Nanophotonics 2021; 10(12): 3161–3168 Research Article Keegan Guidolin, Lili Ding, Juan Chen, Brian C. Wilson and Gang Zheng* Porphyrin-lipid nanovesicles (Porphysomes) are effective photosensitizers for photodynamic therapy https://doi.org/10.1515/nanoph-2021-0220 and complete tumor response rates (15 vs. 25%, p = 0.52). Received May 6, 2021; accepted June 9, 2021; Hence, porphysome nanoparticles are an effective PDT published online June 22, 2021 agent and have the additional advantages of multimodal diagnostic and therapeutic applications arising from their Abstract: Porphysomes (PS) are liposome-like nano- intrinsic structure. Porphysomes may also be the first particles comprising pyropheophorbide-conjugated single all-organic agent capable of concurrent PDT phospholipids that have demonstrated potential as and PTT. multimodal theranostic agents for applications that include phototherapies, targeted drug delivery and in vivo Keywords: cancer; nanomedicine; nanoparticles; photo- fluorescence, photoacoustic, magnetic resonance or dynamic therapy; photofrin; porphysome. positron emission imaging. Previous therapeutic appli- cations focused primarily on photothermal therapy (PTT) and suggested that PSs require target-triggered activation 1 Introduction for use as photodynamic therapy (PDT) sensitizers. Here, athymic nude mice bearing subcutaneous A549 human Porphysomes (PSs) are nanoparticles (∼100 nm) composed lung tumors were randomized into treatment and control of pyropheophorbide-conjugated phospholipid (pyro-lipid) groups: PS-PDT at various doses, PS-only and no treat- subunits that self-assemble into liposome-like structures, ment negative controls, as well as positive controls using each containing ∼80,000 porphyrin molecules [1]. They are the clinical photosensitizer Photofrin. Animals were fol- preferentially taken up and retained in solid tumors via the lowed for 30 days post-treatment. PS-PDT at all doses enhanced permeability and retention (EPR) effect and sub- demonstrated a significant tumor ablative effect, with the sequently taken up by cancer cells and disrupted into pyro- greatest effect seen with 10 mg/kg PS at a drug-light in- lipid subunits [1]. Previous studies have suggested that the terval of 24 h. By comparison, negative controls (PS-only, PSs can be exploited in both their structurally intact state Photofrin-only, and no treatment) showed uncontrolled (i.e., as nanoparticles) and in their disrupted state (i.e., as tumor growth. PDT with Photofrin at 5 mg/kg and PS at pyro-lipid subunits). In the former state, absorption of 10 mg/kg demonstrated similar tumor growth suppression light energy is dissipated through thermal conversion and no significant fluorescence emission or photochemistry occurs due to the tight packing of porphyrin molecules in the porphyrin-lipid bilayer, resulting in a quenching of *Corresponding author: Gang Zheng, Department of Surgery, >99% [1–7]. Upon disruption, the pyro-lipid subunits are University of Toronto, Toronto, ON, Canada; and Department of unquenched, enabling fluorescence and photochemical Medical Biophysics, University of Toronto, Toronto, ON, Canada, reactions [2, 4, 7, 8]. These previous studies suggest that the E-mail: [email protected] conversion of PSs from their intact to their disrupted state is Keegan Guidolin, Department of Surgery, University of Toronto, Toronto, ON, Canada; Princess Margaret Cancer Centre, Toronto, ON, time dependent, though the relative populations of intact Canada; and Institute of Biomedical Engineering, University of and disrupted PSs at any given time point are not well Toronto, Toronto, ON, Canada. https://orcid.org/0000-0001-6482- characterized. 8024 PSs in various formulations have been shown to be Lili Ding and Juan Chen, Princess Margaret Cancer Centre, Toronto, effective multimodality agents for theranostic applications, ON, Canada including in vivo photoacoustic imaging and photothermal Brian C. Wilson, Princess Margaret Cancer Centre, Toronto, ON, Canada; and Department of Medical Biophysics, University of therapy (PTT) in the intact state, fluorescence imaging after Toronto, Toronto, ON, Canada unquenching, and positron emission tomography via 64Cu Open Access. © 2021 Keegan Guidolin et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 International License. 3162 K. Guidolin et al.: Porphysomes are effective photosensitizers for PDT chelation or magnetic resonance imaging via Mn chelation 2 Materials and methods in either state [1–8]. Disrupted PSs have also been shown to produce reactive oxygen species upon irradiation at the 2.1 Cell culture and animal models main 671 nm pyro absorption wavelength, providing a rationale for their use as photodynamic sensitizers [8]. PSs A549 human lung cancer cells (American Type Culture Collection, conjugated to folate have been used to deliver target- Manassas, VA, USA) were cultured in F12K media supplemented with triggered PDT in different tumor models. Limited prior fetal bovine serum at a final concentration of 10% and prepared for studies of the untargeted PSs showed low PDT