Liposomal formulation of polyacrylate-peptide conjugate as a new vaccine candidate against cervical cancer

Improving the efficacy of peptide vaccines in cancer immunotherapy

Peptide vaccines have shown great potential in cancer immunotherapy by targeting tumor antigens and activating the patient's immune system to mount a specific response against cancer cells. However, the efficacy of peptide vaccines in inducing a sustained immune response and achieving clinical benefit remains a major challenge. In this review, we discuss the current status of peptide vaccines in cancer immunotherapy and strategies to improve their efficacy. We summarize the recent advancements in the development of peptide vaccines in pre-clinical and clinical settings, including the use of novel adjuvants, neoantigens, nano-delivery systems, and combination therapies. We also highlight the importance of personalized cancer vaccines, which consider the unique genetic and immunological profiles of individual patients. We also discuss the strategies to enhance the immunogenicity of peptide vaccines such as multivalent peptides, conjugated peptides, fusion proteins, and self-assembled peptides. Although, peptide vaccines alone are weak immunogens, combining peptide vaccines with other immunotherapeutic approaches and developing novel approaches such as personalized vaccines can be promising methods to significantly enhance their efficacy and improve the clinical outcomes for cancer patients.

A Comprehensive View of the Cancer-Immunity Cycle (CIC) in HPV-Mediated Cervical Cancer and Prospects for Emerging Therapeutic Opportunities

Cervical cancer (CC) is the fourth most common cancer in women worldwide, with more than 500,000 new cases each year and a mortality rate of around 55%. Over 80% of these deaths occur in developing countries. The most important risk factor for CC is persistent infection by a sexually transmitted virus, the human papillomavirus (HPV). Conventional treatments to eradicate this type of cancer are accompanied by high rates of resistance and a large number of side effects. Hence, it is crucial to devise novel effective therapeutic strategies. In recent years, an increasing number of studies have aimed to develop immunotherapeutic methods for treating cancer. However, these strategies have not proven to be effective enough to combat CC. This means there is a need to investigate immune molecular targets. An adaptive immune response against cancer has been described in seven key stages or steps defined as the cancer-immunity cycle (CIC). The CIC begins with the release of antigens by tumor cells and ends with their destruction by cytotoxic T-cells. In this paper, we discuss several molecular alterations found in each stage of the CIC of CC. In addition, we analyze the evidence discovered, the molecular mechanisms and their relationship with variables such as histological subtype and HPV infection, as well as their potential impact for adopting novel immunotherapeutic approaches.

Liposomal Formulations of a Polyleucine-Antigen Conjugate as Therapeutic Vaccines against Cervical Cancer

Human papilloma virus (HPV) is responsible for all cases of cervical cancer. While prophylactic vaccines are available, the development of peptide-based vaccines as a therapeutic strategy is still under investigation. In comparison with the traditional and currently used treatment strategies of chemotherapy and surgery, vaccination against HPV is a promising therapeutic option with fewer side effects. A peptide derived from the HPV-16 E7 protein, called 8Qm, in combination with adjuvants showed promise as a therapeutic vaccine. Here, the ability of polymerized natural amino acids to act as a self-adjuvating delivery system as a therapeutic vaccine was investigated for the first time. Thus, 8Qm was conjugated to polyleucine by standard solid-phase peptide synthesis and self-assembled into nanoparticles or incorporated in liposomes. The liposome bearing the 8Qm conjugate significantly increased mice survival and decreased tumor growth after a single immunization. Further, these liposomes eradicated seven-day-old well-established tumors in mice. Dendritic cell (DC)-targeting moieties were introduced to further enhance vaccine efficacy, and the newly designed liposomal vaccine was tested in mice bearing 11-day-old tumors. Interestingly, these DCs-targeting moieties did not significantly improve vaccine efficacy, whereas the simple liposomal formulation of 8Qm-polyleucine conjugate was still effective in tumor eradication. In summary, a peptide-based anticancer vaccine was developed that stimulated strong cellular immune responses without the help of a classical adjuvant.

Polyacrylate-GnRH Peptide Conjugate as an Oral Contraceptive Vaccine Candidate

Contraceptive vaccines are designed to elicit immune responses against major components of animal reproductive systems. These vaccines, which are most commonly administered via injection, typically target gonadotropin-releasing hormone (GnRH). However, the need to restrain animals for treatment limits the field applications of injectable vaccines. Oral administration would broaden vaccine applicability. We explored contraceptive vaccine candidates composed of GnRH peptide hormone, universal T helper PADRE (P), and a poly(methylacrylate) (PMA)-based delivery system. When self-assembled into nanoparticles, PMA-P-GnRH induced the production of high IgG titers after subcutaneous and oral administration in mice. PADRE was then replaced with pig T helper derived from the swine flu virus, and the vaccine was tested in pigs. High levels of systemic antibodies were produced in pigs after both injection and oral administration of the vaccine. In conclusion, we developed a simple peptide–polymer conjugate that shows promise as an effective, adjuvant-free, oral GnRH-based contraceptive vaccine.

