Changes in tumor hypoxia induced by mild temperature hyperthermia as assessed by dual-tracer immunohistochemistry

A review of recent advances in the use of complex metal nanostructures for biomedical applications from diagnosis to treatment

Complex metal nanostructures represent an exceptional category of materials characterized by distinct morphologies and physicochemical properties. Nanostructures with shape anisotropies, such as nanorods, nanostars, nanocages, and nanoprisms, are particularly appealing due to their tunable surface plasmon resonances, controllable surface chemistries, and effective targeting capabilities. These complex nanostructures can absorb light in the near-infrared, enabling noteworthy applications in nanomedicine, molecular imaging, and biology. The engineering of targeting abilities through surface modifications involving ligands, antibodies, peptides, and other agents potentiates their effects. Recent years have witnessed the development of innovative structures with diverse compositions, expanding their applications in biomedicine. These applications encompass targeted imaging, surface-enhanced Raman spectroscopy, near-infrared II imaging, catalytic therapy, photothermal therapy, and cancer treatment. This review seeks to provide the nanomedicine community with a thorough and informative overview of the evolving landscape of complex metal nanoparticle research, with a specific emphasis on their roles in imaging, cancer therapy, infectious diseases, and biofilm treatment. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Diagnostic Tools > Diagnostic Nanodevices.

Hypoxia signaling in cancer: Implications for therapeutic interventions

Hypoxia is a persistent physiological feature of many different solid tumors and a key driver of malignancy, and in recent years, it has been recognized as an important target for cancer therapy. Hypoxia occurs in the majority of solid tumors due to a poor vascular oxygen supply that is not sufficient to meet the needs of rapidly proliferating cancer cells. A hypoxic tumor microenvironment (TME) can reduce the effectiveness of other tumor therapies, such as radiotherapy, chemotherapy, and immunotherapy. In this review, we discuss the critical role of hypoxia in tumor development, including tumor metabolism, tumor immunity, and tumor angiogenesis. The treatment methods for hypoxic TME are summarized, including hypoxia-targeted therapy and improving oxygenation by alleviating tumor hypoxia itself. Hyperoxia therapy can be used to improve tissue oxygen partial pressure and relieve tumor hypoxia. We focus on the underlying mechanisms of hyperoxia and their impact on current cancer therapies and discuss the prospects of hyperoxia therapy in cancer treatment.

Copolymerized carbon nitride nanoparticles for near-infrared II photoacoustic-guided synergistic photothermal/radiotherapy

Nanotheranostic agents that integrate diagnosis and treatment are promising for precision medicine, but they encounter some obstacles such as penetration depth and efficiency. In this study, novel carbon nitride-rose bengal nanoparticles (CN-RB NPs) with a graphite carbon nitride skeleton were synthesized by one-step thermal copolymerization. The enhanced absorption in the near-infrared-II region (NIR-II) endows CN-RB NPs with an excellent photothermal effect under 1064 nm laser irradiation, as well as an obvious photoacoustic signal for imaging in vivo. Interestingly, due to the introduced iodine element, CN-RB NPs exhibit enhanced radiation therapy, indicating that CN-RB NPs can achieve ideal therapeutic outcome through collaborative photothermal/radiation therapy under the guidance of NIR-II photoacoustic imaging. Moreover, CN-RB NPs demonstrate minimal side effects and long-term biological stability after 14 days. Therefore, the proposed new multifunctional nano-platform CN-RB NPs hold great potential in the application of deep therapeutics.

Functional ultrasound-triggered phase-shift perfluorocarbon nanodroplets for cancer therapy

In recent years, because of their unique properties, the use of perfluorocarbon nanodroplets (PFC NDs) in ultrasound-mediated tumor theranostics has attracted increasing interest. PFC is one of the most stable organic compounds with high hydrophobicity. Phase-shift PFC NDs can be transformed into highly echogenic microbubbles for ultrasound and photoacoustic imaging by ultrasound and laser light. In addition, in the process of acoustic droplet vaporization, PFC NDs with cavitation nuclei can be combined with a variety of ultrasound technologies to produce cavitation effects for tumor ablation, antivascular therapy and release of therapeutic agents loaded in nanodroplets. Moreover, they can also be used to overcome tumor hypoxia by virtue of high oxygen solubility. In this review, first the preparation and stabilization of PFC NDs are summarized and then the issues and outlook are discussed. More importantly, multifunctional platforms based on PFC NDs for cancer diagnostics, therapy and theranostics are reviewed in detail.

Low-Temperature Photothermal Therapy: Strategies and Applications

Although photothermal therapy (PTT) with the assistance of nanotechnology has been considered as an indispensable strategy in the biomedical field, it still encounters some severe problems that need to be solved. Excessive heat can induce treated cells to develop thermal resistance, and thus, the efficacy of PTT may be dramatically decreased. In the meantime, the uncontrollable diffusion of heat can pose a threat to the surrounding healthy tissues. Recently, low-temperature PTT (also known as mild PTT or mild-temperature PTT) has demonstrated its remarkable capacity of conquering these obstacles and has shown excellent performance in bacterial elimination, wound healing, and cancer treatments. Herein, we summarize the recently proposed strategies for achieving low-temperature PTT based on nanomaterials and introduce the synthesis, characteristics, and applications of these nanoplatforms. Additionally, the combination of PTT and other therapeutic modalities for defeating cancers and the synergistic cancer therapeutic effect of the combined treatments are discussed. Finally, the current limitations and future directions are proposed for inspiring more researchers to make contributions to promoting low-temperature PTT toward more successful preclinical and clinical disease treatments.

Progress in the therapeutic applications of polymer-decorated black phosphorus and black phosphorus analog nanomaterials in biomedicine

Wonderful black phosphorus (BP) and some BP analogs (BPAs) have been increasingly studied for their biomedical applications owing to their fascinating properties and biodegradability, but opportunities and challenges have always coexisted in their study. Poor stability upon exposure to the natural environment is the major obstacle hampering their in vivo applications. BP/polymer and BPAs/polymer nanocomposites can not only efficiently prevent their oxidation and aggregation but also exhibit "biological activity" due to synergistic effects. In this review, we briefly describe the synthesis methods and stability strategies of BP/polymer and BPAs/polymer. Then, advances pertaining to their exciting therapeutic applications in various fields are systematically introduced, such as cancer therapy (phototherapy, drug delivery, and synergistic immunotherapy), bone regeneration, and neurogenesis. Some challenges for future clinical trials and possible directions for further study are finally discussed.

