Greg O. Cron

Rapid monitoring of oxygenation by (19)F magnetic resonance imaging : simultaneous comparison with fluorescence quenching

The aim of this study was to develop an MRI fluorocarbon oximetry technique using snapshot inversion recovery and compare it with fluorescence quenching fiber‐optic probe oximetry (OxyLite) performed simultaneously in experimental mouse tumors. The oxygen reporter probe hexafluorobenzene (HFB) was injected directly into the tumors, along with the insertion of the OxyLite probe. Tumor oxygenation (pO2) was modified using carbogen or lethal doses of the anesthetic gas. MRI pO2 maps were generated in 1.5 min with an in‐plane spatial resolution of 1.88 mm. MRI and OxyLite showed consistent baseline and postmortem pO2 values. Increases in tumor pO2 during carbogen breathing showed similar kinetics for the two methods. The pO2 values observed using the OxyLite corresponded with relatively hypoxic values observed by MRI. The apparent discrepancy between mean values might be due to the difference in sampling volumes of the techniques and the observation of multiple locations using 19F MRI versus a single location using the large optical fiber. Overall, the present method provides a rapid way to map the tumor oxygenation and is particularly suitable to monitor acute changes of pO2 in tumors. Magn Reson Med, 2009.

Botulinum toxin potentiates cancer radiotherapy and chemotherapy.

PURPOSE: Structural and functional abnormalities in the tumor vascular network are considered factors of resistance of solid tumors to cytotoxic treatments. To increase the efficacy of anticancer treatments, efforts must be made to find new strategies for transiently opening the tumor vascular bed to alleviate tumor hypoxia (source of resistance to radiotherapy) and improve the delivery of chemotherapeutic agents. We hypothesized that Botulinum neurotoxin type A (BoNT-A) could interfere with neurotransmitter release at the perivascular sympathetic varicosities, leading to inhibition of the neurogenic contractions of tumor vessels and therefore improving tumor perfusion and oxygenation. EXPERIMENTAL DESIGN: To test this hypothesis, BoNT-A was injected locally into mouse tumors (fibrosarcoma FSaII, hepatocarcinoma transplantable liver tumor), and electron paramagnetic resonance oximetry was used to monitor pO(2) in vivo repeatedly for 4 days. Additionally, contrast-enhanced magnetic resonance imaging was used to measure tumor perfusion in vivo. Finally, isolated arteries were mounted in wire myograph to monitor specifically the neurogenic tone developed by arterioles that were co-opted by the surrounding growing tumor cells. RESULTS: Using these tumor models, we showed that local administration of BoNT-A (two sites; dose, 29 units/kg) substantially increases tumor oxygenation and perfusion, leading to a substantial improvement in the tumor response to radiotherapy (20 Gy of 250-kV radiation) and chemotherapy (cyclophosphamide, 50 mg/kg). This observed therapeutic gain results from an opening of the tumor vascular bed by BoNT-A because we showed that BoNT-A could inhibit neurogenic tone in the tumor vasculature. CONCLUSIONS: The opening of the vascular bed induced by BoNT-A offers a way to significantly increase the response of tumors to radiotherapy and chemotherapy.

Arterial input functions determined from MR signal magnitude and phase for quantitative dynamic contrast-enhanced MRI in the human pelvis.

Dynamic contrast‐enhanced (DCE) MRI is often used to measure the transfer constant (Ktrans) and distribution volume (ve) in pelvic tumors. For optimal accuracy and reproducibility, one must quantify the arterial input function (AIF). Unfortunately, this is challenging due to inflow and signal saturation. A potential solution is to use MR signal phase (ϕ), which is relatively unaffected by these factors. We hypothesized that phase‐derived AIFs (AIFϕ) would provide more reproducible Ktrans and ve values than magnitude‐derived AIFs (AIF|S|). We tested this in 27 prostate dynamic contrast‐enhanced MRI studies (echo time = 2.56 ms, temporal resolution = 13.5 s), using muscle as a standard. AIFϕ peak amplitude varied much less as a function of measurement location (inferior–superior) than AIF|S| (5.6 ± 0.6 mM vs. 2.6 ± 1.5 mM), likely as a result of ϕ inflow insensitivity. However, our main hypothesis was not confirmed. The best AIF|S| provided similar reproducibility versus AIFϕ (interpatient muscle Ktrans = 0.039 ± 0.021 min−1 vs. 0.037 ± 0.025 min−1, ve = 0.090 ± 0.041 vs. 0.062 ± 0.022, respectively). Magn Reson Med, 2011.

Complex relationship between changes in oxygenation status and changes in R*2: the case of insulin and NS-398, two inhibitors of oxygen consumption

Insulin and NS‐398 have been reported to inhibit oxygen consumption in experimental tumor models, thereby increasing oxygenation and radiosensitization. The aim of this work was to use MRI to study changes in murine FSaII tumor hemodynamics after administration of those oxygen consumption inhibitors. A multiple‐echo gradient‐echo (GRE) MRI sequence (4.7 T) was used to map changes in three factors: the GRE signal (at TE = 20 ms), the parameter S0 (theoretical signal at TE = 0 ms), and the relaxation rate R  *2 . Perfusion maps were obtained by dynamic contrast‐enhanced (DCE) MRI. Insulin caused a significant decrease in the tumor blood oxygen level‐dependent (BOLD) signal over time. factor This was likely the result of decreased blood flow, since both S0 and the percentage of perfused tumor decreased as well. Tumor R  *2 did not change significantly in response to the treatments, which is surprising considering that other non‐MRI techniques (electron paramagnetic resonance (EPR) oximetry and fiber‐optic probes) have shown that tumor oxygenation increases after treatment. This suggests that metabolic changes associated with vasoactive challenges may have an unpredictable influence on blood saturation and R  *2 . In conclusion, this study further emphasizes the fact that changes in BOLD signal and R  *2 in tumors do not depend uniquely on changes in oxygenation status. Magn Reson Med, 2006.

NK-Cell Recruitment Is Necessary for Eradication of Peritoneal Carcinomatosis with an IL12-Expressing Maraba Virus Cellular Vaccine

Antitumor vaccines are still inefficient. However, when tumor cells were infected ex vivo with an IL12-expressing oncolytic virus and used as a vaccine, peritoneal carcinomatosis mouse models showed a 90% cure rate and protective immunity from rechallenge. Despite improvements in chemotherapy and radical surgical debulking, peritoneal carcinomatosis (PC) remains among the most common causes of death from abdominal cancers. Immunotherapies have been effective for selected solid malignancies, but their potential in PC has been little explored. Here, we report that intraperitoneal injection of an infected cell vaccine (ICV), consisting of autologous tumor cells infected ex vivo with an oncolytic Maraba MG1 virus expressing IL12, promotes the migration of activated natural killer (NK) cells to the peritoneal cavity in response to the secretion of IFNγ-induced protein-10 (IP-10) from dendritic cells. The recruitment of cytotoxic, IFNγ-secreting NK cells was associated with reduced tumor burden and improved survival in a colon cancer model of PC. Even in mice with bulky PC (tumors > 8 mm), a complete radiologic response was demonstrated within 8 to14 weeks, associated with 100% long-term survival. The impact of MG1-IL12-ICV upon NK-cell recruitment and function observed in the murine system was recapitulated in human lymphocytes exposed to human tumor cell lines infected with MG1-IL12. These findings suggest that an MG1-IL12-ICV is a promising therapy that could provide benefit to the thousands of patients diagnosed with PC each year. Cancer Immunol Res; 5(3); 211–21. ©2017 AACR.

19F NMR in vivo spectroscopy reflects the effectiveness of perfusion-enhancing vascular modifiers for improving gemcitabine chemotherapy

