The enhancing effects of hyperbaric oxygen on mouse skin carcinogenesis

From Low to No O2-Dependent Hypoxia Photodynamic Therapy (hPDT): A New Perspective

The advent of photochemical techniques has revolutionized the landscape of biology and medical sciences. Especially appealing in this context is photodynamic therapy (PDT), which is a photon-initiated treatment modality that uses cytotoxic reactive oxygen species (ROS) to kill malignant cells. In the past decade, PDT has risen to the forefront of cancer therapy. Its optical control enables noninvasive and spatiotemporal manipulation of the treatment process, and its photoactive nature allows unique patterns to avoid drug resistance to conventional chemotherapeutics. However, despite the impressive advances in this field, achieving widespread clinical adoption of PDT remains difficult. A major concern is that in the hostile tumor microenvironment, tumor cells are hypoxic, which hinders ROS generation during PDT action. To overcome this "Achilles' heel", current strategies focus primarily on the improvement of the intratumoral O₂ perfusion, while clinical trials suggest that O₂ enrichment may promote cancer cell proliferation and metastasis, thereby making FDA approval and clinical transformation of these paradigms challenging.In an effort to improve hypoxia photodynamic therapy (hPDT) in the clinic, we have explored "low to no O₂-dependent" photochemical approaches over the years to combat hypoxia-induced resistance. In this Account, we present our contributions to this theme during the past 5 years, beginning with low O₂-dependent approaches (e.g., type I superoxide radical (O₂^•-) generator, photodynamic O₂-economizer, mitochondrial respiration inhibition, cellular self-protective pathway modulation, etc.) and progressing to O₂-independent strategies (e.g., autoadaptive PDT/PTT complementary therapy, O₂-independent artificial photoredox catalysis in cells). These studies have attracted tremendous attention. Particularly in the pioneering work of 2018, we presented the first demonstration that the O₂^•--mediated partial O₂-recyclability mechanism can overcome PDT resistance ( J. Am. Chem. Soc. 2018, 140, 14851-14859). This launched an era of renewed interest in type I PDT, resulting in a plethora of new O₂^•- photogenerators developed by many groups around the world. Moreover, with the discovery of O₂-independent photoredox reactions in living cells, artificial photoredox catalysis has emerged as a new field connecting photochemistry and biomedicine, stimulating the development of next-generation phototherapeutic tools ( J. Am. Chem. Soc. 2022, 144, 163-173). Our recent work also disclosed that "photoredox catalysis in cells" might be a general mechanism of action of PDT ( Proc. Natl. Acad. Sci. U.S.A. 2022, 119, e2210504119). These emergent concepts, molecular designs, photochemical mechanisms, and applications in cancer diagnosis and therapeutics, as well as pros and cons, are discussed in depth in this Account. It is expected that our contributions to date will be of general use to researchers and inspire future efforts to identify more promising hPDT approaches that better meet the clinical needs of cancer therapy.

An oxygen-economical nano-photosensitizer with a high photodynamic therapeutic outcome via simultaneous reduction of the cellular respiration and oxygen depletion of PDT

The development of photodynamic nanomedicines that can alleviate intratumoral oxygen deficiency during photodynamic therapy (PDT) is of great significance for improving the therapeutic outcome of solid tumors characterized by severe hypoxia. Massive oxygen consumption due to vigorous cellular respiration, i.e., mitochondrial-associated oxidative phosphorylation (OXPHOS), is another major cause of severe tumor hypoxia in addition to insufficient oxygen supply. Moreover, oxygen depletion during PDT further exacerbates the shortage of intratumoral oxygen. In this work, we engineered a novel oxygen-economical nano-photosensitizer via co-encapsulation of an OXPHOS inhibitor (ATO) and a newly developed type-I photosensitizer (IPS) into a polymeric micelle of PEG-b-PCL. By controlling the length of hydrophobic PCL segments, we successfully optimized the micelle size to around 30 nm for enhanced tumor penetration. The orchestration of the two functional components, ATO and IPS, can simultaneously hinder the two major tumor oxygen-consuming pathways, where ATO targets mitochondrial complex III to inhibit cellular respiration, while IPS generates ROS through a low oxygen-consuming type-I photochemical pathway, enabling remarkable PDT efficacies in both hypoxic cells and a 4T1 tumor-bearing BALB/c mouse model. This work sheds new light on the construction of nano-photosensitizers to rejuvenate PDT against hypoxic solid tumors.

