Tumor-activated in situ synthesis of single-atom catalysts for O2-independent photodynamic therapy based on water-splitting.

Single-atom catalysts (SACs) have attracted interest in photodynamic therapy (PDT), while they are normally limited by the side effects on normal tissues and the interference from the Tumor Microenvironment (TME). Here we show a TME-activated in situ synthesis of SACs for efficient tumor-specific water-based PDT. Upon reduction by upregulated GSH in TME, C3N4-Mn SACs are obtained in TME with Mn atomically coordinated into the cavity of C3N4 nanosheets. This in situ synthesis overcomes toxicity from random distribution and catalyst release in healthy tissues. Based on the Ligand-to-Metal charge transfer (LMCT) process, C3N4-Mn SACs exhibit enhanced absorption in the red-light region. Thereby, a water-splitting process is induced by C3N4-Mn SACs under 660 nm irradiation, which initiates the O2-independent generation of highly toxic hydroxyl radical (·OH) for cancer-specific PDT. Subsequently, the ·OH-initiated lipid peroxidation process is demonstrated to devote effective cancer cell death. The in situ synthesized SACs facilitate the precise cancer-specific conversion of inert H2O to reactive ·OH, which facilitates efficient cancer therapy in female mice. This strategy achieves efficient and precise cancer therapy, not only avoiding the side effects on normal tissues but also overcoming tumor hypoxia.

A multifunctional cascade enzyme system for enhanced starvation/chemodynamic combination therapy against hypoxic tumors.

Starvation therapy has shown promise as a cancer treatment, but its efficacy is often limited when used alone. In this work, a multifunctional nanoscale cascade enzyme system, named CaCO3@MnO2-NH2@GOx@PVP (CMGP), was fabricated for enhanced starvation/chemodynamic combination cancer therapy. CMGP is composed of CaCO3 nanoparticles wrapped in a MnO2 shell, with glucose oxidase (GOx) adsorbed and modified with polyvinylpyrrolidone (PVP). MnO2 decomposes H2O2 in cancer cells into O2, which enhances the efficiency of GOx-mediated starvation therapy. CaCO3 can be decomposed in the acidic cancer cell environment, causing Ca2+ overload in cancer cells and inhibiting mitochondrial metabolism. This synergizes with GOx to achieve more efficient starvation therapy. Additionally, the H2O2 and gluconic acid produced during glucose consumption by GOx are utilized by MnO2 with catalase-like activity to enhance O2 production and Mn2+ release. This process accelerates glucose consumption, reactive oxygen species (ROS) generation, and CaCO3 decomposition, promoting the Ca2+ release. CMGP can alleviate tumor hypoxia by cycling the enzymatic cascade reaction, which increases enzyme activity and combines with Ca2+ overload to achieve enhanced combined starvation/chemodynamic therapy. In vitro and in vivo studies demonstrate that CMGP has effective anticancer abilities and good biosafety. It represents a new strategy with great potential for combined cancer therapy.

Oxygen-enhanced MRI assessment of tumour hypoxia in head and neck cancer is feasible and well tolerated in the clinical setting.

