Application of a whole-body pharmacokinetic model for targeted radionuclide therapy to NM404 and FLT

Mixing Matrix-corrected Whole-body Pharmacokinetic Modeling Using Longitudinal Micro-computed Tomography and Fluorescence-mediated Tomography

PURPOSE

Pharmacokinetic modeling can be applied to quantify the kinetics of fluorescently labeled compounds using longitudinal micro-computed tomography and fluorescence-mediated tomography (μCT-FMT). However, fluorescence blurring from neighboring organs or tissues and the vasculature within tissues impede the accuracy in the estimation of kinetic parameters. Contributions of elimination and retention activities of fluorescent probes inside the kidneys and liver can be hard to distinguish by a kinetic model. This study proposes a deconvolution approach using a mixing matrix to model fluorescence contributions to improve whole-body pharmacokinetic modeling.

PROCEDURES

In the kinetic model, a mixing matrix was applied to unmix the fluorescence blurring from neighboring tissues and blood vessels and unmix the fluorescence contributions of elimination and retention in the kidney and liver compartments. Accordingly, the kinetic parameters of the hepatobiliary and renal elimination routes and five major retention sites (the kidneys, liver, bone, spleen, and lung) were investigated in simulations and in an in vivo study. In the latter, the pharmacokinetics of four fluorescently labeled compounds (indocyanine green (ICG), HITC-iodide-microbubbles (MB), Cy7-nanogels (NG), and OsteoSense 750 EX (OS)) were evaluated in BALB/c nude mice.

RESULTS

In the simulations, the corrected modeling resulted in lower relative errors and stronger linear relationships (slopes close to 1) between the estimated and simulated parameters, compared to the uncorrected modeling. For the in vivo study, MB and NG showed significantly higher hepatic retention rates (P<0.05 and P<0.05, respectively), while OS had smaller renal and hepatic retention rates (P<0.01 and P<0.01, respectively). Additionally, the bone retention rate of OS was significantly higher (P<0.01).

CONCLUSIONS

The mixing matrix correction improves pharmacokinetic modeling and thus enables a more accurate assessment of the biodistribution of fluorescently labeled pharmaceuticals by μCT-FMT.

In Silico Docking of Alkylphosphocholine Analogs to Human Serum Albumin Predicts Partitioning and Pharmacokinetics

Alkylphosphocholine (APC) analogs are a novel class of broad-spectrum tumor-targeting agents that can be used for both diagnosis and treatment of cancer. The potential for clinical translation for APC analogs will strongly depend on their pharmacokinetic (PK) profiles. The aim of this work was to understand how the chemical structures of various APC analogs impact binding and PK. To achieve this aim, we performed in silico docking analysis, in vitro and in vivo partitioning experiments, and in vivo PK studies. Our results have identified 7 potential high-affinity binding sites of these compounds on human serum albumin (HSA) and suggest that the size of the functional group directly influences the albumin binding, partitioning, and PK. Namely, the bulkier the functional groups, the weaker the agent binds to albumin, the more the agent partitions onto lipoproteins, and the less time the agent spends in circulation. The results of these experiments provide novel molecular insights into the binding, partitioning, and PK of this class of compounds and similar molecules as well as suggest pharmacological strategies to alter their PK profiles. Importantly, our methodology may provide a way to design better drugs by better characterizing the PK profile for lead compound optimization.

