A limiting factor for the progress of radionuclide-based cancer diagnostics and therapy--availability of suitable radionuclides

Radiation-targeted immunotherapy: A new perspective in cancer radiotherapy

In contemporary oncology, radiation therapy and immunotherapy stand as critical treatments, each with distinct mechanisms and outcomes. Radiation therapy, a key player in cancer management, targets cancer cells by damaging their DNA with ionizing radiation. Its effectiveness is heightened when used alongside other treatments like surgery and chemotherapy. Employing varied radiation types like X-rays, gamma rays, and proton beams, this approach aims to minimize damage to healthy tissue. However, it is not without risks, including potential damage to surrounding normal cells and side effects ranging from skin inflammation to serious long-term complications. Conversely, immunotherapy marks a revolutionary step in cancer treatment, leveraging the body's immune system to target and destroy cancer cells. It manipulates the immune system's specificity and memory, offering a versatile approach either alone or in combination with other treatments. Immunotherapy is known for its targeted action, long-lasting responses, and fewer side effects compared to traditional therapies. The interaction between radiation therapy and immunotherapy is intricate, with potential for both synergistic and antagonistic effects. Their combined use can be more effective than either treatment alone, but careful consideration of timing and sequence is essential. This review explores the impact of various radiation therapy regimens on immunotherapy, focusing on changes in the immune microenvironment, immune protein expression, and epigenetic factors, emphasizing the need for personalized treatment strategies and ongoing research to enhance the efficacy of these combined therapies in cancer care.

Cyclotron production of 103Pd using a liquid target

INTRODUCTION

In this work, we present the first feasibility study on the production of the medically important radionuclide ¹⁰³Pd via the ¹⁰³Rh(p,n)¹⁰³Pd reaction by cyclotron irradiation of a liquid target. Using a liquid target removes the time consuming and complex dissolution process of rhodium post-irradiation due to its chemically inactive nature and thereby will improve the accessibility of this radioisotope.

METHODS

Liquid targets made from Rh(NO₃)₃·×H₂O salt dissolved in de-ionized water were irradiated using a 12 MeV beam at the TR13 cyclotron at TRIUMF, Vancouver.

RESULTS

A maximum EOB activity of 1.03 ± 0.05 MBq was achieved with the tested conditions, sufficient for basic radiochemistry studies. An effective separation method using anion exchange chromatography is reported using 1 M HNO₃ as an eluent for rhodium (90.1 ± 2.1 % recovery) and a 1:1 mixture of 0.5 M NH₃ + NH₄Cl palladium eluent (103.8 ± 2.3 % recovery). The solution showed good in-target pressure stability. However, the production efficiency decreased significantly with higher solution concentrations and irradiation lengths which puts into question the scaling potential of this method.

CONCLUSION

This proof-of-concept study has demonstrated the potential for using liquid targets as complementary production method of ¹⁰³Pd for research purposes. The liquid target route faces several scaling challenges but can nonetheless improve the availability of ¹⁰³Pd and consequently aid in widening its utility for radiopharmaceuticals.

Experimental α-particle radioimmunotherapy of breast cancer using 227Th-labeled p-benzyl-DOTA-trastuzumab

Background

The aim of the present study was to explore the biodistribution, normal tissue toxicity, and therapeutic efficacy of the internalizing low-dose rate alpha-particle-emitting radioimmunoconjugate ²²⁷Th-trastuzumab in mice with HER2-expressing breast cancer xenografts.

Methods

Biodistribution of ²²⁷Th-trastuzumab and ²²⁷Th-rituximab in nude mice bearing SKBR-3 xenografts were determined at different time points after injection. Tumor growth was measured after administration of ²²⁷Th-trastuzumab, ²²⁷Th-rituximab, cold trastuzumab, and saline. The toxicity of ²²⁷Th-trastuzumab was evaluated by measurements of body weight, blood cell, and clinical chemistry parameters, as well as histological examination of tissue specimens.

Results

The tumor uptake reached peak levels of 34% ID/g (4.6 kBq/g) 3 days after injection of 400 kBq/kg of ²²⁷Th-trastuzumab. The absorbed radiation dose to tumor was 2.9 Gy, while it was 2.4 Gy to femur due to uptake of the daughter nuclide ²²³Ra in bone; the latter already explored in clinical phases I and II trials without serious toxicity. A significant dose-dependent antitumor effect was observed for dosages of 200, 400, and 600 kBq/kg of ²²⁷Th-trastuzumab but no effect of 400 and 600 kBq/kg ²²⁷Th-rituximab (non-tumor binding). No serious delayed bone marrow or normal organ toxicity was observed, but there was a statistical significant reduction in blood cell parameters for the highest-dose group of ²²⁷Th-trastuzumab treatment.

