Photonuclear production and antitumor effect of radioactive cisplatin (195mPt)

Photonuclear production of medical radioisotopes 161Tb and 155Tb

The production possibility of ¹⁶¹Tb and ¹⁵⁵Tb by irradiating of natural dysprosium with gamma rays obtained by decelerating an electron beam with an energy of 55 MeV has been demonstrated experimentally. The yield of ¹⁶¹Tb was 14.4 × 10³ Bq × μA^-1 × h^-1 × cm² × g_Dy2O3^-1. Simultaneously, upon irradiation, ¹⁵⁵Dy is formed with the yield of 25 × 10³ Bq × μA^-1 × h^-1 × cm² × g_Dy2O3^-1, which leads to the formation of 1.6 × 10³ Bq × μA^-1 × h^-1 × cm² × g_Dy2O3^-1 of ¹⁵⁵Tb. It has been shown that the isolation of terbium radioisotopes from tens of mg of dysprosium target can be achieved by extraction chromatography, and final separation yield was 39%. The impurity of ¹⁶⁰Tb is 7.3% of the ¹⁶¹Tb activity at EOB.

Challenges and opportunities in the development of metal-based anticancer theranostic agents

Around 10 million fatalities were recorded worldwide in 2020 due to cancer and statistical projections estimate the number to increase by 60% in 2040. With such a substantial rise in the global cancer burden, the disease will continue to impose a huge socio-economic burden on society. Currently, the most widely used clinical treatment modality is cytotoxic chemotherapy using platinum drugs which is used to treat variety of cancers. Despite its clinical success, critical challenges like resistance, off-target side effects and cancer variability often reduce its overall therapeutic efficiency. These challenges require faster diagnosis, simultaneous therapy and a more personalized approach toward cancer management. To this end, small-molecule ‘theranostic’ agents have presented a viable solution combining diagnosis and therapy into a single platform. In this review, we present a summary of recent efforts in the design and optimization of metal-based small-molecule ‘theranostic’ anticancer agents. Importantly, we highlight the advantages of a theranostic candidate over the purely therapeutic or diagnostic agent in terms of evaluation of its biological properties.

Gynaecological Cancer Diagnostics: 99mTc-Cisplatin Complex as a Future Approach for Early, Prompt and Efficient Diagnosis of Gynaecological Cancer

BACKGROUND

Gynaecological cancers (GCCa) are common and have a significant mortality rate all over the world. Early diagnosis of cancer can play a key role in the treatment and survival of a patient. Identification, staging, treatment, and monitoring of gynaecological malignancies is being done successfully by nuclear medicines.

DISCUSSION

Currently, single-photon emission computed tomography (SPECT) and positron emission tomography (PET) centered imaging techniques are being developed for use in patients with GCCa as a diagnostic tool. The present work elucidates several clinical studies on the use of radiopharmaceuticals, based on their effectiveness, in the early detection and management of GCCa. It also highlights the importance of reconsidering the biology for nuclear imaging as a future modality for early, rapid and efficient diagnosis of gynecological cancers. This comprehensive review is a part of our study designed to detect gynaecological cancers at an early stage using radionuclide complex, 99m Tc-Cisplatin.

CONCLUSION

This article summarizes the significance of radioscintigraphy such as single-photon emission computed tomography (SPECT) and PET for identification of GCCa in the experimental humans and animals.

Targeting of radioactive platinum-bisphosphonate anticancer drugs to bone of high metabolic activity

Platinum-based chemotherapeutics exhibit excellent antitumor properties. However, these drugs cause severe side effects including toxicity, drug resistance, and lack of tumor selectivity. Tumor-targeted drug delivery has demonstrated great potential to overcome these drawbacks. Herein, we aimed to design radioactive bisphosphonate-functionalized platinum (^195mPt-BP) complexes to confirm preferential accumulation of these Pt-based drugs in metabolically active bone. In vitro NMR studies revealed that release of Pt from Pt BP complexes increased with decreasing pH. Upon systemic administration to mice, Pt-BP exhibited a 4.5-fold higher affinity to bone compared to platinum complexes lacking the bone-seeking bisphosphonate moiety. These Pt-BP complexes formed less Pt-DNA adducts compared to bisphosphonate-free platinum complexes, indicating that in vivo release of Pt from Pt-BP complexes proceeded relatively slow. Subsequently, radioactive ^195mPt-BP complexes were synthesized using ^195mPt(NO₃)₂(en) as precursor and injected intravenously into mice. Specific accumulation of ^195mPt-BP was observed at skeletal sites with high metabolic activity using micro-SPECT/CT imaging. Furthermore, laser ablation-ICP-MS imaging of proximal tibia sections confirmed that ^195mPt BP co-localized with calcium in the trabeculae of mice tibia.

Auger electrons for cancer therapy - a review

Background

Auger electrons (AEs) are very low energy electrons that are emitted by radionuclides that decay by electron capture (e.g. ¹¹¹In, ⁶⁷Ga, ^99mTc, ^195mPt, ¹²⁵I and ¹²³I). This energy is deposited over nanometre-micrometre distances, resulting in high linear energy transfer (LET) that is potent for causing lethal damage in cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for treatment of cancer. In this review, we describe the radiobiological properties of AEs, their radiation dosimetry, radiolabelling methods, and preclinical and clinical studies that have been performed to investigate AEs for cancer treatment.

