Investigation of Cobalt(III) Cage Complexes as Inhibitors of the Mitochondrial Calcium Uniporter

Abstract

The mitochondrial calcium uniporter (MCU) mediates uptake of calcium ions (Ca 2 + ) into the mitochondria, a process that is vital for maintaining normal cellular function. Inhibitors of the MCU, the most promising of which are dinuclear ruthenium coordination compounds, have found use as both therapeutic agents and tools for studying the importance of this ion channel. In this study, six Co 3 + cage compounds with sarcophagine-like ligands were assessed for their abilities to inhibit MCU-mediated mitochondrial Ca 2 + uptake. These complexes were synthesized and characterized according to literature procedures and then investigated in cellular systems for their MCU-inhibitory activities. Among these six compounds, [Co(sen)] 3 + (3, sen = 5-(4-amino-2-azabutyl)-5-methyl-3,7-diaza-1,9-nonanediamine) was identified to be a potent MCU inhibitor, with IC 50 values of inhibition of 160 and 180 nM in permeabilized HeLa and HEK293T cells, respectively. Furthermore, the cellular uptake of compound 3 was determined, revealing moderate accumulation in cells. Most notably, 3 was demonstrated to operate in intact cells as an MCU inhibitor. Collectively, this work presents the viability of using cobalt coordination complexes as MCU inhibitors, providing a new direction for researchers to investigate.

Structure‐Activity Relationships of Metal‐Based Inhibitors of the Mitochondrial Calcium Uniporter

“…Building upon these prior studies, we investigated a series of different cobalt amine complexes that led to the identification of promising candidates that can inhibit m Ca 2+ uptake in permeabilized cells with nanomolar potency (Figure 10). [63,73] These efforts revealed [Co(sen)] 3+ to be an MCU inhibitor that can operate in intact, non‐permeabilized cells [73] . In addition, docking and site‐directed mutagenesis studies revealed that these compounds most likely interact with the DXXE region of the MCU pore [63] .…”

“…[63,73] These efforts revealed [Co(sen)] 3 + to be an MCU inhibitor that can operate in intact, non-permeabilized cells. [73] In addition, docking and sitedirected mutagenesis studies revealed that these compounds most likely interact with the DXXE region of the MCU pore. [63] Thus, unsurprisingly, this critical motif appears to be a common target for most MCU inhibitors.…”

Radiolabeling Diaminosarcophagine with Cyclotron-Produced Cobalt-55 and [55Co]Co-NT-Sarcage as a Proof of Concept in a Murine Xenograft Model

“…In comparison to NOTA and DOTA, Co-Sar stability/formation constants have not been measured due to their high kinetic inertness, 25 which makes Sar and Sar-derivatives interesting as stabilizers for Co. Additionally, the process to remove Co from Co-Sar complexes requires such stringent conditions that concentrated hydrochloric acid alone is insufficient to fully degrade the complex. 21,28 Given the high stability of Co-Sar complexes in vitro and in vivo, 19,29 along with recent studies highlighting unique biological applications of Co-Sar derivatives in vitro, 23 functionalized Sar compounds could therefore potentially be developed into promising Co-based radiopharmaceuticals. This work starts with an exploration of the labeling conditions for cyclotron-produced 55 Co with DiAmSar (DSar, a derivative of Sar), followed by in vitro/in vivo stability evaluation.…”

“…Cobalt-55 ( t 1/2 = 17.53 h, I β+ = 77%) is quantifiable with positron emission tomography (PET) imaging − and has demonstrated significant potential in preclinical oncology research. − Cobalt-55 can also serve as a diagnostic congener for 58m Co ( t 1/2 = 9.10 h, IC = 100%), a low-energy electron-emitting radionuclide that holds promise for treating small metastatic disease due to its potential to reduce radiation dose to off-target tissues. , Despite Sar synthesis procedures typically beginning with Co-ethylenediamine complexation, − we have not found prior reports of labeling Co to uncoordinated Sar complexes in no-carrier-added conditions. Most Co-radiopharmaceuticals have stabilized Co via 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) ,, and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). ,,,, NOTA can be radiolabeled with Co at room temperature and pH = 4–7, whereas DOTA typically requires additional heating.…”

“…Most Co-radiopharmaceuticals have stabilized Co via 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) ,, and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). ,,,, NOTA can be radiolabeled with Co at room temperature and pH = 4–7, whereas DOTA typically requires additional heating. In comparison to NOTA and DOTA, Co-Sar stability/formation constants have not been measured due to their high kinetic inertness, which makes Sar and Sar-derivatives interesting as stabilizers for Co. Additionally, the process to remove Co from Co-Sar complexes requires such stringent conditions that concentrated hydrochloric acid alone is insufficient to fully degrade the complex. , Given the high stability of Co-Sar complexes in vitro and in vivo, , along with recent studies highlighting unique biological applications of Co-Sar derivatives in vitro, functionalized Sar compounds could therefore potentially be developed into promising Co-based radiopharmaceuticals.…”