Conclusion

Internalizing ²²⁷Th-trastuzumab therapy was well tolerated and resulted in a dose-dependent inhibition of breast cancer xenograft growth. These results warrant further preclinical studies aiming at a clinical trial in breast cancer patients with metastases to bone.

A proposed methodology to select radioisotopes for use in radionuclide therapy

The American Journal of Neuroradiology has played a seminal role in the history of vertebral augmentation (VA). Because VA is increasingly being included in the multidisciplinary management of malignant vertebral compression fractures (VCFs), combined therapeutic approaches that include strategies to treat metastatic disease along with the fracture have become appealing options for patients. To that end, we recently investigated the dosimetric feasibility of treating malignant VCFs with radionuclide therapy. The goal would be to provide local control of the systemic disease beyond the pain relief and structural support provided by polymethylmethacrylate cement. The purpose of this article is to propose a methodology for evaluating radionuclides for use in radiation therapy that takes into account a number of factors including radiation characteristics, biochemical effects, production capacity, and safety. The goal of such a methodology is to introduce a systematic approach to selecting radionuclides in designing treatment regimens and future investigations and also to stimulate discussion and experimentation involving new radionuclides that may provide more effective treatments than the current isotopes in widespread use.

In vitro cytotoxicity of low-dose-rate radioimmunotherapy by the alpha-emitting radioimmunoconjugate Thorium-227-DOTA-rituximab

PURPOSE

To determine whether the low-dose-rate alpha-particle-emitting radioimmunoconjugate (227)Th-1,4,7,10-p-isothiocyanato-benzyl-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-rituximab can be used to inactivate lymphoma cells growing as single cells and small colonies.

METHODS AND MATERIALS

CD20-positive lymphoma cell lines were treated with (227)Th-DOTA-rituximab for 1-5 weeks. To simulate the in vivo situation with continuous but decreasing supply of radioimmunoconjugates from the blood pool, the cells were not washed after incubation with (227)Th-DOTA-rituximab, but half of the medium was replaced with fresh medium, and cell concentration and cell-bound activity were determined every other day after start of incubation. A microdosimetric model was established to estimate the average number of hits in the nucleus for different localizations of activity.

RESULTS

There was a specific targeted effect on cell growth of the (227)Th-DOTA-rituximab treatment. Although the cells were not washed after incubation with (227)Th-DOTA-rituximab, the average contribution of activity in the medium to the mean dose was only 6%, whereas the average contribution from activity on the cells' own surface was 78%. The mean dose rates after incubation with 800 Bq/mL (227)Th-DOTA-rituximab varied from 0.01 to 0.03 cGy/min. The average delay in growing from 10(5) to 10(7) cells/mL was 15 days when the cells were treated with a mean absorbed radiation dose of 2 Gy alpha-particle radiation from (227)Th-DOTA-rituximab, whereas it was 11 days when the cells were irradiated with 6 Gy of X-radiation. The relative biologic effect of the treatment was estimated to be 2.9-3.4.

CONCLUSIONS

The low-dose-rate radioimmunoconjugate (227)Th-DOTA-rituximab is suitable for inactivation of single lymphoma cells and small colonies of lymphoma cells.

Astatine Radiopharmaceuticals: Prospects and Problems

For the treatment of minimum residual diseases such micrometastases and residual tumor margins that remain after debulking of the primary tumor, targeted radiotherapy using radiopharmaceuticals tagged with alpha-particle-emitting radionuclides is very attractive. In addition to the their short range in tissue, which helps minimize harmful effects on adjacent normal tissues, alpha-particles, being high LET radiation, have several radiobiological advantages. The heavy halogen, astatine-211 is one of the prominent alpha-particle-emitting radionuclides in practice. Being a halogen, it can often be incorporated into biomolecules of interest by adapting radioiodination chemistry. A wide spectrum of compounds from the simple [(211)At]astatide ion to small organic molecules, peptides, and large proteins labeled with (211)At have been investigated with at least two reaching the stage of clinical evaluation. The chemistry, cytotoxic advantages, biodistribution studies, and microdosimetry/pharmacokinetic modeling of some of these agents will be reviewed. In addition, potential problems such as the harmful effect of radiolysis on the synthesis, lack of sufficient in vivo stability of astatinated compounds, and possible adverse effects when they are systemically administered will be discussed.

Direct procedure for the production of 211At-labeled antibodies with an epsilon-lysyl-3-(trimethylstannyl)benzamide immunoconjugate

(211)At-labeled tumor-specific antibodies have long been considered for the treatment of disseminated cancer. However, the limited availability of the nuclide and the poor efficacy of labeling procedures at clinical activity levels present major obstacles to their use. This study evaluated a procedure for the direct astatination of antibodies for the production of clinical activity levels.

