Pyroptosis, a new paradigm of immunogenic cell death (ICD), is announced to trigger acute inflammatory responses that potently activate systemic antitumor immunity, offering new possibilities for enhancing tumor immunotherapy. Traditional pyroptosis inducers mainly consist of pathogen/damage-associated molecular patterns (DAMPs), chemotherapeutic drugs and lipopolysaccharide, which usually suffer from the low induction efficiency and long inducing cycle [[1], [2], [3], [4], [5]]. Photopyroptosis which is mainly induced by photodynamic therapy (PDT) and photothermal therapy (PTT), is characterized by the rapid and high-efficiency pyroptosis induction efficiency, coming into vogue recent years [[6], [7], [8], [9], [10], [11]]. The mechanisms of photopyroptosis involve a series of cascade reactions including reactive oxygen species (ROS) generation, mitochondrial membrane damage and activation of NOD-like receptor family pyrin domain containing 3 (NLRP3)/cysteinyl aspartate specific proteinases (caspases)/gasdermins (GSDMs) pathway [12]. The cleavage of GSDMs by the activated caspases releases N-terminal domains (GSDMs-N) to drill pores on cell membranes, resulting in cell swelling, membrane rupture and cellular content release, such as interleukin-1β (IL-1β), interleukin-18 (IL-18) and lactate dehydrogenase (LDH) [[13], [14], [15], [16], [17]]. These tumor-associated antigens (TAAs)-like cellular contents promote the maturation of dendritic cells (DCs) and recruitment of T lymphocytes (TLs) into the tumor microenvironment (TME), validly activating the systemic antitumor immune responses [18,19]. However, the rigorous immunosuppression caused by regulatory T cells (Tregs) severely limits the level and pattern of T-cell homing and activation, thus compromising the photopyroptosis-activated antitumor immunity [20,21]. Therefore, up regulation of TLs/Tregs ratio is crucial for enhancing tumor immunotherapy.

It is reported that serine/threonine protein phosphatase 2A (PP2A) not only negatively modulates the immune function of TLs but also up-regulates the forkhead box P3 (FOXP3) expression and Tregs differentiation from CD4+T lymphocyte clusters, signifying that PP2A is a pivotal immunoregulatory target [[22], [23], [24]]. Building on its targeted immunomodulatory effects on PP2A holoenzyme complexes, demethylcantharidin (DMC) is a promising combination therapeutic agent with photopyroptosis inducers [25,26]. Although several DMC/photopyroptosis inducer codelivery systems have been developed, sophisticated synthetic routes and premature leakage risk are involved [27,28]. Therefore, synergistically delivering two components remains a considerable challenge, especially given their distinct disparities in pharmacokinetics and hydrophilicity. Benefiting from the dynamic reversibility and stimuli-responsive characteristics, supramolecular self-assemblies driven by multifarious noncovalent interactions possess unparalleled edges in the delivery of a variety of therapeutics [[29], [30], [31], [32], [33], [34], [35], [36], [37]]. Owing to their customizable optical properties and superior biocompatibility, BF2-chelated azadipyrromethene (BODIPY) molecules have emerged as critical photopyroptosis inducers. The hydrophobic BODIPY scaffolds can be conjugated with hydrophilic units such as polyethylene glycol (PEG) segments, engineering amphiphilic supramolecular self-assembly systems. In order to meliorate the fast metabolic rate and multiple side effects, such as gastrointestinal reaction, irritation of urinary system and damage of liver and kidney function, DMC can be covalently introduced into supramolecular self-assemblies via the TME-activatable chemical linkages. Hence, the well-designed TME-responsive supramolecular self-assemblies are suitable for modulating the TLs/Tregs ratio to amplify immunotherapy.

Herein, we develop a supramolecular photopyroptosis nanoinducer with a acidity-activatable immunoregulation to enhance tumor immunotherapy (Scheme 1). The hydrophobic photopyroptosis inducer Alk-BODIPY is linked with two hydrophilic PEG chains via the CuI-catalyzed alkyne-azide cycloaddition (CuAAC) “click” reaction. Simultaneously, two hydrophilic DMC molecules are modified on the other end of PEG chains through the acid-liable carboxylic amide bond. Amphiphilic BDM self-assembles into supramolecular nanoparticles (SNPs) relying on the hydrophobic interactions, which are in possession of the strong tumor accumulation capacity due to the enhanced permeability and retention (EPR) effect. The PP2A inhibitory effect of DMC is closed during the blood circulation, but it can be opened on-demand upon the acidic TME-triggered amide bond cleavage, thus specifically suppressing Tregs differentiation. Under near-infrared (NIR) laser irradiation, Alk-BODIPY programmatically activates the caspase-3/GSDME-dependent pyroptotic pathway and exposes DAMPs, efficiently promoting the DCs maturation and TLs infiltration. This ingenious combination of photopyroptosis and PP2A inhibition, as a consequence, effectively increases the TLs/Tregs ratio in TME and comprehensively restrains tumor growth and metastasis in vivo.