Accumulation In Normal Tissues Research Articles

Development of Radiolabeled Probes with Improved Imaging Contrast by Releasing Urinary Excretable Radiolabeled Compounds from Thermosensitive Liposomes in the Blood.

In this study, thermosensitive liposomes (TSLs) encapsulating urinary excretable radiolabeled compounds were developed. We considered that the release of the radiolabeled compounds from the TSLs in the blood by heating the blood in peripheral tissues can achieve rapid clearance of radioactivity, resulting in improved imaging contrast. To demonstrate the hypothesis, classical TSLs mainly composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine with a phase transition temperature of 41 °C were used. The optimal composition of TSLs was determined by an in vitro release test using [111In]In-diethylenetriaminepentaacetic acid (DTPA)-encapsulated liposomes, which showed that the cholesterol content drastically changed the release characteristics of classical TSLs. In the biodistribution experiments, [111In]In-DTPA was significantly released from the TSLs in the blood when the tails of mice were heated at 43 °C. The tumor-to-blood ratio of the heated group was three times higher than that of the nonheated group, and accumulation in normal tissues of the heated group was lower than that of the nonheated group. These results demonstrate the usefulness of the method using TSLs to encapsulate urinary excretable radiolabeled compounds for improving imaging contrast.

Therapeutic Effect of Boron Neutron Capture Therapy on Boronophenylalanine Administration via Cerebrospinal Fluid Circulation in Glioma Rat Models.

In recent years, various drug delivery systems circumventing the blood-brain barrier have emerged for treating brain tumors. This study aimed to improve the efficacy of brain tumor treatment in boron neutron capture therapy (BNCT) using cerebrospinal fluid (CSF) circulation to deliver boronophenylalanine (BPA) to targeted tumors. Previous experiments have demonstrated that boron accumulation in the brain cells of normal rats remains comparable to that after intravenous (IV) administration, despite BPA being administered via CSF at significantly lower doses (approximately 1/90 of IV doses). Based on these findings, BNCT was conducted on glioma model rats at the Kyoto University Research Reactor Institute (KUR), with BPA administered via CSF. This method involved implanting C6 cells into the brains of 8-week-old Wistar rats, followed by administering BPA and neutron irradiation after a 10-day period. In this study, the rats were divided into four groups: one receiving CSF administration, another receiving IV administration, and two control groups without BPA administration, with one subjected to neutron irradiation and the other not. In the CSF administration group, BPA was infused from the cisterna magna at 8 mg/kg/h for 2 h, while in the IV administration group, BPA was intravenously administered at 350 mg/kg via the tail vein over 1.5 h. Thermal neutron irradiation (5 MW) for 20 min, with an average fluence of 3.8 × 1012/cm2, was conducted at KUR's heavy water neutron irradiation facility. Subsequently, all of the rats were monitored under identical conditions for 7 days, with pre- and post-irradiation tumor size assessed through MRI and pathological examination. The results indicate a remarkable therapeutic efficacy in both BPA-administered groups (CSF and IV). Notably, the rats treated with CSF administration exhibited diminished BPA accumulation in normal tissue compared to those treated with IV administration, alongside maintaining excellent overall health. Thus, CSF-based BPA administration holds promise as a novel drug delivery mechanism in BNCT.

Synthesis and Preclinical Evaluation of Urea-Based Prostate-Specific Membrane Antigen-Targeted Conjugates Labeled with 177Lu.

177Lu-labeled small-molecule prostate-specific membrane antigen (PSMA) targeted tracers are therapeutic agents for metastatic castration-resistant prostate cancer. Optimizing molecular design holds the potential to further enhance the pharmacokinetic properties of PSMA-targeted agents while preserving their potent therapeutic effects. In this study, six novel N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-(S)-l-lysine (DCL) urea-based PSMA ligand 2,2',2″,2‴-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid conjugates were synthesized. These conjugates feature polypeptide linkers containing the Phe-Phe peptide sequence and an aromatic fragment at the ε-NH-Lys group of the DCL fragment. The synthesis yielded products with satisfactory yields ranging from 60% to 72%, paving the way for their preclinical evaluation. The labeling of the new variants of urea-based PSMA inhibitors provided a radiochemical yield of over 95%. The 177Lu-labeled conjugates demonstrated specific and moderate affinity binding to PSMA-expressing human cancer cells PC3-pip in vitro and specific accumulation in PSMA-expressing xenografts in vivo. Based on the results, both the lipophilicity and the type of substituent in the linker significantly influence the binding properties of the PSMA inhibitor and its biodistribution profile. Specifically, the studied variants containing a bromine substituent or a hydroxyl group introduced into the aromatic fragment of the phenylalanyl residue in DCL exhibit higher affinities to PSMA compared to variants with only a chlorine-substituted aromatic fragment or variants without any substituents. The [177Lu]Lu-13C with the bromine substituent was characterized by the highest activity accumulation in blood, salivary glands, muscle, bone, and gastrointestinal tract and had inasmuch as an unfavorable pharmacokinetic profile. The negative charge of the carboxyl group in the phenyl moiety of the [177Lu]Lu-13A variant has demonstrated a positive effect on reducing the retention of activity in the liver and the kidneys (the ratio of tumor to kidneys was 1.3-fold). Low accumulation in normal tissues in vivo indicates that this novel PSMA-targeting inhibitor is a promising radioligand.

