Imaging tumor variation in response to photodynamic therapy in pancreatic cancer xenograft models

Advances in the Application of Preclinical Models in Photodynamic Therapy for Tumor: A Narrative Review

Photodynamic therapy (PDT) is a non-invasive laser light local treatment that has been utilized in the management of a wide variety of solid tumors. Moreover, the evaluation of efficacy, adverse reactions, the development of new photosensitizers and the latest therapeutic regimens are inseparable from the preliminary exploration in preclinical studies. Therefore, our aim was to better comprehend the characteristics and limitations of these models and to provide a reference for related research.

METHODS

We searched the databases, including PubMed, Web of Science and Scopus for the past 25 years of original research articles on the feasibility of PDT in tumor treatment based on preclinical experiments and animal models. We provided insights into inclusion and exclusion criteria and ultimately selected 40 articles for data synthesis.

RESULTS

After summarizing and comparing the methods and results of these studies, the experimental model selection map was drawn. There are 7 main preclinical models, which are used for different research objectives according to their characteristics.

CONCLUSIONS

Based on this narrative review, preclinical experimental models are crucial to the development and promotion of PDT for tumors. The traditional animal models have some limitations, and the emergence of organoids may be a promising new insight.

Preparation of zinc phthalocyanine-loaded amphiphilic phosphonium chitosan nanomicelles for enhancement of photodynamic therapy efficacy

To increase the solubility and the encapsulation of zinc phthalocyanine (ZnPc) photosensitizer for photodynamic therapy (PDT), a positively charged amphiphilic phosphonium chitosan nanomicelle with multi-benzene structure was developed, and its application to PDT was explored. N-acetyl-l-phenylalanine-(4-carboxybutyl) triphenylphosphonium bromide chitosan (CTPB-CS-NAP), a chitosan derivative with tunable amphiphilicity, was synthesized first. ZnPc was encapsulated in CTPB-CS-NAP at the critical micelle concentration (CMC) of 4.898 mg/L by a hydrophobic self-assembly method to form ZnPc-loaded nanomicelles (ZnPc@CTPB-CS-NAP). The method gives the highest encapsulation efficiency and drug loading of 89.4 % and 22.3 %, respectively. ZnPc@CTPB-CS-NAP is stably dispersed in aqueous solution and shows the average particle size of 103±5 nm. PDT experiments suggest the phototoxicity of ZnPc@CTPB-CS-NAP is much higher than that of ZnPc, but no obvious dark cytotoxicity is observed. Our study has provided a new strategy for improving the photodynamic therapy efficacy of hydrophobic photosensitizer by the encapsulation with chitosan derivative carriers.

Radiolabeling, In Vitro Cell Uptake, and In Vivo Photodynamic Therapy Potential of Targeted Mesoporous Silica Nanoparticles Containing Zinc Phthalocyanine

Photodynamic therapy (PDT) is a noninvasive therapy based on the photodynamic effect. In this study, we sought to determine intracellular uptake and in vivo photodynamic therapy potential of Zn phthalocyanine-loaded mesoporous silica nanoparticles (MSNP5) against pancreatic cancer cells. MSNP5 were labeled with ¹³¹I; the radiolabeling efficiency was found to 95.5 ± 1.2% in pH 9 and 60 min reaction time. Besides, the highest intracellular uptake yields of ¹³¹I-MSNP5 nanoparticles in MIA PaCa-2, AsPC-1, and PANC-1 cells were determined as 43.9 ± 3.8%, 41.8 ± 0.2%, and 37.9 ± 1.3%, respectively, at 24 h incubation time. In vivo PDT studies were performed with subcutaneous xenograft cancer model nude mice with AsPC-1 pancreatic cancer cells. For photodynamic therapy, 685 nm red laser light 100 J/cm² light dose using and 5-20 μM ZnPc containing MSNP5 concentrations were applied. Histopathological studies revealed that the ratio of necrosis in tumor tissue was higher in the treatment group than the control groups.

