Enhanced intracellular delivery of the reactive oxygen species (ROS)-generating copper chelator D-penicillamine via a novel gelatin--D-penicillamine conjugate

Emerging roles of the copper-CTR1 axis in tumorigenesis

Physiological roles of copper in metabolic homeostasis have been well established, however, whether and how copper is dysregulated in tumors and contributes to tumorigenesis are not recapitulated. Here, we comprehensively summarize the potential origins of copper accumulation in diseases especially in cancers by dysregulating copper transporter 1 (CTR1) or ATPase copper transporting alpha/beta (ATP7A/B) and further demonstrate the underlying mechanism of copper contributing to tumorigenesis. Specifically, in addition to modulating reactive oxygen species (ROS), angiogenesis, immune response, and metabolic homeostasis, copper recently has drawn more attention by directly binding to oncoproteins such as MEK, ULK, Memo, and PDK1 to activate distinct oncogenic signals and account for tumorigenesis. In the end, we disclose the emerging applications of copper in cancer diagnosis and highlight the promising strategies to target the copper-CTR1 axis for cancer therapies.

mtDNA depletion-like syndrome in Wilson disease

BACKGROUND AND AIMS

Wilson disease (WD) is caused by mutations in the copper transporter ATP7B, with its main pathology attributed to copper-mediated oxidative damage. The limited therapeutic effect of copper chelators and the early occurrence of mitochondrial deficits, however, undermine the prevalence of this mechanism.

METHODS

We characterized mitochondrial DNA copy number and mutations as well as bioenergetic deficits in blood from patients with WD and in livers of tx-j mice, a mouse model of hepatic copper accumulation. In vitro experiments with hepatocytes treated with CuSO₄ were conducted to validate in vivo studies.

RESULTS

Here, for the first time, we characterized the bioenergetic deficits in WD as consistent with a mitochondrial DNA depletion-like syndrome. This is evidenced by enriched DNA synthesis/replication pathways in serum metabolomics and decreased mitochondrial DNA copy number in blood of WD patients as well as decreased mitochondrial DNA copy number, increased citrate synthase activity, and selective Complex IV deficit in livers of the tx-j mouse model of WD. Tx-j mice treated with the copper chelator penicillamine, methyl donor choline or both ameliorated mitochondrial DNA damage but further decreased mitochondrial DNA copy number. Experiments with copper-loaded HepG2 cells validated the concept of a direct copper-mitochondrial DNA interaction.

CONCLUSIONS

This study underlines the relevance of targeting the copper-mitochondrial DNA pool in the treatment of WD separate from the established copper-induced oxidative stress-mediated damage.

Synthesis of Gelatin-Based Dual-Targeted Nanoparticles of Betulinic Acid for Antitumor Therapy

Betulinic acid (BA) is a natural antitumor agent and has biological activity against multiple human tumor cell lines with low cytotoxicity to normal cells, while the high hydrophobicity and the short half-life of this compound limit its clinical application. Here, gelatin-based dual-targeted nanoparticles of BA are promising to solve this problem. Hydrophobic BA is loaded in cyclodextrin to increase its solubility and prolong the circulation time in vivo. The nanoscale drug delivery systems can further enhance the bioavailability and the antitumor effect of BA and are passively targeted to the tumor tissue sites by enhanced permeability and retention effect. The RGD sequence of gelatin specifically recognizes tumor cells and brings agents into tumor cells. The nanoparticles were characterized by transmission electron microscopy, Fourier transform infrared, nuclear magnetic resonance, etc. In addition, we observed antitumor activity of the nanoparticles using both cell-based assays and mouse xenograft tumors, which proved that betulinic acid/gelatin-γ-cyclodextrin nanoparticles had a better tumor inhibition effect than betulinic acid/γ-cyclodextrin inclusion compound.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

CD44-specific nanoparticles for redox-triggered reactive oxygen species production and doxorubicin release

