title: Influence of bone marrow stromal microenvironment on forodesine-induced responses in CLL primary cells.
abstract: Forodesine, a purine nucleoside phosphorylase inhibitor, displays in vitro activity in chronic lymphocytic leukemia (CLL) cells in presence of dGuo, which is the basis for an ongoing clinical trial in patients with fludarabine-refractory CLL. Initial clinical data indicate forodesine has significant activity on circulating CLL cells, but less activity in clearing CLL cells from tissues such as marrow. In tissue microenvironments, lymphocytes interact with accessory stromal cells that provide survival and drug-resistance signals, which may account for residual disease. Therefore, we investigated the impact of marrow stromal cells (MSCs) on forodesine-induced response in CLL lymphocytes. We demonstrate that spontaneous and forodesine-induced apoptosis of CLL cells was significantly inhibited by human and murine MSCs. Forodesine-promoted dGuo triphosphate (dGTP) accumulation and GTP and ATP depletion in CLL cells was inhibited by MSCs, providing a mechanism for resistance. Also, MSCs rescued CLL cells from forodesine-induced RNA- and protein-synthesis inhibition and stabilized and increased Mcl-1 transcript and protein levels. Conversely, MSC viability was not affected by forodesine and dGuo. Collectively, MSC-induced biochemical changes antagonized forodesine-induced CLL cell apoptosis. This provides a biochemical mechanism for MSC-derived resistance to forodesine and emphasizes the need to move toward combinations with agents that interfere with the microenvironment's protective role for improving current therapeutic efforts.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Kumudha
authors.initials: K
authors.lastname: Balakrishnan
authors.forename: Jan A
authors.initials: JA
authors.lastname: Burger
authors.forename: Maite P
authors.initials: MP
authors.lastname: Quiroga
authors.forename: Marina
authors.initials: M
authors.lastname: Henneberg
authors.forename: Mary L
authors.initials: ML
authors.lastname: Ayres
authors.forename: William G
authors.initials: WG
authors.lastname: Wierda
authors.forename: Varsha
authors.initials: V
authors.lastname: Gandhi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001853:Bone Marrow / Q000502:physiology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000473:pathology*; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D011684:Purine Nucleosides / Q000494:pharmacology*; D011683:Purine-Nucleoside Phosphorylase / Q000037:antagonists & inhibitors*; D011744:Pyrimidinones / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017154:Stromal Cells / Q000502:physiology*
chemical_list: C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D011684:Purine Nucleosides; D011744:Pyrimidinones; D012333:RNA, Messenger; C113101:forodesine; D011683:Purine-Nucleoside Phosphorylase