Preclinical Characterization of 86/90Y-NM600 in a Variety of Murine and Human Cancer Tumor Models

We characterize the in vivo biodistribution and tumor selectivity of ⁸⁶Y-NM600, a theranostic alkylphosphocholine radiometal chelate with broad tumor selectivity, in a variety of preclinical cancer models. Methods: Mice bearing flank tumors (representative of lung, pancreatic, prostate, liver, skin, and lymphoid cancers) were injected intravenously with 9.25 MBq of ⁸⁶Y-NM600 and imaged longitudinally over 4-5 d using small-animal PET/CT. Percentage injected activity per gram (%IA/g) for each volume of interest was measured at each time point for the organs of interest. Mice were euthanized after the final time point, and the tumor and organs of interest were counted with an automatic γ-counter. Absorbed doses delivered by ⁹⁰Y-NM600 per injected activity (Gy/MBq) were estimated. Mice bearing B78 flank tumors were injected with a prescription of ⁹⁰Y-NM600 that delivered 2.5 Gy of absorbed tumor dose and was compared with an equivalent absorbed dose delivered via external-beam radiotherapy using tumor volume as a measure of response. Histology and complete blood counts were analyzed in naïve C57BL/6 mice that were injected with 9.25 MBq of ⁹⁰Y-NM600 at 5, 10, and 28 d after injection. Results: PET imaging showed consistent tumor accumulation and retention across all tumor models investigated, with little off-target retention of NM600 except in the liver, as is characteristic of hepatobiliary metabolism. The tumor uptake was highest in the pancreatic and lymphoid cancer models, reaching peak concentrations of 9.34 ± 2.66 %IA/g (n = 3) and 9.10 ± 0.13 %IA/g (n = 3), respectively, at approximately 40-48 h after injection. These corresponded to tumor dose estimates of 2.72 ± 0.33 Gy/MBq and 2.67 ± 0.32 Gy/MBq, respectively. In the toxicity study, there were no visible signs of acute toxicity by histology, and perturbation of hematologic parameters was transient when observed, returning to pretherapy levels after 28 d. Conclusion: NM600 is a theranostic agent with a unique ability to selectively target a variety of cancer types, presenting a unique opportunity for PET image-guided targeted radionuclide therapy and combination with immunotherapies.

A new pharmacokinetic model for 90Y-ibritumomab tiuxetan based on 3-dimensional dosimetry

Monoclonal antibodies (mAbs) are key components in several therapies for cancer and inflammatory diseases but current knowledge of their clinical pharmacokinetics and distribution in human tissues remains incomplete. Consequently, optimal dosing and scheduling in clinics are affected. With sequential radiolabeled mAb-based imaging, radiation dosing in tissues/organs can be calculated to provide a better assessment of mAb concentrations in tissues. This is the first pharmacokinetic model of ⁹⁰Y-Ibritumomab tiuxetan (⁹⁰Y-IT) in humans to be described, based on three-dimensional (3D) dosimetry using single-photon emission computed-tomography coupled with computed-tomography. 19 patients with follicular lymphoma were treated initially with ⁹⁰Y-IT in the FIZZ trial. Based on a compartmental approach individualising the vascular compartment within studied organs, this study proposes a reliable pharmacokinetic (PK) five-compartment model replacing the currently used two-compartment model and constitutes a new direction for further research. This model provides exchange constants between the different tissues, Area Under the Curve of ¹¹¹In-IT in blood (AUC) and Mean Residence Time (MRT) that have not been reported so far for IT. Finally, the elimination process appears to occur in a compartment other than the liver or the spleen and suggests the metabolism of mAbs may take place mainly on the vascular compartment level.

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.

Targeted Molecular Radiotherapy of Pediatric Solid Tumors Using a Radioiodinated Alkyl-Phospholipid Ether Analog

