Efficient Prostate Cancer Therapy with Tissue-Specific Homing Peptides Identified by Advanced Phage Display Technology

Biological Activity of Natural and Synthetic Peptides as Anticancer Agents

Cancer is one of the leading causes of morbidity and death worldwide, making it a serious global health concern. Chemotherapy, radiotherapy, and surgical treatment are the most used conventional therapeutic approaches, although they show several side effects that limit their effectiveness. For these reasons, the discovery of new effective alternative therapies still represents an enormous challenge for the treatment of tumour diseases. Recently, anticancer peptides (ACPs) have gained attention for cancer diagnosis and treatment. ACPs are small bioactive molecules which selectively induce cancer cell death through a variety of mechanisms such as apoptosis, membrane disruption, DNA damage, immunomodulation, as well as inhibition of angiogenesis, cell survival, and proliferation pathways. ACPs can also be employed for the targeted delivery of drugs into cancer cells. With over 1000 clinical trials using ACPs, their potential for application in cancer therapy seems promising. Peptides can also be utilized in conjunction with imaging agents and molecular imaging methods, such as MRI, PET, CT, and NIR, improving the detection and the classification of cancer, and monitoring the treatment response. In this review we will provide an overview of the biological activity of some natural and synthetic peptides for the treatment of the most common and malignant tumours affecting people around the world.

Translational use of homing peptides: Tumor and placental targeting

HYPOTHESIS

Tissue-specific homing peptides have been shown to improve chemotherapeutic efficacy due to their trophism for tumor cells. Other sequences that selectively home to the placenta are providing new and safer therapeutics to treat complications in pregnancy. Our hypothesis is that the placental homing peptide RSGVAKS (RSG) may have binding affinity to cancer cells, and that insight can be gained into the binding mechanisms of RSG and the tumor homing peptide CGKRK to model membranes that mimic the primary lipid compositions of the respective cells.

EXPERIMENTS

Following cell culture studies on the binding efficacy of the peptides on a breast cancer cell line, a systematic translational characterization is delivered using ellipsometry, Brewster angle microscopy and neutron reflectometry of the extents, structures, and dynamics of the interactions of the peptides with the model membranes on a Langmuir trough.

FINDINGS

We start by revealing that RSG does indeed have binding affinity to breast cancer cells. The peptide is then shown to exhibit stronger interactions and greater penetration than CGKRK into both model membranes, combined with greater disruption to the lipid component. RSG also forms aggregates bound to the model membranes, yet both peptides bind to a greater extent to the placental than cancer model membranes. The results demonstrate the potential for varying local reservoirs of peptide within cell membranes that may influence receptor binding. The innovative nature of our findings motivates the urgent need for more studies involving multifaceted experimental platforms to explore the use of specific peptide sequences to home to different cellular targets.

New role of bacteriophages in medical oncology

Targeted treatment of cancer is one of the most paramount approaches in cancer treatment. Despite significant advances in cancer diagnosis and treatment methods, there are still significant limitations and disadvantages in the field, including high costs, toxicity, and unwanted damage to healthy cells. The phage display technique is an innovative method for designing carriers containing exogenic peptides with cancer diagnostic and therapeutic properties. Bacteriophages possess unique properties making them effective in cancer treatment. These characteristics include the small size enabling them to penetrate vessels; having no pathogenicity to mammals; easy manipulation of their genetic information and surface proteins to introduce vaccines and drugs to cancer tissues; lower cost of large-scale production; and greater stimulation of the immune system. Bacteriophages will certainly play a more effective role in the future of medical oncology; however, studies are in the early stages of conception and require more extensive research. We aimed in this review to provide some related examples and bring insights into the potential of phages as targeted vectors for use in cancer diagnosis and treatment, especially regarding their capability in gene and drug delivery to cancer target cells, determination of tumor markers, and vaccine design to stimulate anticancer immunity.