BACKGROUND: Tumour hypoxia is a recognised cause of radiotherapy treatment resistance in head and neck squamous cell carcinoma (HNSCC). Current positron emission tomography-based hypoxia imaging techniques are not routinely available in many centres. We investigated if an alternative technique called oxygen-enhanced magnetic resonance imaging (OE-MRI) could be performed in HNSCC. METHODS: A volumetric OE-MRI protocol for dynamic T1 relaxation time mapping was implemented on 1.5-T clinical scanners. Participants were scanned breathing room air and during high-flow oxygen administration. Oxygen-induced changes in T1 times (ΔT1) and R2* rates (ΔR2*) were measured in malignant tissue and healthy organs. Unequal variance t-test was used. Patients were surveyed on their experience of the OE-MRI protocol. RESULTS: Fifteen patients with HNSCC (median age 59 years, range 38 to 76) and 10 non-HNSCC subjects (median age 46.5 years, range 32 to 62) were scanned; the OE-MRI acquisition took less than 10 min and was well tolerated. Fifteen histologically confirmed primary tumours and 41 malignant nodal masses were identified. Median (range) of ΔT1 times and hypoxic fraction estimates for primary tumours were -3.5% (-7.0 to -0.3%) and 30.7% (6.5 to 78.6%) respectively. Radiotherapy-responsive and radiotherapy-resistant primary tumours had mean estimated hypoxic fractions of 36.8% (95% confidence interval [CI] 17.4 to 56.2%) and 59.0% (95% CI 44.6 to 73.3%), respectively (p = 0.111). CONCLUSIONS: We present a well-tolerated implementation of dynamic, volumetric OE-MRI of the head and neck region allowing discernment of differing oxygen responses within biopsy-confirmed HNSCC. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04724096 . Registered on 26 January 2021. RELEVANCE STATEMENT: MRI of tumour hypoxia in head and neck cancer using routine clinical equipment is feasible and well tolerated and allows estimates of tumour hypoxic fractions in less than ten minutes. KEY POINTS: • Oxygen-enhanced MRI (OE-MRI) can estimate tumour hypoxic fractions in ten-minute scanning. • OE-MRI may be incorporable into routine clinical tumour imaging. • OE-MRI has the potential to predict outcomes after radiotherapy treatment.

Enhancing Photothermal/Photodynamic Therapy for Glioblastoma by Tumor Hypoxia Alleviation and Heat Shock Protein Inhibition Using IR820-Conjugated Reduced Graphene Oxide Quantum Dots.

We use low-molecular-weight branched polyethylenimine (PEI) to produce cytocompatible reduced graphene oxide quantum dots (rGOQD) as a photothermal agent and covalently bind it with the photosensitizer IR-820. The rGOQD/IR820 shows high photothermal conversion efficiency and produces reactive oxygen species (ROS) after irradiation with near-infrared (NIR) light for photothermal/photodynamic therapy (PTT/PDT). To improve suspension stability, rGOQD/IR820 was PEGylated by anchoring with the DSPE hydrophobic tails in DSPE-PEG-Mal, leaving the maleimide (Mal) end group for covalent binding with manganese dioxide/bovine serum albumin (MnO2/BSA) and targeting ligand cell-penetrating peptide (CPP) to synthesize rGOQD/IR820/MnO2/CPP. As MnO2 can react with intracellular hydrogen peroxide to produce oxygen for alleviating the hypoxia condition in the acidic tumor microenvironment, the efficacy of PDT could be enhanced by generating more cytotoxic ROS with NIR light. Furthermore, quercetin (Q) was loaded to rGOQD through π-π interaction, which can be released in the endosomes and act as an inhibitor of heat shock protein 70 (HSP70). This sensitizes tumor cells to thermal stress and increases the efficacy of mild-temperature PTT with NIR irradiation. By simultaneously incorporating the HSP70 inhibitor (Q) and the in situ hypoxia alleviating agent (MnO2), the rGOQD/IR820/MnO2/Q/CPP can overcome the limitation of PTT/PDT and enhance the efficacy of targeted phototherapy in vitro. From in vivo study with an orthotopic brain tumor model, rGOQD/IR820/MnO2/Q/CPP administered through tail vein injection can cross the blood-brain barrier and accumulate in the intracranial tumor, after which NIR laser light irradiation can shrink the tumor and prolong the survival times of animals by simultaneously enhancing the efficacy of PTT/PDT to treat glioblastoma.

Towards tumour hypoxia imaging: Incorporating relative oxygen extraction fraction mapping of prostate with multi-parametric quantitative MRI on a 1.5T MR-linac.

