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Radionuclide-based Diagnosis and Therapy of Prostate Cancer
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Sven-Erik Strand, Mohamed Altai, Joanna Strand, David Ulmert
The main source of Actinium-225 is currently 229Th generators (t½=7340 y), which can be milked over a 3-wk period and allow the separation of 225Ra and 225Ac. 225Ac (t½ = 10.0 d; 5.8-MeV α-particle) decays sequentially through 6 dominant daughters to stable 209Bi. Decay of a single 225Ac atom yields 4 net α-disintegrations and 3 β-disintegrations together with the emission of 2 useful γ-emissions. The 225Ac daughter 213Bi (t½ = 45.6 min; 97.8% β, 2.2% 6-MeV α-particle) is also a widely studied radionuclide for targeted α-therapy. Dissociated free 225Ac accumulates primarily in the liver and bone. The 225Ac daughters 221Fr and 213Bi will preferentially accumulate in the kidneys. Together, this makes these organs highly prone to toxic effects caused by 225Ac-based radiopharmaceuticals. The decay scheme of 225Ac can be seen in Figure 19.9 from Schwartz and colleagues [27].
Structures, electronic properties, hydration and UV-vis absorption spectra of actinide motexafins [An-Motex]2+ (An = Ac, Cm, Lr) and [UO2-Motex]1+: insights from DFT calculations
Published in Molecular Physics, 2020
Xiaojun Li, Xiaoyan Cao, Norah Heinz, Michael Dolg
Texaphyrins are tripyrrolic, pentaaza macrocycles that have a strong, but ‘expanded’ resemblance to the porphyrins [1]. The texaphyrins contain five coordinating nitrogen atoms within their central core, which is roughly 20% larger than the one of the porphyrins with merely four coordinating nitrogen atoms. Therefore, texaphyrins can form stable 1:1 complexes with a range of larger metal cations, particularly the trivalent ions of the lanthanide series. The lanthanide (III) texaphyrins were firstly synthesised and structurally characterised using single-crystal X-ray diffraction analysis by Sessler and coworkers [2]. Soon a substitution of the O(CH2)3OH side chains of texaphyrins by O((CH2)2O)3CH3 yielded so-called motexafins (Figure 1), which are more stable macrocycles and have been widely used since then. Moreover, the lanthanide(III) texaphyrins were discovered to be useful due to a wide variety of roles in biomedical areas, i.e. texaphyrins are experimental drugs that are known to localise to cancerous lesions and assist to produce reactive oxygen species (ROS), which lead to aptosis (programmed cell death); they are also used as magnetic resonance imaging (MRI) contrast agents, isotope delivery vehicles, and site-localizing carriers [3]. Recently, it was reported that lanthanide(III) texaphyrins can be used as bioinspired photocatalysts that promote a novel approach to the degradation of curcumin, a 1,3-diketo-containing natural product [4]. The success of the lanthanide(III) texaphyrins encouraged scientists to think about complexes with their heavier f-element homologues and their possible technical usage. It is well known that all isotopes of the actinide elements are radioactive, and some of them are relevant for the production of electricity from nuclear energy, the development of nuclear weapons or medical applications related to their radioactivity. It was found that the α-emitting radionuclide actinium-225 possesses nuclear properties that are highly promising for use in targeted α-therapy (TAT), a therapeutic strategy that employs α-particle emissions to destroy tumours [5]. Unfortunately, the lack of suitable chelating agents for 225Ac is one of the bottlenecks for the stable retention of 225Ac and its progeny to targeting vectors in vivo [5]. Moreover there is also an existing urgent need for chemical tools that can identify, sequester, and quantitate dangerous radioisotopes in vivo [6], as well as for developing chelating agents for the removal of actinide cations accidentally introduced into living organisms. Furthermore, as well known the cleaning-up process of nuclear waste and the work-up of burned nuclear fuels also needs efficient extractants to separate lanthanide(III) from actinide(III) ions [7]. Therefore it is worthwhile to study the actinide(III) texaphyrins/motexafins which might lead to new approaches in biomedical application and waste remediation.