90Y-Daclizumab (Anti-CD25), High-Dose Carmustine, Etoposide, Cytarabine, and Melphalan Chemotherapy and Autologous Hematopoietic Stem Cell Transplant Yielded Sustained Complete Remissions in 4 Patients with Recurrent Hodgkin's Lymphoma.

Background: Despite advances in therapy of Hodgkin's lymphoma (HL), a proportion of patients will not respond or relapse. The authors had previously identified CD25, IL-2Rα, as a target for systemic radioimmunotherapy of HL since most normal cells do not express CD25, but it is expressed by a minority of Hodgkin/Reed-Sternberg (HRS) cells and most Tregs rosetting around HRS cells. Study Design and Treatment: This was a single institution, nonrandomized, open-label phase I/II trial of radiolabeled 90Y-daclizumab, an anti-CD25 monoclonal antibody, BEAM (carmustine, etoposide, cytarabine, and melphalan) conditioning treatment followed by autologous hematopoietic stem cell transplant (ASCT). Four patients with refractory and relapsed HL were treated in this trial with 3 patients receiving a single dose of 564.6-574.6 MBq 90Y-daclizumab and the fourth patient receiving two doses of 580.9-566.1 MBq 90Y-daclizumab followed by high-dose chemotherapy and ASCT. Results: All 4 evaluable patients treated with 90Y-daclizumab obtained complete responses (CRs) that are ongoing 4.5-7 years following their stem cell transplant. The spectrum and severity of adverse events were mild and more importantly none of the patients, including several with multiple therapies before this treatment, developed the myelodysplastic syndrome. Discussion: Targeting by daclizumab was not directed primarily at tumor cells, but rather the nonmalignant CD25-expressing T cells adjacent to the HRS cells and 90Y-daclizumab provided strong enough ß emissions to kill CD25-negative tumor cells at a distance by a crossfire effect. Furthermore, the strong ß irradiation killed normal cells in the tumor microenvironment. Conclusions: 90Y-daclizumab (anti-CD25), high-dose BEAM chemotherapy and ASCT was well tolerated and yielded sustained complete remissions in all 4 patients with recurrent HL patients who completed their treatment. Significance: Despite advances, a proportion of patients with HL will not have a CR to their initial treatment, and some with CRs will relapse. They demonstrated that the addition of 90Y-daclizumab into the preconditioning regimen for refractory and relapsed HL patients with high-dose BEAM chemotherapy and ASCT provided sustained CRs in the 4 patients studied. Two of these patients were highly refractory to multiple prior treatments with bulky disease at entry into this study, including 1 patient who never entered a remission and had failed 6 different therapeutic regimens. Despite the small number of patients treated in this study, the sustained clinical benefit in these patients indicates a highly effective treatment. The daclizumab was directed primarily not at HRS cells themselves but toward nonmalignant T cells rosetting around malignant cells. 90Y provided strong ß emissions that killed antigen nonexpressing tumor cells at a distance by a crossfire effect. Furthermore, the strong ß radiation killed normal cells in the tumor microenvironment that nurtured the malignant cells in the lymphomatous mass. The present study supports expanded analysis of 90Y-daclizumab as part of the regimen of ASCT in patients with refractory and relapsed HL.

Correction: Screening of cancer tissue arrays identifies CXCR4 on adrenocortical carcinoma: correlates with expression and quantification on metastases using 64Cu-plerixafor PET.

[This corrects the article DOI: 10.18632/oncotarget.19945.].

Tumor-Shed Antigen Affects Antibody Tumor Targeting: Comparison of Two 89Zr-Labeled Antibodies Directed against Shed or Nonshed Antigens.

We investigated the effect of shed antigen mesothelin on the tumor uptake of amatuximab, a therapeutic anti-mesothelin mAb clinically tested in mesothelioma patients. The B3 mAb targeting a nonshed antigen was also analyzed for comparison. The mouse model implanted with A431/H9 tumor, which expresses both shed mesothelin and nonshed Lewis-Y antigen, provided an ideal system to compare the biodistribution and PET imaging profiles of the two mAbs. Our study demonstrated that the tumor and organ uptakes of 89Zr-B3 were dose-independent when 3 doses, 2, 15, and 60 µg B3, were compared at 24 h after injection. In contrast, tumor and organ uptakes of 89Zr-amatuximab were dose-dependent, whereby a high dose (60 µg) was needed to achieve tumor targeting comparable to the low dose (2 µg) of 89Zr-B3, suggesting that shed mesothelin may affect amatuximab tumor targeting as well as serum half-life. The autoradiography analysis showed that the distribution of 89Zr-B3 was nonuniform with the radioactivity primarily localized at the tumor periphery independent of the B3 dose. However, the autoradiography analysis for 89Zr-amatuximab showed dose-dependent distribution profiles of the radiolabel; at 10 µg dose, the radiolabel penetrated toward the tumor core with its activity comparable to that at the tumor periphery, whereas at 60 µg dose, the distribution profile became similar to those of 89Zr-B3. These results suggest that shed antigen in blood may act as a decoy requiring higher doses of mAb to improve serum half-life as well as tumor targeting. Systemic mAb concentration should be at a severalfold molar excess to the shed Ag in blood to overcome the hepatic processing of mAb-Ag complexes. On the other hand, mAb concentration should remain lower than the shed Ag concentration in the tumor ECS to maximize tumor penetration by passing binding site barriers.