The power of phages: revolutionizing cancer treatment

Cancer is a devastating disease with a high global mortality rate and is projected to increase further in the coming years. Current treatment options, such as chemotherapy and radiation therapy, have limitations including side effects, variable effectiveness, high costs, and limited availability. There is a growing need for alternative treatments that can target cancer cells specifically with fewer side effects. Phages, that infect bacteria but not eukaryotic cells, have emerged as promising cancer therapeutics due to their unique properties, including specificity and ease of genetic modification. Engineered phages can transform cancer treatment by targeting cancer cells while sparing healthy ones. Phages exhibit versatility as nanocarriers, capable of delivering therapeutic agents like gene therapy, immunotherapy, and vaccines. Phages are extensively used in vaccine development, with filamentous, tailed, and icosahedral phages explored for different antigen expression possibilities. Engineered filamentous phages bring benefits such as built in adjuvant properties, cost-effectiveness, versatility in multivalent formulations, feasibility of oral administration, and stability. Phage-based vaccines stimulate the innate immune system by engaging pattern recognition receptors on antigen-presenting cells, enhancing phage peptide antigen presentation to B-cells and T-cells. This review presents recent phage therapy advances and challenges in cancer therapy, exploring its versatile tools and vaccine potential.

Cell-Membrane-Coated and Cell-Penetrating Peptide-Conjugated Trimagnetic Nanoparticles for Targeted Magnetic Hyperthermia of Prostate Cancer Cells

Prostate malignancy represents the second leading cause of cancer-specific death among the male population worldwide. Herein, enhanced intracellular magnetic fluid hyperthermia is applied in vitro to treat prostate cancer (PCa) cells with minimum invasiveness and toxicity and highly specific targeting. We designed and optimized novel shape-anisotropic magnetic core-shell-shell nanoparticles (i.e., trimagnetic nanoparticles - TMNPs) with significant magnetothermal conversion following an exchange coupling effect to an external alternating magnetic field (AMF). The functional properties of the best candidate in terms of heating efficiency (i.e., Fe₃O₄@Mn_0.5Zn_0.5Fe₂O₄@CoFe₂O₄) were exploited following surface decoration with PCa cell membranes (CM) and/or LN1 cell-penetrating peptide (CPP). We demonstrated that the combination of biomimetic dual CM-CPP targeting and AMF responsiveness significantly induces caspase 9-mediated apoptosis of PCa cells. Furthermore, a downregulation of the cell cycle progression markers and a decrease of the migration rate in surviving cells were observed in response to the TMNP-assisted magnetic hyperthermia, suggesting a reduction in cancer cell aggressiveness.

Peptides Targeting RNA m6 A Methylations Influence the Viability of Cancer Cells

N6-methyladenosine (m6 A) is the most abundant nucleotide modification observed in eukaryotic mRNA. Changes in m6 A levels in transcriptome are tightly correlated to expression levels of m6 A methyltransferases and demethylases. Abnormal expression levels of methyltransferases and demethylases are observed in various diseases and health conditions such as cancer, male infertility, and obesity. This research explores the efficacy of m6 A-modified RNA as an anticancer drug target. We discovered a 12-mer peptide that binds specifically to m6 A-modified RNA using phage display experiments. Our fluorescence-based assays illustrate the selected peptide binds to methylated RNA with lower micromolar affinity and inhibit the binding of protein FTO, a demethylase enzyme specific to m6 A modification. When cancer cell lines were treated with mtp1, it led to an increase in m6 A levels and a decrease in cell viability. Hence our results illustrate the potential of mtp1 to be developed as a drug for cancer.

