Production of the therapeutic radionuclides 193mPt and 195mPt with high specific activity via α-particle-induced reactions on 192Os

Study of activation cross sections of double neutron capture reaction on 193Ir for the reactor production route of radiotherapeutic 195mPt

The radiotherapeutic 195mPt is among the most effective Auger electron emitters of the currently studied radionuclides that have a potential theranostic application in nuclear medicine. Production of 195mPt through double neuron capture of enriched 193Ir followed by β--decay to the radioisotope of interest carried out at the research reactor IBR-2 is described. Because of the high radiation background, radiochemical purification procedure of 195mPt from bulk of iridium was needed to be developed and is detailed here as well. For the first time, cross section and resonance integral for the reaction 194Ir(n,γ)195mIr were determined. Resonance neutrons contribution was established to exceed that of thermal neutrons, and resonance integral for the reaction 194Ir(n,γ)195mIr is calculated to be 2900 b. Specific activity of 195mPt was estimated to reach a value of 38.7 GBq/(g Pt) at IBR-2 by the end of bombardment (EOB).

Platinum nanoparticles labelled with iodine-125 for combined "chemo-Auger electron" therapy of hepatocellular carcinoma

Convenient therapeutic protocols against hepatocellular carcinoma (HCC) exhibit low treatment effectiveness, especially in the context of long-term effects, which is primarily related to late diagnosis and high tumor heterogeneity. Current trends in medicine concern combined therapy to achieve new powerful tools against the most aggressive diseases. When designing modern, multimodal therapeutics, it is necessary to look for alternative routes of specific drug delivery to the cell, its selective (with respect to the tumor) activity and multidirectional action, enhancing the therapeutic effect. Targeting the physiology of the tumor makes it possible to take advantage of certain characteristic properties of the tumor that differentiate it from other cells. In the present paper we designed for the first time iodine-125 labeled platinum nanoparticles for combined "chemo-Auger electron" therapy of hepatocellular carcinoma. High selectivity achieved by targeting the tumor microenvironment of these cells was associated with effective radionuclide desorption in the presence of H₂O₂. The therapeutic effect was found to be correlated with cell damage at various molecular levels including DNA DSBs and was observed in a dose-dependent manner. A three-dimensional tumor spheroid revealed successful radioconjugate anticancer activity with a significant treatment response. A possible concept for clinical application after prior in vivo trials may be achieved via transarterial injection of micrometer range lipiodol emulsions with encapsulated ¹²⁵I-NP. Ethiodized oil gives several advantages especially for HCC treatment; thus bearing in mind a suitable particle size for embolization, the obtained results highlight the exciting prospects for the development of PtNP-based combined therapy.

The role of chemistry in accelerator-based production and separation of radionuclides as basis for radiolabelled compounds for medical applications

Radiochemical separations used in large scale routine production of diagnostic and therapeutic radionuclides at a particle accelerator for patient care are briefly outlined. The role of chemistry at various stages of development of a production route of a novel radionuclide, namely nuclear data measurement, high-current targetry, chemical processing and quality control of the product, is discussed in detail. Special attention is paid to production of non-standard positron emitters (e.g. 44gSc, 64Cu, 68Ga, etc.) at a cyclotron and novel therapeutic radionuclides (e.g. 67Cu, 225Ac, etc.) at an accelerator. Some typical examples of radiochemical methods involved are presented.

Cisplatin - A more Efficient Drug in Combination with Radionuclides?

AIM

The combination of conventional chemotherapeutic drugs with radionuclides or external radiation is discussed for a long period of time. The major advantage of a successful combination therapy is the reduction of severe side effects by decreasing the needed dose and simultaneously increasing therapeutic efficiency.

METHODS

In this study, pUC19 plasmid DNA was incubated with the cytostatic drug cisplatin and additionally irradiated with ^99mTc, ¹⁸⁸Re and ²²³Ra. To verify the contribution of possibly excited platinum atoms to the emission of Auger electrons we determined DNA damages, such as single- and double strand breaks.

RESULTS

The threshold concentration value of cisplatin, which was tolerated by pUC19 plasmid DNA was determined to be 18-24 nM. Nevertheless, even at higher dose values (>100 Gy) and simultaneous incubation of cisplatin to 200 ng plasmid DNA, no significant increase in the number of induced single- and double-strand breaks was obtained, compared to the damage solely caused by the radionuclides.