Heat shock protein 90-targeted photodynamic therapy enables treatment of subcutaneous and visceral tumors

Photodynamic therapy (PDT) ablates malignancies by applying focused near-infrared (nIR) light onto a lesion of interest after systemic administration of a photosensitizer (PS); however, the accumulation of existing PS is not tumor-exclusive. We developed a tumor-localizing strategy for PDT, exploiting the high expression of heat shock protein 90 (Hsp90) in cancer cells to retain high concentrations of PS by tethering a small molecule Hsp90 inhibitor to a PS (verteporfin, VP) to create an Hsp90-targeted PS (HS201). HS201 accumulates to a greater extent than VP in breast cancer cells both in vitro and in vivo, resulting in increased treatment efficacy of HS201-PDT in various human breast cancer xenografts regardless of molecular and clinical subtypes. The therapeutic index achieved with Hsp90-targeted PDT would permit treatment not only of localized tumors, but also more diffusely infiltrating processes such as inflammatory breast cancer.

Elastography Can Map the Local Inverse Relationship between Shear Modulus and Drug Delivery within the Pancreatic Ductal Adenocarcinoma Microenvironment

PURPOSE

High tissue pressure prevents chemotherapeutics from reaching the core of pancreatic tumors. Therefore, targeted therapies have been developed to reduce this pressure. While point probes have shown the effectiveness of these pressure-reducing therapies via single-location estimates, ultrasound elastography is now widely available as an imaging technique to provide real-time spatial maps of shear modulus (tissue stiffness). However, the relationship between shear modulus and the underlying tumor microenvironmental causes of high tissue pressure has not been investigated. In this work, elastography was used to investigate how shear modulus influences drug delivery in situ, and how it correlates with collagen density, hyaluronic acid content, and patent vessel density-features of the tumor microenvironment known to influence tissue pressure.

EXPERIMENTAL DESIGN

Intravenous injection of verteporfin, an approved human fluorescent drug, was used in two pancreatic cancer xenograft models [AsPC-1 (n = 25) and BxPC-3 (n = 25)].

RESULTS

Fluorescence intensity was higher in AsPC-1 tumors than in BxPC-3 tumors (P < 0.0001). Comparing drug uptake images and shear wave elastographic images with histologic images revealed that: (i) drug delivery and shear modulus were inversely related, (ii) shear modulus increased linearly with increasing collagen density, and (iii) shear modulus was marginally correlated with the local assessment of hyaluronic acid content.

CONCLUSIONS

These results demonstrate that elastography could guide targeted therapy and/or identify patients with highly elevated tissue pressure.See related commentary by Nia et al., p. 2024.

Size-dependent Tumor Response to Photodynamic Therapy and Irinotecan Monotherapies Revealed by Longitudinal Ultrasound Monitoring in an Orthotopic Pancreatic Cancer Model

Longitudinal monitoring of tumor size in vivo can provide important biological information about disease progression and treatment efficacy that is not captured by other modes of quantification. Ultrasound enables high-throughput evaluation of orthotopic mouse models via fast acquisition of three-dimensional tumor images and calculation of volume with a reasonable degree of accuracy. Herein, we compare orthotopic pancreatic tumor volume measurements determined by ultrasound with volume measured by calipers and tumor weight, and found strong correlations between the three modalities over a large range of tumor sizes, suggesting ultrasound can accurately quantify tumor volumes in this model. Furthermore, we demonstrate the unique ability of longitudinal treatment monitoring to reveal a tumor size-dependent response to Benzoporphyrin Derivative photodynamic therapy (BPD-PDT) and irinotecan. Small tumors (5-35 mm³ ) were found to respond well to a single round of PDT, while large tumors (35-65 mm³ ) showed no response to the same treatment. These results highlight the role that tumor size can play in preclinical interpretation of treatment response and more generally suggest that careful evaluation of subtle biological features such as this must be carefully considered in order to grant a more comprehensive understanding of disease biology in vivo.