A Robust Oxygen Microbubble Radiosensitizer for Iodine-125 Brachytherapy

Iodine-125 (125I) brachytherapy, a promising form of radiotherapy, is increasingly applied in the clinical treatment of a wide range of solid tumors. However, the extremely hypoxic microenvironment in solid tumors can cause hypoxia-induced radioresistance to 125I brachytherapy, resulting in therapeutic inefficacy. In this study, the aim is to sensitize hypoxic areas in solid tumors using ultrasound-activated oxygen microbubbles for 125I brachytherapy. A modified emulsion freeze-drying method is developed to prepare microbubbles that can be lyophilized for storage and easily reconstituted in situ before administration. The filling gas of the microbubbles is modified by the addition of sulfur hexafluoride to oxygen such that the obtained O2/SF6 microbubbles (OS MBs) achieve a much longer half-life (>3×) than that of oxygen microbubbles. The OS MBs are tested in nasopharyngeal carcinoma (CNE2) tumor-bearing mice and oxygen delivery by the OS MBs induced by ultrasound irradiation relieve hypoxia instantly. The post-treatment results of brachytherapy combined with the ultrasound-triggered OS MBs show a greatly improved therapeutic efficacy compared with brachytherapy alone, illustrating ultrasound-mediated oxygen delivery with the developed OS MBs as a promising strategy to improve the therapeutic outcome of 125I brachytherapy in hypoxic tumors.

Dual-light triggered metabolizable nano-micelles for selective tumor-targeted photodynamic/hyperthermia therapy

Phototherapy, including photodynamic and photothermal therapies, is a non-invasive photo-triggered tumor treatment. Combination therapy and new synergistic therapeutic reagents may hold promise for improving these treatments. Herein, we report an amphiphilic iridium-based photosensitizer (C14-IP2000) loaded with a hydrophobic photo-thermal drug (ZnPc) to form nano-micelles (ZNPs) for dual-light triggered tumor phototherapy. The C14-IP2000 was contained within ZNPs consisting of an iridium complex core decorated with hydrophilic polyethylene glycol chains to extend the time in blood circulation, and two hydrophobic carbon chains to enhance the loading capacity and the hydrophobic interaction with the loaded reagent. The designed ZNPs showed effective blood circulation, passive tumor targeting ability, remarkable photodynamic conversion ability, and good photothermal conversion capability, and therefore may be used for combined tumor ablation. Our results demonstrated that the amphipathic bionic structure of ZNPs not only enables self-assembled reagent fabrication with prolonged circulation time and favorable metabolic characteristics for tumor combination therapy, but also provides a nanostructure strategy for the modification of functionalized reagents.

Preventive intraperitoneal hyperthermic perfusion chemotherapy for patients with T4 stage colon adenocarcinoma

BACKGROUND

Hyperthermic intraperitoneal chemotherapy (HIPEC) has been shown to be an effective treatment for peritoneal tumors; whether preventive HIPEC after radical resection for T4 stage colon adenocarcinoma could decrease peritoneal recurrence remains unknown. The aim of the present study was to compare peritoneal recurrence and short-term survival in patients with T4 stage colon adenocarcinoma undergoing HIPEC plus adjuvant chemotherapy or adjuvant chemotherapy alone following surgery.

METHODS

We retrospectively reviewed T4 stage colon adenocarcinoma patients who had radical tumor resection at our institution between January 2014 and January 2019. Clinical data were extracted from the database at our institution, and patient survival and long-term complications were assessed through repeated outpatient examinations and telephone interviews.

RESULTS

A total of 352 patients were included in this study; 157 patients received postoperative HIPEC plus adjuvant chemotherapy (HIPEC group), 195 patients received adjuvant chemotherapy alone (conventional chemotherapy group). Forty-one (26.1%) patients in the HIPEC group had a peritoneal recurrence and the peritoneum was the first site of tumor recurrence in 6 (14.6%) of them. However, 73 (37.4%) patients experienced peritoneal recurrence in the conventional group, and the peritoneum was the first site of tumor recurrence in 25 (34.2%) (p = 0.019). Disease-free survival in the HIPEC group at 1 and 3 years was 93.3% and 61.1%, respectively, versus 89.3% and 51.7% in the conventional chemotherapy group (p = 0.038). Overall survival in the HIPEC group at 1 and 3 years was 100.0% and 82.7%, respectively, versus 100.0% and 76.9% in the conventional chemotherapy group (p = 0.420). The two groups did not differ with respect to severe complications.

CONCLUSIONS

Preventive HIPEC after radical surgery may decrease peritoneal recurrence and promote disease-free survival for T4 stage colon adenocarcinoma. Large-scale randomized controlled studies are needed to confirm the results of our study.

Cancer Stem Cells and Combination Therapies to Eradicate Them

Cancer stem cells (CSCs) show self-renewal ability and multipotential differentiation, like normal stem or progenitor cells, and which proliferate uncontrollably and can escape the effects of drugs and phagocytosis by immune cells. Traditional monotherapies, such as surgical resection, radiotherapy and chemotherapy, cannot eradicate CSCs, however, combination therapy may be more effective at eliminating CSCs. The present review summarizes the characteristics of CSCs and several promising combination therapies to eradicate them.

Hyperthermic intraperitoneal chemotherapy in ovarian cancer: an update

In the treatment of advanced-stage epithelial ovarian cancer (EOC)-associated surgery and chemotherapy with intravenous platinum/taxane-based therapy most patients had early or late recurrence. Prevention of progression and recurrence is a major objective for the management of EOC. Recently, many clinical studies have evaluated the strategy with hyperthermic intraoperative intraperitoneal (IP) drug delivery. This is an update of hyperthermic intraoperative intraperitoneal chemotherapy (HIPEC) in EOC and a view for future strategies. Until recently studies on HIPEC in patients with EOC were mostly retrospective and heterogeneous. Thanks to recent clinical trials, it is reasonable to conclude that surgical cytoreduction and HIPEC is an interesting approach in the management of EOC without increasing morbidity.

Hollow Mesoporous Tantalum Oxide Based Nanospheres for Triple Sensitization of Radiotherapy

Radiotherapy (RT) is one of the most widely used cancer treatments in the clinical setting, while hypoxia-associated resistance often occurs. Herein, a PEGylated TaOx-based oxygen-carrying nanoplatform was constructed for triple sensitizing tumor radiotherapy. The high-Z element based hollow mesoporous TaOx nanospheres were prepared following the in situ growth of ultrasmall CuS nanocrystals and then packaged with O₂-saturated perfluoropentane (PFP). NIR laser-triggered mild hyperthermia would lead to the increase of intratumoral blood flow, together with the release of O₂, the radiotherapeutic efficiency would be enhanced. Alternatively, radiant energy would be deposited inside the tumor by the Ta element, therefore triple sensitization of radiotherapy could be achieved. The in vivo studies showed that the as-prepared nanospheres could achieve almost total inhibition of tumor growth without obvious side effects, which provides new possibilities for multisensitizing tumor radiotherapy.

