Targeting Hyaluronidase Reduces Stromal Cell Protection Of Chronic Myeloid Leukemia To Imatinib Therapy

An estimated 20-30% of CML patients will become resistant to tyrosine kinase inhibitors (TKIs) including imatinib. Recent reports suggest that CML resistance to TKI9s is driven by interactions with protective microenvironment niches that influence their survival and self-renewal capacity. Hyaluronic acid (HA) has emerged as a key contributor in this phenomenon of CML resistance to TKI’s. HA influences cell viability through molecular weight dependent interactions with cell-surface receptors CD44 and RHAMM. Low molecular weight (LMW) HA, is typically found in association with many cancers including CML and promotes apoptotic resistance, proliferation, and migration of cancer cells. High molecular weight (HMW) HA is primarily produced by fibroblasts and its catabolism to LMW HA is mediated by hyaluronidase (HYAL) activity. HYAL activity may provide a potential therapeutic target in combination with current TKI treatments. Using a co-culture model, we investigated the role of HA produced by bone marrow stromal fibroblasts on CML viability when subject to imatinib (IM) treatment. Furthermore, we investigated the possibility of targeting hyaluronidase as an adjuvant in combination with IM for the treatment of CML. Co-culture with stromal fibroblasts protected CML cells from proliferation inhibition by IM. HA production and its catabolic products including LMW HA were elevated in the supernatant of co-cultures exposed to IM. The expression of genes encoding for HA metabolic proteins including hyaluronic acid synthases and HYALs, were significantly increased in co-cultures subject to IM stress. Additionally, HA treatment of CML mono-culture protected against chemotherapy-induced apoptosis. Treatment of CML co-culture with HYAL inhibitor, glycrrhizic acid (GA), inhibited HYAL activity, greatly reduced proliferation and increased apoptosis of CML cells alone and in combination with IM. This investigation provides additional evidence of the importance of stromal cell support in CML pathology and that resistance to TKI therapy may be mediated in part through upregulation of total HA production and its catabolism. Furthermore, we establish the potent therapeutic effects of GA on CML cells alone and in combination with current IM treatment strategies as a prospective method of circumventing TKI-resistant CML. For the first time we demonstrate GA9s effectiveness as a HYAL inhibitor in culture. HYALs are an attractive target not only in CML resistance but in many cancers due to the reported role of its product, LMW HA, in inflammation, proliferation, and apoptotic resistance. Citation Format: Bryan Hostetler, Olga Uchakina, Robert McKallip. Targeting hyaluronidase reduces stromal cell protection of chronic myeloid leukemia to imatinib therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3848.