first-in-human study.

Podoplanin is a type I transmembrane sialomucin-like glycoprotein that is highly expressed in malignant mesothelioma. The rat-human chimeric antibody NZ-12 has high affinity for human podoplanin and antibody-dependent cellular cytotoxicity and is applicable for radioimmunotherapy (RIT) to enhance the antitumor effect. In the present study, we evaluated the in vivo and in vitro properties of radiolabeled NZ-12 and the antitumor effect of RIT with 90 Y-labeled NZ-12 in an NCI-H226 (H226) malignant mesothelioma xenograft mouse model. 111 In-labeled NZ-12 bound specifically to H226 cells with high affinity, and accumulation was high in H226 tumors but low in major organs. RIT with 90 Y-labeled NZ-12 significantly suppressed tumor growth and prolonged survival without body weight loss and obvious adverse effects. Higher podoplanin expression levels were observed in human mesothelioma specimens, suggesting higher tumor accumulation of 90 Y-labeled NZ-12 in patients compared with the H226 tumor xenografts. Our findings suggest that 90 Y-labeled NZ-12 is a promising RIT agent as a new therapeutic option for malignant mesothelioma that warrants further clinical studies to evaluate the dosimetry and efficacy in patients.

Purpose This study aimed to evaluate the potential of podoplanin (PDPN)-targeted alpharadiotherapy (RIT) for treating malignant mesothelioma.Methods A newly developed anti-PDPN antibody, NZ-16, and a previous anti-PDPN antibody, NZ-12, were assessed. The in vitro properties of radiolabeled antibodies were evaluated by cell binding and competitive inhibition assays using PDPN-expressing NCI-H226 (H226) mesothelioma cells. The biodistribution of 111 In-labeled antibodies was studied in tumorbearing mice. Tumor volumes and body weights of mice treated with 90 Y- and 225 Ac-labeled NZ-16 were measured for 56 days. The absorbed doses were estimated on the basis of the biodistribution data. Pathologic analysis of tumors and organs was conducted.Results The radiolabeled NZ-16 specifically bound to H226 cells with higher affinity than NZ12. The biodistribution studies showed higher tumor uptake of radiolabeled NZ-16 compared with NZ-12. RIT with 225 Ac-labeled NZ-16 (11.1 and 18.5 kBq) had a significantly higher antitumor effect than RIT with 90 Y-labeled NZ-16 (3.7 MBq; P < 0.01). 225 Ac-labeled NZ-16 induced more necrosis compared with 90 Y-labeled NZ-16, but the Ki-67 index and apoptosis rate were similar. The estimated absorbed doses were expected to be tolerable in mice. Temporary body weight loss occurred, but recovered within several days. No visible damage to major organs was detected.Conclusion The novel anti-PDPN antibody NZ-16 was a more effective RIT agent than NZ12. Radiolabeled NZ-16, especially 225 Ac-labeled NZ-16, markedly suppressed tumor growth and prolonged survival without inducing severe adverse effects. RIT with radiolabeled NZ-16 is a promising therapeutic option for malignant mesothelioma.

Due to their short range (2–500 nm), Auger electrons (Auger e-) have the potential to induce nano-scale physiochemical damage to biomolecules. Although DNA is the primary target of Au-ger e-, it remains challenging to maximize the interaction between Auger e- and DNA. To assess the DNA-damaging effect of Auger e- released as close as possible to DNA without chemical damage, we radio-synthesized no-carrier-added (n.c.a.) [189, 191Pt]cisplatin and evaluated both its in vitro properties and DNA-damaging effect. Cellular uptake, intracellular distribution, and DNA binding were investigated, and DNA double-strand breaks (DSBs) were evaluated by im-munofluorescence staining of γH2AX and gel electrophoresis of plasmid DNA. Approximately 20% of intracellular radio-Pt was in a nucleus, and about 2% of intra-nucleus radio-Pt bound to DNA, although uptake of n.c.a. radio-cisplatin was low (0.6% incubated dose after 25-h incuba-tion), resulting in the frequency of cells with γH2AX foci was low (1%). Nevertheless, some cells treated with radio-cisplatin had γH2AX aggregates unlike non-radioactive cisplatin. These findings suggest n.c.a. radio-cisplatin binding to DNA causes severe DSBs by release of Auger e- very close to DNA without chemical damage by carriers. Efficient radio-drug delivery to DNA is necessary for successful clinical application of Auger e-.

In treatment-refractory cancers, tumor tissues damaged by therapy initiate the repair response, therefore, tumor tissues must be exposed to an additional burden before successful repair. We hypothesized that an agent recognizing a molecule that responds to anticancer treatment-induced tissue injury could deliver an additional antitumor agent including a radionuclide to damaged cancer tissues during repair. We selected the extracellular matrix glycoprotein tenascin-C (TNC) as such a molecule, and three antibodies recognizing human and murine TNC were employed to evaluate X-irradiation-induced changes in TNC uptake by subcutaneous tumors. TNC expression was assessed by immunohistochemical staining of BxPC-3 tumors treated with or without X-irradiation (30 Gy) for 7 days. Antibodies against TNC (3&ndash, 6, 12&ndash, 2&ndash, 7, TDEAR) and a control antibody were radiolabeled with 111In and injected into nude mice having BxPC-3 tumors 7 days after X-irradiation, and temporal uptake was monitored for an additional 4 days by biodistribution and single-photon emission computed tomography with computed tomography (SPECT/CT) studies. Intratumoral distribution was analyzed by autoradiography. The immunohistochemical signal for TNC expression was faint in nontreated tumors but increased and expanded with time until day 7 after X-irradiation. Biodistribution studies revealed increased tumor uptake of all three 111In-labeled antibodies and the control antibody. However, a statistically significant increase in uptake was evident only for 111In-labeled 3&ndash, 6 (35% injected dose (ID)/g for 30 Gy vs. 15% ID/g for 0 Gy at day 1, p &lt, 0.01), whereas limited changes in 111In-labeled TDEAR2, 12&ndash, 27, and control antibody were observed (several % ID/g for 0 and 30 Gy). Serial SPECT/CT imaging with 111In-labeled 3&ndash, 6 or control antibody provided consistent results. Autoradiography revealed noticeably stronger signals in irradiated tumors injected with 111In-labeled 3&ndash, 6 compared with each of the nonirradiated tumors and the control antibody. The signals were observed in TNC-expressing stroma. Markedly increased uptake of 111In-labeled 3&ndash, 6 in irradiated tumors supports our concept that an agent, such as an antibody, that recognizes a molecule involved in tissue injury repair, such as TNC, could enhance drug delivery to tumor tissues that have undergone therapy. The combination of antibody 3&ndash, 6 coupled to a tumoricidal drug and conventional therapy has the potential to achieve better outcomes for patients with refractory cancer.

