Effects of metformin on tumor hypoxia and radiotherapy efficacy: a [18F]HX4 PET imaging study in colorectal cancer xenografts

Metformin Radiosensitizing Effect on Hypoxic Oral Squamous Cell Carcinoma Cells by GAPDH and TAGLN2

OBJECTIVE

Tumor hypoxia is associated with a poorer prognosis in cancer patients and can diminish the efficacy of radiation therapy (RT). This study investigates the potential of metformin to enhance radiosensitivity in hypoxic cancer cells.

METHODS

Preliminary experiments were conducted to validate the impact of hypoxia on radiation response. Reactive oxygen species (ROS) levels, cell migration, and cell death were assessed in hypoxic, radiated cells treated with metformin. Proteomic and ontological analyses were employed to identify molecular targets associated with the radiosensitizing effect of metformin. Proteomic and ontological findings were validated through patient samples and in vitro studies.

RESULTS

Metformin amplified cell death, induced DNA fragmentation, decreased cell migration, and elevated ROS levels in hypoxic, radiated cells. Proteomic analyses revealed that GAPDH and TAGLN2 were identified as pivotal targets linked to the radiosensitizing effect of metformin. Oral cancer patients exhibited elevated levels of TAGLN2 and reduced levels of GAPDH. Metformin downregulated TAGLN2 and upregulated GAPDH in hypoxic, radiated cells. Additionally, metformin reduced levels of mutated p53.

CONCLUSIONS

This study suggests that metformin can enhance radiosensitivity in hypoxic cells, operating through modulation of GAPDH and TAGLN2. Furthermore, metformin effectively reduces mutated p53 levels in radiated cells under hypoxic conditions.

Enhancing radiotherapy outcomes in rectal cancer: A systematic review of targeting hypoxia-induced radioresistance

Introduction

Neoadjuvant radiotherapy is successfully used in rectal cancer to improve overall survival. However, treatment response is both unpredictable and variable. There is strong evidence to show that the phenomenon of tumour hypoxia is associated with radioresistance, however the mechanism(s) behind this are poorly understood. Consequently, there have only been a small number of studies evaluating methods targeting hypoxia-induced radioresistance. The purpose of this systematic review is to evaluate the potential effectiveness of targeting hypoxia-induced radioresistance in rectal cancer and provide recommendations for future research in this area.

Methods

A comprehensive literature search was performed following the PRISMA guidelines. This study was registered on the Prospero database (CRD42023441983).

Results

Eight articles met the inclusion criteria. All studies identified were in vitro or in vivo studies, there were no clinical trials. Of the 8 studies identified, 5 assessed the efficacy of drugs which directly or indirectly targeted hypoxia and three that identified potential targets. There was conflicting in vivo evidence for the use of metformin to overcome hypoxia induced radioresistance. Vorinostat, atovaquone, and evofosfamide showed promising preclinical evidence that they can overcome hypoxia-induced radioresistance.

Discussion

The importance of investigating hypoxia-induced radioresistance in rectal cancer is crucial. However, to date, only a small number of preclinical studies exist evaluating this phenomenon. This systematic review highlights the importance of further research to fully understand the mechanism behind this radioresistance. There are promising targets identified in this systematic review however, substantially more pre-clinical and clinical research as a priority for future research is needed.

The role of autophagy in hypoxia-induced radioresistance

Radiotherapy is a widely used treatment modality against cancer, and although survival rates are increasing, radioresistant properties of tumours remain a significant barrier for curative treatment. Tumour hypoxia is one of the main contributors to radioresistance and is common in most solid tumours. Hypoxia is responsible for many molecular changes within the cell which helps tumours to survive under such challenging conditions. These hypoxia-induced molecular changes are predominantly coordinated by the hypoxia inducible factor (HIF) and have been linked with the ability to confer resistance to radiation-induced cell death. To overcome this obstacle research has been directed towards autophagy, a cellular process involved in self degradation and recycling of macromolecules, as HIF plays a large role in its coordination under hypoxic conditions. The role that autophagy has following radiotherapy treatment is conflicted with evidence of both cytoprotective and cytotoxic effects. This literature review aims to explore the intricate relationship between radiotherapy, hypoxia, and autophagy in the context of cancer treatment. It provides valuable insights into the potential of targeting autophagy as a therapeutic strategy to improve the response of hypoxic tumours to radiotherapy.

