Light-Responsive Pt(IV) Prodrugs with Controlled Photoactivation and Low Dark Toxicity.

Light-induced release of cisplatin from Pt(IV) prodrugs represents a promising approach for precise control over the antiproliferative activity of Pt-based chemotherapeutic drugs. This method has the potential to overcome crucial drawbacks of conventional cisplatin therapy, such as high general toxicity toward healthy organs and tissues. Herein, we report two Pt(IV) prodrugs with BODIPY-based photoactive ligands Pt-1 and Pt-2, which were designed using carbamate and triazole linkers, respectively. Both prodrugs demonstrated the ability to release cisplatin under blue light irradiation without the requirement of an external reducing agent. Dicarboxylated Pt-2 prodrug turned out to be more stable in the dark and more sensitive to light than its monocarbamate Pt-1 counterpart; these observations were explained using DFT calculations. The investigation of the photoreduction mechanism of Pt-1 and Pt-2 prodrugs using DFT modeling and ΔG0 PET estimation suggests that the photoinduced electron transfer from the singlet excited state of the BODIPY axial ligand to the Pt(IV) center is the key step in the light-induced release of cisplatin from the complexes. Cytotoxicity studies demonstrated that both prodrugs were nontoxic in the dark and toxic to MCF-7 cells under low-dose irradiation with blue light, and the observed effect was solely due to the cisplatin release from the Pt(IV) prodrugs. Our research presents an elegant synthetic approach to light-activated Pt(IV) prodrugs and presents findings that may contribute to the future rational design of photoactivatable Pt(IV) prodrugs.

The Copper Reduction Potential Determines the Reductive Cytotoxicity: Relevance to the Design of Metal-Organic Antitumor Drugs.

Copper-organic compounds have gained momentum as potent antitumor drug candidates largely due to their ability to generate an oxidative burst upon the transition of Cu2+ to Cu1+ triggered by the exogenous-reducing agents. We have reported the differential potencies of a series of Cu(II)-organic complexes that produce reactive oxygen species (ROS) and cell death after incubation with N-acetylcysteine (NAC). To get insight into the structural prerequisites for optimization of the organic ligands, we herein investigated the electrochemical properties and the cytotoxicity of Cu(II) complexes with pyridylmethylenethiohydantoins, pyridylbenzothiazole, pyridylbenzimidazole, thiosemicarbazones and porphyrins. We demonstrate that the ability of the complexes to kill cells in combination with NAC is determined by the potential of the Cu+2 → Cu+1 redox transition rather than by the spatial structure of the organic ligand. For cell sensitization to the copper-organic complex, the electrochemical potential of the metal reduction should be lower than the oxidation potential of the reducing agent. Generally, the structural optimization of copper-organic complexes for combinations with the reducing agents should include uncharged organic ligands that carry hard electronegative inorganic moieties.

Electrochemical Nanopipette Sensor for In Vitro/In Vivo Detection of Cu2+ Ions.

In vitro/in vivo detection of copper ions is a challenging task but one which is important in the development of new approaches to the diagnosis and treatment of cancer and hereditary diseases such as Alzheimer's, Wilson's, etc. In this paper, we present a nanopipette sensor capable of measuring Cu2+ ions with a linear range from 0.1 to 10 µM in vitro and in vivo. Using the gold-modified nanopipette sensor with a copper chelating ligand, we evaluated the accumulation ability of the liposomal form of an anticancer Cu-containing complex at three levels of biological organization. First, we detected Cu2+ ions in a single cell model of human breast adenocarcinoma MCF-7 and in murine melanoma B16 cells. The insertion of the nanoelectrode did not result in leakage of the cell membrane. We then evaluated the distribution of the Cu-complex in MCF-7 tumor spheroids and found that the diffusion-limited accumulation was a function of the depth, typical for 3D culture. Finally, we demonstrated the use of the sensor for Cu2+ ion detection in the brain of an APP/PS1 transgenic mouse model of Alzheimer's disease and tumor-bearing mice in response to injection (2 mg kg-1) of the liposomal form of the anticancer Cu-containing complex. Enhanced stability and selectivity, as well as distinct copper oxidation peaks, confirmed that the developed sensor is a promising tool for testing various types of biological systems. In summary, this research has demonstrated a minimally invasive electrochemical technique with high temporal resolution that can be used for the study of metabolism of copper or copper-based drugs in vitro and in vivo.