Objective We previously reported In-labeled anti-cadherin17 (CDH17) IgG visualized CDH17-positive gastric cancer xenografts. Unfortunately, a long waiting time was required to obtain high-contrast images due to long blood retention (blood half-life: 26 h). To accelerate blood clearance, we have developed anti-CDH17 minibody (D2101 minibody) and evaluated the pharmacokinetics in gastric cancer mouse models. Methods Two different single chain Fvs (scFvs), D2101 mutant and D2111, were developed from each parental IgG. The binding ability to CDH17 and stability in plasma were evaluated. D2101 minibody, constructed based on D2101 mutant scFv, was labeled with Cu (Cu-D2101 minibody), and the in-vitro and in-vivo properties were evaluated by cell ELISA, biodistribution experiments, and PET imaging in mice bearing CDH17-positive AGS and CDH17-negative MKN74 tumors. Results D2101 mutant and D2111 scFvs showed similar affinities to CDH17. D2101 mutant scFv was more stable than D2111 scFv in plasma. No loss of binding affinity of the D2101 minibody by chelate conjugation and radiolabeling procedures was observed. The biodistribution of Cu-D2101 minibody showed high uptake in AGS tumors and low uptake in MKN74. The blood half-life of Cu-D2101 minibody was 6.5 h. Improved blood clearance of Cu-D2101 minibody provided high tumor-to-blood ratios compared with the previous results of parental IgG in AGS xenograft mice. PET studies showed consistent results with biodistribution studies. Conclusions Cu-D2101 minibody exhibited higher tumor-to-blood ratios at earlier time points than those of the radiolabeled parental IgG. Cu-D2101 minibody has potential as an immunoimaging agent for CDH17-positive tumors.

Background: CD73 is an ectonucleotidase regulating extracellular adenosine concentration and plays an important role in adenosine-mediated immunosuppressive pathways. The efficacy of CD73-targeted therapy depends on the expression levels of CD73, therefore, monitoring CD73 status in cancer patients would provide helpful information for selection of patients who would benefit from CD73-targeted therapy. Here, we evaluated the ability of 111In-labeled antibody 067-213, which has high affinity for human CD73, to act as a noninvasive imaging probe. Methods: Cell binding and competitive inhibition assays for 111In-labeled 067-213 were conducted using MIAPaCa-2 (high CD73 expression) and A431 (low CD73 expression) cells. For in vivo assessments, biodistribution and SPECT/CT studies were conducted in MIAPaCa-2 and A431 tumor-bearing mice. To estimate the absorbed dose in humans, biodistribution and SPECT/CT studies were conducted in healthy rats. Results: 111In-labeled 067-213 bound to MIAPaCa-2 and A431 cells in a CD73-dependent manner and the affinity loss after 111In-labeling was limited. Biodistribution and SPECT/CT studies with 111In-labeled 067-213 in mice showed high uptake in MIAPaCa-2 tumors and lower uptake in A431 tumors. In rats, the probe did not show high uptake in normal organs, including endogenously CD73-expressing organs. The estimated absorbed doses in humans were reasonably low. Conclusions: 111In-labeled 067-213 showed CD73-expression-dependent tumor uptake and low uptake in normal organs and tissues. Radiolabeled 067-213 holds promise as an imaging probe for noninvasive evaluation of CD73 expression levels in patients. Our data encourage further clinical studies to clarify a role for CD73 monitoring in patients receiving CD73-targeted immune therapy.

Highlights • SQAP enhanced tumor uptake and the therapeutic efficacy of radiolabeled anti-tissue factor antibody 1849. • SQAP allows for a reduction of the dose of the therapeutic agent 90Y-labeled 1849 to half. • SQAP did not affect hematologic parameters, or gastrointestinal and respiratory systems in mice. • 90Y-labeled 1849 with SQAP potentially increases exposure of tumors to radiation., α-Sulfoquinovosylacyl-1,3-propanediol (SQAP) is a semi-synthetic derivative of natural sulfoglycolipid that sensitizes tumors to external-beam radiotherapy. How SQAP affects internal radiotherapy, however, is not known. Here, we investigated the effects of SQAP for radioimmunotherapy (RIT) targeting tissue factor (TF) in a stroma-rich refractory pancreatic cancer mouse model, BxPC-3. A low dose of SQAP (2 mg/kg) increased tumor uptake of the 111In-labeled anti-TF antibody 1849, indicating increased tumor perfusion. The addition of SQAP enhanced the growth-inhibitory effect of 90Y-labeled 1849 without leading to severe body weight changes, allowing for the dose of 90Y-labeled 1849 to be reduced to half that when used alone. Histologic analysis revealed few necrotic and apoptotic cells, but Ki-67–positive proliferating cells and increased vascular formation were detected. These results suggest that the addition of a low dose of SQAP may improve the therapeutic efficacy of TF-targeted RIT by increasing tumor perfusion, even for stroma-rich refractory pancreatic cancer., Graphical abstract Image, graphical abstract

Purpose Therapeutic options for patients with malignant pheochromocytoma are currently limited, and therefore new treatment approaches are being sought. Targeted radionuclide therapy provides tumor-specific systemic treatments. The β-emitting radiopharmaceutical meta-131I-iodo-benzylguanidine (131I-MIBG) provides limited survival benefits and has adverse effects. A new generation of radionuclides for therapy using α-particles including meta-211At-astato-benzylguanidine (211At-MABG) are expected to have strong therapeutic effects with minimal side effects. However, this possibility has not been evaluated in an animal model of pheochromocytoma. We aimed to evaluate the therapeutic effects of the α-emitter 211At-MABG in a pheochromocytoma model. Methods We evaluated tumor volume-reducing effects of 211At-MABG using rat pheochromocytoma cell line PC12 tumor-bearing mice. PC12 tumor-bearing mice received intravenous injections of 211At-MABG (0.28, 0.56, 1.11, 1.85, 3.70 and 5.55 MBq; five mice per group). Tumor volumes were evaluated for 8 weeks after 211At-MABG administration. The control group of ten mice received phosphate-buffered saline. Results The 211At-MABG-treated mice showed significantly lower relative tumor growth during the first 38 days than the control mice. The relative tumor volumes on day 21 were 509.2% ± 169.1% in the control mice and 9.6% ± 5.5% in the mice receiving 0.56 MBq (p

