Indium-111 bleomycin complex for radiochemotherapy of head and neck cancer--dosimetric and biokinetic aspects

Radioactive Main Group and Rare Earth Metals for Imaging and Therapy

Radiometals possess an exceptional breadth of decay properties and have been applied to medicine with great success for several decades. The majority of current clinical use involves diagnostic procedures, which use either positron-emission tomography (PET) or single-photon imaging to detect anatomic abnormalities that are difficult to visualize using conventional imaging techniques (e.g., MRI and X-ray). The potential of therapeutic radiometals has more recently been realized and relies on ionizing radiation to induce irreversible DNA damage, resulting in cell death. In both cases, radiopharmaceutical development has been largely geared toward the field of oncology; thus, selective tumor targeting is often essential for efficacious drug use. To this end, the rational design of four-component radiopharmaceuticals has become popularized. This Review introduces fundamental concepts of drug design and applications, with particular emphasis on bifunctional chelators (BFCs), which ensure secure consolidation of the radiometal and targeting vector and are integral for optimal drug performance. Also presented are detailed accounts of production, chelation chemistry, and biological use of selected main group and rare earth radiometals.

Theranostic etoposide phosphate/indium nanoparticles for cancer therapy and imaging

Etoposide phosphate (EP), a water-soluble anticancer prodrug, is widely used for treatment of many cancers. After administration it is rapidly converted to etoposide, its parent compound, which exhibits anticancer activity. Difficulty in parenteral administration necessitates the development of a suitable nanoparticle delivery system for EP. Here we have used indium both as a carrier to deliver etoposide phosphate to tumor cells and as a SPECT imaging agent through incorporation of (111)In. Etoposide phosphate was successfully encapsulated together with indium in nanoparticles, and exhibited dose dependent cytotoxicity and induction of apoptosis in cultured H460 cancer cells via G2/M cell cycle arrest. In a mouse xenograft lung cancer model, etoposide phosphate/indium nanoparticles induce tumor cell apoptosis, leading to significant enhancement of tumor growth inhibition compared to the free drug.

[201Tl](III)-bleomycin for tumor imaging

Due to interesting physical properties and wide availability of thallium-201 as a SPECT radionuclide, the idea of incorporation of this nuclide into biologically active compounds was targeted. Thallium-201 (T 1/2 = 3.04 d) in Tl+ form was converted to Tl3+ cation in presence of O3 in 6 M HCl controlled by RTLC/gel electrophoresis methods. The final evaporated activity was reacted with bleomycin in normal saline to yield [201Tl]BLM at room temperature after 0.5 h (radiochemical yield > 99%) followed by HPLC analysis. The studies showed that thallic ion is mostly incorporated into bleomycin A2 while other species in the pharmaceutical sample almost remain unlabeled. Radiochemical purity of more than 99% was obtained using RTLC, HPLC with specific activity of about 7 Ci/mmol. The stability of the tracer was checked in the final product in presence of human serum at 37 °C up to 3 d. The tracer accumulated in tumors of fibrosarcoma-bearing mice after 72 h.

Indium-111-bleomycin complex in squamous cell cancer xenograft tumors of nude mice

INTRODUCTION

Labeling of bleomycin with Auger-emitter Indium-111 increases cytotoxicity in squamous cell cancer (SCC) cell lines, as we have reported earlier. In this study, we investigated whether (111)In- BLMC is toxic and effective in vivo among SCC-xenografted mice. The influence of (111)InBLMC on the squamous cell carcinoma cell cycle stimulated interest.

MATERIALS AND METHODS

In an animal experiment, 10 SCC-xenografted mice were used, two for demonstrating targeting in gamma-camera images, eight for intraperitoneally receiving NaCl, BLM, or (111)InBLMC as therapy. After a 2-week follow-up, the tumors were analyzed for proliferation (mitoses, Ki-67). DNA flow cytometric analysis was carried out from tumor samples and three UT-SCC cell lines.

RESULTS

Tumors were observed on gamma-camera images in xenografted mice after a (111)InBLMC injection. The UT-SCC-19A-xenografted mouse had a T/non-T uptake of 7.54 at 4 hours after the injection. At the end of the therapeutic trial, the mice were alive. In spite of a small number of animals, our findings indicate that BLM and (111)InBLMC seem to be more effective than NaCl in reducing tumor size. The proliferative activity was strong in BLM and in (111)InBLMC groups, indicating regrowth of the tumors. In DNA analysis, the percentages of cells in the G2/M-phases increased after exposure to BLM and particularly to (111)InBLMC in all three cell lines.

