A Platinum(IV) Anticancer Prodrug Targeting Nucleotide Excision Repair To Overcome Cisplatin Resistance

Emergence of spatio-temporal variations in chemotherapeutic drug efficacy: in-vitro and in-Silico 3D tumour spheroid studies

Background

The mechanisms of action and efficacy of cisplatin and paclitaxel at cell population level are well studied and documented, however the localized spatio-temporal effects of the drugs are less well understood. We explore the emergence of spatially preferential drug efficacy resulting from variations in mechanisms of cell-drug interactions.

Methods

3D spheroids of HeLa-C3 cells were treated with drugs, cisplatin and paclitaxel. This was followed by sectioning and staining of the spheroids to track the spatio-temporal apoptotic effects of the drugs. A mechanistic drug-cell interaction model was developed and simulated to analyse the localized efficacy of these drugs.

Results

The outcomes of drug actions on a local cell population was dependant on the interactions between cell repair probability, intracellular drug concentration and cell’s mitosis phase. In spheroids treated with cisplatin, drug induced apoptosis is found to be scattered throughout the volume of the spheroids. In contrast, effect of paclitaxel is found to be preferentially localized along the periphery of the spheroids. Combinatorial treatments of cisplatin and paclitaxel result in varying levels of cell apoptosis based on the scheduling strategy.

Conclusions

The preferential action of paclitaxel can be attributed to the cell characteristics of the peripheral population. The model simulations and experimental data show that treatments initiated with paclitaxel are more efficacious due to the cascading of spatial effects of the drugs.

CAIXplatins: Highly Potent Platinum(IV) Prodrugs Selective Against Carbonic Anhydrase IX for the Treatment of Hypoxic Tumors

Hypoxia and the acidic microenvironment play a vital role in tumor metastasis and angiogenesis, generally compromising the chemotherapeutic efficacy. This provides a tantalizing angle for the design of platinum(IV) prodrugs for the effective and selective killing of solid tumors. Herein, two carbonic anhydrase IX (CAIX)-targeting platinum(IV) prodrugs have been developed, named as CAIXplatins. Based on their strong affinity for and inhibition of CAIX, CAIXplatins can not only overcome hypoxia and the acidic microenvironment, but also inhibit metabolic pathways of hypoxic cancer cells, resulting in a significantly enhanced therapeutic effect on hypoxic MDA-MB-231 tumors both in vitro and in vivo compared with cisplatin/oxaliplatin, accompanied with excellent anti-metastasis and anti-angiogenesis activities. Furthermore, the cancer selectivity indexes of CAIXplatins are 70-90 times higher than those of cisplatin/oxaliplatin with effectively alleviated side-effects.

A Photocaged, Water-Oxidizing, and Nucleolus-Targeted Pt(IV) Complex with a Distinct Anticancer Mechanism

Targeted anticancer prodrugs that can be controllably activated are highly desired for personalized precision medicine in cancer therapy. Such prodrugs with unique action modes are also promising to overcome drug resistance. Herein, we report coumaplatin, an oxaliplatin-based and photocaged Pt(IV) prodrug, to realize nuclear accumulation along with "on-demand" activation. This prodrug is based on a Pt(IV) complex that can be efficiently photoactivated via water oxidation without the requirement of a reducing agent. Coumaplatin accumulates very efficiently in the nucleoli, and upon photoactivation, this prodrug exhibits a level of photocytotoxicity up to 2 orders of magnitude higher than that of oxaliplatin. Unexpectedly, this prodrug presents strikingly enhanced tumor penetration ability and utilizes a distinct action mode to overcome drug resistance; i.e., coumaplatin but not oxaliplatin induces cell senescence, p53-independent cell death, and immunogenic cell death along with T cell activation. Our findings not only provide a novel strategy for the rational design of controllably activated and nucleolus-targeted Pt(IV) anticancer prodrugs but also demonstrate that accumulating conventional platinum drugs to the nucleus is a practical way to change its canonical mechanism of action and to achieve reduced resistance.

Recent advances in platinum-based chemotherapeutics that exhibit inhibitory and targeted mechanisms of action

Current platinum-based drugs used in chemotherapy, like cisplatin and its derivatives, are greatly limited due to side-effects and drug resistance. This has inspired the search for novel platinum-based drugs that deviate from the conventional mechanism of action seen with current chemotherapeutics. This review highlights recent advances in platinum(II) and platinum(IV)-based complexes that have been developed within the past six years. The platinum compounds explored within this review are those that display a more targeted approach by incorporating ligands that act on selected cellular targets within cancer cells. This includes mitochondria, overexpressed receptors or proteins and enzymes that contribute to cancer cell proliferation. These types of platinum compounds have shown significant improvements in anticancer activity and as such, this review highlights the importance of pursuing these new designed platinum drugs for cancer therapy, with the potential of undergoing clinical trials.