Integrative Role of Hyperbaric Oxygen Therapy on Healthspan, Age-Related Vascular Cognitive Impairment, and Dementia

Growing life expectancy will contribute to the on-going shift towards a world population increasingly comprised of elderly individuals. This demographic shift is associated with a rising prevalence of age-related diseases, among all age-related pathologies it has become crucial to understand the age-associated cognitive changes that remain a major risk factor for the development of vascular cognitive impairment and dementia (VCID). Furthermore, age-related Alzheimer's disease and other neurogenerative diseases with vascular etiology are the most prominent contributing factors for the loss of cognitive function observed in aging. Hyperbaric Oxygen Therapy (HBOT) achieves physiologic effects by increasing oxygen tension (PO2), raising oxygen tissue levels, decreasing intracranial pressure and relieving cerebral edema. Many of the beneficial effects of HBOT exert their protective effects at the level of the microcirculation. Furthermore, the microcirculation's exquisite pervasive presence across every tissue in the body, renders it uniquely able to influence the local environment of most tissues and organs, including the brain. As such, treatments aimed at restoring aging-induced functional and structural alterations of the cerebral microcirculation may potentially contribute to the amelioration of a range of age-related pathologies including vascular cognitive impairment, Alzheimer's disease, and vascular dementias. Despite the presented evidence, the efficacy and safety of HBOT for the treatment of age-related vascular cognitive impairment and dementia remains understudied. The present review aims to examine the existing evidence indicative of a potential therapeutic role for HBOT-induced hyperoxia against age-related cerebromicrovascular pathologies contributing to cognitive impairment, dementia and decreased healthspan in the elderly.

Role of hyperoxic treatment in cancer

IMPACT STATEMENT

Tumor hypoxia promotes cancer cell aggressiveness, and is strongly associated with poor prognosis across multiple tumor types. The hypoxic microenvironments inside tumors also limit the effectiveness of radiotherapy, chemotherapy, and immunotherapy. Several approaches to eliminate hypoxic state in tumors have been proposed to delay cancer progression and improve therapeutic efficacies. This review will summarize current knowledge on hyperoxia, used alone or in combination with other therapeutic modalities, in cancer treatment. Molecular mechanisms and undesired side effects of hyperoxia will also be discussed.

A TRPV1 antagonist, PAC-14028 does not increase the risk of tumorigenesis in chemically induced mouse skin carcinogenesis

PAC-14028 (Asivatrep: C₂₁H₂₂F₅N₃O₃S) cream is a novel, topical nonsteroidal, anti-inflammatory, and TRPV1 (transient receptor potential vanilloid subfamily, member 1) antagonist for the treatment of mild to moderate atopic dermatitis. Concerns about the risk of tumor development by TRPV1 blockade in the skin have been prompted, but these findings were proved to be indirect or are still controversial. This study was tested to determine whether TRPV1 selective antagonist, PAC-14028 cream is safe from the promotion of skin tumorigenesis in the two-stage carcinogenesis model. PAC-14028 cream, 0.25%, 0.5%, or 1.0% was applied once daily topically to mouse skin for up to 24 weeks in two-stage chemical carcinogenesis testing using 7, 12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). Morbidity/death, clinical signs, tumor formation, activity of EGFR/Akt/mTOR signaling, and systemic exposure to PAC-14028 were investigated. Daily dermal administration of PAC-14028, was not skin carcinogenic. There was also no evidence on the activation of EGFR/Akt/mTOR signaling pathway by the topical treatment of PAC-14028. On Day 169, 1.0% (20 mg/kg/day) of PAC-14028 in female mice resulted in a C_max and AUC_0-τ of 12916.0 ng/mL and 78962.9 ng‧hr/mL, respectively. PAC-14028 cream was well tolerated and did not increase the risk of skin tumorigenesis in two-stage carcinogenesis study.

O2 Economizer for Inhibiting Cell Respiration To Combat the Hypoxia Obstacle in Tumor Treatments

Hypoxia, a ubiquitously aberrant phenomenon implicated in tumor growth, causes severe tumor resistance to therapeutic interventions. Instead of the currently prevalent solution through intratumoral oxygen supply, we put forward an "O₂-economizer" concept by inhibiting the O₂ consumption of cell respiration to spare endogenous O₂ and overcome the hypoxia barrier. A nitric oxide (NO) donor responsible for respiration inhibition and a photosensitizer for photodynamic therapy (PDT) are co-loaded into poly(d,l-lactide- co-glycolide) nanovesicles to provide a PDT-specific O₂ economizer. Once accumulating in tumors and subsequently responding to the locally reductive environment, the carried NO donor undergoes breakdown to produce NO for inhibiting cellular respiration, allowing more O₂ in tumor cells to support the profound enhancement of PDT. Depending on the biochemical reallocation of cellular oxygen resource, this O₂-economizer concept offers a way to address the important issue of hypoxia-induced tumor resistance to therapeutic interventions, including but not limited to PDT.

