Tumor Hypoxia Imaging Research Articles

Molecular Imaging of Tumor Hypoxia: Existing Problems and Their Potential Model-Based Solutions.

Molecular imaging of tissue hypoxia generates contrast in hypoxic areas by applying hypoxia-specific tracers in organisms. In cancer tissue, the injected tracer needs to be transported over relatively long distances and accumulates slowly in hypoxic regions. Thus, the signal-to-background ratio of hypoxia imaging is very small and a non-specific accumulation may suppress the real hypoxia-specific signals. In addition, the heterogeneous tumor microenvironment makes the assessment of the tissue oxygenation status more challenging. In this study, the diffusion potential of oxygen and of a hypoxia tracer for 4 different hypoxia subtypes: ischemic acute hypoxia, hypoxemic acute hypoxia, diffusion-limited chronic hypoxia and anemic chronic hypoxia are theoretically assessed. In particular, a reaction-diffusion equation is introduced to quantitatively analyze the interstitial diffusion of the hypoxia tracer [(18)F]FMISO. Imaging analysis strategies are explored based on reaction-diffusion simulations. For hypoxia imaging of low signal-to-background ratio, pharmacokinetic modelling has advantages to extract underlying specific binding signals from non-specific background signals and to improve the assessment of tumor oxygenation. Different pharmacokinetic models are evaluated for the analysis of the hypoxia tracer [(18)F]FMISO and optimal analysis model were identified accordingly. The improvements by model-based methods for the estimation of tumor oxygenation are in agreement with experimental data. The computational modelling offers a tool to explore molecular imaging of hypoxia and pharmacokinetic modelling is encouraged to be employed in the corresponding data analysis.

Synthesis of a 4-nitroimidazole indocyanine dye-conjugate and imaging of tumor hypoxia in BALB/c tumor-bearing female mice

Abstract Extending our previous work with 2-nitroimidazole-indocyanine dye-conjugate 4 , we prepared the 4-nitroimidazole-piperazine-indocyanine derivative ( 6 ). We also prepared imidazole derivative 5 as a control. We compared the in vivo hypoxia targeting performance of both 5 and 6 with the previously tested 4 , and 6 showed a higher fluorescent intensity after 15 min post-injection, about 1.5-fold higher than 4 and 2.5-fold higher than 5 . Cells treated with 6 under hypoxic conditions showed a higher fluorescence yield when compared to the cells kept under normoxic conditions. All findings were supported with fluorescence images of histological sections of tumor samples using a Li-COR scanner and an immunohistochemistry technique for tumor hypoxia.

Kit formulation for preparation and biological evaluation of a novel 99mTc-oxo complex with metronidazole xanthate for imaging tumor hypoxia

Achieving an ideal (99m)Tc labeled nitroimidazole hypoxia marker is still considered to be of great interest. Metronidazole xanthate (MNXT) ligand was synthesized and radiolabeled with (99m)Tc-glucoheptonate (GH) to form the (99m)TcO-MNXT complex, for the potential use as a novel probe for imaging tumor hypoxia. For labeling, (99m)TcO-MNXT was prepared by ligand-exchange reaction with (99m)Tc-GH. The radiochemical purity of the (99m)TcO-MNXT complex was measured by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The distribution coefficient and stability of the complex was investigated. The structure of the (99m)TcO-MNXT complex was verified by preparation and characterization of the corresponding stable rhenium complex. The cellular uptake of the (99m)TcO-MNXT complex was determined in murine sarcoma S180 cell lines under hypoxic and aerobic conditions. The biodistribution and single photon emission computed tomography (SPECT) image studies of the (99m)TcO-MNXT complex were performed in mice bearing S 180 tumor. The radiochemical purity of the (99m)TcO-MNXT complex was over 90%. It had good in vitro stability and its distribution coefficient indicated that it was a hydrophilic complex. When (99m)Tc and Re complexes were coinjected in HPLC, both radioactivity (for (99m)Tc complex) and UV detectors (for Re complex) showed nearly identical HPLC profiles, suggesting their structures are similar. The tumor cell experiment and the biodistribution in mice bearing S 180 tumor showed that the (99m)TcO-MNXT complex had a good hypoxic selectivity and accumulated in the tumor with high uptake and good retention. Single photon emission computed tomography (SPECT) image studies showed that the tumor detection was observable. (99m)TcO-MNXT is prepared from a kit without the need for purification and shows high tumor uptake, tumor/blood and tumor/muscle ratios, suggesting that it would be a promising candidate for imaging tumor hypoxia.