Chemotherapy and Radiofrequency-Induced Mild Hyperthermia Combined Treatment of Orthotopic Pancreatic Ductal Adenocarcinoma Xenografts

Patients with pancreatic ductal adenocarcinomas (PDAC) have one of the poorest survival rates of all cancers. The main reason for this is related to the unique tumor stroma and poor vascularization of PDAC. As a consequence, chemotherapeutic drugs, such as nab-paclitaxel and gemcitabine, cannot efficiently penetrate into the tumor tissue. Non-invasive radiofrequency (RF) mild hyperthermia treatment was proposed as a synergistic therapy to enhance drug uptake into the tumor by increasing tumor vascular inflow and perfusion, thus, increasing the effect of chemotherapy. RF-induced hyperthermia is a safer and non-invasive technique of tumor heating compared to conventional contact heating procedures. In this study, we investigated the short- and long-term effects (~20 days and 65 days, respectively) of combination chemotherapy and RF hyperthermia in an orthotopic PDAC model in mice. The benefit of nab-paclitaxel and gemcitabine treatment was confirmed in mice; however, the effect of treatment was statistically insignificant in comparison to saline treated mice during long-term observation. The benefit of RF was minimal in the short-term and completely insignificant during long-term observation.

Early assessment of tumor response to photodynamic therapy using combined diffuse optical and diffuse correlation spectroscopy to predict treatment outcome

Photodynamic therapy (PDT) of cancer involves the use of a photosensitizer that can be light-activated to eradicate tumors via direct cytotoxicity, damage to tumor vasculature and stimulating the body's immune system. Treatment outcome may vary between individuals even under the same regime; therefore a non-invasive tumor response monitoring system will be useful for personalization of the treatment protocol. We present the combined use of diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) to provide early assessment of tumor response. The relative tissue oxygen saturation (rStO2) and relative blood flow (rBF) in tumors were measured using DOS and DCS respectively before and after PDT with reference to baseline values in a mouse model. In complete responders, PDT-induced decreases in both rStO2 and rBF levels were observed at 3 h post-PDT and the rBF remained low until 48 h post-PDT. Recovery of these parameters to baseline values was observed around 2 weeks after PDT. In partial responders, the rStO2 and rBF levels also decreased at 3 h post PDT, however the rBF values returned toward baseline values earlier at 24 h post-PDT. In contrast, the rStO2 and rBF readings in control tumors showed fluctuations above the baseline values within the first 48 h. Therefore tumor response can be predicted at 3 to 48 h post-PDT. Recovery or sustained decreases in the rBF at 48 h post-PDT corresponded to long-term tumor control. Diffuse optical measurements can thus facilitate early assessment of tumor response. This approach can enable physicians to personalize PDT treatment regimens for best outcomes.

Separation of Solid Stress From Interstitial Fluid Pressure in Pancreas Cancer Correlates With Collagen Area Fraction

Elevated total tissue pressure (TTP) in pancreatic adenocarcinoma is often associated with stress applied by cellular proliferation and hydrated hyaluronic acid osmotic swelling; however, the causal roles of collagen in total tissue pressure have yet to be clearly measured. This study illustrates one direct correlation between total tissue pressure and increased deposition of collagen within the tissue matrix. This observation comes from a new modification to a conventional piezoelectric pressure catheter, used to independently separate and quantify total tissue pressure, solid stress (SS), and interstitial fluid pressure (IFP) within the same tumor location, thereby clarifying the relationship between these parameters. Additionally, total tissue pressure shows a direct correlation with verteporfin uptake, demonstrating the impediment of systemically delivered molecules with increased tissue hypertension.

Interstitial Photodynamic Therapy-A Focused Review

Multiple clinical studies have shown that interstitial photodynamic therapy (I-PDT) is a promising modality in the treatment of locally-advanced cancerous tumors. However, the utilization of I-PDT has been limited to several centers. The objective of this focused review is to highlight the different approaches employed to administer I-PDT with photosensitizers that are either approved or in clinical studies for the treatment of prostate cancer, pancreatic cancer, head and neck cancer, and brain cancer. Our review suggests that I-PDT is a promising treatment in patients with large-volume or thick tumors. Image-based treatment planning and real-time dosimetry are required to optimize and further advance the utilization of I-PDT. In addition, pre- and post-imaging using computed tomography (CT) with contrast may be utilized to assess the response.

