Influence of rhG-CSF scheduling on megakaryocytopoietic recovery following 5-fluorouracil-induced hematotoxicity in splenectomized B6D2F1 mice

Toxicity testing using hematopoietic stem cell assays

For over 40 years, in vitro assays have been used to understand the complex system of hematopoiesis. Now, several of these assays are undergoing resurgence as scientists in academia and industry are discovering how these assays can be utilized in drug discovery and development. These assays use primary cells from various hematopoietic tissues in multiple species to provide high content information. While conditions in the human body cannot be completely reproduced in vitro, hematopoietic colony-forming cell assays are proving to be a clinically relevant tool to evaluate potential toxic effects of new compounds. The ability to use these assays as a replacement of, or in conjunction with, high-throughput screening assays and high priced in vivo assays can improve the success of the decision-making process, saving time and costs during drug development.

Timely Withdrawal of G-CSF Reduces the Occurrence of Thrombocytopenia During Dose-dense Chemotherapy

BACKGROUND

Post chemotherapy Granulocyte colony stimulating factor (G-CSF) reduces leucopenia, while G-CSF priming shortly before chemotherapy increases myelotoxicity. We performed a trial with a two-schedule crossover design to determine the optimal G-CSF schedule for densified 2-weekly chemotherapy.

METHODS

During 2-weekly chemotherapy days 1 and 2, G-CSF was given on days 3-10, with a G-CSF-free interval before the next chemotherapy cycle of 5 days, or on days 3-13, with a G-CSF-free interval of 2 days. In schedule A, cycle II was preceded by a 5 days, cycle III and IV by a 2 days and cycle V by a 5 days G-CSF free interval. In schedule B, this was 2, 5, 5, and 2 days, respectively.

RESULTS

Intra-patient comparison for cycles II versus III and cycles IV versus V showed that platelet (PLT) nadir count was significantly lower for cycles preceded by a 2-days compared to a 5-days G-CSF free interval: mean difference 45.7 x 10(9)/l (95% CI 33.2-58.2, p = 0.0001). Neutrophil count did not differ significantly (p = 0.85).

CONCLUSION

Timely withdrawal of G-CSF in dose-dense chemotherapy reduces chemotherapy-related thrombocytopenia. Leucopenia was not aggravated, reflecting a protective effect of post-chemotherapy G-CSF.

Blood monocyte concentration is critical for enhancement of collateral artery growth

Arteriogenesis has been associated with the presence of monocytes/macrophages within the collateral vessel wall. We tested the hypothesis that arteriogenesis is functionally linked to the concentration of circulating blood monocytes. Monocyte concentrations in peripheral blood were manipulated by single injections of the antimetabolite 5-fluorouracil (5-FU), resulting in a marked rebound effect in New Zealand White rabbits. Collateral artery growth was assessed by the use of a model of acute femoral artery ligation. Seven days after ligation, collateral conductance and the number of visible collateral arteries were increased in the rebound group. This increase was accompanied by an increased monocyte accumulation as demonstrated by immunohistology in the thigh 3 days after surgery. In a second animal model (129S2/SvHsd mice), 5-FU treatment caused a remarkable decrease in blood monocyte numbers at day 4, followed by a rebound effect at day 12. Foot blood flow, assessed by laser-Doppler imaging before and at various time points after surgery, increased from day 7 through day 21 in mice from the rebound group. In contrast, ligation during the phase of monocyte depletion resulted in a reduction of blood flow reconstitution. This inhibition could be reversed by an injection of isolated monocytes. In conclusion, we have demonstrated a functional link between the monocyte concentration in the peripheral blood and the enhancement of arteriogenesis.

Comparison of two different schedules of granulocyte-colony-stimulating factor during treatment for acute lymphocytic leukemia with a hyper-CVAD (cyclophosphamide, doxorubicin, vincristine, and dexamethasone) regimen

BACKGROUND

Although the safety and efficacy of granulocyte-colony-stimulating factor (G-CSF) (filgrastim) in the treatment of hematologic malignancies has been well established, to the authors' knowledge the optimal timing of filgrastim administration during remission induction chemotherapy and consolidation chemotherapy has not been determined. The purpose of the current study was to determine whether a delay in the administration of filgrastim from Day 5 to Day 10 during chemotherapy with a hyper-CVAD (cyclophosphamide, doxorubicin, vincristine, and dexamethasone) regimen resulted in a longer time to neutrophil or platelet count recovery or increased the incidence of infection.