Murine Breast Cancer Radiosensitization Using Oxygen Microbubbles and Metformin: Vessels Are the Key

Radiotherapy is a cornerstone of cancer treatment, but tumor hypoxia and resistance to radiation remain significant challenges. Vascular normalization has emerged as a strategy to improve oxygenation and enhance therapeutic outcomes. In this study, we examine the radiosensitization potential of vascular normalization using metformin, a widely used anti-diabetic drug, and oxygen microbubbles (OMBs). We investigated the synergistic action of metformin and OMBs and the impact of this therapeutic combination on the vasculature, oxygenation, invasiveness, and radiosensitivity of murine 4T1 breast cancer. We employed in vivo Doppler ultrasonographic imaging for vasculature analysis, electron paramagnetic resonance oximetry, and immunohistochemical assessment of microvessels, perfusion, and invasiveness markers. Our findings demonstrate that both two-week metformin therapy and oxygen microbubble treatment normalize abnormal cancer vasculature. The combination of metformin and OMB yielded more pronounced and sustained effects than either treatment alone. The investigated therapy protocols led to nearly twice the radiosensitivity of 4T1 tumors; however, no significant differences in radiosensitivity were observed between the various treatment groups. Despite these improvements, resistance to treatment inevitably emerged, leading to the recurrence of hypoxia and an increased incidence of metastasis.

EPR Investigations to Study the Impact of Mito-Metformin on the Mitochondrial Function of Prostate Cancer Cells

Background: Mito-metformin10 (MM10), synthesized by attaching a triphenylphosphonium cationic moiety via a 10-carbon aliphatic side chain to metformin, is a mitochondria-targeted analog of metformin that was recently demonstrated to alter mitochondrial function and proliferation in pancreatic ductal adenocarcinoma. Here, we hypothesized that this compound may decrease the oxygen consumption rate (OCR) in prostate cancer cells, increase the level of mitochondrial ROS, alleviate tumor hypoxia, and radiosensitize tumors. Methods: OCR and mitochondrial superoxide production were assessed by EPR (9 GHz) in vitro in PC-3 and DU-145 prostate cancer cells. Reduced and oxidized glutathione were assessed before and after MM10 exposure. Tumor oxygenation was measured in vivo using 1 GHz EPR oximetry in PC-3 tumor model. Tumors were irradiated at the time of maximal reoxygenation. Results: 24-hours exposure to MM10 significantly decreased the OCR of PC-3 and DU-145 cancer cells. An increase in mitochondrial superoxide levels was observed in PC-3 but not in DU-145 cancer cells, an observation consistent with the differences observed in glutathione levels in both cancer cell lines. In vivo, the tumor oxygenation significantly increased in the PC-3 model (daily injection of 2 mg/kg MM10) 48 and 72 h after initiation of the treatment. Despite the significant effect on tumor hypoxia, MM10 combined to irradiation did not increase the tumor growth delay compared to the irradiation alone. Conclusions: MM10 altered the OCR in prostate cancer cells. The effect of MM10 on the superoxide level was dependent on the antioxidant capacity of cell line. In vivo, MM10 alleviated tumor hypoxia, yet without consequence in terms of response to irradiation.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

A novel 111indium-labeled dual carbonic anhydrase 9-targeted probe as a potential SPECT imaging radiotracer for detection of hypoxic colorectal cancer cells

Tumor hypoxia is a common feature in colorectal cancer (CRC), and is associated with resistance to radiotherapy and chemotherapy. Thus, a specifically targeted probe for the detection of hypoxic CRC cells is urgently needed. Carbonic anhydrase 9 (CA9) is considered to be a specific marker for hypoxic CRC diagnosis. Here, a nuclear imaging Indium-111 (¹¹¹In)-labeled dual CA9-targeted probe was synthesized and evaluated for CA9 detection in in vitro, in vivo, and in human samples. The CA9-targeted peptide (CA9tp) and CA9 inhibitor acetazolamide (AAZ) were combined to form a dual CA9-targeted probe (AAZ-CA9tp) using an automatic microwave peptide synthesizer, which then was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for radioisotope (¹¹¹In) labeling (¹¹¹In-DOTA-AAZ-CA9tp). The assays for cell binding, stability, and toxicity were conducted in hypoxic CRC HCT15 cells. The analyses for imaging and biodistribution were performed in an HCT15 xenograft mouse model. The binding and distribution of ¹¹¹In-DOTA-AAZ-CA9tp were detected in human CRC samples using microautoradiography. AAZ-CA9tp possessed good CA9-targeting ability in hypoxic HCT15 cells. The dual CA9-targeted radiotracer showed high serum stability, high surface binding, and high affinity in vitro. After exposure of ¹¹¹In-DOTA-AAZ-CA9tp to the HCT15-bearing xenograft mice, the levels of ¹¹¹In-DOTA-AAZ-CA9tp were markedly and specifically increased in the hypoxic tumor tissues compared to control mice. ¹¹¹In-DOTA-AAZ-CA9tp also targeted the areas of CA9 overexpression in human colorectal tumor tissue sections. The results of this study suggest that the novel ¹¹¹In-DOTA-AAZ-CA9tp nuclear imaging agent may be a useful tool for the detection of hypoxic CRC cells in clinical practice.