AIM To investigate the therapeutic effect of combined integrin α6β4-targeted radioimmunotherapy (RIT) and PI3K/mTOR inhibitor BEZ235 in a pancreatic cancer model. METHODS Phosphorylation of Akt, mTOR, the downstream effectors eukaryotic initiation factor 4E binding protein 1 (4EBP1) and S6 ribosomal protein (S6) were evaluated in BxPC-3 human pancreatic cancer cells treated with Yttrium-90 (90Y) labeled anti-integrin α6β4 antibody (ITGA6B4) and BEZ235 by western blotting. The cytotoxic effect of BEZ235 was investigated using a colony formation assay. Therapeutic efficacy enhancement by oral BEZ235 administration was assessed using mice bearing BxPC-3 xenograft tumors. Tumor volume measurements and immunohistochemical analyses (cell proliferation marker Ki-67, DNA damage marker p-H2AX and p-4EBP1 staining) of tumors were performed for evaluation of combined treatment with 90Y-ITGA6B4 plus BEZ235, or each arm alone. RESULTS We found that phosphorylation of Akt (p-Akt), 4EBP1 (p-4EBP1) and S6 (p-S6) was inhibited by BEZ235. Colony formation in BxPC-3 cells was additively suppressed by the combination of 90Y-ITGA6B4 and BEZ235. Pretreatment with BEZ235 before 90Y-ITGA6B4 exposure resulted in significant reduction of cells plating efficiency (PE) (0.54 ± 0.11 vs 2.81 ± 0.14 with 185 kBq/mL 90Y-ITGA6B4 exposure, P < 0.01; 0.39 ± 0.08 vs 1.88 ± 0.09 with 370 kBq/mL 90Y-ITGA6B4 exposure, P < 0.01) when 5 × 103 cells per dish were plated. In vivo , the combined treatment with 90Y-ITGA6B4 plus BEZ235 enhanced the inhibition of tumor growth and statistically significant differences of relative tumor volume were observed for 27 d after the treatment start date when compared with the 90Y-ITGA6B4 single injection treatment (1.03 ± 0.38 vs 1.5 ± 0.15 at Day 27, P < 0.05), and for 41 d when compared with the BEZ235 treatment alone (1.8 ± 0.7 vs 3.14 ± 1.19 at Day 41, P < 0.05). Tumors from treatment groups showed reduction in volumes, decreased Ki-67-positive cells, increased p-H2AX-positive cells and decreased p-4EBP1 expression. CONCLUSION The therapeutic efficacy of 90Y-ITGA6B4-RIT can be improved by combining with dual PI3K and mTOR inhibitor, BEZ235, in a pancreatic cancer model suggesting potential clinical application. Key words: Radioimmunotherapy; Pancreatic cancer; anti-integrin α6β4 antibody; Yttrium-90; NVP-BEZ235

Upregulated monocarboxylate transporters (MCTs) in tumors are considered diagnostic imaging targets. Herein, we synthesized the positron emission tomography probe candidates coumarin analogs 2 and 3, and showed 55 times higher affinity of 2 for MCTs than a representative MCT inhibitor. Whereas [11C] 2 showed low tumor accumulation, probably due to adduct formation with plasma proteins, [11C]2 showed high initial brain uptake, suggesting that the scaffold of 2 has properties that are preferable in imaging probes for the astrocyte–neuron lactate shuttle. Although further optimization of 2 is required, our findings can be used to inform the development of MCT-targeted imaging agents. 2017 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license

Due to their short-range (2–500 nm), Auger electrons (Auger e−) have the potential to induce nano-scale physiochemical damage to biomolecules. Although DNA is the primary target of Auger e−, it remains challenging to maximize the interaction between Auger e− and DNA. To assess the DNA-damaging effect of Auger e− released as close as possible to DNA without chemical damage, we radio-synthesized no-carrier-added (n.c.a.) [189, 191Pt]cisplatin and evaluated both its in vitro properties and DNA-damaging effect. Cellular uptake, intracellular distribution, and DNA binding were investigated, and DNA double-strand breaks (DSBs) were evaluated by immunofluorescence staining of γH2AX and gel electrophoresis of plasmid DNA. Approximately 20% of intracellular radio-Pt was in a nucleus, and about 2% of intra-nucleus radio-Pt bound to DNA, although uptake of n.c.a. radio-cisplatin was low (0.6% incubated dose after 25-h incubation), resulting in the frequency of cells with γH2AX foci was low (1%). Nevertheless, some cells treated with radio-cisplatin had γH2AX aggregates unlike non-radioactive cisplatin. These findings suggest n.c.a. radio-cisplatin binding to DNA causes severe DSBs by the release of Auger e− very close to DNA without chemical damage by carriers. Efficient radio-drug delivery to DNA is necessary for successful clinical application of Auger e−.

To explore suitable imaging probes for early and specific detection of pancreatic cancer, we demonstrated that α6β4 integrin is a good target and employed single-photon emission computed tomography (SPECT) or near-infrared (NIR) imaging for immunotargeting. Expression levels of α6β4 were examined by Western blotting and flow cytometry in certain human pancreatic cancer cell lines. The human cell line BxPC-3 was used for α6β4-positive and a mouse cell line, A4, was used for negative counterpart. We labeled antibody against α6β4 with Indium-111 (111In) or indocyanine green (ICG). After injection of 111In-labeled probe to tumor-bearing mice, biodistribution, SPECT, autoradiography (ARG), and immunohistochemical (IHC) studies were conducted. After administration of ICG-labeled probe, in vivo and ex vivo NIR imaging and fluorescence microscopy of tumors were performed. BxPC-3 tumor showed a higher radioligand binding in SPECT and higher fluorescence intensity as well as a delay in the probe washout in NIR imaging when compared to A4 tumor. The biodistribution profile of 111In-labeled probe, ARG, and IHC confirmed the α6β4 specific binding of the probe. Here, we propose that α6β4 is a desirable target for the diagnosis of pancreatic cancer and that it could be detected by radionuclide imaging and NIR imaging using a radiolabeled or ICG-labeled α6β4 antibody.

