Imaging of the Mouse Lymphatic Sinus during Early Stage Lymph Node Metastasis Using Intranodal Lymphangiography with X-ray Micro-computed Tomography

Development of an intranodal drug delivery system using a mouse model with lymphadenopathy: novel discoveries and clinical application

INTRODUCTION

The low drug delivery rate of systemic chemotherapy to metastatic lymph nodes (LNs) may be due to tumor growth without tumor neovascularization in the LNs, loss of existing blood vessels and lymph sinuses due to the tumor growth, and increased intranodal pressure. The lymphatic drug delivery system (LDDS) is a method of injecting anticancer drugs directly into the LNs and can overcome these problems. The world's first specific clinical study using the LDDS for head and neck cancer started in 2024 in Japan. In this review, the background of the development of LDDS up to the present clinical trials is described.

AREAS COVERED

The MXH10/Mo-lpr/lpr (MXH10/Mo/lpr) recombinant inbred model mouse, vascular and lymphatic flow through LNs, the clinical N0 (cN0) LN model, preclinical studies of the LDDS, and its clinical application to treat head and neck cancer.

EXPERT OPINION

Conventionally, hematogenous and lymphatic administration have been the focus of attention for drug delivery to LNs. The LDDS is a method for injecting drugs directly to LNs, so it is important to develop a solvent and injecting method that can increase the uniformity of drug distribution within LNs.

The Value of Micro-CT in the Diagnosis of Lung Carcinoma: A Radio-Histopathological Perspective

Micro-computed tomography (micro-CT) is a relatively new imaging modality and the three-dimensional (3D) images obtained via micro-CT allow researchers to collect both quantitative and qualitative information on various types of samples. Micro-CT could potentially be used to examine human diseases and several studies have been published on this topic in the last decade. In this study, the potential uses of micro-CT in understanding and evaluating lung carcinoma and the relevant studies conducted on lung and other tumors are summarized. Currently, the resolution of benchtop laboratory micro-CT units has not reached the levels that can be obtained with light microscopy, and it is not possible to detect the histopathological features (e.g., tumor type, adenocarcinoma pattern, spread through air spaces) required for lung cancer management. However, its ability to provide 3D images in any plane of section, without disturbing the integrity of the specimen, suggests that it can be used as an auxiliary technique, especially in surgical margin examination, the evaluation of tumor invasion in the entire specimen, and calculation of primary and metastatic tumor volume. Along with future developments in micro-CT technology, it can be expected that the image resolution will gradually improve, the examination time will decrease, and the relevant software will be more user friendly. As a result of these developments, micro-CT may enter pathology laboratories as an auxiliary method in the pathological evaluation of lung tumors. However, the safety, performance, and cost effectiveness of micro-CT in the areas of possible clinical application should be investigated. If micro-CT passes all these tests, it may lead to the convergence of radiology and pathology applications performed independently in separate units today, and the birth of a new type of diagnostician who has equal knowledge of the histological and radiological features of tumors.

Combination therapy of lymphatic drug delivery and total body irradiation in a metastatic lymph node and lung mouse model

Chemotherapy using a lymphatic drug delivery system (LDDS) targeting lymph nodes (LNs) in the early stage of metastasis has a superior antitumor effect to systemic chemotherapy. An LDDS produces a higher drug retention rate and tissue selectivity in LNs. To expand the therapeutic coverage of LDDS from local treatment of metastatic LNs to prevention of distant metastases, the combination of treatment with therapies that enhance systemic tumor immune effects is an important therapeutic strategy. Recently, total body irradiation (TBI) has been shown to activate immune responses and alter the tumor microenvironment. Here we show that combination therapy with TBI and LDDS improves the antitumor effect of metastatic LNs and lung metastasis. Tumor cells were inoculated into the subiliac LN (SiLN) to induce metastasis into the proper axillary LN (PALN) and lung in a mouse model. TBI was carried out on day 4 after inoculation using a gamma irradiator. Lymphatic drug delivery into the accessory axillary LN was used to treat PALN. In vivo bioluminescence imaging, high-frequency ultrasound, and histology showed that combination therapy using TBI (total dose 1.0 Gy once) and the LDDS suppressed tumor growth in LNs and lung metastases and was more effective than using LDDS or TBI alone. Quantitative RT-PCR of spleens after combination therapy revealed increased expression of CD4, CD8, and IL-12b, indicating an activated immune response. The results show that combination therapy with TBI and LDDS is a method to improve the efficacy of LN metastases and distant metastases therapy and is a promising novel approach to treat cancer patients.

