Hybrid Metal-Phenol Nanoparticles with Polydopamine-like Coating for PET/SPECT/CT Imaging.

The validation of metal-phenolic nanoparticles (MPNs) in preclinical imaging studies represents a growing field of interest due to their versatility in forming predesigned structures with unique properties. Before MPNs can be used in medicine, their pharmacokinetics must be optimized so that accumulation in nontargeted organs is prevented and toxicity is minimized. Here, we report the fabrication of MPNs made of a coordination polymer core that combines In(III), Cu(II), and a mixture of the imidazole 1,4-bis(imidazole-1-ylmethyl)-benzene and the catechol 3,4-dihydroxycinnamic acid ligands. Furthermore, a phenolic-based coating was used as an anchoring platform to attach poly(ethylene glycol) (PEG). The resulting MPNs, with effective hydrodynamic diameters of around 120 nm, could be further derivatized with surface-embedded molecules, such as folic acid, to facilitate in vivo targeting and multifunctionality. The prepared MPNs were evaluated for in vitro plasma stability, cytotoxicity, and cell internalization and found to be biocompatible under physiological conditions. First, biomedical evaluations were then performed by intrinsically incorporating trace amounts of the radioactive metals 111In or 64Cu during the MPN synthesis directly into their polymeric matrix. The resulting particles, which had identical physicochemical properties to their nonradioactive counterparts, were used to perform in vivo single-photon emission computed tomography (SPECT) and positron emission tomography (PET) in tumor-bearing mice. The ability to incorporate multiple metals and radiometals into MPNs illustrates the diverse range of functional nanoparticles that can be prepared with this approach and broadens the scope of these nanoconstructs as multimodal preclinical imaging agents.

Selective alpha-particle mediated depletion of tumor vasculature with vascular normalization.

BACKGROUND: Abnormal regulation of angiogenesis in tumors results in the formation of vessels that are necessary for tumor growth, but compromised in structure and function. Abnormal tumor vasculature impairs oxygen and drug delivery and results in radiotherapy and chemotherapy resistance, respectively. Alpha particles are extraordinarily potent, short-ranged radiations with geometry uniquely suitable for selectively killing neovasculature. METHODOLOGY AND PRINCIPAL FINDINGS: Actinium-225 ((225)Ac)-E4G10, an alpha-emitting antibody construct reactive with the unengaged form of vascular endothelial cadherin, is capable of potent, selective killing of tumor neovascular endothelium and late endothelial progenitors in bone-marrow and blood. No specific normal-tissue uptake of E4G10 was seen by imaging or post-mortem biodistribution studies in mice. In a mouse-model of prostatic carcinoma, (225)Ac-E4G10 treatment resulted in inhibition of tumor growth, lower serum prostate specific antigen level and markedly prolonged survival, which was further enhanced by subsequent administration of paclitaxel. Immunohistochemistry revealed lower vessel density and enhanced tumor cell apoptosis in (225)Ac-E4G10 treated tumors. Additionally, the residual tumor vasculature appeared normalized as evident by enhanced pericyte coverage following (225)Ac-E4G10 therapy. However, no toxicity was observed in vascularized normal organs following (225)Ac-E4G10 therapy. CONCLUSIONS: The data suggest that alpha-particle immunotherapy to neovasculature, alone or in combination with sequential chemotherapy, is an effective approach to cancer therapy.

Increased levels of comet-detected spermatozoa DNA damage following in vivo isotopic- or X-irradiation of spermatogonia.

To investigate whether DNA damage arising in spermatogenic germ cells can be detected in resultant sperm, we have irradiated murine testis and collected spermatozoa from the vas deferens 45 days later. These cells were derived from spermatogonia present at the time of irradiation. Two forms of irradiation were used, external X-rays (4Gy) and internal auger electrons from contamination of the male mouse with the isotope Indium-114m (1.85MBq), which was localised in the testis. Both forms of irradiation produced a profound fall in vas deferens sperm count and testis weight, Indium-114m being more effective. Using the neutral Comet assay for double strand break detection, significant increases in sperm comet tail length and moment were observed. The levels of damage were similar for both treatments. Care had to be taken during the assay to distinguish between sperm and somatic cells as the proportion of the latter increased after irradiation. We conclude that the comet assay can detect DNA damage in spermatozoa after the in vivo exposure of male germ cells to a known testicular genotoxic agent. The assay may be useful for the assessment of sperm DNA damage (double stranded) associated with male infertility and post-fertilization developmental abnormalities in the offspring.