Hyperthermia can alter tumor physiology and improve chemo- and radio-therapy efficacy

Hyperthermia has demonstrated clinical success in improving the efficacy of both chemo- and radio-therapy in solid tumors. Pre-clinical and clinical research studies have demonstrated that targeted hyperthermia can increase tumor blood flow and increase the perfused fraction of the tumor in a temperature and time dependent manner. Changes in tumor blood circulation can produce significant physiological changes including enhanced vascular permeability, increased oxygenation, decreased interstitial fluid pressure, and reestablishment of normal physiological pH conditions. These alterations in tumor physiology can positively impact both small molecule and nanomedicine chemotherapy accumulation and distribution within the tumor, as well as the fraction of the tumor susceptible to radiation therapy. Hyperthermia can trigger drug release from thermosensitive formulations and further improve the accumulation, distribution, and efficacy of chemotherapy.

Bimetallic nanodots for tri-modal CT/MRI/PA imaging and hypoxia-resistant thermoradiotherapy in the NIR-II biological windows

Hypoxic tumor microenvironment leads to resistance or failure of radiotherapy (RT). As a non-invasive therapy, photothermal therapy (PTT) can improve the tumor hypoxic microenvironment in addition to directly killing tumor cells. PTT combined with RT (thermoradiotherapy) becomes an emerging treatment. Multi-functional nanoparticles used for hypoxia-resistant thermoradiotherapy in the second near-infrared (NIR-II) biological windows (1000-1700 nm) are urgently needed to be developed. Here, a facil method synthesis of ultra-small cysteamine (Cys)-coated FePd bimetallic nanodots (NDs) is reported. These NDs can not only produce effective hyperthermia (35.4%) when irradiated in the NIR-II region (1064 nm) but also have an enhanced radiation effect due to i) Hypoxic improvement in tumor tissues by photothermal treatment in the NIR-II Biological Windows can greatly enhance the sensitivity of tumor cells to radiotherapy ii) The ability of NDs to deposit radiation energy in tumors has further enhanced the sensitivity of tumor cells to radiotherapy. Meanwhile, NDs was a contrast agent for tri-modal imaging including computed tomography (CT)/magnetic resonance imaging (MRI)/photoacoustic imaging (PAI) in vitro and in vivo. Both in vitro and in vivo tests demonstrated good biocompatibility and excellent stability of NDs, indicating great potential for clinical applications.

Hybrid Protein Nano-Reactors Enable Simultaneous Increments of Tumor Oxygenation and Iodine-131 Delivery for Enhanced Radionuclide Therapy

It is hard for current radionuclide therapy to render solid tumors desirable therapeutic efficacy owing to insufficient tumor-targeted delivery of radionuclides and severe tumor hypoxia. In this study, a biocompatible hybrid protein nanoreactor composed of human serum albumin (HSA) and catalase (CAT) molecules is constructed via glutaraldehyde-mediated crosslinking. The obtained HSA-CAT nanoreactors (NRs) show retained and well-protected enzyme stability in catalyzing the decomposition of H₂ O₂ and enable efficient labeling of therapeutic radionuclide iodine-131 (¹³¹ I). Then, it is uncovered that such HSA-CAT NRs after being intravenously injected into tumor-bearing mice exhibit efficient passive tumor accumulation as vividly visualized under the fluorescence imaging system and gamma camera. As the result, such HSA-CAT NRs upon tumor accumulation would significantly attenuate tumor hypoxia by decomposing endogenous H₂ O₂ produced by cancer cells to molecular oxygen, and thereby remarkably improve the therapeutic efficacy of radionuclide ¹³¹ I. This study highlights the concise preparation of biocompatible protein nanoreactors with efficient tumor homing and hypoxia attenuation capacities, thus enabling greatly improved tumor radionuclide therapy with promising potential for future clinical translation.

W-doped TiO2 nanoparticles with strong absorption in the NIR-II window for photoacoustic/CT dual-modal imaging and synergistic thermoradiotherapy of tumors

Multifunctional nanomaterials that have integrated diagnostic and therapeutic functions and low toxicity, and can enhance treatment efficacy through combination therapy have drawn tremendous amounts of attention. Herein, a newly developed multifunctional theranostic agent is reported, which is PEGylated W-doped TiO2 (WTO) nanoparticles (NPs) synthesized via a facile organic route, and the results demonstrated strong absorbance of these WTO NPs in the second near-infrared (NIR-II) window due to successful doping with W. These PEGylated WTO NPs can absorb both NIR-II laser and ionizing radiation, rendering them well suited for dual-modal computed tomography/NIR-II photoacoustic imaging and synergistic NIR-II photothermal/radiotherapy of tumors. In addition, the long-term in vivo studies indicated that these PEGylated WTO NPs had no obvious toxicity on mice in vivo, and they can be cleared after a 30-day period. In summary, this multifunctional theranostic agent can absorb both NIR-II laser and ionizing radiation with negligible toxicity and rapid clearance, therefore it has great promise for applications in imaging and therapeutics in biomedicine.

MSOT/CT/MR imaging-guided and hypoxia-maneuvered oxygen self-supply radiotherapy based on one-pot MnO2-mSiO2@Au nanoparticles

Radiotherapy (RT) is one of the most widely applied treatments for cancer therapy in clinics. Herein, we constructed innovative multifunctional nanotheranostic MnO2-mSiO2@Au-HA nanoparticles (MAHNPs) based on one-pot MnO2-mSiO2 nanohybrids (MNHs) and gold nanoparticles (AuNPs) for multispectral optoacoustic tomography (MSOT)/computed tomography (CT) and magnetic resonance (MR) imaging-guided hypoxia-maneuvered radiotherapy. The MNHs were prepared via a facile one-pot approach, which avoided the leakage of MnO2 nanoparticles and increased the synthetic efficiency. The Mn2+ ions triggered the breakdown of endogenous H2O2 to generate O2 to convert the hypoxic tumor micro-environment (TME), thus enhancing radiotherapy by self-supply oxygen. In addition, hyaluronic acid (HA) was employed to modify the surface of the MnO2-mSiO2@Au nanoparticles to improve their biocompatibility and cellular uptake. The well-designed nanoparticles could perform remarkable photothermal therapy (PTT) and hypoxia-maneuvered radiotherapy (RT) simultaneously and MSOT/CT/MR imaging. The in vivo studies showed that the MAHNPs achieved almost total suppression of tumor growth without observable recurrence, which raises new possibilities for clinical nanotheranostics with multimodal diagnostic and therapeutic coalescent design.

