Photobac derived from bacteriochlorophyll-a shows potential for treating brain tumor in animal models by photodynamic therapy with desired pharmacokinetics and limited toxicity in rats and dogs.

Photobac is a near infrared photosensitizer (PS) derived from naturally occurring bacteriochlorophyll- a, with a potential for treating a variety of cancer types (U87, F98 and C6 tumor cells in vitro). The main objective of the studies presented herein was to evaluate the efficacy, toxicity and pharmacokinetic profile of Photobac in animals (mice, rats and dogs) and submit these results to the United States Food and Drug Administration (US FDA) for its approval to initiate Phase I human clinical trials of glioblastoma, a deadly cancer disease with no long term cure. The photodynamic therapy (PDT) efficacy of Photobac was evaluated in mice subcutaneously implanted with U87 tumors, and in rats bearing C6 tumors implanted in brain. In both tumor types, the Photobac-PDT was quite effective. The long-term cure in rats was monitored by magnetic resonance imaging (MRI) and histopathology analysis. A detailed pharmacology, pharmacokinetics and toxicokinetic study of Photobac was investigated in both non-GLP and GLP facilities at variable doses following the US FDA parameters. Safety Pharmacology studies suggest that there is no phototoxicity, cerebral or retinal toxicity with Photobac. No metabolites of Photobac were observed following incubation in rat, dog, mini-pig and human hepatocytes. Based on current biological data, Photobac-IND received the approval for Phase-I human clinical trials to treat Glioblastoma (brain cancer), which is currently underway at our institute. Photobac has also received an orphan drug status from the US FDA, because of its potential for treating Glioblastoma as no effective treatment is currently available for this deadly disease.

The Development of Nonthermal Plasma and Tirapazamine as a Novel Combination Therapy to Treat Melanoma In Situ.

Although melanoma accounts for only 5.3% of skin cancer, it results in >75% of skin-cancer-related deaths. To avoid disfiguring surgeries on the head and neck associated with surgical excision, there is a clear unmet need for other strategies to selectively remove cutaneous melanoma lesions. Mohs surgery is the current treatment for cutaneous melanoma lesions and squamous and basal cell carcinoma. While Mohs surgery is an effective way to remove melanomas in situ, normal tissue is also excised to achieve histologically negative margins. This paper describes a novel combination therapy of nonthermal plasma (NTP) which emits a multitude of reactive oxygen species (ROS) and the injection of a pharmaceutical agent. We have shown that the effects of NTP are augmented by the DNA-damaging prodrug, tirapazamine (TPZ), which becomes a free radical only in conditions of hypoxemia, which is often enhanced in the tumor microenvironment. In this study, we demonstrate the efficacy of the combination therapy through experiments with B16-F10 and 1205 Lu metastatic melanoma cells both in vitro and in vivo. We also show the safety parameters of the therapy with no significant effects of the therapy when applied to porcine skin. We show the need for the intratumor delivery of TPZ in combination with the surface treatment of NTP and present a model of a medical device to deliver this combination therapy. The importance of functional gap junctions is indicated as a mechanism to promote the therapeutic effect. Collectively, the data support a novel therapeutic combination to treat melanoma and the development of a medical device to deliver the treatment in situ.

Phospholipid Encapsulation of an Anti-Fibrotic Endopeptide to Enhance Cellular Uptake and Myocardial Retention.

