A High Throughput Approach for Designing Polymers That Mimic the TRAIL Protein

Combination of multivalent DR5 receptor clustering agonists and histone deacetylase inhibitors for treatment of colon cancer

Death Receptor 5 (DR5) targeted therapies offer significant promise due to their pivotal role in mediating the extrinsic pathway of apoptosis. Despite DR5 overexpression in various malignancies and the potential of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), clinical applications of anti-DR5 monoclonal antibodies (mAbs) have been hampered by suboptimal outcomes potentially due to lack of receptor clustering. To address the limitation, we developed N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-based conjugates integrating multiple copies of DR5-targeting peptide (cyclic WDCLDNRIGRRQCVKL; cDR5) to enhance receptor clustering and apoptosis. Three conjugates with variable number of cDR5 were prepared and denoted as PH-cDR5 (high valence), PM-cDR5 (medium valence) and PL-cDR5 (low valence). Our studies in TRAIL-sensitive and resistant cancer cell lines demonstrated that the HPMA copolymer-peptide conjugates (P-cDR5) significantly improved DR5 receptor clustering and induced apoptosis effectively. In TRAIL-sensitive colon cancer cells (COLO205, HCT-116), P-cDR5 showed efficacy comparable to anti-DR5 mAb Drozitumab (DRO), but P-cDR5 outperformed DRO in TRAIL-resistant cells (HT-29), highlighting the importance of efficient receptor clustering. In COLO205 cells PM-cDR5 exhibited an IC50 of 94 pM, while PH-cDR5 had an even lower IC50 of 15 pM (based on cDR5 equivalent concentration), indicating enhanced potency of the multivalent HPMA copolymer-based system with a flexible polymer backbone in comparison with the IC50 for TRAIL at 0.12 nM. Combining P-cDR5 with valproic acid, a histone deacetylase inhibitor, resulted in further enhancement of apoptosis inducing efficacy, along with destabilizing mitochondrial membranes and increased sensitivity of TRAIL-resistant cells. These findings suggest that attaching multiple cDR5 peptides to a flexible water-soluble polymer carrier not only overcomes the limitations of previous designs but also offers a promising avenue for treating resistant cancers, pointing toward the need for further preclinical exploration and validation of this innovative strategy.

Collapsed Star Copolymers Exhibiting Near Perfect Mimicry of the Therapeutic Protein "TRAIL"

Here we introduce amphiphilic star polymers as versatile protein mimics capable of approximating the activity of certain native proteins. Our study focuses on designing a synthetic polymer capable of replicating the biological activity of TRAIL, a promising anticancer protein that shows very poor circulation half-life. Successful protein mimicry requires precise control over the presentation of receptor-binding peptides from the periphery of the polymer scaffold while maintaining enough flexibility for protein-peptide binding. We show that this can be achieved by building hydrophobic blocks into the core of a star-shaped polymer, which drives unimolecular collapse in water. By screening a library of diblock copolymer stars, we were able to design structures with IC50's of ∼4 nM against a colon cancer cell line (COLO205), closely approximating the activity of the native TRAIL protein. This finding highlights the broad potential for simple synthetic polymers to mimic the biological activity of complex proteins.

The Role of TRAIL Signaling in Cancer: Searching for New Therapeutic Strategies

Cancer continues to pose a significant threat to global health, with its status as a leading cause of death remaining unchallenged. Within the realm of cancer research, the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) stands out as a critical player, having been identified in the 1990s as the tenth member of the TNF family. This review examines the pivotal role of TRAIL in cancer biology, focusing on its ability to induce apoptosis in malignant cells through both endogenous and exogenous pathways. We provide an in-depth analysis of TRAIL's intracellular signaling and intercellular communication, underscoring its potential as a selective anticancer agent. Additionally, the review explores TRAIL's capacity to reshape the tumor microenvironment, thereby influencing cancer progression and response to therapy. With an eye towards future developments, we discuss the prospects of harnessing TRAIL's capabilities for the creation of tailored, precision-based cancer treatments, aiming to enhance efficacy and improve patient survival rates.