Hypoxia plays a central role in tumour radioresistance. Reliable tumour hypoxia imaging would allow the monitoring of tumour response and a more personalized adaptation of radiotherapy planning. Here, we showed a proof of concept of the feasibility and repeatability of relative oxygen extraction fraction (rOEF) mapping of prostate using multi-parametric quantitative MRI (qMRI) achieved for the first time on a 1.5T MR-linac. T2, T2* relaxation times maps, and intra-voxel incoherent motion (IVIM) parametric maps mapping were computed on a 29 years old healthy volunteer. R2' and rOEF maps were calculated based on a multi-parametric model. Long-term repeatability and repeatability coefficient (RC) were determined for each parameter according to QIBA recommendations. Mean values for the entire healthy prostate were 0.99 ± 0.14 × 10-3 mm/s2, 81 ± 2.1 × 10-3 mm/s2, 21.6 ± 3.6%, 92.7 ± 19.7 ms and 62.4 ± 17.3 ms for Dslow, Dfast, f, T2 and T2*, respectively. R2' and rOEF in the prostate were 6.1 ± 3.4 s-1 and 18.2 ± 10.1% respectively. The RC of rOEF was 4.43%. Long-term repeatability of quantitative parameters based on a test-retest ranged from 2 to 18%. qMRI parameters are measurable and repeatable on 1.5T MR LINAC. From T2, T2* and IVIM parameters maps, we were able to obtain a rOEF mapping of the prostate. These results are the first step to a non-invasive imaging of tumour hypoxia during radiotherapy leading to a biological image-guided adaptive radiotherapy.

Essential role of PLD2 in hypoxia-induced stemness and therapy resistance in ovarian tumors.

BACKGROUND: Hypoxia in solid tumors is an important source of chemoresistance that can determine poor patient prognosis. Such chemoresistance relies on the presence of cancer stem cells (CSCs), and hypoxia promotes their generation through transcriptional activation by HIF transcription factors. METHODS: We used ovarian cancer (OC) cell lines, xenograft models, OC patient samples, transcriptional databases, induced pluripotent stem cells (iPSCs) and Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq). RESULTS: Here, we show that hypoxia induces CSC formation and chemoresistance in ovarian cancer through transcriptional activation of the PLD2 gene. Mechanistically, HIF-1α activates PLD2 transcription through hypoxia response elements, and both hypoxia and PLD2 overexpression lead to increased accessibility around stemness genes, detected by ATAC-seq, at sites bound by AP-1 transcription factors. This in turn provokes a rewiring of stemness genes, including the overexpression of SOX2, SOX9 or NOTCH1. PLD2 overexpression also leads to decreased patient survival, enhanced tumor growth and CSC formation, and increased iPSCs reprograming, confirming its role in dedifferentiation to a stem-like phenotype. Importantly, hypoxia-induced stemness is dependent on PLD2 expression, demonstrating that PLD2 is a major determinant of de-differentiation of ovarian cancer cells to stem-like cells in hypoxic conditions. Finally, we demonstrate that high PLD2 expression increases chemoresistance to cisplatin and carboplatin treatments, both in vitro and in vivo, while its pharmacological inhibition restores sensitivity. CONCLUSIONS: Altogether, our work highlights the importance of the HIF-1α-PLD2 axis for CSC generation and chemoresistance in OC and proposes an alternative treatment for patients with high PLD2 expression.

Recent advances in hypoxia-activated compounds for cancer diagnosis and treatment.

Hypoxia, as a prevalent feature of solid tumors, is correlated with tumorigenesis, proliferation, and invasion, playing an important role in mediating the drug resistance and affecting the cancer treatment outcomes. Due to the distinct oxygen levels between tumor and normal tissues, hypoxia-targeted therapy has attracted significant attention. The hypoxia-activated compounds mainly depend on reducible organic groups including azo, nitro, N-oxides, quinones and azide as well as some redox-active metal complex that are selectively converted into active species by the increased reduction potential under tumor hypoxia. In this review, we briefly summarized our current understanding on hypoxia-activated compounds with a particular highlight on the recently developed prodrugs and fluorescent probes for tumor treatment and diagnosis. We have also discussed the challenges and perspectives of small molecule-based hypoxia-activatable prodrug for future development.