BACKGROUND: Cardioprotective effects of N-acetyl-ser-asp-lys-pro (Ac-SDKP) have been reported in preclinical models of myocardial remodeling. However, the rapid degradation of this endogenous peptide in vivo limits its clinical use. METHOD: To prolong its bioavailability, Ac-SDKP was encapsulated by phosphocholine lipid bilayers (liposomes) similar to mammalian cell membranes. The physical properties of the liposome structures were assessed by dynamic light scattering and scanning electron microscopy. The uptake of Ac-SDKP by RAW 264.7 macrophages and human and murine primary cardiac fibroblasts was confirmed by fluorescence microscopy and flow cytometry. Spectrum computerized tomography and competitive enzyme-linked immunoassays were performed to measure the ex vivo cardiac biodistribution of Ac-SDKP. The biological effects of this novel synthetic compound were examined in cultured macrophages and cardiac fibroblasts and in a murine model of acute myocardial infarction induced by permanent coronary artery ligation. RESULTS: A liposome formulation resulted in the greater uptake of Ac-SDKP than the naked peptide by cultured RAW 264.7 macrophages and cardiac fibroblasts. Liposome-delivered Ac-SDKP decreased fibroinflammatory genes in cultured cardiac fibroblasts co-treated with TGF-ß1 and macrophages stimulated with LPS. Serial tissue and serum immunoassays showed the high bioavailability of Ac-SDKP in mouse myocardium and in circulation. Liposome-delivered Ac-SDKP improved cardiac function and reduced myocardial fibroinflammatory responses in mice with acute myocardial infarction. CONCLUSION: Encapsulation of Ac-SDKP in a cell membrane-like phospholipid bilayer enhances its plasma and tissue bioavailability and offers cardioprotection against ischemic myocardial injury. Future clinical trials can use this novel approach to test small protective endogenous peptides in myocardial remodeling.

PET Imaging of Hepatocellular Carcinoma Using ZD2-(68Ga-NOTA).

Purpose: We tested a recently developed short peptide radioligand for PET imaging of hepatocellular carcinoma (HCC) by targeting an oncoprotein, extra-domain B fibronectin (EDB-FN) in the tumor microenvironment. Methods: The radioligand consists of a small linear peptide ZD2 with 68Ga-NOTA chelator, and specifically binds to EDB-FN. PET images were acquired dynamically for 1 hour after intravenously (i.v.) injecting 37 MBq (1.0 mCi) of the radioligand into the woodchuck model of naturally occurring HCC. Woodchuck HCC originated from chronic viral hepatitis infection, which recapitulates the corresponding human primary liver cancer. The animals were euthanized post-imaging for tissue collection and validation. Results: For ZD2 avid liver tumors, the radioligand accumulation plateaued a few minutes after injection, while the liver background uptake stabilized 20 min post-injection. The status of EDB-FN in woodchuck HCC was confirmed by histology and validated by PCR and western blocking. Conclusion: We have showed the viability of using the ZD2 short peptide radioligand targeting EDB-FN in liver tumor tissue for PET imaging of HCC, which can potentially impact the clinical care for HCC patients.

Imaging of Tumor-Associated Vascular Prostate-Specific Membrane Antigen in Woodchuck Model of Hepatocellular Carcinoma.

BACKGROUND AND AIMS: Radiolabeled short peptide ligands targeting prostate-specific membrane antigen (PSMA) were developed initially for imaging and treatment of prostate cancers. While many nonprostate solid tumors including hepatocellular carcinoma (HCC) express little PSMA, their neovasculature expresses a high level of PSMA, which is avid for Gallium-68-labeled PSMA-targeting radio-ligand (68Ga-PSMA-11) for positron emission tomography (PET). However, the lack of a spontaneous animal model of tumor-associated vascular PSMA overexpression has hindered the development and assessment of PSMA-targeting radioligands for imaging and therapy of the nonprostatic cancers. We identified detectable indigenous PSMA expression on tumor neovascular endothelia in a naturally occurring woodchuck model of HCC. METHODS: Molecular docking was performed with 3 bait PSMA ligands and compared between human and woodchuck PSMA. Initially, PET images were acquired dynamically after intravenously injecting 37 MBq (1.0 mCi) of 68Ga-PSMA-11 into woodchuck models of HCC. Subsequently, 10-minute static PET scans were conducted for other animals 1-hour after injection due to HCC and liver background uptake stabilization at 30-45 minutes after injection. Liver tissue samples were harvested after imaging, fresh-frozen for quantitative reverse transcription polymerase chain reaction and western blot for validation, or fixed for histology for correlation. RESULTS: Our preclinical studies confirmed the initial clinical findings of 68Ga-PSMA-11 uptake in HCC. The agents (ligands and antibodies) developed against human PSMA were found to be reactive against the woodchuck PSMA. CONCLUSION: This animal model offers a unique opportunity for investigating the biogenesis of tumor-associated vascular PSMA, its functional role(s), and potentials for future treatment strategies targeting tumor vascular PSMA using already developed PSMA-targeting agents.