A Potent Cancer Vaccine Adjuvant System for Particleization of Short, Synthetic CD8+ T Cell Epitopes

Short major histocompatibility complex (MHC) class I (MHC-I)-restricted peptides contain the minimal biochemical information to induce antigen (Ag)-specific CD8⁺ cytotoxic T cell responses but are generally ineffective in doing so. To address this, we developed a cobalt-porphyrin (CoPoP) liposome vaccine adjuvant system that induces rapid particleization of conventional, short synthetic MHC-I epitopes, leading to strong cellular immune responses at nanogram dosing. Along with CoPoP (to induce particle formation of peptides), synthetic monophosphoryl lipid A (PHAD) and QS-21 immunostimulatory molecules were included in the liposome bilayer to generate the "CPQ" adjuvant system. In mice, immunization with a short MHC-I-restricted peptide, derived from glycoprotein 70 (gp70), admixed with CPQ safely generated functional, Ag-specific CD8⁺ T cells, resulting in the rejection of multiple tumor cell lines, with durable immunity. When cobalt was omitted, the otherwise identical peptide and adjuvant components did not result in peptide binding and were incapable of inducing immune responses, demonstrating the importance of stable particle formation. Immunization with the liposomal vaccine was well-tolerated and could control local and metastatic disease in a therapeutic setting. Mechanistic studies showed that particle-based peptides were better taken up by antigen-presenting cells, where they were putatively released within endosomes and phagosomes for display on MHC-I surfaces. On the basis of the potency of the approach, the platform was demonstrated as a tool for in vivo epitope screening of peptide microlibraries comprising a hundred peptides.

Cholic Acid-based Delivery System for Vaccine Candidates against Group A Streptococcus

Peptide-based subunit vaccines require an immunostimulant (adjuvant) and/or delivery system to protect the antigenic peptide from degradation and induce the desired immunity. Currently available adjuvants are either too toxic for human use (experimental adjuvants) or they are limited for use in particular vaccines or licensed countries (commercial adjuvants). Therefore, there is an immediate need for novel adjuvants that are both safe and effective. Herein, we assessed the ability of cholic acid (a major bile acid) as a nontoxic, biodegradable, human-derived, potent vaccine delivery system. An antigenic peptide derived from Group A Streptococcus was conjugated to hydrophobic cholic acid via solid phase peptide synthesis to produce lipopeptide that self-assembled into rod-like nanoparticles under aqueous conditions. Following intranasal immunization in mice, this lipopeptide was capable of inducing the production of opsonic epitope-specific antibodies on its own and in liposomal formulation. The cholic acid-based conjugate induced significantly stronger humoral immune responses than cholera toxin-based adjuvant. Thus, we demonstrated, for the first time, capability of the human-derived lipid to act as a built-in immunoadjuvant for vaccines.

Precision Nanomedicine Vol. 1, Issue 3, Table of Contents

Prec. Nanomed. 2018 Oct;1(3):183-193. BASIC RESEARCH From the Clinical Editor: The number of women affected by cervical cancer worldwide is very significant and the disease is associated with human papilloma virus (HPV) infection. Although the use of HPV vaccines has proven to be useful in disease protection, they only work in women who have never been infected by HPV previously. Thus, the development of a therapeutic vaccine that targets HPV-infected cells is needed for women who are already infected with the virus. In this study, the authors describe the use of a self-adjuvating polymer-based delivery system for the development of a therapeutic vaccine. Therefore, while efforts are progressing, vaccine candidates are still required against late stage cervical cancer via improving the vaccine delivery system. Authors demonstrate that the combination of polymer-based and liposome delivery systems may be effective without the use of additional adjuvant and with just a single dose immunization. This finding has potential importance for other cancer vaccines as well. Prec. Nanomed. 2018 Oct;1(3):173-182 POTENTIAL CLINICAL SIGNIFICANCE From the Clinical Editor: The treatment of triple-negative breast cancer is often difficult due to frequent resistance to doxorubicin. Using different nano-formulations based on sol-gel technology to encapsulate doxorubicin, the authors here showed enhanced dose-response metrics and tumor cell kill of these cancer cells due to an increased drug accumulation in the local tumor environment. This platform shows early promise in terms of eventual clinical translatability. Prec. Nanomed. 2018 Oct;1(3):194-207. BASIC RESEARCH From the Clinical Editor: Surgical resection remains the main treatment modality for pancreatic cancer. Thus, the ability to delineate the tumor accurately during operation is important to ensure all tumor cells are resected. Here, the authors describe the development of a multimodal imaging probe using nanospheres to target epithelial cells of pancreatic cancer. The specificity to target only tumor cells was clearly shown in both in-vitro and in-vivo experiments. This technology may provide a new fluorescence imaging technique to help the field of surgical oncology in the future. Prec. Nanomed. 2018 Oct;1(3):208-217. BASIC RESEARCH From the Clinical Editor: Preclinical characterization of nanotechnology-based products is essential for translating innovative applications into clinics. In addition to the innate immune system complement activation plays an important role in regulating the adaptive immune response. Undesirable activation of the complement system in response to new composites may lead to hypersensitivity reactions. The authors describe the importance of mouse strain selection for in vitro complement activation analysis addressing also the existence of inter- and intraspecies variability.