Cisplatin and its platinum analogues, carboplatin and oxaliplatin, are some of the most widely used cancer chemotherapeutics. However, although cisplatin and carboplatin are primarily used in germ cell, breast and lung malignancies, oxaliplatin is instead used almost exclusively in colorectal and other gastrointestinal cancers. Here, we utilize a unique multi-platform genetic approach to study the mechanism of action of these clinically established platinum anti-cancer agents as well as more recently developed cisplatin analogues. We show that oxaliplatin, unlike cisplatin and carboplatin, does not kill cells via the DNA damage response. Rather, oxaliplatin kills cells by inducing ribosome biogenesis stress. This difference in drug mechanism explains the distinct clinical implementation of oxaliplatin relative to cisplatin and may enable mechanistically informed selection of distinct platinum drugs for distinct malignancies. These data highlight the functional diversity of core components of front line cancer therapy and the potential benefits of applying a mechanism-based rationale to the use of our current arsenal of anti-cancer drugs.

Monofunctional platinum(II) complexes of general formula cis-[Pt(NH 3 ) 2 (N-heterocycle)Cl]Cl bind DNA at a single site, inducing little distortion in the double helix. Despite this behavior, these compounds display significant antitumor properties, with a different spectrum of activity than that of classic bifunctional cross-linking agents like cisplatin. To discover the most potent monofunctional platinum(II) compounds, the N-heterocycle was systematically varied to generate a small library of new compounds, with guidance from the X-ray structure of RNA polymerase II (Pol II) stalled at a monofunctional pyriplatin-DNA adduct. In pyriplatin, the N-heterocycle is pyridine. The most effective complex evaluated was phenanthriplatin, cis-[Pt(NH 3 ) 2 (phenanthridine)Cl]NO 3 , which exhibits significantly greater activity than the Food and Drug Administration-approved drugs cisplatin and oxaliplatin. Studies of phenanthriplatin in the National Cancer Institute 60-cell tumor panel screen revealed a spectrum of activity distinct from that of these clinically validated anticancer agents. The cellular uptake of phenanthriplatin is substantially greater than that of cisplatin and pyriplatin because of the hydrophobicity of the phenanthridine ligand. Phenanthriplatin binds more effectively to 5′-deoxyguanosine monophosphate than to N-acetyl methionine, whereas pyriplatin reacts equally well with both reagents. This chemistry supports DNA as a viable cellular target for phenanthriplatin and suggests that it may avoid cytoplasmic platinum scavengers with sulfur-donor ligands that convey drug resistance. With the use of globally platinated Gaussia luciferase vectors, we determined that phenanthriplatin inhibits transcription in live mammalian cells as effectively as cisplatin, despite its inability to form DNA cross-links. (Fig. 1), are currently among the most effective chemotherapies in clinical use for the treatment of cancers (1). These Pt-based anticancer agents typically form bifunctional intra-and interstrand DNA cross-links through covalent bonds with purine nucleobases. These cross-links inhibit transcription and result in cell death (2, 3). Platinum-based drugs are limited by side effects and poor activity in certain types of cancer resulting from acquired or intrinsic resistance (1-3). These limitations evoke a need for new platinum-based chemotherapeutics with novel mechanisms of action.One approach that we have used to circumvent the shortcomings of classic bifunctional platinum-based drugs has been to revisit cationic, monofunctional platinum complexes previously demonstrated to display significant anticancer activity in animal tumor models (4). In contrast to monofunctional platinum(II) compounds, such as [Pt(dien)Cl] + (dien = diethylenetriamine) (5) and [Pt(NH 3 ) 3 Cl] + (6), which early work proved to be inactive, the compound pyriplatin [cis-diamminepyridinechloroplatinum(II)] (Fig. 1) and several of its analogs have significant antineoplastic activity. Moreover, the profile of cellular response to thes...