Screening of cancer tissue arrays identifies CXCR4 on adrenocortical carcinoma: correlates with expression and quantification on metastases using 64Cu-plerixafor PET.

Expression of the chemokine receptor CXCR4 by many cancers correlates with aggressive clinical behavior. As part of the initial studies in a project whose goal was to quantify CXCR4 expression on cancers non-invasively, we examined CXCR4 expression in cancer samples by immunohistochemistry using a validated anti-CXCR4 antibody. Among solid tumors, we found expression of CXCR4 on significant percentages of major types of kidney, lung, and pancreatic adenocarcinomas, and, notably, on metastases of clear cell renal cell carcinoma and squamous cell carcinoma of the lung. We found particularly high expression of CXCR4 on adrenocortical cancer (ACC) metastases. Microarrays of ACC metastases revealed correlations between expression of CXCR4 and other chemokine system genes, particularly CXCR7/ACKR3, which encodes an atypical chemokine receptor that shares a ligand, CXCL12, with CXCR4. A first-in-human study using 64Cu-plerixafor for PET in an ACC patient prior to resection of metastases showed heterogeneity among metastatic nodules and good correlations among PET SUVs, CXCR4 staining, and CXCR4 mRNA. Additionally, we were able to show that CXCR4 expression correlated with the rates of growth of the pulmonary lesions in this patient. Further studies are needed to understand better the role of CXCR4 in ACC and whether targeting it may be beneficial. In this regard, non-invasive methods for assessing CXCR4 expression, such as PET using 64Cu-plerixafor, should be important investigative tools.

Pharmacokinetics and microbiodistribution of 64Cu-labeled collagen-binding peptides in chronic myocardial infarction.

OBJECTIVES: The aim of the study is to evaluate the pharmacokinetics and microbiodistribution of Cu-labeled collagen-binding peptides. METHODS: The affinity constant (KD), association (ka), and dissociation rate constant (kd) for the peptide collagelin or its analog (named CRPA) binding to collagen were measured by biolayer interferometric analysis. Rats (n=4-5) with myocardial infarction or normal were injected intravenously with the Cu-labeled peptides or Cu-DOTA as a control. Dynamic PET imaging was performed for 60 min at 7-8 weeks after infarct. Fluorine-18 fluorodeoxyglucose PET imaging was performed to identify the viable myocardium. To validate the PET images, slices of heart samples from the base to the apex were analyzed using autoradiography and histology. RESULT: The peptides bound to collagen with a KD of ∼0.9 µmol/l. The Cu-peptides and Cu-DOTA accumulated in the infarct area (confirmed by autoradiography and histology images) within 1 min of injection and were excreted rapidly through the renal system. The blood clearance curves were biphasic with elimination half-lives of 21.9±2.4, 26.2±4.6, and 21.2±2.1 min for Cu-CRPA, Cu-collagelin, and the control Cu-DOTA, respectively. The clearance half-lives from the focal fibrotic tissue (24.1±1.5, 25.6±8.0, and 21.4±1.3 min, respectively) and remote myocardium (20.8±0.7, 21.0±5.5, and 19.1±2.4 min, respectively) were not significantly different. The uptake ratios of infarct-to-remote myocardium (1.93±0.18, 2.15±0.38, and 1.88±0.08, respectively) for Cu-CRPA, Cu-collagelin, and Cu-DOTA remained stable for the time period between 10 and 60 min. CONCLUSION: The distribution of the Cu-collagelin probes corresponds to the heterogeneous distribution of expanded extracellular space in the setting of myocardial infarction. The overall washout rate from the fibrous tissue was determined by the slow washout rate (t1/2≥20 min) of the peptides from the extracellular space to the vasculature, not by the dissociation rate (t1/2<2 min) of the Cu-peptides from collagen.

Activatable iRGD-based peptide monolith: Targeting, internalization, and fluorescence activation for precise tumor imaging.