Radionuclide Reporter Imaging to Visualize Tumor Hypoxia Ex Vivo and In Vivo.

In vitro studies using cell culture, including three-dimensional cultures without the involvement of tumor vessels, have limitations in simulating complex intratumoral hypoxic conditions in live subjects. To generate experimental hypoxic conditions closer to those observed in humans in clinical settings, in vivo studies are necessary. In addition, visible light generated via bioluminescence and fluorescence is generally unsuitable for in vivo experiments because of low tissue penetration. Furthermore, near-infrared light (NIR), which has the highest tissue penetration among lights of different wavelengths, cannot be assessed precisely in vivo because of the difficulty in correcting tissue absorption and scatter. For in vivo quantitative analyses, imaging modalities that use high tissue-penetrating signals, such as computed tomography (CT) using X-rays, radionuclide imaging using γ-rays, and magnetic resonance imaging (MRI) using electromagnetic waves, are ideal.Therefore, as an advanced protocol for this research purpose, we provide ex vivo and in vivo methods to investigate the genetic response of multiple copies of hypoxia response elements (HREs) to tumor hypoxia in terms of intensity and intratumoral distribution using a human sodium/iodide symporter (hNIS) reporter gene and radionuclide reporter probes (radioiodine and its chemical analog Tc-99m) based on our previous research. This protocol includes cloning an hNIS reporter construct with multiple copies of HREs, establishing stable cell lines of the reporter construct, preparing a mouse subcutaneous xenograft model, and evaluating the genetic response of multiple HREs to tumor hypoxia using digital autoradiography (ARG) ex vivo and using single-photon emission computed tomography (SPECT) or positron emission tomography (PET) in vivo.

Cleanroom-Free Microfluidic Device for Natural Induction of Hypoxia in 2D and 3D Tumor Models.

Hypoxia is a common and critical feature of solid tumors that contributes to the plasticity and heterogeneity of the cancer cells. Cancer cell populations take on a region-specific adaptation induced by hypoxia, and each cancer cell population will show different levels of sensitivity and resistance to cancer therapeutics. Therefore, a faithful recapitulation of tumor hypoxia that allows for accurate assessments of hypoxia-induced adaptations, heterogeneity, and response to therapy is needed to develop new therapeutic approaches. The existing hypoxic tumor models rely on complex fabrication methods and external gas sources that make them unfavorable for the early-stage screening of new therapeutics. Here, we demonstrate how to establish a cleanroom-free microfluidic device that supports both 2D and 3D hypoxic tumor modeling through natural cancer cell metabolism and confirm the induction of the hypoxic gradient.

Concomitant [18F]F-FAZA and [18F]F-FDG Imaging of Gynecological Cancer Xenografts: Insight into Tumor Hypoxia.