The poor prognosis of pancreatic cancer requires the development of more effective therapy. CD147 expresses in pancreatic cancer with high incidence and has a crucial role in invasion and metastasis. We developed a fully human monoclonal antibody (059-053) with high affinity for CD147. Here we evaluated the efficacy of combined treatment using radioimmunotherapy (RIT) with 90Y-labeled 059-053 and gemcitabine in a BxPC-3 xenograft mouse model. Expression of CD147 and matrix metalloproteinase-2 (MMP2) in BxPC-3 tumors was evaluated. In vitro and in vivo properties of 059-053 were evaluated using 111In-labeled 059-053 and a pancreatic cancer model BxPC-3. Tumor volume and body weight were periodically measured in mice receiving gemcitabine, RIT, and both RIT and gemcitabine (one cycle and two cycles). High expression of CD147 and MMP2 was observed in BxPC-3 tumors and suppressed by 059-053 injection. Radiolabeled 059-053 bound specifically to BxPC-3 cells and accumulated highly in BxPC-3 tumors but low in major organs. Combined treatment using RIT with gemcitabine (one cycle) significantly suppressed tumor growth and prolonged survival with tolerable toxicity. The two-cycle regimen had the highest anti-tumor effect, but was not tolerable. Combined treatment with 90Y-labeled 059-053 and gemcitabine is a promising therapeutic option for pancreatic cancer.

Tissue factor (TF) has emerged as a critical factor in oncogenic events, leading to the development of TF‑targeted diagnostic and therapeutic approaches. A non‑invasive imaging method to evaluate target molecule expression with high sensitivity and high quantitative ability is imperative for selecting the appropriate patients for TF‑targeted therapy. To elucidate the potential of 111In‑labeled anti‑TF antibody 1849 (111In‑1849) as an immuno‑single photon emission computed tomography (SPECT) probe targeting TF, we evaluated TF‑dependent in vitro binding as well as in vivo biodistribution and tumor accumulation of 111In‑1849 in pancreatic cancer cells/models with varying TF expression levels. TF expression levels in five human pancreatic cancer cell lines, BxPC‑3, BxPC‑3‑TF‑knockout (BxPC‑3‑TFKO), Capan‑1, PSN‑1 and SUIT‑2, were examined by immunofluorescence. Binding of 111In‑1849 to each cell line was assessed. Biodistribution and imaging studies were also conducted in tumor‑bearing mice. Furthermore, the relationship of TF expression with cell binding and tumor uptake was analyzed. In the immunofluorescence studies, BxPC‑3 exhibited the highest TF expression, followed by Capan‑1, PSN‑1, SUIT‑2 and BxPC‑3‑TFKO. Cell binding assays revealed that BxPC‑3 cells had the highest 111In‑1849 binding, followed by PSN‑1, Capan‑1 and SUIT‑2; no binding was detected in BxPC‑3‑TFKO cells. The BxPC‑3 xenograft was clearly visualized on 111In‑1849 SPECT/CT, and the highest uptake was detected on day 4. The biodistribution of 111In‑1849 on day 4 revealed that tumor uptake ranged from 8.68 to 50.58% of the injected dose per gram of tissue; BxPC‑3 had the highest uptake and SUIT‑2 had the lowest. TF expression was significantly associated with cell binding (R2=0.79, P

Scirrhous gastric cancer (SGC) is a recalcitrant tumor, which is among the most lethal cancers. A critical issue for the improvement of SGC prognosis is the lack of an effective imaging method for accurate detection and diagnosis. Because combined nuclear medicine imaging with magnetic resonance imaging (MRI) has the ability to detect cancer with high sensitivity, and quantitation and spatial resolution, it has potential to overcome the issues with SGC detection. Herein, we designed and synthesized a new block copolymer poly(ethylene glycol)-b-poly(γ-benzyl L-glutamate) linked with a chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA-PEG-b-PBLG) to provide a platform for multimodal tomographic imaging. We then successfully prepared DOTA-functionalized polymeric micelles (DOTA/m) measuring 30 nm in diameter, which is an appropriate size to penetrate deeply into tumors with thick fibrosis, including SGC. 111In-labeled DOTA/m highly accumulated in Colon-26 tumors (mouse colon cancer with hyperpermeability), but also in OCUM-2 M LN tumors (SGC with hypopermeability), clearly depicting both tumors by single photon emission computed tomography (SPECT). Gd-labeled DOTA/m clearly visualized OCUM-2 M LN tumors by MRI with high spatial resolution. Moreover, 111In/Gdlabeled micelles, as well as the mixture of 111In- and Gd-labeled DOTA/m demonstrated the capability of this system for selective multimodal SPECT/MR imaging of SCG. Our findings support 111In/Gd-DOTA-labeled micelles as a clinical translationable modality for multimodal tomographic imaging capable of detecting SGC

The positron emission tomography (PET) probe, 2-amino-[3-¹¹C]isobutyric acid ([3-¹¹C]AIB), is reported to accumulate less in inflammatory lesions than 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) and has the potential for evaluation of the efficacy of radiotherapy. To determine whether [3-¹¹C]AIB is useful to monitor early metabolic change in tumors after radiotherapy, we evaluated the temporal change in [3-¹¹C]AIB tumor uptake, tumor volume, histological features and expression of amino acid transporters early after radiotherapy in a mouse tumor model. PET with [3-¹¹C]AIB was conducted in mice bearing a subcutaneous tumor (SY, derived from small cell lung cancer) in two schedules: schedule 1, before (day -1) and after (days 1 and 3) 15 Gy of radiation and schedule 2, days -1, 1 and 5. [3-¹¹C]AIB tumor uptake tended to increase on day 1 after irradiation and decreased thereafter. Tumor uptake was not correlated with tumor volume in schedule 1. Although tumor uptake was correlated with tumor volume in schedule 2, this correlation was lost when the day 5 data of greatly reduced tumor volumes were excluded. In a separate group of tumor-bearing mice, excised tumor sections were stained with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) or anti-Ki-67 antibody. There was no correlation between tumor uptake and percentages of TUNEL- or Ki-67-positive cells. Expression of amino acid transporters, SLC38A1, SLC38A2 and SLC38A4, was determined by real-time RT-PCR. SLC38A1 and SLC38A2 were expressed in SY tumors, and a significant correlation was observed between [3-¹¹C]AIB tumor uptake and SLC38A1 expression. In conclusion, early change in [3-¹¹C]AIB tumor uptake after irradiation reflected the temporal change in amino acid transporter expression, while it was independent of change in tumor volume, apoptosis and cell proliferation. PET with [3-¹¹C]AIB has the potential for use in non-invasive evaluation of early metabolic change after irradiation before morphological change of tumors.

