Expression of a novel peptide derived from PCNA damages DNA and reverses cisplatin resistance

Precision peptide disruptors: The next generation of targeted therapeutics in oncology

Therapeutically targeting the pathologically remodelled protein-protein interaction network in cancer with peptide disruptors increasingly represents a clinically attractive approach to treating recalcitrant cancers. In this review, we map the pre-clinical and clinical-stage peptide disruptor landscape within an oncology-specific context and discuss key clinical examples that are making significant impact to patients; demonstrating a key role for peptide disruptors in precision medicine as a next-generation targeted therapeutic.

Recent Advances in Therapeutic Peptides: Innovations and Applications in Treating Infections and Diseases

Peptides have become a powerful frontier in modern medicine, offering a promising therapeutic solution for various diseases and advancing rapidly in pharmaceutical development. These small amino acid chains, with their innovative design, have attracted significant attention due to their versatility and high receptor specificity, which minimizes off-target effects, along with enhanced therapeutic efficacy, biodegradability, low toxicity, and minimal immunogenicity. They are being explored for use in several clinical domains, like metabolic diseases, immunomodulation, and cancer. Furthermore, antimicrobial peptides (AMPs) have grown to be a promising strategy to combat the worldwide challenge of antibiotic resistance, demonstrating promising results against multidrug-resistant organisms. Both natural and engineered peptides have been discovered and investigated, whereas numerous others are progressing toward clinical trials in a number of therapeutic domains. Recent improvements with surface modification, such as peptide engineering, peptide cyclization, PEGylation, and the utilization of synthetic amino acids to enhance their pharmacokinetic profiles and overcome the inherent disadvantages of these peptides have made it possible for the area to continue to advance. Moreover, their therapeutic potential has been further enhanced by innovative delivery methods, such as self-assembling peptides, nanocarriers, and alternate routes of administration. This Review critically states the potential of peptides as versatile therapeutics along with their modifications and advancements to drive the significant progress to treat infections and chronic diseases, along with their potential benefits and challenges.

Targeting proliferating cell nuclear antigen (PCNA) for cancer therapy

Proliferating cell nuclear antigen (PCNA) is an essential scaffold protein in many cellular processes. It is best known for its role as a DNA sliding clamp and processivity factor during DNA replication, which has been extensively reviewed by others. However, the importance of PCNA extends beyond its DNA-associated functions in DNA replication, chromatin remodelling, DNA repair and DNA damage tolerance (DDT), as new non-canonical roles of PCNA in the cytosol have recently been identified. These include roles in the regulation of immune evasion, apoptosis, metabolism, and cellular signalling. The diverse roles of PCNA are largely mediated by its myriad protein interactions, and its centrality to cellular processes makes PCNA a valid therapeutic anticancer target. PCNA is expressed in all cells and plays an essential role in normal cellular homeostasis; therefore, the main challenge in targeting PCNA is to selectively kill cancer cells while avoiding unacceptable toxicity to healthy cells. This chapter focuses on the stress-related roles of PCNA, and how targeting these PCNA roles can be exploited in cancer therapy.

Therapeutic Targeting of DNA Replication Stress in Cancer

This article reviews the currently used therapeutic strategies to target DNA replication stress for cancer treatment in the clinic, highlighting their effectiveness and limitations due to toxicity and drug resistance. Cancer cells experience enhanced spontaneous DNA damage due to compromised DNA replication machinery, elevated levels of reactive oxygen species, loss of tumor suppressor genes, and/or constitutive activation of oncogenes. Consequently, these cells are addicted to DNA damage response signaling pathways and repair machinery to maintain genome stability and support survival and proliferation. Chemotherapeutic drugs exploit this genetic instability by inducing additional DNA damage to overwhelm the repair system in cancer cells. However, the clinical use of DNA-damaging agents is limited by their toxicity and drug resistance often arises. To address these issues, the article discusses a potential strategy to target the cancer-associated isoform of proliferating cell nuclear antigen (caPCNA), which plays a central role in the DNA replication and damage response network. Small molecule and peptide agents that specifically target caPCNA can selectively target cancer cells without significant toxicity to normal cells or experimental animals.

The role of peptides in reversing chemoresistance of breast cancer: current facts and future prospects

Breast cancer is the first malignant tumor in women, and its incidence is also increasing year by year. Chemotherapy is one of the standard therapies for breast cancer, but the resistance of breast cancer cells to chemotherapy drugs is a huge challenge for the effective treatment of breast cancer. At present, in the study of reversing the drug resistance of solid tumors such as breast cancer, peptides have the advantages of high selectivity, high tissue penetration, and good biocompatibility. Some of the peptides that have been studied can overcome the resistance of tumor cells to chemotherapeutic drugs in the experiment, and effectively control the growth and metastasis of breast cancer cells. Here, we describe the mechanism of different peptides in reversing breast cancer resistance, including promoting cancer cell apoptosis; promoting non-apoptotic regulatory cell death of cancer cells; inhibiting the DNA repair mechanism of cancer cells; improving the tumor microenvironment; inhibiting drug efflux mechanism; and enhancing drug uptake. This review focuses on the different mechanisms of peptides in reversing breast cancer drug resistance, and these peptides are also expected to create clinical breakthroughs in promoting the therapeutic effect of chemotherapy drugs in breast cancer patients and improving the survival rate of patients.