Boron-Containing Mesoporous Silica Nanoparticles with Effective Delivery and Targeting of Liver Cancer Cells for Boron Neutron Capture Therapy.

Nanocarriers have been researched comprehensively for the development of novel boron-containing agents in boron neutron capture therapy (BNCT). We designed and synthesized a multifunctional mesoporous silica nanoparticle (MSN)-based boron-containing agent. The latter was coated with a lipid bilayer (LB) and decorated with SP94 peptide (SFSIIHTPILPL) on the surface as SP94-LB@BA-MSN. The latter incorporated boric acid (BA) into hydrophobic mesopores, coated with an LB, and modified with SP94 peptide on the LB. SP94-LB@BA-MSN enhanced nano interface tumor-targeting ability but also prevented the premature release of drugs, which is crucial for BNCT because adequate boron content in tumor sites is required. SP94-LB@BA-MSN showed excellent efficacy in the BNCT treatment of HepG-2 cells. In animal studies with tumor-bearing mice, SP94-LB@BA-MSN exhibited a satisfactory accumulation at the tumor site. The boron content reached 40.18 ± 5.41 ppm in the tumor site 4 h after injection, which was 8.12 and 15.51 times higher than those in mice treated with boronated phenylalanine and those treated with BA. For boron, the tumor-to-normal tissue ratio was 4.41 ± 1.13 and the tumor-to-blood ratio was 5.92 ± 0.45. These results indicated that nanoparticles delivered boron to the tumor site effectively while minimizing accumulation in normal tissues. In conclusion, this composite (SP94-LB@BA-MSN) shows great promise as a boron-containing delivery agent for the treatment of hepatocellular carcinoma using BNCT. These findings highlight the potential of MSNs in the field of BNCT.

Matrix metalloproteinase-sensitive size-shrinkable liposomes targeting activated macrophages for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease characterized by inflammation, swelling, pain, and cartilage and bone destruction. Exploiting the pathophysiological characteristics of matrix metalloproteinases (MMPs), which are enzymes overexpressed at the inflammation site in RA, has resulted in the development of inflammation-responsive drug delivery vectors. We here prepared a multifunctional microenvironment-responsive liposome with MMP-responsive and particle-size-shrinking properties to target macrophages at inflammation sites. In this liposome, triptolide (TP) was encapsulated in a biofilm-like bilayer with mannose-conjugated DSPE-PEG2000 as the targeting molecule and the enzyme-sensitive peptide PVGLIG as the linker arm connecting DSPE-PEG5000, which formed a hydrated membrane envelope on the liposome surface, prolonging liposome circulation while preventing the active targeting molecule from binding to normal macrophages throughout the body and reducing drug accumulation in normal tissues, thereby alleviating efficacy and reducing toxic side effects. In the joint inflammation microenvironment, PVGLIG was cleaved by overexpressed MMPs, the hydration layer of PEG5000 detached, and the target ligand Man was exposed, thereby leading to Man uptake by activated macrophages and exerting an anti-RA effect. Through in vivo and in vitro evaluations, liposomes were found to effectively target inflammation sites and enrich activated macrophages. They also inhibited osteoclastogenesis and the release of inflammatory cytokines, reactive oxygen species, and MMPs. This offers a promising new strategy in which anti-inflammatory and osteoprotective effects are combined for comprehensive RA treatment.