The role of peptide-based therapeutics in oncotherapy

Cancer is the second leading cause of death worldwide, and the search for specialised therapy options has been a challenge for decades. The emergence of active targeted therapies provides the opportunity to treat cancerous tissues without harming healthy ones due to peculiar physiological changes. Herein, peptides and peptide analogs have been gaining a lot of attention over the last decade, especially for the on-site delivery of therapeutics to target tissues in order to achieve efficient and reliable cancer treatment. Combining peptides with highly efficient drug delivery platforms could potentially eliminate off-target adverse effects encountered during active targeting of conventional chemotherapeutics. Small size, ease of production and characterisation, low immunogenicity and satisfactory binding affinity of peptides offer some advantages over other complex targeting moiety, no wonder the market of peptide-based drugs continues to expand expeditiously. It is estimated that the global peptide drug market will be worth around USD 48.04 billion by 2025, with a compound annual growth rate of 9.4%. In this review, the current state of art of peptide-based therapeutics with special interest on tumour targeting peptides has been discussed. Moreover, various active targeting strategies such as the use functionalised peptides or peptide analogs are also elaborated.

Peptides-based therapy and diagnosis. Strategies for non-invasive therapies in cancer

In recent years, remarkable progress was registered in the field of cancer research. Though, cancer still represents a major cause of death and cancer metastasis a problem seeking for urgent solutions as it is the main reason for therapeutic failure. Unfortunately, the most common chemotherapeutic agents are non-selective and can damage healthy tissues and cause side effects that affect dramatically the quality of life of the patients. Targeted therapy with molecules that act specifically at the tumour sites interacting with overexpressed cancer receptors is a very promising strategy for achieving the specific delivery of anticancer drugs, radioisotopes or imaging agents. This review aims to give an overview on different strategies for targeting cancer cell receptors localised either at the extracellular matrix or at the cell membrane. Molecules like antibodies, aptamers and peptides targeting the cell surface are presented with advantages and disadvantages, with emphasis on peptides. The most representative peptides are described, including cell penetrating peptides, homing and anticancer peptides with particular consideration on recent discoveries.

Paving the way for small-molecule drug discovery

Small-molecule drugs are organic compounds affecting molecular pathways by targeting important proteins, which have a low molecular weight, making them penetrate cells easily. Small-molecule drugs can be developed from leads derived from rational drug design or isolated from natural resources. As commonly used medications, small-molecule drugs can be taken orally, which enter cells to act on intracellular targets. These characteristics make small-molecule drugs promising candidates for drug development, and they are increasingly favored in the pharmaceutical market. Despite the advancements in molecular genetics and effective new processes in drug development, the drugs currently used in clinical practice are inadequate due to their poor efficacy or severe side effects. Therefore, developing new safe and efficient drugs is a top priority for disease control and curing.

Phage display screening identifies a prostate specific antigen (PSA)-/lo prostate cancer cell specific peptide to retard castration resistance of prostate cancer

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To our knowledge, this is the first study to identify a peptide (named as “TAP1”) that specifically binds with PSA^−/lo prostate cancer cells.

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TAP1 inhibited PCa growth both in vitro and in vivo.

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TAP1 also improved the anti-tumor effect of the anti-androgens and chemotherapeutic agents in vitro.

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The effects of TAP1 might at least in part by shortening the lengths of telomeres and decreasing the expression of HOXB9 and TGF-β2.

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Our results indicated that therapeutic peptides that specifically target prostate cancer stem cell might be a very valuable and promising approach to overcome chemoresistance and prevent recurrence in patients with PCa.