Succinate dehydrogenase inversely regulates red cell distribution width and healthy life span in chronically hypoxic mice.

Increased red cell distribution width (RDW), which measures erythrocyte mean corpuscular volume (MCV) variability (anisocytosis), has been linked to early mortality in many diseases and in older adults through unknown mechanisms. Hypoxic stress has been proposed as a potential mechanism. However, experimental models to investigate the link between increased RDW and reduced survival are lacking. Here, we show that lifelong hypobaric hypoxia (~10% O2) increased erythrocyte numbers, hemoglobin, and RDW, while reducing longevity in male mice. Compound heterozygous knockout (hKO) mutations in succinate dehydrogenase (Sdh; mitochondrial complex II) genes Sdhb, Sdhc, and Sdhd reduced Sdh subunit protein levels, reduced RDW, and increased healthy life span compared with WT mice in chronic hypoxia. RDW-SD, a direct measure of MCV variability, and the SD of MCV showed the most statistically significant reductions in Sdh hKO mice. Tissue metabolomic profiling of 147 common metabolites showed the largest increase in succinate with elevated succinate/fumarate and succinate/oxoglutarate (2-ketoglutarate) ratios in Sdh hKO mice. These results demonstrate that mitochondrial complex II level is an underlying determinant of both RDW and healthy life span in hypoxia and suggest that therapeutic targeting of Sdh might reduce high RDW-associated clinical mortality in hypoxic diseases.

Depleting receptor tyrosine kinases EGFR and HER2 overcomes resistance to EGFR inhibitors in colorectal cancer.

BACKGROUND: Epidermal growth factor receptor (EGFR) inhibitors, including cetuximab and panitumumab, are valuable therapeutics for colorectal cancer (CRC), but resistance to these inhibitors is common. The reason for such resistance is not well understood, which hampers development of better therapeutic strategies. Although activating mutations in KRAS, BRAF and PIK3CA are considered major drivers of CRC resistance to EGFR inhibitors, therapeutic targeting of these drug resistance drivers has not produced substantial clinical benefit. METHODS: We exploited cell lines and mouse tumor models (cell line xenografts and patient derived xenografts) for experiments of genetic and pharmacologic depletion of EGFR and/or its family member HER2, including EGFR mutants, inhibition of EGFR ligand shedding, and biochemical analysis of signaling proteins, to delineate the mechanism of CRC resistance to EGFR inhibitors and to assess the therapeutic activity of PEPDG278D, which is a recombinant human protein that induces the degradation of both EGFR and HER2. RESULTS: The sensitivity of CRC cells to cetuximab and panitumumab correlates with the ability of these drugs to induce EGFR downregulation. PEPDG278D strongly inhibits oncogenic signaling and growth of CRC cells by causing profound depletion of EGFR and HER2, regardless of activating mutations of KRAS, BRAF and PIK3CA. siRNA knockdown of EGFR or HER2 also inhibits CRC cells resistant to EGFR inhibitors. Tumors harboring mutated KRAS, BRAF and/or PIK3CA also overexpress EGFR ligands, further suggesting that EGFR signaling remains important to the tumors. While excessive tumor-generated high-affinity EGFR ligands block target engagement by PEPDG278D, aderbasib, an inhibitor of ADAM10 and ADAM17, enables PEPDG278D to exert strong antitumor activity by inhibiting ligand shedding. Moreover, adding fluorouracil, which is commonly used in CRC treatment, to the combination of PEPDG278D and aderbasib further enhances tumor inhibition. CONCLUSIONS: Our study shows that CRC resistance to EGFR inhibitors results primarily from the inability of the inhibitors to downregulate their target and that a PEPDG278D-based combination treatment overcomes the resistance.

Tumor-Avid 3-(1'-Hexyloxy)ethyl-3-devinylpyrpyropheophorbide-a (HPPH)-3Gd(III)tetraxetan (DOTA) Conjugate Defines Primary Tumors and Metastases.

3-(1'-Hexyloxyethyl)-3-devinylpyropheophorbide-a (HPPH or Photochlor), a tumor-avid chlorophyll a derivative currently undergoing human clinical trials, was conjugated with mono-, di-, and tri-Gd(III)tetraxetan (DOTA) moieties. The T1/T2 relaxivity and in vitro PDT efficacy of these conjugates were determined. The tumor specificity of the most promising conjugate was also investigated at various time points in mice and rats bearing colon tumors, as well as rabbits bearing widespread metastases from VX2 systemic arterial disseminated metastases. All the conjugates showed significant T1 and T2 relaxivities. However, the conjugate containing 3-Gd(III)-aminoethylamido-DOTA at position 17 of HPPH demonstrated great potential for tumor imaging by both MR and fluorescence while maintaining its PDT efficacy. At an MR imaging dose (10 µmol/kg), HPPH-3Gd(III)DOTA did not cause any significant organ toxicity in mice, indicating its potential as a cancer imaging (MR and fluorescence) agent with an option to treat cancer by photodynamic therapy (PDT).

In Vivo Models for Studying Interstitial Photodynamic Therapy of Locally Advanced Cancer.

Interstitial photodynamic therapy (I-PDT) is a promising therapy considered for patients with locally advanced cancer. In I-PDT, laser fibers are inserted into the tumor for effective illumination and activation of the photosensitizer in a large tumor. The intratumoral light irradiance and fluence are critical parameters that affect the response to I-PDT. In vivo animal models are required to conduct light dose studies, to define optimal irradiance and fluence for I-PDT. Here we describe two animal models with locally advanced tumors that can be used to evaluate the response to I-PDT. One model is the C3H mouse bearing large subcutaneous SCCVII carcinoma (400-600 mm3). Using this murine model, multiple light regimens with one or two optical fibers with cylindrical diffuser ends (cylindrical diffuser fiber, CDF) can be used to study tumor response to I-PDT. However, tissue heating may occur when 630 nm therapeutic light is delivered through CDF at an intensity ≥60 mW/cm and energy ≥100 J/cm. These thermal effects can impact tumor response while treating locally advanced mice tumors. Magnetic resonance imaging and thermometry can be used to study these thermal effects. A larger animal model, New Zealand White rabbit with VX2 carcinoma (~5000 mm3) implanted in either the sternomastoid (neck implantation model) or the biceps femoris muscle (thigh implantation model), can be used to study I-PDT with image-based pretreatment planning using computed tomography. In the VX2 model, the light delivery can include the use of multiple laser fibers to test light dosimetry and delivery that are relevant for clinical use of I-PDT.

Fungal mycobiome drives IL-33 secretion and type 2 immunity in pancreatic cancer.

TH2 cells and innate lymphoid cells 2 (ILC2) can stimulate tumor growth by secreting pro-tumorigenic cytokines such as interleukin-4 (IL-4), IL-5, and IL-13. However, the mechanisms by which type 2 immune cells traffic to the tumor microenvironment are unknown. Here, we show that oncogenic KrasG12D increases IL-33 expression in pancreatic ductal adenocarcinoma (PDAC) cells, which recruits and activates TH2 and ILC2 cells. Correspondingly, cancer-cell-specific deletion of IL-33 reduces TH2 and ILC2 recruitment and promotes tumor regression. Unexpectedly, IL-33 secretion is dependent on the intratumoral fungal mycobiome. Genetic deletion of IL-33 or anti-fungal treatment decreases TH2 and ILC2 infiltration and increases survival. Consistently, high IL-33 expression is observed in approximately 20% of human PDAC, and expression is mainly restricted to cancer cells. These data expand our knowledge of the mechanisms driving PDAC tumor progression and identify therapeutically targetable pathways involving intratumoral mycobiome-driven secretion of IL-33.

Using Mice to Model Human Disease: Understanding the Roles of Baseline Housing-Induced and Experimentally Imposed Stresses in Animal Welfare and Experimental Reproducibility.

Mice are the most common animal used to study disease, but there are real concerns about the reproducibility of many of these experiments. This review discusses how several different sources of chronic stress can directly impact experimental outcomes. Mandated housing conditions induce an underappreciated level of chronic stress but are not usually considered or reported as part of the experimental design. Since chronic stress plays a critical role in the development and progression of many somatic diseases including cancer, obesity, and auto-immune diseases, this baseline stress can directly affect outcomes of such experiments. To study the role of stress in both physical and psychiatric diseases, there has been a proliferation of protocols for imposing chronic stress on mice. For somatic diseases, biomarkers can be used to compare the models with the disease in patients, but to evaluate the validity of psychiatric models, behavioral tests are carried out to assess changes in behavior and these tests may themselves cause an underappreciated degree of additional stress. Therefore, it is important for animal welfare to reduce baseline stress and select the most humane protocols for inducing and assessing chronic stress to obtain the most reliable outcomes.

Small Endogeneous Peptide Mitigates Myocardial Remodeling in a Mouse Model of Cardioselective Galectin-3 Overexpression.

BACKGROUND: Myocardial Gal3 (galectin-3) expression is associated with cardiac inflammation and fibrosis. Increased Gal3 portends susceptibility to heart failure and death. There are no data reporting the causative role of Gal3 to mediate cardiac fibro-inflammatory response and heart failure. METHODS: We developed a cardioselective Gal3 gain-of-function mouse (Gal3+/+) using α-myosin heavy chain promotor. We confirmed Gal3-transgene expression with real-time polymerase chain reaction and quantified cardiac/circulating Gal3 with Western blot and immunoassays. We used echocardiogram and cardiac magnetic resonance imaging to measure cardiac volumes, function, and myocardial velocities. Ex vivo, we studied myocardial inflammation/fibrosis and downstream TGF (transforming growth factor) ß1-mRNA expression. We examined the effects of acute myocardial ischemia in presence of excess Gal3 by inducing acute myocardial infarction in mice. Two subsets of mice including mice treated with N-acetyl-seryl-aspartyl-lysyl-proline (a Gal3-inhibitor) and mice with genetic Gal3 loss-of-function (Gal3-/-) were studied for comparative analysis of Gal3 function. RESULTS: Gal3+/+ mice had increased cardiac/circulating Gal3. Gal3+/+ mice showed excess pericardial fat pad, dilated ventricles and cardiac dysfunction, which was partly normalized by N-acetyl-seryl-aspartyl-lysyl-proline. Cardiac magnetic resonance imaging showed reduced myocardial contractile velocities in Gal3+/+. The majority of Gal3+/+ mice did not survive acute myocardial infarction, and the survivors had profound cardiac dysfunction. Myocardial histology of Gal3+/+ mice showed macrophage/mast-cell infiltration, fibrosis and higher TGFß1-mRNA expression, which were mitigated by both Gal3 gene deletion and N-acetyl-seryl-aspartyl-lysyl-proline administration. CONCLUSIONS: Our study shows that cardioselective Gal3 overexpression leads to multiple cardiac phenotypic defects including ventricular dilation and cardiac dysfunction. Pharmacological Gal3 inhibition conferred protective effects with reduction of inflammation and fibrosis. Our study highlights the importance of translational studies to counteract Gal3 function and prevent cardiac dysfunction.

Liver background uptake of [18F]FLT in PET imaging.