Formulation and Characterization Studies of Paclitaxel Incorporated Kollidon® SR and Chitosan Nanoparticles: An In vitro Evaluation for Potential Use for Colorectal Cancer Treatment

Background: Chemotherapy is regarded as first-line therapy in various cancer types besides surgical procedures. However, lack of cell selectivity and poor drug targeting to the cancer zone of the active agents results in accumulation in normal tissues with considerably high severe side effects. Therefore, novel drug delivery systems are required to enhance cancer treatment. Objective: In this study, Paclitaxel (PTX) incorporated Kollidon® SR (KSR) and Chitosan (CS) based polymeric nanoparticles were prepared for potential use for colorectal cancer treatment. Methods: Polymeric nanoparticles were prepared by spray dying method. Physicochemical characterization studies were performed with particle size (PS), polydispersity index (PDI), zeta potential (ZP), drug loading (DL %), encapsulation efficiency (EE %) and structural evaluations using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H-NMR) analyses. Cytotoxicity of the nanoparticles was screened on HT-29 (human colorectal adenocarcinoma) and HTC-15 (Dukes' type C, colorectal adenocarcinoma) cell lines with MTT assay. Results: Analysis revealed the successful incorporation of PTX into the polymeric lattices. Particles showed cytotoxic activity on HT-29 and HTC-15 cell lines, depending on the application dose after 48 hours. Nanoparticles also remained stable at 5°C ± 3°C and 25°C ± 2°C (60% ± 5 Relative Humidity (RH)) during the storage period of 6 months. Conclusion: As a result of the study, KSR and CS-based nanoparticles could be regarded as promising nano-carriers for improved therapeutic efficacy of PTX for colorectal cancer treatment.

Marriage of a Dual-Plasmonic Interface and Optical Microfiber for NIR-II Cancer Theranostics.

The use of light as a powerful tool for disease treatment has introduced a new era in tumor treatment and provided abundant opportunities for light-based tumor theranostics. This work reports a photothermal theranostic fiber integrating cancer detection and therapeutic functions. Its self-heating effect can be tuned at ultralow powers and used for self-heating detection and tumor ablation. The fiber, consisting of a dual-plasmonic nanointerface and an optical microfiber, can be used to distinguish cancer cells from normal cells, quantify cancer cells, perform hyperthermal ablation of cancer cells, and evaluate the ablation efficacy. Its cancer cell ablation rate reaches 89% in a single treatment. In vitro and in vivo studies reveal quick, deep-tissue photonic hyperthermia in the NIR-II window, which can markedly ablate tumors. The marriage of a dual-plasmonic nanointerface and an optical microfiber presents a novel paradigm in photothermal therapy, offering the potential to surmount the challenges posed by limited light penetration depth, nonspecific accumulation in normal tissues, and inadvertent damage in current methods. This work thus provides insight for the exploration of an integrated theranostic platform with simultaneous functions in cancer diagnostics, therapeutics, and postoperative monitoring for future practical applications.

Synthesis and Evaluation of 177Lu-DOTA-PD-L1-i and 225Ac-HEHA-PD-L1-i as Potential Radiopharmaceuticals for Tumor Microenvironment-Targeted Radiotherapy.

Current cancer therapies focus on reducing immunosuppression and remodeling the tumor microenvironment to inhibit metastasis, cancer progression, and therapeutic resistance. Programmed death receptor 1 (PD-1) is expressed on immune T cells and is one of the so-called checkpoint proteins that can suppress or stop the immune response. To evade the immune system, cancer cells overexpress a PD-1 inhibitor protein (PD-L1), which binds to the surface of T cells to activate signaling pathways that induce immune suppression. This research aimed to synthesize PD-L1 inhibitory peptides (PD-L1-i) labeled with lutetium-177 (177Lu-DOTA-PD-L1-i) and actinium-225 (225Ac-HEHA-PD-L1-i) and to preclinically evaluate their potential as radiopharmaceuticals for targeted radiotherapy at the tumor microenvironment level. Using PD-L1-i peptide as starting material, conjugation with HEHA-benzene-SCN and DOTA-benzene-SCN was performed to yield DOTA-PD-L1-i and HEHA-PD-L1-I, which were characterized by FT-IR, UV-vis spectroscopy, and HPLC. After labeling the conjugates with 225Ac and 177Lu, cellular uptake in HCC827 cancer cells (PD-L1 positive), conjugate specificity evaluation by immunofluorescence, radiotracer effect on cell viability, biodistribution, biokinetics, and assessment of radiation absorbed dose in mice with in duced lung micrometastases were performed. 225Ac-HEHA-PD-L1-i and 177Lu-DOTA-PD-L1-i, obtained with radiochemical purities of 95 ± 3% and 98.5 ± 0.5%, respectively, showed in vitro and in vivo specific recognition for the PD-L1 protein in lung cancer cells and high uptake in HCC287 lung micrometastases (>30% ID). The biokinetic profiles of 177Lu-DOTA-PD-L1-i and 225Ac-DOTA-PD-L1-i showed rapid blood clearance with renal and hepatobiliary elimination and no accumulation in normal tissues. 225Ac-DOTA-PD-L1-i produced a radiation dose of 5.15 mGy/MBq to lung micrometastases. In the case of 177Lu-DOTA-PD-L1-i, the radiation dose delivered to the lung micrometastases was ten times (43 mGy/MBq) that delivered to the kidneys (4.20 mGy/MBq) and fifty times that delivered to the liver (0.85 mGy/MBq). Therefore, the radiotherapeutic PD-L1-i ligands of 225Ac and 177Lu developed in this research could be combined with immunotherapy to enhance the therapeutic effect in various types of cancer.

Computational simulations of tumor growth and treatment response: Benefits of high-frequency, low-dose drug regimens and concurrent vascular normalization.

Implementation of effective cancer treatment strategies requires consideration of how the spatiotemporal heterogeneities within the tumor microenvironment (TME) influence tumor progression and treatment response. Here, we developed a multi-scale three-dimensional mathematical model of the TME to simulate tumor growth and angiogenesis and then employed the model to evaluate an array of single and combination therapy approaches. Treatments included maximum tolerated dose or metronomic (i.e., frequent low doses) scheduling of anti-cancer drugs combined with anti-angiogenic therapy. The results show that metronomic therapy normalizes the tumor vasculature to improve drug delivery, modulates cancer metabolism, decreases interstitial fluid pressure and decreases cancer cell invasion. Further, we find that combining an anti-cancer drug with anti-angiogenic treatment enhances tumor killing and reduces drug accumulation in normal tissues. We also show that combined anti-angiogenic and anti-cancer drugs can decrease cancer invasiveness and normalize the cancer metabolic microenvironment leading to reduced hypoxia and hypoglycemia. Our model simulations suggest that vessel normalization combined with metronomic cytotoxic therapy has beneficial effects by enhancing tumor killing and limiting normal tissue toxicity.

The ubiquitin ligase TRIM21 regulates mutant p53 accumulation and gain of function in cancer.

The tumor suppressor TP53 is the most frequently mutated gene in human cancers. Mutant p53 (mutp53) proteins often accumulate to very high levels in human cancers to promote cancer progression through the gain-of-function (GOF) mechanism. Currently, the mechanism underlying mutp53 accumulation and GOF is incompletely understood. Here, we identified TRIM21 as a critical E3 ubiquitin ligase of mutp53 by screening for specific mutp53-interacting proteins. TRIM21 directly interacted with mutp53 but not WT p53, resulting in ubiquitination and degradation of mutp53 to suppress mutp53 GOF in tumorigenesis. TRIM21 deficiency in cancer cells promoted mutp53 accumulation and GOF in tumorigenesis. Compared with p53R172H knockin mice, which displayed mutp53 accumulation specifically in tumors but not normal tissues, TRIM21 deletion in p53R172H knockin mice resulted in mutp53 accumulation in normal tissues, an earlier tumor onset, and a shortened life span of mice. Furthermore, TRIM21 was frequently downregulated in some human cancers, including colorectal and breast cancers, and low TRIM21 expression was associated with poor prognosis in patients with cancers carrying mutp53. Our results revealed a critical mechanism underlying mutp53 accumulation in cancers and also uncovered an important tumor-suppressive function of TRIM21 and its mechanism in cancers carrying mutp53.

Structural Determination of the Nanocomplex of Borate with Styrene-Maleic Acid Copolymer-Conjugated Glucosamine Used as a Multifunctional Anticancer Drug.

The development of effective anticancer drugs is essential for chemotherapy that specifically targets cancer tissues. We recently synthesized a multifunctional water-soluble anticancer polymer drug consisting of styrene-maleic acid copolymer (SMA) conjugated with glucosamine and boric acid (BA) (SGB complex). It demonstrated about 10 times higher tumor-selective accumulation compared with accumulation in normal tissues because of the enhanced permeability and retention effect, and it inhibited tumor growth via glycolysis inhibition, mitochondrial damage, and thermal neutron irradiation. Gaining insight into the anticancer effects of this SGB complex requires a determination of its structure. We therefore investigated the chemical structure of the SGB complex by means of nuclear magnetic resonance, infrared (IR) spectroscopy, and liquid chromatography-mass spectrometry. To establish the chemical structure of the SGB complex, we synthesized a simple model compound─maleic acid-glucosamine (MAG) conjugate─by using a maleic anhydride (MA) monomer unit instead of the SMA polymer. We obtained two MAG-BA complexes (MAGB) with molecular weights of 325 and 343 after the MAG reaction with BA. We confirmed, by using IR spectroscopy, that MAGB formed a stable complex via an amide bond between MA and glucosamine and that BA bound to glucosamine via a diol bond. As a result of this chemical design, identified via analysis of MAGB, the SGB complex can release BA and demonstrate toxicity to cancer cells through inhibition of lactate secretion in mild hypoxia that mimics the tumor microenvironment. For clinical application of the SGB complex, we confirmed that this complex is stable in the presence of serum. These findings confirm that our design of the SGB complex has various advantages in targeting solid cancers and exerting therapeutic effects when combined with neutron irradiation.