A disulfide-bridged cyclic RGD peptide, named iRGD (internalizing RGD, c(CRGDK/RGPD/EC)), is known to facilitate tumor targeting as well as tissue penetration. After the RGD motif-induced targeting on αv integrins expressed near tumor tissue, iRGD encounters proteolytic cleavage to expose the CendR motif that promotes penetration into cancer cells via the interaction with neuropilin-1. Based on these proteolytic cleavage and internalization mechanism, we designed an iRGD-based monolithic imaging probe that integrates multiple functions (cancer-specific targeting, internalization and fluorescence activation) within a small peptide framework. To provide the capability of activatable fluorescence signaling, we conjugated a fluorescent dye to the N-terminal of iRGD, which was linked to the internalizing sequence (CendR motif), and a quencher to the opposite C-terminal. It turned out that fluorescence activation of the dye/quencher-conjugated monolithic peptide probe requires dual (reductive and proteolytic) cleavages on both disulfide and amide bond of iRGD peptide. Furthermore, the cleavage of the iRGD peptide leading to fluorescence recovery was indeed operative depending on the tumor-related angiogenic receptors (αvß3 integrin and neuropilin-1) in vitro as well as in vivo. Compared to an 'always fluorescent' iRGD control probe without quencher conjugation, the dye/quencher-conjugated activatable monolithic peptide probe visualized tumor regions more precisely with lower background noise after intravenous injection, owing to the multifunctional responses specific to tumor microenvironment. All these results, along with minimal in vitro and in vivo toxicity profiles, suggest potential of the iRGD-based activatable monolithic peptide probe as a promising imaging agent for precise tumor diagnosis.

64Cu-DOTA as a surrogate positron analog of Gd-DOTA for cardiac fibrosis detection with PET: pharmacokinetic study in a rat model of chronic MI.

OBJECTIVES: The aim of this study was to investigate the pharmacokinetics of (64)Cu-DOTA (1,4,7,10-azacyclododecane-N,N',N'',N'''-tetraacetic acid), a positron surrogate analog of the late gadolinium (Gd)-enhancement cardiac magnetic resonance agent, Gd-DOTA, in a rat model of chronic myocardial infarction (MI) and its microdistribution in the cardiac fibrosis by autoradiography. METHODS: DOTA was labeled with (64)Cu-acetate. CD rats (n=5) with MI by left anterior descending coronary artery ligation and normal rats (n=6) were injected intravenously with (64)Cu-DOTA (18.5 MBq, 0.02 mmol DOTA/kg). Dynamic PET imaging was performed for 60 min after injection. (18)F-Fluorodeoxyglucose ([(18)F]-FDG) PET imaging was performed to identify the viable myocardium. For the region of interest analysis, the (64)Cu-DOTA PET image was coregistered to the [(18)F]-FDG PET image. To validate the PET images, slices of heart samples from the base to the apex were analyzed using autoradiography and by histological staining with Masson's trichrome. RESULTS: (64)Cu-DOTA was rapidly taken up in the infarct area. The time-activity curves demonstrated that (64)Cu-DOTA concentrations in the blood, fibrotic tissue, and perfusion-rich organs peaked within a minute post injection; thereafter, it was rapidly washed out in parallel with blood clearance and excreted through the renal system. The blood clearance curve was biphasic, with a distribution half-life of less than 3 min and an elimination half-life of ∼21.8 min. The elimination half-life of (64)Cu-DOTA from the focal fibrotic tissue (∼22.4 min) and the remote myocardium (∼20.1 min) was similar to the blood elimination half-life. Consequently, the uptake ratios of focal fibrosis-to-blood and remote myocardium-to-blood remained stable for the time period between 10 and 60 min. The corresponding ratios obtained from images acquired from 30 to 60 min were 1.09 and 0.59, respectively, indicating that the concentration of (64)Cu-DOTA in the focal fibrosis was 1.85 (1.09/0.59) times greater than that in the remote myocardium. Thus, this finding indicates that the extracellular volume fraction was 1.85 times greater in the focal fibrosis than in the remote myocardium. The accumulation of (64)Cu-DOTA in fibrotic tissue was further supported by autoradiography and histology images. The autoradiography images of (64)Cu-DOTA in the fibrotic tissues were qualitatively superimposed over the histology images of the fibrotic tissues. The histology images of the infarct areas were characterized by a heterogeneous distribution of thin bands of fibrotic collagen, myocytes, and expanded extracellular space. CONCLUSION: (64)Cu-DOTA is a useful surrogate positron analog of Gd-DOTA, enabling quantitative measurement of the uptake values in fibrotic tissues by dynamic PET imaging and calculation of the extracellular volume fractions of the fibrotic tissues. At a microscopic level, the distribution of (64)Cu-DOTA is nonuniform, corresponding to the heterogeneous distribution of expanded extracellular space in the setting of MI.