Application of 18F-FMISO for tumor hypoxia imaging

Hypoxia is the combined result of tumor over-growth and vascular structural abnormalities. Hypoxia is related to tumor invasiveness, radioresistance, and chemoresistance. 18F-fluoromisoni-dzole (18F-FMISO) can selectively bind to hypoxic tissues of malignant tumors, and is thus useful for imaging of tumor hypoxia in cancer diagnosis and treatment. This review summarizes the state-of-art research of 18F-FMISO in comparison with other hypoxic agents when applied to animals and clinical studies. Key words: Nitroimidazoles; Isotope labeling; Fluorine radioisotopes; Cell hypoxia; Trends

(68) Ga]-HP-DO3A-nitroimidazole: a promising agent for PET detection of tumor hypoxia.

The goal of this study is to evaluate a new (68) Ga-based imaging agent for detecting tumor hypoxia using positron emission tomography (PET). The new hypoxia targeting agent reported here, [(68) Ga]-HP-DO3A-nitroimidazole ([(68) Ga]-HP-DO3A-NI), was constructed by linking a nitroimidazole moiety with the macrocyclic ligand component of ProHance®, HP-DO3A. The hypoxia targeting capability of this agent was evaluated in A549 lung cancer cells in vitro and in SCID mice bearing subcutaneous A549 tumor xenografts. The cellular uptake assays showed that significantly more [(68) Ga]-HP-DO3A-NI accumulates in hypoxic tumor cells at 30, 60 and 120 min than in the same cells exposed to 21% O2 . The agent also accumulated in hypoxic tumors in vivo to give a tumor/muscle ratio (T/M) of 5.0 ± 1.2 (n = 3) as measured by PET at 2 h post-injection (p.i.). This was further confirmed by ex vivo biodistribution data. In addition, [(68) Ga]-HP-DO3A-NI displayed very favorable pharmacokinetic properties, as it was cleared largely through the kidneys with little to no accumulation in liver, heart or lung (%ID/g < 0.5%) at 2 h p.i. The specificity of the agent for hypoxic tissues was further validated in a comparative study with a control compound, [(68) Ga]-HP-DO3A, which lacks the nitroimidazole moiety, and by PET imaging of tumor-bearing mice breathing air versus 100% O2 . Given the commercial availability of cGMP (68) Ge/(68) Ga generators and the ease of (68) Ga labeling, the new agent could potentially be widely applied for imaging tumor hypoxia prior to radiation therapy.

A limited overlap between intratumoral distribution of 1-(5-fluoro-5-deoxy-α-D-arabinofuranosyl)-2-nitroimidazole and copper-diacetyl-bis[N(4)-methylthiosemicarbazone

