title: Effects of in vivo treatment with PIXY321 (GM-CSF/IL-3 fusion protein) on proliferation kinetics of bone marrow and blood myeloid progenitor cells in patients with sarcoma.
abstract: PIXY321, a stimulator of multipotent colony-forming units (CFU-GEMM), burst-forming unit-erythroid (BFU-E), and colony-forming units granulocyte/macrophage (CFU-GM) progenitor cell proliferation in vitro, is currently being assessed in phase-I/-II clinical trials. We evaluated kinetics of CFU-GEMM, BFU-E, and CFU-GM proliferation in bone marrow (BM), blood, and granulocyte (CFU-G) and macrophage (CFU-M) progenitors in BM of chemotherapy-naive patients with sarcoma-administered PIXY321 (25 to 1000 micrograms/m2/day subcutaneously for 14 days). BM and/or blood cells from three to four patients at each dosage were assessed before, during, 1 to 2 days, and 7 days following treatment with PIXY321. Cells were pulse-treated in vitro with or without high-specific activity tritiated thymidine (3H-dThr) (to assess the percentage of progenitors in S-phase of cell cycle) and cultured for immature and more mature subsets of CFU-GEMM, BFU-E, CFU-GM, and for CFU-G and CFU-M. Despite heterogeneity in baseline cycling status of progenitors in BM, administration of 125 to 500 micrograms PIXY321 to patients at least doubled (p < 0.001) cycling rates of all BM progenitors. The cycling rates of blood progenitors increased from a slow or non-cycling state to > 38% cells in cycle. Within 1 to 2 days after cessation of PIXY321 infusion, all progenitors were in a slow or noncycling phase below that of many of the pre-BM samples (immature and mature CFU-GM and mature BFU-E) or were back to background levels (CFU-G, CFU-M, CFU-GEMM, and immature BFU-E). These cycling effects were similar to those previously noted for BM CFU-GM and BFU-E in patients on clinical trial with GM-CSF. In contrast, higher dosages of PIXY321, especially 1000 micrograms, increased cycling of BM and blood progenitor cells early during treatment, but cycling rates decreased while patients were still being administered PIXY321; decreased cycling was maintained after cessation of PIXY321. PIXY321 is thus highly active in vivo as a stimulator of multipotential and more lineage-restricted progenitors. The kinetics of progenitor cell proliferation noted in this study highlight differences seen with GM-CSF and G-CSF. The effects described here could be of relevance in design of future clinical trials using PIXY321 as an adjunct treatment in patients undergoing cytoreductive therapy.
authors.affiliation: Department of Medicine (Hematology/Oncology), Indiana University School of Medicine, Indianapolis.
authors.forename: H E
authors.initials: HE
authors.lastname: Broxmeyer
authors.forename: L
authors.initials: L
authors.lastname: Benninger
authors.forename: S
authors.initials: S
authors.lastname: Cooper
authors.forename: N
authors.initials: N
authors.lastname: Hague
authors.forename: R S
authors.initials: RS
authors.lastname: Benjamin
authors.forename: S
authors.initials: S
authors.lastname: Vadhan-Raj
mesh_terms: D001773:Blood Cells / Q000166:cytology; D001854:Bone Marrow Cells; D002455:Cell Division / Q000187:drug effects; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006410:Hematopoiesis / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000166:cytology; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D016196:S Phase / Q000187:drug effects; D012509:Sarcoma / Q000188:drug therapy*
chemical_list: D007377:Interleukin-3; C078524:PIXY321 fusion protein, recombinant; D011993:Recombinant Fusion Proteins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor