Pan-caspase inhibition as a potential host-directed immunotherapy against MRSA and other bacterial skin infections

Abstract

Staphylococcus aureus causes most skin infections in humans, and the emergence of methicillin-resistant S. aureus (MRSA) strains is a serious public health threat. There is an urgent clinical need for nonantibiotic immunotherapies to treat MRSA infections and prevent the spread of antibiotic resistance. Here, we investigated the pan-caspase inhibitor quinoline–valine–aspartic acid–difluorophenoxymethyl ketone (Q-VD-OPH) for efficacy against MRSA skin infection in mice. A single systemic dose of Q-VD-OPH decreased skin lesion sizes and reduced bacterial burden compared with vehicle-treated or untreated mice. Although Q-VD-OPH inhibited inflammasome-dependent apoptosis-associated speck-like protein containing caspase activation and recruitment domain (ASC) speck formation and caspase-1–mediated interleukin-1β (IL-1β) production, Q-VD-OPH maintained efficacy in mice deficient in IL-1β, ASC, caspase-1, caspase-11, or gasdermin D. Thus, Q-VD-OPH efficacy was independent of inflammasome-mediated pyroptosis. Rather, Q-VD-OPH reduced apoptosis of monocytes and neutrophils. Moreover, Q-VD-OPH enhanced necroptosis of macrophages with concomitant increases in serum TNF and TNF-producing neutrophils, monocytes/macrophages, and neutrophils in the infected skin. Consistent with this, Q-VD-OPH lacked efficacy in mice deficient in TNF (with associated reduced neutrophil influx and necroptosis), in mice deficient in TNF/IL-1R and anti-TNF antibody-treated WT mice. In vitro studies revealed that combined caspase-3, caspase-8, and caspase-9 inhibition reduced apoptosis, and combined caspase-1, caspase-8, and caspase-11 inhibition increased TNF, suggesting a mechanism for Q-VD-OPH efficacy in vivo. Last, Q-VD-OPH also had a therapeutic effect against Streptococcus pyogenes and Pseudomonas aeruginosa skin infections in mice. Collectively, pan-caspase inhibition represents a potential host-directed immunotherapy against MRSA and other bacterial skin infections.

Dendritic cell immunoreceptor drives atopic dermatitis by modulating oxidized CaMKII-involved mast cell activation

“…To further characterize the cockroach allergen–induced skin inflammation, percentages of T cells, ILC2, and mast cells from biopsies of the lesional skins of CRE-treated or untreated mice were evaluated by using flow cytometry as previously described ( 48 ). The gating strategy for the flow cytometry analysis is provided in Supplemental Figure 1 , A and B (supplemental material available online with this article; https://doi.org/10.1172/jci.insight.152559DS1 ).…”

“…Flow cytometry was performed as previously described ( 48 ). Briefly, 10 mm skin punch biopsies were collected, minced, and enzymatically digested in 3 mL RPMI containing 100 μg/mL DNaseI (Sigma-Aldrich) and 1.67 Wunsch U/mL Liberase TL (Roche) for 1 hour at 37°C and shaken at 140 rpm.…”

Inflammasome activation by Gram-positive bacteria: Mechanisms of activation and regulation

“…Staphylococcus aureus is responsible for human infections such as pneumonia, endocarditis and sepsis with high morbidity/mortality and consequent increase in hospital costs ( 117 ). S. aureus can manipulate cell death by apoptosis, necrosis or pyroptosis to colonize and establish infection in different hosts ( 118 ). The inflammasome plays a crucial role in rising an effective immune response against S. aureus infection, controlling bacterial load and the magnitude of the adaptive immune response ( 7 ).…”

Gasdermin E: A Prospective Target for Therapy of Diseases

“…Due to the extensive interaction between caspases and gasdermins in the diseases, the inhibition of caspases activity by pan-caspase inhibitors has been used in experimental studies to significantly inhibit the gasdermin-mediated programmed cell death ( Zhang J. et al, 2020 ; Alphonse et al, 2021 ; Li J. et al, 2021 ). However, there is an urgent need for specific targeted drugs to enter our vision as the extent of the role of the gasdermin protein varies between diseases.…”