External-beam radiotherapy plays a critical role in the treatment of most pediatric solid tumors. Particularly in children, achieving an optimal therapeutic index to avoid damage to normal tissue is extremely important. Consequently, in metastatic disease, the utility of external-beam radiotherapy is limited. Molecular radiotherapy with tumor-targeted radionuclides may overcome some of these challenges, but to date there exists no single cancer-selective agent capable of treating various pediatric malignancies independently of their histopathologic origin. We tested the therapeutic potential of the clinical-grade alkyl-phospholipid ether analog CLR1404, 18-(p-iodophenyl)octadecyl phosphocholine, as a scaffold for tumor-targeted radiotherapy of pediatric malignancies. Methods: Uptake of CLR1404 by pediatric solid tumor cells was tested in vitro by flow cytometry and in vivo by PET/CT imaging and dosimetry. The therapeutic potential of ¹³¹I-CLR1404 was evaluated in xenograft models. Results: In vitro, fluorescent CLR1404-BODIPY showed significant selective uptake in a variety of pediatric cancer lines compared with normal controls. In vivo tumor-targeted uptake in mouse xenograft models using ¹²⁴I-CLR1404 was confirmed by imaging. Single-dose intravenous injection of ¹³¹I-CLR1404 significantly delayed tumor growth in all rodent pediatric xenograft models and extended animal survival while demonstrating a favorable side effect profile. Conclusion:¹³¹I-CLR1404 has the potential to become a tumor-targeted radiotherapeutic drug with broad applicability in pediatric oncology. Because ¹³¹I-CLR1404 has entered clinical trials in adults, our data warrant the development of pediatric clinical trials for this particularly vulnerable patient population.

Breast cancer imaging using the near-infrared fluorescent agent, CLR1502

Positive margins after breast conservation surgery represent a significant problem in the treatment of breast cancer. The near-infrared fluorescence agent CLR1502 (Cellectar Biosciences, Madison, WI) was studied in a preclinical breast cancer model to determine imaging properties and ability to detect small islands of malignancy. Nude mice bearing human breast cancer flank xenografts were given a systemic injection of CLR1502, and imaging was performed using LUNA (Novadaq Technologies Inc., Richmond, BC) and Pearl Impulse (LI-COR Biosciences, Lincoln, NE) devices. Normal tissues were examined for fluorescence signal, and conventional and fluorescence histology was performed using the Odyssey scanner. Peak tumor to background ratio occurred 2 days after injection with CLR1502. The smallest amount of tumor that was imaged and detected using these devices was 1.9 mg, equivalent to 1.9 × 10⁶ cells. The highest fluorescence signal was seen in tumor and normal lymph node tissue, and the lowest fluorescence signal was seen in muscle and plasma. Human breast cancer tumors can be imaged in vivo with multiple optical imaging platforms using CLR1502. This pilot study supports further investigations of this fluorescent agent for improving surgical resection of malignancies, with the goal of eventual clinical translation.

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.

Plumbagin Inhibits Prostate Carcinogenesis in Intact and Castrated PTEN Knockout Mice via Targeting PKCε, Stat3, and Epithelial-to-Mesenchymal Transition Markers

Prostate cancer continues to remain the most common cancer and the second leading cause of cancer-related deaths in American males. The Pten deletions and/or mutations are frequently observed in both primary prostate cancers and metastatic prostate tissue samples. Pten deletion in prostate epithelium in mice results in prostatic intraepithelial neoplasia (PIN), followed by progression to invasive adenocarcinoma. The Pten conditional knockout mice [(Pten-loxp/loxp:PB-Cre4(+)) (Pten-KO)] provide a unique preclinical model to evaluate agents for efficacy for both the prevention and treatment of prostate cancer. We present here for the first time that dietary plumbagin, a medicinal plant-derived naphthoquinone (200 or 500 ppm) inhibits tumor development in intact as well as castrated Pten-KO mice. Plumbagin has shown no signs of toxicity at either of these doses. Plumbagin treatment resulted in a decrease expression of PKCε, AKT, Stat3, and COX2 compared with the control mice. Plumbagin treatment also inhibited the expression of vimentin and slug, the markers of epithelial-to-mesenchymal transition (EMT) in prostate tumors. In summary, the results indicate that dietary plumbagin inhibits growth of both primary and castration-resistant prostate cancer (CRPC) in Pten-KO mice, possibly via inhibition of PKCε, Stat3, AKT, and EMT markers (vimentin and slug), which are linked to the induction and progression of prostate cancer.