Metabolic Rewiring in Radiation Oncology Toward Improving the Therapeutic Ratio

To meet the anabolic demands of the proliferative potential of tumor cells, malignant cells tend to rewire their metabolic pathways. Although different types of malignant cells share this phenomenon, there is a large intracellular variability how these metabolic patterns are altered. Fortunately, differences in metabolic patterns between normal tissue and malignant cells can be exploited to increase the therapeutic ratio. Modulation of cellular metabolism to improve treatment outcome is an emerging field proposing a variety of promising strategies in primary tumor and metastatic lesion treatment. These strategies, capable of either sensitizing or protecting tissues, target either tumor or normal tissue and are often focused on modulating of tissue oxygenation, hypoxia-inducible factor (HIF) stabilization, glucose metabolism, mitochondrial function and the redox balance. Several compounds or therapies are still in under (pre-)clinical development, while others are already used in clinical practice. Here, we describe different strategies from bench to bedside to optimize the therapeutic ratio through modulation of the cellular metabolism. This review gives an overview of the current state on development and the mechanism of action of modulators affecting cellular metabolism with the aim to improve the radiotherapy response on tumors or to protect the normal tissue and therefore contribute to an improved therapeutic ratio.

Targeting Oxidative Phosphorylation to Increase the Efficacy of Radio- and Immune-Combination Therapy

As tumors grow, they upregulate glycolytic and oxidative metabolism to support their increased and altered energetic demands. These metabolic changes have major effects on the tumor microenvironment. One of the properties leading to this aberrant metabolism is hypoxia, which occurs when tumors outgrow their often-chaotic vasculature. This scarcity of oxygen is known to induce radioresistance but can also have a disrupting effect on the antitumor immune response. Hypoxia inhibits immune effector cell function, while immune cells with a more suppressing phenotype become more active. Therefore, hypoxia strongly affects the efficacy of both radiotherapy and immunotherapy, as well as this therapy combination. Inhibition of oxidative phosphorylation (OXPHOS) is gaining interest for its ability to combat tumor hypoxia, and there are strong indications that this results in a reactivation of the immune response. This strategy decreases oxygen consumption, leading to better oxygenation of hypoxic tumor areas and eventually an increase in immunogenic cell death induced by radio-immunotherapy combinations. Promising preclinical improvements in radio- and immunotherapy efficacy have been observed by the hypoxia-reducing effect of OXPHOS inhibitors and several compounds are currently in clinical trials for their anticancer properties. Here, we will review the pharmacologic attenuation of tumor hypoxia using OXPHOS inhibitors, with emphasis on their impact on the intrinsic antitumor immune response and how this affects the efficacy of (combined) radio- and immunotherapy.

Emerging strategies to target cancer metabolism and improve radiation therapy outcomes

Cancer-specific metabolic changes support the anabolic needs of the rapidly growing tumor, maintain a favorable redox balance, and help cells adapt to microenvironmental stresses like hypoxia and nutrient deprivation. Radiation is extensively applied in a large number of cancer treatment protocols but despite its curative potential, radiation resistance and treatment failures pose a serious problem. Metabolic control of DNA integrity and genomic stability can occur through multiple processes, encompassing cell cycle regulation, nucleotide synthesis, epigenetic regulation of gene activity, and antioxidant defenses. Given the important role of metabolic pathways in oxidative damage responses, it is necessary to assess the potential for tumor-specific radiosensitization by novel metabolism-targeted therapies. Additionally, there are opportunities to identify molecular and functional biomarkers of vulnerabilities to combination treatments, which could then inform clinical decisions. Here, we present a curated list of metabolic pathways in the context of ionizing radiation responses. Glutamine metabolism influences DNA damage responses by mechanisms such as synthesis of nucleotides for DNA repair or of glutathione for ROS detoxification. Repurposed oxygen consumption inhibitors have shown promising radiosensitizing activity against murine model tumors and are now in clinical trials. Production of 2-hydroxy glutarate by isocitrate dehydrogenase1/2 neomorphic oncogenic mutants interferes with the function of α-ketoglutarate-dependent enzymes and modulates Ataxia Telangiectasia Mutated (ATM) signaling and glutathione pools. Radiation-induced oxidative damage to membrane phospholipids promotes ferroptotic cell loss and cooperates with immunotherapies to improve tumor control. In summary, there are opportunities to enhance the efficacy of radiotherapy by exploiting cell-inherent vulnerabilities and dynamic microenvironmental components of the tumor.

Hypoxia PET Imaging with [18F]-HX4-A Promising Next-Generation Tracer

Hypoxia—a common feature of the majority of solid tumors—is a negative prognostic factor, as it is associated with invasion, metastasis and therapy resistance. To date, a variety of methods are available for the assessment of tumor hypoxia, including the use of positron emission tomography (PET). A plethora of hypoxia PET tracers, each with its own strengths and limitations, has been developed and successfully validated, thereby providing useful prognostic or predictive information. The current review focusses on [18F]-HX4, a promising next-generation hypoxia PET tracer. After a brief history of its development, we discuss and compare its characteristics with other hypoxia PET tracers and provide an update on its progression into the clinic. Lastly, we address the potential applications of assessing tumor hypoxia using [18F]-HX4, with a focus on improving patient-tailored therapies.