Increasing the antitumor efficacy of doxorubicin-loaded liposomes with peptides anchored via a chelator lipid

Surface Modification of Lipid-Based Nanoparticles

There is a growing interest in the development of lipid-based nanocarriers for multiple purposes, including the recent increase of these nanocarriers as vaccine components during the COVID-19 pandemic. The number of studies that involve the surface modification of nanocarriers to improve their performance (increase the delivery of a therapeutic to its target site with less off-site accumulation) is enormous. The present review aims to provide an overview of various methods associated with lipid nanoparticle grafting, including techniques used to separate grafted nanoparticles from unbound ligands or to characterize grafted nanoparticles. We also provide a critical perspective on the usefulness and true impact of these modifications on overcoming different biological barriers, with our prediction on what to expect in the near future in this field.

Using peptides to promote delivery and improve anti-tumour efficacy of liposomal drug

Liposomal drugs exhibit advantages for cancer therapy, but efficacy is often limited by their rapid clearance from blood by the reticuloendothelial system, and an inability to target and penetrate tumours. Interestingly, a 21-amino acid SIRP-α- (signal regulatory protein-α) interacting 'self' peptide is reported to inhibit uptake by phagocytes. Also, 'iRGD' a 9-amino acid cyclic peptide that binds αvβ3 integrins and neuropilin-1 (NRP-1), promotes targeting and penetration of drug into tumours. Here we explore the potential of nitrilotriacetic acid-ditetra-decylamine (NTA₃-DTDA)-containing liposomes (NTA-liposomes) engrafted with His-tagged forms of 'self' peptide (pCD47) to prolong circulation time in blood after iv administration, and of iRGD peptide (piRGD) to enhance treatment efficacy of doxorubicin-containing liposomes (Caelyx). Our results show that pre-incubation of murine phagocytic DC2.4 and RAW246.7 cells with pCD47 inhibits uptake of NTA-liposomes in vitro, but engraftment of pCD47 surprisingly reduces liposome lifetime in blood. Engraftment of piRGD promoted binding of NTA-liposomes to murine B16 melanoma and CT26 colorectal carcinoma cells in vitro. Importantly, iv administration of piRGD-engrafted Caelyx was found to significantly inhibit tumour growth and prolong survival in both B16 and CT26 murine tumour models. Our results show that engraftment of piRGD onto Caelyx is a convenient strategy to enhance treatment efficacy.

Nanomedicine as a potent strategy in melanoma tumor microenvironment

Melanoma originated from melanocytes is the most aggressive type of skin cancer. Despite considerable progresses in clinical treatment with the discovery of BRAF or MEK inhibitors and monoclonal antibodies, the durability of response to treatment is often limited to the development of acquired resistance and systemic toxicity. The limited success of conventional treatment highlights the importance of understanding the role of melanoma tumor microenvironment in tumor developement and drug resistance. Nanoparticles represent a promising strategy for the development of new cancer treatments able to improve the bioavailability of drugs and increase their penetration by targeting specifically tumors cells and/or tumor environment. In this review, we will discuss the main influence of tumor microenvironment in melanoma growth and treatment outcome. Furthermore, third generation loaded nanotechnologies represent an exciting tool for detection, treatment, and escape from possible mechanism of resistance mediated by tumor microenvironment, and will be highlighted in this review.

Biotin-conjugated fusogenic liposomes for high-quality cell purification

Purification of defined cell populations from mixed primary cell sources is essential for many biomedical and biotechnological applications but often very difficult to accomplish due to missing specific surface markers. In this study, we developed a new approach for efficient cell population separation based on the specific membrane fusion characteristics of distinct cell types upon treatment with fusogenic liposomes. When such liposomes are conjugated with biotin, specific cell populations can be efficiently surface functionalized by biotin after liposomal treatment while other populations remain unlabeled. Due to the high affinity of biotin for avidin-like proteins, biotin functionalized cells are ideal targets for conjugation of e.g. avidin tagged magnetic beads, fluorophores or antibodies with bioanalytical relevance. Here, based on the differential biotinylation of distinct cell populations high quality separation of cardiac fibroblasts from myocytes, and cerebromicrovascular endothelial cells from fibroblasts was successfully established.

Ligation strategies for targeting liposomal nanocarriers

Liposomes have been exploited for pharmaceutical purposes, including diagnostic imaging and drug and gene delivery. The versatility of liposomes as drug carriers has been demonstrated by a variety of clinically approved formulations. Since liposomes were first reported, research of liposomal formulations has progressed to produce improved delivery systems. One example of this progress is stealth liposomes, so called because they are equipped with a PEGylated coating of the liposome bilayer, leading to prolonged blood circulation and improved biodistribution of the liposomal carrier. A growing research area focuses on the preparation of liposomes with the ability of targeting specific tissues. Several strategies to prepare liposomes with active targeting ligands have been developed over the last decades. Herein, several strategies for the functionalization of liposomes are concisely summarized, with emphasis on recently developed technologies for the covalent conjugation of targeting ligands to liposomes.