Oxygen Production of Modified Core-Shell CuO@ZrO2 Nanocomposites by Microwave Radiation to Alleviate Cancer Hypoxia for Enhanced Chemo-Microwave Thermal Therapy

There are acknowledged risks of metastasis of cancer cells and obstructing cancer treatment from hypoxia. In this work, we design a multifunctional nanocomposite for treating hypoxia based on the oxygen release capability of CuO triggered by microwave (MW). Core-shell CuO@ZrO₂ nanocomposites are prepared by confining CuO nanoparticles within the cavities of mesoporous ZrO₂ hollow nanospheres. 1-Butyl-3-methylimidazolium hexafluorophosphate (IL) is loaded to the CuO@ZrO₂ nanocomposites for improving microwave thermal therapy (MWTT). 1-Tetradecanol (PCM) is introduced to regulate the release of chemotherapeutic drugs of doxorubicin (DOX). Thus, the IL-DOX-PCM-CuO@ZrO₂ multifunctional (IDPC@Zr) nanocomposites are obtained. Finally, IDPC@Zr nanocomposites are modified by monomethoxy polyethylene glycol sulfhydryl (mPEG-SH, 5 kDa) (IDPC@Zr-PEG nanocomposites). IDPC@Zr-PEG nanocomposites can produce oxygen in the tumor microenvironment during the course of tumor treatment, thereby alleviating the hypoxic state and improving the therapeutic effect. In vivo antitumor experiments demonstrate a very high tumor inhibition rate of 92.14%. In addition, computed tomography (CT) imaging contrast of the nanocomposites can be enhanced due to the high atomic number of Zr. Therefore, IDPC@Zr-PEG nanocomposites can be applied for monitoring the tumor-treatment process in real time. This combined therapy offers many opportunities, such as the production of oxygen from CuO nanoparticles by MW to alleviate hypoxia, the enhancement of combined treatment of MWTT and chemotherapy, and the potential application of CT imaging to visualize the treatment process, which therefore provides a promising method for the clinical treatment of tumors in the future.

How to Modulate Tumor Hypoxia for Preclinical In Vivo Imaging Research

Tumor hypoxia is related with tumor aggressiveness, chemo- and radiotherapy resistance, and thus a poor clinical outcome. Therefore, over the past decades, every effort has been made to develop strategies to battle the negative prognostic influence of tumor hypoxia. For appropriate patient selection and follow-up, noninvasive imaging biomarkers such as positron emission tomography (PET) radiolabeled ligands are unprecedentedly needed. Importantly, before being able to implement these new therapies and potential biomarkers into the clinical setting, preclinical in vivo validation in adequate animal models is indispensable. In this review, we provide an overview of the different attempts that have been made to create differential hypoxic in vivo cancer models with a particular focus on their applicability in PET imaging studies.

Recent Advances in Functional-Polymer-Decorated Transition-Metal Nanomaterials for Bioimaging and Cancer Therapy

In this review, we focus on recent advances in the synthesis of polymer-functionalized transition-metal-based nanomaterials and follow this up by discussing their applications in bioimaging diagnosis and cancer therapy. Transition-metal-based nanomaterials show great potential in cancer therapy owing to their intensive near-IR absorption, excellent photothermal conversion efficiency, strong X-ray attenuation, and magnetic properties. Functional polymers are usually introduced by a one-step or multistep method to further endow these nanomaterials with great biocompatibility and physiological stability. Polymer-decorated transition-metal nanomaterials show great potential in multimodal imaging diagnosis (photoacoustic imaging, computed tomography, photoluminescence imaging, positron emission tomography, etc.) and cancer therapy (chemotherapy, photothermal therapy, microwave therapy, radiotherapy, photodynamic therapy). At the end of this review, the prospects of these polymer-decorated transition-metal-based nanomaterials are also discussed.

Heated Intraperitoneal Chemotherapy in the Management of Advanced Ovarian Cancer

Heated intraperitoneal chemotherapy (HIPEC) has several potential benefits. Higher doses of chemotherapy can be used with HIPEC because the plasma-peritoneal barrier results in little absorption into the blood stream. HIPEC offers higher peritoneal penetration in comparison to an intravenous (IV) regimen and does not have the traditional normothermic intraperitoneal (IP) regimen limitation of post-operative adhesions. Hyperthermia itself has cytotoxic effects and can potentiate antineoplastic effects of chemotherapy in part by increasing the depth of tumor penetration by up to 3 mm. For the treatment of ovarian cancer, HIPEC has been evaluated in the recurrent setting with secondary cytoreduction. Recent studies, including a prospective trial, have evaluated its role in primary management of ovarian cancer. This review summarizes previous and ongoing studies regarding the use of HIPEC in the management of ovarian cancer.

Prussian blue nanoparticles: Synthesis, surface modification, and application in cancer treatment

This review outlines recently developed Prussian blue nanoparticle (PB NPs)-based multimodal imaging-guided chemo-photothermal strategies for cancer diagnosis and treatment in order to provide insight into the future of the field. The primary limitation of existing therapeutics is the lack of selectivity in drug delivery: they target healthy and cancerous cells alike. In this paper, we provide a thorough review of diverse synthetic and surface engineering techniques for PB NP fabrication. We have elucidated the various targeting approaches employed to deliver the therapeutic and imaging ligands into the tumor area, and outlined methods for enhancement of the tumor ablative ability of the NPS, including several important combinatorial approaches. In addition, we have summarized different in vitro and in vivo effects of PB NP-based therapies used to overcome both systemic and tumor-associated local barriers. An important new approach - PB NP-based immune drug delivery, which is an exciting and promising strategy to overcome cancer resistance and tumor recurrence - has been discussed. Finally, we have discussed the current understanding of the toxicological effects of PB NPs and PB NP-based therapeutics. We conclude that PB NP-based multimodal imaging-guided chemo-photothermal therapy offers new treatment strategies to overcome current hurdles in cancer diagnosis and treatment.

Core-shell TaOx@MnO2 nanoparticles as a nano-radiosensitizer for effective cancer radiotherapy

Improving tumor oxygenation and concentrating X-ray radiation energy inside the tumor have received considerable attention in cancer radiotherapy. Herein, core-shell tantalum oxide@manganese dioxide (TaOx@MnO₂) nanostructures are prepared as an efficient radiosensitizer for enhancing radiotherapy (RT). In these nanostructures, the TaOx core serves as a RT sensitizer that efficiently concentrates X-ray radiation energy inside the tumor, while the MnO₂ shell may trigger the decomposition of endogenous H₂O₂ in the tumor microenvironment (TME) to generate oxygen and overcome hypoxia-associated radiation resistance. In vitro and in vivo experiments demonstrated that the synthesized TaOx@MnO₂-PEG nanostructures could accomplish an excellent synergistic radiotherapy sensitization effect. Furthermore, TaOx@MnO₂-PEG nanoparticles could also serve as promising agents for MR/CT dual-modal imaging. In brief, our study highlights a new type of multifunctional radiosensitizer agent to enhance radiotherapy treatment by means of simultaneously concentrating radiation energy inside tumors and overcoming tumor hypoxia, promising for applications in tumor radiotherapy.