Recent advances in peptide-based therapeutic strategies for breast cancer treatment

Breast cancer is the leading cause of cancer-related fatalities in female worldwide. Effective therapies with low side effects for breast cancer treatment and prevention are, accordingly, urgently required. Targeting anticancer materials, breast cancer vaccines and anticancer drugs have been studied for many years to decrease side effects, prevent breast cancer and suppress tumors, respectively. There are abundant evidences to demonstrate that peptide-based therapeutic strategies, coupling of good safety and adaptive functionalities are promising for breast cancer therapy. In recent years, peptide-based vectors have been paid attention in targeting breast cancer due to their specific binding to corresponding receptors overexpressed in cell. To overcome the low internalization, cell penetrating peptides (CPPs) could be selected to increase the penetration due to the electrostatic and hydrophobic interactions between CPPs and cell membranes. Peptide-based vaccines are at the forefront of medical development and presently, 13 types of main peptide vaccines for breast cancer are being studied on phase III, phase II, phase I/II and phase I clinical trials. In addition, peptide-based vaccines including delivery vectors and adjuvants have been implemented. Many peptides have recently been used in clinical treatments for breast cancer. These peptides show different anticancer mechanisms and some novel peptides could reverse the resistance of breast cancer to susceptibility. In this review, we will focus on current studies of peptide-based targeting vectors, CPPs, peptide-based vaccines and anticancer peptides for breast cancer therapy and prevention.

Novel Peptide Therapeutic Approaches for Cancer Treatment

Peptides are increasingly being developed for use as therapeutics to treat many ailments, including cancer. Therapeutic peptides have the advantages of target specificity and low toxicity. The anticancer effects of a peptide can be the direct result of the peptide binding its intended target, or the peptide may be conjugated to a chemotherapy drug or radionuclide and used to target the agent to cancer cells. Peptides can be targeted to proteins on the cell surface, where the peptide–protein interaction can initiate internalization of the complex, or the peptide can be designed to directly cross the cell membrane. Peptides can induce cell death by numerous mechanisms including membrane disruption and subsequent necrosis, apoptosis, tumor angiogenesis inhibition, immune regulation, disruption of cell signaling pathways, cell cycle regulation, DNA repair pathways, or cell death pathways. Although using peptides as therapeutics has many advantages, peptides have the disadvantage of being easily degraded by proteases once administered and, depending on the mode of administration, often have difficulty being adsorbed into the blood stream. In this review, we discuss strategies recently developed to overcome these obstacles of peptide delivery and bioavailability. In addition, we present many examples of peptides developed to fight cancer.

Targeting Proliferating Cell Nuclear Antigen (PCNA) as an Effective Strategy to Inhibit Tumor Cell Proliferation

Targeting highly proliferating cells is an important issue for many types of aggressive tumors. Proliferating Cell Nuclear Antigen (PCNA) is an essential protein that participates in a variety of processes of DNA metabolism, including DNA replication and repair, chromatin organization and transcription and sister chromatid cohesion. In addition, PCNA is involved in cell survival, and possibly in pathways of energy metabolism, such as glycolysis. Thus, the possibility of targeting this protein for chemotherapy against highly proliferating malignancies is under active investigation. Currently, approaches to treat cells with agents targeting PCNA rely on the use of small molecules or on peptides that either bind to PCNA, or act as a competitor of interacting partners. Here, we describe the status of the art in the development of agents targeting PCNA and discuss their application in different types of tumor cell lines and in animal model systems.

Quantitative proteomic analysis of enhanced cellular effects of electrochemotherapy with Cisplatin in triple-negative breast cancer cells