A liposomal drug platform overrides peptide ligand targeting to a cancer biomarker, irrespective of ligand affinity or density

One method for improving cancer treatment is the use of nanoparticle drugs functionalized with targeting ligands that recognize receptors expressed selectively by tumor cells. In theory such targeting ligands should specifically deliver the nanoparticle drug to the tumor, increasing drug concentration in the tumor and delivering the drug to its site of action within the tumor tissue. However, the leaky vasculature of tumors combined with a poor lymphatic system allows the passive accumulation, and subsequent retention, of nanosized materials in tumors. Furthermore, a large nanoparticle size may impede tumor penetration. As such, the role of active targeting in nanoparticle delivery is controversial, and it is difficult to predict how a targeted nanoparticle drug will behave in vivo. Here we report in vivo studies for α_vβ₆-specific H2009.1 peptide targeted liposomal doxorubicin, which increased liposomal delivery and toxicity to lung cancer cells in vitro. We systematically varied ligand affinity, ligand density, ligand stability, liposome dosage, and tumor models to assess the role of active targeting of liposomes to α_vβ₆. In direct contrast to the in vitro results, we demonstrate no difference in in vivo targeting or efficacy for H2009.1 tetrameric peptide liposomal doxorubicin, compared to control peptide and no peptide liposomes. Examining liposome accumulation and distribution within the tumor demonstrates that the liposome, and not the H2009.1 peptide, drives tumor accumulation, and that both targeted H2009.1 and untargeted liposomes remain in perivascular regions, with little tumor penetration. Thus H2009.1 targeted liposomes fail to improve drug efficacy because the liposome drug platform prevents the H2009.1 peptide from both actively targeting the tumor and binding to tumor cells throughout the tumor tissue. Therefore, using a high affinity and high specificity ligand targeting an over-expressed tumor biomarker does not guarantee enhanced efficacy of a liposomal drug. These results highlight the complexity of in vivo targeting.

Recent trends in multifunctional liposomal nanocarriers for enhanced tumor targeting

Liposomes are delivery systems that have been used to formulate a vast variety of therapeutic and imaging agents for the past several decades. They have significant advantages over their free forms in terms of pharmacokinetics, sensitivity for cancer diagnosis and therapeutic efficacy. The multifactorial nature of cancer and the complex physiology of the tumor microenvironment require the development of multifunctional nanocarriers. Multifunctional liposomal nanocarriers should combine long blood circulation to improve pharmacokinetics of the loaded agent and selective distribution to the tumor lesion relative to healthy tissues, remote-controlled or tumor stimuli-sensitive extravasation from blood at the tumor's vicinity, internalization motifs to move from tumor bounds and/or tumor intercellular space to the cytoplasm of cancer cells for effective tumor cell killing. This review will focus on current strategies used for cancer detection and therapy using liposomes with special attention to combination therapies.

Peptide targeted lipid nanoparticles for anticancer drug delivery

Encapsulating anticancer drugs in nanoparticles has proven to be an effective mechanism to alter the pharmacokinetic and pharmacodynamic profiles of the drugs, leading to clinically useful cancer therapeutics like Doxil and DaunoXome. Underdeveloped tumor vasculature and lymphatics allow these first-generation nanoparticles to passively accumulate within the tumor, but work to create the next-generation nanoparticles that actively participate in the tumor targeting process is underway. Lipid nanoparticles functionalized with targeting peptides are among the most often studied. The goal of this article is to review the recently published literature of targeted nanoparticles to highlight successful designs that improved in vivo tumor therapy, and to discuss the current challenges of designing these nanoparticles for effective in vivo performance.

Effective tumor targeting and enhanced anti-tumor effect of liposomes engrafted with peptides specific for tumor lymphatics and vasculature

The use of liposomes to target drugs to tumors represents an attractive therapeutic strategy, especially when used with convenient targeting moieties such as peptides. Here we explored several peptides for their ability to target liposomes to tumors. The metal chelator lipid 3(nitrilotriacetic acid)-ditetradecylamine (NTA(3)-DTDA) was incorporated into liposomes to enable the engraftment of His-tagged peptides containing targeting motifs specific for tumor vasculature markers VEGFR-1 (p39-Flt-1) and neuropilin-1 (p24-NRP-1), or a motif known to accumulate in hypoxic areas of tumors (p47-LyP-1). Peptide-engrafted liposomes were examined for their biodistribution and anti-tumor effects after i.v. administration. Our results show that radiolabelled liposomes engrafted with either p24-NRP-1 or p47-LyP-1 and then injected into mice bearing subcutaneous B16-F1 tumors, show increased accumulation in the tumor. For p24-NRP-1-liposomes, tumor targeting was significantly increased when the stabilizing lipid phosphatidylethanolamine polyethylene glycol-750 (PE-PEG(750)) was used instead of PE-PEG(2000) in the liposome lipid mixture. Importantly, compared to the controls, p24-NRP-1 liposomes containing 10 mol% PE-PEG(750) and loaded with doxorubicin significantly inhibited the rate of tumor growth in the tumor-bearing mice. Our findings demonstrate that the use of drug-containing liposomes incorporating NTA(3)-DTDA and engrafted with NRP-1 targeting peptide is a convenient strategy to enhance the therapeutic effect of non-targeted doxorubicin.