HER1-Targeted 86Y-Panitumumab Possesses Superior Targeting Characteristics than 86Y-Cetuximab for PET Imaging of Human Malignant Mesothelioma Tumors Xenografts

Malignant mesothelioma (MM), a rare form of cancer is often associated with previous exposure to fibrous minerals, such as asbestos. Asbestos exposure increases HER1-activity and expression in pre-clinical models. Additionally, HER1 over-expression is observed in the majority of MM cases. In this study, the utility of HER1-targeted chimeric IgG(1), cetuximab, and a human IgG(2), panitumumab, radiolabeled with (86)Y, were evaluated for PET imaging to detect MM non-invasively in vivo, and to select an antibody candidate for radioimmunotherapy (RIT).Radioimmunoconjugates (RICs) of cetuximab and panitumumab were prepared by conjugation with CHX-A''-DTPA followed by radiolabeling with (86)Y. The HER1 expression of NCI-H226, NCI-H2052, NCI-H2452 and MSTO-211H human mesothelioma cells was characterized by flow cytometry. In vivo biodistribution, pharmacokinetic analysis, and PET imaging were performed in tumor bearing athymic mice.In vivo studies demonstrated high HER1 tumor uptake of both RICs. Significant reduction in tumor uptake was observed in mice co-injected with excess mAb (0.1 mg), demonstrating that uptake in the tumor was receptor specific. Significant differences were observed in the in vivo characteristics of the RICs. The blood clearance T(½)α of (86)Y-cetuximab (0.9-1.1 h) was faster than (86)Y-panitumumab (2.6-3.1 h). Also, the tumor area under the curve (AUC) to liver AUC ratios of (86)Y-panitumumab were 1.5 to 2.5 times greater than (86)Y-cetuximab as observed by the differences in PET tumor to background ratios, which could be critical when imaging orthotopic tumors and concerns regarding radiation doses to normal organs such as the liver.This study demonstrates the more favorable HER1-targeting characteristics of (86)Y-panitumumab than (86)Y-cetuximab for non-invasive assessment of the HER1 status of MM by PET imaging. Due to lower liver uptake, panitumumab based immunoconjugates may fare better in therapy than corresponding cetuximab based immunoconjugates

Bench to Bedside: Stability Studies of GMP Produced Trastuzumab-TCMC in Support of a Clinical Trial

The first-in-human phase 1 clinical radioimmunotherapy (RIT) trial with 212Pb-1,4,7,10-tetraaza-1,4,7,10-tetra-(2-carbamoylmethyl)-cyclododecane-trastuzumab (212Pb-TCMC-trastuzumab) was completed in October 2014 as a joint effort at the University of Alabama (UAB) and the University of California San Diego Moores Cancer Center. The preliminary reports indicate that after five dose-levels of intraperitoneally administered 212Pb-TCMC-trastuzumab, patients with carcinomatosis experienced minimal agent-related toxicity. This report presents the data accumulated to date on the stability of the clinical grade, produced according to current good manufacturing practices (cGMP), TCMC-trastuzumab conducted in support of that clinical trial. Of the eleven tests performed with the cGMP TCMC-trastuzumab all but one remained within specifications throughout the 5 year testing period. The protein concentration varied by 0.01 mg/mL at 48 months. Two other assays, ion-exchange high performance liquid chromatography (IEX-HPLC) and a competitive radioimmunoassay (RIA) indicated that the cGMP TCMC-trastuzumab integrity may be changing, although the change thus far is within specifications. Subsequent stability testing will confirm if a trend has truly developed. The cGMP TCMC-trastuzumab was also evaluated for tolerance to higher temperatures and the potential of storage at −80 °C. The immunoconjugate proved stable when subjected to the lower temperatures and to multiple freeze-thaw cycles. The size exclusion (SE) HPLC analysis of the 203Pb-TCMC-trastuzumab was the only indicator that cGMP TCMC-trastuzumab may be sensitive to storage at 37 °C for 3 months

Mechanisms of Cell Killing Response from Low Linear Energy Transfer (LET) Radiation Originating from 177Lu Radioimmunotherapy Targeting Disseminated Intraperitoneal Tumor Xenografts