Cytotoxicity with Auger electron-emitting radionuclides delivered by antibodies.

We investigated the in vitro cytotoxic potential of Auger electron-emitting radionuclides delivered to the cytoplasm or, more specifically, to lysosomes, via antibodies. The antibody (Ab) used was LL1, which is specific for CD74, an epitope of the major histocompatibility complex (MHC) class II antigen invariant chain, Ii, present on the cell surface. It is taken up in large amounts, approximately 10(7) Ab molecules per cell per day, and delivered to lysosomes. The radioisotopes tested included (111)In, 99mTc and 125I. With sufficient specific activity, approximately 10 mCi/mg Ab, all of these isotopes were potent cytotoxic agents. 125I was active only if a "residualizing" form was used, meaning a form that is trapped within cells after catabolism of the Ab to which it was conjugated (conventional oxidative iodination produces a non-residualizing label). The conjugates of (111)In and 99mTc used are known to be residualizing. One hundred percent cell kill in vitro was obtained with (111)In and 125I, under conditions in which a non-reactive control Ab, conjugated in the same way, produced no significant toxicity. 99mTc was also potent and specific, but appeared somewhat less active than the other isotopes under the conditions evaluated. Although few Abs are accreted by cells at the same rate as LL1, it may be possible to use other Abs to deliver similar amounts of radioactivity, if Abs with higher specific activity can be produced. Such conjugated radioisotopes may be useful for attacking tumor cells in vivo, particularly for single cells or micrometastases.

Testicular toxicity of the transferrin binding radionuclide 114mIn in adult and neonatal rats.

Adult (70 d) and neonatal (7 d) male rats were dosed (i.p.) with 37 MBq/kg (1 mCi/kg; approximately 1 microgram elemental indium/kg) 114mIn, a transferrin-binding radionuclide. In adults, approximately 0.25% of the injected activity localised within the testis by 48 h postinjection and remained constant for up to 63 d. In neonates, 0.06% of the activity was in the testis by 48 h, and this declined such that by 63 d only 0.03% remained. At 63 d, treated rats had reduced sperm head counts and abnormal testicular histology that was more marked in animals dosed as adults than as neonates. In vitro, uptake of 114mIn into seminiferous tubules isolated from 7-, 20-, or 70-d-old rats was compared with that of 125I. Both radionuclides were readily accumulated by the tubules. Whilst 114In uptake into 20- and 70-d tubules was inhibited by excess transferrin, uptake into 7-d tubules was unchanged. 125I uptake was not affected by excess transferrin. These data support the contention that some radionuclides may cross the blood-testis barrier by utilisation of the physiologic iron-transferrin pathway, which may lead to greater testicular damage in adult compared to neonatal animals.

Preclinical evaluation of intravenously administered 111In- and 90Y-labeled B72.3 immunoconjugate (GYK-DTPA) in beagle dogs.

B72.3, a monoclonal antibody with reactivity against human adenocarcinomas was obtained from the Cytogen Corporation in the form of an immunoconjugate coupled with linker-chelator GYK-DTPA by using proprietary carbohydrate directed site specific chemistry. The immunoconjugate was radiolabeled with indium-111 or yttrium-90. A preclinical analysis was performed in 10 normal beagle dogs. The pharmacokinetics of intravenously administered indium- and yttrium-labeled immunoconjugates were compared serially in blood, bone marrow and urine samples. Compared to 90Y less of the 111In label ended up in urine and more was found in blood and bone marrow. Indium-labeled B72.3 GYK-DTPA had relatively higher uptake in most glandular tissues than 111In-labeled antiferritin immunoconjugate. Bone marrow toxicity was the dose limiting side effect after intravenous infusion of 90Y-labeled B72.3 GYK-DTPA. Toxicity was also observed in the liver but not in other organ systems. Recently other investigators obtained similar results with these immunoconjugates in human patients. A preclinical pharmacokinetic analysis of radioimmunoconjugates in beagle dogs provided useful information regarding bone marrow toxicity, liver toxicity and in vivo instability of the immunoconjugate. Data suggest that for future trials in human patients, a more stable chelated immunoconjugate for yttrium is needed to achieve less liver uptake and a better correlation with the 111In-labeled product than the 90Y-labeled B72.3 GYK-DTPA used in this investigation.