CD44-specific and redox-responsive nanoparticles were prepared by coating a bioreducible chitosan-based nanoparticles with hyaluronic acid for intracellular glutathione-triggered reactive oxygen species (ROS) production and doxorubicin (DOX) release. Chitosan (CS) was conjugated with a copper chelator, D-penicillamine (D-pen), to obtain a CS-SS-D-pen conjugate through the formation of a disulfide bond. D-pen release from the conjugate was triggered by intracellular glutathione (GSH) via reducing biologically reversible disulfide bonds. Self-assembled CS-SS-D-pen nanoparticles were prepared through ionotropic gelation with tripolyphosphate and subsequently coated with hyaluronic acid (HA). The HA-coated CS-SS-D-pen NPs were reduced by GSH to release free D-pen and trigger ROS production via a series of reactions involving Cu(II)-catalyzed D-pen oxidation and H2O2 generation. DOX was loaded into the HA-coated CS-SS-D-pen NPs by a method involving the complexation of DOX with Cu(II) ions. The Cu(II)-DOX complex-loaded NPs exhibited redox-responsive release properties which accelerated DOX release at a higher glutathione level (10mM). Confocal fluorescence microscopy demonstrated that the Cu(II)-DOX-loaded NPs effectively delivered DOX to human colon adenocarcinoma cells (HT-29) by active targeting via HA-CD44 interactions. Intracellular ROS generated from the HA-coated CS-SS-D-pen NPs sensitized cancer cells to DOX-induced cytotoxicity. In vitro cytotoxicity assays revealed that Cu(II)-DOX-loaded NPs sensitized cells to DOX-induced cytotoxicity in CD44-overexpressing HT-29 cells compared to CD44 low-expressing HCT-15 cells.

STATEMENT OF SIGNIFICANCE

In this manuscript, we develop a CD44-targetable loaded with nanoparticles Cu(II)-DOX complex. The nanoparticles exhibited redox-responsive properties, which triggered reactive oxygen species (ROS) production and accelerated DOX release. The Cu(II)-DOX-loaded nanoparticle sensitized cells to DOX-induced cytotoxicity in CD44-overexpressing HT-29 cells. To our knowledge, this is the first report showing the combination of CD44-targeting and redox-responsive property for triggering ROS production and subsequent drug release. We believe our findings would appeal to the readership of Acta Biomaterialia because the study bring new and interesting ideals in the development of specific and stimuli-responsive nanoparticles as drug carrier for cancer therapy.

Cancer cell-selective killing polymer/copper combination

Chemotherapy has been adopted for cancer treatment for decades. However, its efficacy and safety are frequently compromised by the multidrug-resistance of cancer cells and the poor cancer cell selectivity of anticancer drugs. Hereby, we report a combination of a pyridine-2-thiol containing polymer and copper which can effectively kill a wide spectrum of cancer cells, including drug resistant cancer cells, while sparing normal cells. The polymer nanoparticle enters cells via an exofacial thiol facilitated route, and releases active pyridine-2-thiol with the help of intracellularly elevated glutathione (GSH). Due to their high GSH level, cancer cells are more vulnerable to the polymer/copper combination. In addition, RNA microarray analysis revealed that the treatment can reverse cancer cells' upregulated oncogenes (CIRBP and STMN1) and downregulated tumor suppressor genes (CDKN1C and GADD45B) to further enhance the selectivity for cancer cells.

Biocompatible D-Penicillamine Conjugated Au Nanoparticles: Targeting Intracellular Free Copper Ions for Detoxification

High thiophillicicity of the Au-nanoparticle (Au NP) surface leads to covalent attachment of D-penicillamine molecules to Au NPs to form biocompatible D-penicillamine conjugated Au NPs. The latter are highly water-dispersible, exhibit no cytotoxicity, and can readily penetrate the cell membrane to target intracellular free copper ions for selective copper detoxification in the presence of the other divalent essential metal ions including Zn(II), Fe(II), Mn(II), Ca(II), and Mg(II), thus opening up a new avenue for improving the efficacy and pharmacokinetics of D-penicillamine, an important clinical drug currently used to treat the copper overload-related diseases and disorders.