Biodegradable Hollow Mesoporous Organosilica Nanotheranostics for Mild Hyperthermia-Induced Bubble-Enhanced Oxygen-Sensitized Radiotherapy

Alleviation of tumor hypoxia has been the premise for improving the effectiveness of radiotherapy, which hinges upon the advanced delivery and rapid release of oxygen within the tumor region. Herein, we propose a "bubble-enhanced oxygen diffusion" strategy to achieve whole tumor oxygenation for significant radiation enhancement based on the "bystander effect". Toward this end, sub-50 nm CuS-modified and ⁶⁴Cu-labeled hollow mesoporous organosilica nanoparticles were constructed for tumor-specific delivery of O₂-saturated perfluoropentane (PFP). Through the aid of PFP gasification arising from NIR laser-triggered mild hyperthermia, simultaneous PET/PA/US multimodality imaging and rapid oxygen diffusion across the tumor can be achieved for remarkable hypoxic radiosensitization. Furthermore, the multifunctional oxygen-carrying nanotheranostics also allow for other oxygen-dependent treatments, thus greatly advancing the development of bubble-enhanced synergistic therapy platforms.

Detection of Treatment Success after Photodynamic Therapy Using Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Early evaluation of response to therapy is crucial for selecting the optimal therapeutic follow-up strategy for cancer patients. PDT is a photochemistry-based treatment modality that induces tumor tissue damage by cytotoxic oxygen radicals, generated by a pre-injected photosensitive drug upon light irradiation of tumor tissue. Vascular shutdown is an important mechanism of tumor destruction for most PDT protocols. In this study, we assessed the suitability of Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) to evaluate treatment efficacy within a day after photodynamic therapy (PDT), using the tumor vascular response as a biomarker for treatment success. Methods: DCE-MRI at 7 T was used to measure the micro-vascular status of subcutaneous colon carcinoma tumors before, right after, and 24 h after PDT in mice. Maps of the area under the curve (AUC) of the contrast agent concentration were calculated from the DCE-MRI data. Besides, tracer kinetic parameters including K^trans were calculated using the standard Tofts-Kermode model. Viability of tumor tissue at 24 h after PDT was assessed by histological analysis. Results: PDT led to drastic decreases in AUC and K^trans or complete loss of enhancement immediately after treatment, indicating a vascular shutdown in treated tumor regions. Histological analysis demonstrated that the treatment induced extensive necrosis in the tumors. For PDT-treated tumors, the viable tumor fraction showed a strong correlation (ρ ≥ 0.85) with the tumor fraction with K^trans > 0.05 min^-1 right after PDT. The viable tumor fraction also correlated strongly with the enhanced fraction, the average K^trans , and the fraction with K^trans > 0.05 min^-1 at 24 h after PDT. Images of the viability stained tumor sections were registered to the DCE-MRI data, demonstrating a good spatial agreement between regions with K^trans > 0.05 min^-1 and viable tissue regions. Finally, 3D post-treatment viability detection maps were constructed for the tumors of three mice by applying a threshold (0.05 min^-1) to K^trans at 24 h after PDT. As a proof of principle, these maps were compared to actual tumor progression after one week. Complete tumor response was correctly assessed in one animal, while residual viable tumor tissue was detected in the other two at the locations where residual tumor tissue was observed after one week. Conclusion: This study demonstrates that DCE-MRI is an effective tool for early evaluation of PDT tumor treatment.

Effect of Electro-Acupuncture on Neuroplasticity of Spinal Cord-Transected Rats

BACKGROUND This study aimed to evaluate the effects of electro-acupuncture (EA) on neuroplasticity associated with the expressions of neurotrophic factors (NTFs) and their receptors in rats subjected to spinal cord transection (SCT). MATERIAL AND METHODS A total of 144 rats were randomly divided into 3 groups (n=48 per group): sham-operated group, SCT group, and EA (electro-acupuncture) group. Rats in SCT and EA groups received spinal cord transection at T10-T11 vertebral levels. Then, EA group rats received EA treatment. Reverse transcription polymerase chain reaction was used to detect NTFs and receptors at the mRNA level. In situ hybridization (ISH) and immunohistochemistry (IHC) were used to detect the expression of NTFs and their receptors. Basso, Beattie, Bresnahan (BBB) scores and cortical somato-sensory evoked potentials (CSEP) were evaluated to assess the recovery of motor and sensory functions. We also measured BDA (Biotinylated dextran amine) axonal tracing, CGRP (Calcitonin gene-related peptide), GAP-43 (Growth-associated protein), and synaptophysin immunohistochemistry (IHC). RESULTS EA treatment led to obvious improvement in hindlimb locomotor and sensory functions. CNTF, FGF-2, and TrkB mRNA were significantly upregulated, while NGF, PDGF, TGF-b1, IGF-1, TrkA, and TrkC mRNA were concomitantly downregulated in the caudal spinal segment (CSS) following EA. Immunohistochemistry demonstrated an increased number of CGRP fibers, GAP-43, and synaptophysin profiles in the CSS in the EA rats. CONCLUSIONS EA may promote the recovery of neuroplasticity in rats subjected to SCT. This could be attributed to the systematic regulation of NTFs and their receptors after EA.

Ultrasmall Semimetal Nanoparticles of Bismuth for Dual-Modal Computed Tomography/Photoacoustic Imaging and Synergistic Thermoradiotherapy

Multifunctional nanomaterials with integrated diagnostic and therapeutic functions, combination therapy to enhance treatment efficacy, as well as low toxicity have drawn tremendous attentions. Herein, we report a multifunctional theranostic agent based on peptide (LyP-1)-labeled ultrasmall semimetal nanoparticles of bismuth (Bi-LyP-1 NPs). Ultrasmall Bi NPs (3.6 nm) were facilely synthesized using oleylamine as the reducing agent and exhibited a higher tumor accumulation after being conjugated with the tumor-homing peptide LyP-1. The abilities to absorb both ionizing radiation and the second near-infrared (NIR-II) window laser radiation ensured that Bi-LyP-1 NPs are capable of dual-modal computed tomography/photoacoustic imaging and efficient synergistic NIR-II photothermal/radiotherapy of tumors. Moreover, Bi-LyP-1 NPs could be rapidly cleared from mice through both renal and fecal clearance and almost completely cleared after 30 days. Such multifunctional nanoparticles as efficient cancer theranostic agents, coupled with fast clearance and low toxicity, shed light on the future use of semimetal nanoparticles for biomedicine.

PB@Au Core-Satellite Multifunctional Nanotheranostics for Magnetic Resonance and Computed Tomography Imaging in Vivo and Synergetic Photothermal and Radiosensitive Therapy

To integrate multiple diagnostic and therapeutic strategies on a single particle through simple and effective methods is still challenging for nanotheranostics. Herein, we develop multifunctional nanotheranostic PB@Au core-satellite nanoparticles (CSNPs) based on Prussian blue nanoparticles (PBNPs) and gold nanoparticles (AuNPs), which are two kinds of intrinsic theranostic nanomaterials, for magnetic resonance (MR)-computed tomography (CT) imaging and synergistic photothermal and radiosensitive therapy (PTT-RT). PBNPs as cores enable T₁- and T₂-weighted MR contrast and strong photothermal effect, while AuNPs as satellites offer CT enhancement and radiosensitization. As revealed by both MR and CT imaging, CSNPs realized efficient tumor localization by passively targeted accumulation after intravenous injection. In vivo studies showed that CSNPs resulted in synergistic PTT-RT action to achieve almost entirely suppression of tumor growth without observable recurrence. Moreover, no obvious systemic toxicity of mice confirmed good biocompatibility of CSNPs. These results raise new possibilities for clinical nanotheranostics with multimodal diagnostic and therapeutic coalescent design.