Drug formulation augments the therapeutic response of carboplatin administered through a lymphatic drug delivery system

Treatment of metastatic lymph nodes (LNs) is challenging due to their unique architecture and biophysical traits. Systemic chemotherapy fails to impede tumor progression in LNs due to poor drug uptake and retention by LNs, resulting in fatal systemic metastasis. To effectively treat LN metastasis, achieving specific and prolonged retention of chemotherapy drugs in the tumor-draining LNs is essential. The lymphatic drug-delivery system (LDDS) is an ultrasound-guided drug-delivery methodology for administration of drugs to LNs that addresses these requirements. However, early-stage metastatic LNs have an additional set of drug transport barriers, such as elevated intranodal pressure and viscosity, that negatively impact drug diffusion. In the present study, using formulations of elevated osmotic pressure and viscosity relative to saline, we sought to favorably alter the LN's physical environment and study its impact on pharmacokinetics and consequently the therapeutic efficacy of carboplatin delivered using the LDDS. Our study confirmed the capability of a drug formulation with elevated osmotic pressure and viscosity to alter the architecture of LNs, as it caused notable expansion of the lymphatic sinus. Additionally, the study delineated an optimal range of osmotic pressure and viscosity, centered around 1897 kPa and 11.5 mPa·s, above and below which therapeutic efficacy was found to decline markedly. These findings suggest that formulation osmotic pressure and viscosity are parameters that require critical consideration as they can both hinder and promote tumorigenesis. The facile formulation reported here has wide-ranging applicability across cancer spectrums and is thus anticipated to be of great clinical benefit.

Intranodal delivery of modified docetaxel: Innovative therapeutic method to inhibit tumor cell growth in lymph nodes

Delivery of chemotherapeutic agents into metastatic lymph nodes (LNs) is challenging as they are unevenly distributed in the body. They are difficult to access via traditional systemic routes of drug administration, which produce significant adverse effects and result in low accumulation of drugs into the cancerous LN. To improve the survival rate of patients with LN metastasis, a lymphatic drug delivery system (LDDS) has been developed to target metastatic LN by delivering chemotherapy agents into sentinel LN (SLN) under ultrasound guidance. The LDDS is an advanced method that can be applied in the early stage of the progression of tumor cells in the SLN before tumor mass formation has occurred. Here we investigated the optimal physicochemical ranges of chemotherapeutic agents’ solvents with the aim of increasing treatment efficacy using the LDDS. We found that an appropriate osmotic pressure range for drug administration was 700–3,000 kPa, with a viscosity < 40 mPa⋅s. In these physicochemical ranges, expansion of lymphatic vessels and sinuses, drug retention, and subsequent antitumor effects could be more precisely controlled. Furthermore, the antitumor effects depended on the tumor progression stage in the SLN, the injection rate, and the volumes of administered drugs. We anticipate these optimal ranges to be a starting point for developing more effective drug regimens to treat metastatic LN with the LDDS.

Characterizing perfusion defects in metastatic lymph nodes at an early stage using high-frequency ultrasound and micro-CT imaging

A perfusion defect in a metastatic lymph node (LN) can be visualized as a localized area of low contrast on contrast-enhanced CT, MRI or ultrasound images. Hypotheses for perfusion defects include abnormal hemodynamics in neovascular vessels or a decrease in blood flow in pre-existing blood vessels in the parenchyma due to compression by LN tumor growth. However, the mechanisms underlying perfusion defects in LNs during the early stage of LN metastasis have not been investigated. We show that tumor mass formation with very few microvessels was associated with a perfusion defect in a non-enlarged LN at the early stage of LN metastasis in a LN adenopathy mouse (LN size circa 10 mm). We found in a mouse model of LN metastasis, induced using non-keratinizing tumor cells, that during the formation of the perfusion defect in a non-enlarged LN, the number of blood vessels ≤ 50 μm in diameter decreased, while those of > 50 μm in diameter increased. The methods used were contrast-enhanced high-frequency ultrasound and contrast-enhanced micro-CT imaging systems, with a maximum spatial resolution of > 30 μm. Furthermore, we found no tumor angiogenesis or oxygen partial pressure (pO₂) changes in the metastatic LN. Our results demonstrate that the perfusion defect appears to be a specific form of tumorigenesis in the LN, which is a vascular-rich organ. We anticipate that a perfusion defect on ultrasound, CT or MRI images will be used as an indicator of a non-enlarged metastatic LN at an early stage.