Animal models for photodynamic therapy (PDT)

Photodynamic therapy (PDT) combines visible light and photosensitizing dyes. Different animal models have been used to test PDT for cancer, infectious disease and cardiovascular disease. Mouse models of tumours include subcutaneous, orthotopic, syngeneic, xenograft, autochthonous and genetically modified.

Photodynamic therapy (PDT) employs non-toxic dyes called photosensitizers (PSs), which absorb visible light to give the excited singlet state, followed by the long-lived triplet state that can undergo photochemistry. In the presence of ambient oxygen, reactive oxygen species (ROS), such as singlet oxygen and hydroxyl radicals are formed that are able to kill cancer cells, inactivate microbial pathogens and destroy unwanted tissue. Although there are already several clinically approved PSs for various disease indications, many studies around the world are using animal models to investigate the further utility of PDT. The present review will cover the main groups of animal models that have been described in the literature. Cancer comprises the single biggest group of models including syngeneic mouse/rat tumours that can either be subcutaneous or orthotopic and allow the study of anti-tumour immune response; human tumours that need to be implanted in immunosuppressed hosts; carcinogen-induced tumours; and mice that have been genetically engineered to develop cancer (often by pathways similar to those in patients). Infections are the second biggest class of animal models and the anatomical sites include wounds, burns, oral cavity, ears, eyes, nose etc. Responsible pathogens can include Gram-positive and Gram-negative bacteria, fungi, viruses and parasites. A smaller and diverse group of miscellaneous animal models have been reported that allow PDT to be tested in ophthalmology, atherosclerosis, atrial fibrillation, dermatology and wound healing. Successful studies using animal models of PDT are blazing the trail for tomorrow's clinical approvals.

Porphyrin-based photosensitizers and the corresponding multifunctional nanoplatforms for cancer-imaging and phototherapy

This review article briefly describes: (a) the advantages in developing multifunctional nanoparticles for cancer-imaging and therapy, (b) the advantages and limitations of most of the porphyrin-based compounds in fluorescence imaging and photodynamic therapy (PDT), (c) problems associated with current Food and Drug Administration (FDA) approved photosensitizers, (d) challenges in developing in vivo target-specific PDT agents, (e) development of porphyrin-based nuclear-imaging agents (PET, SPECT) with an option of PDT, (f) the importance of light dosimetry in PDT, (g) the role of whole body or local hyperthermia in enhancing tumor-uptake, tumor-imaging and phototherapy and finally, (h) the advantages of photosensitizer-gold nanocages (Ps- Au NC) in photoacoustic and PDT.

Quantitative in vivo immunohistochemistry of epidermal growth factor receptor using a receptor concentration imaging approach

As receptor-targeted therapeutics become increasingly used in clinical oncology, the ability to quantify protein expression and pharmacokinetics in vivo is imperative to ensure successful individualized treatment plans. Current standards for receptor analysis are performed on extracted tissues. These measurements are static and often physiologically irrelevant; therefore, only a partial picture of available receptors for drug targeting in vivo is provided. Until recently, in vivo measurements were limited by the inability to separate delivery, binding, and retention effects, but this can be circumvented by a dual-tracer approach for referencing the detected signal. We hypothesized that in vivo receptor concentration imaging (RCI) would be superior to ex vivo immunohistochemistry (IHC). Using multiple xenograft tumor models with varying EGFR expression, we determined the EGFR concentration in each model using a novel targeted agent (anti-EGFR affibody-IRDye800CW conjugate) along with a simultaneously delivered reference agent (control affibody-IRDye680RD conjugate). The RCI-calculated in vivo receptor concentration was strongly correlated with ex vivo pathologist-scored IHC and computer-quantified ex vivo immunofluorescence. In contrast, no correlation was observed with ex vivo Western blot analysis or in vitro flow-cytometry assays. Overall, our results argue that in vivo RCI provides a robust measure of receptor expression equivalent to ex vivo immunostaining, with implications for use in noninvasive monitoring of therapy or therapeutic guidance during surgery.