Glycoprotein Ib-regulated micro platelet ghost for biosafe distribution and photothermal oncotherapy

Despite the tremendous theranostics potential of nano-scale drug delivery system (NDDS) in oncology field, their tumor-targeting efficiency and safety remain major challenges due to their proneness of off-target accumulation through widespread vascular endothelial gaps (up to 1μm). To address this problem, in this research, micro-sized cellular platelet "ghosts" (PGs, 1.32μm, platelet without inner granules and coagulation) were employed as carriers to ship hollow gold nanoparticles (HGNs, 58.7nm), forming a hierarchical biosafe system (PG@HGNs) to reduce normal tissue interception and enhance tumor targeting delivery of HGNs for improved photothermal therapy. PGs were prepared by an optimized "swelling-extrusion-elution" method, HGNs were loaded in PGs (PG@HGNs) through a "hypotonic dialysis" method and the safety and biodistribution of the system was evaluated in vitro and in vivo. In in vitro condition that stimulated the tumoral vessel acidic microenvironment (pH=6.5), PG@HGNs were demonstrated with enhanced membrane fluidity through down-regulation of the glycoprotein Ib expressed on the PGs. This change induced a burst release of nano-sized HGNs which were capable to traverse vascular endothelium layer on a tumor-endothelial cell transwell model, whilst the micro-sized PG carriers were intercepted. In comparison to nano-sized platelet membrane-coated carriers (PM@HGNs), PG@HGNs showed enhanced internalization and cytotoxicity to 4T1 cells. In animal models, PG@HGNs remarkably prolonged circulation most likely due to the presence of "self-recognition" receptor-CD47 of PGs, and effectively reduced normal tissue interception via the micro-scale size effect. These both contributed to the significantly improved tumor targeting efficiency of HGNs. PG@HGNs generated the greater antitumor photothermal efficacy alongside safety in the animals compared to PM@HGNs. Collectively, this study demonstrated the potential of the micro-scale PGs equipped with adjusted membrane GP Ib as biosafe vehicles for HGNs or possibly other nanodrugs. THE STATEMENT OF SIGNIFICANCE: Despite the tremendous theranostics potentials, the safety and tumor-targeting efficiency of nano-scale drug delivery systems (NDDS) are compromised by their undesirable accumulation in normal tissues with widespread vascular endothelial gaps, such as many tumor-targeted NDDSs still accumulated much in liver and/or spleen. Herein, we explored a micro-nano biomimetic cascade delivery system to address the above drawbacks. By forming a hierarchical biosafe system, micro-sized platelet "ghost" (PGs, 1.32μm) was employed as tumor-targeted delivery carrier to transport hollow gold nanoparticles (HGNs, 58.7nm). It was demonstrated that this micro-size system could maintain platelet membrane structure thus prolong in vivo circulation, while avoiding extravasation into normal tissues. PG@HGNs could sensitively respond to the acidic microenvironment near tumor vessel via down-regulation of glycoprotein Ib and rapidly release "nano-bullets"-HGNs to further penetrate into the tumor tissues through EPR effect, thus enhancing photothermal efficacy generated by HGNs under NIR irradiation. Collectively, the micro-scaled PGs could be biosafe vehicles for improved tumor-targeted delivery of HGNs or possibly other nanodrugs.

First Clinical Results of Fluorescence Lifetime-enhanced Tumor Imaging Using Receptor-targeted Fluorescent Probes.

Fluorescence molecular imaging, using cancer-targeted near infrared (NIR) fluorescent probes, offers the promise of accurate tumor delineation during surgeries and the detection of cancer specific molecular expression in vivo. However, nonspecific probe accumulation in normal tissue results in poor tumor fluorescence contrast, precluding widespread clinical adoption of novel imaging agents. Here we present the first clinical evidence that fluorescence lifetime (FLT) imaging can provide tumor specificity at the cellular level in patients systemically injected with panitumumab-IRDye800CW, an EGFR-targeted NIR fluorescent probe. We performed wide-field and microscopic FLT imaging of resection specimens from patients injected with panitumumab-IRDye800CW under an FDA directed clinical trial. We show that the FLT within EGFR-overexpressing cancer cells is significantly longer than the FLT of normal tissue, providing high sensitivity (>98%) and specificity (>98%) for tumor versus normal tissue classification, despite the presence of significant nonspecific probe accumulation. We further show microscopic evidence that the mean tissue FLT is spatially correlated (r > 0.85) with tumor-specific EGFR expression in tissue and is consistent across multiple patients. These tumor cell-specific FLT changes can be detected through thick biological tissue, allowing highly specific tumor detection and noninvasive monitoring of tumor EFGR expression in vivo. Our data indicate that FLT imaging is a promising approach for enhancing tumor contrast using an antibody-targeted NIR probe with a proven safety profile in humans, suggesting a strong potential for clinical applications in image guided surgery, cancer diagnostics, and staging.

