Perfusion CT estimates photosensitizer uptake and biodistribution in a rabbit orthotopic pancreatic cancer model: a pilot study

Photosensitizer spatial heterogeneity and its impact on personalized interstitial photodynamic therapy treatment planning

Significance

Personalized photodynamic therapy (PDT) treatment planning requires knowledge of the spatial and temporal co-localization of photons, photosensitizers (PSs), and oxygen. The inter- and intra-subject variability in the photosensitizer concentration can lead to suboptimal outcomes using standard treatment plans.

Aim

We aim to quantify the PS spatial variation in tumors and its effect on PDT treatment planning solutions.

Approach

The spatial variability of two PSs is imaged at various spatial resolutions for an orthotopic rat glioma model and applied in silico to human glioblastoma models to determine the spatial PDT dose, including in organs at risk. An open-source interstitial photodynamic therapy (iPDT) planning tool is applied to these models, deriving the spatial photosensitizer quantification resolution that consistently impacts iPDT source placement and power allocation.

Results

The ex vivo studies revealed a bimodal photosensitizer distribution in the tumor. The concentration of the PS can vary by a factor of 2 between the tumor core and rim, with slight variation within the core but a factor of 5 in the rim. An average sampling volume of 1    mm 3 for photosensitizer quantification will result in significantly different iPDT planning solutions for each case.

Conclusions

Assuming homogeneous photosensitizer distribution results in suboptimal therapeutic outcomes, we highlight the need to predict the photosensitizer distribution before source placement for effective treatment plans.

Endoscopic ultrasound guided interventions in the management of pancreatic cancer

There has been a growing interest in developing endoscopic ultrasound (EUS)-guided interventions for pancreatic cancer, some of which have become standard of care. There are two main factors that drive these advancements to facilitate treatment of patients with pancreatic cancer, ranging from direct locoregional therapy to palliation of symptoms related to inoperable pancreatic cancer. Firstly, an upper EUS has the capability to access the entire pancreas-lesions in the pancreatic head and uncinate process can be accessed from the duodenum, and lesions in the pancreatic body and tail can be accessed from the stomach. Secondly, there has been a robust development of devices that allow through-the-needle interventions, such as placement of fiducial markers, brachytherapy, intratumoral injection, gastroenterostomy creation, and ablation. While these techniques are rapidly emerging, data from a multicenter randomized controlled trial for some procedures are awaited prior to their adoption in clinical settings.

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.

Comparative analysis of two mathematical algorithms for the calculation of computed tomography perfusion parameters in the healthy and diseased pancreas

BACKGROUND

The maximum slope (MS) and deconvolution (DC) algorithms are commonly used to post-process computed tomography perfusion (CTP) data. This study aims to analyze the differences between MS and DC algorithms for the calculation of pancreatic CTP parameters.

METHODS

The pancreatic CTP data of 57 patients were analyzed using MS and DC algorithms. Two blinded radiologists calculated pancreatic blood volume (BV) and blood flow (BF). Interobserver correlation coefficients were used to evaluate the consistency between two radiologists. Paired t-tests, Pearson linear correlation analysis, and Bland-Altman analysis were performed to evaluate the correlation and consistency of the CTP parameters between the two algorithms.

RESULTS

Among the 30 subjects with normal pancreas, the BV values in the three pancreatic regions were higher in the case of the MS algorithm than in the case of the DC algorithm (t = 39.35, p < 0.001), and the BF values in the three pancreatic regions were slightly higher for the MS algorithm than for the DC algorithm (t = 2.19, p = 0.031). Similarly, among the 27 patients with acute pancreatitis, the BV values obtained using the MS methods were higher than those obtained using the DC methods (t = 54.14, p < 0.001). Furthermore, the BF values were higher with the MS methods than the DC methods (t = 8.45, p < 0.001). Besides, Pearson linear correlation and Bland-Altman analysis showed that the BF and BV values showed a good correlation and a bad consistency between the two algorithms.

CONCLUSIONS

The BF and BV values measured using MS and DC algorithms had a good correlation but were not consistent.