BACKGROUND/AIM: Herein we assessed the feasibility of imaging protocols using both hypoxia-specific [18F]F-FAZA and [18F]F-FDG in bypassing the limitations derived from the non-specific findings of [18F]F-FDG PET imaging of tumor-related hypoxia. MATERIALS AND METHODS: CoCl2-generated hypoxia was induced in multidrug resistant (Pgp+) or sensitive (Pgp-) human ovarian (Pgp- A2780, Pgp+ A2780AD), and cervix carcinoma (Pgp- KB-3-1, Pgp+ KB-V-1) cell lines to establish corresponding tumor-bearing mouse models. Prior to [18F]F-FDG/[18F]F-FAZA-based MiniPET imaging, in vitro [18F]F-FDG uptake measurements and western blotting were used to verify the presence of hypoxia. RESULTS: Elevated GLUT-1, and hexokinase enzyme-II expression driven by CoCl2-induced activation of hypoxia-inducible factor-1α explains enhanced cellular [18F]F-FDG accumulation. No difference was observed in the [18F]F-FAZA accretion of Pgp+ and Pgp- tumors. Tumor-to-muscle ratios for [18F]F-FAZA measured at 110-120 min postinjection (6.2±0.1) provided the best contrasted images for the delineation of PET-oxic and PET-hypoxic intratumor regions. Although all tumors exhibited heterogenous uptake of both radiopharmaceuticals, greater differences for [18F]F-FAZA between the tracer avid and non-accumulating regions indicate its superiority over [18F]F-FDG. Spatial correlation between [18F]F-FGD and [18F]F-FAZA scans confirms that hypoxia mostly occurs in regions with highly active glucose metabolism. CONCLUSION: The addition of [18F]F-FAZA PET to [18F]F-FGD imaging may add clinical value in determining hypoxic sub-regions.

Preclinical multi-physiologic monitoring of immediate-early responses to diverse treatment strategies in breast cancer by optoacoustic imaging.

Optoacoustic imaging enables the measurement of tissue oxygen saturation (sO2) and blood perfusion while being utilized for detecting tumor microenvironments. Our aim was to employ multispectral optoacoustic tomography (MSOT) to assess immediate-early changes of hemoglobin level and sO2 within breast tumors during diverse treatments. Mouse breast cancer models were allocated into four groups: control, everolimus (EVE), paclitaxel (PTX), and photodynamic therapy (PDT). Hemoglobin was quantified daily, as well as sO2 and blood perfusion were verified by immunohistochemical (IHC) staining. MSOT showed a temporal window of enhanced oxygenation and improved perfusion in EVE and PTX groups, while sO2 consistently remained below baseline in PDT. The same results were obtained for the IHC. Therefore, MSOT can monitor tumor hypoxia and indirectly reflect blood perfusion in a non-invasive and non-labeled way, which has the potential to monitor breast cancer progression early and enable individualized treatment in clinical practice.

Current advances in modulating tumor hypoxia for enhanced therapeutic efficacy.

Hypoxia is a common feature of most solid tumors, which promotes the proliferation, invasion, metastasis, and therapeutic resistance of tumors. Researchers have been developing advanced strategies and nanoplatforms to modulate tumor hypoxia to enhance therapeutic effects. A timely review of this rapidly developing research topic is therefore highly desirable. For this purpose, this review first introduces the impact of hypoxia on tumor development and therapeutic resistance in detail. Current developments in the construction of various nanoplatforms to enhance tumor treatment in response to hypoxia are also systematically summarized, including hypoxia-overcoming, hypoxia-exploiting, and hypoxia-disregarding strategies. We provide a detailed discussion of the rationale and research progress of these strategies. Through a review of current trends, it is hoped that this comprehensive overview can provide new prospects for clinical application in tumor treatment. STATEMENT OF SIGNIFICANCE: As a common feature of most solid tumors, hypoxia significantly promotes tumor progression. Advanced nanoplatforms have been developed to modulate tumor hypoxia to enhanced therapeutic effects. In this review, we first introduce the impact of hypoxia on tumor progression. Current developments in the construction of various nanoplatforms to enhance tumor treatment in response to hypoxia are systematically summarized, including hypoxia-overcoming, hypoxia-exploiting, and hypoxia-disregarding strategies. We discuss the rationale and research progress of the above strategies in detail, and finally introduce future challenges for treatment of hypoxic tumors. By reviewing the current trends, this comprehensive overview can provide new prospects for clinical translatable tumor therapy.

A simulation study on the radiation-induced immune response of tumors after single fraction high-dose irradiation.