Radiation dosimetry and efficacy of an 89Zr/225Ac-labeled humanized anti-MUC5AC antibody

IntroductionTheranostic applications are currently difficult to achieve owing to the limited evaluation of suitable chelators for therapeutic nuclides, such as 225Ac and 227Th. With a focus on targeted α therapy and theranostics using human IgG as a drug-delivery system (i.e., combining highly cytotoxic α-particle emitter radiation with efficient tumor targeting), we developed a recombinant humanized Nd2 (hNd2) as an anti-MUC5AC antibody since MUC5AC is highly expressed in patients with pancreatic cancer. Therefore, we aimed to evaluate the performance of 89Zr- (for diagnosis) and 225Ac- (for therapy) labeling of these antibodies using well-controlled radioisotope (RI)-labeling technology in pancreatic cancer mouse models. Methods89Zr-labeled hNd2 (NMK89) and 225Ac-labeled hNd2 (NMT25) were manufactured by chemical conjugation using affinity peptides. A binding assay and the evaluation of plasma stability were performed in vitro to confirm the properties of NMK89 and NMT25. In vivo, we evaluated biodistribution, positron emission tomography (PET)/computed tomography (CT) imaging, antitumor effects, and toxicity. Moreover, the exposure dose in humans was estimated based on the biodistribution evaluation in normal mice. ResultsNMK89 and NMT25 showed binding specificity to MUC5AC and stability with radiochemical purity ≥90% in mice and human plasma following incubation for 168 h. NMK89 showed high accumulation in tumors and low non-specific accumulation in normal tissues. The antitumor effect of NMT25 was dose-dependent and significantly suppressed tumor growth in the NMT25 treatment groups compared with the control group (p < 0.05). NMK89 and NMT25 showed similar pharmacokinetics and biodistribution characteristics. Additionally, the human estimated exposure dose of NMK89 and NMT25 was confirmed, and the effective dose of NMK89 and NMT25 was 0.33 mSv/MBq and 177.5 mSv/MBq, respectively. ConclusionNMK89 showed specific accumulation in the MUC5AC-expressing tumors, while NMT25 showed strong antitumor effects. These results suggest NMK89 and NMT25 as promising theranostic agents for pancreatic cancer.

Clinical Applications and the Roles of Transporters in Disposition, Tumor Targeting, and Tissue Toxicity of meta-Iodobenzylguanidine (mIBG).

Transporters on the plasma membrane of tumor cells are promising molecular "Trojan horses" to deliver drugs and imaging agents into cancer cells. Radioiodine-labeled meta-iodobenzylguanidine (mIBG) is used as a diagnostic agent (123I-mIBG) and a targeted radiotherapy (131I-mIBG) for neuroendocrine cancers. mIBG enters cancer cells through the norepinephrine transporter (NET) where the radioactive decay of 131I causes DNA damage, cell death, and tumor necrosis. mIBG is predominantly eliminated unchanged by the kidney. Despite its selective uptake by neuroendocrine tumors, mIBG accumulates in several normal tissues and leads to tissue-specific radiation toxicities. Emerging evidences suggest that the polyspecific organic cation transporters play important roles in systemic disposition and tissue-specific uptake of mIBG. In particular, human organic cation transporter 2 (hOCT2) and toxin extrusion proteins 1 and 2-K (hMATE1/2-K) likely mediate renal secretion of mIBG whereas hOCT1 and hOCT3 may contribute to mIBG uptake into normal tissues such as the liver, salivary glands, and heart. This mini-review focuses on the clinical applications of mIBG in neuroendocrine cancers and the differential roles of NET, OCT and MATE transporters in mIBG disposition, response and toxicity. Understanding the molecular mechanisms governing mIBG transport in cancer and normal cells is a critical step for developing strategies to optimize the efficacy of 131I-mIBG while minimizing toxicity in normal tissues. Significance Statement Radiolabeled mIBG has been used as a diagnostic tool and as radiotherapy for neuroendocrine cancers and other diseases. NET, OCT and MATE transporters play differential roles in mIBG tumor targeting, systemic elimination, and accumulation in normal tissues. The clinical use of mIBG as a radiopharmaceutical in cancer diagnosis and treatment can be further improved by taking a holistic approach considering mIBG transporters in both cancer and normal tissues.

