In vitro and in vivo effects of a farnesyltransferase inhibitor on Nf1-deficient hematopoietic cells

Oncogenic RAS alleles encode proteins that accumulate in the guanosine trip hosphate (GTP)-bound state. Because post-translational processing of Pas by farnesyltransferase is essential for biologic function, inhibitors of this enzyme have been developed as rational cancer therapeutics. We have invest igated farnesyltransferase inhibitor (FTI) L-744,832 in an in vivo murine m odel of myeloid leukemia that is associated with inactivation of the Nf1 tu mor suppressor gene. Nf1 encodes a GTPase activating protein for Pas, and N f1-deficient (Nf1-/-) hematopoietic cells show hyperactive Pas signaling th rough the mitogen-activated protein (MAP) kinase pathway. L-744,832 inhibit ed H-Ras prenylation in cell lines and in primary hematopoietic cells and a brogated the in vitro growth of myeloid progenitor colonies in response to granulocyte-macrophage colony-stimulating factor (GM-CSF). This FTI also pa rtially blocked GM-CSF-induced MAP kinase activation, but did not reduce co nstitutively elevated levels of MAP kinase activity in primary Nf1-/- cells . Injection of a single dose of 40 or 80 mg/kg of L-744,832 increased the a mount of unprocessed H-Ras in bone marrow cells, but had no detectable effe ct on N-Ras, Adoptive transfer of Nf1-/- hematopoietic cells into irradiate d mice induces a myeloproliferative disorder that did not respond to L-744, 832 treatment. We speculate that the lack of efficacy in this model is due to the resistance of N-Ras and K-Ras processing to inhibition by this FTI, (C) 1999 by The American Society of Hematology.