Comparison of conventional and novel PET tracers for imaging mesothelioma in nude mice with subcutaneous and intrapleural xenografts

Efficacy Evaluation of Combination Treatment Using Gemcitabine and Radioimmunotherapy with 90Y-Labeled Fully Human Anti-CD147 Monoclonal Antibody 059-053 in a BxPC-3 Xenograft Mouse Model of Refractory Pancreatic Cancer

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.

Antitumor effects of radionuclide treatment using α-emitting meta-211At-astato-benzylguanidine in a PC12 pheochromocytoma model

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 < 0.01). In addition, the mice treated with 0.28, 0.56 and 1.11 MBq of ²¹¹At-MABG showed only a temporary weight reduction, with recovery in weight by day 10.

CONCLUSION

²¹¹At-MABG exhibited a strong tumor volume-reducing effect in a mouse model of pheochromocytoma without weight reduction. Therefore, ²¹¹At-MABG might be an effective therapeutic agent for the treatment of malignant pheochromocytoma.

Evaluation of DNA synthesis with carbon-11-labeled 4′-thiothymidine

In the cancer research field, the preferred method for evaluating the proliferative activity of cancer cells in vivo is to measure DNA synthesis rates. The cellular proliferation rate is one of the most important cancer characteristics, and represents the gold standard of pathological diagnosis. Positron emission tomography (PET) has been used to evaluate in vivo DNA synthetic activity through visualization of enhanced nucleoside metabolism. However, methods for the quantitative measurement of DNA synthesis rates have not been fully clarified. Several groups have been engaged in research on 4′-[methyl-¹¹C]-thiothymidine (¹¹C-4DST) in an effort to develop a PET tracer that allows quantitative measurement of in vivo DNA synthesis rates. This mini-review summarizes the results of recent studies of the in vivo measurement of cancer DNA synthesis rates using ¹¹C-4DST.

Blockade of aquaporin 1 inhibits proliferation, motility, and metastatic potential of mesothelioma in vitro but not in an in vivo model

BACKGROUND

Malignant mesothelioma (MM) is an aggressive tumor of the serosal membranes, mostly the pleura. It is related to asbestos exposure and has a poor prognosis. MM has a long latency period, and incidence is predicted to remain stable or increase until 2020. Currently, no biomarkers for a specific targeted therapy are available. Previously, we observed that expression of aquaporin 1 (AQP1) was an indicator of prognosis in two independent cohorts. Here we determine whether AQP1 inhibition has therapeutic potential in the treatment of MM.

METHODS

Functional studies were performed with H226 cells and primary MM cells harvested from pleural effusions. AQP1 expression and mesothelial phenotype was determined by immunohistochemistry. AQP1 function was inhibited by a pharmacological blocker (AqB050) or AQP1-specific siRNA. Cell proliferation, migration, and anchorage-independent cell growth were assessed. A nude mouse heterotopic xenograft model of MM was utilised for the in vivo studies.

RESULTS

Inhibition of AQP1 significantly decreases cell proliferation, metastatic potential, and motility without inducing nonspecific cytotoxicity or increasing apoptosis. In vivo blockade of AQP1 had no biologically significant effect on growth of established tumours.

CONCLUSIONS

Targeted blockade of AQP1 restricts MM growth and migration in vitro. Further work is warranted to fully evaluate treatment potential in vivo.

Quantifying initial cellular events of mouse radiation lymphomagenesis and its tumor prevention in vivo by positron emission tomography and magnetic resonance imaging

Radiation-induced thymic lymphoma (RITL) in mice is induced by fractionated whole-body X-irradiation (FX) and has served as a useful model for studying radiation carcinogenesis. In this model, the initial postirradiation cellular events in the thymus and bone marrow (BM) are critically important for tumorigenesis, and BM transplantation (BMT) prevents RITL. However, direct assessment of these events is so far restricted by the lack of noninvasive monitoring techniques. Here, we have developed positron emission tomography (PET) and magnetic resonance imaging (MRI) methods to quantify the events critical for RITL development and the effects of BMT in living animals. Apparent diffusion coefficients (ADCs) were calculated from diffusion-weighted MRI to evaluate the changes in the BM of mice receiving FX. ADC values dramatically changed in the irradiated BM, corresponding to pathological findings of the irradiated BM, returning to normal levels following BMT sooner than with spontaneous recovery. PET with 4'-[methyl-(11)C]thiothymidine, a novel tracer for cell proliferation, revealed that the irradiated thymus showed significantly higher tracer uptake than the unirradiated thymus 1 week after FX. Interestingly, its increased uptake was completely abolished by BMT, even with very few donor-derived cells in the thymus. Thereafter, the thymus receiving BMT had significantly increased tracer uptake. These findings suggest that BMT first suppresses FX-induced aberrant thymocyte proliferation and then accelerates thymic regeneration. This study demonstrates the feasibility of using PET and MRI for noninvasive monitoring of tumorigenic cellular processes in an animal model of radiation-induced cancer.