TLD1433 Photosensitizer Inhibits Conjunctival Melanoma Cells in Zebrafish Ectopic and Orthotopic Tumour Models

The ruthenium-based photosensitizer (PS) TLD1433 has completed a phase I clinical trial for photodynamic therapy (PDT) treatment of bladder cancer. Here, we investigated a possible repurposing of this drug for treatment of conjunctival melanoma (CM). CM is a rare but often deadly ocular cancer. The efficacy of TLD1433 was tested on several cell lines from CM (CRMM1, CRMM2 and CM2005), uveal melanoma (OMM1, OMM2.5, MEL270), epidermoid carcinoma (A431) and cutaneous melanoma (A375). Using 15 min green light irradiation (21 mW/cm², 19 J.cm^-2, 520 nm), the highest phototherapeutic index (PI) was reached in CM cells, with cell death occurring via apoptosis and necrosis. The therapeutic potential of TLD1433 was hence further validated in zebrafish ectopic and newly-developed orthotopic CM models. Fluorescent CRMM1 and CRMM2 cells were injected into the circulation of zebrafish (ectopic model) or behind the eye (orthotopic model) and 24 h later, the engrafted embryos were treated with the maximally-tolerated dose of TLD1433. The drug was administrated in three ways, either by (i) incubating the fish in drug-containing water (WA), or (ii) injecting the drug intravenously into the fish (IV), or (iii) injecting the drug retro-orbitally (RO) into the fish. Optimally, four consecutive PDT treatments were performed on engrafted embryos using 60 min drug-to-light intervals and 90 min green light irradiation (21 mW/cm², 114 J.cm^-2, 520 nm). This PDT protocol was not toxic to the fish. In the ectopic tumour model, both systemic administration by IV injection and RO injection of TLD1433 significantly inhibited growth of engrafted CRMM1 and CRMM2 cells. However, in the orthotopic model, tumour growth was only attenuated by localized RO injection of TLD1433. These data unequivocally prove that the zebrafish provides a fast vertebrate cancer model that can be used to test the administration regimen, host toxicity and anti-cancer efficacy of PDT drugs against CM. Based on our results, we suggest repurposing of TLD1433 for treatment of incurable CM and further testing in alternative pre-clinical models.

Co-Administered Polymeric Nano-Antidotes for Improved Photo-Triggered Response in Glioblastoma

Polymer-based nanoparticles (NPs) are useful vehicles in treating glioblastoma because of their favorable characteristics such as small size and ability to cross the blood–brain barrier, as well as reduced immunogenicity and side effects. The use of a photosensitizer drug such as Verteporfin (BPD), in combination with a pan-vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor (TKI), Cediranib (CED), encapsulated in NPs will provide the medical field with new research on the possible ways to treat glioblastoma. Concomitant administration of BPD and CED NPs have the potential to induce dual photocytotoxic and cytostatic effects in U87 MG cells by (1) remotely triggering BPD through photodynamic therapy by irradiating laser at 690 nm and subsequent production of reactive oxygen species and (2) inhibiting cell proliferation by VEGFR interference and growth factor signaling mechanisms which may allow for longer progression free survival in patients and fewer systemic side effects. The specific aims of this research were to synthesize, characterize and assess cell viability and drug interactions for polyethylene-glycolated (PEGylated) polymeric based CED and BPD NPs which were less than 100 nm in size for enhanced permeation and retention effects. Synergistic effects were found using the co-administered therapies compared to the individual drugs. The major goal of this research was to investigate a new combination of photodynamic-chemotherapy drugs in nano-formulation for increased efficacy in glioblastoma treatment at reduced concentrations of therapeutics for enhanced drug delivery in vitro.