Radiolabeled antibodies (mAbs) provide efficient tools for cancer therapy. The combination of low energy β−-emissions (500 keVmax; 130 keVave) along with a γ-emission for imaging makes 177Lu (T1/2 = 6.7 day) a suitable radionuclide for radioimmunotherapy (RIT) of tumor burdens possibly too large to treat with α-particle radiation. RIT with 177Lu-trastuzumab has proven to be effective for treatment of disseminated HER2 positive peritoneal disease in a pre-clinical model. To elucidate mechanisms originating from this RIT therapy at the molecular level, tumor bearing mice (LS-174T intraperitoneal xenografts) were treated with 177Lu-trastuzumab comparatively to animals treated with a non-specific control, 177Lu-HuIgG, and then to prior published results obtained using 212Pb-trastuzumab, an α-particle RIT agent. 177Lu-trastuzumab induced cell death via DNA double strand breaks (DSB), caspase-3 apoptosis, and interfered with DNA-PK expression, which is associated with the repair of DNA non-homologous end joining damage. This contrasts to prior results, wherein 212Pb-trastuzumab was found to down-regulate RAD51, which is involved with homologous recombination DNA damage repair. 177Lu-trastuzumab therapy was associated with significant chromosomal disruption and up-regulation of genes in the apoptotic process. These results suggest an inhibition of the repair mechanism specific to the type of radiation damage being inflicted by either high or low linear energy transfer radiation. Understanding the mechanisms of action of β−- and α-particle RIT comparatively through an in vivo tumor environment offers real information suitable to enhance combination therapy regimens involving α- and β−-particle RIT for the management of intraperitoneal disease

Cell Killing Mechanisms and Impact on Gene Expression by Gemcitabine and 212Pb-Trastuzumab Treatment in a Disseminated i.p. Tumor Model.

In pre-clinical studies, combination therapy with gemcitabine and targeted radioimmunotherapy (RIT) using 212Pb-trastuzumab showed tremendous therapeutic potential in the LS-174T tumor xenograft model of disseminated intraperitoneal disease. To better understand the underlying molecular basis for the observed cell killing efficacy, gene expression profiling was performed after a 24 h exposure to 212Pb-trastuzumab upon gemcitabine (Gem) pre-treatment in this model. DNA damage response genes in tumors were quantified using a real time quantitative PCR array (qRT-PCR array) covering 84 genes. The combination of Gem with α-radiation resulted in the differential expression of apoptotic genes (BRCA1, CIDEA, GADD45α, GADD45γ, IP6K3, PCBP4, RAD21, and p73), cell cycle regulatory genes (BRCA1, CHK1, CHK2, FANCG, GADD45α, GTSE1, PCBP4, MAP2K6, NBN, PCBP4, and SESN1), and damaged DNA binding and repair genes (BRCA1, BTG2, DMC1, ERCC1, EXO1, FANCG, FEN1, MSH2, MSH3, NBN, NTHL1, OGG1, PRKDC, RAD18, RAD21, RAD51B, SEMA4G, p73, UNG, XPC, and XRCC2). Of these genes, the expression of CHK1, GTSE1, EXO1, FANCG, RAD18, UNG and XRCC2 were specific to Gem/212Pb-trastuzumab administration. In addition, the present study demonstrates that increased stressful growth arrest conditions induced by Gem/212Pb-trastuzumab could suppress cell proliferation possibly by up-regulating genes involved in apoptosis such as p73, by down-regulating genes involved in cell cycle check point such as CHK1, and in damaged DNA repair such as RAD51 paralogs. These events may be mediated by genes such as BRCA1/MSH2, a member of BARC (BRCA-associated genome surveillance complex). The data suggest that up-regulation of genes involved in apoptosis, perturbation of checkpoint genes, and a failure to correctly perform HR-mediated DSB repair and mismatch-mediated SSB repair may correlate with the previously observed inability to maintain the G2/M arrest, leading to cell death

H2BZmacropa-NCS: A Bifunctional Chelator for Actinium-225 Targeted Alpha Therapy.