Downregulation of thymidylate synthase and E2F1 by arsenic trioxide in mesothelioma

Malignant pleural mesothelioma is a global health issue. Arsenic trioxide (ATO) has been shown to suppress thymidylate synthase (TYMS) in lung adenocarcinoma and colorectal cancer, and induce apoptosis in acute promyelocytic leukemia. With TYMS as a putative therapeutic target, the effect of ATO in mesothelioma was therefore studied. A panel of 5 mesothelioma cell lines was used to study the effect of ATO on cell viability, protein expression, mRNA expression and TYMS activity by MTT assay, western blot, qPCR and tritium-release assay, respectively. The knockdown of TYMS and E2F1 was performed with a specific siRNA. Phosphatidylserine externalization and mitochondrial membrane depolarization were measured by Annexin V and JC-1 staining respectively. The in vivo effect of ATO was studied using a nude mouse xenograft model. Application of ATO demonstrated anticancer effects in the cell line model with clinically achievable concentrations. Downregulation of TYMS protein (except H226 cells and 1.25 µM ATO in H2052 cells) and mRNA expression (H28 cells), pRB1 (H28 cells) and E2F1 and TYMS activity (except H226 cells) were also evident. E2F1 knockdown decreased cell viability more significantly than TYMS knockdown. In general, thymidine kinase 1, ribonucleotide reductase M1, c-myc and skp2 were downregulated by ATO. p-c-Jun was downregulated in H28 cells while upregulated in 211H cells. Phosphatidylserine externalization, mitochondrial membrane depolarization, downregulation of Bcl-2 and Bcl-xL, and upregulation of Bak and cleaved caspase-3 were observed. In the H226 xenograft model, the relative tumor growth was aborted, and E2F1 was downregulated while cleaved caspase-3 was elevated and localized to the nucleus in the ATO treatment group. ATO has potent antiproliferative and cytotoxic effects in mesothelioma in vitro and in vivo, partially mediated through E2F1 targeting (less effect through TYMS targeting). There is sound scientific evidence to support the clinical application of ATO in treatment of mesothelioma.

Translational advances in pleural malignancies

Pleural malignancies, including primary malignant pleural mesothelioma and secondary pleural metastasis of various tumours resulting in malignant pleural effusion, are frequent and lethal diseases that deserve devoted translational research efforts for improvements to be introduced to the clinic. This paper highlights select clinical advances that have been accomplished recently and that are based on preclinical research on pleural malignancies. Examples are the establishment of folate antimetabolites in mesothelioma treatment, the use of PET in mesothelioma management and the discovery of mesothelin as a marker of mesothelioma. In addition to established translational advances, this text focuses on recent research findings that are anticipated to impact clinical pleural oncology in the near future. Such progress has been substantial, including the development of a genetic mouse model of mesothelioma and of transplantable models of pleural malignancies in immunocompetent hosts, the deployment of stereological and imaging methods for integral assessment of pleural tumour burden, as well as the discovery of the therapeutic potential of aminobiphosphonates, histone deacetylase inhibitors and ribonucleases against malignant pleural disease. Finally, key obstacles to overcome towards a more rapid advancement of translational research in pleural malignancies are outlined. These include the dissection of cell-autonomous and paracrine pathways of pleural tumour progression, the study of mesothelioma and malignant pleural effusion separately from other tumours at both the clinical and preclinical levels, and the expansion of tissue banks and consortia of clinical research of pleural malignancies.

A Multimodality Imaging Review of Malignant Pleural Mesothelioma Response Assessment

Assessment of response is important to interpret early phase clinical trial results and to guide individual patient management. In malignant pleural mesothelioma (MPM), the circumferential growth pattern of the disease, the presence of pleural effusion and atelectasis, and the common use of pleurodesis make this a challenging task for imaging specialists and clinicians. This article reviews the current evidence for radiological and positron emission tomography (PET) response assessment in MPM, and the pitfalls and challenges in its application. Current research and future directions in radiological and PET response are discussed, including the use of novel radiotracers.

Multimodality Imaging Review of Malignant Pleural Mesothelioma Diagnosis and Staging

Early diagnosis and accurate disease staging in patients with malignant pleural mesothelioma (MPM) are essential in classifying such patients into prognostic subgroups to allow delivery of stage-specific therapies. This review addresses the current status of multimodality imaging in the diagnosis and staging of MPM. Clinical, research, and future directions in computed tomography (CT), magnetic resonance imaging, and PET/CT diagnosis and staging of MPM are discussed, including the use of novel PET probes. The article concludes with important take-home messages summarized as the pearls and pitfalls of each diagnostic modality in the diagnosis and staging of patients with MPM.