Due to the lack of the three main receptors, triple negative breast cancer (TNBC) is refractive to standard chemotherapy. Hence, alternate therapies are needed. TNBCs utilize glycolysis, which heightens their growth, proliferation, invasiveness, chemotherapeutic resistance and poor therapeutic response. This calls for novel therapeutic strategies to target these metabolic vulnerabilities present in TNBC. Electroporation-mediated chemotherapy, known as electrochemotherapy (ECT) is gaining momentum as an attractive alternative. However, its molecular mechanisms need better understanding. Towards this, label-free quantitative proteomics is utilized to gain insight into the anticancer mechanisms of ECT using electrical pulses (EP) and Cisplatin (CsP) on MDA-MB-231, human TNBC cells. The results indicate that EP + CsP significantly downregulated 14 key glycolysis proteins (including ENO1, LDHA, LDHB, ACSS2, ALDOA, and PGK1), compared to CsP alone. EP + CsP caused a switch in the metabolism with upregulation of 34 oxidative phosphorylation pathway proteins and 18 tricarboxylic acid (TCA) cycle proteins compared to CsP alone, accompanied by the upregulation of proteins linked to several metabolic reactions, which produce TCA cycle intermediates. Moreover, EP + CsP promoted multiple pathways to cause 1.3-fold increase in the reactive oxygen species concentration and induced apoptosis. The proteomics results correlate well with cell viability, western blot, and qPCR data. While some effects were similar for EP, more comprehensive and long-lasting effects were observed for EP + CsP, which demonstrate the potential of EP + CsP against TNBC cells.

Recognition of a Key Anchor Residue by a Conserved Hydrophobic Pocket Ensures Subunit Interface Integrity in DNA Clamps

Sliding clamp proteins encircle duplex DNA and are involved in processive DNA replication and the DNA damage response. Clamp proteins are ring-shaped oligomers (dimers or trimers) and are loaded onto DNA by an ATP-dependent clamp loader complex that ruptures the interface between two adjacent subunits. Here we measured the solution dynamics of the human clamp protein, proliferating cell nuclear antigen, by monitoring the change in the fluorescence of a site-specifically labeled. To unravel the origins of clamp subunit interface stability, we carried out comprehensive comparative analysis of the interfaces of seven sliding clamps. We used computational modeling (molecular dynamic simulations and MM/GBSA binding energy decomposition analyses) to identify conserved networks of hydrophobic residues critical for clamp stability and ring-opening dynamics. The hydrophobic network is shared among clamp proteins and exhibits a "key in a keyhole" pattern where a bulky aromatic residue from one clamp subunit is anchored into a hydrophobic pocket of the opposing subunit. Bioinformatics and dynamic network analyses showed that this oligomeric latch is conserved across DNA sliding clamps from all domains of life and dictates the dynamics of clamp opening and closing.

The Anticancer Activity of a First-in-class Small-molecule Targeting PCNA

PURPOSE

Proliferating cell nuclear antigen (PCNA) plays an essential role in regulating DNA synthesis and repair and is indispensable to cancer cell growth and survival. We previously reported a novel cancer associated PCNA isoform (dubbed caPCNA), which was ubiquitously expressed in a broad range of cancer cells and tumor tissues, but not significantly in nonmalignant cells. We found the L126-Y133 region of caPCNA is structurally altered and more accessible to protein-protein interaction. A cell-permeable peptide harboring the L126-Y133 sequence blocked PCNA interaction in cancer cells and selectively kills cancer cells and xenograft tumors. On the basis of these findings, we sought small molecules targeting this peptide region as potential broad-spectrum anticancer agents.

EXPERIMENTAL DESIGN

By computer modeling and medicinal chemistry targeting a surface pocket partly delineated by the L126-Y133 region of PCNA, we identified a potent PCNA inhibitor (AOH1160) and characterized its therapeutic properties and potential toxicity.

RESULTS

AOH1160 selectively kills many types of cancer cells at below micromolar concentrations without causing significant toxicity to a broad range of nonmalignant cells. Mechanistically, AOH1160 interferes with DNA replication, blocks homologous recombination-mediated DNA repair, and causes cell-cycle arrest. It induces apoptosis in cancer cells and sensitizes them to cisplatin treatment. AOH1160 is orally available to animals and suppresses tumor growth in a dosage form compatible to clinical applications. Importantly, it does not cause significant toxicity at 2.5 times of an effective dose.

CONCLUSIONS

These results demonstrated the favorable therapeutic properties and the potential of AOH1160 as a broad-spectrum therapeutic agent for cancer treatment.

Molecular approaches to potentiate cisplatin responsiveness in carcinoma therapeutics

Cisplatin has been considered as the crucial regimen of widely prescribed chemotherapy treatment for cancer. The advancing treatment of cancers has reached the border line, where tumors show resistance to cisplatin and may thwart its use. Other than issues of drug resistance, cisplatin has been reported to evince side effects such as nephrotoxicity and ototoxicity. Therefore, there is a compelling need to untangle the problems associated with cisplatin treatment in carcinoma. Areas covered: In this review, we summarize the current status of combinatorial options to bring about better pre-clinical and clinical cisplatin drug responses in carcinoma. We begin with problems associated with cisplatin drugs and current avenues such as depicting molecular modulation of enhanced influx and reduced efflux. We also discuss the scope of the DNA damage response landscape and contribution of regulatory small RNAs towards potentiation of cisplatin responses. Expert commentary: The extensive use of cisplatin and incessant high drug dose have prompted the scientific community to limit the burden of cisplatin without compromising therapeutic success. Currently, there are reports on the potential use of other non-toxic small molecule inhibitors, interference RNAs and peptide mimetics to get rid of cellular adversities responsible for cisplatin resistance and high dose effects.