efficacy; injection in a 1 : 1 mixture of phosphate buffered saline and Matrigel Foxn1nu however, these studies were neither systematic nor opti- (Corning Inc., Corning, NY, USA). Female Hsd:athymic nude mice (Envigo, Indianapolis, IN, USA), aged 8–10 weeks, underwent mized [2, 8]. subcutaneous injection of 5 × 106 A549 cells in the right shoulder. Since the activation wavelength for both PS-PTT and Tumor growth was monitored and, upon reaching 5 mm in the PS-PDT is 671 nm, PS holds the potential to be the first single maximum dimension, the mice were randomized into various treatment agent, single wavelength, all-organic photosensitizer that and control groups. An a priori humane endpoint of 500 mm3 maximum can accomplish both PTT and PDT using a dual population tumor volume was set. All animal studies were conducted in compli- of intact PSs in the extracellular matrix and disrupted PSs in ance with institutional guidelines (University Health Network, Toronto, Canada). the intracellular space (Figure 1). It must first be established that untargeted PSs can accomplish PDT. Hence, the objectives of the present study were to test if PSs can be used 2.2 Photosensitizer and light administration as a practical PDT agent, to determine the optimum treat- ment conditions for this, and to compare PS-PDT to PDT Porphysomes were prepared according to previously published pro- tocols [1]. Photofrin (PHO) was generously provided by Pinnacle Bi- using Photofrin (PHO, Pinnacle Biologics, Bannockburn, IL, ologics (Bannockburn, IL). Following randomization, photosensitizer USA), a long-established, clinically-approved, porphyrin- was administered intravenously by bolus tail vein injection at an based PDT agent [9–12]. appropriate drug-light interval (DLI) before light irradiation. PS was Figure 1: Schematic diagram of the distribution and activity of porphysome nanoparticles and dissociated pyro-lipid in the tumor. When irradiated with 671 nm light, the intact porphysomes in the extracellular space respond photothermally (lower panel, right), while the 1 disrupted intracellular porphysomes (pyro-lipid) are unquenched and generate reactive oxygen species (ROS; e.g., O2) for photodynamic therapy (lower panel, left). K. Guidolin et al.: Porphysomes are effective photosensitizers for PDT 3163 administered in doses of 5, 7.5 or 10 mg (of pyropheophorbide-lipid) 2.5 Analysis per kg of animal body weight, and PHO was administered at 5 mg/kg of animal body weight; each was diluted with phosphate-buffered saline In each animal, the tumor volume post treatment was normalized to to a total volume of 250 μl per dose. Diode lasers at 671 and 630 nm the pre-treatment volume. Complete response was defined as the were used for PS and PHO activation, respectively (Figures S1 and S2). absence of detectable tumor upon dissection at the end of the 30-day Under general anesthesia (2–3% inhaled isoflurane) and with minimal follow-up period (i.e., cure). ANOVA was performed to assess for ambient lighting, the treatment light was delivered via an optical fiber differences in the relative tumor size between groups. Fisher’s exact as a 10 mm diameter circular spot centered on the tumor. The energy test was used to compare cure rates between groups. Log-rank density was measured prior to each treatment using a calibrated power (Mantel-Cox) tests were conducted for comparison of survival curves. meter (Thorlabs Inc., Newton, NJ, USA). A total light dose of 135 J/cm2 Statistical analysis was performed using GraphPad Prism software; was delivered at 100 mW/cm2 over 1350 s (22.5 min). Animals were p < 0.05 were considered significant. protected from scattered light using an opaque mask with a 10 mm diameter hole. 2.3 Study metrics 3 Results Following treatment, the mice were followed for 30 days and the tumor In the first experiment, the maximum increase in tumor size was measured using calipers 3 times per week. Photographs of surface temperature recorded at any time during treatment tumors were taken, and the animals were weighed on each occasion. (n = 3) was 1.8 °C. All PS-PDT treated tumors demonstrated fi Humane sacri ce by anesthetic overdose was carried out after 30 days at least partial response, with growth curves that were or if tumors reached 500 mm3 volume, whichever came first. Animals significantly different from the untreated groups: Figure 2. were considered to have reached a “mortality” endpoint if they required sacrifice because their tumor volume was >500 mm3. The strongest response was observed in the group treated with 10 mg/kg PS at 24 h DLI; followed by 7.5 mg/kg at 24 h, 5 mg/kg at 24 h and 10 mg/kg at 48 h. Tumor size was 2.4 Study aims the smallest at 10–15 d post treatment, at which time the distinction between the treatment groups was most 2 The first aim of this study was to confirm that irradiation at 100 mW/cm evident; tumor regrowth was evident thereafter. Figure 3 and the highest planned PS dose (10 mg/kg) and 24 h drug-light interval compares the tumor responses at each PS dose with follow- (DLI) did not produce significant thermal conversion.