DESCRIPTION: (Applicant's Abstract) The overall objective of this application is to decipher molecular and pharmacodynamic factors in patients with acute promyelocytic leukemia (APL) that determine the therapeutic effectiveness and development of resistance to all-trans-retinoic acid (tRA), leading to improved cure rates of this relatively rare disease and providing greater understanding of the mechanisms of tRA bioactivity that may help guide the application of this unique and relatively benign form of therapy to other malignancies. The applicant will build upon important leads from previous studies and upon established relationships with principal clinical investigators and institutions essential for the provision of critical patient materials and for clinically testing the significance of laboratory findings within the context of Oncology Cooperative Group protocol trials. The Specific Aims are: (1) to definitively determine the relationship of molecular variations in the APL-specific fusion gene product PML-RARa to tRA responsiveness and clinical outcome; (2) to determine the molecular basis and biological significance of altered forms of PML-RARa mRNA, which encode aberrant truncated PML proteins and can be associated with tRA-resistance; (3) to determine if four factors that can affect in vivo tRA disposition, plasma pharmacokinetics, APL cell tRA uptake and metabolism and APL cellular RA binding protein-II (CRABP-II), are coordinately related to one another and/or to clinical outcome; (4) to determine the molecular mechanism of reduced APL cell sensitivity to tRA-induced in vitro differentiation consistently observed in relapse cells from tRA-treated patients; and (5) to determine the prognostic significance of variations in the presence and level of subclinical (minimal) residual disease (MRD), as detected by persistence of PML-RARa mRNA, following different forms of protocol-directed therapy. The investigations will employ a range of molecular, pharmacological and biological techniques, particularly reverse transcriptase-polymerase chain reaction (RT-PCR), DNA cloning and sequencing, in vitro transcription and translation analysis, high performance liquid chromatography and various types of tissue culture including transfection studies utilizing expression vectors. All studies require detailed, computerized specimen and data analysis, storage and retrieval systems, which will conform with stringent guidelines for laboratory studies associated with Phase III clinical trials established by the Eastern Cooperative Oncology Group (ECOG) Laboratory Committee and various levels of statistical analysis under supervision by the ECOG Statistical Center.