Establishment of a Non-Invasive Semi-Quantitative Bioluminescent Imaging Method for Monitoring of an Orthotopic Esophageal Cancer Mouse Model

Orthotopic models of various types of tumors are widely used in anti-tumor therapeutic experiments in preclinical studies. However, there are few ways to appropriately monitor therapeutic effect in orthotopic tumor models, especially for tumors invisible from the outside. In this study we aimed to establish a non-invasive semi-quantitative bioluminescent imaging method of monitoring an orthotopic esophageal cancer mouse model. We confirmed that the TE8 esophageal cancer cell line implanted orthotopically into the abdominal esophagus of nu/nu mice (n = 5) developed not only a main tumor at the implanted site, but also local lymph node metastases and peritoneal disseminations within 6 weeks after inoculation. We established a TE8 cell line that stably expressed the firefly luciferase gene (TE8-Luc). We showed that TE8-Luc cells implanted subcutaneously into nu/nu mice (n = 5) grew over time until 5 weeks after inoculation. Tumor volume was strongly correlated with luminescent intensity emitted from the tumor, which was quantified using the IVIS imaging system. We then showed that TE8-Luc cells implanted orthotopically into the mouse abdominal esophagus (n = 8) also formed a tumor and that the luminescent intensity of such a tumor, as detected by IVIS, increased over time until 7 weeks after inoculation and was therefore likely to reflect tumor progression. We therefore propose that this orthotopic esophageal cancer model, monitored using the non-invasive semi-quantitative IVIS imaging system, will be useful for in vivo therapeutic experiments against esophageal cancer. This experimental setting is expected to contribute to the development of novel therapeutic technologies for esophageal cancer in preclinical studies.

Enhancement of phototoxicity against human pancreatic cancer cells with photosensitizer-encapsulated amphiphilic sodium alginate derivative nanoparticles

Photosensitizer-encapsulated amphiphilic sodium alginate derivative (Photosan-CSAD) nanoparticles were prepared because of their ability to enhance phototoxicity in the photodynamic therapy of pancreatic cancer. These nanoparticles are spherical, 150-250 nm in size as determined by transmission electron microscopy, and have negative zeta potentials. Upon incubation with human pancreatic cancer cells, the Photosan-CSAD nanoparticles showed high fluorescence activity and reactive oxygen species generation, resulting in strong phototoxicity. However, no dark toxicity was observed. Apoptosis played a leading role in the cell death process induced by the Photosan phototoxicity. These results demonstrate that the Photosan-CSAD nanoparticles are a candidate for the photodynamic therapy of pancreatic cancer.

Phase I/II study of verteporfin photodynamic therapy in locally advanced pancreatic cancer

Background:

Patients with pancreatic cancer have a poor prognosis apart from the few suitable for surgery. Photodynamic therapy (PDT) produces localised tissue necrosis but previous studies using the photosensitiser meso-tetrahydroxyphenylchlorin (mTHPC) caused prolonged skin photosensitivity. This study assessed a shorter acting photosensitiser, verteporfin.

Methods:

Fifteen inoperable patients with locally advanced cancers were sensitised with 0.4 mg kg⁻¹ verteporfin. After 60–90 min, laser light (690 nm) was delivered via single (13 patients) or multiple (2 patients) fibres positioned percutaneously under computed tomography (CT) guidance, the light dose escalating (initially 5 J, doubling after each three patients) until 12 mm of necrosis was achieved consistently.

Results:

In all, 12 mm lesions were seen consistently at 40 J, but with considerable variation in necrosis volume (mean volume 3.5 cm³ at 40 J). Minor, self-limiting extrapancreatic effects were seen in multifibre patients. No adverse interactions were seen in patients given chemotherapy or radiotherapy before or after PDT. After PDT, one patient underwent an R0 Whipple's pancreaticoduodenectomy.

Conclusions:

Verteporfin PDT-induced tumour necrosis in locally advanced pancreatic cancer is feasible and safe. It can be delivered with a much shorter drug light interval and with less photosensitivity than with older compounds.

