The deoxycytidine analog 1-[beta-D-arabinofuranosyl]cytosine (ara-C) is an extremely effective agent widely used for clinical management of human myeloid leukemias. While the precise nature of the mechanism through which this agent promotes leukemic cell death is unknown, the response to ara-C paradoxically is comprised of both pro-apoptotic and anti-apoptotic signals. Particularly significant is recruitment by ara-C of the mitogen activated protein kinase (MAPK) cascade; this response apparently stems from stimulation of cPKC/nPKC through sustained generation of the cytoprotective lipid messenger diglyceride, and consequent activation of the Raf-1->MEK1->ERK1->ERK2 sequence. The implications of this are striking, as they suggest that the cytoprotective influence of this signaling mechanisms constitutes an intrinsically self-limiting aspect of ara-C action that reduces the drug's cytotoxic potential. Interruption of this pathway at various levels enhances the anti-leukemic action of ara-C. Agents that promote pharmacological reductions in cPKC/nPKC activity by either chronic down- regulation or inhibition acute (e.g., bryostatin 1, safingol) are already under study in clinical trial as chemopotentiators for use with several mainstream anti-neoplastic agents. Analogous interference with MAPK further downstream has not been attempted, however. Preliminary data indicate that the MAPK cascade represents a critical target for a novel chemosensitizing paradigm, inasmuch as ara-C lethality is synergistically increased by pharmacological disruption of the MEK-ERK module by inhibitors of MEK1. The use of these agents will be characterized in detail, and validated using selective molecular ablations of individual elements comprising this pathway. In addition, the potential importance of a pprimary MAPK target, MAPK target, NFkappaB, will be similarly evaluated through pharmacological and molecular approaches. It is anticipated that the proposed studies will provide the basis for new and innovative and chemopotentiating strategies will be used with ara-C, and potentially for other chemotherapeutic agents as well.
