Delivering More Payload (High DAR ADCs)

Advancing targeted combination chemotherapy in triple negative breast cancer: nucleolin aptamer-mediated controlled drug release

BACKGROUND

Triple-negative breast cancer (TNBC) is a recurrent, heterogeneous, and invasive form of breast cancer. The treatment of TNBC patients with paclitaxel and fluorouracil in a sequential manner has shown promising outcomes. However, it is challenging to deliver these chemotherapeutic agents sequentially to TNBC tumors. We aim to explore a precision therapy strategy for TNBC through the sequential delivery of paclitaxel and fluorouracil.

METHODS

We developed a dual chemo-loaded aptamer with redox-sensitive caged paclitaxel for rapid release and non-cleavable caged fluorouracil for slow release. The binding affinity to the target protein was validated using Enzyme-linked oligonucleotide assays and Surface plasmon resonance assays. The targeting and internalization abilities into tumors were confirmed using Flow cytometry assays and Confocal microscopy assays. The inhibitory effects on TNBC progression were evaluated by pharmacological studies in vitro and in vivo.

RESULTS

Various redox-responsive aptamer-paclitaxel conjugates were synthesized. Among them, AS1411-paclitaxel conjugate with a thioether linker (ASP) exhibited high anti-proliferation ability against TNBC cells, and its targeting ability was further improved through fluorouracil modification. The fluorouracil modified AS1411-paclitaxel conjugate with a thioether linker (FASP) exhibited effective targeting of TNBC cells and significantly improved the inhibitory effects on TNBC progression in vitro and in vivo.

CONCLUSIONS

This study successfully developed fluorouracil-modified AS1411-paclitaxel conjugates with a thioether linker for targeted combination chemotherapy in TNBC. These conjugates demonstrated efficient recognition of TNBC cells, enabling targeted delivery and controlled release of paclitaxel and fluorouracil. This approach resulted in synergistic antitumor effects and reduced toxicity in vivo. However, challenges related to stability, immunogenicity, and scalability need to be further investigated for future translational applications.

Structure-Activity Relationships of Antibody-Drug Conjugates: A Systematic Review of Chemistry on the Trastuzumab Scaffold

Antibody-drug conjugates (ADCs) are a rapidly growing class of cancer therapeutics that seek to overcome the low therapeutic index of conventional cytotoxic agents. However, realizing this goal has been a significant challenge. ADCs comprise several independently modifiable components, including the antibody, payload, linker, and bioconjugation method. Many approaches have been developed to improve the physical properties, potency, and selectivity of ADCs. The anti-HER-2 antibody trastuzumab, first approved in 1998, has emerged as an exceptional targeting agent for ADCs, as well as a broadly used platform for testing new technologies. The extensive work in this area enables the comparison of various linker strategies, payloads, drug-to-antibody ratios (DAR), and mode of attachment. In this review, these conjugates, ranging from the first clinically approved trastuzumab ADC, ado-trastuzumab emtansine (Kadcyla), to the latest variants are described with the goal of providing a broad overview, as well as enabling the comparison of existing and emerging conjugate technologies.

Diazido Macrocyclic Sulfates as a Platform for the Synthesis of Sequence-Defined Polymers for Antibody Drug Conjugates

To improve the efficacy of antibody drug conjugates (ADCs), there has been significant focus on increasing the drug-to-antibody ratio (DAR) in order to deliver more payload. However, due to the...

Polyethylene glycol-based linkers as hydrophilicity reservoir for antibody-drug conjugates