Discordance in lymphoid tissue recovery following stem cell transplantation in rhesus macaques: an in vivo imaging study.

Ionizing irradiation is used routinely to induce myeloablation and immunosuppression. However, it has not been possible to evaluate the extent of ablation without invasive biopsy. For lymphoid recovery, peripheral blood (PB) lymphocytes (PBLs) have been used for analysis, but they represent <2% of cells in lymphoid tissues (LTs). Using a combination of single-photon emission computed tomography imaging and a radiotracer ((99m)Tc-labeled rhesus immunoglobulin G1 anti-CD4R1 (Fab')2), we sequentially imaged CD4(+) cell recovery in rhesus macaques following total body irradiation (TBI) and reinfusion of vector-transduced, autologous CD34(+) cells. Our results present for the first time a sequential, real-time, noninvasive method to evaluate CD4(+) cell recovery. Importantly, despite myeloablation of circulating leukocytes following TBI, total depletion of CD4(+) lymphocytes in LTs such as the spleen is not achieved. The impact of TBI on LTs and PBLs is discordant, in which as few as 32.4% of CD4(+) cells were depleted from the spleen. In addition, despite full lymphocyte recovery in the spleen and PB, lymph nodes have suboptimal recovery. This highlights concerns about residual disease, endogenous contributions to recovery, and residual LT damage following ionizing irradiation. Such methodologies also have direct application to immunosuppressive therapy and other immunosuppressive disorders, such as those associated with viral monitoring.

90Y-daclizumab, an anti-CD25 monoclonal antibody, provided responses in 50% of patients with relapsed Hodgkin's lymphoma.

Despite significant advances in the treatment of Hodgkin's lymphoma (HL), a significant proportion of patients will not respond or will subsequently relapse. We identified CD25, the IL-2 receptor alpha subunit, as a favorable target for systemic radioimmunotherapy of HL. The scientific basis for the clinical trial was that, although most normal cells with exception of Treg cells do not express CD25, it is expressed by a minority of Reed-Sternberg cells and by most polyclonal T cells rosetting around Reed-Sternberg cells. Forty-six patients with refractory and relapsed HL were evaluated with up to seven i.v. infusions of the radiolabeled anti-CD25 antibody (90)Y-daclizumab. (90)Y provides strong ß emissions that kill tumor cells at a distance by a crossfire effect. In 46 evaluable HL patients treated with (90)Y-daclizumab there were 14 complete responses and nine partial responses; 14 patients had stable disease, and nine progressed. Responses were observed both in patients whose Reed-Sternberg cells expressed CD25 and in those whose neoplastic cells were CD25(-) provided that associated rosetting T cells expressed CD25. As assessed using phosphorylated H2AX (γ-H2AX) as a bioindicator of the effects of radiation exposure, predominantly nonmalignant cells in the tumor microenvironment manifested DNA damage, as reflected by increased expression of γ-H2AX. Toxicities were transient bone-marrow suppression and myelodysplastic syndrome in six patients who had not been evaluated with bone-marrow karyotype analyses before therapy. In conclusion, repeated (90)Y-daclizumab infusions directed predominantly toward nonmalignant T cells rosetting around Reed-Sternberg cells provided meaningful therapy for select HL patients.

Tumor and organ uptake of (64)Cu-labeled MORAb-009 (amatuximab), an anti-mesothelin antibody, by PET imaging and biodistribution studies.

OBJECTIVES: To investigate the effect of the injection dose of MORAb-009 (amatuximab, an anti-mesothelin monoclonal antibody), the tumor size and the level of shed mesothelin on the uptake of the antibody in mesothelin-positive tumor and organs by biodistribution (BD) and positron emission tomography (PET) imaging studies. METHODS: 2-S-(4-Isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) was conjugated to amatuximab and labeled with (64)CuCl2 in 0.25 M acetate buffer, pH4.2. The resulting (64)Cu-NOTA-amatuximab was purified with a PD 10 column. To investigate the dose effect or the effect of tumor size, the BD was performed in groups of nude mice (n=5) with mesothelin-expressing A431/H9 tumors (range, 80-300 mm(3)) one day after iv injection of (64)Cu-NOTA-amatuximab (10 µCi) containing a total amatuximab dose of 2, 30, or 60 µg. The BD and PET imaging were also investigated 3, 24 and 48 h after injecting a total dose of 30 µg (10 µCi for BD), and 2 or 60 µg (300 µCi for PET), respectively. RESULTS: Comparing the results of the BDs from three different injection doses, the major difference was shown in the uptake (%ID/g) of the radiolabel in tumor, liver and blood. The tumor uptake and blood retention from 30 and 60 µg doses were greater than those from 2 µg dose, whereas the liver uptake was smaller. The BD studies also demonstrated a positive correlation between tumor size (or the level of shed mesothelin in blood) and liver uptake. However, there was a negative correlation between tumor size (or the shed mesothelin level) and tumor uptake and between tumor size and blood retention. These findings were confirmed by the PET imaging study, which clearly visualized the tumor uptake with the radiolabel concentrated in the tumor core and produced a tumor to liver ratio of 1.2 at 24h post-injection with 60 µg amatuximab, whereas the injection of 2 µg amatuximab produced a tumor to liver ratio of 0.4 at 24h post-injection. CONCLUSION: Our studies using a nude mouse model of A431/H9 tumor demonstrated that the injection of a high amatuximab dose (30 to 60 µg) could provide a beneficial effect in maximizing tumor uptake while maintaining minimum liver and spleen uptakes of the radiolabel, and in facilitating its penetration into the tumor core.