It's Getting Hot in Here: Targeting Cancer Stem-like Cells with Hyperthermia

Cancer stem-like cells (CSCs) are a subset of cancer cells that are resistant to conventional radiotherapy and chemotherapy. As such, CSCs have been recognized as playing a large role in tumor initiation and recurrence. Although hyperthermia is broadly used in cancer treatment either alone or in combination with radio- or chemo-therapy, its potential to target CSCs is not well understood. In this review, we discuss different types of hyperthermia and potential mechanisms of action in cancer treatment, particularly in regards to killing CSCs.

TaOx decorated perfluorocarbon nanodroplets as oxygen reservoirs to overcome tumor hypoxia and enhance cancer radiotherapy

Cancer radiotherapy (RT) is a clinically used tumor treatment strategy applicable for a wide range of solid tumors. However, during RT treatment of tumors, only a small portion of applied ionizing irradiation energy is absorbed by the tumor, in which the largely hypoxic microenvironment also limits the anti-tumor efficacy of RT. In this work, we rationally fabricate polyethylene glycol (PEG) stabilized perfluorocarbon (PFC) nano-droplets decorated with TaOx nanoparticles (TaOx@PFC-PEG) as a multifunctional RT sensitizer. The obtained TaOx@PFC-PEG nanoparticles on one hand can absorb X-ray by TaOx to concentrate radiation energy within tumor cells, on the other hand after saturating PFC with oxygen will act as an oxygen reservoir to gradually release oxygen and improve tumor oxygenation. As the result, remarkably enhanced in vivo RT treatment is achieved with TaOx@PFC-PEG nanoparticles in our mouse tumor model experiments. Our work thus presents a new nanotechnology strategy to enhance RT-induced tumor treatment by simultaneously concentrating radiation energy within tumors and improving tumor oxygenation, using one multifunctional agent.

Catalase-Loaded TaOx Nanoshells as Bio-Nanoreactors Combining High-Z Element and Enzyme Delivery for Enhancing Radiotherapy

A novel type of bio-nanoreactor with catalase loaded inside TaOx hollow nanoshells is fabricated via a mild one-step method. Such bio-nanoreactors could efficiently improve the tumor oxygenation by supplying oxygen via decomposition of endogenic H2 O2 in a tumor microenvironment, and thus synergistically enhance the efficacy of cancer radiotherapy by both depositing radiation energy within the tumor and overcoming hypoxia-induced radiotherapy resistance.

Rhenium-188 Labeled Tungsten Disulfide Nanoflakes for Self-Sensitized, Near-Infrared Enhanced Radioisotope Therapy

Radioisotope therapy (RIT), in which radioactive agents are administered or implanted into the body to irradiate tumors from the inside, is a clinically adopted cancer treatment method but still needs improvement to enhance its performances. Herein, it is found that polyethylene glycol (PEG) modified tungsten disulfide (WS2 ) nanoflakes can be easily labeled by (188) Re, a widely used radioisotope for RIT, upon simple mixing. Like other high-Z elements acting as radiosensitizers, tungsten in the obtained (188) Re-WS2 -PEG would be able to absorb ionization radiation generated from (188) Re, enabling ''self-sensitization'' to enhance the efficacy of RIT as demonstrated in carefully designed in vitro experiments of this study. In the meanwhile, the strong NIR absorbance of WS2 -PEG could be utilized for NIR light-induced photothermal therapy (PTT), which if applied on tumors would be able to greatly relieve their hypoxia state and help to overcome hypoxia-associated radioresistance of tumors. Therefore, with (188) Re-WS2 -PEG as a multifunctional agent, which shows efficient passive tumor homing after intravenous injection, in vivo self-sensitized, NIR-enhanced RIT cancer treatment is realized, achieving excellent tumor killing efficacy in a mouse tumor model. This work presents a new concept of applying nanotechnology in RIT, by delivering radioisotopes into tumors, self-sensitizing the irradiation-induced cell damage, and modulating the tumor hypoxia state to further enhance the therapeutic outcomes.

Perfluorocarbon-Loaded Hollow Bi2Se3 Nanoparticles for Timely Supply of Oxygen under Near-Infrared Light to Enhance the Radiotherapy of Cancer

Hollow Bi2 Se3 nanoparticles prepared by a cation exchange method are loaded with perfluorocarbon as an oxygen carrier. With these nanoparticles, a promising concept is demonstrated to enhance radiotherapy by not only using their X-ray-absorbing ability to locally concentrate radiation energy in the tumor, but also employing near-infrared light to trigger burst release of oxygen from the nanoparticles to overcome hypoxia-associated radio-resistance.

Long-Term Survival for Platinum-Sensitive Recurrent Ovarian Cancer Patients Treated with Secondary Cytoreductive Surgery Plus Hyperthermic Intraperitoneal Chemotherapy (HIPEC)

BACKGROUND

To analyze the 5- and 7-year survival outcomes for women with platinum-sensitive recurrent epithelial ovarian cancer (REOC) who underwent secondary cytoreductive surgery (SCS) plus platinum-based hyperthermic intraperitoneal chemotherapy (HIPEC).

METHODS

From the electronic databases of the Department of Obstetrics and Gynecology at the Catholic University of the Sacred Heart of Rome and of the S. Orsola Hospital, University of Bologna, a consecutive series of REOC patients were selected using the following inclusion criteria: primary platinum-free interval (PFI-1) of 6 months or longer, completeness of secondary cytoreduction score (CC) of 1 or lower, minimum follow-up period of 48 months, Eastern Cooperative Group (ECOG) performance status at recurrence of 1 or less, and platinum-based HIPEC. Progression-free survival (PFS) and post-relapse survival (PRS) were calculated as the time between SCS + HIPEC and secondary recurrence or death, respectively.

RESULTS

The final study population included 70 women with platinum-sensitive REOC. The median follow-up time was 73 months (range 48-128 months), and the median PFI-1 was 19 months (range 6-100 months). At the time of recurrence, the median peritoneal cancer index was 7 (range 1-21), and a CC score of 0 was achieved for 62 patients (88.6 %). As the HIPEC drug, we used oxaliplatin in 17 cases (38.6 %) and cisplatin in 43 cases (61.4 %). No postoperative deaths were observed, and the complication rate for grades 3 and 4 disease was 8.6 %. The median PFS duration was 27 months (range 5-104 months), and the 5- and 7-year PRS rates were respectively 52.8 and 44.7 %, (median PRS 63 months).

CONCLUSIONS

The current study demonstrated favorable 5- and 7-year PRS rates for platinum-sensitive REOC patients undergoing SCS + HIPEC, which encourages the inclusion of patients in randomized clinical trials for definitive conclusions to be drawn.

