[124I]CLR1404 PET/CT in High-Grade Primary and Metastatic Brain Tumors.

PURPOSE: There is a continuous search for imaging techniques with high sensitivity and specificity for brain tumors. Positron emission tomography (PET) imaging has shown promise, though many PET agents either have a low tumor specificity or impractical physical half-lives. [124I]CLR1404 is a small molecule alkylphosphocholine analogue that is thought to bind to plasma membrane lipid rafts and has shown high tumor-to-background ratios (TBR) in a previous pilot study in brain tumor patients. This study attempts to define the clinical value of [124I]CLR1404 PET/CT (aka CLR124). PROCEDURES: Adult patients with new or suspected recurrence of high-grade primary or metastatic brain tumors (N = 27) were injected with [124I]CLR1404 followed by PET/CT at 6, 24, and 48 h. Standard uptake values (SUV) and TBR values were calculated for all time points. Uptake of [124I]CLR1404 was qualitatively assessed, compared with magnetic resonance imaging (MRI), and correlated with clinical outcome. Final diagnosis (N = 25) was established based on surgically resected tissue or long-term follow-up. RESULTS: Positive uptake with high TBR was detected in all but one patient with a final diagnosis of primary/recurrent brain tumor (12/13) and in less than half of patients with treatment-related changes (5/12). Concordance between [124I]CLR1404 uptake and contrast enhancement on MRI was seen in < 40 %, with no concordance between T2-hyperintensities and uptake. No significant difference in overall outcome was found between patients with and without [124I]CLR1404 uptake. CONCLUSIONS: The uptake pattern in these patients suggests a very high sensitivity of [124I]CLR1404 PET/CT for diagnosing tumor tissue; however, tumor specificity needs to be further defined. Relative lack of concordance with standard MRI characteristics suggests that [124I]CLR1404 PET/CT provides additional information about brain tumors compared to MRI alone, potentially improving clinical decision-making.

CLR 125 Auger Electrons for the Targeted Radiotherapy of Triple-Negative Breast Cancer.

PURPOSE: Auger electrons emitted by radioisotopes such as 125I have a high linear energy transfer and short mean-free path in tissue (<10 µm), making them suitable for treating micrometastases while sparing normal tissues. The authors developed and subsequently investigated a cancer cell-selective small molecule phospholipid ether analog to deliver 125I to triple-negative breast cancer (TNBC) cells in vivo. METHODS: A Current Good Manufacturing Practice (cGMP) method to radiolabel 125I-CLR1404 (CLR 125) with >95% radiochemical purity was established. To estimate CLR 125 in vivo dosimetry and identify dose-limiting organs, the biodistribution of the analog compound 124I-CLR1404 (CLR 124) was investigated using micro-positron emission tomography (PET)/computed tomography (CT) in conjunction with a Monte Carlo dosimetry platform to estimate CLR 125 dosimetry. In vivo antitumor efficacy was tested by injecting nude mice bearing either MDA-MB-231-luc orthotopic xenografts or lung metastases with 74 MBq (3.7 GBq/kg) of CLR 125 or an equivalent mass amount of nonradiolabeled CLR 125. Longitudinal tumor measurements using calipers and bioluminescence imaging were obtained for the xenografts and lung metastases, respectively. RESULTS: Dosimetry analysis estimated that CLR 125 would impart the largest absorbed dose to the tumor per injected activity (0.261 ± 0.023 Gy/MBq) while the bone marrow, which is generally the dose-limiting organ for CLR1404, appears to have the lowest (0.063 ± 0.005 Gy/MBq). At administered activities of up to 74 MBq (3.7 GBq/kg), mice did not experience signs of toxicity. In addition, a single dose of CLR 125 reduced the volume of orthotopic primary TNBC xenografts by ∼60% compared to control vehicle (p < 0.001) and significantly extended survival. In addition, CLR 125 was efficacious against preclinical metastatic TNBC models by inhibiting the progression of micrometastases (p < 0.01). CONCLUSIONS: Targeted radionuclide therapy with CLR 125 displayed significant antitumor efficacy in vivo, suggesting promise for treatment of TNBC micrometastases.

PET/CT imaging of the diapeutic alkylphosphocholine analog 124I-CLR1404 in high and low-grade brain tumors.

