Heparanase is required for activation of macrophages by chemotherapy

Introduction. Heparanase is an endo-β-D-glucuronidase capable of cleaving heparan sulfate (HS) side chains at a limited number of sites. Heparanase activity has long been correlated with the metastatic potential of tumor-derived cells, attributed to enhanced cell dissemination as a consequence of HS cleavage and remodeling of the extracellular matrix (ECM) barrier that underlies epithelial and endothelial cells. Recent studies provided compelling evidence that ties heparanase levels with all steps of tumor formation including tumor initiation, growth, metastasis, and chemo-resistance, thus encouraging the development of heparanase inhibitors as anti-cancer and anti-inflammatory drugs. Mechanistic studies on heparanase action have focused primarily on its expression by tumor cells and revealed that heparanase promotes an aggressive tumor behavior via multiple mechanisms. Yet, non-tumor (host) cells including macrophages can also upregulate heparanase expression upon activation and thereby contribute to cancer progression. Here, we examined the effect of chemotherapy (i.e., Taxotere, cisplatin) on heparanase expression by macrophages.

Methods. Peritoneal macrophages were isolated from thioglycolate-treated wild-type (wt) and heparanase-knockout (KO) mice, exposed to Taxotere or cisplatin, and the expression levels of heparanase and selected cytokines were examined by qPCR. In a functional assay, Lewis lung carcinoma cells were implanted subcutaneously together with untreated (control) or Taxotere-treated macrophages and tumor growth was inspected.

Results. Only modest, 2-fold increase of heparanase expression was noted in peritoneal macrophages isolated from control mice and exposed to chemotherapy. However, the expression of cytokines such as TNFα (15-fold), IL6 (10-fold), and MIP2 (60-fold) was markedly induced by Taxotere. In striking contrast, no induction of cytokine expression was evident in macrophages isolated from Hpa-KO mice, suggesting that induction of cytokines by chemotherapeutics is heparanase-dependent. Mechanistically, cytokine induction by Taxotere involves stress signaling because inhibitors of JNK and PERK (an ER stress response effector) practically block this induction. Furthermore, Taxotere seems to elicit an epigenetic response. This is concluded because inhibitors of EZH2 (responsible for histone H3K27 methylation), completely block MIP2 induction by Taxotere. Notably, implantation of LLC cells with an equal number of macrophages treated with Taxotere resulted in 4-fold bigger tumors vs control, untreated macrophages, associating with increased VEGF levels and higher vascular density.

Conclusions. Chemotherapeutics activate macrophages, evident by a burst in cytokine levels, in heparanase-dependent manner. Notably, chemotherapy re-program macrophages toward pro-tumorigenic, thus clearly emphasizing the significance of host heparanase in tumor growth and chemoresistance.