CONCLUSION

We thereby conclude that there is no direct dependence of the mechanism of strand break induction to the absence or presence of platinum atoms attached to the DNA. Reported increasing DNA damages in therapy approaches on a cellular level strongly depend on the study design and are mainly influenced by repair mechanisms in living cells. Nevertheless, the use of radioactive cisplatin, containing the Auger electron emitter ¹⁹¹Pt, ^193mPt or ^195mPt, is a bright prospect for future therapy by killing tumor cells combining two operating principles: a cytostatic drug and a radiopharmaceutical at the same time.

Production of 191Pt from an iridium target by vertical beam irradiation and simultaneous alkali fusion

We have developed a new method for producing ¹⁹¹Pt from an iridium target. Alkali fusion of iridium was successfully performed using a vertical beam irradiation method and a mixed target of Ir and Na₂O₂, which resulted in easy dissolution of the irradiated iridium target. A trace amount of Pt^ⅣCl₆^2- was isolated from bulk Ir^ⅣCl₆^2- by solvent extraction and anion exchange chromatography. The production yield of ¹⁹¹Pt was 7.1 ± 0.4 (MBq/μA h, EOB) by proton irradiation at 30 MeV. The radioplatinum product (n.c.a.) was prepared at a radiochemical purity of 97% for Pt^ⅣCl₆^2-, and 95% for Pt^ⅡCl₄^2-, respectively.

Excitation functions of proton- and deuteron-induced nuclear reactions on natural iridium for the production of 191Pt

We studied the excitation functions of residual radionuclides produced via proton and deuteron bombardment on natural iridium in the energy ranges of 30-15 MeV and 50-15 MeV, respectively. A conventional stacked-foil activation technique combined with HPGe γ-ray spectrometry was used to measure the excitation functions for ^{189, 191}Pt and ^{189, 190g, 192g, 194g}Ir radionuclide production. Theoretical thick target yields were estimated to be 172 MBq/µA h and 192 MBq/µA h via the ¹⁹³Ir(p,3n)¹⁹¹Pt reaction at 29.6-17.5 MeV and the ¹⁹³Ir(d,4n)¹⁹¹Pt reaction at 40.3-23.8 MeV, respectively. The feasibility of ¹⁹¹Pt production from an iridium target was discussed, and compared with previously reported methods for the production of ¹⁹¹Pt.

Measurement of activation cross sections of alpha particle induced reactions on iridium up to an energy of 50 MeV

Cross sections of alpha particle induced nuclear reactions on iridium were investigated using a 51.2-MeV alpha particle beam. The standard stacked-foil target technique and the activation method were applied. The activity of the reaction products was assessed without chemical separation using high resolution gamma-ray spectrometry. Excitation functions for production of gold, platinum and iridium isotopes (^196m2Au, ^196m,gAu, ^195m,gAu, ¹⁹⁴Au, ^193 m,gAu, ¹⁹²Au, ^191m,gAu, ¹⁹¹Pt, ^195mPt, ^194gIr, ^194mIr, ^192gIr, ^190gIr and ¹⁸⁹Ir) were determined and compared with available earlier measured experimental data and results of theoretical calculations using TALYS code system. Cross section data were reported for the first time for the ^natIr(α,x)^196m2Au, ^natIr(α,x)^196m,gAu, ^natIr(α,x)¹⁹¹Pt, ^natIr(α,x)^195mPt, ^natIr(α,x)^194gIr, ^natIr(α,x)^194mIr, ^natIr(α,x)^190gIr and ^natIr(α,x)¹⁸⁹Ir processes. A possible production route for ^195mPt, the potentially important radionuclide in nuclear medicine, is discussed.

Nuclear data for production and medical application of radionuclides: Present status and future needs

INTRODUCTION

The significance of nuclear data in the choice and medical application of a radionuclide is considered: the decay data determine its suitability for organ imaging or internal therapy and the reaction cross section data allow optimisation of its production route. A brief discussion of reaction cross sections and yields is given.

STANDARD RADIONUCLIDES

The standard SPECT, PET and therapeutic radionuclides are enumerated and their decay and production data are considered. The status of nuclear data is generally good. Some existing discrepancies are outlined. A few promising alternative production routes of ^99mTc and ⁶⁸Ga are discussed.

RESEARCH-ORIENTED RADIONUCLIDES

The increasing significance of non-standard positron emitters in organ imaging and of low-energy highly-ionizing radiation emitters in internal therapy is discussed, their nuclear data are considered and a brief review of their status is presented. Some other related nuclear data issues are also mentioned.

