Hyaluronan, angiogenesis and malignant disease

Dear Sir, We congratulate Dr. Lokeshwar’s group for another landmark paper in this journal, wherein they demonstrated that the saliva of patients with high-grade head-and-neck squamous cell carcinoma contained both high and low m.w. HA.1 The latter, i.e., o-HA, is generated when HAase, an endoglycosidase, degrades HA. Although the authors did allude to the issue of HA and its relevance to angiogenesis, we highlight here its pathologic relevance in human malignancy and present our supporting unpublished data. The angiogenic activity of HA is dependent on its molecular mass. High m.w. nHA is antiangiogenic, whereas almost 2 decades ago we reported that HA degradation products of a specific size (3–25 disaccharide units) induce angiogenesis in vivo.2 Subsequently, we have shown that o-HA fragments of 3–10 disaccharides were angiogenic in several in vivo assays and stimulated EC migration, proliferation and sprout formation.3–6 The biological activities of HA are mediated through interaction with cell surface receptors such as CD44, resulting in activation of intracellular signalling events. In collaboration with Dr. R. Montesano’s group, we found that HA degradation products influence EC invasion of a 3-D ECM.7 o-HA acted synergistically with vascular endothelial growth factor but not basic fibroblast growth factor. We reported that o-HA induces phosphorylation and activation of mitogen-activated protein kinase in bovine ECs, as well as upregulating the early response genes c-fos, c-jun and jun-B, which control the expression of other genes, including those of matrix-degrading proteases.8 Because HA acts via its receptor, CD44, it is conceivable that o-HA promotes cell invasion and tube formation by activating intracellular signalling pathways that result in modulation of pericellular proteolysis. Also, o-HA induced multiple signalling pathways involved in EC migration, proliferation and wound healing.9,10 More relevant to Lokeshwar’s publication is our finding that sera of children with renal tumours contain o-HA. Briefly, renal tumours are one of the major groups of childhood solid malignancy,Wilms’ tumour (nephroblastoma) being the most frequent in this group. Another kidney tumour BMRTC has been distinguished from Wilms’ tumour.11 BMRTC comprises about 4% of all primary renal neoplasms in childhood. In the Manchester region, with a population of 1 million children, we expect to encounter approximately one BMRTC case every 5 years. BMRTC has been associated with poor prognosis, unlike Wilms’ tumour.11 Furthermore, in contrast to Wilms’ tumour, BMRTC occurs predominantly in boys and, as the name implies, frequently metastasises to bone (in 60% of cases compared to 1% for Wilms’ tumour). HA is a normal component of human serum. Its half-life in the circulation is 2.5–5.5 min and its mean serum concentration, 42 25 g/l in healthy adults.12 In contrast to patients with Wilms’ tumour and mesothelioma, patients with many other types of cancer have serum HA levels within the normal range.13,14 It is possible that the m.w. of HA, rather than its level in serum, may be pathognomonic for certain cancers. Indeed, we found that the HA level in the sera of normal children was barely detectable and had a m.w. of 1 to 5 x 10.5 In both Wilms’ and BMRTC patients, very high levels of HA were found in preoperative serum samples; these fell markedly following surgical excision of tumours.15 We also demonstrated the presence of low m.w. HA (similar to the angiogenic fragment of HA) in the sera of BMRTC patients. In contrast, high m.w. HA (which is not angiogenic) was found in the sera of Wilms’ patients. Following surgery in BMRTC patients, not only did serum HA levels fall to a value within normal ranges but also the HA which remained was of high m.w. We now have unpublished data to show that tissue culture medium from BMRTC cells, in contrast to Wilms’ tumours, contains low m.w. o-HA. Furthermore, FPLC separation of HAase-digested n-HA (kindly provided by Dr. I. Scott, Unilever, London, UK) has enabled us to narrow down the HA size to between 5 and 7 disaccharides, which continue to retain their angiogenic potential. None of these disaccharides individually was able to induce angiogenesis in chicken CAM assay. However, in combination, they had the ability to induce angiogenesis in vivo and EC migration in vitro. Future studies should be directed toward ascertaining whether the size of o-HA is a hallmark of a certain type of malignancy. Yours sincerely, Mark SLEVIN, David WEST, Pat KUMAR, Paul Rooney and Shant KUMAR