Nuclear magnetic resonance spectroscopy of fluorine‐19 (19F NMR) has proven useful for evaluating kinetics of fluorinated chemotherapy drugs in tumors in vivo. This work investigated how three perfusion‐enhancing vascular modifiers (BQ123, thalidomide, and Botulinum neurotoxin type A [BoNT‐A]) would affect the chemotherapeutic efficacy of gemcitabine, a fluorinated drug widely used in human cancer treatment. Murine tumor growth experiments demonstrated that only BoNT‐A showed a strong trend to enhance tumor growth inhibition by gemcitabine (1.7 days growth delay, P = 0.052, Student t‐test). In accord with these results, 19F NMR experiments showed that only BoNT‐A increased significantly the uptake of gemcitabine in tumors (50% increase, P = 0.0008, Student t‐test). Further experiments on gemcitabine kinetics (NMR vs time) and distribution (19F MRI) confirmed the uptake‐enhancing properties of BoNT‐A. The results of this study demonstrate that 19F NMR can monitor modulation of the pharmacokinetics of fluorinated chemotherapy drugs in tumors. The results also show that 19F NMR data can give a strong indication of the effectiveness of perfusion‐enhancing vascular modifiers for improving gemcitabine chemotherapy in murine tumors. 19F NMR is a promising tool for preclinical evaluation of such vascular modifiers and may ultimately be used in the clinic to monitor how these modifiers affect chemotherapy. Magn Reson Med, 2007.

PET imaging of a collagen matrix reveals its effective injection and targeted retention in a mouse model of myocardial infarction.

Injectable biomaterials have shown promise for cardiac regeneration therapy. However, little is known regarding their retention and distribution upon application in vivo. Matrix imaging would be useful for evaluating these important properties. Herein, hexadecyl-4-[(18)F]fluorobenzoate ((18)F-HFB) and Qdot labeling was used to evaluate collagen matrix delivery in a mouse model of myocardial infarction (MI). At 1 wk post-MI, mice received myocardial injections of (18)F-HFB- or Qdot-labeled matrix to assess its early retention and distribution (at 10 min and 2h) by positron emission tomography (PET), or fluorescence imaging, respectively. PET imaging showed that the bolus of matrix at 10 min redistributed evenly within the ischemic territory by 2h. Ex vivo biodistribution revealed myocardial matrix retention of ∼ 65%, which correlated with PET results, but may be an underestimate since (18)F-HFB matrix labeling efficiency was ∼ 82%. For covalently linked Qdots, labeling efficiency was ∼ 96%. Ex vivo Qdot quantification showed that ∼ 84% of the injected matrix was retained in the myocardium. Serial non-invasive PET imaging and validation by fluorescence imaging confirmed the effectiveness of the collagen matrix to be retained and redistributed within the infarcted myocardium. This study identifies matrix-targeted imaging as a promising modality for assessing the biodistribution of injectable biomaterials for application in the heart.

Multi-parametric (mp) MRI of prostatic ductal adenocarcinoma.

Prostatic ductal adenocarcinoma (DCa) is an aggressive variant of conventional adenocarcinoma (CCa) with mixed DCa and CCa tumors comprising up to 5% of all prostate cancers. DCa may be underestimated on T2‐weighted (T2W) MRI. This study assessed the mp‐MRI appearance of DCa as compared with CCa.

Dynamic contrast-enhanced MRI in mice at high field: Estimation of the arterial input function can be achieved by phase imaging

Quantitative dynamic contrast‐enhanced MRI requires an accurate arterial input function (AIF). At high field, increased susceptibility effects and decreased longitudinal relaxivity of contrast agents lead to predominant T2* effects in blood vessels, producing a dip in signal during passage of the contrast agent bolus. This study determined phase‐derived AIFs in mice at 11.7 T.

Dynamic contrast-enhanced MRI in mouse tumors at 11.7 T: comparison of three contrast agents with different molecular weights to assess the early effects of combretastatin A4

Dynamic contrast‐enhanced (DCE)‐MRI is useful to assess the early effects of drugs acting on tumor vasculature, namely anti‐angiogenic and vascular disrupting agents. Ultra‐high‐field MRI allows higher‐resolution scanning for DCE‐MRI while maintaining an adequate signal‐to‐noise ratio. However, increases in susceptibility effects, combined with decreases in longitudinal relaxivity of gadolinium‐based contrast agents (GdCAs), make DCE‐MRI more challenging at high field. The aim of this work was to explore the feasibility of using DCE‐MRI at 11.7 T to assess the tumor hemodynamics of mice. Three GdCAs possessing different molecular weights (gadoterate: 560 Da, 0.29 mmol Gd/kg; p846: 3.5 kDa, 0.10 mmol Gd/kg; and p792: 6.47 kDa, 0.15 mmol Gd/kg) were compared to see the influence of the molecular weight in the highlight of the biologic effects induced by combretastatin A4 (CA4).