Antibody-drug conjugates (ADCs) are an established therapeutic entity in which potent cytotoxic drugs are conjugated to a monoclonal antibody. In parallel with the great emphasis put on novel site-specific bioconjugation technologies, future advancements in this field also rely on exploring novel linker-drug architectures that improve the efficacy and stability of ADCs. In this context, the use of hydrophilic linkers represents a valid strategy to mask or reduce the inherent hydrophobicity of the most used cytotoxic drugs and positively impact the physical stability and in vivo performance of ADCs. Here, we describe the use of linkers containing monodisperse poly(ethylene glycol) (PEG) moieties for the construction of highly-loaded lysine-conjugated ADCs. The studied ADCs differ in the positioning of PEG (linear or pendant), the bonding type with the antibody (amide or carbamate), and the drug-to-antibody ratio (DAR). These ADCs were first evaluated for their stability in solution under thermal stress, showing that both the drug-linker-polymer design and the nature of the antibody-linker bonding are of great importance for their physical and chemical stability. Amide-coupled ADCs bearing two pendant 12-unit poly(ethylene glycol) chains within the drug-linker structure were the best performing conjugates, distancing themselves from the ADCs obtained with a conventional linear 24-unit PEG oligomer or the linker of Kadcyla®. The pharmacokinetic profiles of amide-linked ADCs, with a linear or pendant configuration of the PEG, were tested in mice in comparison to Kadcyla®. Total antibody pharmacokinetics paralleled the trends in aggregation tendency, with slower clearance rates for the ADCs based on the pendant drug-linker format. The above-mentioned findings have provided important clues on the drug-linker design and revealed that the positioning and configuration of a PEG unit have to be carefully tuned to achieve ADCs with improved stability and pharmacokinetics.

An update on actively targeted liposomes in advanced drug delivery to glioma

High-grade glioma is one of the most aggressive types of cancer with a low survival rate ranging from 12 to 15 months after the first diagnosis. Though being the most common strategy for glioma therapy, conventional chemotherapy suffers providing the therapeutic dosage of common therapeutics mostly because of limited permeability of blood-brain barrier (BBB), and blood-brain tumor barrier (BBTB) to anticancer agents. Among various nanoformulations, liposomes are considered as the most popular carriers aimed for glioma therapy. However, non-targeted liposomes which passively accumulate in most of the cancer tissues mainly through the enhanced permeation and retention effect (EPR), may not be applicable for glioma therapy due to BBB tight junctions. In the recent decade, the surface modification of liposomes with different active targeting ligands has shown promising results by getting different chemotherapeutics across the BBB and BBTB and leading them into the glioma cells. The present review discusses the major barriers for drug delivery systems to glioma, elaborates the existing mechanisms for liposomes to traverse across the BBB, and explores the main strategies for incorporation of targeting ligands onto the liposomes. It subsequently investigates the most recent and relevant studies of actively targeted liposomes modified with antibodies, aptamers, monosaccharides, polysaccharides, proteins, and peptides applied for effective glioma therapy, and highlights the common challenges facing this area. Finally, the actively targeted liposomes undergoing preclinical and clinical studies for delivery of different anticancer agents to glioma cells will be reviewed.

Monomethyl Auristatin E Grafted-Liposomes to Target Prostate Tumor Cell Lines

Novel nanomedicines have been engineered to deliver molecules with therapeutic potentials, overcoming drawbacks such as poor solubility, toxicity or short half-life. Lipid-based carriers such as liposomes represent one of the most advanced classes of drug delivery systems. A Monomethyl Auristatin E (MMAE) warhead was grafted on a lipid derivative and integrated in fusogenic liposomes, following the model of antibody drug conjugates. By modulating the liposome composition, we designed a set of particles characterized by different membrane fluidities as a key parameter to obtain selective uptake from fibroblast or prostate tumor cells. Only the fluid liposomes made of palmitoyl-oleoyl-phosphatidylcholine and dioleoyl-phosphatidylethanolamine, integrating the MMAE-lipid derivative, showed an effect on prostate tumor PC-3 and LNCaP cell viability. On the other hand, they exhibited negligible effects on the fibroblast NIH-3T3 cells, which only interacted with rigid liposomes. Therefore, fluid liposomes grafted with MMAE represent an interesting example of drug carriers, as they can be easily engineered to promote liposome fusion with the target membrane and ensure drug selectivity.