Contrast enhanced-magnetic resonance imaging as a surrogate to map verteporfin delivery in photodynamic therapy

The use of in vivo contrast-enhanced magnetic resonance (MR) imaging as a surrogate for photosensitizer (verteporfin) dosimetry in photodynamic therapy of pancreas cancer is demonstrated by correlating MR contrast uptake to ex vivo fluorescence images on excised tissue. An orthotopic pancreatic xenograft mouse model was used for the study. A strong correlation (r = 0.57) was found for bulk intensity measurements of T1-weighted gadolinium enhancement and verteporfin fluorescence in the tumor region of interest. The use of contrast-enhanced MR imaging shows promise as a method for treatment planning and photosensitizer dosimetry in human photodynamic therapy (PDT) of pancreas cancer.

PDT dose parameters impact tumoricidal durability and cell death pathways in a 3D ovarian cancer model

The successful implementation of photodynamic therapy (PDT)-based regimens depends on an improved understanding of the dosimetric and biological factors that govern therapeutic variability. Here, the kinetics of tumor destruction and regrowth are characterized by systematically varying benzoporphyrin derivative (BPD)-light combinations to achieve fixed PDT doses (M × J cm(-2)). Three endpoints were used to evaluate treatment response: (1) Viability evaluated every 24 h for 5 days post-PDT; (2) Photobleaching assessed immediately post-PDT; and (3) Caspase-3 activation determined 24 h post-PDT. The specific BPD-light parameters used to construct a given PDT dose significantly impact not only acute cytotoxic efficacy, but also treatment durability. For each dose, PDT with 0.25 μM BPD produces the most significant and sustained reduction in normalized viability compared to 1 and 10 μM BPD. Percent photobleaching correlates with normalized viability for a range of PDT doses achieved within BPD concentrations. To produce a cytotoxic response with 10 μM BPD that is comparable to 0.25 and 1 μM BPD a reduction in irradiance from 150 to 0.5 mW cm(-2) is required. Activated caspase-3 does not correlate with normalized viability. The parameter-dependent durability of outcomes within fixed PDT doses provides opportunities for treatment customization and improved therapeutic planning.

Aminolevulinic acid (ALA): photodynamic detection and potential therapeutic applications

Aminolevulinic acid (ALA) is a heme precursor that may have potential applications for photodynamic detection and photodynamic therapy-based treatment of solid tumors in a variety of malignancies. ALA may have a role in other applications in surgical oncology based on its ability to discriminate neoplastic tissue from adjacent normal tissue. In this review, we provide a comprehensive summary of the published studies of ALA in noncutaneous solid malignancies.

In vivo quantification of tumor receptor binding potential with dual-reporter molecular imaging

PURPOSE

Receptor availability represents a key component of current cancer management. However, no approaches have been adopted to do this clinically, and the current standard of care is invasive tissue biopsy. A dual-reporter methodology capable of quantifying available receptor binding potential of tumors in vivo within a clinically relevant time scale is presented.

PROCEDURES

To test the methodology, a fluorescence imaging-based adaptation was validated against ex vivo and in vitro measures of epidermal growth factor receptor (EGFR) binding potential in four tumor lines in mice, each line expected to express a different level of EGFR.

RESULTS

A strong correlation was observed between in vivo and ex vivo measures of binding potential for all tumor lines (r = 0.99, p < 0.01, slope = 1.80 ± 0.48, and intercept = -0.58 ± 0.84) and between in vivo and in vitro for the three lines expressing the least amount of EGFR (r = 0.99, p < 0.01, slope = 0.64 ± 0.32, and intercept = 0.47 ± 0.51).

CONCLUSIONS

By providing a fast and robust measure of receptor density in tumors, the presented methodology has powerful implications for improving choices in cancer intervention, evaluation, and monitoring, and can be scaled to the clinic with an imaging modality like SPECT.

Dual-tracer background subtraction approach for fluorescent molecular tomography

Diffuse fluorescence tomography requires high contrast-to-background ratios to accurately reconstruct inclusions of interest. This is a problem when imaging the uptake of fluorescently labeled molecularly targeted tracers in tissue, which can result in high levels of heterogeneously distributed background uptake. We present a dual-tracer background subtraction approach, wherein signal from the uptake of an untargeted tracer is subtracted from targeted tracer signal prior to image reconstruction, resulting in maps of targeted tracer binding. The approach is demonstrated in simulations, a phantom study, and in a mouse glioma imaging study, demonstrating substantial improvement over conventional and homogenous background subtraction image reconstruction approaches.