Patients with prostate cancer (PCa) will eventually progress to castrate-resistant prostate cancer (CRPC) after androgen deprivation therapy (ADT) treatment. Prostate-specific antigen (PSA)^−/lo cells which harbor self-renewing long-term tumor-propagating cells that can be enriched using ALDH+CD44+α2β1+ and can initiate tumor development may represent a critical source of CRPC cells. Our purpose was to find a peptide that specifically targets PSA^−/lo PCa cells to retard the development of CRPC. PSA⁺ and PSA^−/lo cells were successfully separated from LNCaP xenograft tumors after prostate- PSAP-GFP vector infection and FACS. A variety of PSA^−/lo cells specifically targeting peptide (named as “TAP1” targeted affinity peptide 1) was identified by using phage display library screening. The highest binding rate in TAP1 binding cell subpopulations are identified to be among ALDH⁺CD44⁺CXCR4⁺CD24⁺ cells. TAP1 significantly inhibited PCa growth both in vitro and in vivo. TAP1 significantly improved the anti-proliferation effect of the anti-androgens (Charcoal dextran-stripped serum (CDSS)+Bicalutamide, Enzalutamide) and chemotherapeutic agents (Abiraterone, Docetaxel, Etoposide) in vitro. TAP1 treatment shortens the length of telomeres in ALDH⁺CD44⁺CXCR4⁺CD24⁺ cells and significantly reduces the expression of Homeobox B9 (HOXB9) and TGF-β2. In conclusion, PSA^−/lo PCa cell-specific targeting peptide (TAP1) that suppressed PCa cell growth both in vitro and in vivo and improved the drug sensitivities of anti-androgens and chemotherapeutic agents at least through shortening the length of telomere and reducing the expression of HOXB9 and TGF-β2. Therapeutic peptides that specifically target prostate cancer stem cell might be a very valuable and promising approach to overcome chemoresistance and prevent recurrence in patients with PCa.

Application of Phage-Displayed Peptides in Tumor Imaging Diagnosis and Targeting Therapy

Phage display is an effective and powerful technique that provides a route to discovery unique peptides targeting to tumor cells. Specifically binding peptides are considered as the valuable target directing molecule fragments with potential efficiency to improve the current tumor clinic, and offer new approaches for tumor prevention, diagnosis and treatment. We focus on the recent advances in the isolation of tumor-targeting peptides by biopanning methods, with particular emphasis on molecular imaging, and pharmaceutical targeting therapy.

Phage Display to Augment Biomaterial Function

Biomaterial design relies on controlling interactions between materials and their biological environments to modulate the functions of proteins, cells, and tissues. Phage display is a powerful tool that can be used to discover peptide sequences with high affinity for a desired target. When incorporated into biomaterial design, peptides identified via phage display can functionalize material surfaces to control the interaction between a biomaterial and its local microenvironment. A targeting peptide has high specificity for a given target, allowing for homing a specific protein, cell, tissue, or other material to a biomaterial. A functional peptide has an affinity for a given protein, cell, or tissue, but also modulates its target's activity upon binding. Biomaterials can be further enhanced using a combination of targeting and/or functional peptides to create dual-functional peptides for bridging two targets or modulating the behavior of a specific protein or cell. This review will examine current and future applications of phage display for the augmentation of biomaterials.

Determination and characterisation of the surface charge properties of the bacteriophage M13 to assist bio-nanoengineering

To truly understand the mechanisms behind the supramolecular self-assembly of nanocomponents, the characterisation of their surface properties is crucial. M13 emerged as a practical nanocomponent for bio-nanoassemblies of functional materials and devices, and its popularity is increasing as time goes by. The investigation performed in this study provides important information about the surface charge and the surface area of M13 determined through the comparison of structural data and the measurement of ζ-potential at pH ranging between 2 and 11. The developed methodologies along with the experimental findings can be subsequently exploited as a novel and convenient prediction tool of the total charge of modified versions of M13. This, in turn, will facilitate the design of the self-assembly strategies which would combine the virus building block with other micro and nano components via intermolecular interactions.

Evolving a Peptide: Library Platforms and Diversification Strategies

Peptides are widely used in pharmaceutical industry as active pharmaceutical ingredients, versatile tools in drug discovery, and for drug delivery. They find themselves at the crossroads of small molecules and proteins, possessing favorable tissue penetration and the capability to engage into specific and high-affinity interactions with endogenous receptors. One of the commonly employed approaches in peptide discovery and design is to screen combinatorial libraries, comprising a myriad of peptide variants of either chemical or biological origin. In this review, we focus mainly on recombinant peptide libraries, discussing different platforms for their display or expression, and various diversification strategies for library design. We take a look at well-established technologies as well as new developments and future directions.