Results

AEs are most lethal to cancer cells when emitted near the cell nucleus and especially when incorporated into DNA (e.g. ¹²⁵I-IUdR). AEs cause DNA damage both directly and indirectly via water radiolysis. AEs can also kill targeted cancer cells by damaging the cell membrane, and kill non-targeted cells through a cross-dose or bystander effect. The radiation dosimetry of AEs considers both organ doses and cellular doses. The Medical Internal Radiation Dose (MIRD) schema may be applied. Radiolabelling methods for complexing AE-emitters to biomolecules (antibodies and peptides) and nanoparticles include radioiodination (¹²⁵I and ¹²³I) or radiometal chelation (¹¹¹In, ⁶⁷Ga, ^99mTc). Cancer cells exposed in vitro to AE-emitting radiotherapeutic agents exhibit decreased clonogenic survival correlated at least in part with unrepaired DNA double-strand breaks (DSBs) detected by immunofluorescence for γH2AX, and chromosomal aberrations. Preclinical studies of AE-emitting radiotherapeutic agents have shown strong tumour growth inhibition in vivo in tumour xenograft mouse models. Minimal normal tissue toxicity was found due to the restricted toxicity of AEs mostly on tumour cells targeted by the radiotherapeutic agents. Clinical studies of AEs for cancer treatment have been limited but some encouraging results were obtained in early studies using ¹¹¹In-DTPA-octreotide and ¹²⁵I-IUdR, in which tumour remissions were achieved in several patients at administered amounts that caused low normal tissue toxicity, as well as promising improvements in the survival of glioblastoma patients with ¹²⁵I-mAb 425, with minimal normal tissue toxicity.

Conclusions

Proof-of-principle for AE radiotherapy of cancer has been shown preclinically, and clinically in a limited number of studies. The recent introduction of many biologically-targeted therapies for cancer creates new opportunities to design novel AE-emitting agents for cancer treatment. Pierre Auger did not conceive of the application of AEs for targeted cancer treatment, but this is a tremendously exciting future that we and many other scientists in this field envision.

Photonuclear production, chemistry, and in vitro evaluation of the theranostic radionuclide 47Sc

Background

In molecular imaging and nuclear medicine, theranostic agents that integrate radionuclide pairs are successfully being used for individualized care, which has led to rapidly growing interest in their continued development. These compounds, which are radiolabeled with one radionuclide for imaging and a chemically identical or similar radionuclide for therapy, may improve patient-specific treatment and outcomes by matching the properties of different radionuclides with a targeting vector for a particular tumor type. One proposed theranostic radionuclide is scandium-47 (⁴⁷Sc, T_1/2 = 3.35 days), which can be used for targeted radiotherapy and may be paired with the positron emitting radionuclides, ⁴³Sc (T_1/2 = 3.89 h) and ⁴⁴Sc (T_1/2 = 3.97 h) for imaging. The aim of this study was to investigate the photonuclear production of ⁴⁷Sc via the ⁴⁸Ti(γ,p)⁴⁷Sc reaction using an electron linear accelerator (eLINAC), separation and purification of ⁴⁷Sc, the radiolabeling of somatostatin receptor-targeting peptide DOTATOC with ⁴⁷Sc, and in vitro receptor-mediated binding of [⁴⁷Sc]Sc-DOTATOC in AR42J somatostatin receptor subtype two (SSTR2) expressing rat pancreatic tumor cells.

Results

The rate of ⁴⁷Sc production in a stack of natural titanium foils (n = 39) was 8 × 10⁷ Bq/mA·h (n = 3). Irradiated target foils were dissolved in 2.0 M H₂SO₄ under reflux. After dissolution, trivalent ⁴⁷Sc ions were separated from natural Ti using AG MP-50 cation exchange resin. The recovered ⁴⁷Sc was then purified using CHELEX 100 ion exchange resin. The average decay-corrected two-step ⁴⁷Sc recovery (n = 9) was (77 ± 7)%. A radiolabeling yield of > 99.9% of [⁴⁷Sc]Sc-DOTATOC (0.384 mg in 0.3 mL) was achieved using 1.7 MBq of ⁴⁷Sc. Blocking studies using Octreotide illustrated receptor-mediated uptake of [⁴⁷Sc]Sc-DOTATOC in AR42J cells.

Conclusions

⁴⁷Sc can be produced via the ⁴⁸Ti(γ,p)⁴⁷Sc reaction and separated from natural Ti targets with a yield and radiochemical purity suitable for radiolabeling of peptides for in vitro studies. The data in this work supports the potential use of eLINACs for studies of photonuclear production of medical radionuclides and the future development of high-intensity eLINAC facilities capable of producing relevant quantities of carrier-free radionuclides currently inaccessible via routine production pathways or limited due to costly enriched targets.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0515-8) contains supplementary material, which is available to authorized users.