Techniques for studying membrane pores

A Cytotoxic T Lymphocyte-Inspiring Microscale System for Cancer Immunotherapy

Adoptive T cell therapy (ACT) is an emerging cancer immunotherapy undergoing clinical evaluation, showing significant promise in the treatment of solid tumors. However, the clinical translation of ACT is hindered by its time-, labor-, and financial-consuming procedures, heterogeneity of cytotoxic T lymphocytes (CTLs), and immunosuppressive tumor microenvironment. Herein, we have developed a bionic cytotoxic T lymphocyte-inspiring microscale system (CTLiMS) composed of mesoporous silica dioxide microspheres containing membrane-disrupting boron clusters (BICs) and proapoptotic monomethyl auristatin E (MMAE) peptides. The BICs were found to disrupt the integrity of cancer cell membranes and enhance the internalization of MMAE, effectively mimicking the biological functions of perforin and granzymes released by CTLs to destroy cancer cells. As expected, the CTLiMSs demonstrated exceptional in vitro anticancer activity, inducing cancer cell apoptosis and exhibiting strong antiproliferative effects. Notably, CTLiMS treatment was demonstrated to induce immunogenic cell death of cancer cells as a result of Ca2+ and MMAE influx and subsequent production of reactive oxygen species. The animal studies demonstrated that the CTLiMS treatment led to efficient repression of the tumor growth. Furthermore, the CTLiMS administration resulted in favorable antitumor immunotherapeutic effects, as shown by significant inhibition of distant tumors, increased immune cell infiltration, and elevated plasma levels of pro-inflammatory cytokines. This pilot study using CTLiMSs for cancer immunotherapy offers an innovative bionic strategy for the future advancement of adoptive T cell therapy.

Temperature Control of the Self-Assembly Process of 4-Aminoquinoline Amphiphile: Selective Construction of Perforated Vesicles and Nanofibers, and Structural Restoration Capability

The construction of diverse and distinctive self-assembled structures in water, based on the control of the self-assembly processes of artificial small molecules, has received considerable attention in supramolecular chemistry. Cage-like perforated vesicles are distinctive and interesting self-assembled structures. However, the development of self-assembling molecules that can easily form perforated vesicles remains challenging. This paper reports a lower critical solution temperature (LCST) behavior-triggered self-assembly property of a 4-aminoquinoline (4-AQ)-based amphiphile with a tetra(ethylene glycol) chain, in HEPES buffer (pH 7.4). This property allows to form perforated vesicles after heating at 80 °C (> LCST). The self-assembly process of the 4-AQ amphiphile can be controlled by heating at 80 °C (> LCST) or 60 °C (< LCST). After cooling to room temperature, the selective construction of the perforated vesicles and nanofibers was achieved from the same 4-AQ amphiphile. Furthermore, the perforated vesicles exhibited slow morphological transformation into intertwined-like nanofibers but were easily restored by brief heating above the LCST.

Pore-Forming Proteins: From Pore Assembly to Structure by Quantitative Single-Molecule Imaging

Pore-forming proteins (PFPs) play a central role in many biological processes related to infection, immunity, cancer, and neurodegeneration. A common feature of PFPs is their ability to form pores that disrupt the membrane permeability barrier and ion homeostasis and generally induce cell death. Some PFPs are part of the genetically encoded machinery of eukaryotic cells that are activated against infection by pathogens or in physiological programs to carry out regulated cell death. PFPs organize into supramolecular transmembrane complexes that perforate membranes through a multistep process involving membrane insertion, protein oligomerization, and finally pore formation. However, the exact mechanism of pore formation varies from PFP to PFP, resulting in different pore structures with different functionalities. Here, we review recent insights into the molecular mechanisms by which PFPs permeabilize membranes and recent methodological advances in their characterization in artificial and cellular membranes. In particular, we focus on single-molecule imaging techniques as powerful tools to unravel the molecular mechanistic details of pore assembly that are often obscured by ensemble measurements, and to determine pore structure and functionality. Uncovering the mechanistic elements of pore formation is critical for understanding the physiological role of PFPs and developing therapeutic approaches.

Single-molecule analysis of the entire perfringolysin O pore formation pathway

The cholesterol-dependent cytolysin perfringolysin O (PFO) is secreted by Clostridium perfringens as a bacterial virulence factor able to form giant ring-shaped pores that perforate and ultimately lyse mammalian cell membranes. To resolve the kinetics of all steps in the assembly pathway, we have used single-molecule fluorescence imaging to follow the dynamics of PFO on dye-loaded liposomes that lead to opening of a pore and release of the encapsulated dye. Formation of a long-lived membrane-bound PFO dimer nucleates the growth of an irreversible oligomer. The growing oligomer can insert into the membrane and open a pore at stoichiometries ranging from tetramers to full rings (~35 mers), whereby the rate of insertion increases linearly with the number of subunits. Oligomers that insert before the ring is complete continue to grow by monomer addition post insertion. Overall, our observations suggest that PFO membrane insertion is kinetically controlled.