High liver uptake presents a problem for 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) as a radiotracer for imaging cellular proliferation in the liver with positron emission tomography (PET). This investigation re-visited some issues related to the high liver background uptake of [18F]FLT with an animal model of woodchucks. Several enzymes involved in the hepatic catabolism of FLT, thymidine phosphorylase (TP, TYMP), uridine 5'-diphospho-glucuronosyl-transferases (UDP-GTs, short for UGTs), and ß-glucuronidase (GUSB), their homology as well as hepatic expression between the human and the woodchuck was examined. Inhibitors of these enzymes, TP inhibitor (TPI) tipiracil hydrochloride, UGT inhibitor probenecid, ß-glucuronidase inhibitor L-aspartate, were administered to the animals at human equivalent doses either intravenously (i.v.) and orally before the injection of tracer-dose [18F]FLT for PET imaging to examine any changes in liver uptake. Liver tissue samples were harvested from the animals after PET imaging and used to perform polymerase chain reaction (PCR) for TP expression or assays for enzymatic activities of TP and ß-glucuronidase. Non-radiolabeled (cold) FLT was also applied for enzyme saturation. Animals administered with TPI displayed lower radioactivity in the liver in comparison with the baseline scan. The application of probenecid did not change [18F]FLT liver uptake even though it reduced renal uptake. L-aspartate reduced the liver background uptake of [18F]FLT slightly. The application of cold FLT reduced overall uptake of [18F]FLT including the liver background. Therefore, the combined application of cold FLT and [18F]FLT merits further clinical investigation for reducing liver background uptake of [18F]FLT.

Highlights on the imaging (nuclear/fluorescence) and phototherapeutic potential of a tri-functional chlorophyll-a analog with no significant toxicity in mice and rats.

Herein we report the positron emission tomography (PET) imaging potential of a 124I-labeled radiopharmaceutical (PET-ONCO). In tumored mice, it shows high uptake in a variety of tumors: brain (GL261, U87), Colon (Colon26), lung (Lewis lung), breast (4 T1), bladder (UMUC3), pancreas (PANC-1) implanted in mice. This agent also shows promise for imaging associated metastatic disease (breast to lung, to bone). Interestingly, the iodinated compound derived from chlorophyll-a, in combination with the corresponding 124I-analog, can serve as a dual imaging agent (PET/fluorescence, complimentary to each other), with an option of photodynamic therapy (PDT). In contrast to Fluorine-18 (half-life 110 min), the Iodine-124 radionuclide has a physical half-life of roughly 4 days. Thus, unlike 18F-FDG, PET-ONCO can be transported longer distances. While the time for optimal tumor-uptake was observed at 24 h, improved tumor contrasts of both primary and metastasis were obtained at 48 and 72 h post- injection (i. v.) of PET-ONCO. In both mice and rats at a single dose study, PET-ONCO did not show any organ toxicity.

A Translational Hepatic Artery Infusion (HAI) Model for Hepatocellular Carcinoma in Woodchucks.

BACKGROUND: Woodchucks (Marmota monax) are a well-accepted animal model for the investigation of spontaneous hepatocellular carcinoma (HCC). As HCC tumors obtain nutrient blood supply exclusively from the hepatic artery, hepatic artery infusion (HAI) has been applied to HCC. However, there is a scarcity of experimental animal models to standardize drug regimens and examine novel agents. The purpose of this study was to establish an HAI model in woodchucks. MATERIALS AND METHODS: HAI ports were placed in the gastroduodenal artery (GDA) of 11 woodchucks. The ports were infused with either a vehicle (dextrose 5% in water) or an experimental drug, CBL0137, once a week for 3 wk. Technical success rates, anatomical variation, morbidity and mortality, and tumor responses between groups were analyzed. RESULTS: The GDA access was feasible and reproducible in all woodchucks (11/11). The average operation time was 95 ± 20 min with no increase in the levels of liver enzymes detected from either infusate. The most common morbidity of CBL0137 therapy was anorexia after surgery. One woodchuck died due to hemorrhage at the gallbladder removal site from hepatic coagulopathy. Significantly higher CBL0137 concentrations were measured in the liver compared with blood after each HAI. Tumor growth was suppressed after multiple CBL0137 HAI treatments which corresponded to greater T cell infiltration and increased tumor cell apoptosis. CONCLUSIONS: HAI via GDA was a feasible and reproducible approach with low morbidity and mortality in woodchucks. The described techniques serve as a reliable platform for the identification and characterization of therapeutics for HCC.