CLR1404 is a cancer-selective alkyl phosphocholine (APC) analog that can be radiolabeled with 124I for PET imaging, 131I for targeted radiotherapy and/or SPECT imaging, or 125I for targeted radiotherapy. Studies have demonstrated avid CLR1404 uptake and prolonged retention in a broad spectrum of preclinical tumor models. The purpose of this pilot trial was to demonstrate avidity of 124I-CLR1404 in human brain tumors and develop a framework to evaluate this uptake for use in larger studies. 12 patients (8 men and 4 women; mean age of 43.9 ± 15.1 y; range 23-66 y) with 13 tumors were enrolled. Eleven patients had suspected tumor recurrence and 1 patient had a new diagnosis of high grade tumor. Patients were injected with 185 MBq ± 10% of 124I-CLR1404 followed by PET/CT imaging at 6-, 24-, and 48-hour. 124I-CLR1404 PET uptake was assessed qualitatively and compared with MRI. After PET image segmentation SUV values and tumor to background ratios were calculated. There was no significant uptake of 124I-CLR1404 in normal brain. In tumors, uptake tended to increase to 48 hours. Positive uptake was detected in 9 of 13 lesions: 5/5 high grade tumors, 1/2 low grade tumors, 1/1 meningioma, and 2/4 patients with treatment related changes. 124I-CLR1404 uptake was not detected in 1/2 low grade tumors, 2/4 lesions from treatment related changes, and 1/1 indeterminate lesion. For 6 malignant tumors, the average tumor to background ratios (TBR) were 9.32 ± 4.33 (range 3.46 to 15.42) at 24 hours and 10.04 ± 3.15 (range 5.17 to 13.17) at 48 hours. For 2 lesions from treatment related change, the average TBR were 5.05 ± 0.4 (range 4.76 to 5.33) at 24 hours and 4.88 ± 1.19 (range 4.04 to 5.72) at 48 hours. PET uptake had areas of both concordance and discordance compared with MRI. 124I-CLR1404 PET demonstrated avid tumor uptake in a variety of brain tumors with high tumor-to-background ratios. There were regions of concordance and discordance compared with MRI, which has potential clinical relevance. Expansion of these studies is required to determine the clinical significance of the 124I-CLR1404 PET findings.

Impact of PET and MRI threshold-based tumor volume segmentation on patient-specific targeted radionuclide therapy dosimetry using CLR1404.

Variations in tumor volume segmentation methods in targeted radionuclide therapy (TRT) may lead to dosimetric uncertainties. This work investigates the impact of PET and MRI threshold-based tumor segmentation on TRT dosimetry in patients with primary and metastatic brain tumors. In this study, PET/CT images of five brain cancer patients were acquired at 6, 24, and 48 h post-injection of 124I-CLR1404. The tumor volume was segmented using two standardized uptake value (SUV) threshold levels, two tumor-to-background ratio (TBR) threshold levels, and a T1 Gadolinium-enhanced MRI threshold. The dice similarity coefficient (DSC), jaccard similarity coefficient (JSC), and overlap volume (OV) metrics were calculated to compare differences in the MRI and PET contours. The therapeutic 131I-CLR1404 voxel-level dose distribution was calculated from the 124I-CLR1404 activity distribution using RAPID, a Geant4 Monte Carlo internal dosimetry platform. The TBR, SUV, and MRI tumor volumes ranged from 2.3-63.9 cc, 0.1-34.7 cc, and 0.4-11.8 cc, respectively. The average ± standard deviation (range) was 0.19 ± 0.13 (0.01-0.51), 0.30 ± 0.17 (0.03-0.67), and 0.75 ± 0.29 (0.05-1.00) for the JSC, DSC, and OV, respectively. The DSC and JSC values were small and the OV values were large for both the MRI-SUV and MRI-TBR combinations because the regions of PET uptake were generally larger than the MRI enhancement. Notable differences in the tumor dose volume histograms were observed for each patient. The mean (standard deviation) 131I-CLR1404 tumor doses ranged from 0.28-1.75 Gy GBq-1 (0.07-0.37 Gy GBq-1). The ratio of maximum-to-minimum mean doses for each patient ranged from 1.4-2.0. The tumor volume and the interpretation of the tumor dose is highly sensitive to the imaging modality, PET enhancement metric, and threshold level used for tumor volume segmentation. The large variations in tumor doses clearly demonstrate the need for standard protocols for multimodality tumor segmentation in TRT dosimetry.