Navigating the Expansive Landscapes of Soft Materials: A User Guide for High-Throughput Workflows

Synthetic polymers are highly customizable with tailored structures and functionality, yet this versatility generates challenges in the design of advanced materials due to the size and complexity of the design space. Thus, exploration and optimization of polymer properties using combinatorial libraries has become increasingly common, which requires careful selection of synthetic strategies, characterization techniques, and rapid processing workflows to obtain fundamental principles from these large data sets. Herein, we provide guidelines for strategic design of macromolecule libraries and workflows to efficiently navigate these high-dimensional design spaces. We describe synthetic methods for multiple library sizes and structures as well as characterization methods to rapidly generate data sets, including tools that can be adapted from biological workflows. We further highlight relevant insights from statistics and machine learning to aid in data featurization, representation, and analysis. This Perspective acts as a "user guide" for researchers interested in leveraging high-throughput screening toward the design of multifunctional polymers and predictive modeling of structure-property relationships in soft materials.

Peptide-Conjugated Micelles Make Effective Mimics of the TRAIL Protein for Driving Apoptosis in Colon Cancer

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) drives apoptosis selectively in cancer cells by clustering death receptors (DR4 and DR5). While it has excellent in vitro selectivity and toxicity, the TRAIL protein has a very low circulation half-life in vivo, which has hampered clinical development. Here, we developed core-cross-linked micelles that present multiple copies of a TRAIL-mimicking peptide at its surface. These micelles successfully induce apoptosis in a colon cancer cell line (COLO205) via DR4/5 clustering. Micelles with a peptide density of 15% (roughly 1 peptide/45 nm2) displayed the strongest activity with an IC50 value of 0.8 μM (relative to peptide), demonstrating that the precise spatial arrangement of ligands imparted by a protein such as a TRAIL may not be necessary for DR4/5/signaling and that a statistical network of monomeric ligands may suffice. As micelles have long circulation half-lives, we propose that this could provide a potential alternative drug to TRAIL and stimulate the use of micelles in other membrane receptor clustering networks.

Recent developments in visible light induced polymerization towards its application to nanopores

Visible light induced polymerizations are a strongly emerging field in recent years. Besides the often mild reaction conditions, visible light offers advantages of spatial and temporal control over chain growth, which makes visible light ideal for functionalization of surfaces and more specifically of nanoscale pores. Current challenges in nanopore functionalization include, in particular, local and highly controlled polymer functionalizations. Using spatially limited light sources such as lasers or near field modes for light-induced polymer functionalization is envisioned to allow local functionalization of nanopores and thereby improve nanoporous material performance. These light sources are usually providing visible light while classical photopolymerizations are mostly based on UV-irradiation. In this review, we highlight developments in visible light induced polymerizations and especially in visible light induced controlled polymerizations as well as their potential for nanopore functionalization. Existing examples of visible light induced polymerizations in nanopores are emphasized.

A fully automated platform for photoinitiated RAFT polymerization

Oxygen tolerant polymerizations including Photoinduced Electron/Energy Transfer-Reversible Addition-Fragmentation Chain-Transfer (PET-RAFT) polymerization allow for high-throughput synthesis of diverse polymer architectures on the benchtop in parallel. Recent developments have further increased throughput using liquid handling robotics to automate reagent handling and dispensing into well plates thus enabling the combinatorial synthesis of large polymer libraries. Although liquid handling robotics can enable automated polymer reagent dispensing in well plates, photoinitiation and reaction monitoring require automation to provide a platform that enables the reliable and robust synthesis of various polymer compositions in high-throughput where polymers with desired molecular weights and low dispersity are obtained. Here, we describe the development of a robotic platform to fully automate PETRAFT polymerizations and provide individual control of reactions performed in well plates. On our platform, reagents are automatically dispensed in well plates, photoinitiated in individual wells with a custom-designed lightbox until the polymerizations are complete, and monitored online in real-time by tracking fluorescence intensities on a fluorescence plate reader, with well plate transfers between instruments occurring via a robotic arm. We found that this platform enabled robust parallel polymer synthesis of both acrylate and acrylamide homopolymers and copolymers, with high monomer conversions and low dispersity. The successful polymerizations obtained on this platform make it an efficient tool for combinatorial polymer chemistry. In addition, with the inclusion of machine learning protocols to help navigate the polymer space towards specific properties of interest, this robotic platform can ultimately become a self-driving lab that can dispense, synthesize, and monitor large polymer libraries.

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X-CuII/L). The role of PC was to trigger and drive the polymerization, while X-CuII/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X-CuII/L, generating CuI/L activator and PC˙+. The ATRP ligand (L) used in excess then reduced the PC˙+, closing the photocatalytic cycle. The continuous reduction of X-CuII/L back to CuI/L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X-CuII/L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.

The challenges of controlling polymer synthesis at the molecular and macromolecular level

In this Perspective, we outline advances and challenges in controlling the structure of polymers at various size regimes in the context of structural features such as molecular weight distribution, end groups, architecture, composition and sequence.