Correlation of intracellular oxygen and cell metabolism by simultaneous PLIM of phosphorescent TLD1433 and FLIM of NAD(P)H

During photodynamic therapy (PDT), disruption of cell respiration and metabolic changes could be one of the first events. Photophysical characteristics of the photosensitizer (PS) and its specific redox potential define consumption of molecular oxygen followed by generation of reactive oxygen species. The potential PS TLD1433 is based on transition metal Ru(II) and possess an oxygen-dependent luminescence. This enables the study of oxygen consumption by PS-phosphorescence lifetime imaging (PLIM) and simultaneously changes the cellular metabolic state by nicotinamide adenine dinucleotide (NAD(P)H)-fluorescence lifetime imaging (FLIM). Within this study, localization and cellular function of TLD1433 is investigated in bladder carcinoma cells using time-resolved and confocal laser scanning microscopy. Simultaneous FLIM/PLIM of NAD(P)H and TLD1433 during PDT correlated oxygen consumption, redox state and cellular energy metabolism. Our investigations aimed to provide a personalized protocol in theranostic PDT procedures and demonstrate the potential use of TLD1433 PDT also under hypoxic conditions, which are otherwise difficult to treat.

Photonanomedicine: a convergence of photodynamic therapy and nanotechnology

As clinical nanomedicine has emerged over the past two decades, phototherapeutic advancements using nanotechnology have also evolved and impacted disease management. Because of unique features attributable to the light activation process of molecules, photonanomedicine (PNM) holds significant promise as a personalized, image-guided therapeutic approach for cancer and non-cancer pathologies. The convergence of advanced photochemical therapies such as photodynamic therapy (PDT) and imaging modalities with sophisticated nanotechnologies is enabling the ongoing evolution of fundamental PNM formulations, such as Visudyne®, into progressive forward-looking platforms that integrate theranostics (therapeutics and diagnostics), molecular selectivity, the spatiotemporally controlled release of synergistic therapeutics, along with regulated, sustained drug dosing. Considering that the envisioned goal of these integrated platforms is proving to be realistic, this review will discuss how PNM has evolved over the years as a preclinical and clinical amalgamation of nanotechnology with PDT. The encouraging investigations that emphasize the potent synergy between photochemistry and nanotherapeutics, in addition to the growing realization of the value of these multi-faceted theranostic nanoplatforms, will assist in driving PNM formulations into mainstream oncological clinical practice as a necessary tool in the medical armamentarium.

A ruthenium(ii) based photosensitizer and transferrin complexes enhance photo-physical properties, cell uptake, and photodynamic therapy safety and efficacy

Metal-based photosensitizers are of interest as their absorption and chemical binding properties can be modified via the use of different ligands. Ru(2+) based photosensitizers are known to be effective photodynamic therapy (PDT) agents against bacteria, whereas use for oncological indications in vivo has not been demonstrated with the same level of evidence. We present data showing that premixing the Ru(2+)-complex TLD1433 with transferrin increases the molar extinction coefficient, including longer activation wavelengths, reduces photobleaching rates, and reduces the toxicity of the complex improving overall PDT efficacy. As the transferrin receptor is upregulated in most malignancies, premixing the Ru(2+) complex with transferrin converts the active pharmaceutical ingredient TLD1433 into a drug of potentially considerable clinical utility.

Photodynamic therapy for cancer of the pancreas – The story so far

Pancreatic cancer has long been a leading cause of cancer death. Few patients are suitable for surgery and for those who are not, the response to treatment is generally poor. No more than about 10% survive for more than a year. Recent research has focused on focal treatment for local disease control. This review covers the development of one of the most promising options, photodynamic therapy (PDT).

This review covers pre-clinical and clinical studies. Laboratory work was designed to understand the effect of PDT on the normal pancreas and surrounding tissues and on transplanted cancers in the hamster pancreas to ensure safety prior to clinical application. Essentially all clinical studies have been undertaken in University College Hospital, London. Phase-I studies used the photosensitisers mTHPC and verteporfin in patients with localised but inoperable cancers.

Laboratory results showed that normal pancreas, bile duct, liver, stomach and major blood vessels could tolerate PDT without any unacceptable effects on the structure and function of these organs. Necrosis that healed safely was documented in transplanted cancers. The clinical trials showed that focal necrosis could be produced in inoperable cancers with acceptable levels of complications, but considerable refinements of treatment delivery and monitoring are required before the technique will be ready for assessment in controlled clinical trials.

PDT is showing promise for the minimally invasive treatment of localised pancreatic cancers, but it is still at an early stage of development. Much more work will be necessary to optimise techniques for applying PDT to these cancers and for combining it with other therapeutic options such as chemotherapy.

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.