Patients with cancer can develop metastatic disease after latency periods that range from years to decades. This latency can be explained by the occurrence of dormant micrometastatic tumor cells. The mechanisms that trigger dormant tumor cells to “be activated” and subsequently progress to an actively growing metastatic lesion and cause a late relapse are essentially unknown. However, recent data indicate that these mechanisms are largely influenced by the microenvironment of the secondary site. The main goal of our study was to evaluate the role of the lung microenvironment in the regulation of dormancy of neuroblastoma micrometastasis (MicroNB) and their progression toward macrometastasis (MacroNB). We hypothesize that factors present in the lung microenvironment inhibit the propagation of MicroNB cells, preventing them from forming overt lung metastasis. This study indeed shows that lung-derived factors significantly reduce the viability of MicroNB cells, induce a G0-G1 cell cycle arrest accompanied by a down-regulation of Cyclin D1 and decrease ERK and FAK phosphorylation in these cells. Utilizing biochemical separation methods, we isolated and identified the lung-derived factor responsible for the viability inhibitory effect to be mouse hemoglobin subunit beta-2 (HBB2). Purified human hemoglobin beta subunit (HBB) of 147 amino acid residues, which shares a 80% sequence identity to mouse HBB2, had comparable cytostatic/cytotoxic effects on neuroblastoma cells, while the alpha subunit of human hemoglobin was inactive. We identified the inhibitory active fragment of HBB to be a 15 amino acid sequence in the C-terminus of the protein. Treatment with this short inhibitory peptide significantly inhibits neuroblastoma local tumor growth and lung metastasis. HBB2 is thus a candidate for a new anticancer drug.
© 2014 by Lippincott Williams & Wilkins