Inhibition of hyaluronic acid formation sensitizes chronic myelogenous leukemia to treatment with doxorubicin.

In the current study we examined the ability of 4-methylumbelliferone (4-MU), which can inhibit hyaluronic acid synthesis, to sensitize K562 chronic myelogenous leukemia (CML) cells to doxorubicin therapy. Exposure of K562 cells to doxorubicin led to increased hyaluronic acid synthase (HAS) gene expression and increased levels of cell surface hyaluronic acid. Furthermore, exposure of K562 cells to exogenous HA caused resistance to doxorubicin-induced cell death. The combination of low dose 4-MU and doxorubicin led to increased apoptosis when compared to higher doses of any agent alone. Additionally, treatment with 4-MU led to a significant reduction in doxorubicin-induced increase in HA cell surface expression. Mechanistically, 4-MU treatment led to an increase in p38 activation and PARP cleavage. The role of p38 in 4-MU/doxorubicin-treated K562 cells was confirmed when p38 inhibitors led to protection from 4-MU/doxorubicin-induced apoptosis. Together, results from this study suggest that treatment with 4-MU increases the sensitivity of CML to chemotherapeutics by decreasing their HA-mediated resistance to apoptosis.