Liposomal form of 2-alkylthioimidazolone-based copper complexes for combined cancer therapy.

Aim: To develop an optimized approach for encapsulating a 2-alkylthioimidazolone-based copper coordination compound within liposomes, which could offer treatment of cancer and bacterial infections by reactive oxygen species generation toxicity mechanisms. Materials & methods: For drug-loaded liposome preparation, lipids and drug mixture in organic solvents was injected into copper salt solution, forming a coordination compound simultaneously embedded in the lipid bilayer. In vitro tests were performed on MCF7 and MDA-MB-231 breast cancer cells. Results: Liposomes had a loading capacity of up to 1.75% (molar drug-to-lipid ratio). In vitro tests showed increased viability and accumulation of the liposomal formulation compared with free drug as well as lack of cytotoxicity in hepatocytes. Conclusion: This optimized technique for encapsulating large copper complexes in liposomes could be used to improve their delivery and better treat cancer and bacterial infections.

This work introduces a new technique for copper-containing drugs encapsulation in a drug-delivery system. The drug, a promising copper compound, is embedded in lipid nanovesicles ­ tiny fat particles ­ for intravenous injection. In addition to chemical characterization of the obtained drug form, tests on cancer cells showed a noticeable effect, whereas healthy cell types were not harmed. Copper possesses not only anticancer effects but also antimicrobial properties, which are also shown by the drug form, and a test of combined suppression of cancer cell lines and bacteria was successful. Hence, the obtained drug form has the potential for dual treatment of cancer and bacterial infections.

Recent Advances in 64Cu/67Cu-Based Radiopharmaceuticals.

Copper-64 (T1/2 = 12.7 h) is a positron and beta-emitting isotope, with decay characteristics suitable for both positron emission tomography (PET) imaging and radiotherapy of cancer. Copper-67 (T1/2 = 61.8 h) is a beta and gamma emitter, appropriate for radiotherapy ß-energy and with a half-life suitable for single-photon emission computed tomography (SPECT) imaging. The chemical identities of 64Cu and 67Cu isotopes allow for convenient use of the same chelating molecules for sequential PET imaging and radiotherapy. A recent breakthrough in 67Cu production opened previously unavailable opportunities for a reliable source of 67Cu with high specific activity and purity. These new opportunities have reignited interest in the use of copper-containing radiopharmaceuticals for the therapy, diagnosis, and theranostics of various diseases. Herein, we summarize recent (2018-2023) advances in the use of copper-based radiopharmaceuticals for PET, SPECT imaging, radiotherapy, and radioimmunotherapy.

Photoinduced Reduction of Novel Dual-Action Riboplatin Pt(IV) Prodrug.

Controlled photoreduction of Pt(IV) prodrugs is a challenging task due to the possibility of targeted light-controlled activation of anticancer agents without affecting healthy tissues. Also, a conjugation of photosensitizers and clinically used platinum drugs into one Pt(IV) prodrug allows combining photodynamic therapy and chemotherapy approaches into one molecule. Herein, we designed the cisplatin-based Pt(IV) prodrug Riboplatin with tetraacetylriboflavin in the axial position. A novel Pt(IV) prodrug is able to act both as a photodynamic therapy (PDT) agent through the conversion of ground-state 3O2 to excited-state 1O2 and as an agent of photoactivated chemotherapy (PACT) through releasing of cisplatin under gentle blue light irradiation, without the requirement of a reducing agent. The light-induced behavior of Riboplatin was investigated using an electrochemical sensor in MCF-7 tumor spheroids. Photocontrolled cisplatin release and ROS generation were detected electrochemically in real time. This appears to be the first confirmation of simultaneous photoactivated release of anticancer drug cisplatin and ROS from a dual-action Pt(IV) prodrug observed from the inside of living tumor spheroids.