The Dolaflexin-based Antibody-Drug Conjugate XMT-1536 Targets the Solid Tumor Lineage Antigen SLC34A2/NaPi2b

Target selection for antibody-drug conjugates (ADC) frequently focuses on identifying antigens with differential expression in tumor and normal tissue, to mitigate the risk of on-target toxicity. However, this strategy restricts the possible target space. SLC34A2/NaPi2b is a sodium phosphate transporter expressed in a variety of human tumors including lung and ovarian carcinoma, as well as the normal tissues from which these tumors arise. Previous clinical trials with a NaPi2b targeting MMAE-ADCs have shown objective durable responses. However, the protein-based biomarker assay developed for use in that study was unable to discern a statistically significant relationship between NaPi2b protein expression and the probability of response. XMT-1536 is a NaPi2b targeting ADC comprised of a unique humanized antibody conjugated with 10-15 auristatin F- hydroxypropylamide (AF-HPA) payload molecules via the Dolaflexin platform. AF-HPA is a cell-permeable, antimitotic compound that is slowly metabolized intratumorally to an active, very low-permeable metabolite, auristatin F (AF), resulting in controlled bystander killing. We describe the preclinical in vitro and in vivo antitumor effects of XMT-1536 in models of ovarian and lung adenocarcinoma. Pharmacokinetic analysis showed approximately proportional increases in exposure in rat and monkey. Systemic free AF-HPA and AF concentrations were observed to be low in all animal species. Finally, we describe a unique IHC reagent, generated from a chimeric construct of the therapeutic antibody, that was used to derive a target expression and efficacy relationship in a series of ovarian primary xenograft cancer models.

Marine sponge-derived/inspired drugs and their applications in drug delivery systems

Oceans harbor a vast biodiversity that is not represented in terrestrial habitats. Marine sponges have been the richest source of marine natural products reported to date, and sponge-derived natural products have served as inspiration for the development of several drugs in clinical use. However, many promising sponge-derived drug candidates have been stalled in clinical trials due to lack of efficacy, off-target toxicity, metabolic instability or poor pharmacokinetics. One possible solution to this high clinical failure rate is to design drug delivery systems that deliver drugs in a controlled and specific manner. This review critically analyzes drugs/drug candidates inspired by sponge natural products and the potential use of drug delivery systems as a new strategy to enhance the success rate for translation into clinical use.

Antibody-mediated drug delivery

Passive and active targeted nanoparticulate delivery systems show promise to compensate for lacking properties of conventional therapy such as side effects, insufficient efficiency and accumulation of the drug at target site, poor pharmacokinetic properties etc. For active targeting, physically or covalently conjugated ligands, including monoclonal antibodies and their fragments, are consistently used and researched for targeting delivery systems or drugs to their target site. Currently, there are several FDA approved actively targeted antibody-drug conjugates, whereas no active targeted delivery system is in clinical use at present. However, efforts to successfully formulate actively targeted delivery systems continue. The scope of this review will be the use of monoclonal antibodies and their fragments as targeting ligands. General information about targeted delivery and antibodies will be given at the first half of the review. As for the second half, fragmentation of antibodies and conjugation approaches will be explained. Monoclonal antibodies and their fragments as targeting ligands and approaches for conjugating these ligands to nanoparticulate delivery systems and drugs will be the main focus of this review, polyclonal antibodies will not be included.

Polymeric Engineering of Aptamer-Drug Conjugates for Targeted Cancer Therapy

Nucleic acid aptamers, also known as "chemical antibodies", have been widely employed in targeted cancer therapy and diagnosis. For example, aptamer-drug conjugates (ApDCs), through covalent conjugation of cytotoxic warheads to aptamers, have demonstrated anticancer efficacy both in vitro and in vivo. However, a general strategy to endow ApDCs with enhanced biostability, prolonged circulation half-life, and high drug loading content remained elusive. Herein, we present a polymeric approach to engineer ApDCs via conjugation of cell-targeting aptamers with water-soluble polyprodrugs containing a reductive environmentally sensitive prodrug and biocompatible brush-like backbone. The resultant high-drug loading Aptamer-PolyproDrug Conjugates (ApPDCs) exhibited high nuclease resistance, extended in vivo circulation time, specific recognition, and cellular uptake to target cells, reduction-triggered and fluorescent-reporting drug release, and effective cytotoxicity. We could also further expand this design principle toward combination therapy by using two kinds of therapeutic drugs with distinct pharmacological mechanisms.