Impact of C4'-O-Alkyl Linker on in Vivo Pharmacokinetics of Near-Infrared Cyanine/Monoclonal Antibody Conjugates.

Near-infrared (NIR) fluorophores have several advantages over visible-light fluorophores, including superior tissue penetration and lower autofluorescence. We recently accessed a new class of readily synthesized NIR cyanines containing a novel C4'-O-alkyl linker, which provides both high chemical stability and excellent optical properties. In this study, we provide the first in vivo analysis of this new class of compounds, represented by the tetrasulfonate FNIR-774 (Frederick NIR 774). Monoclonal antibody (mAb) conjugates of FNIR-774 were compared to conjugates of the commercially available dye (IRDye800CW (IR800)), one of the most widely used NIR fluorophores for clinical translation. Both dyes were conjugated to panitumumab (pan) or cetuximab (cet) with ratios of 1:2 or 1:5. Conjugates of both dyes demonstrated similar quenching capacity, stability, and brightness in target cells in vitro. In contrast, in vivo imaging in mice showed different pharmacokinetics between pan-FNIR-774 (1:5) and pan-IR800 (1:5), or cet-FNIR-774 (1:5) and cet-IR800 (1:5). Particularly at the higher labeling density, mAb-FNIR-774 conjugates showed superior specific accumulation in tumors compared with mAb-IR800 conjugates. Thus, FNIR-774 conjugates showed superior in vivo pharmacokinetics compared with IR800 conjugates, independent of the mAb. These results suggest that FNIR-774 is a promising fluorescent probe for NIR optical imaging.

Glypican-3 targeted human heavy chain antibody as a drug carrier for hepatocellular carcinoma therapy.

Glypican-3 (GPC3) represents an attractive target for hepatocellular carcinoma (HCC) therapy because it is highly expressed in HCC but not in adult normal tissue. Recently, high affinity anti-GPC3 antibodies have been developed; however, full antibodies may not penetrate evenly into tumor parenchyma, reducing their effectiveness. In this study, we compared a whole IgG antibody, anti-GPC3 YP7, with an anti-GPC3 human heavy chain antibody, HN3, with regard to their relative therapeutic effects. Both YP7 and HN3 bound to GPC3-positive A431/G1 cells and were internalized by the cells by in vitro evaluation with (125)I- and (111)In-radiolabeling antibodies. In vivo biodistribution and tumor accumulation was performed with (111)In-labeled antibodies, and intratumoral microdistribution was evaluated using fluorescently labeled antibodies (IR700). HN3 showed similar high tumor accumulation but superior homogeneity within the tumor compared with YP7. Using the same IR700 conjugated antibodies photoimmunotherapy (PIT) was performed in vitro and in a tumor-bearing mouse model in vivo. PIT with IR700-HN3 and IR700-YP7 demonstrated that comparable results could be achieved despite of low reaccumulation 24 h after the first NIR light exposure. These results indicated that a heavy-chain antibody, HN3, showed more favorable characteristics than YP7, a conventional IgG, as a therapeutic antibody platform for designing molecularly targeted agents against HCC.

Photoimmunotherapy of hepatocellular carcinoma-targeting Glypican-3 combined with nanosized albumin-bound paclitaxel.