PURPOSE: We investigated radiation-induced antitumor immunity and its suppression by hypoxia-inducible factor (HIF-1α) for radiosurgery (SRS) using an improved cellular automata (CA) model. METHOD: A two-dimensional Cellular Automata (CA) model was employed to simulate the impact of radiation on cancer cell death and subsequent immune responses. Cancer cells died from direct cell death from radiation and indirect cell death due to radiation-induced vascular damage. The model also incorporated radiation-induced immunity and immuno-suppression. It was incorporated into the model assuming that the death of cancer cells generates effector cells, forming complexes with cancer cells, and high radiation doses lead to vascular damage, inducing tumor hypoxia and increasing HIF-1α expression. The model was validated and subjected to sensitivity analysis by evaluating tumor volume changes post-irradiation and exploring the effects and sensitivity of radiation-induced immune responses. RESULTS: The ratios of the tumor volume at 360 days post-irradiation and the SRS day (rTV) decreased with a higher PME, a higher Pcomp, and a lower ThHIF. The rTVs were 4.6 and 2.0 for PME = 0.1 and 0.9, 12.0 and 2.2 for Pcomp = 0.1 and 0.9, and 1.5 and 15.3 for ThHIF = 0.1 and 10.0, respectively. CONCLUSIONS: By modeling the activation and deactivation of the effectors, the improved CA model showed that the radiation-induced immunogenic cell death in the tumor caused a decrease in the post-irradiation volume by a factor of four for the therapeutic doses relative to non-immune reaction cases. Furthermore, the suppressive effects of HIF-1α induced by hypoxia decreased radiation-induced immune effects by more than 50.

Impact of formulation on solid oxygen-entrapping materials to overcome tumor hypoxia.

Tumor hypoxia, resulting from rapid tumor growth and aberrant vascular proliferation, exacerbates tumor aggressiveness and resistance to treatments like radiation and chemotherapy. To increase tumor oxygenation, we developed solid oxygen gas-entrapping materials (O2-GeMs), which were modeled after clinical brachytherapy implants, for direct tumor implantation. The objective of this study was to investigate the impact different formulations of solid O2-GeMs have on the entrapment and delivery of oxygen. Using a Parr reactor, we fabricated solid O2-GeMs using carbohydrate-based formulations used in the confectionary industry. In evaluating solid O2-GeMs manufactured from different sugars, the sucrose-containing formulation exhibited the highest oxygen concentration at 1 mg/g, as well as the fastest dissolution rate. The addition of a surface coating to the solid O2-GeMs, especially polycaprolactone, effectively prolonged the dissolution of the solid O2-GeMs. In vivo evaluation confirmed robust insertion and positioning of O2-GeMs in a malignant peripheral nerve sheath tumor, highlighting potential clinical applications.

Tumor hypoxia and role of hypoxia-inducible factor in oral cancer.

BACKGROUND: Head and neck cancer (HNC) is one of the most frequent malignancies in Asian males with a poor prognosis. Apart from well-known prognostic indicators, markers of tumor hypoxia can help us predict response to treatment and survival. METHODS: A review of the literature on the present evidence and potential clinical importance of tumor hypoxia in head and neck cancer was carried out. The data obtained from the literature search is presented as a narrative review. RESULTS: The literature shows possible associations between prognosis and low tumor oxygenation. Intermediate hypoxia biomarkers like HIF-1, GLUT-1, miRNA, and lactate, can help in predicting the response to therapy and survival as their altered expression is related to prognosis. CONCLUSIONS: Hypoxia is common in HNC and can be detected by use of biomarkers. The tumors that show expression of hypoxia biomarkers have poor prognosis except for patients with human papilloma virus-associated or VHL-associated cancers. Therapeutic targeting of hypoxia is emerging; however, it is still in its nascent stage, with increasing clinical trials hypoxia is set to emerge as an attractive therapeutic target in HNC.

Mitochondrial-Targeting Nanotrapper Captured Copper Ions to Alleviate Tumor Hypoxia for Amplified Photoimmunotherapy in Breast Cancer.

