Preclinical Pharmacokinetic and Safety Studies of Copper-Diacetyl-Bis(N4-Methylthiosemicarbazone) (Cu-ATSM): Translational Studies for Internal Radiotherapy

Unveiling the promising anticancer effect of copper-based compounds: a comprehensive review

Copper is a necessary micronutrient for maintaining the well-being of the human body. The biological activity of organic ligands, especially their anticancer activity, is often enhanced when they coordinate with copper(I) and (II) ions. Copper and its compounds are capable of inducing tumor cell death through various mechanisms of action, including activation of apoptosis signaling pathways by reactive oxygen species (ROS), inhibition of angiogenesis, induction of cuproptosis, and paraptosis. Some of the copper complexes are currently being evaluated in clinical trials for their ability to map tumor hypoxia in various cancers, including locally advanced rectal cancer and bulky tumors. Several studies have shown that copper nanoparticles can be used as effective agents in chemodynamic therapy, phototherapy, hyperthermia, and immunotherapy. Despite the promising anticancer activity of copper-based compounds, their use in clinical trials is subject to certain limitations. Elevated copper concentrations may promote tumor growth, angiogenesis, and metastasis by affecting cellular processes.

Pharmacokinetics of CuGTSM, a Novel Drug Candidate, in a Mouse Model of Menkes Disease

PURPOSE

Menkes disease is a rare hereditary disease in which systemic deficiency of copper due to mutation of the ATP7A gene causes severe neurodegenerative disorders. The present parenteral drugs have limited efficacy, so there is a need for an efficacious drug that can be administered orally. This study focused on glyoxal-bis (N(4)-methylthiosemicarbazonato)-copper(II (CuGTSM), which has shown efficacy in macular mice, a murine model of Menkes disease, and examined its pharmacokinetics. In addition, nanosized CuGTSM (nCuGTSM) was prepared, and the effects of nanosizing on CuGTSM pharmacokinetics were investigated.

METHODS

CuGTSM or nCuGTSM (10 mg/kg) was administered orally to male macular mice or C3H/HeNCrl mice (control), and plasma was obtained by serial blood sampling. Plasma concentrations of CuGTSM and GTSM were measured by LC-MS/MS and pharmacokinetic parameters were calculated.

RESULTS

When CuGTSM was administered orally, CuGTSM and GTSM were both detected in the plasma of both mouse strains. When nCuGTSM was administered, the C_max was markedly higher, and the mean residence time was longer than when CuGTSM was administered for both CuGTSM and GTSM in both mouse strains. With macular mice, the AUC ratio (GTSM/CuGTSM) was markedly higher and the plasma CuGTSM concentration was lower than with C3H/HeNCrl mice when either CuGTSM or nCuGTSM was administered.

CONCLUSION

Absorption of orally administered CuGTSM was confirmed in macular mice, and the nano-formulation improved the absorption and retention of CuGTSM in the body. However, the plasma concentration of CuGTSM was lower in macular mice than in control mice, suggesting easier dissociation of CuGTSM.

Hypoxia imaging and theranostic potential of [64Cu][Cu(ATSM)] and ionic Cu(II) salts: a review of current evidence and discussion of the retention mechanisms

Background

Tumor hypoxia (low tissue oxygenation) is an adverse condition of the solid tumor environment, associated with malignant progression, radiotherapy resistance, and poor prognosis. One method to detect tumor hypoxia is by positron emission tomography (PET) with the tracer [⁶⁴Cu][Cu-diacetyl-bis(N(4)-methylthiosemicarbazone)] ([⁶⁴Cu][Cu(ATSM)]), as demonstrated in both preclinical and clinical studies. In addition, emerging studies suggest using [⁶⁴Cu][Cu(ATSM)] for molecular radiotherapy, mainly due to the release of therapeutic Auger electrons from copper-64, making [⁶⁴Cu][Cu(ATSM)] a “theranostic” agent. However, the radiocopper retention based on a metal-ligand dissociation mechanism under hypoxia has long been controversial. Recent studies using ionic Cu(II) salts as tracers have raised further questions on the original mechanism and proposed a potential role of copper itself in the tracer uptake. We have reviewed the evidence of using the copper radiopharmaceuticals [^60/61/62/64Cu][Cu(ATSM)]/ionic copper salts for PET imaging of tumor hypoxia, their possible therapeutic applications, issues related to the metal-ligand dissociation mechanism, and possible explanations of copper trapping based on studies of the copper metabolism under hypoxia.

Results

We found that hypoxia selectivity of [⁶⁴Cu][Cu(ATSM)] has been clearly demonstrated in both preclinical and clinical studies. Preclinical therapeutic studies in mice have also demonstrated promising results, recently reporting significant tumor volume reductions and improved survival in a dose-dependent manner. Cu(II)-[Cu(ATSM)] appears to be accumulated in regions with substantially higher CD133⁺ expression, a marker for cancer stem cells. This, combined with the reported requirement of copper for activation of the hypoxia inducible factor 1 (HIF-1), provides a possible explanation for the therapeutic effects of [⁶⁴Cu][Cu(ATSM)]. Comparisons between [⁶⁴Cu][Cu(ATSM)] and ionic Cu(II) salts have showed similar results in both imaging and therapeutic studies, supporting the argument for the central role of copper itself in the retention mechanism.

Conclusions

We found promising evidence of using copper-64 radiopharmaceuticals for both PET imaging and treatment of hypoxic tumors. The Cu(II)-[Cu(ATSM)] retention mechanism remains controversial and future mechanistic studies should be focused on understanding the role of copper itself in the hypoxic tumor metabolism.