Abstract 119: The influence of CD44/HA signaling on CML survival and resistance to tyrosine kinase inhibitor treatment

The development of tyrosine kinase inhibitors (TKIs) such as imatinib has greatly improved the prognosis and survival of patients diagnosed with chronic myeloid leukemia (CML). However, many CML patients relapse due to the presence of minimal residual disease and the development of TKI resistance. It is unknown exactly what causes the relapse, but based on research from our laboratory we hypothesize that hyaluronic acid (HA) produced by fibroblasts in the microenvironment of the bone marrow provide for a protective environment preventing the tumor cells from therapy-induced cell death or senescence. The purpose of this study is to determine the influence that HA and its binding to its receptor (CD44) has on CML survival and resistance development. Initially, we examined the effect that stromal cell derived and/or exogenously added HA has on CML resistance to imatinib. Cell survival, apoptosis, HA production, and signaling events elicited by the interactions of HA with CD44 was examined using methods such as ELISA, western blotting, and MTT analysis. Furthermore, we examined the potential therapeutic use of compounds known to alter HA production and/or signaling for the treatment of CML. Our study demonstrates increased cell survival when the tumor cells are co-cultured with fibroblasts or have exogenous HA added to them after imatinib treatment. Additionally, we show that knocking out hyaluronic acid synthases reduces this protective effect. This data supports our hypothesis and we believe it could help lead to improved therapeutic treatment for CML.

Note: This abstract was not presented at the meeting.

Citation Format: Kylie Humphries, Olga Uchakina, Bryan Hostetler, Robert McKallip. The influence of CD44/HA signaling on CML survival and resistance to tyrosine kinase inhibitor treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 119.

Potential mechanisms of cellular injury following exposure to a physiologically relevant species of inorganic mercury

Mercury is a toxic metal that is found ubiquitously in the environment. Humans are exposed to different forms of mercury via ingestion, inhalation, and/or dermal absorption. Following exposure, mercuric ions may gain access to target cells and subsequently lead to cellular intoxication. The mechanisms by which mercury accumulation leads to cellular injury and death are not understood fully. Therefore, purpose of this study was to identify the specific intracellular mechanisms that are altered by exposure to inorganic mercury (Hg²⁺). Normal rat kidney (NRK) cells were exposed to a physiologically relevant form of Hg²⁺, as a conjugate of cysteine (10 μM or 50 μM). Alterations in oxidative stress were estimated by measuring lipid peroxidation and mitochondrial oxidative stress. Alterations in actin and tubulin were measured using specific fluorescent dyes. Calcium levels were measured using Fluo-3 AM Calcium Indicator while autophagy was identified with Premo^™ Autophagy Sensor LC3B-GFP. The current findings show that exposure to Hg²⁺ leads to enhanced oxidative stress, alterations in cytoskeletal structure, increases in intracellular calcium, and enhanced autophagy. We have established a more complete understanding of intoxication and cellular injury induced by a relevant form of Hg²⁺ in proximal tubule cells.

Abstract 3848: 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 TKI's 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 GA's 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.

Hyaluronic Acid Inhibitor 4-Methylumbelliferone Activates the Intrinsic Apoptosis Pathway in K562 Chronic Myelogenous Leukemia Cells

BACKGROUND

As an inhibitor of hyaluronic acid (HA) synthesis, 4-methylumbelliferone (4-MU) has been shown to induce apoptosis of various types of cancer cells. However, the potential impact of 4-MU-induced apoptosis on leukemia cells via modulation of HA is not well-known.

MATERIALS AND METHODS

We examined apoptosis of chronic myelogenous leukemia (CML) cells after treatment with 4-MU using annexin V/propidium iodide (V/PI) analysis and poly (ADP-ribose) polymerase (PARP) cleavage. We further examined the mechanisms of 4-MU-induced apoptosis by measuring mitochondrial membrane potential and reactive oxygen species generation. Using real-time PCR, and western blot analysis we examined signaling pathways involved in apoptosis.

RESULTS

The current study demonstrated that treatment of CML cells with 4-MU led to induction of apoptosis through PARP cleavage and loss of mitochondria membrane potential. Mechanistically, 4-MU led to increased p53 mRNA expression, elevated cytoplasmic protein levels of cytochrome c and B-cell lymphoma-2-associated X (BAX) and reduced levels of B-cell lymphoma-2 (BCL2) expression. Addition of exogenous soluble HA was able to protect 4-MU-exposed cells from apoptosis.

CONCLUSION

Our findings suggest that 4-MU induces apoptosis in CML cells by activating components associated with the intrinsic apoptosis pathway.