Luminol Chemiluminescence Reports Photodynamic Therapy‐Generated Neutrophil Activity In Vivo and Serves as a Biomarker of Therapeutic Efficacy

Abstract

Inflammatory cells, most especially neutrophils, can be a necessary component of the anti-tumor activity occurring after administration of photodynamic therapy. Generation of neutrophil responses has been suggested to be particularly important in instances when the delivered PDT dose is insufficient. In these cases, the release of neutrophil granules and engagement of anti-tumor immunity may play an important role in eliminating residual disease. Herein, we utilize in vivo imaging of luminol chemiluminescence to non-invasively monitor neutrophil activation after PDT administration. Studies were performed in the AB12 murine model of mesothelioma, treated with Photofrin-PDT. Luminol-generated chemiluminescence increased transiently 1h after PDT, followed by a subsequent decrease at 4h after PDT. The production of luminol signal was not associated with the influx of Ly6G+ cells, but was related to oxidative burst, as an indicator of neutrophil function. Most importantly, greater levels of luminol chemiluminescence 1h after PDT was prognostic of a complete response at 90 days after PDT. Taken together, this research supports an important role for early activity by Ly6G+ cells in the generation of long-term PDT responses in mesothelioma, and it points to luminol chemiluminescence as a potentially useful approach for preclinical monitoring of neutrophil activation by PDT.

Photodynamic Therapy and Immune Checkpoint Blockade†

“…We have studied this in the murine mesothelioma line AE17 that has been transfected with soluble ovalbumin and human mesothelin (AE17ova, meso). Photofrin-PDT at 135 J cm À2 promotes a dramatic accumulation of Ly6G+ cells into tumors at 24 h, which is consistent with previous studies (28,29) (Fig. 3B).…”

“…produced by PDT-induced tissue damage recruit myeloid cells like neutrophils and functionally immunosuppressive neutrophil/monocyte populations (myeloid-derived suppressor cells; MDSCs). PDT has been shown to increase the population of intratumoral neutrophils to over 30% of the total viable cell population at 24 h after treatment (28,29), although this does depend on the PDT dose and other treatment-dependent variables (30). Neutrophils are then involved in the coordination of the subsequent immune response by secreting chemotactic signals that recruit immature dendritic cells (31) and can influence dendritic cell activation following degranulation through release of various alarmins (32) or by release of TNFa (33).…”

Preclinical and Clinical Evidence of Immune Responses Triggered in Oncologic Photodynamic Therapy: Clinical Recommendations

“…Moreover, serum levels of a immunosuppressive cytokine TGF-β were shown to decline at 4 h after PDT [63]. Together, these clinical data support the stimulatory effect of PDT on acute immune responses, which is consistent with the observations from preclinical studies [22][23][24]51,52]. However, these responses seem to maintain within a week, after which they tend to decline, and become non-detectable after one month [64][65][66], suggesting a transient inflammatory response following PDT.…”

“…Within 5 min, high numbers of neutrophils can already be seen at the treated tumor site [22], and this lasts until 24 h after PDT. More recently, a noninvasive manner has been developed to monitor neutrophil activation at the tumor site using in vivo imaging of luminol chemiluminescence [23]. Of note, pronounced neutrophilia in blood was also observed in mice treated with Photofrin-PDT, which is composed of an early wave of elevation in blood neutrophil levels during the initial hours (3-4 h), followed by an even more pronounced increase around 8-10 h after PDT [24][25][26].…”

Aspects of Photodynamic Inactivation of Bacteria

“…One of the well-studied and most effective chemical reactions involving light emission is oxidation of luminol [52,54,55]. Most applications of this reaction are associated with treatment of cancers [55][56][57]. Use of chemiluminescence as a light source for PACT has not been studied as extensively.…”