Glypican-3-Targeted 227Th α-Therapy Reduces Tumor Burden in an Orthotopic Xenograft Murine Model of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a significant cause of morbidity and mortality worldwide, with limited therapeutic options for advanced disease. Targeted α-therapy is an emerging class of targeted cancer therapy in which α-particle-emitting radionuclides, such as 227Th, are delivered specifically to cancer tissue. Glypican-3 (GPC3) is a cell surface glycoprotein highly expressed on HCC. In this study, we describe the development and invivo efficacy of a 227Th-labeled GPC3-targeting antibody conjugate (227Th-octapa-αGPC3) for treatment of HCC in an orthotopic murine model. Methods: The chelator p-SCN-Bn-H4octapa-NCS (octapa) was conjugated to a GPC3-targeting antibody (αGPC3) for subsequent 227Th radiolabeling (octapa-αGPC3). Conditions were varied to optimize radiolabeling of 227Th. In vitro stability was evaluated by measuring the percentage of protein-bound 227Th by γ-ray spectroscopy. An orthotopic athymic Nu/J murine model using HepG2-Red-FLuc cells was developed. Biodistribution and blood clearance of 227Th-octapa-αGPC3 were evaluated in tumor-bearing mice. The efficacy of 227Th-octapa-αGPC3 was assessed in tumor-bearing animals with serial measurement of serum α-fetoprotein at 23 d after injection. Results: Octapa-conjugated αGPC3 provided up to 70% 227Th labeling yield in 2 h at room temperature. In the presence of ascorbate, at least 97.8% of 227Th was bound to αGPC3-octapa after 14 d in phosphate-buffered saline. In HepG2-Red-FLuc tumor-bearing mice, highly specific GPC3 targeting was observed, with significant 227Th-octapa-αGPC3 accumulation in the tumor over time and minimal accumulation in normal tissue. Twenty-three days after treatment, a significant reduction in tumor burden was observed in mice receiving a 500 kBq/kg dose of 227Th-octapa-αGPC3 by tail-vein injection. No acute off-target toxicity was observed, and no animals died before termination of the study. Conclusion:227Th-octapa-αGPC3 was observed to be stable invitro; maintain high specificity for GPC3, with favorable biodistribution invivo; and result in significant antitumor activity without significant acute off-target toxicity in an orthotopic murine model of HCC.

Organic Cation Transporter 3 Mediates Tissue Uptake and Accumulation of meta-iodobenzylguanidine (mIBG)

Radioiodinated meta-iodobenzylguanidine (131I-mIBG) is utilized as a targeted radiotherapy for neuroendocrine cancers.131I-mIBG selectively accumulates in the cancer cells through uptake by the norepinephrine transporter. However, whole-body scintigraphy also shows extensive mIBG uptake and accumulation in several normal tissues (e.g. salivary glands, liver, heart) via mechanisms that are not fully understood. The accumulation of radioactive 131I-mIBG in these tissues is associated with a range of adverse reactions and tissue damages due to the unnecessary radiation exposure. We hypothesize that the efficacy and safety of 131I-mIBG can be improved by selectively inhibiting mIBG uptake in healthy tissues without affecting its uptake in tumor cells. The goal of this study is to elucidate the impact of organic cation transporter 3 (OCT3) on the in vivo pharmacokinetics andtissue distribution of mIBG using a mouse model with genetic deletion of Oct3. Additionally, we conducted in vitro studies in HEK293 cell lines stably transfected with mouse Oct3 (mOct3) and human OCT1-3 (hOCT1-3) to determine the uptake kinetics of mIBG and dose-dependent inhibition of OCT1-3-mediated uptake of mIBG. The in vitro kinetic analysis revealed similar apparent affinities in the uptake of mIBG by hOCT3 and mOct3 (Km of 14.5 ± 7.1 and 29.4 ± 3.4 µM, respectively), suggesting minimal species difference in mIBG transport by OCT3. Interestingly, hOCT3-mediated uptake of mIBG was inhibited by crizotinib (IC50 of 2.1 ± 0.3 µM) and crizotinib was 6.7-fold and 18-fold more potent towards hOCT3 than for hOCT2 and hOCT1, respectively. For the in vivo pharmacokinetic studies, full concentration-time profiles were determined to calculate mIBG exposure, defined as area under the concentration-time curve (AUC), in the plasma and each analyzed tissue. After retro-orbital injection (10 mg/kg), mIBG exhibited extensive accumulation in all tested tissues with exposures ranging from 4 to 90-fold higher than the plasma AUC in Oct3+/+ mice. In contrast, deletion of Oct3 significantly reduced mIBG exposure in the salivary glands by approximately 40%. The exposure of mIBG in the skeletal muscle, heart, and the lungs were also significantly reduced in Oct3-/- mice, demonstrating an important role of Oct3 in mediating uptake and accumulation of mIBG in various healthy tissues. On the other hand, the plasma concentration-time profiles of mIBG were similar between the Oct3+/+ and Oct3-/- mice with no significant changes in systemic AUC and other pharmacokinetic parameters. Additionally, no changes were observed between the two groups in the kidney, the main route of elimination for mIBG, suggesting that Oct3 does not contribute to the renal elimination of mIBG. In summary, we demonstrated that OCT3-mediated uptake of mIBG can be selectively inhibited and that blocking this pathway leads to decreased mIBG uptake and accumulation in normal tissues. Furthermore, these findings support inhibition of OCT3 as a viable clinical strategy to reduce 131I-mIBG accumulation and toxicity in healthy tissues in cancer patients undergoing radiotherapy.