AIM: Effectiveness of Glypican-3 (GPC3)-targeted photoimmunotherapy (PIT) combined with the nanoparticle albumin-bound paclitaxel (nab-paclitaxel) for hepatocellular carcinoma was evaluated. MATERIALS & METHODS: GPC3 expressing A431/G1 cells were incubated with a phthalocyanine-derivative, IRDye700DX (IR700), conjugated to an anti-GPC3 antibody, IR700-YP7 and exposed to near-infrared light. Therapeutic experiments combining GPC3-targeted PIT with nab-paclitaxel were performed in A431/G1 tumor-bearing mice. RESULTS: IR700-YP7 bound to A431/G1 cells and induced rapid target-specific necrotic cell death by near-infrared light exposure in vitro. IR700-YP7 accumulated in A431/G1 tumors. Tumor growth was inhibited by PIT compared with nontreated control. Additionally, PIT dramatically increased nab-paclitaxel delivery and enhanced the therapeutic effect. CONCLUSION: PIT targeting GPC3 combined with nab-paclitaxel is a promising method for treating hepatocellular carcinoma.

(99m)Tc-labeled porphyrin-lipid nanovesicles.

Porphyrin-lipid nanovesicles (PLN) have been developed with intrinsic capabilities as activatable multimodal photonic contrast agents. Radiolabeling of PLN encapsulating drugs could eventually be able to provide quantitative in vivo information for diagnosing and treating diseases. In this study, we developed (99m)Tc-labeled porphyrin-lipid nanovesicles ((99m)Tc-PLN) as a cargo-encapsulated formulation without significant impact on liposome integrity and encapsulation stability. 50 mM calcein was encapsulated into PLN by probe sonication. The size of the PLN was about 150 nm. The PLN were then reacted with (99m)Tc using SnCl2 dissolved in 1 mM HCl as a reducing agent and incubated for 10 min at 22 °C. The radiolabeling efficiency and stability of (99m)Tc-PLN were evaluated by instant thin-layer chromatography and low-pressure liquid chromatography (LPLC). (99m)Tc labeling was successful with a >92% labeling efficiency. LPLC showed that the liposomal elution peaks of the porphyrin-lipid and the calcein overlapped with the radioactivity elution peak of (99m)Tc-labeled PLN. The (99m)Tc-labeling procedure did not change the size of PLN. Encapsulated calcein remained inert inside PLN. Thus, this work lays out a simple and effective radiolabeling method using SnCl2 in HCl in the preparation of (99m)Tc-PLN.

Photoimmunotherapy targeting prostate-specific membrane antigen: are antibody fragments as effective as antibodies?

UNLABELLED: Photoimmunotherapy is a highly cell-selective cancer therapy based on an armed antibody conjugate with a phthalocyanine-based photosensitizer, IR700. Photoimmunotherapy induces rapid and highly specific necrosis in targeted cancer cells after exposure to near-infrared (NIR) light. Cells not expressing the antigen are not affected. To date, photoimmunotherapy has been demonstrated only with full antibody-IR700 conjugates. In this study, small and bivalent antibody fragments, including anti-prostate-specific membrane antigen (PSMA) diabody (Db) and minibody (Mb), were compared with intact IgG for their effectiveness as photoimmunotherapy agents. METHODS: Radioiodinated antibody and antibody fragments with (125)I were used to determine the timing of maximum binding of each anti-PSMA antibody fragment on the cell surface in vivo in mice bearing either PSMA-positive or -negative PC3 tumors. Then therapeutic efficacy of photoimmunotherapy was examined by exposing mice to NIR light at 2 time points based on the time of maximum cell surface binding at 6 h after injection for Db-IR700 and 24 h after injection for Mb-IR700 and IgG-IR700 as well as 24 h after the peak uptake times. RESULTS: Photoimmunotherapy with the same molar concentration of PSMA-Db-IR700, PSMA-Mb-IR700, and PSMA-IgG-IR700 conjugate showed similar therapeutic effects in vitro and in vivo on PSMA-positive PC3 tumor xenografts in cytotoxicity and survival curves (P > 0.05). CONCLUSION: The use of PSMA-Db-IR700 conjugate results in the shortest time interval between injection and NIR exposure without compromising therapeutic effects of photoimmunotherapy.

Immuno-PET imaging of tumor endothelial marker 8 (TEM8).