Bottom-Up Synthesis of Metal-Ion-Doped WS₂ Nanoflakes for Cancer Theranostics

Recently, two-dimensional transition metal dichalcogenides (TMDCs) have received tremendous attention in many fields including biomedicine. Herein, we develop a general method to dope different types of metal ions into WS2 nanoflakes, a typical class of TMDCs, and choose Gd(3+)-doped WS2 (WS2:Gd(3+)) with polyethylene glycol (PEG) modification as a multifunctional agent for imaging-guided combination cancer treatment. While WS2 with strong near-infrared (NIR) absorbance and X-ray attenuation ability enables contrasts in photoacoustic (PA) imaging and computed tomography (CT), Gd(3+) doping offers the nanostructure a paramagnetic property for magnetic resonance (MR) imaging. As revealed by trimodal PA/CT/MR imaging, WS2:Gd(3+)-PEG nanoflakes showed efficient tumor homing after intravenous injection. In vivo cancer treatment study further uncovered that WS2:Gd(3+)-PEG could not only convert NIR light into heat for photothermal therapy (PTT) but also enhance the ionizing irradiation-induced tumor damage to boost radiation therapy (RT). Owing to the improved tumor oxygenation after the mild PTT, the combination of PTT and RT induced by WS2:Gd(3+)-PEG resulted in a remarkable synergistic effect to destroy cancer. Our work highlights the promise of utilizing inherent physical properties of TMDC-based nanostructures, whose functions could be further enriched by elementary doping, for applications in multimodal bioimaging and synergistic cancer therapy.

Core-Shell MnSe@Bi2 Se3 Fabricated via a Cation Exchange Method as Novel Nanotheranostics for Multimodal Imaging and Synergistic Thermoradiotherapy

MnSe@Bi2 Se3 core-shell nanostructures with highly integrated imaging and therapy functions are fabricated by a simple cation exchange method. Using those nanoparticles as a theranostic agent, a promise concept is further demonstrated to enhance conventional radiotherapy by: i) using X-ray absorbing agents to locally concentrate radiation energy and ii) employing near-infrared-light-triggered photothermal therapy to overcome hypoxia-associated radioresistance.

(18)F-fluoromisonidazole PET reveals spatial and temporal heterogeneity of hypoxia in mouse models of human non-small-cell lung cancer

AIM

To noninvasively observe dynamic changes in tumor hypoxia in mouse models of human non-small-cell lung cancer (NSCLC) using (18)F-fluoromisonidazole PET.

MATERIALS & METHODS

Nude mice with NSCLC H460 and A549 subcutaneous xenografts were coinjected intravenously with (18)F-fluoromisonidazole and the hypoxia marker pimonidazole, and observed by serial PET scans. After sacrifice, the tumor distribution of (18)F-fluoromisonidazole and pimonidazole was compared by digital autoradiography and microscopy, respectively.

RESULTS

The NSCLC hypoxic microenvironment was spatially heterogeneous. Serial PET scans over 48 h revealed an apparent change in the intratumoral distribution of (18)F-fluoromisonidazole.

CONCLUSION

The tumor hypoxic microenvironment is spatially and temporally heterogeneous, and hypoxic cancer cells have a shorter life span when growing in vivo. Therefore, the concept of hypoxic resistance and hypoxia-targeting therapy of macroscopic tumors should be revisited.

Hypoxia targeted bifunctional suicide gene expression enhances radiotherapy in vitro and in vivo

PURPOSE

To investigate whether hypoxia targeted bifunctional suicide gene expression-cytosine deaminase (CD) and uracil phosphoribosyltransferase (UPRT) with 5-FC treatments can enhance radiotherapy.

MATERIALS AND METHODS

Stable transfectants of R3327-AT cells were established which express a triple-fusion-gene: CD, UPRT and monomoric DsRed (mDsRed) controlled by a hypoxia inducible promoter. Hypoxia-induced expression/function of CDUPRTmDsRed was verified by western blot, flow cytometry, fluorescent microscopy, and cytotoxicity assay of 5-FU and 5-FC. Tumor-bearing mice were treated with 5-FC and local radiation. Tumor volume was monitored and compared with those treated with 5-FC or radiation alone. In addition, the CDUPRTmDsRed distribution in hypoxic regions of tumor sections was visualized with fluorescent microscopy.

RESULTS

Hypoxic induction of CDUPRTmDsRed protein correlated with increased sensitivity to 5-FC and 5-FU. Significant radiosensitization effects were detected after 5-FC treatments under hypoxic conditions. In the tumor xenografts, the distribution of CDUPRTmDsRed expression visualized with fluorescence microscopy was co-localized with the hypoxia marker pimonidazole positive staining cells. Furthermore, administration of 5-FC to mice in combination with local irradiation resulted in significant tumor regression, as in comparison with 5-FC or radiation treatments alone.

CONCLUSIONS

Our data suggest that the hypoxia-inducible CDUPRT/5-FC gene therapy strategy has the ability to specifically target hypoxic cancer cells and significantly improve the tumor control in combination with radiotherapy.

Hyperthermically induced changes in high spectral and spatial resolution MR images of tumor tissue--a pilot study

This pilot study investigated the feasibility of using MRI based on BOLD (blood-oxygen-level-dependent) contrast to detect physiological effects of locally induced hyperthermia in a rodent tumor model. Nude mice bearing AT6.1 rodent prostate tumors inoculated in the hind leg were imaged using a 9.4 T scanner using a multi-gradient echo pulse sequence to acquire high spectral and spatial resolution (HiSS) data. Temperature increases of approximately 6 °C were produced in tumor tissue using fiber-optic-guided light from a 250 W halogen lamp. HiSS data were acquired over three slices through the tumor and leg both prior to and during heating. Water spectra were produced from these datasets for each voxel at each time point. Time-dependent changes in water resonance peak width were measured during 15 min of localized tumor heating. The results demonstrated that hyperthermia produced both significant increases and decreases in water resonance peak width. Average decreases in peak width were significantly larger in the tumor rim than in normal muscle (p = 0.04). The effect of hyperthermia in tumor was spatially heterogeneous, i.e. the standard deviation of the change in peak width was significantly larger in the tumor rim than in normal muscle (p = 0.005). Therefore, mild hyperthermia produces spatially heterogeneous changes in water peak width in both tumor and muscle. This may reflect heterogeneous effects of hyperthermia on local oxygenation. The peak width changes in tumor and muscle were significantly different, perhaps due to abnormal tumor vasculature and metabolism. Response to hyperthermia measured by MRI may be useful for identifying and/or characterizing suspicious lesions as well as guiding the development of new hyperthermia protocols.