Imaging of non-small cell lung cancers with a monoclonal antibody, KC-4G3, which recognizes a human milk fat globule antigen.

To determine the role of lung cancer tumor imaging with monoclonal antibodies directed against high molecular weight human milk fat globule antigens, we administered i.v. 111In-KC-4G3 to 24 patients with advanced non-small cell lung cancer. One mg of 111In-KC-4G3 was mixed with 0, 9, 49, 99, or 499 mg of unlabeled KC-4G3 and infused i.v. over 1 to 5 h. The mean 111In-KC-4G3 radiochemical purity was greater than 97% and the resultant immunoreactivity averaged 62%. Successful imaging of cancer sites was accomplished in 92% of 24 patients, and 57% of 91 total lesions were visualized. Successful localization of tumor sites related to size (P less than 0.001), with 81% of lesions greater than 3.0 cm in diameter, 50% of lesions 1.5 to 3 cm, and 6% of lesions less than 1.5 cm successfully imaging, and to location (P less than 0.05), with 69% of pulmonary lesions, 80% of soft tissue lesions, and only 32% of bone metastases being visualized. Nonspecific reticulo-endothelial uptake of radioactivity was a major problem. Approximately 35% of 111In was chelated to serum transferrin by 24 and 48 h after infusion. The mean t 1/2 beta for plasma radioisotope and immunoreactive KC-4G3 was 29 and 27 h, respectively. There was no correlation between total infused antibody dose and imaging success or between total dose and effect on 111In and KC-4G3 kinetics. Circulating free KC-4 antigen was measurable in all but one patient before study. Tumor biopsy following infusion could demonstrate antibody presence but not saturable antigen binding. We conclude that (a) 111In-KC-4G3 demonstrates successful tumor localization in non-small cell lung cancers bearing generally high expression of its antigen and (b) further investigations to diminish nonspecific radioactivity for imaging and utilization of high dose radiolabeled antibody for therapeutic intent are warranted.

The radiation dose to cells in vitro from intracellular indium-111.

Most of the radionuclides used in nuclear medicine emit low energy Auger electrons following radioactive decay. These emissions, if intracellular, could irreparably damage the radiosensitive structures of the cell. The resulting radiation dose, which is a measure of biological damage in the affected cell, could be many times the average radiation dose to the associated organ. In this series of experiments, the radiation dose to the nucleus of a chinese hamster V79 cell was determined for the intracellular radiopharmaceutical 111indium-oxine. Assuming the cell nucleus to be the radiosensitive volume, the radiation dose would be primarily due to the low energy Auger electrons. A much smaller dose would be absorbed from the penetrating X- and gamma-rays and internal conversion electrons released from other radiolabelled cells in the culture. The radiation dose to the cell from the intranuclear decay of 111In was empirically established from cell survival studies to be 3.5 mGy/decay, using cobalt-60 as a reference radiation. The average dose to V79 cells from extracellular 111In (i.e., from 111In located outside the target cell) was calculated to be 5.8 pGy/decay. This suggests that for an intracellular radiopharmaceutical, the radiation dose of consequence would be delivered by the low energy Auger electrons. In contrast, Auger electrons from an extracellular radiopharmaceutical could not directly damage the cell nucleus and therefore would not contribute to the radiation dose.

Radiation toxicity of indium-111-2-mercaptopyridine-N-oxide on HeLa S-3 cells.

As one of a series of systematic studies to determine the cytotoxicity of radiopharmaceuticals, indium-111-2-mercaptopyridine-N-oxide (111In-merc) was studied using a monolayer of HeLa S-3 cells. Exponentially growing cells were incubated with up to 2.96 MBq/ml (80 microCi/ml) of 111In-merc (molecular ratio of In/Cd to merc was 1:1000) in phosphate buffered saline for up to 240 min at room temperature. Surviving fractions were assayed by the colony-forming method. The cell uptake curve was upward concave with increasing activity and was saturated after an incubation time of 60 min. A clonogenic assay resulted in an exponential dose-survival curve with a shoulder (D0 of 0.44 MBq/ml (12 microCi/ml); n = 5), and an upward concave time-survival relationship. Merc alone and decayed In-merc were non-toxic at the equivalent range, substantiating radiation-induced cytotoxicity of 111In-merc.