Contribution of electrospray mass spectrometry for the characterization, design, and development of nitrido technetium and rhenium heterocomplexes as potential radiopharmaceuticals

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.

Nitrido Technetium-99 m Core in Radiopharmaceutical Applications: Four Decades of Research

The knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing efficient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes.

Drug composition matters: the influence of carrier concentration on the radiochemical purity, hydroxyapatite affinity and in-vivo bone accumulation of the therapeutic radiopharmaceutical 188Rhenium-HEDP

INTRODUCTION

(188)Rhenium-HEDP is an effective bone-targeting therapeutic radiopharmaceutical, for treatment of osteoblastic bone metastases. It is known that the presence of carrier (non-radioactive rhenium as ammonium perrhenate) in the reaction mixture during labeling is a prerequisite for adequate bone affinity, but little is known about the optimal carrier concentration.

METHODS

We investigated the influence of carrier concentration in the formulation on the radiochemical purity, in-vitro hydroxyapatite affinity and the in-vivo bone accumulation of (188)Rhenium-HEDP in mice.

RESULTS

The carrier concentration influenced hydroxyapatite binding in-vitro as well as bone accumulation in-vivo. Variation in hydroxyapatite binding with various carrier concentrations seemed to be mainly driven by variation in radiochemical purity. The in-vivo bone accumulation appeared to be more complex: satisfactory radiochemical purity and hydroxyapatite affinity did not necessarily predict acceptable bio-distribution of (188)Rhenium-HEDP.

CONCLUSIONS

For development of new bisphosphonate-based radiopharmaceuticals for clinical use, human administration should not be performed without previous animal bio-distribution experiments. Furthermore, our clinical formulation of (188)Rhenium-HEDP, containing 10 μmol carrier, showed excellent bone accumulation that was comparable to other bisphosphonate-based radiopharmaceuticals, with no apparent uptake in other organs.

ADVANCES IN KNOWLEDGE

Radiochemical purity and in-vitro hydroxyapatite binding are not necessarily predictive of bone accumulation of (188)Rhenium-HEDP in-vivo.

IMPLICATIONS FOR PATIENT CARE

The formulation for (188)Rhenium-HEDP as developed by us for clinical use exhibits excellent bone uptake and variation in carrier concentration during preparation of this radiopharmaceutical should be avoided.

Rhenium and technetium tricarbonyl, {M(CO)3} (+) (M = Tc, Re), binding to mammalian metallothioneins: new insights into chemical and radiopharmaceutical implications

This paper deals with the binding of the four mammalian metallothioneins (MTs) to the organometallic metal fragment {fac-M(CO)3}(+) (M = (99)Tc, Re), which is highly promising for the preparation of second-generation radiopharmaceuticals. The study of the transmetallation reaction between zinc and rhenium in Zn7-MT1 by means of UV-vis and CD spectroscopy demonstrated the incorporation of the {fac-Re(CO)3}(+) fragment to the MTs. This reaction should be performed at 70 °C to accelerate the reaction rate, a result that is consistent with the reported reactivity of the rhenium fragment. ESI-TOF MS demonstrated the formation of mixed-metal species as Zn6,{Re(CO)3}-MT, Zn6,{Re(CO)3}2-MT, and Zn5,{Re(CO)3}3-MT, as well as the different reactivity of the four MT isoforms. Hence, Zn-MT3 showed the highest reactivity, in agreement with its high Cu-thionein character, whereas Zn-MT2 exhibited the lowest reactivity, in line with its high Zn-thionein character. The reactivity of the Zn-loaded forms of MT1 and MT4 is intermediate between those of MT3 and MT2. The study of the binding of the {fac-(99)Tc(CO)3}(+) fragment to MTs showed a significant and very interesting different reactivity in relation to rhenium. The transmetallation reaction is much more effective with technetium than with rhenium and significant amounts of mixed Zn x ,{(99)Tc(CO)3} y -MT species were formed with the four MT isoforms whereas only MT3 rendered similar amounts of rhenium derivatives. The results obtained in this study support the possible use of technetium for labelling mammalian metallothioneins and also for possible radiopharmaceutical applications.

Characterisation via electrospray ionisation multistage mass spectrometry of three related series of nitrido technetium complexes containing phosphinothiolate and dithiocarbamate ligands

Nine nitrido technetium compounds comprising bis-substituted Tc(N)(PS)(2) (1-4) (PS = bidentate phosphinothiolate ligands) and Tc(N)(dtc)(2) (5, 6) derivatives (dtc = bidentate dithiocarbamate), and mixed-ligand Tc(N)(PS)(dtc) (7-9) species, were subjected to electrospray ionisation mass spectrometry and MS(n) experiments. Bis-substituted phosphinothiolato complexes 1-4 lead to the straightforward formation of dinuclear species reasonably originating from proton bound dimers. These dinuclear species do not show, under collisionally induced fragmentation processes, the formation of monomeric units but cleavages related to the ligand framework, thereby proving the high stability of the [Tc--H(+)--Tc] bond. Bis-dithiocarbamate compounds 5 and 6 show, instead, abundant [M+H](+), [M+Na](+) and [2M+Na](+) ions, and their collisionally induced fragmentations are highly favoured with cleavages related to the C--N and C--S bonds. During these processes, the coordination of a water molecule to [MH-L](+) product ions is observed, as proved by the collisionally induced H(2)O loss detected for this species. Mixed-ligand compounds 7 and 8 show the protonated molecules and Na(+)-cationised ions with fragmentation processes related to the dithiocarbamate moiety. This behaviour indicates that coordination of ether- and ester-substituted dithiocarbamates to the [Tc [triple chemical bond] N] group is weaker than that of phosphinothiolates. Conversely, diethyldithiocarbamate inserted in mixed complex 9 enhances both C--N and Tc--S bonds, and fragmentation processes suggest that metal-phosphinothiolate and metal-dithiocarbamate show comparable strength.

Electrospray mass spectrometry of a series of mixed nitrido 99gTc- heterocomplexes conjugated with bioactive molecules

Electrospray ionization mass spectrometry (ESI-MS) was successfully employed for the identification of six nitrido technetium mixed ligand complexes with a general formula of [99gTc(N)(O,S-BID)(PNP)], where PNP represents a heterodiphosphine and O,S-BID represents a simple dianionic bidentate ligand (compounds 1-3) or a more sophisticated N-substituted O,S-cysteine framework conjugated with a bio- active molecule (BAM) (compounds 4-6). In spite of similar coordination spheres exhibited by all the complexes investigated, simple co-ordination compounds 1-3 displayed collisionally-induced fragmentation processes (MSn) different from those observed in biomolecule-containing compounds 4-6. In the latter, more decomposition channels were observed. This behavior is likely to be associated with some additional intramolecular contacts of the biomolecule (or part of the biomolecule) with pendant group(s) incorporated in the PNP-co-ligand. This view is further supported by the observations arising from both in vitro binding affinity experiments and nuclear magnetic resonance investigations. The presence of cationized forms for all compounds 1-6 and the practical lack of the [2M + Na]+ species for biomolecule-containing compounds 4-6 provided further evidence of a subtly different structural conformation.