Hypoxia is a pervasive feature of solid tumors, which significantly limits the therapeutic effect of photodynamic therapy (PDT) and further influences the immunotherapy efficiency in breast cancer. However, the transient alleviation of tumor hypoxia fails to address the underlying issue of increased oxygen consumption, resulting from the rapid proliferation of tumor cells. At present, studies have found that the reduction of the oxygen consumption rate (OCR) by cytochrome C oxidase (COX) inhibition that induced oxidative phosphorylation (OXHPOS) suppression was able to solve the proposed problem. Herein, we developed a specific mitochondrial-targeting nanotrapper (I@MSN-Im-PEG), which exhibited good copper chelating ability to inhibit COX for reducing the OCR. The results proved that the nanotrapper significantly alleviated the hypoxic tumor microenvironment by copper chelation in mitochondria and enhanced the PDT effect in vitro and in vivo. Meanwhile, the nanotrapper improved photoimmunotherapy through both enhancing PDT-induced immunogenetic cell death (ICD) effects and reversing Treg-mediated immune suppression on 4T1 tumor-bearing mice. The mitochondrial-targeting nanotrapper provided a novel and efficacious strategy to enhance the PDT effect and amplify photoimmunotherapy in breast cancer.

Exploring chronic and transient tumor hypoxia for predicting the efficacy of hypoxia-activated pro-drugs.

Hypoxia, a low level of oxygen in the tissue, arises due to an imbalance between the vascular oxygen supply and oxygen demand by the surrounding cells. Typically, hypoxia is viewed as a negative marker of patients' survival, because of its implication in the development of aggressive tumors and tumor resistance. Several drugs that specifically target the hypoxic cells have been developed, providing an opportunity for exploiting hypoxia to improve cancer treatment. Here, we consider combinations of hypoxia-activated pro-drugs (HAPs) and two compounds that transiently increase intratumoral hypoxia: a vasodilator and a metabolic sensitizer. To effectively design treatment protocols with multiple compounds we used mathematical micro-pharmacology modeling and determined treatment schedules that take advantage of heterogeneous and dynamically changing oxygenation in tumor tissue. Our model was based on data from murine pancreatic cancers treated with evofosfamide (as a HAP) and either hydralazine (as a vasodilator), or pyruvate (as a metabolic sensitizer). Subsequently, this model was used to identify optimal schedules for different treatment combinations. Our simulations showed that schedules of HAPs with the vasodilator had a bimodal distribution, while HAPs with the sensitizer showed an elongated plateau. All schedules were more successful than HAP monotherapy. The three-compound combination had three local optima, depending on the HAPs clearance from the tissue interstitium, each two-fold more effective than baseline HAP treatment. Our study indicates that the three-compound therapy administered in the defined order will improve cancer response and that designing complex schedules could benefit from the use of mathematical modeling.

Synergistic cerium oxide nanozymes: targeting DNA damage and alleviating tumor hypoxia for improved NSCLC radiotherapy efficiency.

Radiotherapy (RT) is one of the important treatment modalities for non-small cell lung cancer (NSCLC). However, the maximum radiation dose that NSCLC patient can receive varies little. Therefore, the exploitation of novel RT sensitization approaches is a critical need for the clinical treatment. RT resistance in NSCLC is linked to tumor microenvironment (TME) hypoxia, cell cycle arrest and associated genetic alterations. Here, we designed a novel method for targeted delivery of quercetin (QT) and CeO2 to enhance RT sensitivity. We loaded QT into CeO2@ZIF-8-HA nanoparticles to prevent its degradation in the circulatory system and successfully delivered QT and CeO2 targeted to NSCLC tumors. Under the protection and targeted delivery of Zeolitic Imidazolate Framework-8 (ZIF-8), the nanocomplexes exhibited excellent catalytic mimetic activity in decomposing H2O2 into O2, thus significantly reversing the hypoxia of TME, while the radiosensitizer QT caused DNA damage directly after RT. In a subcutaneous tumor model, CeO2@ZIF-8-HA overcame radiation resistance and enhanced therapeutic efficacy. This multiple sensitization strategy combining delivery of QT and CeO2@ZIF-8-HA nanozymes opens a promising approach for RT of NSCLC.