Positron emission tomography (PET) imaging of tumor hypoxia provides valuable information for cancer treatment planning. Two types of PET tracers, nitroimidazole compounds and [62,64Cu] copper-diacetyl-bis[N(4)-methylthio- semicarbazone] (Cu-ATSM), have been used for imaging hypoxic tumors. High accumulation of these tracers in tumors was shown to predict poor prognosis. Both similar and different intratumoral distributions of these PET tracers have been reported with some studies questioning the dependence of the Cu-ATSM accumulation on hypoxia. In the present study, we compared the intratumoral distribution and cellular uptake of 1-(5-fluoro-5-deoxy-α-D-arabinofuranosyl)-2-nitroimidazole(FAZA) and Cu-ATSM. Intratumoral distributions of FAZA and Cu-ATSM compared by double tracer autoradiography in xenografts of 8cancer cell lines and 3cancer tissue originated spheroids (CTOSs) showed that only a limited overlap was observed between the regions with high levels of FAZA and Cu-ATSM accumulation in all the xenografts. Immunohistochemistry in the regions enriched with FAZA and Cu-ATSM in xenografts demonstrated that pimonidazole adducts were in regions that accumulated high levels of FAZA, while HIF-1α was in areas enriched with either tracer. In addition, we examined the cellular uptake of FAZA and Cu-ATSM at different levels of oxygen concentration in 4cell lines and revealed that cellular uptake of FAZA was increased with the decrease of oxygen concentration from 20 to 2 and from 2 to 1%, while the Cu-ATSM uptake increased with the decrease of oxygen concentration from 20 to 2%, but did not increase with the decrease from 2 to 1%. Our findings indicate that intratumoral distributions of FAZA and Cu-ATSM were essentially non-overlapping and although hypoxia affects the buildup of both tracers, the accumulation of Cu-ATSM occurred at milder hypoxia compared to the conditions required for the accumulation of FAZA. Therefore, accumulation levels of FAZA and Cu-ATSM may be considered as independent biomarkers.

Is carbonic anhydrase IX a validated target for molecular imaging of cancer and hypoxia?

The presence of hypoxia is a general feature of most solid malignancies, and hypoxia is considered as one of major factors for anticancer therapy failure. Carbonic anhydrase IX (CAIX) has been reported to be an endogenous hypoxia marker, CAIX monoclonal antibodies, their segments and inhibitors are developed for CAIX imaging. However, growing evidence indicates that CAIX expression under hypoxia condition may be cancer cell lines or cancer-type dependent. Here we review the current literature on CAIX and discuss the advantage and limitation of CAIX as a target for tumor hypoxia imaging. Accordingly, CAIX would be unreliable as a universal target for cancer and tumor hypoxia visualization.

Luminescent difluoroboron β-diketonate PEG-PLA oxygen nanosensors for tumor imaging.

Surface modification of nanoparticles and biosensors is a dynamic, expanding area of research for targeted delivery in vivo. For more efficient delivery, surfaces are PEGylated to impart stealth properties, long circulation, and enable enhanced permeability and retention (EPR) in tumor tissues. Previously, BF2 dbm(I)PLA was proven to be a good oxygen nanosensor material for tumor hypoxia imaging in vivo, though particles were applied directly to the tumor and surrounding region. Further surface modification is needed for this dual-emissive oxygen sensitive material for effective intravenous (IV) administration and passive and active delivery to tumors. In this paper, an efficient synthesis of a new dual-emissive material BF2 dbm(I)PLA-mPEG is presented and in vitro stability studies are conducted. It is found that fabricated nanoparticles are stable for 24 weeks as a suspension, while after 25 weeks the nanoparticles swell and both dye and polymer degradation escalates. Preliminary studies show BF2 dbm(I)PLA-mPEG nanoparticle accumulation in a window chamber mammary tumor 24 h after IV injection into mice (C57Bl/6 strain) enabling tumor oxygen imaging.

Phase 1 Trial of Bevacizumab With Concurrent Chemoradiation Therapy for Squamous Cell Carcinoma of the Head and Neck With Exploratory Functional Imaging of Tumor Hypoxia, Proliferation, and Perfusion