Validating the disruption of proliferating cell nuclear antigen interactions in the development of targeted cancer therapeutics

Human DNA replication and repair is a highly coordinated process involving the specifically timed actions of numerous proteins and enzymes. Many of these proteins require interaction with proliferating cell nuclear antigen (PCNA) for activation within the process. The interdomain connector loop (IDCL) of PCNA provides a docking site for many of those proteins, suggesting that this region is critically important in the regulation of cellular function. Previous work in this laboratory has demonstrated that a peptide mimicking a specific region of the IDCL (caPeptide) has the ability to disrupt key protein-protein interactions between PCNA and its binding partners, thereby inhibiting DNA replication within the cells. In this study, we confirm the ability of the caPeptide to disrupt DNA replication function using both intact cell and in vitro DNA replication assays. Further, we were able to demonstrate that treatment with caPeptide results in a decrease of polymerase δ activity that correlates with the observed decrease in DNA replication. We have also successfully developed a surface plasmon resonance (SPR) assay to validate the disruption of the PCNA-pol δ interaction with caPeptide.

Myricetin induces apoptosis via endoplasmic reticulum stress and DNA double-strand breaks in human ovarian cancer cells

The mechanisms underlying myricetin-induced cancer cell apoptosis remain to be elucidated. Certain previous studies have shown that myricetin induces apoptosis through the mitochondrial pathway. Apoptosis, however, can also be induced by other classical pathways, including endoplasmic reticulum (ER) stress and DNA double-strand breaks (DSBs). The aim of the present study was to assess whether these two apoptotic pathways are involved in myricetin-induced cell death in SKOV3 ovarian cancer cells. The results revealed that treatment with myricetin inhibited viability of SKOV3 cells in a dose-dependent manner. Myricetin induced nuclear chromatin condensation and fragmentation, and also upregulated the protein levels of active caspase 3 in a time-dependent manner. In addition, myricetin upregulated ER stress-associated proteins, glucose-regulated protein-78 and C/EBP homologous protein in SKOV3 cells. Phosphorylation of H₂AX, a marker of DNA DSBs, was revealed to be upregulated in myricetin-treated cells. The data indicated that myricetin induces DNA DSBs and ER stress, which leads to apoptosis in SKOV3 cells.

The Mechanism by Which MYCN Amplification Confers an Enhanced Sensitivity to a PCNA-Derived Cell Permeable Peptide in Neuroblastoma Cells

Dysregulated expression of MYC family genes is a hallmark of many malignancies. Unfortunately, these proteins are not amenable to blockade by small molecules or protein-based therapeutic agents. Therefore, we must find alternative approaches to target MYC-driven cancers. Amplification of MYCN, a MYC family member, predicts high-risk neuroblastoma (NB) disease. We have shown that R9-caPep blocks the interaction of PCNA with its binding partners and selectively kills human NB cells, especially those with MYCN amplification, and we now show the mechanism. We found elevated levels of DNA replication stress in MYCN-amplified NB cells. R9-caPep exacerbated DNA replication stress in MYCN-amplified NB cells and NB cells with an augmented level of MYC by interfering with DNA replication fork extension, leading to Chk1 dependence and susceptibility to Chk1 inhibition. We describe how these effects may be exploited for treating NB.

2-Deoxy-d-Glucose Sensitizes Human Ovarian Cancer Cells to Cisplatin by Increasing ER Stress and Decreasing ATP Stores in Acidic Vesicles

Cisplatin is a commonly used chemotherapeutic agent; however, the development of acquired resistance limits its application. Here, we demonstrate that 2-deoxy-d-glucose (2-DG) enhanced the antitumor effects of cisplatin in SKOV3 cells, which include inhibition of proliferation and promotion of apoptosis. Additionally, either cisplatin or 2-DG alone could upregulate the endoplasmic reticulum (ER) stress-associated protein glucose-regulated protein-78 (GRP78). Moreover, exposure to 2-DG increased the expression of GRP78 induced by cisplatin. Cisplatin also upregulated ER stress-associated apoptotic protein 153/C/EBP homology protein (CHOP) in SKOV3 cells. While treatment with 2-DG alone could not upregulate the CHOP expression, a combination of both 2-DG and cisplatin increased the protein levels of CHOP above those induced by Cisplatin alone. Finally, cisplatin mediated an increase in ATP stores within acidic vesicles, whereas 2-DG decreased this effect. These data demonstrate that 2-DG sensitizes SKOV3 cells to cisplatin by increasing ER stress and decreasing ATP stores in acidic vesicles.