CONCLUSIONS

The effect of BLM is preserved after the adding of Auger-emitter In-111. Tumor-seeking (111)InBLMC can be administered safely at tumor-decreasing concentrations in xenograft head and neck cancers. To demonstrate the antitumor effect of (111)InBLMC, the experiments should be extended to include a larger number of mice. BLM, and especially (111)InBLMC, seems to induce alteration in the cell cycle by producing a G2/M block. The verification of the result requires repeated in vitro experiments.

Low-energy electron emitters for targeted radiotherapy of small tumours

The possibility of using electron emitters to cure a cancer with metastatic spread depends on the energy of the emitted electrons. Electrons with high energy will give a high, absorbed dose to large tumours, but the absorbed dose to small tumours or single tumour cells will be low, because the range of the electrons is too long. The fraction of energy absorbed within the tumour decreases with increasing electron energy and decreasing tumour size. For tumours smaller than 1 g, the tumour-to-normal-tissue mean absorbed dose-rate ratio, TND, will be low, e.g. for 131I and 90Y, because of the high energy of the emitted electrons. For radiotherapy of small tumours, radionuclides emitting charged particles with short ranges (a few microm) are required. A mathematical model was constructed to evaluate the relation between TND and electron energy, photon-to-electron energy ratio, p/e, and tumour size. Criteria for the selection of suitable radionuclides for the treatment of small tumours were defined based on the results of the TND model. In addition, the possibility of producing such radionuclides and their physical and chemical properties were evaluated. Based on the mathematical model, the energy of the emitted electrons should be < or = 40 keV for small tumours (< 1000 cells), and the photon-to-electron energy ratio, p/e, should be < or = 2 to achieve a high TND. Using the selection criteria defined, five low-energy electron emitters were found to be suitable: 58Co, 103mRh, 119Sb, 161Ho, and 189mOs. All of these nuclides decay by internal transition or electron capture, which yields conversion and Auger electrons, and it should be possible to produce most of them in therapeutic amounts. The five low-energy electron-emitting radionuclides identified may be relevant in the radiation treatment of small tumours, especially if bound to internalizing radiopharmaceuticals.

114mIn, a candidate for radionuclide therapy: low-energy cyclotron production and labeling of DTPA-D-phe-octreotide

A method for production of carrier-free (114m)In (half-life 49.5 days), which is a potential radionuclide for radionuclide therapy of slowly growing tumors, is presented. A target consisting of five enriched cadmium ((114)Cd) foils, each 50 microm thick, was irradiated by protons (from 12.6-6.5 MeV) giving a target yield of 0. 8 MBq/microAh. A simple and cost-efficient thermal diffusion method was used for the separation. The irradiated target foils were heated for 2 h at 306 degrees C and then etched in 0.05 M HCl. The obtained cadmium/indium solution was purified using a cation ion-exchange resin (AG 1 x 8, Bio-Rad Laboratories, Hercules, CA USA). An overall yield of approximately 60% was obtained, whereas the loss of the target material was <1% per separation cycle. The (114m)In production gave (114m)In with high specific radioactivity and was successfully used to label diethylenetriamine pentaacetic acid (DTPA)-D-Phe-octreotide. Furthermore, no difference in biodistribution between [(114m)In]- and [(111)In]-DTPA-D-Phe(1)-octreotide in tumor-bearing nude mice was seen. The high radionuclide uptake in the tumors indicates a good receptor binding of the labeled octreotide.

Radioimmunotherapy of human glioma xenografts in nude mice by indium-111 labelled internalising monoclonal antibody

The potential of 111Indium (111In)-labelled internalising anti-integrin alpha 3 antibody GA17 in the radioimmunotherapy of human glioblastoma xenografts in nude mice was investigated. A radioisotope retention assay showed a rapid release of radioiodine from the glioblastoma cells after the binding of 125I-GA17, whilst 111In-GA17 was retained in the cells for a longer time period. The glioblastoma xenografts showed a high and prolonged uptake of 111In-GA17, and tumour uptake of 125I-GA17 was lower and decreased with time. In the mice which received two injections of 18.5 MBq of 111In-GA17, the growth of the subcutaneous tumour was significantly suppressed compared with the untreated group and mice injected with an 111In-labelled control antibody. These results indicate that GA17 was internalized into the glioblastoma cells and that 111In was retained within the cancer cells. The injection of a high-dose of 111In-GA17 can suppress the growth of tumour xenografts in nude mice.

Metal complexes of bleomycin: evaluation of [Rh-105]-bleomycin for use in targeted radiotherapy

Bleomycin has been used as a carrier for several radioisotopes; however, its potential for clinical use has been limited either by the in vivo stability of the complexes or the half-life of the isotope used. The chemical, biological, and radiological properties of 105Rhodium appear to make it an ideal choice for targeted radiotherapy. The synthesis and purification of a hereto unreported 105Rhodium-bleomycin (105Rh-BLM) complex is described. The stability of this complex in plasma is sufficient to allow targeted delivery of the radioisotope. 57Cobalt-bleomycin was studied under identical conditions for comparative purposes. The suitability of 105Rh-BLM for targeted therapy, which appears to be limited by the renal clearance of this agent, is discussed.