Cisplatin and other DNA-damaging chemotherapeutics are widely used to treat a broad spectrum of malignancies. However, their application is limited by both intrinsic and acquired chemoresistance. Most mutations that result from DNA damage are the consequence of error-prone translesion DNA synthesis, which could be responsible for the acquired resistance against DNAdamaging agents. Recent studies have shown that the suppression of crucial gene products (e.g., REV1, REV3L) involved in the errorprone translesion DNA synthesis pathway can sensitize intrinsically resistant tumors to chemotherapy and reduce the frequency of acquired drug resistance of relapsed tumors. In this context, combining conventional DNA-damaging chemotherapy with siRNAbased therapeutics represents a promising strategy for treating patients with malignancies. To this end, we developed a versatile nanoparticle (NP) platform to deliver a cisplatin prodrug and REV1/ REV3L-specific siRNAs simultaneously to the same tumor cells. NPs are formulated through self-assembly of a biodegradable poly(lactide-coglycolide)-b-poly(ethylene glycol) diblock copolymer and a self-synthesized cationic lipid. We demonstrated the potency of the siRNA-containing NPs to knock down target genes efficiently both in vitro and in vivo. The therapeutic efficacy of NPs containing both cisplatin prodrug and REV1/REV3L-specific siRNAs was further investigated in vitro and in vivo. Quantitative realtime PCR results showed that the NPs exhibited a significant and sustained suppression of both genes in tumors for up to 3 d after a single dose. Administering these NPs revealed a synergistic effect on tumor inhibition in a human Lymph Node Carcinoma of the Prostate xenograft mouse model that was strikingly more effective than platinum monotherapy.siRNA delivery | chemosensitivity | combination therapy A dvances in genomics and cell biology have highlighted the heterogeneity and complexity of cancer. It is generally accepted that cancer is usually the result of a combination of interconnected disease pathways that may not be treated effectively with 1D therapeutic mechanisms (1). The inhibition of a pathway by a single-drug therapy often results in the emergence of drug resistance and tumor relapse, largely because of pathway redundancy, cross-talk, compensatory and neutralizing actions, and antitarget activities that commonly occur with single-drug cancer therapy (2). In some cases, relapse can result in the emergence of phenotypically distinct and possibly more virulent tumors. For example, treatment of prostatic adenocarcinoma with androgen ablation therapies, such as abiraterone or enzalutamide, results in the development of abiraterone or enzalutamide refractory castration-resistant prostate cancer that is phenotypically nonadenocarcinoma and represents a rare and often lethal form of prostate cancer with a neuroendocrine phenotype (3).Platinum agents are among the most widely used cytotoxic agents for cancer therapy. Cisplatin and other DNA adductforming chemotherapeutics caus...

Extensive evidence points to oxidative stress as a key event in the pathogenesis and exacerbation of Alzheimer's Disease (AD).[1] Transition metals, such as Zn, Fe, and Cu, are present in elevated concentrations in AD brain deposits, composed primarily of 40-or 42-mer amyloid beta (Aβ) peptides. The redox-active copper(II) ion binds to the unstructured, hydrophilic N terminus of Aβ; [1g,2] and the ability of copper to promote the formation of reactive oxygen species (ROS) and cause neuronal death by interaction with Aβ has been demonstrated in vitro. [1a,c,3,4] ROS formation is proposed to occur by interaction of reduced Cu I -Aβ with O 2 or H 2 O 2 . However, few direct studies of Cu I binding or reactivity with Aβ peptides or fragments have been reported. [5,6] We have studied the interactions of the hydrophilic N-terminal region of the Aβ peptide with Cu I . An understanding of the full redox competency of Cu-Aβ, leading to ROS formation and oxidative stress (that is, to cause events associated with the onset of AD), is incomplete without elucidation of the structure/function relationships of the reduced (active) copper(I)-peptide complexes. We report herein studies on the interaction of Cu I ions with small portions of the Aβ peptide incorporating specific metal-binding (His6, His13, His14) or potentially redoxactive (Tyr10) residues (Figure 1). Of considerable interest are the contiguous His13 and His14 residues. We have previously reported studies on Cu I complexes of modified (by end-capping and/or regiospecific N ε -or N δ -alkylation) His-His dipeptides which, significantly, adopt a two-coordinate, near-linear N His -Cu I -N His environment. [6] In this report, we demonstrate that Cu I complexes of longer Aβ peptide fragments adopt the same apparent two-coordinate structure in the solid state and aqueous solution. Preliminary reactivity investigations, described here, indicate that the His13-Cu I -His14 moiety is the active part of the structure, responsible for copper-Aβ reactivity.A range of peptides ( Figure 1) were synthesized and purified by reverse-phase (RP) HPLC to a single peak. Their identity and purity were confirmed by ESI mass spectrometry. The peptides

Modified His−His dipeptides have been reacted with copper(I) salts to model active-site Cu ions bound by contiguous His residues in certain oxygen-activating copper proteins, as well as amyloid β-peptide. Chelation of copper(I) by these ligands affords linear, two-coordinate complexes as studied structurally by X-ray absorption spectroscopy. The complexes are robust toward oxidation, showing limited to no reactivity with O2, and they bind CO weakly. Reaction with a third ligand (N-methylimidazole) affords complexes with a markedly different structure (distorted T-shaped) and reactivity, binding CO and oxidizing rapidly upon exposure to dioxygen.