D-penicillamine and other low molecular weight thiols: review of anticancer effects and related mechanisms

Low molecular weight thiols (LMWTs) like N-acetyl cysteine, D-penicillamine, captopril, Disulfiram and Amifostine, etc. have been used as chemo-preventive agents. Recent studies have reported cell growth inhibition and cytotoxicity in several different types of cancer cells following treatment with several LMWTs. Cytotoxic and cytostatic effects of LMWTs may involve interaction of the thiol group with cellular lipids, proteins, intermediates or enzymes. Some of the mechanisms that have been proposed include a p53 mediated apoptosis, thiyl radical induced DNA damage, membrane damage through lipid peroxidation, anti-angiogenic effects induced by inhibition of matrix metalloproteinase enzymes and angiostatin generation. LMWTs are strong chelators of transition metals like copper, nickel, zinc, iron and cobalt and may cause metal co-factor depletion resulting in cytotoxicity. Oxidation of thiol group can also generate cytotoxic reactive oxygen species (ROS).

Polypeptide conjugates of D-penicillamine and idarubicin for anticancer therapy

We investigated anticancer therapy with a novel combination of D-penicillamine (D-pen) and Idarubicin (Ida) in a synthetic dual drug conjugate (DDC). D-pen and Ida were covalently linked to poly(α)-L-glutamic acid (PGA) via reducible disulfide and acid-sensitive hydrazone bonds, respectively. The DDCs showed cell uptake and sustained release of the bound drugs in conditions mimicking the intracellular release media (10mM glutathione and pH 5.2). The in-vitro cytotoxicity of DDCs was comparable to unconjugated Ida in several sensitive and resistant cancer cell lines and correlated with the rate of cell uptake. In a single equivalent-dose pharmacokinetic study, DDCs enhanced the drug exposure by 7-fold and prolonged the plasma circulation half-life (t(1/2)) by 5-fold over unconjugated Ida. The therapeutic index of DDCs was 2-3-fold higher than unconjugated drugs. DDCs caused 89% tumor growth inhibition compared to 60% by unconjugated Ida alone and led to significant enhancement in the median survival (17%) of athymic nu/nu mice bearing NCI-H460 tumor xenografts.

Intracellular delivery of the reactive oxygen species generating agent D-penicillamine upon conjugation to poly-L-glutamic acid

D-penicillamine is an aminothiol that is cytotoxic to cancer cells and generates dose dependent reactive oxygen species (ROS) via copper catalyzed oxidation. However, the delivery of D-pen to cancer cells remains a challenge due to its high hydrophilicity, highly reactive thiol group and impermeability to the cell membrane. To overcome this challenge, we investigated a novel poly-L-glutamic acid (PGA) conjugate of D-pen (PGA-D-pen) where D-pen was conjugated to PGA modified with 2-(2-pyridyldithio)-ethylamine (PDE) via disulfide bonds. Confocal microscopy and cell uptake studies showed that the fluorescently labeled PGA-D-pen was taken up by human leukemia cells (HL-60) in a time dependent manner. Treatment of HL-60, murine leukemia cells (P388) and human breast cancer cells (MDA-MB-468) with PGA-D-pen resulted in dose dependent cytotoxicity and elevation of intracellular ROS levels. PGA-D-pen induced apoptosis in HL-60 cells which was verified by Annexin V binding. The in vivo evaluation of the conjugate in the P388 murine leukemia model (intraperitoneal) resulted in significant enhancement in the survival of CD2F1 mice over vehicle control.

Development of next-generation photolabile copper cages with improved copper binding properties

Seven new nitrogen-donor ligands that contain a photoactive nitrophenyl group within the ligand backbone have been prepared and evaluated for their binding affinity for copper(ii) and zinc(ii). Among this series, the ligand 3Gcage (pyridine-2-carboxylic acid {1-(2-nitro-phenyl)-3-[(pyridin-2-ylmethyl)-amino]-propyl}-amide) has the best affinity for copper(ii), with an apparent dissociation constant at pH 7.4 of 0.18 fM. Exposure of buffered aqueous solutions of 3Gcage or Cu(ii)-bound 3Gcage to UV light induces bond cleavage in the ligand backbone, which reduces the denticity of the ligands. The quantum yields of photolysis for 3Gcage in the absence and presence of Cu(ii) are 0.66 and 0.43, respectively. Prior to photolysis, the 3Gcage ligand inhibits copper from generating hydroxyl radicals in the presence of hydrogen peroxide and ascorbic acid; however, hydroxyl radical formation increases by more than 300% following light activation, showing that the reactivity of the copper center can be triggered by light.