Nitroimidazole derivatives potentiated against tumor hypoxia: Design, synthesis, antitumor activity, molecular docking study, and QSAR study.

A hypoxic environment occurs predominantly in tumors. During the growth phase of a tumor, it grows until it exceeds its blood supply, leaving regions of the tumor in which the oxygen pressure is dramatically low. They are virtually absent in normal tissues, thus creating perfect conditions for selective bioreductive therapy of tumors. To this aim, a novel series of cytotoxic radiosensitizer agents were synthesized by linking the nitroimidazole scaffold with oxadiazole or triazole rings. The majority of the compounds exhibited moderate to excellent antiproliferative activities toward HCT116 cell line under normoxic and hypoxic conditions. The structure-activity relationship study revealed that compounds containing the free thiol group either in the oxadiazoles 11a,b or the triazoles 21a,b-23a,b demonstrated the strongest antiproliferative activity, which proves that the free thiol group plays a crucial role in the antiproliferative activity of our compounds under both normoxic (half-maximal inhibitory concentration [IC50 ] = 12.50-24.39 µM) and hypoxic conditions (IC50 = 4.69-11.56 µM). Radiosensitizing assay of the four most active cytotoxic compounds 11b and 21-23b assured the capability of the compounds to enhance the sensitivity of the tumor cells to the DNA damaging activity of γ-radiation (IC50 = 2.23-5.18 µM). To further investigate if the cytotoxicity of our most active compounds was due to a specific signaling pathway, the online software SwissTargetPrediction was exploited and a molecular docking study was done that proposed cyclin-dependent kinase 2 (CDK2) enzyme to be the most promising target. The CDK2 inhibitory assay assured this assumption as five out of six compounds demonstrated a comparable inhibitory activity with roscovitine, among which compound 21b showed threefold more potent inhibitory activity in comparison with the reference compound. A further biological evaluation proved compound 21b to have an apoptotic activity and cell cycle arrest activity at the G1 and S phases. During the AutoQSAR analysis, the model demonstrated excellent regression between the predicted and experimental activity with r2 = 0.86. Subsequently, we used the model to predict the activity of the test set compounds that came with r2 = 0.95.

Tumor hypoxia and radiotherapy: A major driver of resistance even for novel radiotherapy modalities.

Hypoxia in solid tumors is an important predictor of poor clinical outcome to radiotherapy. Both physicochemical and biological processes contribute to a reduced sensitivity of hypoxic tumor cells to ionizing radiation and hypoxia-related treatment resistances. A conventional low-dose fractionated radiotherapy regimen exploits iterative reoxygenation in between the individual fractions, nevertheless tumor hypoxia still remains a major hurdle for successful treatment outcome. The technological advances achieved in image guidance and highly conformal dose delivery make it nowadays possible to prescribe larger doses to the tumor as part of single high-dose or hypofractionated radiotherapy, while keeping an acceptable level of normal tissue complication in the co-irradiated organs at risk. However, we insufficiently understand the impact of tumor hypoxia to single high-doses of RT and hypofractionated RT. So-called FLASH radiotherapy, which delivers ionizing radiation at ultrahigh dose rates (> 40 Gy/sec), has recently emerged as an important breakthrough in the radiotherapy field to reduce normal tissue toxicity compared to irradiation at conventional dose rates (few Gy/min). Not surprisingly, oxygen consumption and tumor hypoxia also seem to play an intriguing role for FLASH radiotherapy. Here we will discuss the role of tumor hypoxia for radiotherapy in general and in the context of novel radiotherapy treatment approaches.