METHODS

The monoclonal antibody trastuzumab was conjugated with the reagent N-succinimidyl-3-(trimethylstannyl)benzoate, and the immunoconjugate was labeled with astatine. Before astatination of the conjugated antibody, the nuclide was activated with N-iodosuccinimide. The labeling reaction was evaluated in terms of reaction time, volume of reaction solvent, immunoconjugate concentration, and applied activity. The quality of the astatinated antibodies was determined by in vitro analysis and biodistribution studies in nude mice.

RESULTS

The reaction proceeded almost instantaneously, and the results indicated a low dependence on immunoconjugate concentration and applied activity. Radiochemical labeling yields were in the range of 68%-81%, and a specific radioactivity of up to 1 GBq/mg could be achieved. Stability and radiochemical purity were equal to or better than those attained with a conventional 2-step procedure. Dissociation constants for directly astatinated, conventionally astatinated, and radioiodinated trastuzumab were 1.0+/-0.06 (mean+/-SD), 0.44+/-0.06, and 0.29+/-0.02 nM, respectively. The tissue distribution in non-tumor-bearing nude mice revealed only minor differences in organ uptake relative to that obtained with the conventional method.

CONCLUSION

The direct astatination procedure enables the high-yield production of astatinated antibodies with radioactivity in the amounts required for clinical applications.

Preparation of TH227-labeled radioimmunoconjugates, assessment of serum stability and antigen binding ability

In this study, the feasibility of constructing radioimmunoconjugates by using the novel therapeutic candidate alpha-emitter, (227)Th, was evaluated. By use of the bifunctional chelator, p-SCN-benzyl-DOTA, (227)Th was conjugated to the two monoclonal antibodies, rituximab and trastuzumab. Their stability in 80% fetal bovine serum at 37 degrees C was measured. The immunoreactive fractions were determined by using CD20- and HER/2-positive cells, respectively. The overall labeling yield spanned from 6% to 17%. The radioimmunoconjugates demonstrated a relevant stability in serum and showed appropriate antigen-binding abilities.

Cancer 'chemotherapia specifica' ninety years after Paul Ehrlich

From his student days throughout his whole life, Paul Ehrlich tried hard to obtain 'chemotherapia specifica' for the harmless systemic therapy of infectious diseases. Given the poor therapeutic benefit obtained with cytotoxic therapeutic agents and empirical radiopharmaceuticals, so far used only for neoadjuvant and adjuvant treatments of cancer, we have tried to develop Paul Ehrlich's 'chemotherapia specifica' for safe and effective therapy of cancers in cigarette smokers. With the help of sector-field inductively coupled plasma mass spectrometry, we have tried to find the metabolic action of cigarette smoke constituents in the cancerous organ. On the basis of these results we are synthesizing pharmaceuticals and radiopharmaceuticals to purge the tobacco-constituent metabolic products that cause cancer. The purity, stability and chemical nature of the pharmaceuticals and radiopharmaceuticals required for therapy have been studied by chromatography and electrophoresis. The cancer specificity of the therapeutic agent has been examined by the total body distribution of its gamma- and beta-labelled species in solution. At present, a bladder cancer-specific therapeutic agent is being developed.

Radiobromination of humanized anti-HER2 monoclonal antibody trastuzumab using N-succinimidyl 5-bromo-3-pyridinecarboxylate, a potential label for immunoPET

Combining the specificity of radioimmunoscintigraphy and the high sensitivity of PET in an in vivo detection technique could improve the quality of nuclear diagnostics. Positron-emitting nuclide (76)Br (T(1/2)=16.2 h) might be a possible candidate for labeling monoclonal antibodies (mAbs) and their fragments, provided that the appropriate labeling chemistry has been established. For internalizing antibodies, such as the humanized anti-HER2 monoclonal antibody, trastuzumab, radiobromine label should be residualizing, i.e., ensuring that radiocatabolites are trapped intracellularly after the proteolytic degradation of antibody. This study evaluated the chemistry of indirect radiobromination of trastuzumab using N-succinimidyl 5-(tributylstannyl)-3-pyridinecarboxylate. Literature data indicated that the use of this method provided residualizing properties for iodine and astatine labels on some antibodies. An optimized "one-pot" procedure produced an overall labeling efficiency of 45.5+/-1.2% over 15 min. The bromine label was stable under physiological and denaturing conditions. The labeled trastuzumab retained its capacity to bind specifically to HER2-expressing SKOV-3 ovarian carcinoma cells in vitro (immunoreactivity more than 75%). However, in vitro cell test did not demonstrate that the radiobromination of trastuzumab using N-succinimidyl 5-bromo-3-pyridinecarboxylate improves cellular retention of radioactivity in comparison with the use of N-succinimidyl 4-bromobenzoate.