Fetal haemoglobin (HbF) as an immunohistochemical tumour marker in bone marrow and spleen

Considerations on the possible origins of fetal hemoglobin cells produced in developing tumors

Although tumor angiogenesis in relation to cancer therapy has been widely investigated for more than four decades, its counterpart tumor hematopoiesis has not been equally considered. In that respect, in our long-term immunohistochemical examination of fetal hemoglobin (HbF) cells in various solid tumors, we have observed signs of fetal hematopoiesis in situ within the tumors. We hypothesize that this observed fetal hematopoiesis, involving angiogenesis, mirrors mammalian blood system development in the embryo and the fetus; this is consistent with the concept of the hemogenic endothelial progenitor, common to endothelial and hemopoietic cells. Based on this assumption, there should exist in tumors at least two routes of hematoangiogenesis: one of fetal (HbF) hematopoiesis and the other of adult (HbA) hematopoiesis, each one deserving a different therapeutic approach. In the fetal route, HbF should support tumor growth by virtue of its high oxygen affinity.

A potential role of fetal hemoglobin in the development of multidrug resistance

Our previous data from a human leukemic cell line made resistant to the nucleoside analog (NA) 9-β-D-arabinofuranosylguanine (AraG) revealed a massive upregulation of fetal hemoglobin (HbF) genes and the ABCB1 gene coding for the multidrug resistance P-glycoprotein (P-gp). The expression of these genes is regulated through the same mechanisms, with activation of the p38-MAPK pathway and inhibition of methylation making transcription factors more accessible to activate these genes. We could show that AraG, as well as other NAs, and P-gp substrates could induce global DNA demethylation and induction of Hbγ and P-gp both at the mRNA and protein expression level. We speculate that the expression of HbF prior to drug exposure or in drug-resistant cell lines is a strategy of the cancer to gain more oxygen, and thereby survival benefits. We also believe that P-gp may be induced in order to excrete Hb degradation products from the cells that would otherwise be toxic. By using Hbγ siRNA and pharmacological inhibitors of HbF production we here present a possible relationship between HbF induction and multi-drug resistance in a human leukemia cell line model.