Study of the physicochemical properties of drugs suitable for administration using a lymphatic drug delivery system

Lymph node (LN) metastasis is thought to account for 20‐30% of deaths from head and neck cancer. The lymphatic drug delivery system (LDDS) is a new technology that enables the injection of drugs into a sentinel LN (SLN) during the early stage of tumor metastasis to treat the SLN and secondary metastatic LNs. However, the optimal physicochemical properties of the solvent used to carry the drug have not been determined. Here, we show that the osmotic pressure and viscosity of the solvent influenced the antitumor effect of cisplatin (CDDP) in a mouse model of LN metastasis. Tumor cells were inoculated into the proper axillary LN (PALN), and the LDDS was used to inject CDDP solution into the subiliac LN (SiLN) to treat the tumor cells in the downstream PALN. CDDP dissolved in saline had no therapeutic effects in the PALN after it was injected into the SiLN using the LDDS or into the tail vein (as a control). However, CDDP solution with an osmotic pressure of ~ 1,900 kPa and a viscosity of ~ 12 mPa⋅s suppressed tumor growth in the PALN after it was injected into the SiLN using the LDDS. The high osmotic pressure dilated the lymphatic vessels and sinuses to enhance drug flow in the PALN, and the high viscosity increased the retention of CDDP in the PALN. Our results demonstrate that optimizing the osmotic pressure and viscosity of the solvent can enhance the effects of CDDP, and possibly other anticancer drugs, after administration using the LDDS.

Characterization of an angular domain fluorescence optical projection tomography system for mesoscopic lymph node imaging

Transmittance and fluorescence optical projection tomography can offer high-resolution and high-contrast visualization of whole biological specimens; however, applications are limited to samples exhibiting minimal light scattering. Our previous work demonstrated that angular-domain techniques permitted imaging of ∼1cm diameter noncleared lymph nodes because of their low scattering nature. Here, an angle-restricted transmittance/fluorescence system is presented and characterized in terms of geometric and fluorescence concentration reconstruction accuracy as well as spatial resolution, depth of focus, and fluorescence limits of detection. Using lymph node mimicking phantoms, results demonstrated promising detection and localization capabilities relevant for clinical lymph node applications.

Analysis of tumor vascularization in a mouse model of metastatic lung cancer

Therapies targeting tumor vasculature would improve the treatment of lung metastasis, although the early changes in vascular structure are incompletely understood. Here, we show that obstructive metastatic foci in lung arterioles decrease the pulmonary vascular network. To generate a mouse model of lung metastasis activation, luciferase-expressing tumor cells were inoculated into the subiliac lymph node (SiLN) of an MXH10/Mo-lpr/lpr mouse, and metastatic tumor cells in the lungs were activated by SiLN resection. Activation of metastases was monitored by in vivo bioluminescence imaging. Pulmonary blood vessel characteristics were analyzed using ex vivo micro-computed tomography. The enhanced permeability and retention (EPR) effect in neovasculature after tumor cell activation was evaluated from the accumulation of intravenously injected indocyanine green (ICG) liposomes. Metastatic foci in lung arterioles were investigated histologically. Micro-computed tomography revealed decreases in pulmonary blood vessel length, volume and number of branching nodes during the early stage of metastasis caused by metastatic foci. ICG liposome accumulation by the EPR effect was not detected. Histology identified metastatic foci in lung arterioles. The lack of an EPR effect after the formation of metastatic foci in lung arterioles makes conventional systemic chemotherapy ineffective for lung metastasis. Thus, alternative therapeutic methods of drug delivery are needed.