The Latest Developments in Imaging of Fibroblast Activation Protein.

Fibroblast activation protein (FAP), a membrane-anchored peptidase, is highly expressed in cancer-associated fibroblasts in more than 90% of epithelial tumors and contributes to progression and worse prognosis of different cancers. Therefore, FAP is considered a promising target for radionuclide-based approaches for diagnosis and treatment of tumors and for the diagnosis of nonmalignant diseases associated with a remodeling of the extracellular matrix. Accordingly, a variety of quinolone-based FAP inhibitors (FAPIs) coupled to chelators were developed displaying specific binding to human and murine FAP with a rapid and almost complete internalization. Because of a high tumor uptake and a very low accumulation in normal tissues, as well as a rapid clearance from the circulation, a high contrast is obtained for FAPI PET/CT imaging even at 10 min after tracer administration. Moreover, FAPI PET/CT provides advantages over 18F-FDG PET/CT in several tumor entities for initial staging and detection of tumor recurrence and metastases, including peritonitis carcinomatosa.

Metal Organic Frameworks as Drug Targeting Delivery Vehicles in the Treatment of Cancer.

In recent years, metal organic frameworks (MOFs) have been widely developed as vehicles for the effective delivery of drugs to tumor tissues. Due to the high loading capacity and excellent biocompatibility of MOFs, they provide an unprecedented opportunity for the treatment of cancer. However, drugs which are commonly used to treat cancer often cause side effects in normal tissue accumulation. Therefore, the strategy of drug targeting delivery based on MOFs has excellent research significance. Here, we introduce several intelligent targeted drug delivery systems based on MOFs and their characteristics as drug-loading systems, and the challenges of MOFs are discussed. This article covers the following types of MOFs: Isoreticular Metal Organic Frameworks (IRMOFs), Materials of Institute Lavoisier (MILs), Zeolitic Imidazolate Frameworks (ZIFs), University of Oslo (UiOs), and MOFs-based core-shell structures. Generally, MOFs can be reasonably controlled at the nanometer size to effectively achieve passive targeting. In addition, different ligands can be modified on MOFs for active or physicochemical targeting. On the one hand, the targeting strategy can improve the concentration of the drugs at the tumor site to improve the efficacy, on the other hand, it can avoid the release of the drugs in normal tissues to improve safety. Despite the challenges of clinical application of MOFs, MOFs have a number of advantages as a kind of smart delivery vehicle, which offer possibilities for clinical applications.

Polymeric modification of gemcitabine via cyclic acetal linkage for enhanced anticancer potency with negligible side effects

Gemcitabine (GEM) is a powerful anticancer drug for various cancers. However, the anticancer efficacy and the side effects should be addressed for effective therapeutics. To this end, we created a GEM-conjugated polymer (P-GEM) based on cyclic acetal linkage as a delivery carrier of GEM. The obtained P-GEM stably conjugated GEM at physiological pH (i.e., bloodstream), but released GEM in response to acidic environments such as endosome/lysosome. After systemic administration of P-GEM for mice bearing subcutaneous tumors, it achieved prolonged blood circulation and enhanced tumor accumulation relative to free GEM system. In addition, the polymer-drug conjugate structure of P-GEM realized effective distribution in the tumor tissues toward the induction of apoptosis in most areas of the tumor sites. Of note, the molecular design of P-GEM achieved minimal accumulation in normal tissues, resulting in negligible GEM-derived adverse effects (e.g., gastrointestinal toxicity and hematotoxicity). Ultimately, even four times smaller dose of P-GEM on a GEM basis realized comparable/higher tumor growth suppression effect for two distinct pancreatic tumor models, compared to free GEM system. The obtained results suggest the huge potential of the present design of GEM-conjugated polymer for anticancer therapeutics.