Kinetics of 111In-labeled bleomycin in patients with brain tumors: compartmental vs. non-compartmental models

The kinetics of an indium-111 labeled bleomycin complex (111In-BLMC) after rapid intravenous injection in patients with brain tumors was quantified by using compartmental and non-compartmental models. The models were applied to data obtained from 10 glioma, one meningioma, and one adenocarcinoma brain metastasis patients. Blood and urine samples from all the patients and tumor samples from three patients were collected. The mean transit time of 111In-BLMC in the plasma pool was 14 +/- 7 min without and 1.8 +/- 0.6 h when accounting for recirculation, and 13 +/- 4 h in the total body pool. The mean plasma clearance of 111In-BLMC was 0.3 +/- 0.1 m/blood/min and the mean half-life in urine was 3.5 +/- 0.6 h. The mean transfer coefficients for the open three-compartmental model were: excretion from plasma = 0.02 +/- 0.01, from depot to plasma = (12 +/- 9)*10(-4), from plasma to depot = 0.01 +/- 0.01, from tumor to plasma = 0.39 +/- 0.19 and from plasma to tumor = 1.11 +/- 0.57, all in units minute-1. The mean turnover time from the tumor was 4.5 +/- 2.7 min and from the depot 20 +/- 8 h. It is concluded that both compartmental and non-compartmental models are sufficient to describe the kinetics of indium-111 labeled bleomycin complex. The non-compartmental model is more practical and to some extent more efficient in describing the in vivo behaviors of 111In-BLMC than the compartmental model. The compartmental model used provides estimates of both extraction and excretion from the plasma and tumor.

Squamous cell cancer cell lines: sensitivity to bleomycin and suitability for animal xenograft studies

Bleomycin (BLM) is a natural antibiotic, toxic to dividing cells (G2/M-phase), also proven effective in squamous cell carcinomas (SCC). We have clinically shown that a short-range beta-emitting radionuclide combined to bleomycin (In-111-BLMC) is a tumor-targeting agent in SCCs. With higher radionuclide activities it may be possible to develop a more effective agent, to be tested in animal studies. Using a 96-well clonogenic assay we investigated three SCC cell lines, grown in our own laboratory. IC20, IC50 and IC90 values for BLM were determined. The UT-SCC-12A and UT-SCC-12B cells were originated from a primary tumor and a metastasis of the same patient. UT-SCC-12A cells were also inoculated subcutaneously into nude mice and the tumor growth was analysed. The IC50 value for UT-SCC-19A cell line was 4.0 +/- 1.3 nM. UT-SCC-12A and UT-SCC-12B were both more resistant to BLM; IC50 values were 14.2 +/- 2.8 nM and 13.0 +/- 1.1 nM, respectively. Within 35 days the weight of nude mice increased 2.8 +/- 0.6g. At 25 and 35 days after tumor inoculations the tumor volumes were 111 +/- 51 mm3 and 874 +/- 577 mm3, respectively. The calculated doubling time was 3.86 +/- 0.76 days. SCC cell lines demonstrate different sensitivity to BLM. Our SCC tumor xenograft model showed a rapid growth proper for radiochemotherapeutic studies using In-111-BLMC. The uptake of In-111-BLMC in vivo has been directly proportional to proliferation activity, and the tumors with high binding capacity could be predicted from animal model dose calculations.

Somatostatin receptor imaging of olfactory neuroblastoma

Neural-crest tumours, including neuroblastomas, express somatostatin receptors. This can be shown by radionuclide labelling of octreotide, a somatostatin analogue. Studies on imaging with this substance have dealt with childhood neuroblastomas. Olfactory neuroblastoma (aesthesioneuroblastoma) is a rare tumour in which somatostatin receptor content has not been analysed, nor have radionuclide methods for diagnostic purposes been described. We report a case of olfactory neuroblastoma, in which scanning with 111In-labelled octreotide was performed. A strong uptake was seen at the base of the skull. This was confirmed as a recurrent tumour by magnetic resonance (MR) imaging. Uptake was also observed in the neck and chest, indicating extensive spread of the disease. Somatostatin receptor expression has been shown to correlate with prognosis in childhood neuroblastoma. The accuracy of labelled octreotide in the diagnosis of olfactory neuroblastoma indicates that it might be useful in radionuclide therapy of patients with advanced disease, when no other treatment modalities are available.