PURPOSE: Genz-644282 [8,9-dimethoxy-5-(2-N-methylaminoethyl)-2,3-methylenedioxy-5H-dibenzo[c,h][1,6]naphthyridin-6-one] has emerged as a promising candidate for antitumor agents. This report describes the bone marrow colony-forming unit, granulocyte macrophage (CFU-GM) and tumor cell CFU activity of topoisomerase I (Top1) inhibitors, such as Genz-644282, topotecan, irinotecan/SN-38, and ARC-111, and examines their activity in several human tumor xenograft models. EXPERIMENTAL DESIGN: Colony-forming assays were conducted with mouse and human bone marrow and eight human tumor cell lines. In addition, 29 human tumor cell lines representing a range of histology and potential resistance mechanisms were assayed for sensitivity to Genz-644282 in a 72-hour exposure assay. The efficacy of Genz-644282 was compared with standard anticancer drugs (i.e., irinotecan, docetaxel, and dacarbazine) in human tumor xenografts of colon cancer, renal cell carcinoma, non-small cell lung cancer, and melanoma. RESULTS: Human bone marrow CFU-GM was more sensitive to the Top1 inhibitors than was mouse bone marrow CFU-GM. The ratio of mouse to human IC(90) values was more than 10 for the camptothecins and less than 10 for Genz-644282, which had more potency as a cytotoxic agent toward human tumor cells in culture than the camptothecins in the colony-forming and 72-hour proliferation assays. Genz-644282 has superior or equal antitumor activity in the human tumor xenografts than the standard drug comparators. CONCLUSIONS: On the basis of preclinical activity and safety, Genz-644282 was selected for development and is currently undergoing phase 1 clinical trial.

Umbilical cord blood (UCB) preparation needs to be optimized in order to develop more simplified procedures for volume reduction, as well as to reduce the amount of contaminating cells within the final stem cell transplant. We evaluated a novel filter device (StemQuick((TM))E) and compared it with our routine buffy coat (BC) preparation procedure for the enrichment of hematopoietic progenitor cells (HPCs). Two groups of single or pooled UCB units were filtered (each n = 6), or equally divided in two halves and processed by filtration and BC preparation in parallel (n = 10). The engraftment capacity of UCB samples processed by whole blood (WB) preparation was compared with paired samples processed by filtration in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse animal model. Filtration of UCB units in the two groups with a mean volume of 87.8 and 120.7 ml, respectively, and nucleated cell (NC) content of 9.7 and 23.8 x 10(8) resulted in a sufficient mean cell recovery for mononucleated cells ([MNCs] 74.2%-77.5%), CD34(+) cells (76.3%-79.0%), and colony-forming cells (64.1%-86.3%). Moreover, we detected a relevant depletion of the transplants for RBCs (89.2%-90.0%) and platelets ([PLTs] 77.5%-86.1%). In contrast, the mean depletion rate using BC processing proved to be significantly different for PLTs (10%, p = 0.03) and RBCs (39.6%, p textless 0.01). The NC composition showed a highly significant increase in MNCs and a decrease in granulocytes after filtration (p textless 0.01), compared with a less significant MNC increase in the BC group (p textless 0.05). For mice transplanted with WB-derived progenitors, we observed a mean of 15.3% +/- 15.5% of human CD45(+) cells within the BM compared with 19.9% +/- 16.8% for mice transplanted with filter samples (p = 0.03). The mean percentage of human CD34(+) cells was 4.2% +/- 3.1% for WB samples and 4.5% +/- 3.2% for filter samples (p = 0.68). As the data of NOD/SCID mice transplantation demonstrated a significant engraftment capacity of HPCs processed by filtration, no negative effect on the engraftment potential of filtered UCB cells versus non-volume-reduced cells from WB transplants was found. The StemQuick((TM))E filter devices proved to be a useful tool for Good Manufacturing Practices conform enrichment of HPCs and MNCs out of UCB. Filtration enables a quick and standardized preparation of a volume-reduced UCB transplant, including a partial depletion of granulocytes, RBCs, and PLTs without the need for centrifugation. Therefore, it seems very probable that filter-processed UCB transplants will also result in sufficient hematopoietic reconstitution in humans.

We have used a murine retrovirus vector containing an enhanced green fluorescent protein complimentary DNA (EGFP cDNA) to dynamically follow vector-expressing cells in the peripheral blood (PB) of transplanted rhesus macaques. Cytokine mobilized CD34(+) cells were transduced with an amphotropic vector that expressed EGFP and a dihydrofolate reductase cDNA under control of the murine stem cell virus promoter. The transduction protocol used the CH-296 recombinant human fibronectin fragment and relatively high concentrations of the flt-3 ligand and stem cell factor. Following transplantation of the transduced cells, up to 55% EGFP-expressing granulocytes were obtained in the peripheral circulation during the early posttransplant period. This level of myeloid marking, however, decreased to 0.1% or lower within 2 weeks. In contrast, EGFP expression in PB lymphocytes rose from 2%-5% shortly following transplantation to 10% or greater by week 5. After 10 weeks, the level of expression in PB lymphocytes continued to remain at 3%-5% as measured by both flow cytometry and Southern blot analysis, and EGFP expression was observed in CD4(+), CD8(+), CD20(+), and CD16/56(+) lymphocyte subsets. EGFP expression was only transiently detected in red blood cells and platelets soon after transplantation. Such sustained levels of lymphocyte marking may be therapeutic in a number of human gene therapy applications that require targeting of the lymphoid compartment. The transient appearance of EGFP(+) myeloid cells suggests that transduction of a lineage-restricted myeloid progenitor capable of short-term engraftment was obtained with this protocol. (Blood. 2000;95:445-452)

