Synthesis, proteolytic stability, and in vitro evaluation of DOTA conjugated p160 peptide based radioconjugates: [177Lu]Lu-DOTA-p160

In this work, we describe the synthesis, in vitro stability, and preliminary biological evaluation of [¹⁷⁷Lu]Lu-DOTA-p160 peptide-based radiopharmaceuticals. Our findings highlight that all DOTA-p160-peptide radioconjugates exhibit favorable proteolytic and enzymatic stability with a prolonged half-life in human plasma and serum. Cell uptake studies carried out on MCF-7 cell line revealed saturable binding of the radioconjugates in the nanomolar range, thereby demonstrating their promising potential in the imaging and therapy of breast tumors.

Gallium and indium complexes with new hexadentate bis(semicarbazone) and bis(thiosemicarbazone) chelators

The synthesis of two new hexadentate potentially tetra-anionic acyclic chelators, an N2O4-donor bis(semicarbazone) (H4bsc) and an N2O2S2-donor bis(thiosemicarbazone) (H4btsc), is described. Coordination reactions of the ligands with gallium and indium precursors were investigated and yielded the complexes [Ga(Hbsc)] (1) and [In(Hbtsc)] (2), respectively. Ligands and complexes structures were confirmed by several techniques, including FTIR, NMR (1H, 13C, COSY, HSQC), ESI(+)-MS and single crystal X-ray diffraction analysis. The radioactive congeners [67Ga(Hbsc)] (1*) and [111In(Hbtsc)] (2*) were also synthesized and their radiolabeling yield and radiochemical purity were certified by HPLC and ITLC analyses. Biodistribution assays in groups of CD-1 mice showed a high uptake of both radiocomplexes in liver and intestine where 1* presented higher retention. In vitro and in vivo assays revealed higher stability of 1* compared with 2*, namely in the blood. The results suggest that radiocomplex 1* is a candidate for further investigation as it could be prepared in high yields (>95%), at low temperature (20-25 °C) and at fast reaction time (15 min), which are very desirable synthesis conditions for potential new radiopharmaceuticals.

Cyclen-based Gd3+ complexes as MRI contrast agents: Relaxivity enhancement and ligand design

Magnetic Resonance Imaging (MRI) is a noninvasive radiology technique used to examine the internal organs of human body. It is useful for the diagnosis of structural abnormalities in the body. Contrast agents are used to increase the sensitivity of this technique. 1,4,7,10-Tetraazacyclododecane (cyclen) is a macrocyclic tetraamine. Its derivatives act as useful ligands to produce stable complexes with Gd³⁺ ion. Such chelates are investigated as MRI contrast agents. Free Gd³⁺ ion is extremely toxic for in vivo use. Upon complexation with a cyclen-based ligand, it is trapped in the preformed central cavity of the ligand resulting in the formation of a highly stable Gd³⁺-chelate. Better kinetic and thermodynamic stability of cyclen-based MRI contrast agents decrease their potential toxicity for in vivo use. Consequently, such agents have proved to be safest for clinical applications. Relaxivity is the most important parameter used to measure the effectiveness of a contrast agent. A number of factors influence this parameter. This article elucidates detailed strategies to increase relaxivity of cyclen-based MRI contrast agents. 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) are two key ligands derived from cyclen. They also act as building blocks for the synthesis of novel ligands. A few important methodologies for the synthesis of DOTA and DO3A derivatives are described. Moreover, the coordination geometry of chelates formed by these ligands and their derivatives is discussed as well. Novel ligands can be developed by the appropriate derivatization of DOTA and DO3A. Gd³⁺-chelates of such ligands prove to be useful MRI contrast agents of enhanced relaxivity, greater stability, better clearance, lesser toxicity and higher water solubility.

Vectors for the delivery of radiopharmaceuticals in cancer therapeutics

Internal radiation using radiopharmaceuticals promises efficient cancer therapeutics. The specificity and selectivity required for screening and pinpointing tumor cells for cell-kill has been made possible by targeted ligands based on 'magic bullet' and tracer principle- theories nearing a century. Overexpression of certain receptors has been exploited using biomolecules for targeting. The pragmatic analysis, however, is not as promising compared with the theoretical knowledge of available gamut of vectors and targets. The complex interplay of in vitro and in vivo parameters, and the effect of radionuclides involve a systematic assessment of radiopharmaceuticals as diagnostic and therapeutic agent. This review presents different vectors with their pros and cons, present status and recent design variations followed by a future perspective based on novel approaches.

Evaluation of methionine and tryptophan derivatised vehicles: Met-ac-TE3A/Trp-ac-TE3A for tumor imaging

Two novel amino acid (methionine and tryptophan) appended 1,4,8,11-tetraazacyclotetradecane triacetate (TE3A) compounds Met-ac-TE3A and Trp-ac-TE3A were synthesized and evaluated for imaging applications.