title: Combined preconditioning and in vivo chemoselection with 6-thioguanine alone achieves highly efficient reconstitution of normal hematopoiesis with HPRT-deficient bone marrow.
abstract: Purine analogs such as 6-thioguanine (6TG) cause myelotoxicity upon conversion into nucleotides by hypoxanthine-guanine phosphoribosyltransferase (HPRT). Here we have developed a novel and highly efficient strategy employing 6TG as a single agent for both conditioning and in vivo chemoselection of HPRT-deficient hematopoietic stem cells. The dose-response and time course of 6TG myelotoxicity were first compared in HPRT wild-type mice and HPRT-deficient transgenic mice. Dosage and schedule parameters were optimized to employ 6TG for myelosuppressive conditioning, immediately followed by in vivo chemoselection of HPRT-deficient transgenic donor bone marrow (BM) transplanted into syngeneic HPRT wild-type recipients. At appropriate doses, 6TG induced selective myelotoxicity without any adverse effects on extrahematopoietic tissues in HPRT wild-type mice, while hematopoietic stem cells deficient in HPRT activity were highly resistant to its cytotoxic effects. Combined 6TG conditioning and post-transplantation chemoselection consistently achieved ∼95% engraftment of HPRT-deficient donor BM, with low overall toxicity. Long-term reconstitution of immunophenotypically normal BM was achieved in both primary and secondary recipients. Our results provide proof-of-concept that single-agent 6TG can be used for both myelosuppressive conditioning without requiring irradiation and for in vivo chemoselection of HPRT-deficient donor cells. Our results show that by applying the myelosuppressive effects of 6TG both before (as conditioning) and after transplantation (as chemoselection), highly efficient engraftment of HPRT-deficient hematopoietic stem cells can be achieved.
authors: Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors: Katrin
authors: K
authors: Hacke
authors: Akos
authors: A
authors: Szakmary
authors: Andrew R
authors: AR
authors: Cuddihy
authors: Nora
authors: N
authors: Rozengurt
authors: Nathan A
authors: NA
authors: Lemp
authors: Jiri
authors: J
authors: Aubrecht
authors: Gregory W
authors: GW
authors: Lawson
authors: Nagesh P
authors: NP
authors: Rao
authors: Gay M
authors: GM
authors: Crooks
authors: Robert H
authors: RH
authors: Schiestl
authors: Noriyuki
authors: N
authors: Kasahara
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000187:drug effects* / Q000201:enzymology; D016026:Bone Marrow Transplantation; D004305:Dose-Response Relationship, Drug; D006410:Hematopoiesis / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D007041:Hypoxanthine Phosphoribosyltransferase / Q000172:deficiency* / Q000378:metabolism; D007274:Injections, Intraperitoneal; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D013866:Thioguanine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D013997:Time Factors; D019172:Transplantation Conditioning
chemical_list: D007041:Hypoxanthine Phosphoribosyltransferase; D013866:Thioguanine