Predictive in vitro hematotoxicity assays using human cells will provide estimation of tolerable level and aid considerably the development of agents with greater therapeutic activity and less toxicity. Human hematopoietic cells can be derived from three sources: human bone marrow by sternal or femoral aspiration, mobilized peripheral blood, or umbilical cord blood samples collected from placentas after deliveries. Because of the difficulties to have a continuous supply of bone marrow cells from normal human donors and the related ethical problems, we performed a study to compare the sensitivity of human bone marrow cells (h-BMC) and human cord blood cells (h-CBC) to chemicals in order to confirm if h-CBC can readily replace bone marrow cells in checking the sensitivity of GM-CFU progenitors to drugs as preliminarily reported in literature. Our results showed that the prediction of IC50 values in human model is quite similar by using h-BMC or h-CBC. On the contrary, the type of medium influenced in a significant way the ICs determination of some drugs.

Recombinant retroviruses offer many advantages for the genetic modification of human hematopoietic cells, although their use in clinical protocols has thus far given disappointing results. There is therefore an important need to develop new strategies that will allow effectively transduced primitive hematopoietic target populations to be both rapidly characterized and isolated free of residual nontransduced but biologically equivalent cells. To address this need, we constructed a murine stem cell virus (MSCV)-based retroviral vector containing the 228-bp coding sequence of the murine heat-stable antigen (HSA) and generated helper virus-free amphotropic MSCV-HSA producer cells by transfection of GP-env AM12 packaging cells. Light density and, in some cases, lineage marker-negative (lin-) normal human marrow or mobilized peripheral blood cells preactivated by exposure to interleukin-3 (IL-3), IL-6, and Steel factor in vitro for 48 hours were then infected by cocultivation with these MSCV-HSA producer cells for a further 48 hours in the presence of the same cytokines. Fluorescence-activated cell sorting (FACS) analysis of the cells 24 hours later showed 21% to 41% (mean, 27%) of those that were still CD34+ to have acquired the ability to express HSA. The extent of gene transfer to erythroid and granulopoietic progenitors (burst-forming unit-erythroid and colony-forming unit-granulocyte-macrophage), as assessed by the ability of these cells to form colonies of mature progeny in the presence of normally toxic concentrations of G418, averaged 11% and 12%, respectively, in 6 experiments. These values could be increased to 100% and 77%, respectively, by prior isolation of the CD34+HSA+ cell fraction and were correspondingly decreased to an average of 2% and 5%, respectively, in the CD34+HSA- cells. In addition, the extent of gene transfer to long-term culture-initiating cells (LTC-IC) was assessed by G418 resistance. The average gene transfer to LTC-IC-derived colony-forming cells in the unsorted population was textless or = 7% in 4 experiments. FACS selection of the initially CD34+HSA+ cells increased this value to 86% and decreased it to 3% for the LTC-IC plated from the CD34+HSA- cells. Transfer of HSA gene expression to a phenotypically defined more primitive subpopulation of CD34+ cells, ie, those expressing little or no CD38, could also be shown by FACS analysis of infected populations 24 hours after infection. These findings underscore the potential use of retroviral vectors encoding HSA for the specific identification and non-toxic selection immediately after infection of retrovirally transduced populations of primitive human hematopoietic cells. In addition, such vectors should facilitate the subsequent tracking of their marked progeny using multiparameter flow cytometry.

The synthetic cytokine (Synthokine) SC-55494 is a high-affinity interleukin-3 (IL-3) receptor ligand that stimulates greater in vitro multilineage hematopoietic activity than native IL-3, while inducing no significant increase in inflammatory activity relative to native IL-3. The aim of this study was to investigate the in vivo hematopoietic response of rhesus monkeys receiving Synthokine after radiation-induced marrow aplasia. Administration schedule and dose of Synthokine were evaluated. All animals were total-body irradiated (TBI) with 700 cGy 60Co gamma radiation on day 0. Beginning on day 1, cohorts of animals (n = 5) received Synthokine subcutaneously (SC) twice daily with 25 micrograms/kg/d or 100 micrograms/kg/d for 23 days or 100 micrograms/kg/d for 14 days. Control animals (n = 9) received human serum albumin SC once daily at 15 micrograms/kg/d for 23 days. Complete blood counts were monitored for 60 days postirradiation and the durations of neutropenia (NEUT; absolute neutrophil count [ANC] textless 500/microL) and thrombocytopenia (THROM; platelet count textless 20,000/microL) were assessed. Synthokine significantly (P textless .05) reduced the duration of THROM versus the HSA-treated animals regardless of dose or protocol length. The most striking reduction was obtained in the animals receiving 100 micrograms/kg/d for 23 days (THROM = 3.5 v 12.5 days in HSA control animals). Although the duration of NEUT was not significantly altered, the depth of the nadir was significantly lessened in all animal cohorts treated with Synthokine regardless of dose versus schedule length. Bone marrow progenitor cell cultures indicated a beneficial effect of Synthokine on the recovery of granulocyte-macrophage colony-forming units that was significantly higher at day 24 post-TBI in both cohorts treated at 25 and 100 micrograms/kg/d for 23 days relative to the control animals. Plasma pharmacokinetic parameters were evaluated in both normal and irradiated animals. Pharmacokinetic analysis performed in irradiated animals after 1 week of treatment suggests an effect of repetitive Synthokine schedule and/or TBI on distribution and/or elimination of Synthokine. These data show that the Synthokine, SC55 94, administered therapeutically post-TBI, significantly enhanced platelet recovery and modulated neutrophil nadir and may be clinically useful in the treatment of the myeloablated host.