High vascular delivery of EGF, but low receptor binding rate is observed in AsPC-1 tumors as compared to normal pancreas

PURPOSE

Cellular receptor targeted imaging agents present the potential to target extracellular molecular expression in cancerous lesions; however, the image contrast in vivo does not reflect the magnitude of overexpression expected from in vitro data. Here, the in vivo delivery and binding kinetics of epidermal growth factor receptor (EGFR) was determined for normal pancreas and AsPC-1 orthotopic pancreatic tumors known to overexpress EGFR.

PROCEDURES

EGFR in orthotopic xenograft AsPC-1 tumors was targeted with epidermal growth factor (EGF) conjugated with IRDye800CW. The transfer rate constants (k(e), K₁₂, k₂₁, k₂₃, and k₃₂) associated with a three-compartment model describing the vascular delivery, leakage rate and binding of targeted agents were determined experimentally. The plasma excretion rate, k (e), was determined from extracted blood plasma samples. K₁₂, k₂₁, and k₃₂ were determined from ex vivo tissue washing studies at time points ≥ 24 h. The measured in vivo uptake of IRDye800CW-EGF and a non-targeted tracer dye, IRDye700DX-carboxylate, injected simultaneously was used to determined k₂₃.

RESULTS

The vascular exchange of IRDye800CW-EGF in the orthotopic tumor (K₁₂ and k₂₁) was higher than in the AsPC-1 tumor as compared to normal pancreas, suggesting that more targeted agent can be taken up in tumor tissue. However, the cellular associated (binding) rate constant (k₂₃) was slightly lower for AsPC-1 pancreatic tumor (4.1 × 10(-4) s(-1)) than the normal pancreas (5.5 × 10(-4) s(-1)), implying that less binding is occurring.

CONCLUSIONS

Higher vascular delivery but low cellular association in the AsPC-1 tumor compared to the normal pancreas may be indicative of low receptor density due to low cellular content. This attribute of the AsPC-1 tumor may indicate one contributing cause of the difficulty in treating pancreatic tumors with cellular targeted agents.

Propentofylline decreases tumor growth in a rodent model of glioblastoma multiforme by a direct mechanism on microglia

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain cancer, with a median survival of less than 2 years after diagnosis. The tumor microenvironment plays a critical role in tumor invasion and progression. Microglia and infiltrating macrophages are the most abundant immune cells in the tumor. In the present study, we demonstrate that systemic propentofylline (PPF), an atypical methylxanthine with central nervous system (CNS) glial modulating and anti-inflammatory actions, significantly decreased tumor growth in a CNS-1 rat model of GBM by targeting microglia and not tumor cells. Rats received tumor injections of 1 × 10(5) CNS-1 cells in the right striatum with daily intraperitonial injections of PPF (50 mg/kg) or saline beginning the day of tumor injection. PPF did not cause apoptosis or decrease proliferation of CNS-1 tumor cells. Furthermore, we demonstrate, using in vitro methods, that PPF decreased microglial migration toward CNS-1 tumor cells and decreased MMP-9 expression. The effects of PPF were shown to be specific to microglia and not peripheral macrophages. These results support a differential functional role of resident microglia and infiltrating macrophages in the brain tumor environment. Our data highlight microglia as a crucial target for future therapeutic development and present PPF as a possible drug for treatment of human GBM.

Pancreatic cancer screening employing noncontrast magnetic resonance imaging combined with ultrasonography

PURPOSE

We have conducted an initial evaluation on the potential of combining noncontrast magnetic resonance imaging (MRI) and ultrasonography (US) to screen for pancreatic cancer.

MATERIALS AND METHODS

An independent ethics committee approved this study. A total of 2511 patients who underwent US were enrolled. Among them, noncontrast MRI was performed in patients in whom the entire pancreas was difficult to depict or in those with US-suspected pancreatic lesions. In total, using 1.5-T MRI, T1- and T2-weighted imaging, magnetic resonance cholangiopancreatography, and diffusion-weighted imaging, we acquired a variety of images. The efficacy of US and MRI in screening for pancreatic lesions, including pancreatic cancer, was evaluated.