MicroC(3): an ex vivo microfluidic cis-coculture assay to test chemosensitivity and resistance of patient multiple myeloma cells.

Chemosensitivity and resistance assays (CSRAs) aim to direct therapies based upon ex vivo responses of patient tumor cells to chemotherapeutic drugs. However, successful CSRAs are yet to be developed. Here, we exposed primary CD138(+) multiple myeloma (MM) cells to bortezomib, a clinical proteasome inhibitor, in microfluidic-cis-coculture (MicroC(3)) incorporating the patient's own CD138(-) tumor-companion mononuclear cells to integrate some of the patients' own tumor microenvironment components in the CSRA design. Statistical clustering techniques segregated MicroC(3) responses into two groups which correctly identified all seventeen patients as either clinically responsive or non-responsive to bortezomib-containing therapies. In contrast, when the same patient MM samples were analyzed in the absence of the CD138(-) cells (monoculture), the tumor cell responses did not segregate into clinical response clusters. Thus, MicroC(3) identified bortezomib-therapy MM patient responses making it a viable CSRA candidate toward enabling personalized therapy.

Tumor-selective anti-cancer effects of the synthetic alkyl phosphocholine analog CLR1404 in neuroblastoma.

Neuroblastoma (NB) is the most common extracranial solid tumor in children and is associated with high mortality in advanced stages. Survivors suffer from long-term treatment-related sequelae. Thus, new targeted treatment options are urgently needed. 18-(p-[(127)I] iodophenyl) octadecyl phosphocholine (CLR1404) is a novel, broadly tumor targeted small molecule drug suitable for intravenous injection with highly selective tumor uptake. As a carrier molecule for radioactive iodine, CLR1404 is in clinical trials as cancer imaging agent and radiotherapeutic drug. Chemically, CLR1404 belongs to the anti-tumor alkyl phospholipids, a class of drugs known to have intrinsic cytotoxic effects on cancer cells. Therefore, we hypothesized that CLR1404 could be a tumor-targeted anti-cancer agent for neuroblastoma, and investigated its effect in vitro and in vivo. CLR1404 was taken up by NB cells in a highly tumor-selective manner both in vitro and in vivo, confirmed by flow cytometry and PET/CT imaging of mouse flank xenografts with (124)I-CLR1404, respectively. Using flow cytometry, MTT assay, Western blotting and caspase 3/7 assay, we confirm that in vitro treatment with CLR1404 leads to robust apoptosis and cell death in multiple NB cell lines and is associated with Akt inhibition, while sparing normal cells. Treatment with CLR1404 in doses of 10 or 30 mg/kg administered by intravenous injection once weekly for 7 weeks significantly inhibited the tumor growth rate in a mouse flank xenograft model of NB (P<0.001) when compared to control cohorts, without causing drug-related hematotoxicity or other noticeable adverse effects, which was determined by serial tumor volume measurements, complete blood counts, and monitoring of animal-specific health parameters. We conclude that CLR1404 warrants clinical exploration as a novel, tumor selective anticancer agent in NB and potentially other cancers.

A phase 1 study of 131I-CLR1404 in patients with relapsed or refractory advanced solid tumors: dosimetry, biodistribution, pharmacokinetics, and safety.

INTRODUCTION: (131)I-CLR1404 is a small molecule that combines a tumor-targeting moiety with a therapeutic radioisotope. The primary aim of this phase 1 study was to determine the administered radioactivity expected to deliver 400 mSv to the bone marrow. The secondary aims were to determine the pharmacokinetic (PK) and safety profiles of (131)I-CLR1404. METHODS: Eight subjects with refractory or relapsed advanced solid tumors were treated with a single injection of 370 MBq of (131)I-CLR1404. Whole body planar nuclear medicine scans were performed at 15-35 minutes, 4-6, 18-24, 48, 72, 144 hours, and 14 days post injection. Optional single photon emission computed tomography imaging was performed on two patients 6 days post injection. Clinical laboratory parameters were evaluated in blood and urine. Plasma PK was evaluated on (127)I-CLR1404 mass measurements. To evaluate renal clearance of (131)I-CLR1404, urine was collected for 14 days post injection. Absorbed dose estimates for target organs were determined using the RADAR method with OLINDA/EXM software. RESULTS: Single administrations of 370 MBq of (131)I-CLR1404 were well tolerated by all subjects. No severe adverse events were reported and no adverse event was dose-limiting. Plasma (127)I-CLR1404 concentrations declined in a bi-exponential manner with a mean t½ value of 822 hours. Mean Cmax and AUC(0-t) values were 72.2 ng/mL and 15753 ng • hr/mL, respectively. An administered activity of approximately 740 MBq is predicted to deliver 400 mSv to marrow. CONCLUSIONS: Preliminary data suggest that (131)I-CLR1404 is well tolerated and may have unique potential as an anti-cancer agent. TRIAL REGISTRATION: ClinicalTrials.gov NCT00925275.