Objective Pancreatic cancer is aggressive and its prognosis remains poor; thus, effective therapy is urgently needed. Transferrin receptor (TfR) is highly expressed in pancreatic cancer and is considered to be a good candidate for molecular-targeted therapy. We radiolabeled and evaluated fully human anti-TfR monoclonal antibodies as a new PET probe for evaluating the biodistribution of the anti-TfR antibody in pancreatic cancer. Materials and methods TfR expression was evaluated in four human pancreatic cancer (MIAPaCa-2, PANC-1, BxPC-3, and AsPC-1) and murine A4 cell lines. The binding of 125I-labeled anti-TfR antibodies (TSP-A01, TSP-A02, TSP-A03, and TSP-A04) to MIAPaCa-2 cells was compared. 125I-labeled, 67Ga-labeled, and 89Zr-labeled TSP-A01 were evaluated by cell binding, competitive inhibition, and internalization assays. Biodistribution studies of 125I-labeled and 89Zr-labeled TSP-A01 were conducted in mice bearing MIAPaCa-2 and A4 tumors. PET imaging with [89Zr]TSP-A01 was carried out. Results MIAPaCa-2 cells showed the highest TfR expression in vitro and in vivo, whereas A4 cells showed no expression. Of the four antibodies, [125I]TSP-A01 showed the highest binding to MIAPaCa-2 cells, but not to A4 cells. The dissociation constant of TSP-A01 was 0.29 nmol/l. Uptake of radiolabeled TSP-A01, especially [89Zr]TSP-A01, was significantly higher in MIAPaCa-2 tumors than in A4 tumors. PET with [89Zr]TSP-A01 clearly visualized MIAPaCa-2 xenografts but not A4 xenografts. Conclusion [89Zr]TSP-A01 is a promising PET probe for evaluating the accumulation of anti-TfR antibody in pancreatic cancer and has the potential to facilitate the selection of appropriate patients who would benefit from anti-TfR antibody therapy.

The worldwide incidence of the highly aggressive tumor mesothelioma is expected to increase. Mesothelioma is classified into three main histological subtypes: epithelioid, sarcomatoid and biphasic. Although the pathological diagnostic markers for epithelioid are established, to date no adequate marker for sarcomatoid mesothelioma has been found. Thus, a reliable diagnostic marker of sarcomatoid mesothelioma is necessary. In this study, to identify an unknown protein with 120 kDa expressed only in the mesothelioma cell line 211H, we conducted proteomic analysis and found five candidate proteins. One such protein, AHNAK, was highly expressed in all seven mesothelioma cell lines (211H, H28, H226, H2052, H2452, MESO1 and MESO4), but not in the mesothelial cell line MeT-5A by RT-PCR and immunofluorescence staining. Furthermore, we confirmed high AHNAK expression not only in xenografts but also in human mesothelioma specimens including sarcomatoid, epithelioid and biphasic mesothelioma using immunohistochemical staining. These findings suggest that AHNAK has the potential to be a new marker for detecting mesothelioma. Since AHNAK is involved in cell migration and invasion in other metastatic tumor cells, we conducted migration and invasion assays in mesothelioma cell lines. The number of migrating cells in six of seven mesothelioma cell lines and the number of invading cells in all seven cell lines were significantly increased compared with those in MeT-5A. Knockdown of AHNAK significantly reduced the cell migration and invasion ability in all seven mesothelioma cell lines. These results support further clinical evaluation of the association of AHNAK and metastasis in mesothelioma.

Transferrin receptor (TfR) is an attractive molecule for targeted therapy of cancer. Various TfR-targeted therapeutic agents such as anti-TfR antibodies conjugated with anticancer agents have been developed. An antibody that recognizes both human and murine TfR is needed to predict the toxicity of antibody-based agents before clinical trials, there is no such antibody to date. In this study, a new fully human monoclonal antibody TSP-A18 that recognizes both human and murine TfR was developed and the correlation analysis of the radiolabeled antibody uptake and TfR expression in two murine strains was conducted. TSP-A18 was selected using extracellular portions of human and murine TfR from a human antibody library. The cross-reactivity of TSP-A18 with human and murine cells was confirmed by flow cytometry. Cell binding and competitive inhibition assays with [111In]TSP-A18 showed that TSP-A18 bound highly to TfR-expressing MIAPaCa-2 cells with high affinity. Biodistribution studies of [111In]TSP-A18 and [67Ga]citrate (a transferrin-mediated imaging probe) were conducted in C57BL/6J and BALB/c-nu/nu mice. [111In]TSP-A18 was accumulated highly in the spleen and bone containing marrow component of both strains, whereas high [67Ga]citrate uptake was only observed in bone containing marrow component and not in the spleen. Western blotting indicated the spleen showed the strongest TfR expression compared with other organs in both strains. There was significant correlation between [111In]TSP-A18 uptake and TfR protein expression in both strains, whereas there was significant correlation of [67Ga]citrate uptake with TfR expression only in C57BL/6J. These findings suggest that the difference in TfR expression between murine strains should be carefully considered when testing for the toxicity of anti-TfR antibody in mice and the uptake of anti-TfR antibody could reflect tissue TfR expression more accurately compared with that of transferrin-mediated imaging probe such as [67Ga]citrate.

Objective: 2-Deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) accumulates in tumors and also during active inflammation, including therapy-related inflammation. Additional PET tracers that are less avid to inflammation could be useful in differentiating cancer from inflammation and could complement the limitation of [18F]FDG-PET. 2-Amino-[3-11C]isobutyric acid ([3-11C]AIB) is a potential PET tracer for this purpose. We compared [3-11C]AIB and [18F]FDG uptakes in tumors and acute inflammation in a mouse model. \nMethods: Acute inflammatory lesions were induced in the hind legs of tumor-bearing mice by intramuscular injection of turpentine, and we conducted biodistribution and dynamic PET studies on [3-11C]AIB and [18F]FDG. \nResults: [3-11C]AIB tumor uptake increased with time and was statistically significantly higher than [18F]FDG uptake. In inflamed muscles, [3-11C]AIB uptake was statistically significantly lower than [18F]FDG uptake, and the tumor-to-inflammation ratio for [3-11C]AIB was statistically significantly higher than that for [18F]FDG. \nConclusion: [3-11C]AIB accumulates more selectively in tumor tissue than does [18F]FDG and thus has the potential of discriminating between tumors and inflammatory lesions better and of complementing the limitation of [18F]FDG.