Expression of hypoxia-inducible factor 1α predicts clinical outcome after preoperative hyperthermo-chemoradiotherapy for locally advanced rectal cancer

Hypoxia-inducible factor 1α (HIF-1α) is an intrinsic marker of tumor hypoxia. It has been considered that hypoxic conditions reduce radiosensitivity, but the role of HIF-1α in patients treated with preoperative therapy for rectal cancer is still unclear. The aim of this study was to evaluate the predictive value of tumor response to preoperative hyperthermo-chemoradiotherapy (HCRT) and the prognostic significance of HIF-1α expression in patients with locally advanced rectal cancer. Between 2003 and 2006, 50 patients with histologically proven rectal adenocarcinoma who underwent HCRT followed by surgery were investigated. HIF-1α expression was immunohistochemically evaluated using pre-treatment biopsies. The total radiation dose was 40-50 Gy and chemotherapy consisted of 5-FU and LV administered by continuous infusion on Day 1-5, Day 15-19, and Day 29-33 during radiotherapy. Hyperthermia treatment was performed for once a week for 2-5 sessions. The surgical operation was performed 8 weeks after HCRT and each resected specimen was graded by histological criteria of the Japanese Classification of Colorectal Carcinoma. The effects of HIF-1α on clinical outcomes were analyzed by univariate and multivariate analysis. Positive HIF-1α expression was recognized in 42.0% of samples (21/50). Resected specimens that showed pathological grades 1, 2, and 3 numbered 17, 24, and 9 cases, respectively. There were no significant differences between the HIF-1α-positive group and HIF-1α-negative group for pathological grading and pCR. Overall survival (OS) rate at 3 years in the HIF-1α-negative group was 85.2%, which was significantly better than the 60.6% in the HIF-1α-positive group. Recurrence-free survival (RFS) rate at 3 years in the HIF-1α-negative group was 82.8%, being significantly better than 47.6% in the HIF-1α-positive group. In addition, elevated HIF-1α expression was significantly correlated with recurrence-free survival and metastasis-free survival rate in multivariate analysis. HIF-1α expression might be predictive of recurrence-free survival and metastasis-free survival rate for rectal cancer patients treated with HCRT.

Pathophysiological and vascular characteristics of tumours and their importance for hyperthermia: heterogeneity is the key issue

Tumour blood flow before and during clinically relevant mild hyperthermia exhibits pronounced heterogeneity. Flow changes upon heating are not predictable and are both spatially and temporally highly variable. Flow increases may result in improved heat dissipation to the extent that therapeutically relevant tissue temperatures may not be achieved. This holds especially true for tumours or tumour regions in which flow rates are substantially higher than in the surrounding normal tissues. Changes in tumour oxygenation tend to reflect alterations in blood flow upon hyperthermia. An initial improvement in the oxygenation status, followed by a return to baseline levels (or even a drop to below baseline at high thermal doses) has been reported for some tumours, whereas a predictable and universal occurrence of sustained increases in O(2) tensions upon mild hyperthermia is questionable and still needs to be verified in the clinical setting. Clarification of the pathogenetic mechanisms behind possible sustained increases is mandatory. High-dose hyperthermia leads to a decrease in the extracellular and intracellular pH and a deterioration of the energy status, both of which are known to be parameters capable of acting as direct sensitisers and thus pivotal factors in hyperthermia treatment. The role of the tumour microcirculatory function, hypoxia, acidosis and energy status is complex and is further complicated by a pronounced heterogeneity. These latter aspects require additional critical evaluation in clinically relevant tumour models in order for their impact on the response to heat to be clarified.

The effect of mild temperature hyperthermia on tumour hypoxia and blood perfusion: relevance for radiotherapy, vascular targeting and imaging

Clinically achievable mild temperature local hyperthermia (<43 degrees C) has been demonstrated to be an effective adjuvant to radiotherapy in pre-clinical and clinical studies. In this article, we briefly review the recent progress in the following areas: (1) the effect of mild temperature hyperthermia (MTH) on tumour hypoxia and blood perfusion as assessed by dual marker immunohistochemistry (IHC); (2) the kinetics of MTH induced changes in tumour hypoxia; (3) the potential role of heat-induced tumour reoxygenation on radio- and chemo-sensitisation; (4) the potential role of MTH in combination with vascular targeting agents (VTAs) on tumour response; and (5) non-invasive detection of changes in tumour oxygenation and blood perfusion. It is shown that MTH, by itself or in combination with VTAs, leads to changes in tumour perfusion and oxygenation with potential for radio- and chemo-sensitisation.

Imaging tumour physiology and vasculature to predict and assess response to heat

The vascular supply of tumours and the tumour microenvironment both play an important role when tumours are treated with hyperthermia. Blood flow is one of the major vehicles by which heat is dissipated thus the vascular supply will influence the ability to heat the tumour. It also influences the type of microenvironment that exists within tumours, and it is now well-established that cells existing in areas of oxygen deficiency, nutrient deprivation and acidic conditions are more sensitive to the effect of hyperthermia. The vascular supply and microenvironment are also affected by hyperthermia. In general, mild heat temperatures transiently improve blood flow and oxygenation, while higher hyperthermia temperatures cause vascular collapse and so increase the adverse microenvironmental conditions. Being able to image these vascular and microenvironmental parameters both before and after heating will help in our ability to predict and assess response. Here we review the various techniques that can be applied to supply this information, especially using non-invasive imaging approaches.

Detection of hypoxia in microscopic tumors using 131I-labeled iodo-azomycin galactopyranoside (131I-IAZGP) digital autoradiography

PURPOSE

Previous studies have shown that tumors less than 1 mm diameter derived from HT29 colorectal cancer cells are extremely hypoxic when grown intraperitoneally or intradermally in nude mice, whereas those of greater size (approximately 1-4 mm diameter) are not significantly hypoxic. The object of this study was to determine if digital autoradiography using the radiolabeled hypoxia imaging tracer iodo-azomycin galactopyranoside ((131)I-IAZGP) could detect hypoxia in this model.

METHODS

Microscopic HT29 tumors were grown as disseminated peritoneal disease and intradermally in nude mice. Tumors ranged in size from a few hundred microns to several millimeters in diameter. Animals were intravenously administered (131)I-IAZGP and pimonidazole 2 h before sacrifice. Following sacrifice, the intratumoral distribution of (131)I-IAZGP was assessed by digital autoradiography and compared with immunofluorescence microscopic images of pimonidazole binding and carbonic anhydrase IX (CAIX) expression.

RESULTS

The distributions of (131)I-IAZGP, pimonidazole, and CAIX expression were similar. Tumors less than 1 mm diameter displayed high (131)I-IAZGP uptake; these tumors also stained strongly for pimonidazole and CAIX. Larger tumors (approximately 1-4 mm diameter) were not significantly hypoxic and had low (131)I-IAZGP accumulation.

CONCLUSION

(131)I-IAZGP can detect hypoxia in microscopic tumors. Microscopic tumors are useful models for the validation of hypoxia radiotracers, and digital autoradiography is an appropriate technique for studying the distribution of hypoxia radiotracers in microscopic tumors.