RESULTS

Of 2511 patients, 184 underwent MRI, and the pancreas was demonstrated in all of them. Among the 2511, five pancreatic cancers were detected by MRI combined with US (detection rate 0.20%). Of the five pancreatic cancers, three were detected by US (detection rate 0.12%) and two by MRI. Four of the five pancreatic cancers were resectable.

CONCLUSION

By combining noncontrast MRI with US, pancreatic cancer can be detected with high accuracy. Other pancreatic lesions that require follow-up, including intraductal papillary mucinous neoplasms, can also be detected. Thus, pancreatic cancer screening with a combination of US and MRI is suggested.

Imaging evaluation of therapeutic response in patients with pancreatic cancer: recent advances

Chemoradiotherapy is the primary choice of non-surgical treatment of advanced pancreatic cancer, and diagnostic imaging plays an important role in objectively assessing early therapeutic response. This article systematically reviews the criteria for evaluation of therapeutic response in solid tumors and their application in pancreatic cancer, highlighting some key contents in imaging evaluation of therapeutic response in patients with pancreatic cancer.

Advances in photodynamic therapy for the treatment of hilar biliary tract cancer

The prognosis of patients with nonresectable hilar biliary tract cancer (hBTC) is poor. Responsiveness to chemotherapy or radiochemotherapy is moderate at best, and patients are at a high risk of dying early from complications of local tumor infiltration (e.g., cholestasis, septic cholangitis, empyema or liver failure) rather than systemic disease. Therefore, palliative local therapy for the prevention of tumor complications plays a central role and still yields the longest survival times. Photodynamic therapy (PDT) is a local-ablative, tumor tissue-specific treatment currently representing the standard of care for nonresectable hBTC. Throughout the literature, PDT plus biliary drainage achieves median survival times in the range of 9-21 months (average 14-16 months), compared with approximately 6 months for drainage only. This article summarizes the recent advances in preclinical and clinical experience of PDT for hBTC, including experimental in vitro and in vivo studies, clinical studies and an overview of the ongoing clinical trials.

Quantifying receptor density in vivo using a dual-probe approach with fluorescence molecular imaging

Molecular imaging technologies are advancing rapidly and optical techniques in particular are set to play a large role in preclinical pharmaceutical testing. These approaches, however, are generally unable to quantify the level of expression of imaging probe reporters. In this study a novel method of quantification is presented using dual-probe fluorescence imaging, where an endothelial growth factor receptor (EGFR) fluorescent probe was paired with a non-targeted probe before being injected, and tracer kinetic compartmental modeling was used to determine EGFR expression in a region of interest from the uptake curves of the two drugs in that region. The approach was tested out in a simulation experiment and then applied in an in vivo study in one mouse to investigate EGFR expression in various tissue types (pancreas, pancreas tumor, and leg). The binding potentials (a unitless correlate of target availability) of EGFR expression in the various tissue types were 8.57, 25.64, and 0.11 for the pancreas, pancreas tumor, respectively. For the pancreas and leg, these results correlate well with expected levels of EGFR expression, with the pancreas demonstrating a much higher expression than the skin and also as expected, the tumor expressed much more EGFR than either healthy tissue.

Development and applications of photo-triggered theranostic agents

Theranostics, the fusion of therapy and diagnostics for optimizing efficacy and safety of therapeutic regimes, is a growing field that is paving the way towards the goal of personalized medicine for the benefit of patients. The use of light as a remote-activation mechanism for drug delivery has received increased attention due to its advantages in highly specific spatial and temporal control of compound release. Photo-triggered theranostic constructs could facilitate an entirely new category of clinical solutions which permit early recognition of the disease by enhancing contrast in various imaging modalities followed by the tailored guidance of therapy. Finally, such theranostic agents could aid imaging modalities in monitoring response to therapy. This article reviews recent developments in the use of light-triggered theranostic agents for simultaneous imaging and photoactivation of therapeutic agents. Specifically, we discuss recent developments in the use of theranostic agents for photodynamic-, photothermal- or photo-triggered chemotherapy for several diseases.