Mesothelioma is an aggressive tumor caused by asbestos exposure, the incidence of which is predicted to increase globally. The prognosis of patients with mesothelioma undergoing conventional therapy is poor. Radiation therapy for mesothelioma is of limited use because of the intrinsic radioresistance of tumor cells compared with surrounding normal tissue. Thus, a novel molecular-targeted radiosensitizing agent that enhances the radiosensitivity of mesothelioma cells is required to improve the therapeutic efficacy of radiation therapy. ZDHHC8 knockdown reduces cell survival and induces an impaired G(2) /M checkpoint after X-irradiation in HEK293 cells. In the present study, we further analyzed the effect of the combination of ZDHHC8 knockdown and X-irradiation and assessed its therapeutic efficacy in mesothelioma models. SiRNA-induced ZDHHC8 knockdown in 211H and H2052 mesothelioma cells significantly reduced cell survival after X-irradiation. In 211H cells treated with ZDHHC8 siRNA and X-irradiation, the G(2) /M checkpoint was impaired and there was an increase in the number of cells with micronuclei, as well as apoptotic cells, in vitro. In 211H tumor-bearing mice, ZDHHC8 siRNA and X-irradiation significantly suppressed tumor growth, whereas ZDHHC8 siRNA alone did not. Immunohistochemical analysis showed decreased cell proliferation and induction of apoptosis in tumors treated with ZDHHC8 siRNA and X-irradiation, but not with ZDHHC8 siRNA alone. These results suggest that ZDHHC8 knockdown with X-irradiation induces chromosomal instability and apoptosis through the impaired G(2) /M checkpoint. In conclusion, the combination of ZDHHC8 siRNA and X-irradiation has the potential to improve the therapeutic efficacy of radiation therapy for malignant mesothelioma.

Introduction C-kit is an important diagnostic and therapeutic target molecule for several malignancies, and c-kit-targeted drugs have been used clinically. Because abundant c-kit expression in tumors is a prerequisite for successful c-kit-targeted therapy, imaging of c-kit expression is expected to play a pivotal role in the therapeutic decision for each patient. We evaluated 64 Cu-labeled Fab of anti-c-kit antibody 12A8 as a positron emission tomography (PET) imaging probe. Methods 111 In- or 125 I-Labeled 12A8 Fab was evaluated in vitro by cell binding, competitive inhibition and cellular internalization assays, and in vivo by biodistribution in mice bearing c-kit-expressing and -non-expressing tumors. Next, Fab fragment was labeled with the positron emitter 64 Cu and evaluated by PET. Results Radiolabeled 12A8 Fab showed specific binding to c-kit-expressing cells with high affinity and internalized into cells after binding to c-kit on cell surface. Although tumor accumulation of [ 111 In]Fab was lower than that of [ 111 In]IgG, the faster blood clearance of [ 111 In]Fab provided higher tumor-to-blood ratio at 6 h postinjection onwards. Blood clearance of 64 Cu-labeled 12A8 Fab was slower than that of [ 111 In]Fab, but PET using [ 64 Cu]Fab clearly visualized the tumor at 6 h postinjection onwards. Conclusion The 64 Cu-labeled 12A8 Fab could be used for c-kit-specific PET imaging and might help in selecting appropriate patients for c-kit-targeted treatments.

The use of tumor-suppressor gene p53 as an anticancer therapeutic has been vigorously investigated. However, progress has met with limited success to date. Some major drawbacks are the difficulty in achieving controllable and efficient gene transfer as well as in analyzing the transferred gene expression in real time and the treatment response in a timely manner. Thus, development of novel gene transfer vector with a regulative gene expression system coupled with the reporter gene, by which transgene can be monitored simultaneously, is critical. Moreover, noninvasive imaging-based assessment of the therapeutic response to exogenous wild-type p53 gene transfer is crucial for refining treatment protocols. In this study, as a simple preclinical model, we constructed a doxycycline-regulated bidirectional vector harboring a reporter gene encoding red fluorescence protein and p53. Then, we determined the controllable and simultaneously coordinated expression of both proteins and the p53-mediated anticancer effects in vitro and in vivo. Next, we observed that cells or tumors with induced p53 overexpression exhibited decreased uptake of [(14)C]FDG in cellular assay and [(18)F]FDG in positron emission tomography (PET) imaging. Thus, by coupling with bidirectional vector, controllable p53 transfer was achieved and the capability of fluoro-2-deoxy-D-glucose (FDG)-PET to assess the therapeutic response to p53 gene therapy was evidently confirmed, which may have an impact on the improvement of p53 gene therapy.

BACKGROUND Malignant mesothelioma is a highly aggressive form of cancer. Curative surgery is the only effective therapy for mesothelioma, and therefore early diagnosis is important. However, early diagnosis is difficult using current diagnostic imaging techniques, and a new imaging method for early diagnosis is urgently required. We evaluated the affinity of radiolabeled monoclonal antibodies to the C-terminal fragment of ERC/mesothelin for this purpose. METHODS In-labeled or I-labeled IgG against C-terminal fragment of ERC and its Fab fragment were evaluated in vitro by cell binding, competitive inhibition, and cellular internalization assays, and in vivo by biodistribution in mice bearing ERC-expressing tumors. Next, the Fab fragment was labeled with the positron emitter Cu and evaluated by positron emission tomography (PET). RESULTS Radiolabeled IgG and Fab showed specific binding to ERC-expressing mesothelioma cells with high affinity. Both radiolabeled IgG and Fab internalized into cells after binding to ERC on the cell surface. In-labeled IgG accumulated in ERC-expressing tumors and resulted in a moderate tumor-to-blood ratio at 4 days after injection. Furthermore, PET using Cu-labeled Fab visualized the tumor at 6 h after injection. CONCLUSION Cu-labeled Fab can be useful for ERC-specific PET imaging, and can thus facilitate improved diagnosis of patients with early-stage mesothelioma.