Actinium-225 (225Ac) is one of the most promising radionuclides for targeted alpha therapy (TAT). With a half-life of 9.92 days and a decay chain that emits four high-energy α particles, 225Ac is well-suited for TAT when conjugated to macromolecular targeting vectors that exhibit extended in vivo circulation times. The implementation of 225Ac in these targeted constructs, however, requires a suitable chelator that can bind and retain this radionuclide in vivo. Previous work has demonstrated the suitability of a diaza-18-crown-6 macrocyclic chelator H2macropa for this application. Building upon these prior efforts, in this study, two rigid variants of H2macropa, which contain either one (H2BZmacropa) or two (H2BZ2macropa) benzene rings within the macrocyclic core, were synthesized and investigated for their potential use for 225Ac TAT. The coordination chemistry of these ligands with La3+, used as a nonradioactive model for Ac3+, was carried out. Both NMR spectroscopic and X-ray crystallographic studies of the La3+ complexes of these ligands revealed similar structural features to those found for the related complex of H2macropa. Thermodynamic stability constants of the La3+ complexes, however, were found to be 1 and 2 orders of magnitude lower than those of H2macropa for H2BZmacropa and H2BZ2macropa, respectively. The decrease in thermodynamic stability was rationalized via the use of density functional theory calculations. 225Ac radiolabeling and serum stability studies with H2BZmacropa showed that this chelator compares favorably with H2macropa. Based on these promising results, a bifunctional version of this chelator, H2BZmacropa-NCS, was synthesized and conjugated to the antibody codrituzumab (GC33), which targets the liver cancer biomarker glypican-3 (GPC3). The resulting GC33-BZmacropa conjugate and an analogous GC33-macropa conjugate were evaluated for their 225Ac radiolabeling efficiencies, antigen-binding affinities, and in vivo biodistribution in HepG2 liver cancer tumor-bearing mice. Although both conjugates were comparably effective in their radiolabeling efficiencies, [225Ac]Ac-GC33-BZmacropa showed slightly poorer serum stability and biodistribution than [225Ac]Ac-GC33-macropa. Together, these results establish H2BZmacropa-NCS as a new bifunctional chelator for the preparation of 225Ac radiopharmaceuticals

In Vivo Imaging of Peripheral Benzodiazepine Receptors in Mouse Lungs: A Biomarker of Inflammation

The ability to visualize the immune response with radioligands targeted to immune cells will enhance our understanding of cellular responses in inflammatory diseases. Peripheral benzodiazepine receptors (PBR) are present in monocytes and neutrophils as well as in lung tissue. We used lipopolysaccharide (LPS) as a model of inflammation to assess whether the PBR could be used as a noninvasive marker of inflammation in the lungs. Planar imaging of mice administrated 10 or 30 mg/kg LPS showed increased [123I]-(R)-PK11195 radioactivity in the thorax 2 days after LPS treatment relative to control. Following imaging, lungs from control and LPS-treated mice were harvested for ex vivo gamma counting and showed significantly increased radioactivity above control levels. The specificity of the PBR response was determined using a blocking dose of nonradioactive PK11195 given 30 min prior to radiotracer injection. Static planar images of the thorax of nonradioactive PK11195 pretreated animals showed a significantly lower level of radiotracer accumulation in control and in LPS-treated animals (p < .05). These data show that LPS induces specific increases in PBR ligand binding in the lungs. We also used in vivo small-animal PET studies to demonstrate increased [11C]-(R)-PK11195 accumulation in the lungs of LPS-treated mice. This study suggests that measuring PBR expression using in vivo imaging techniques may be a useful biomarker to image lung inflammation

Synthesis and in vivo evaluation of a 99m/99Tc-DADT-Benzovesamicol: a potential marker for cholinergic neurons

The diaminodithiol (DADT) ligand has been conjugated to the neuromuscular blocking agent benzovesamicol (BVM) in the 5-position. DADT-BVM 1 was synthesized by coupling of 5-aminomethylbenzovesamicol with a BCA thiolactone reagent. 99mTc radiolabeling of 1 with [99mTc]glucoheptonate gave a 4.7:1 mixture of two 99mTc complexes as determined by HPLC. Biodistribution data of the major [99mTc]-1 complex in CD-1 mice (n = 4-5) showed very little uptake and no regional selectivity in the mouse brain. At all time points examined, the lung and liver showed the highest uptake. For whole brain, the % injected dose values were 0.27, 0.12, 0.04 and 0.01% at t = 1, 5, 30 and 240 min. The major [99mTc]-1 product exhibited a log P = 3.13 +/- 0.06 (SD) with an IC50 = 140-280 nM for the corresponding [99Tc]-1 vs ( - )-N-[3H]methyl-5-aminobenzovesamicol. The low brain uptake of [99mTc]-1 vs 5-iodobenzovesamicol is attributed to its higher molecular weight (752) and lower binding affinity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31807/1/0000753.pd