Translational feasibility and efficacy of nasal photodynamic disinfection of SARS-CoV-2

Abstract

The lack of therapeutic options to fight Covid-19 has contributed to the current global pandemic. Despite the emergence of effective vaccines, development of broad-spectrum antiviral treatment remains a significant challenge, in which antimicrobial photodynamic therapy (aPDT) may play a role, especially at early stages of infection. aPDT of the nares with methylene blue (MB) and non-thermal light has been successfully utilized to inactivate both bacterial and viral pathogens in the perioperative setting. Here, we investigated the effect of MB-aPDT to inactivate human betacoronavirus OC43 and SARS-CoV-2 in vitro and in a proof-of-principle COVID-19 clinical trial to test, in a variety of settings, the practicality, technical feasibility, and short-term efficacy of the method. aPDT yielded inactivation of up to 6-Logs in vitro, as measured by RT-qPCR and infectivity assay. From a photo-physics perspective, the in vitro results suggest that the response is not dependent on the virus itself, motivating potential use of aPDT for local destruction of SARS-CoV-2 and its variants. In the clinical trial we observed variable effects on viral RNA in nasal-swab samples as assessed by RT-qPCR attributed to aPDT-induced RNA fragmentation causing falsely-elevated counts. However, the viral infectivity in clinical nares swabs was reduced in 90% of samples and undetectable in 70% of samples. This is the first demonstration based on quantitative clinical viral infectivity measurements that MB-aPDT is a safe, easily delivered and effective front-line technique that can reduce local SARS-CoV-2 viral load.

Figure 1

aPDT response in HCoV-OC43 inoculum. (A) RT-PCR analysis, showing the reduction in viral RNA copies per μl of total extracted RNA as a function of MB photosensitizer concentration for different light doses (coloured lines). (B) Corresponding infectivity measurements expressed as median tissue culture infection dose (TCID₅₀). Data points are mean ± 1 standard deviation for n = 3–6 replicates. All aPDT protocols demonstrated significantly reduced viral RNA copies/μl and TCID compared to controls (light only, MB only, and no treatment groups, P < 0.05).

Figure 2

Effect of in vitro MB-aPDT treatment in SARS-CoV-2 patient-derived samples. (A) RT-qPCR analysis of 6 samples treated with MB-aPDT (10 min incubation at 10 μM and 30 J cm⁻²), together with control untreated and light-only or MB-only controls. *Samples with undetectable level of SARS-CoV-2. (B) Representative cytopathic effect (CPE) slides for aPDT-treated and control untreated samples #1 and #4. No viral load can be seen post-aPDT. In P0d4 and P1d4, P represents the cell passage number and d the day of analysis. Significant reductions were observed between the aPDT and control groups in both viral RNA copies/μl and infectivity (P < 0.05).

Figure 3

Flow diagram.

Figure 4

Effect of MB-aPDT on SARS-CoV-2 infectivity in clinical samples. (A) Change in viral RNA copies following nasal aPDT vs. pre-treatment load in the same nostril, as measured by RT-qPCR. Black circle 72 J cm⁻², blue square 36 J cm⁻². (B) Representative microscope images of inoculated Vero-76 cells. The cytopathic effect seen in the pre-treatment samples is not observed post-aPDT. (C) Individual clinical sample results, showing Cq values and viral RNA copy number per μL from RT-qPCR, together with the P0d4 and P1d4 infectivity results. The samples are labeled as in the Supplementary material that presents the complete data set.

Figure 5

Illustration of the photodisinfection procedure in the anterior nares. (A) Photosensitizer application, (B) illumination pointing towards the forehead, (C) light applicator repositioning emphasizing the anterior nostril, (D) illumination of the anterior nostrils. This illustration was designed by Ondine Medical Inc.