Acute allograft rejection remains a major complication after liver transplantation. We report a semiquantitative imaging method of detecting acute allograft rejection with 18F-FDG PET. Methods: Syngeneic and allogeneic transplanted rats, with or without immunosuppressive treatment, were subjected to serial PET. Autoradiography of the liver was conducted in both the syngeneic and the allogeneic rats. Results: A significant increment of 18F-FDG accumulation in liver allografts was observed by PET on day 2. The 18F-FDG signal was concentrated in the area where inflammatory cells around the vessels were detected by autoradiography. Allotransplanted rats treated with an immunosuppressive agent displayed a marked decrease in hepatic 18F-FDG uptake, compared with allotransplanted rats that were not treated. Conclusion:18F-FDG PET may be a valid method for facilitating the development of protocols to diagnose graft rejection and to monitor the efficacy of immunosuppressive therapy.

Genomic instability is considered a hallmark of carcinogenesis, and dysfunction of DNA repair and cell cycle regulation in response to DNA damage caused by ionizing radiation are thought to be important factors in the early stages of genomic instability. We performed cell-based functional screening using an RNA interference library targeting 200 genes in human cells. We identified three known and nine new radiation susceptibility genes, eight of which are linked directly or potentially with cell cycle progression. Cell cycle analysis on four of the genes not previously linked to cell cycle progression demonstrated that one, ZDHHC8, was associated with the G(2)/M checkpoint in response to DNA damage. Further study of the 12 radiation susceptibility genes identified in this screen may help to elucidate the molecular mechanisms of cell cycle progression, DNA repair, cell death, cell growth and genomic instability, and to develop new radiation sensitizing agents for radiotherapy.

Breast cancer is the most common cancer in women. Although advances in diagnostic imaging for early detection, surgical techniques and chemotherapy have improved overall survival, the prognosis of patients with metastatic breast cancer remains poor. Understanding cancer cell dynamics in the metastatic process is important to develop new therapeutic strategies. Experimental animal models and imaging would be powerful tools for understanding of the molecular events of multistep process of metastasis. In the present study, to develop a new cancer cell line that is applicable to bioluminescence and fluorescence imaging, we transfected the expression vector of a green fluorescent protein ZsGreen1 into a metastatic cell line 5a-D-Luc, which is a subclone of the MDA-MB-231 breast cancer cell line expressing luciferase, and established a new tumor cell line 5a-D-Luc-ZsGreen expressing both luciferase and ZsGreen1. The 5a-D-Luc-ZsGreen cells proliferate more rapidly and have a more invasive phenotype compared with 5a-D-Luc cells following intracardiac injection. Metastasis sites were easily detected in the whole body by bioluminescence imaging and in excised tissues by ex vivo fluorescence imaging. The fluorescence of 5a-D-Luc-ZsGreen cells was not lost after formalin fixation and decalcification. It enabled us to easily evaluate tumor spread and localization at the cellular level in microscopic analysis. The strong fluorescence of 5a-D-Luc-ZsGreen cells allowed for real-time imaging of circulating tumor cells in cerebral blood vessels of live animals immediately after intracardiac injection of cells using two-photon laser-scanning microscopy. These findings suggest that the 5a-D-Luc-ZsGreen cells would be a useful tool for research on mechanisms of metastatic process in animal models.

Preoperative noninvasive imaging to estimate the quantity and spatial distribution of protoporphyrin IX (PpIX) accumulation in tumors induced by 5-aminolevulinic acid (ALA) administration is expected to improve the efficacy of ALA-based fluorescence-guided resection and photo- and sonodynamic therapies. PpIX synthesis from exogenous ALA has been reported to be regulated by ALA influx or ALA dehydratase (ALAD) activity, which catalyzes the first step of the synthesis. In this study, we characterized the properties of a 11C-labeled ALA analog, 5-amino-4-oxo-[6-11C]hexanoic acid (11C-MALA), as a PET tracer to estimate PpIX accumulation. Methods: In vitro uptake of 11C-MALA and 3H-ALA was determined in 5 tumor cell lines after 10-min incubation with each tracer at 37°C. The expression levels of ALAD were determined by Western blot analysis. In vivo distribution and dynamic PET studies were conducted in tumor-bearing mice. In vitro and in vivo accumulation of ALA-induced PpIX was determined by measuring fluorescence in extracts of cells or tumors. Results: In vitro uptake of 11C-MALA in 5 tumor cell lines was correlated with ALAD expression levels and PpIX accumulation. In vivo biodistribution and dynamic PET studies showed that 11C-MALA was rapidly incorporated into tumors, and the tumor-to-muscle ratio of 11C-MALA at 1 min after injection was significantly correlated with that of 3H-ALA. 11C-MALA in tumors was continuously decreased thereafter, and the elimination rate of 11C-MALA from AsPC-1 tumors with the highest ALAD expression level was slower than from other tumors with lower expression levels. These results suggest that the influx and intracellular retention of 11C-MALA reflect ALA influx and ALAD expression levels, respectively. Tumor accumulation of 11C-MALA at 60 min after injection was strongly correlated with PpIX accumulation in tumor tissues. Conclusion:11C-MALA PET has the potential to noninvasively estimate the quantitative and spatial accumulation of exogenous ALA-induced PpIX.

INTRODUCTION: Pancreatic cancer is an aggressive cancer and its prognosis remains poor. Therefore, additional effective therapy is required to augment and/or complement current therapy. CD147, high expression in pancreatic cancer, is involved in the metastatic process and is considered a good candidate for targeted therapy. CD147-specfic imaging could be useful for selection of appropriate patients. Therefore, we evaluated the potential of a fully human anti-CD147 monoclonal antibody 059-053 as a new positron emission tomography (PET) probe for pancreatic cancer. METHODS: CD147 expression was evaluated in four pancreatic cancer cell lines (MIA Paca-2, PANC-1, BxPC-3, and AsPC-1) and a mouse cell line A4 as a negative control. Cell binding, competitive inhibition and internalization assays were conducted with (125)I-, (67)Ga-, or (89)Zr-labeled 059-053. In vivo biodistribution of (125)I- or (89)Zr-labeled 059-053 was conducted in mice bearing MIA Paca-2 and A4 tumors. PET imaging with [(89)Zr]059-053 was conducted in subcutaneous and orthotopic tumor mouse models. RESULTS: Among four pancreatic cancer cell lines, MIA Paca-2 cells showed the highest expression of CD147, while A4 cells had no expression. Immunohistochemical staining showed that MIA Paca-2 xenografts also highly expressed CD147 in vivo. Radiolabeled 059-053 specifically bound to MIA Paca-2 cells with high affinity, but not to A4. [(89)Zr]059-053 uptake in MIA Paca-2 tumors increased with time from 11.0±1.3% injected dose per gram (ID/g) at day 1 to 16.9±3.2% ID/g at day 6, while [(125)I]059-053 uptake was relatively low and decreased with time, suggesting that 059-053 was internalized into tumor cells in vivo and (125)I was released from the cells. PET with [(89)Zr]059-053 clearly visualized subcutaneous and orthotopic tumors. CONCLUSION: [(89)Zr]059-053 is a promising PET probe for imaging CD147 expression in pancreatic cancer and has the potential to select appropriate patients with CD147-expressing tumors who could gain benefit from anti-CD147 therapy.

