Lineage non-specific down regulation of P210bcr/abl in the CML cell line, KU-812-F, during differentiation

Induced dendritic cell differentiation of chronic myeloid leukemia blasts is associated with down-regulation of BCR-ABL

Although differentiation of leukemic blasts to dendritic cells (DC) has promise in vaccine strategies, the mechanisms underlying this differentiation and the differences between leukemia and normal progenitor-derived DC are largely undescribed. In the case of chronic myeloid leukemia (CML), understanding the relationship between the induction of DC differentiation and the expression of the BCR-ABL oncogene has direct relevance to CML biology as well as the development of new therapeutic approaches. We now report that direct activation of protein kinase C (PKC) by the phorbol ester PMA in the BCR-ABL(+) CML cell line K562 and primary CML blasts induced nonterminal differentiation into cells with typical DC morphology (cytoplasmic dendrites), characteristic surface markers (MHC class I, MHC class II, CD86, CD40), chemokine and transcription factor expression, and ability to stimulate T cell proliferation (equivalent to normal monocyte-derived DC). PKC-induced differentiation was associated with down-regulation of BCR-ABL mRNA expression, protein levels, and kinase activity. This down-regulation appeared to be signaled through the mitogen-activated protein kinase pathway. Therefore, PKC-driven differentiation of CML blasts into DC-like cells suggests a potentially novel strategy to down-regulate BCR-ABL activity, yet raises the possibility that CML-derived DC vaccines will be less effective in presenting leukemia-specific Ags.

Highly efficient elimination of Philadelphia leukemic cells by exposure to bcr/abl antisense oligodeoxynucleotides combined with mafosfamide

Synthetic oligodeoxynucleotides complementary to the break-point junction of bcr-abl transcripts selectively inhibit the proliferation of Philadelphia-positive leukemic cells, but residual leukemic cells persist in antisense oligodeoxynucleotides-treated cultures. Cyclophosphamide derivatives such as mafosfamide and 4-hydroperoxycyclophosphamide are used at high doses for purging of Philadelphia leukemic cells from marrows but such treatment can be associated with delayed engraftment and prolonged cytopenias. To develop a more effective procedure that might optimize the killing of leukemia cells and the sparing of normal hematopoietic progenitor cells, a 1:1 mixture of Philadelphia leukemic cells and normal bone marrow cells was exposed to a combination of a low dose of mafosfamide and bcr-abl antisense oligodeoxynucleotides and assayed for growth ability in clonogenic assays and in immunodeficient mice. Bcr-abl transcripts were not detected in residual colonies, and cytogenetic analysis of individual colonies revealed a normal karyotype. Normal but not leukemic hematopoietic colonies of human origin were also detected in marrows of immunodeficient mice 1 mo after injection of the treated cells. Our results indicate that a combination of a conventional chemotherapeutic agent and a tumor-specific antisense oligodeoxynucleotide is highly effective in killing leukemic cells and in sparing a much higher number of normal progenitor cells as compared with high-dose mafosfamide treatment. This offers the prospect of a novel and more selective ex vivo treatment of chronic myelogenous leukemia.