Highly efficient syntheses of [methyl-11C]thymidine and its analogue 4'-[methyl-11C]thiothymidine as nucleoside PET probes for cancer cell proliferation by Pd(0)-mediated rapid C-[11C]methylation

Pd(0)-mediated rapid couplings of CH(3)I (and then [(11)C]CH(3)I) with excess 5-tributylstannyl-2'-deoxyuridine and -4'-thio-2'-deoxyuridine were investigated for the syntheses of [methyl-(11)C]thymidine and its stable analogue, 4'-[methyl-(11)C]thiothymidine as PET probes for cancer diagnosis. The previously reported conditions were attempted using Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3) (1 : 4 in molar ratio) at 130 °C for 5 min in DMF, giving desired products only in 32 and 30% yields. Therefore, we adapted the current reaction conditions developed in our laboratory for heteroaromatic compounds. The reaction using CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1 : 25 : 1 : 32 : 2 : 5) at 80 °C gave thymidine in 85% yield. Whereas, CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuBr/CsF (1 : 25 : 1 : 32 : 2 : 5) including another CuBr/CsF system promoted the reaction at a milder temperature (60 °C), giving thymidine in 100% yield. Chemo-response of thiothymidine-precursor was different from thymidine system. Thus, the above optimized conditions including CuBr/CsF system gave 4'-thiothymidine only in 40% yield. The reaction using 5-fold amount of CuBr/CsF at 80 °C gave much higher yield (83%), but unexpectedly, the reaction was accompanied by a considerable amount of undesired destannylated product. Such destannylation was greatly suppressed by changing to a CuCl/K(2)CO(3) system using CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1 : 25 : 1 : 32 : 2 : 5) at 80 °C, giving the 4'-thiothymidine in 98% yield. The each optimized conditions were successfully applied to the syntheses of the corresponding PET probes in 87 and 93% HPLC analytical yields. [(11)C]Compounds were isolated by preparative HPLC after the reaction conducted under slightly improved conditions, exhibiting sufficient radioactivity of 3.7-3.8 GBq and specific radioactivity of 89-200 GBq µmol(-1) with radiochemical purity of ≥99.5% for animal and human PET studies.

Novel human single chain antibody fragments that are rapidly internalizing effectively target epithelioid and sarcomatoid mesotheliomas

Human antibodies targeting all subtypes of mesothelioma could be useful to image and treat this deadly disease. Here we report tumor targeting of a novel internalizing human single chain antibody fragment (scFv) labeled with (⁹⁹m)Tc ((⁹⁹m)Tc-M40) in murine models of mesothelioma of both epithelioid (M28) and sarcomatoid (VAMT-1) origins. (⁹⁹m)Tc-M40 was taken up rapidly and specifically by both subtype tumor cells in vitro, with 68% to 92% internalized within 1 hour. The specificity of binding was evidenced by blocking (up to 95%) with 10-fold excess of unlabeled M40. In animal studies, tumors of both subtypes were clearly visualized by SPECT/CT as early as 1 hour postinjection of (⁹⁹m)Tc-M40. Tumor uptake measured as percent of injected dose per gram tissue (%ID/g) at 3 hours was 4.38 and 5.84 for M28 and VAMT-1 tumors, respectively, significantly greater than all organs or tissues studied (liver, 2.62%ID/g; other organs or tissues <1.7%ID/g), except the kidneys (130.7%ID/g), giving tumor-to-blood ratios of 5:1 and 7:1 and tumor-to-muscle ratios of 45:1 and 60:1, for M28 and VAMT-1, respectively. The target-mediated uptake was confirmed by a nearly 70% reduction in tumor activity following administration of 10-fold excess of unlabeled scFv. Taken together, these results indicate that M40 can rapidly and specifically target epithelioid and sarcomatoid tumor cells, demonstrating the potential of this agent as a versatile targeting ligand for imaging and therapy of all subtypes of mesothelioma.

Development of positron emission tomography probe of 64Cu-labeled anti-C-kit 12A8 Fab to measure protooncogene C-kit expression

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.

Development of positron emission tomography imaging by 64Cu-labeled Fab for detecting ERC/mesothelin in a mesothelioma mouse model

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.

C-kit-targeted imaging of gastrointestinal stromal tumor using radiolabeled anti-c-kit monoclonal antibody in a mouse tumor model

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 = 2.2-7.1x10(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.