Tumor endothelial marker 8 (TEM8) is a cell surface receptor that is highly expressed in a variety of human tumors and promotes tumor angiogenesis and cell growth. Antibodies targeting TEM8 block tumor angiogenesis in a manner distinct from the VEGF receptor pathway. Development of a TEM8 imaging agent could aid in patient selection for specific antiangiogenic therapies and for response monitoring. In these studies, L2, a therapeutic anti-TEM8 monoclonal IgG antibody (L2mAb), was labeled with (89)Zr and evaluated in vitro and in vivo in TEM8 expressing cells and mouse xenografts (NCI-H460, DLD-1) as a potential TEM8 immuno-PET imaging agent. (89)Zr-df-L2mAb was synthesized using a desferioxamine-L2mAb conjugate (df-L2mAb); (125)I-L2mAb was labeled directly. In vitro binding studies were performed using human derived cell lines with high, moderate, and low/undetectable TEM8 expression. (89)Zr-df-L2mAb in vitro autoradiography studies and CD31 IHC staining were performed with cryosections from human tumor xenografts (NCI-H460, DLD-1, MKN-45, U87-MG, T-47D, and A-431). Confirmatory TEM8 Western blots were performed with the same tumor types and cells. (89)Zr-df-L2mAb biodistribution and PET imaging studies were performed in NCI-H460 and DLD-1 xenografts in nude mice. (125)I-L2mAb and (89)Zr-df-L2mAb exhibited specific and high affinity binding to TEM8 that was consistent with TEM8 expression levels. In NCI-H460 and DLD-1 mouse xenografts nontarget tissue uptake of (89)Zr-df-L2mAb was similar; the liver and spleen exhibited the highest uptake at all time points. (89)Zr-L2mAb was highly retained in NCI-H460 tumors with <10% losses from day 1 to day 3 with the highest tumor to muscle ratios (T:M) occurring at day 3. DLD-1 tumors exhibited similar pharmacokinetics, but tumor uptake and T:M ratios were reduced ∼2-fold in comparison to NCI-H460 at all time points. NCI-H460 and DLD-1 tumors were easily visualized in PET imaging studies despite low in vitro TEM8 expression in DLD-1 cells indicating that in vivo expression might be higher in DLD-1 tumors. From in vitro autoradiography studies (89)Zr-df-L2mAb specific binding was found in 6 tumor types (U87-MG, NCI-H460, T-47D MKN-45, A-431, and DLD-1) which highly correlated to vessel density (CD31 IHC). Westerns blots confirmed the presence of TEM8 in the 6 tumor types but found undetectable TEM8 levels in DLD-1 and MKN-45 cells. This data would indicate that TEM8 is associated with the tumor vasculature rather than the tumor tissue, thus explaining the increased TEM8 expression in DLD-1 tumors compared to DLD-1 cell cultures. (89)Zr-df-L2mAb specifically targeted TEM8 in vitro and in vivo although the in vitro expression was not necessarily predictive of in vivo expression which seemed to be associated with the tumor vasculature. In mouse models, (89)Zr-df-L2mAb tumor uptakes and T:M ratios were sufficient for visualization during PET imaging. These results would suggest that a TEM8 targeted PET imaging agent, such as (89)Zr-df-L2mAb, may have potential clinical, diagnostic, and prognostic applications by providing a quantitative measure of tumor angiogenesis and patient selection for future TEM8 directed therapies.

Minibody-indocyanine green based activatable optical imaging probes: the role of short polyethylene glycol linkers.

Minibodies show rapider blood clearance than IgGs due to smaller size that improves target-to-background ratio (TBR) in in vivo imaging. Additionally, the ability to activate an optical probe after binding to the target greatly improves the TBR. An optical imaging probe based on a minibody against prostate-specific membrane antigen (PSMA-MB) and conjugated with an activatable fluorophore, indocyanine green (ICG), was designed to fluoresce only after binding to cell-surface PSMA. To further reduce background signal, short polyethylene glycol (PEG) linkers were employed to improve the covalent bonding ratio of ICG. New PSMA-MBs conjugated with bifunctional ICG derivatives specifically visualized PSMA-positive tumor xenografts in mice bearing both PSMA-positive and -negative tumors within 6 h postinjection. The addition of short PEG linkers significantly improved TBRs; however, it did not significantly alter the biodistribution. Thus, minibody-ICG conjugates could be a good alternative to IgG-ICG in the optical cancer imaging for further clinical applications.

Photoimmunotherapy: comparative effectiveness of two monoclonal antibodies targeting the epidermal growth factor receptor.

Photoimmunotherapy (PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by photosensitizers after exposure to near infrared (NIR) light. Herein we compare two commonly available anti-EGFR monoclonal antibodies, cetuximab and panitumumab, for their effectiveness as PIT agents in EGFR positive tumor models. A photosensitizer, IR-700, conjugated to either cetuximab (cet-IR700) or panitumumab (pan-IR700), was evaluated using EGFR-expressing A431 and MDAMB468-luc cells in 2D- and 3D-culture. PIT was conducted with irradiation of NIR light after exposure of the sample or animal to each conjugate. In vivo PIT was performed with fractionated exposure of NIR light after injection of each agent into A431 xenografts or a MDAMB468-luc orthotopic tumor bearing model. Cet-IR700 and pan-IR700 bound with equal affinity to the cells in 2D-culture and penetrated equally into the 3D-spheroid, resulting in identical PIT cytotoxic effects in vitro. In contrast, in vivo anti-tumor effects of PIT with cet-IR700 were inferior to that of pan-IR700. Assessment of the biodistribution showed lower accumulation into the tumors and more rapid hepatic catabolism of cet-IR700 compared to pan-IR700. Although cet-IR700 and pan-IR700 showed identical in vitro characteristics, pan-IR700 showed better therapeutic tumor responses than cet-IR700 in in vivo mice models due to the prolonged retention of the conjugate in the circulation, suggesting that retention in the circulation is advantageous for tumor responses to PIT. These results suggest that the choice of monoclonal antibody in photosensitizer conjugates may influence the effectiveness of PIT.