PRODUCTION OF RADIONUCLIDES USING NEWER TECHNOLOGIES

The data needs arising from new directions in radionuclide applications (multimode imaging, theranostic approach, radionanoparticles, etc.) are considered. The future needs of data associated with possible utilization of newer irradiation technologies (intermediate energy cyclotron, high-intensity photon accelerator, spallation neutron source, etc.) are outlined.

CONCLUSION

Except for a few small discrepancies, the available nuclear data are sufficient for routine production and application of radionuclides. Considerable data needs exist for developing novel radionuclides for applications. The developing future technologies for radionuclide production will demand further data-related activities.

Uses of alpha particles, especially in nuclear reaction studies and medical radionuclide production

Alpha particles exhibit three important characteristics: scattering, ionisation and activation. This article briefly discusses those properties and outlines their major applications. Among others, α-particles are used in elemental analysis, investigation and improvement of materials properties, nuclear reaction studies and medical radionuclide production. The latter two topics, dealing with activation of target materials, are treated in some detail in this paper. Measurements of excitation functions of α-particle induced reactions shed some light on their reaction mechanisms, and studies of isomeric cross sections reveal the probability of population of high-spin nuclear levels. Regarding medical radionuclides, an overview is presented of the isotopes commonly produced using α-particle beams. Consideration is also given to some routes which could be potentially useful for production of a few other radionuclides. The significance of α-particle induced reactions to produce a few high-spin isomeric states, decaying by emission of low-energy conversion or Auger electrons, which are of interest in localized internal radiotherapy, is outlined. The α-particle beam, thus broadens the scope of nuclear chemistry research related to development of non-standard positron emitters and therapeutic radionuclides.

The present and future of medical radionuclide production

Medical radionuclide production technology is well established. Both reactors and cyclotrons are utilized for production; the positron emitters, however, are produced exclusively using cyclotrons. A brief survey of the production methods of most commonly used diagnostic and therapeutic radionuclides is given. The emerging radionuclides are considered in more detail. They comprise novel positron emitters and therapeutic radionuclides emitting low-range electrons and α-particles. The possible alternative production routes of a few established radionuclides, like 68Ga and 99mTc, are discussed. The status of standardisation of production data of the commonly used as well as of some emerging radionuclides is briefly mentioned. Some notions on anticipated future trends in the production and application of radionuclides are considered.

New trends in nuclear data research for medical radionuclide production

Nuclear reaction cross section data are of great significance in optimisation of production routes of radionuclides. This article deals with some newer aspects of data research related to production of both standard and novel radionuclides. The recent work to standardise the known data is discussed and new measurements with regard to further optimisation of production routes of some commonly used radionuclides are mentioned. Attempts to increase the specific activity of some reactor-produced radionuclides through the use of charged-particle induced reactions are outlined. The jeopardy in the supply of99mTcviaa fission-produced99Mo/99mTc generator is considered and its possible direct production at a cyclotron is briefly discussed. Regarding the novel radionuclides, development work is presently focussed on non-standard positron emitters for diagnosis and on low-range highly ionising radiation emitters for internal radiotherapy. Recent nuclear reaction cross section measurements related to the production of the two types of radionuclides are briefly reviewed and some anticipated trends in nuclear data research are considered.

Small scale production of high purity 193mPt by the 192Os(α,ߙ3n)-process

Some production aspects of the Auger electron emitter 193mPt (T 1/2=4.33 d) through the 192Os(α,ߙ3n)-process were investigated. Relatively thick targets of 99.65% enriched 192Os, prepared by pressing or electrolytic deposition, were irradiated with 40 MeV α-particles for 3 h at a nominal beam current of 1.6 μA. The radioplatinum formed was chemically separated with a yield of 90% and the expensive target material was recovered with a yield of 85%. The radioactivity of 193mPt was determined by high resolution X-ray spectrometry. The radionuclidic purity of 193mPt amounted to 99%, the level of 195mPt and 191Pt impurities being each 0.5%. The batch yield of 193mPt achieved was about 10 MBq with a specific activity of 1 GBq/μg Pt. Both the batch yield and the specific activity could be appreciably increased through improved targetry. A comparison of the cyclotron and reactor production routes of 193mPt shows that the (n,ߙγ) reaction leads to high production yields but the α-particle induced reaction results in a product of higher radionuclidic purity and four orders of magnitude higher specific activity of 193mPt.