Further application of hyperbaric oxygen in prostate cancer

Hyperbaric oxygen therapy (HBOT) has been used as an adjuvant treatment for multiple pathological states, which involves hypoxic conditions. Over the past 50 years, HBOT has been recommended and used in a wide variety of medical conditions, clinically in the treatment of ischemic or nonhealing wounds and radiation-injured tissue, and in the treatment of malignancy. The mechanism of this treatment is providing oxygen under pressure which is higher than the atmosphere thus increasing tissue oxygen concentration. When cells get enough oxygen in the microenvironment, they become active and replicate effectively. Prostate cancer is the second most common cancer and the fifth leading cause of cancer death among male around the world. It is estimated that more than 29,000 men died from metastatic prostate cancer in 2014. With the development of the prostate-specific antigen-based screening technology, prostate cancer incidence has increased markedly over time. According to the survey, the morbidity and mortality of prostate cancer have surpassed bladder cancer and renal carcinoma, becoming the most common cancer in urology in Chinese adults. Nowadays, the main solution to deal with prostate cancer is still the surgical ways, including laparoscopic radical prostatectomy and robot-assisted radical prostatectomy. Nevertheless, the complications of the surgical treatment have not been completely avoided. HBOT has gained great clinical recognition over the decade. It has been demonstrated that HBOT has considerable effects on carcinoma, especially on decreasing complications and improving mortality. So, it is important to combine the HBOT with patients who suffer from prostate cancer. This review illuminates the effect and underlying mechanism of the HBOT in prostate cancer for further clinical application.

Normobaric hyperoxia inhibits the progression of lung cancer by inducing apoptosis

Hypoxia is a critical characteristic of solid tumors with respect to cancer cell survival, angiogenesis, and metastasis. Hyperoxic treatment has been attempted to reverse hypoxia by enhancing the amount of dissolved oxygen in the plasma. In this study, we evaluated the effects of normobaric hyperoxia on the progression of lung cancer to determine whether oxygen toxicity can be used in cancer therapy. Following a tail vein injection of the Lewis lung carcinoma cells, C57BL/6J mice were exposed to a 24-h normobaric hyperoxia/normoxia cycle for two weeks. In addition, A549 lung cancer cells were incubated in a normobaric hyperoxia chamber for a 24-h period. As a result, the size and number of tumors in the lung decreased significantly with exposure to normobaric hyperoxia in the mouse model. Cell viability, colony-forming ability, migration, and invasion all decreased significantly in A549 cells exposed to normobaric hyperoxia and the normal control group exposed to normobaric hyperoxia showed no significant damage. Oxidative stress was more prominent with exposure to normobaric hyperoxia in cancer cells. A549 cells exposed to normobaric hyperoxia showed a significantly higher cell apoptosis ratio compared with A549 cells without normobaric hyperoxia exposure and normal human lung cells (BEAS-2B cells). The Bax/Bcl-2 mRNA expression ratio also increased significantly. Changes in the key regulators of apoptosis were similar between in vivo and in vitro conditions. The p-ERK level decreased, while the p-JNK level increased, after normobaric hyperoxia exposure in A549 cells. This study demonstrated the role of normobaric hyperoxia in inhibiting lung cancer. Normal tissue and cells showed no significant hyperoxic damage in our experimental setting. The anti-tumor effect of normobaric hyperoxia may due to the increased reactive oxygen species activity and apoptosis, which is related to the mitogen-activated protein kinase pathway. Impact statement Normobaric hyperoxia (NBO) is a feasible therapy for cancer with a low complication rate. Although NBO may be beneficial in cancer treatment, very few studies have been conducted; thus, the evidence is thin. This is the first study to clearly demonstrate morphological changes in lung cancer with NBO exposure and to investigate the underlying mechanisms both in vivo and in vitro. This study will arouse interest in NBO treatment and promote further research.

Hyperbaric oxygen as an adjunctive therapy in treatment of malignancies, including brain tumours

Hyperbaric oxygen (HBO) therapy is widely used as an adjunctive treatment for various pathological states, predominantly related to hypoxic and/or ischaemic conditions. It also holds promise as an approach to overcoming the problem of oxygen deficiency in the poorly oxygenated regions of the neoplastic tissue. Occurrence of local hypoxia within the central areas of solid tumours is one of the major issues contributing to ineffective medical treatment. However, in anti-cancer therapy, HBO alone gives a limited curative effect and is typically not applied by itself. More often, HBO is used as an adjuvant treatment along with other therapeutic modalities, such as radio- and chemotherapy. This review outlines the existing data regarding the medical use of HBO in cancer treatment, with a particular focus on the use of HBO in the treatment of brain tumours. We conclude that the administration of HBO can provide many clinical benefits in the treatment of tumours, including management of highly malignant gliomas. Applied immediately before irradiation, it is safe and well tolerated by patients, causing rare and limited side effects. The results obtained with a combination of HBO/radiotherapy protocol proved to be especially favourable compared to radiation treatment alone. HBO can also increase the cytostatic effect of certain drugs, which may render standard chemotherapy more effective. The currently available data support the legitimacy of conducting further research on the use of HBO in the treatment of malignancies.