An Antitumor Bis(N-Heterocyclic Carbene)Platinum(II) Complex That Engages Asparagine Synthetase as an Anticancer Target

New anticancer platinum(II) compounds with distinctive modes of action are appealing alternatives to combat the drug resistance and improve the efficacy of clinically used platinum chemotherapy. Herein, we describe a rare example of an antitumor Pt^II complex targeting a tumor-associated protein, rather than DNA, under cellular conditions. Complex [(bis-NHC)Pt(bt)]PF₆ (1 a; Hbt=1-(3-hydroxybenzo[b]thiophen-2-yl)ethanone) overcomes cisplatin resistance in cancer cells and displays significant tumor growth inhibition in mice with higher tolerable doses compared to cisplatin. The cellular Pt species shows little association with DNA, and localizes in the cytoplasm as revealed by nanoscale secondary ion mass spectrometry. An unbiased thermal proteome profiling experiment identified asparagine synthetase (ASNS) as a molecular target of 1 a. Accordingly, 1 a treatment reduced the cellular asparagine levels and inhibited cancer cell proliferation, which could be reversed by asparagine supplementation. A bis-NHC-ligated Pt species generated from the hydrolysis of 1 a forms adducts with thiols and appears to target an active-site cysteine of ASNS.

Designing luminescent ruthenium prodrug for precise cancer therapy and rapid clinical diagnosis

The effective design of a targeted drug delivery system could improve the therapeutic efficacy of anticancer drugs by reducing their undesirable adsorption and toxic side effects. Here, an RGD-peptide functionalized and bioresponsive ruthenium prodrug (Ru-RGD) was designed for both cancer therapy and clinical diagnosis. This prodrug can be selectively delivered to cervical tumor sites to enhance theranostic efficacy. The benzimidazole-based ligand of the complex is susceptible to acidic conditions so, after reaching the tumor microenvironment, ligand substitution occurs and the therapeutic drug is released. The deep-red emissions produced by both one-photon and two-photon excitation increases the potential of Ru-RGD for use in the deep tissue imaging of 3D tumor spheroids. The specific accumulation of the Ru prodrug in tumor sites allows for precise tumor diagnosis and therapy in vivo. Luminescence staining of 38 clinical patient specimens shows that Ru-RGD exhibits differences in binding capability between cervical cancer and normal tissue, with a sensitivity of 95% and a specificity of 100%. This study thus provides an approach for the effective design and application of targeted metal complexes in cancer therapy and clinical diagnosis.

Tailoring Platinum(IV) Amphiphiles for Self-Targeting All-in-One Assemblies as Precise Multimodal Theranostic Nanomedicine

Drug, targeting ligand, and imaging agent are the three essential components in a nanoparticle-based drug delivery system. However, tremendous batch-to-batch variation of composition and drug content typically accompany the current approaches of building these components together. Herein, we report the design of photoactivatable platinum(IV) (Pt(IV)) amphiphiles containing one or two hydrophilic lactose targeting ligands per hydrophobic Pt(IV) prodrug for an all-in-one precise nanomedicine. Self-assembly of these Pt(IV) amphiphiles results in either micelle or vesicle formation with a fixed Pt/targeting moiety ratio and a constantly high content of Pt. The micelles and vesicles are capable of hepatoma cell-targeting, fluorescence/Pt-based CT imaging and have shown effective anticancer efficacy under laser irradiation in vitro and in vivo. This photoactivatable, active self-targeting, and multimodal theranostic amphiphile strategy shows great potential in constructing precise nanomedicine.

Towards rational design of RAD51-targeting prodrugs: platinumIV–artesunate conjugates with enhanced cytotoxicity against BRCA-proficient ovarian and breast cancer cells

Pt^IV–Artesunate prodrugs target the homologous recombination protein RAD51 and exhibit higher cytotoxicity against BRCA-proficient ovarian and breast cancer cells than cisplatin.

Reversal of cisplatin resistance in human gastric cancer cells by a wogonin-conjugated Pt(IV) prodrug via attenuating Casein Kinase 2-mediated Nuclear Factor-κB pathways

Pt(IV) prodrugs, with two additional coordination sites in contrast to Pt(II) drugs, have been actively studied nowadays, for they can perform well in enhancing the accumulation and retention of the corresponding Pt(II) drugs in cancer cells. Our designed Pt(II) drug, DN604, was recently found to exhibit significant anticancer activity and low toxicity, while, wogonin, a naturally O-methylated flavones, has been widely investigated for its tumor therapeutic potential. Thus, two Pt(IV)-based prodrugs were derived by addition of a wogonin unit to the axial position of DN604 and its analogue DN603 via a linker group. In vitro cytotoxicity assay indicated that the resulting compound 8 not only inherited the genotoxicity of DN604 on gastric cancer cells, but also obtained the COX inhibitory property arising from wogonin. Further studies revealed that compound 8 caused the accumulation of ROS production and decreased the mitochondrial membrane potential (ΔΨm). The CK2α kinase activity assay, ChIP and luciferase assays showed that CK2 plays an important role in the blockade of compound 8 on activated NF-κB survival pathways, which were established for sensitivity of cancer cells to platinum drugs. Similarly in vivo, in nude mice with SGC-7901/cDDP xenografts, compound 8 improved the effectiveness of DN604 via reversing tumor resistance and maintaining low toxicity. Overall, compound 8 is a promising Pt(IV) prodrug, which could be used to promote the anticancer activity of its counterpart Pt(II) species and reverse drug resistance via attenuating CK2-mediated NF-κB pathways during platinum-based chemotherapies.