Biotinylated Pt(IV) prodrugs with elevated lipophilicity and cytotoxicity.

A design of Pt(IV) prodrugs with tumor cell targeting moieties leading to increased selectivity is of interest. Herein, we designed a novel Pt(IV) prodrugs with COX-inhibitor naproxen, long-chain hydrophobic stearic acid moiety and biotin as axial ligands. We have established that for Pt(IV) prodrugs with biotin and naproxen or stearate in axial position, the lipophilicity rather than biotin receptors expression is the main factor of cytotoxicity. We also monitored the reduction speed of Pt(IV) prodrug 3 with naproxen and biotin in axial positions in A549 cells using XANES and demonstrated that the prodrug gradually releases cisplatin within 20 hours of incubation.

Recent Advances in Light-Controlled Activation of Pt(IV) Prodrugs.

Pt(IV) prodrugs remain one of the most promising alternatives to conventional Pt(II) therapy due to their versatility in axial ligand choice and delayed mode of action. Selective activation from an external source is especially attractive due to the opportunity to control the activity of an antitumor drug in space and time and avoid damage to normal tissues. In this review, we discuss recent advances in photoabsorber-mediated photocontrollable activation of Pt(IV) prodrugs. Two main approaches developed are the focus of the review. The first one is the photocatalytic strategy based on the flavin derivatives that are not covalently bound to the Pt(IV) substrate. The second one is the conjugation of photoactive molecules with the Pt(II) drug via axial position, yielding dual-action Pt(IV) molecules capable of the controllable release of Pt(II) cytotoxic agents. Thus, Pt(IV) prodrugs with a light-controlled mode of activation are non-toxic in the absence of light, but show high antiproliferative activity when irradiated. The susceptibility of Pt(IV) prodrugs to photoreduction, photoactivation mechanisms, and biological activity is considered in this review.

Electrochemical Detection of a Novel Pt(IV) Prodrug with the Metronidazole Axial Ligand in the Hypoxic Area.

We report herein a Pt(IV) prodrug with metronidazole in axial positions Pt-Mnz. The nitroaromatic axial ligand was conjugated with a cisplatin scaffold to irreversibly reduce under hypoxic conditions, thereby retaining the Pt(IV) prodrug in the area of hypoxia. X-ray near-edge adsorption spectroscopy (XANES) on dried drug-preincubated tumor cell samples revealed a gradual release of cisplatin from the Pt-Mnz prodrug instead of rapid intracellular degradation. The ability of the prodrug to penetrate into three-dimensional (3D) spheroid cellular cultures was evaluated by a novel electrochemical assay via a platinum-coated carbon nanoelectrode, capable of single-cell measurements. Using a unique technique of electrochemical measurements in single tumor spheroids, we were able to both detect the real-time response of the axial ligand to hypoxia and establish the depth of penetration of the drug into the tumor model.

Pt(IV) Prodrugs with Non-Steroidal Anti-inflammatory Drugs in the Axial Position.

We report herein the design, synthesis, and biological investigation of a series of novel Pt(IV) prodrugs with non-steroidal anti-inflammatory drugs naproxen, diclofenac, and flurbiprofen, as well as these with stearic acid in the axial position. Six Pt(IV) prodrugs 5-10 were designed, which showed superior antiproliferative activity compared to cisplatin as well as an ability to overcome tumor cell line resistance to cisplatin. By tuning the drug lipophilicity via variation of the axial ligands, the most potent Pt(IV) prodrug 7 was obtained, with an enhanced cellular accumulation of up to 153-fold that of cisplatin and nanomolar cytotoxicity both in 2D and 3D cell cultures. Pt2+ species were detected at different depths of MCF-7 spheroids after incubation with Pt(IV) prodrugs using a Pt-coated carbon nanoelectrode. Cisplatin accumulation in vivo in the murine mammary EMT6 tumor tissue of BALB/c mice after Pt(IV) prodrug injection was proved electrochemically as well. The drug tolerance study on BALB/c mice showed good tolerance of 7 in doses up to 8 mg/kg.