Impact of Hyaluronic Acid on the Cutaneous T-Cell Lymphoma Microenvironment: A Novel Anti-Tumor Mechanism of Bexarotene.

Background: Cutaneous T-cell lymphoma (CTCL) is a type of non-Hodgkin's lymphoma that primarily affects the skin, rich in hyaluronic acid (HA). HA is a component of the extracellular matrix in the dermis and likely affects the development of CTCL, but the mechanism is poorly understood. Here we show that low-molecular-weight HA (LMWHA) possibly exacerbates CTCL, and bexarotene, already used in CTCL treatment, decreases HA production.

Methods: We conducted immunohistochemistry, qRT-PCR, immunoblotting, and HA quantification using both mouse and human specimens to evaluate the impact of HA on CTCL. Additionally, we assessed the effect of bexarotene, which is already used for CTCL treatment, on HA metabolism.

Results: HA expression was higher in patients' serum and skin sections than in healthy controls. HA extracted from the skin of mice inoculated with tumors showed an increase in LMWHA. LMWHA increased lymphoma cell proliferation in vitro and accelerated tumor formation in mice in vivo. LMWHA also created a favorable environment for tumor cells by affecting fibroblasts, vascular endothelial cells, and tumor-associated macrophages. Thus, increased levels of HA, mainly LMWHA, exacerbate CTCL progression by affecting tumor cells and their microenvironment. Bexarotene treatment reduced the amount of total HA in murine tumor-inoculated skin, as well as the supernatant of cultured normal human dermal fibroblasts (NHDFs) and HuT78 cells. Detailed in vitro analyses showed that bexarotene treatment decreased HA synthase (HAS)1 and HAS2 expression in NHDFs and HAS1 and HAS3, and CEMIP expression in HuT78 cells. Chromatin immunoprecipitation assays revealed that bexarotene reduced retinoid X receptor-α binding to the HAS1 and HAS2 promoters in NHDFs.

Conclusions: Bexarotene potentially exerts its anti-tumor effect by reducing HA levels through decreased expression of HAS. These findings provide new insights into the process of CTCL development and additional insights regarding bexarotene treatment.