Tumor-line specific causes of intertumor heterogeneity in blood supply in human melanoma xenografts

Metastatic pathway and the microvascular and physicochemical microenvironments of human melanoma xenografts

BACKGROUND

Malignant melanoma of the skin can metastasize through blood vessels and lymphatics. The primary tumor develops a vascular microenvironment characterized by abnormal blood vessels and lymphatics and a physicochemical microenvironment characterized by low oxygen tension, regions with hypoxic tissue, and high interstitial fluid pressure (IFP). This study aimed at identifying relationships between the metastatic route of melanomas and characteristic features of the microvascular and physicochemical microenvironments of the primary tumor.

METHODS

Two patient-derived xenograft (PDX) models (E-13, N-15) and four cell line-derived xenografts (CDX) models (C-10, D-12, R-18, T-22) of human melanoma were included in the study. Tumors were transplanted to an orthotopic site in BALB/c-nu/nu mice, and when the tumors had grown to a volume of 500-600 mm3, the IFP of the primary tumor was measured and the hypoxia marker pimonidazole was administered before the host mouse was euthanized. The primary tumor, lungs, and six pairs of lymph nodes were evaluated by examining hematoxylin/eosin-stained and immunostained histological preparations. The expression of angiogenesis-related genes was assessed by quantitative PCR.

RESULTS

C-10, D-12, and E-13 tumors disseminated primarily by the hematogenous route and developed pulmonary metastases. These tumors showed high angiogenic activity and high expression of the F3 gene as well as ANGPT2 and TIE1, genes encoding proteins of the angiopoietin-tie system. N-15, R-18, and T-22 tumors disseminated mainly by the lymphogenous route and developed metastases in draining lymph nodes. These tumors had highly elevated IFP and showed high expression of NRP2, a gene encoding neuropilin-2.

CONCLUSION

The primary metastatic route of orthotopic human melanoma xenografts and the development of lung and lymph node metastases are influenced significantly by the microvascular and physicochemical microenvironments of the primary tumor.

Intravital Insights into Heterogeneity, Metastasis, and Therapy Responses

Tumor progression is driven by a series of genetic and microenvironmental changes. These events lead to heterogeneous tumors which consist of a variety of cells from which some cells may possess properties which promote survival after therapy and metastasis. Recent advances in intravital microscopy (IVM) have enabled visualization of this tumor heterogeneity over time at a single-cell resolution. We highlight here the latest IVM studies that have revealed the dynamic interactions between the tumor cells and their local microenvironment. We review the most recent data that exposes how these dynamic interactions cause an additional increase in tumor heterogeneity, resulting in multiple metastatic strategies and facilitating therapy resistance.