Most solid cancers spread to new sites via the lymphatics before hematogenous dissemination. However, only a small fraction of an intravenously administered anti‐cancer drug enters the lymphatic system to reach metastatic lymph nodes (LN). Here, we show that the enhanced permeability and retention (EPR) effect is not induced during the early stages of LN metastasis. Luciferase‐expressing tumor cells were injected into the subiliac LN of the MXH10/Mo‐lpr/lpr mouse to induce metastasis to the proper axillary LN (PALN). In vivo biofluorescence imaging was used to confirm metastasis induction and to quantify the EPR effect, measured as PALN accumulation of intravenously injected indocyanine green (ICG) liposomes. PALN blood vessel volume changes were measured by contrast‐enhanced high‐frequency ultrasound imaging. The volume and density of blood vessels in the PALN increased until day 29 after inoculation, whereas the LN volume remained constant. ICG retention was first detected on day 29 post‐inoculation. While CD31‐positive cells increased up to day 29 post‐inoculation, α‐smooth muscle actin‐positive cells were detected on day 29 post‐inoculation for the first time. These results suggest that the EPR effect was not induced in the early stages of LN metastasis; therefore, systemic chemotherapy would likely not be beneficial during the early stages of LN metastasis. The development of an alternative drug delivery system, independent of the EPR effect, is required for the treatment of LN metastasis.

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.

Systemic delivery of an anti-cancer agent often leads to only a small fraction of the administered dose accumulating in target sites. Delivering anti-cancer agents through the lymphatic network can achieve more efficient drug delivery for the treatment of lymph node metastasis. We show for the first time that polymeric gold nanorods (PAuNRs) can be delivered efficiently from an accessory axillary lymph node to a tumor-containing proper axillary lymph node, enabling effective treatment of lymph node metastasis. In a mouse model of metastasis, lymphatic spread of tumor was inhibited by lymphatic-delivered PAuNRs and near-infrared laser irradiation, with the skin temperature controlled by cooling. Unlike intravenous injection, lymphatic injection delivered PAuNRs at a high concentration within a short period. The results show that lymphatic administration has the potential to deliver anti-cancer agents to metastatic lymph nodes for inhibition of tumor growth and could be developed into a new therapeutic method.

Metastatic lymph nodes ( LN s) may be the origin of systemic metastases. It will be important to develop a strategy that prevents systemic metastasis by treating these LN s at an early stage. False‐negative metastatic LN s, which are found during the early stage of metastasis development, are those that contain tumor cells but have a size and shape similar to LN s that do not host tumor cells. Here, we show that 5‐fluorouracil (5‐ FU ), delivered by means of a novel lymphatic drug delivery system ( LDDS ), can treat LN s with false‐negative metastases in a mouse model. The effects of 5‐ FU on four cell lines were investigated using in vitro cytotoxicity and cell survival assays. The therapeutic effects of LDDS ‐administered 5‐ FU on false‐negative metastatic LN s were evaluated using bioluminescence imaging, high‐frequency ultrasound ( US ), and histology in MHX 10/Mo‐ lpr / lpr mice. These experimental animals develop LN s that are similar in size to human LN s. We found that all cell lines showed sensitivity to 5‐ FU in the in vitro assays. Furthermore, a concentration‐dependent effect of 5‐ FU to inhibit tumor growth was observed in tumor cells with low invasive growth characteristics, although a significant reduction in metastatic LN volume was not detected in MHX 10/Mo‐ lpr / lpr mice. Adverse effects of 5‐ FU were not detected. 5‐Fluorouracil administration with a LDDS is an effective treatment method for false‐negative metastatic LN s. We anticipate that the delivery of anticancer drugs by a LDDS will be of great benefit in the prevention and treatment of cancer metastasis via LN s.

Lymph node (LN) dissection is a crucial procedure for cancer staging, diagnosis and treatment, and for predicting patient survival. Activation of lung metastatic lesions after LN dissection has been described for head and neck cancer and breast cancer. Preclinical studies have reported that dissection of a tumor‐bearing LN is involved in the activation and rapid growth of latent tumor metastases in distant organs, but it is also important to understand how normal (non‐tumor‐bearing) LN resection influences secondary cancer formation. Here, we describe how the resection of tumor‐bearing and non‐tumor‐bearing LN affects distant metastases in MXH10/Mo‐lpr/lpr mice. Tumor cells were administered intravenously and/or intranodally into the right subiliac lymph node (SiLN) to create a mouse model of lung metastasis. Luciferase imaging revealed that tumor cells in the lung were activated after resection of the SiLN, irrespective of whether it contained tumor cells. No luciferase activity was detected in the lungs of mice that did not undergo LN resection (excluding the intravenous inoculation group). Our results indicate that resection of an LN can activate distant metastases regardless of whether the LN contains tumor cells. Hence, lung metastatic lesions are suppressed while metastatic LN are present but activated after LN resection. If this phenomenon occurs in patients with cancer, it is likely that lung metastatic lesions may be activated by elective LN dissection in clinical N0 cases. The development of minimally invasive cancer therapy without surgery would help to minimize the risk of activation of distant metastatic lesions by LN resection.