Delayed response to proton beam treatment of hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) has become one of the leading causes of cancer death worldwide. There has been anecdotal report regarding the effectiveness of proton beam treatment for HCC. In this pre-clinical investigation, the woodchuck model of viral hepatitis infection-induced HCC was used for proton beam treatment experiment. The radiopaque fiducial markers that are biodegradable were injected around the tumor under ultrasound guidance to facilitate positioning in sequential treatments. An α cradle mode was used to ensure reproducibility of animal positioning on the treatment couch. A CT scan was performed first for contouring by a radiation oncologist. The CT data set with contours was then exported for dose planning. Three fractionations, each 750 CcGyE, were applied every other day with a Mevion S250 passive scattering proton therapy system. Multiphase contrast-enhanced CT scans were performed after the treatment and at later times for follow-ups. 3 weeks post-treatment, shrinking of the HCC nodule was detected and constituted to a partial response (30% reduction along the long axis). By week nine after treatment, the nodule disappeared during the arterial phase of multiphase contrast-enhanced CT scan. Pathological evaluation corroborated with this imaging response. A delayed, but complete imaging response to proton beam treatment applied to HCC was achieved with this unique and clinically relevant animal model of HCC.

Development and Validation of a Clinically Relevant Workflow for MR-Guided Volumetric Arc Therapy in a Rabbit Model of Head and Neck Cancer.

There is increased interest in the use of magnetic resonance imaging (MRI) for guiding radiation therapy (RT) in the clinical setting. In this regard, preclinical studies can play an important role in understanding the added value of MRI in RT planning. In the present study, we developed and validated a clinically relevant integrated workflow for MRI-guided volumetric arc therapy (VMAT) in a VX2 rabbit neck tumor model of HNSCC. In addition to demonstrating safety and feasibility, we examined the therapeutic impact of MR-guided VMAT using a single high dose to obtain proof-of-concept and compared the response to conventional 2D-RT. Contrast-enhanced MRI (CE-MRI) provided excellent soft tissue contrast for accurate tumor segmentation for VMAT. Notably, MRI-guided RT enabled improved tumor targeting ability and minimal dose to organs at risk (OAR) compared to 2D-RT, which resulted in notable morbidity within a few weeks of RT. Our results highlight the value of integrating MRI into the workflow for VMAT for improved delineation of tumor anatomy and optimal treatment planning. The model combined with the multimodal imaging approach can serve as a valuable platform for the conduct of preclinical RT trials.

Irradiance, Photofrin® Dose and Initial Tumor Volume are Key Predictors of Response to Interstitial Photodynamic Therapy of Locally Advanced Cancers in Translational Models.

The objective of the present study was to develop a predictive model for Photofrin® -mediated interstitial photodynamic therapy (I-PDT) of locally advanced tumors. Our finite element method was used to simulate 630-nm intratumoral irradiance and fluence for C3H mice and New Zealand White rabbits bearing large squamous cell carcinomas. Animals were treated with light only or I-PDT using the same light settings. I-PDT was administered with Photofrin® at 5.0 or 6.6 mg kg-1 , 24 h drug-light interval. The simulated threshold fluence was fixed at 45 J cm-2 while the simulated threshold irradiance varied, intratumorally. No cures were obtained in the mice treated with a threshold irradiance of 5.4 mW cm-2 . However, 20-90% of the mice were cured when the threshold irradiances were ≥8.6 mW cm-2 . In the rabbits treated with I-PDT, 13 of the 14 VX2 tumors showed either local control or were cured when threshold irradiances were ≥15.3 mW cm-2 and fluence was 45 J cm-2 . No tumor growth delay was observed in VX2 treated with light only (n = 3). In the mouse studies, there was a high probability (92.7%) of predicting cure when the initial tumor volume was below the median (493.9 mm3 ) and I-PDT was administered with a threshold intratumoral irradiance ≥8.6 mW cm-2 .