A phase 1 trial was completed to examine the safety and feasibility of combining bevacizumab with radiation and cisplatin in patients with locoregionally advanced squamous cell carcinoma of the head and neck (HNSCC) treated with curative intent. Additionally, we assessed the capacity of bevacizumab to induce an early tumor response as measured by a series of biological imaging studies. All patients received a single induction dose of bevacizumab (15 mg/kg) delivered 3 weeks (±3 days) before the initiation of chemoradiation therapy.After the initial dose of bevacizumab, comprehensive head and neck chemoradiation therapy was delivered with curative intent to 70 Gy in 33 fractions with concurrent weekly cisplatin at 30 mg/m(2) and bevacizumab every 3 weeks (weeks 1, 4, 7) with dose escalation from 5 to 10 to 15 mg/kg. All patients underwent experimental imaging with [(18)F]fluorothymidine positron emission tomography (FLT-PET) (proliferation), [(61)Cu]Cu-diacetyl-bis(N4-methylthiosemicarbazone) PET (Cu-ATSM-PET) (hypoxia), and dynamic contrast-enhanced computed tomography (DCE-CT) (perfusion) at 3 time points: before bevacizumab monotherapy, after bevacizumab monotherapy, and during the combined therapy course. Ten patients were enrolled. All had stage IV HNSCC, all achieved a complete response to treatment, and 9 of 10 remain alive, with a mean survival time of 61.3 months. All patients experienced grade 3 toxicity, but no dose-limiting toxicities or significant bleeding episodes were observed. Significant reductions were noted in tumor proliferation (FLT-PET), tumor hypoxia (Cu-ATSM-PET), and DCE-CT contrast enhancement after bevacizumab monotherapy, with further decreases in FLT-PET and Cu-ATSM-PET during the combined therapy course. The incorporation of bevacizumab into comprehensive chemoradiation therapy regimens for patients with HNSCC appears safe and feasible. Experimental imaging demonstrates measureable changes in tumor proliferation, hypoxia, and perfusion after bevacizumab monotherapy and during chemoradiation therapy. These findings suggest opportunities to preview the clinical outcomes for individual patients and thereby design personalized therapy approaches in future trials.

A (99m)Tc-labeled misonidazole analogue: step toward a (99m)Tc-alternative to [18F]fluromisonidazole for detecting tumor hypoxia.

The PET radiopharmaceutical [(18)F]Fluromisonidazole ([(18)F]FMISO) is presently the agent of choice for the clinical imaging of tumor hypoxia. Considering the logistic advantages of (99m)Tc and wider availability of SPECT machines, a (99m)Tc-radiopharmaceutical for this purpose constitutes an attractive choice. In the work presented here, a misonidazole analogue was radiolabeled with (99m)Tc(CO)3 core and the complex was evaluated in Swiss mice bearing fibrosarcoma tumor. The results obtained are compared with the biodistribution of [(18)F]FMISO carried out in the same tumor-bearing animal model. Misonidazole-(99m)Tc(CO)3 complex showed significant uptake and retention in tumor. Notably, the rate of clearance of misonidazole complex from the tumor was slower than that of [(18)F]FMISO. The maximum tumor/muscle ratio obtained with misonidazole-(99m)Tc(CO)3 complex was significantly higher than that of [(18)F]FMISO. The study constitutes a positive step toward the development of a (99m)Tc-analogue of [(18)F]FMISO.

Fluorescent/phosphorescent dual-emissive conjugated polymer dots for hypoxia bioimaging.

A kind of fluorescent/phosphorescent dual-emissive conjugated polyelectrolyte has been prepared by introducing phosphorescent platinum(ii) porphyrin (O2-sensitive) into a fluorene-based conjugated polyelectrolyte (O2-insensitive), which can form ultrasmall conjugated polymer dots (FP-Pdots) in the phosphate buffer solution (PBS) via self-assembly caused by their amphiphilic structures with hydrophobic backbones and hydrophilic side chains. These FP-Pdots can exhibit an excellent ratiometric luminescence response to O2 content with high reliability and full reversibility for measuring oxygen levels, and the excellent intracellular ratiometric O2 sensing properties of the FP-Pdots nanoprobe have also been confirmed by the evident change in the Ired/Iblue ratio values in living cells cultured at different O2 concentrations. To confirm the reliability of the O2 sensing measurements of the FP-Pdots nanoprobe, O2 quenching experiments based on lifetime measurements of phosphorescence from Pt(ii) porphyrin moieties have also been carried out. Utilizing the sensitivity of the long phosphorescence lifetime from Pt(ii) porphyrins to oxygen, the FP-Pdots have been successfully applied in time-resolved luminescence imaging of intracellular O2 levels, including photoluminescence lifetime imaging and time-gated luminescence imaging, which will evidently improve the sensing sensitivity and reliability. Finally, in vivo oxygen sensing experiments were successfully performed by luminescence imaging of tumor hypoxia in nude mice.

