Abstract 3111: Elevated expression of hyaluronan synthase 2 associates with poor prognosis in diffusely infiltrating astrocytomas

Diffusely infiltrating astrocytomas are central nervous system tumors originating from astrocytic glial cells or their precursor cells. In this retrospective study we investigated the content of hyaluronan and the expression of hyaluronan metabolizing enzymes and its cell surface receptor, CD44, in these aggressive tumors. Hyaluronan is a large extracellular matrix molecule synthesized by three hyaluronan synthases (HAS1-3) on the plasma membrane and degraded by two hyaluronidases (HYAL1-2). In many tumors, aberrant hyaluronan metabolism implicates aggressive disease progression and metastatic potential.

Our material consisted of 165 diffusely infiltrating astrocytomas (WHO grades II-IV). Tumor samples were processed into tissue microarray (TMA) blocks. The TMA sections were stained for hyaluronan, CD44, HAS1, HAS2, HAS3 and HYAL2. The staining intensity of astrocytomas was evaluated with a four-level scoring (0-3; no color, weak, moderate and strong) by two independent observers. The immunostaining results were compared with χ2 -test or with Kruskal-Wallis test for correlation with clinicopathological parameters and survival analyses were done with Kaplan-Meier log rank test and Cox regression.

Hyaluronan and CD44 were strongly expressed in astrocytic gliomas but their expression did not correlate with WHO grade, cell proliferation activity by Ki-67, p53 status, epidermal growth factor receptor (EGFR) amplification or IDH1 mutation. Whereas HAS2 staining intensity showed a significant correlation with IDH1 mutation. Tumors with high HAS2 expression were IDH1 negative (p = 0.003). In addition, in non-parametric tests increased HAS2 staining intensity showed association with increased cell proliferation (p = 0.013) and in log rank test with decreased overall survival of patients (p = 0.001). Variables included in the multivariable Cox regression analysis were HAS2 staining intensity, p53 status, EGFR amplification, IDH1 mutation and WHO tumor grade; in this analysis HAS2 expression turned out to be a significant independent prognostic factor (p = 0.008). This study indicates that elevated expression of HAS2 is associated with glioma progression and suggests that HAS2 has a prognostic significance in diffusely infiltrating astrocytomas.

Citation Format: Mari J. Poukka, Hannu Haapasalo, Kirsi J. Rilla, Kristiina Tyynelä-Korhonen, Ylermi Soini, Sanna M. Pasonen-Seppänen. Elevated expression of hyaluronan synthase 2 associates with poor prognosis in diffusely infiltrating astrocytomas. [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 3111.

4-Methylumbelliferone inhibits hyaluronan synthesis by depletion of cellular UDP-glucuronic acid and downregulation of hyaluronan synthase 2 and 3

Hyaluronan accumulation on cancer cells and their surrounding stroma predicts an unfavourable disease outcome, suggesting that hyaluronan enhances tumor growth and spreading. 4-Methylumbelliferone (4-MU) inhibits hyaluronan synthesis and retards cancer spreading in experimental animals through mechanisms not fully understood. These mechanisms were studied in A2058 melanoma cells, MCF-7 and MDA-MB-361 breast, SKOV-3 ovarian and UT-SCC118 squamous carcinoma cells by analysing hyaluronan synthesis, UDP-glucuronic acid (UDP-GlcUA) content, and hyaluronan synthase (HAS) mRNA levels. The maximal inhibition in hyaluronan synthesis ranged 22-80% in the cell lines tested. Active glucuronidation of 4-MU produced large quantities of 4-MU-glucuronide, depleting the cellular UDP-GlcUA pool. The maximal reduction varied between 38 and 95%. 4-MU also downregulated HAS mRNA levels: HAS3 was 84-60% lower in MDA-MB-361, A2058 and SKOV-3 cells. HAS2 was the major isoenzyme in MCF-7 cells and lowered by 81%, similar to 88% in A2058 cells. These data indicate that both HAS substrate and HAS2 and/or HAS3 mRNA are targeted by 4-MU. Despite different target point sensitivities, the reduction of hyaluronan caused by 4-MU was associated with a significant inhibition of cell migration, proliferation and invasion, supporting the importance of hyaluronan synthesis in cancer, and the therapeutic potential of hyaluronan synthesis inhibition.