Biodistribution of (99m)tc labeled integrin antagonist.

The selective targeting of an integrin αvß3 receptor using radioligands may enable the assessment of angiogenesis and integrin αvß3 receptor status in tumors. The aim of this research was to label a peptidomimetic integrin αvß3 antagonist (PIA) with (99m)Tc(CO)3 and to test its receptor targeting properties in nude mice bearing receptor-positive tumors. PIA was reacted with tris-succinimidyl aminotriacetate (TSAT) (20 mM) as a PIA per TSAT. The product, PIA-aminodiacetic acid (ADA), was radiolabeled with [(99m)Tc(CO)3(H2O)3](+1), and purified sequentially on a Sep-Pak C-18 cartridge followed by a Sep-Pak QMA anion exchange cartridge. Using gradient C-18 reverse-phase HPLC, the radiochemical purity of (99m)Tc(CO)3-ADA-PIA (retention time, 10.5 min) was confirmed to be > 95%. Biodistribution analysis was performed in nude mice (n = 5 per time point) bearing receptor-positive M21 human melanoma xenografts. The mice were administered (99m)Tc(CO)3-ADA-PIA intravenously. The animals were euthanized at 0.33, 1, and 2 hr after injection for the biodistribution study. A separate group of mice were also co-injected with 200 µg of PIA and euthanized at 1 hr to quantify tumor uptake. (99m)Tc(CO)3-ADA-PIA was stable in phosphate buffer for 21 hr, but at 3 and 6 hr, 7.9 and 11.5% of the radioactivity was lost as histidine, respectively. In tumor bearing mice, (99m)Tc(CO)3-ADA-PIA accumulated rapidly in a receptor-positive tumor with a peak uptake at 20 min, and rapid clearance from blood occurring primarily through the hepatobiliary system. At 20 min, the tumor-toblood ratio was 1.8. At 1 hr, the tumor uptake was 0.47% injected dose (ID)/g, but decreased to 0.12% ID/g when co-injected with an excess amount of PIA, indicating that accumulation was receptor mediated. These results demonstrate successful (99m)Tc labeling of a peptidomimetic integrin antagonist that accumulated in a tumor via receptor-specific binding. However, tumor uptake was very low because of low blood concentrations that likely resulted from rapid uptake of the agent into the hepatobiliary system. This study suggests that for (99m)Tc(CO)3-ADA-PIA to be useful as a tumor detection agent, it will be necessary to improve receptor binding affinity and increase the hydrophilicity of the product to minimize rapid hepatobiliary uptake.

(99m)Tc-labeled therapeutic inhaled amikacin loaded liposomes.

The radiolabeling of the liposome surface can be a useful tool for in vivo tracking of therapeutic drug loaded liposomes. We investigated radiolabeling therapeutic drug (i.e. an antibiotic, amikacin) loaded liposomes with (99m)Tc, nebulization properties of (99m)Tc-labeled liposomal amikacin for inhalation ((99m)Tc-LAI), and its stability by size exclusion low-pressure liquid chromatography (LPLC). LAI was reacted with (99m)Tc using SnCl2 dissolved in ascorbic acid as a reducing agent for 10 min at room temperature. The labeled products were then purified by anion exchange resin. The purified (99m)Tc-LAI in 1.5% NaCl solution was incubated at 4 °C to assess its stability by LPLC. The purified (99m)Tc-LAI was subjected to studies with a clinically used nebulizer (PARI eFlow®) and the Anderson Cascade Impactor (ACI). The use of ascorbic acid at 0.91 mM resulted in a quantitative labeling efficiency. The LPLC profile showed that the liposomal peak of LAI detected by a UV monitor at both 200 nm and 254 nm overlapped with the radioactivity peak of (99m)Tc-LAI, indicating that (99m)Tc-LAI is suitable for tracing LAI. The ACI study demonstrated that the aerosol droplet size distribution determined gravimetrically was similar to that determined by radioactivity. The liposome surface labeling method using SnCl2 in 0.91 mM ascorbic acid produced (99m)Tc-LAI with a high labeling efficiency and stability that are adequate to evaluate the deposition and clearance of inhaled LAI in the lung by gamma scintigraphy.