Introduction Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor arising from the gastrointestinal tract and highly expresses mutated c-kit. We aimed to develop a specific and sensitive method for detecting GISTs using radiolabeled anti-c-kit monoclonal antibody. Methods A mutated c-kit-expressing cell clone was established by transfecting an expressing vector of mutated c-kit gene into HEK293 human embryonic kidney cells. The tumors were developed by inoculating c-kit-expressing cells into nude mice. 125 I- and 111 In-labeled anti-c-kit antibodies (12A8 and 41A11) were evaluated in vitro by cell binding, competitive inhibition and cellular internalization assays, and in vivo by biodistribution and imaging studies in tumor-bearing mice. Results Both 125 I- and 111 In-labeled antibodies showed specific binding with c-kit-expressing cells with high affinity (dissociation constants=2.2–7.1×10 9 M −1 ). Internalization assay showed that 125 I-labeled antibodies were rapidly internalized and dehalogenated, with the release of 125 I from the cells, resulting in reduction of cell-associated radioactivity with time. In contrast, 111 In-labeled antibody was internalized but did not result in the reduced radioactivity associated with tumor cells. Reflecting this phenomenon, the in vivo tumor uptake of 125 I-labeled antibody was low on Day 1, further decreasing with time, while tumor uptake of 111 In-labeled antibody was high on Day 1, further increasing with time. The xenografted tumor was clearly visualized by scintigraphy after injection of 111 In-labeled antibody. Conclusion The anti-c-kit monoclonal antibody labeled with a metal radionuclide would be promising for c-kit-targeted imaging of GISTs.

Introduction Malignant mesothelioma is a highly aggressive tumor originating in the pleura, peritoneum and pericardium, and the prognosis of patients undergoing current treatment remains poor. To develop new therapies, it is important to have a noninvasive imaging system for evaluating the efficacy of such prospective treatments. We have established clinically relevant mouse models and evaluated conventional and novel positron emission tomography (PET) tracers. Methods Epithelioid and sarcomatoid mesothelioma cells were inoculated subcutaneously and intrapleurally into nude mice. Biodistribution and PET imaging studies were conducted by injecting [ 18 F]fluoro-2-deoxy-d-glucose (FDG), 3′-[ 18 F]fluoro-3′-doxythymidine (FLT) or 4′-methyl-[ 11 C]thiothymidine (S-dThd) into the mouse models. In vitro cellular uptake of [ 14 C]FDG and [ 3 H]FLT and thymidine kinase 1 (TK 1 ) activity in both cell lines were measured. Expression of glucose transporter 1 (GLUT-1) and Ki-67 in xenografted tumors was evaluated by immunohistochemical staining. Results In epithelioid mesothelioma models, biodistribution experiments showed that tumor uptake of [ 11 C]S-dThd was significantly higher than that of [ 18 F]FDG. On the other hand, in sarcomatoid models, [ 18 F]FDG showed significantly higher accumulation than the other two tracers. These differential uptakes of the three tracers were confirmed by PET imaging. The cellular uptake of [ 14 C]FDG and [ 3 H]FLT and TK 1 activity in sarcomatoid cells were higher than those of epithelioid cells. GLUT-1 protein was strongly expressed in sarcomatoid but not in epithelioid tumor. We observed a high percentage of Ki-67-positive cells in both epithelioid and sarcomatoid tumors. Conclusions We established nude mouse models of epithelioid and sarcomatoid subtypes of mesothelioma. PET tracers applicable for the evaluation of epithelioid and sarcomatoid mesothelioma would vary: [ 18 F]FLT and [ 11 C]S-dThd seemed suitable for the epithelioid subtype and [ 18 F]FDG seemed suitable for the sarcomatoid subtype in our mouse models. Our results indicated that cellular uptake and TK 1 activity in vitro are not always consistent with tracer uptake of [ 18 F]FLT and [ 11 C]S-dThd in vivo. These mouse models and PET imaging might be useful tools for evaluating new and effective treatments in mesothelioma.

Radiotherapy can cause unacceptable levels of damage to normal tissues in some cancer patients. To understand the molecular mechanisms underlying radiation-induced physiological responses, and to be able to predict the radiation susceptibility of normal tissues in individual patients, it is important to identify a comprehensive set of genes responsible for radiation susceptibility. We have developed a simple and rapid 96-well screening protocol using cell proliferation assays and RNA interference to identify genes associated with radiation susceptibility. We evaluated the performance of alamarBlue-, BrdU-, and sulforhodamine B-based cell proliferation assays using the 96-well format. Each proliferation assay detected the known radiation susceptibility gene, PRKDC. In a trial screen using 28 shRNA vectors, another known gene, CDKN1A, and one new radiation susceptibility gene, ATP5G3, were identified. Our results indicate that this method may be useful for large-scale screens designed to identify novel radiation susceptibility genes.

Malignant mesothelioma is a highly aggressive tumor arising from serosal surfaces of the pleura and is triggered by past exposure to asbestos. Currently, there is no widely accepted treatment for mesothelioma. Development of effective drug treatments for human cancers requires identification of therapeutic molecular targets. We therefore conducted a large-scale functional screening of mesothelioma cells using a genome-wide small interfering RNA library. We determined that knockdown of 39 genes suppressed mesothelioma cell proliferation. At least seven of the 39 genes— COPA, COPB2, EIF3D, POLR2A, PSMA6, RBM8A , and RPL18A —would be involved in anti-apoptotic function. In particular, the COPA protein was highly expressed in some mesothelioma cell lines but not in a pleural mesothelial cell line. COPA knockdown induced apoptosis and suppressed tumor growth in a mesothelioma mouse model. Therefore, COPA may have the potential of a therapeutic target and a new diagnostic marker of mesothelioma.