Alkylphosphocholine analogs for broad-spectrum cancer imaging and therapy.

Many solid tumors contain an overabundance of phospholipid ethers relative to normal cells. Capitalizing on this difference, we created cancer-targeted alkylphosphocholine (APC) analogs through structure-activity analyses. Depending on the iodine isotope used, radioiodinated APC analog CLR1404 was used as either a positron emission tomography (PET) imaging ((124)I) or molecular radiotherapeutic ((131)I) agent. CLR1404 analogs displayed prolonged tumor-selective retention in 55 in vivo rodent and human cancer and cancer stem cell models. (131)I-CLR1404 also displayed efficacy (tumor growth suppression and survival extension) in a wide range of human tumor xenograft models. Human PET/CT (computed tomography) and SPECT (single-photon emission computed tomography)/CT imaging in advanced-cancer patients with (124)I-CLR1404 or (131)I-CLR1404, respectively, demonstrated selective uptake and prolonged retention in both primary and metastatic malignant tumors. Combined application of these chemically identical APC-based radioisosteres will enable personalized dual modality cancer therapy of using molecular (124)I-CLR1404 tumor imaging for planning (131)I-CLR1404 therapy.

Computational modelling of anti-angiogenic therapies based on multiparametric molecular imaging data.

Computational tumour models have emerged as powerful tools for the optimization of cancer therapies; ideally, these models should incorporate patient-specific imaging data indicative of therapeutic response. The purpose of this study was to develop a tumour modelling framework in order to simulate the therapeutic effects of anti-angiogenic agents based upon clinical molecular imaging data. The model was applied to positron emission tomography (PET) data of cellular proliferation and hypoxia from a phase I clinical trial of bevacizumab, an antibody that neutralizes the vascular endothelial growth factor (VEGF). When using pre-therapy PET data in combination with literature-based dose response parameters, simulated follow-up hypoxia data yielded good qualitative agreement with imaged hypoxia levels. Improving the quantitative agreement with follow-up hypoxia and proliferation PET data required tuning of the maximum vascular growth fraction (VGF(max)) and the tumour cell cycle time to patient-specific values. VGF(max) was found to be the most sensitive model parameter (CV = 22%). Assuming availability of patient-specific, intratumoural VEGF levels, we show how bevacizumab dose levels can potentially be 'tailored' to improve levels of tumour hypoxia while maintaining proliferative response, both of which are critically important in the context of combination therapy. Our results suggest that, upon further validation, the application of image-driven computational models may afford opportunities to optimize dosing regimens and combination therapies in a patient-specific manner.

An imaging-based tumour growth and treatment response model: investigating the effect of tumour oxygenation on radiation therapy response.

A multiscale tumour simulation model employing cell-line-specific biological parameters and functional information derived from pre-therapy PET/CT imaging data was developed to investigate effects of different oxygenation levels on the response to radiation therapy. For each tumour voxel, stochastic simulations were performed to model cellular growth and therapeutic response. Model parameters were fitted to published preclinical experiments of head and neck squamous cell carcinoma (HNSCC). Using the obtained parameters, the model was applied to a human HNSCC case to investigate effects of different uniform and non-uniform oxygenation levels and results were compared for treatment efficacy. Simulations of the preclinical studies showed excellent agreement with published data and underlined the model's ability to quantitatively reproduce tumour behaviour within experimental uncertainties. When using a simplified transformation to derive non-uniform oxygenation levels from molecular imaging data, simulations of the clinical case showed heterogeneous tumour response and variability in radioresistance with decreasing oxygen levels. Once clinically validated, this model could be used to transform patient-specific data into voxel-based biological objectives for treatment planning and to investigate biologically optimized dose prescriptions.