METHODS

One hundred ninety-nine patients who achieved complete disease remission after a single course of induction chemotherapy were considered for evaluation. Induction chemotherapy was with hyper-CVAD (fractionated cyclophosphamide, 300 mg/m2, twice daily for Days 1-3; doxorubicin, 50 g/m2, on Day 4; vincristine, 2 mg, on Days 4 and 11; and dexamethasone, 40 mg, on Days 1-4 and Days 11-14), which also was given in odd-numbered consolidation Courses 3, 5, and 7. Even-numbered courses (Courses 2, 4, 6, and 8) were comprised of methotrexate, 200 mg/m2, over 2 hours followed by 800 mg/m2 over 24 hours on Day 1; cytarabine, 3 g/m2, every 12 hours for 4 doses over 2 days (Days 2 and 3); and intravenous methylprednisolone, 50 mg, twice daily on Days 1-3 (MTX/ara-C regimen). Two sequential treatment groups were assessable based on timing of the filgrastim administration; 151 patients received filgrastim starting on Day 5 (D5) of induction chemotherapy and 48 patients received filgrastim starting on Day 10 (D10).

RESULTS

Time to neutrophil recovery was shorter for the D5 group than for the D10 group during induction chemotherapy (18 days vs. 19 days; P = 0.04) and hyper-CVAD Courses 3 and 5 (12 days vs. 15 days during Course 3, P < 0.001; and 13 days vs. 16 days during Course 5, P = 0.002). There was no apparent significant difference between the two groups with regard to time to neutrophil recovery during the MTX/ara-C courses or the last hyper-CVAD course. Delay in the administration of filgrastim did not appear to result in an increase in time to platelet count recovery or in the incidence of infection; however, there was an increased incidence of mucositis during induction chemotherapy.

CONCLUSIONS

For a hyper-CVAD and MTX/ara-C regimen, the results of the current study have shown that the administration of filgrastim can be delayed until Day 10 without increasing the risk of treatment-related morbidity during consolidation chemotherapy. During induction chemotherapy, delay in the administration of filgrastim may result in a slight increase in the time to neutrophil count recovery and risk of mucositis, but there is no apparent associated increase in the risk of infection.

Augmentation of megakaryocytopoiesis within the hematopoietic microenvironment of human granulocyte colony-stimulating factor transgenic mice

OBJECTIVE

Megakaryocytopoiesis was dramatically augmented in human granulocyte colony-stimulating factor transgenic mice (G-Tg) compared to littermates. We examined the characteristics of megakaryocytes and megakaryocyte progenitor cells in these mice.

MATERIALS AND METHODS

The numbers of colony-forming unit megakaryocytes (CFU-MK) and megakaryocytes in hematopoietic organs were counted. The megakaryocytes of G-Tg were examined ultrastructurally, and bone marrow transplantation studies using congenic G-Tg (Ly5.2) and C57BL/6 (Ly5.1) were performed. The number of day-14 colony-forming unit spleen (CFU-S) that contained megakaryocytes in [Ly5.1 > G-Tg] and [G-Tg > Ly5.1] mice also was counted.

RESULTS

The number of CFU-MK increased markedly in the spleen, bone marrow, and peripheral blood. The number of megakaryocytes in the spleen and bone marrow also were increased in G-Tg mice. Ultrastructural analyses revealed that megakaryocytes in G-Tg mice were immature. Bone marrow transplantation studies of [Ly5.1 > G-Tg] mice resulted in a significantly increased number of megakaryocytes compared to [G-Tg > Ly5.1] mice. The number of day-14 CFU-S that contained megakaryocytes was increased markedly in [Ly5.1 > G-Tg] mice compared to [G-Tg > Ly5.1] mice. In vitro differentiation of megakaryocytes in [Ly5.1 > G-Tg] mice was induced by interleukin-11 and thrombopoietin.

CONCLUSION

The results showed that the hematopoietic marrow microenvironment of G-Tg is important in augmenting megakaryocytopoiesis. [Ly5.1 > G-Tg] mice are potentially useful as a source of murine megakaryocytes and their progenitors.