A turn-on fluorescent probe for tumor hypoxia imaging in living cells.

A novel "turn-on" fluorescent probe HP for hypoxia imaging was designed and synthesized based on rhodamine B and a naphthalimide fluorophore. The fluorescence of HP is very weak owing to the FRET effect from rhodamine B to the azo-naphthalimide unit. Under hypoxia conditions, the azo-bond is reduced and the fluorescence at 581 nm enhances dramatically as a result of disintegration of the quencher structure. Verified by the cyclic voltammetry reduction potential and proposed product HPN, the probe HP could undergo the chemical and cytochrome P450 enzymatic reduction quickly. When cultured with HeLa cells, HP showed remarkable fluorescence differences at various oxygen concentrations, and the ratio of fluorescence intensity between hypoxic and normoxic cells could reach 9 fold.

Imaging tumour hypoxia with positron emission tomography.

Hypoxia, a hallmark of most solid tumours, is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. Given its prominent role in oncology, accurate detection of hypoxia is important, as it impacts on prognosis and could influence treatment planning. A variety of approaches have been explored over the years for detecting and monitoring changes in hypoxia in tumours, including biological markers and noninvasive imaging techniques. Positron emission tomography (PET) is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels. This review provides an overview of imaging hypoxia with PET, with an emphasis on the advantages and limitations of the currently available hypoxia radiotracers.

Abstract 4302: The development study of hypoxia responsive chemiluminescent probe for tumor hypoxia imaging

Abstract Introduction: The tumor microenvironment is recognized as a major factor that influences not only the response to conventional anticancer therapies but also the potential for malignant progression and metastasis. Therefore, it is considered that tumor hypoxia imaging is critical for cancer diagnosis and therapy. As optical modalities offer the advantages of non-invasive, easy-to-handle, and cost-effective imaging, much effort has been done to develop synthetic fluorescent imaging probes for tumor hypoxia. In particular, we focus our attention on chemiluminescence imaging which can avoid interference from tissue autofluorescence and scattering light. We therefore show the development of hypoxia responsive chemiluminescent probe, which has the advantage of lower detection limits and improved signal-to-noise ratio compared to existing fluorescent probes. Results and discussion: In our molecular design, luminescence is derived from 1,2-dioxetane cleavage triggered by hypoxia-selective enzymatic reduction of electron-deficient aromatics. At the start, nitrobenzyl moiety was chosen as a bioreductively cleavable protective group linked to 1,2-dioxetane moiety through phenyl ether linker to construct synthetic probe NB-Adm. The compound was synthesized from 2-adamantanone in 19% (overall yield, 6 steps). Then NB-Adm was attempted to be reduced by nitroreductase, however, no luminescence was observed. HPLC analysis of the reaction mixture indicated that our expected reduction did not occur, probably because bulky adamantane moiety prevented the enzymatic reaction owing to steric hindrance. Therefore, a self-immolative linker was employed to keep away 1,2-dioxetane moiety from enzyme recognition moiety. In this time, quinone moiety was chosen as a protective group which was expected to be better substrate than nitrophenyl one in terms of their redox potential. This newly designed compound, TMQ-Adm was synthesized from 2-adamantanone in 16% (overall yield, 6 steps). By the use of TMQ-Adm, we successfully observed luminescent emission from the reaction with nitroreductase. This implied that our bioredctively activatable probe can be applicable for chemiluminescence imaging for tumor hypoxia. Now we are investigating to develop chemiluminescent probe to realize in vivo imaging of tumor hypoxia by improving luminescent quantum yield under physiological condition. Citation Format: Kensuke Okuda, Toru Ban, Tasuku Hirayama, Hideko Nagasawa. The development study of hypoxia responsive chemiluminescent probe for tumor hypoxia imaging. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4302. doi:10.1158/1538-7445.AM2014-4302

Serial Imaging of Tumor Hypoxia in Early Stage Non-Small Cell Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy

Serial Imaging of Tumor Hypoxia in Early Stage Non-Small Cell Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy

18F-misonidazole Pet Tumor Hypoxia Imaging During Chemoradiation Therapy For HNSCC - Correlation To Outcome

18F-misonidazole Pet Tumor Hypoxia Imaging During Chemoradiation Therapy For HNSCC - Correlation To Outcome

Acyclic chelating ligands for PET imaging of tumor hypoxia with Ga-68

Acyclic chelating ligands for PET imaging of tumor hypoxia with Ga-68

Synthesis and biological evaluation of 99mTcO-MNXT as a novel tumor hypoxia imaging agent

Synthesis and biological evaluation of 99mTcO-MNXT as a novel tumor hypoxia imaging agent

Synthesis and biological evaluation of novel 99mTcN-labeled bisnitroimidazole complexes containing monoamine-monoamide dithiol as potential tumor hypoxia markers

Tumor hypoxia can decrease the efficacy of clinical therapy due to resistance toward radiation damage and chemotherapy, thus detection of tumor hypoxia by radiolabeled hypoxia markers is important for the control of tumor. Radiopharmaceuticals with two bioreductive groups, such as propylene amine oxime-bisnitroimidazole or monoamine-monoamide dithiol (MAMA) -bisnitroimidazole, have potential to improve hypoxia selectivity. In order to obtain radiopharmaceuticals with better features, we synthesized two novel [99mTcN]2+ complexes with bisnitroimidazole moieties and MAMA ligand for targeting tumor hypoxia. Their physicochemical characters and biodistribution were also investigated. Both the [99mTcN]2+ complexes show good stability and hydrophilicity. They show faster clearance from blood and soft tissues, better tumor retention and favorable tumor-to-tissue ratios compared with a control complex without nitroimidazole group. In addition, both of them show more favorable biodistribution patterns than the corresponding [99mTcO]3+ complexes. These results indicate that the 99mTcN-labeled MAMA-bisnitroimidazole complexes would have potential to image tumor hypoxia in vivo.

WE-G-BRD-06: Variation in Dynamic Positron Emission Tomography Imaging of Tumor Hypoxia in Early Stage Non-Small Cell Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy

Purpose: Tumor hypoxia is correlated with treatment failure. To date, there are no published studies investigating hypoxia in non-small cell lung cancer (NSCLC) patients undergoing SBRT. We aim to use 18F-fluoromisonidazole (18F-FMISO) positron emission tomography (PET) imaging to non-invasively quantify the tumor hypoxic volume (HV), to elucidate potential roles of reoxygenation and tumor vascular response at high doses, and to identify an optimal prognostic imaging time-point. Methods: SBRT-eligible patients with NSCLC tumors >1cm were prospectively enrolled in an IRB-approved study. Computed Tomography and dynamic PET images (0–120min, 150–180min, and 210–240min post-injection) were acquired using a Siemens BiographmCT PET/CT scanner. 18F-FMISO PET was performed on a single patient at 3 different time points around a single SBRT delivery of 18 Gy and HVs were compared using a tumor-to-blood ratio (TBR)>1.2 and rate of influx (Ki)>0.0015 (Patlak). Results: Results from our first patient showed substantial temporal changes in HV following SBRT. Using a TBR threshold >1.2 and summed images 210–240min, the HVs were 19%, 31% and 13% of total tumor volume on day 0, 2 (48 hours post-SBRT), and 4 (96 hours post-SBRT). The absolute volume of hypoxia increased by nearly a factor of 2 after 18 Gy and then decreased almost to baseline 96 hours later. Selected imaging timepoints resulted in temporal changes in HV quantification obtained with TBR. Ki, calculated using 4-hour dynamic data, evaluated HVs as 22%, 75% and 21%, respectively. Conclusions: ith the results of only one patient, this novel pilot study highlights the potential benefit of 18F-FMISO PET imaging as results indicate substantial temporal changes in tumor HV post-SBRT. Analysis suggests that TBR is not a robust parameter for accurate HV quantification and heavily influenced by imaging timepoint selection. Kinetic modeling parameters are more sensitive and may aid in future treatment individualization based on patient-specific biological information.