Photodynamic Priming Improves the Anti-Migratory Activity of Prostaglandin E Receptor 4 Antagonist in Cancer Cells In Vitro

Photodynamic priming modulates cellular ATP levels to overcome P-glycoprotein-mediated drug efflux in chemoresistant triple-negative breast cancer

P-glycoprotein (P-gp, ABCB1) is a well-researched ATP-binding cassette (ABC) drug efflux transporter linked to the development of cancer multidrug resistance (MDR). Despite extensive studies, approved therapies to safely inhibit P-gp in clinical settings are lacking, necessitating innovative strategies beyond conventional inhibitors or antibodies to reverse MDR. Photodynamic therapy is a globally approved cancer treatment that uses targeted, harmless red light to activate non-toxic photosensitizers, confining its cytotoxic photochemical effects to disease sites while sparing healthy tissues. This study demonstrates that photodynamic priming (PDP), a sub-cytotoxic photodynamic therapy process, can inhibit P-gp function by modulating cellular respiration and ATP levels in light accessible regions. Using chemoresistant (VBL-MDA-MB-231) and chemosensitive (MDA-MB-231) triple-negative breast cancer cell lines, we showed that PDP decreases mitochondrial membrane potential by 54.4% ± 30.4 and reduces mitochondrial ATP production rates by 94.9% ± 3.46. Flow cytometry studies showed PDP can effectively improve the retention of P-gp substrates (calcein) by up to 228.4% ± 156.3 in chemoresistant VBL-MDA-MB-231 cells, but not in chemosensitive MDA-MB-231 cells. Further analysis revealed that PDP did not alter the cell surface expression level of P-gp in VBL-MDA-MB-231 cells. These findings indicate that PDP can reduce cellular ATP below the levels that is required for the function of P-gp and improve intracellular substrate retention. We propose that PDP in combination with chemotherapy drugs, might improve the efficacy of chemotherapy and overcome cancer MDR.

Engineering photodynamics for treatment, priming and imaging

Photodynamic therapy (PDT) is a photochemistry-based treatment approach that relies on the activation of photosensitizers by light to locally generate reactive oxygen species that induce cellular cytotoxicity, in particular for the treatment of tumours. The cytotoxic effects of PDT are depth-limited owing to light penetration limits in tissue. However, photodynamic priming (PDP), which inherently occurs during PDT, can prime the tissue microenvironment to adjuvant therapies beyond the direct PDT ablative zone. In this Review, we discuss the underlying mechanisms of PDT and PDP, and their application to the treatment of cancer, outlining how PDP can permeabilize the tumour vasculature, overcome biological barriers, modulate multidrug resistance, enhance immune responses, increase tumour permeability and enable the photochemical release of drugs. We further examine the molecular engineering of photosensitizers to improve their pharmacodynamic and pharmacokinetic properties, increase their molecular specificity and allow image guidance of PDT, and investigate engineered cellular models for the design and optimization of PDT and PDP. Finally, we discuss alternative activation sources, including ultrasound, X-rays and self-illuminating compounds, and outline key barriers to the clinical translation of PDT and PDP.

Exploiting Unique Features of Microneedles to Modulate Immunity

Microneedle arrays (MNAs) are small patches containing hundreds of short projections that deliver signals directly to dermal layers without causing pain. These technologies are of special interest for immunotherapy and vaccine delivery because they directly target immune cells concentrated in the skin. The targeting abilities of MNAs result in efficient immune responses-often more protective or therapeutic-compared to conventional needle delivery. MNAs also offer logistical benefits, such as self-administration and transportation without refrigeration. Thus, numerous preclinical and clinical studies are exploring these technologies. Here the unique advantages of MNA, as well as critical challenges-such as manufacturing and sterility issues-the field faces to enable widespread deployment are discussed. How MNA design parameters can be exploited for controlled release of vaccines and immunotherapies, and the application to preclinical models of infection, cancer, autoimmunity, and allergies are explained. Specific strategies are also discussed to reduce off-target effects compared to conventional vaccine delivery routes, and novel chemical and manufacturing controls that enable cargo stability in MNAs across flexible intervals and temperatures. Clinical research using MNAs is then examined. Drawbacks of MNAs and the implications, and emerging opportunities to exploit MNAs for immune engineering and clinical use are concluded.

Transient fluid flow improves photoimmunoconjugate delivery and photoimmunotherapy efficacy

Circulating drugs in the peritoneal cavity is an effective strategy for advanced ovarian cancer treatment. Photoimmunotherapy, an emerging modality with potential for the treatment of ovarian cancer, involves near-infrared light activation of antibody-photosensitizer conjugates (photoimmunoconjugates) to generate cytotoxic reactive oxygen species. Here, a microfluidic cell culture model is used to study how fluid flow-induced shear stress affects photoimmunoconjugate delivery to ovarian cancer cells. Photoimmunoconjugates are composed of the antibody, cetuximab, conjugated to the photosensitizer, and benzoporphyrin derivative. Longitudinal tracking of photoimmunoconjugate treatment under flow conditions reveals enhancements in subcellular photosensitizer accumulation. Compared to static conditions, fluid flow-induced shear stress at 0.5 and 1 dyn/cm2 doubled the cellular delivery of photoimmunoconjugates. Fluid flow-mediated treatment with three different photosensitizer formulations (benzoporphyrin derivative, photoimmunoconjugates, and photoimmunoconjugate-coated liposomes) led to enhanced phototoxicity compared to static conditions. This study confirms the fundamental role of fluid flow-induced shear stress in the anti-cancer effects of photoimmunotherapy.

Critical PDT theory II: Current concepts and indications

While photodynamic therapy (PDT) is effective for the eradication of select neoplasia and certain other pathologic conditions, it has yet to achieve wide acceptance in clinical medicine. A variety of factors contribute to this situation including relations with the pharmaceutical industry that have often been problematic. Some current studies relating to photodynamic effects are 'phenomenological', i.e., they describe phenomena that only reiterate what is already known. The net result has been a tendency of granting agencies to become disillusioned with support for PDT research. This report is intended to provide some thoughts on current research efforts that improve clinical relevance and those that do not.

Critical PDT Theory III: Events at the Molecular and Cellular Level

Photodynamic therapy (PDT) is capable of eradicating neoplastic cells that are accessible to sufficient light and oxygen. There is adequate information now available for assessing conditions where PDT might be the therapy of choice, but limited access to clinical facilities and impediments to regulatory approval of new agents have limited clinical usage. Early reports mainly involved clinical data with few thoughts towards finding death pathways. In 2022, there is a clear understanding of the determinants of successful tumor eradication. While PDT may be the optimal method for many clinical indications, support for this approach has lagged. This report provides a commentary on some elements of recent progress in PDT at the molecular and cellular levels, along with a discussion of some of the limitations in current research efforts.