p53 Is Not Required for Regulation of Apoptosis or Radioprotection by Interleukin-3

Radioprotective Agents: Strategies and Translational Advances

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

The influence of p53 functions on radiation-induced inflammatory bystander-type signaling in murine bone marrow

Radiation-induced bystander and abscopal effects, in which DNA damage is produced by inter-cellular communication, indicate mechanisms of generating damage in addition to those observed in directly irradiated cells. In this article, we show that the bone marrow of irradiated p53(+/+) mice, but not p53(-/-) mice, produces the inflammatory pro-apoptotic cytokines FasL and TNF-α able to induce p53-independent apoptosis in vitro in nonirradiated p53(-/-) bone marrow cells. Using a congenic sex-mismatch bone marrow transplantation protocol to generate chimeric mice, p53(-/-) hemopoietic cells functioning in a p53(+/+) bone marrow stromal microenvironment exhibited greater cell killing after irradiation than p53(-/-) hemopoietic cells in a p53(-/-) microenvironment. Cytogenetic analysis demonstrated fewer damaged p53(-/-) cells in a p53(+/+) microenvironment than p53(-/-) cells in a p53(-/-) microenvironment. Using the two different model systems, the findings implicate inflammatory tissue processes induced as a consequence of p53-dependent cellular responses to the initial radiation damage, producing cytokines that subsequently induce ongoing p53-independent apoptosis. As inactivation of the p53 tumor suppressor pathway is a common event in malignant cells developing in a stromal microenvironment that has normal p53 function, the signaling processes identified in the current investigations have potential implications for disease pathogenesis and therapy.

Cyclin D1 mediates resistance to apoptosis through upregulation of molecular chaperones and consequent redistribution of cell death regulators

Cyclin D1 is a key regulator of cell proliferation. It also controls other aspects of the cell fate, such as cellular senescence, apoptosis and tumourigenesis. We used B-lymphoid cell lines producing cyclin D1 to investigate the role of this protein in B-cell lymphomas and leukaemias. Constitutive low levels of cyclin D1 had no effect per se on cell proliferation, but conferred resistance to various apoptotic stimuli in B cells. Activation of the pro-apoptotic protein, Bax, was reduced and mitochondrial permeabilization and phosphatidylserine exposure following cytokine withdrawal were delayed in cyclin D1-producing cells. Proteomic analysis showed that the presence of cyclin D1 led to intracellular accumulation of various molecular chaperones. The chaperone, heat shock protein (Hsp)70, bound to both Bax and the mitochondrial apoptosis inducing factor following cytokine withdrawal, and impeded inhibitors of kappaB (IkappaB)-mediated inhibition of nuclear factor-kappaB anti-apoptotic signalling. Impairment of Hsp70 activity--using a pharmacological Hsp inhibitor or transfecting cells with an Hsp70-blocking antibody--restored the cellular response to mitochondrial apoptosis triggering. Thus, constitutive de-novo cyclin D1 production in B cells delays commitment to apoptosis by inducing Hsp70 chaperoning activity on pre- and post-mitochondrial pro-apoptotic factors.

The BH3-only protein Puma plays an essential role in cytokine deprivation induced apoptosis of mast cells

Mast cells play critical roles in the regulation of inflammation. One characteristic feature of mast cells is their relatively long lifespan in vivo. Members of the Bcl-2 protein family are regulators of cell survival and apoptosis, where the BH3-only proteins are critical proapoptotic proteins. In this study we investigated the role of the BH3-only proteins Noxa, Bad, Bim, Bmf, Bid, and Puma in apoptosis of mucosal-like mast cells (MLMCs) and connective tissue-like mast cells (CTLMCs). We demonstrate that Puma is critical for the induction of mast-cell death following cytokine deprivation and treatment with the DNA-damaging agent etoposide in MLMCs and CTLMCs. Using p53-/- mast cells, we found that cytokine deprivation-induced apoptosis, in contrast to that elicited by etoposide, is p53-independent. Interestingly, mast cells deficient in FOXO3a, previously proposed as a transcription factor for Puma induction in response to growth factor deprivation, were markedly resistant to cytokine withdrawal compared with wild-type cells. Moreover, overexpression of phosphorylation-deficient, constitutively active FOXO3a caused an up-regulation of Puma. In conclusion, our data demonstrate a pivotal role for Puma in the regulation of cytokine deprivation-induced mast-cell apoptosis and suggest a plausible role for Puma in the regulation of mast cell numbers in vivo.

Impact of five prophylactic filgrastim schedules on hematologic toxicity in early breast cancer patients treated with epirubicin and cyclophosphamide

PURPOSE

To evaluate the comparative efficacy of varying intensity schedules of recombinant human granulocyte colony-stimulating factor (G-CSF; filgrastim) support in preventing febrile neutropenia in early breast cancer patients treated with relatively high-dose epirubicin plus cyclophosphamide (EC).

PATIENTS AND METHODS

From October 1991 to April 1994, 506 stage I and II breast cancer patients were randomly assigned to receive, in a factorial 2 x 2 design, epirubicin 120 mg/m2 and cyclophosphamide 600 mg/m2 intravenously on day 1 every 21 days for 4 cycles +/- lonidamine +/- G-CSF. The following five consecutive G-CSF schedules were tested every 100 randomly assigned patients: (1) 480 microg/d subcutaneously days 8 to 14; (2) 480 microg/d days 8, 10, 12, and 14; (3) 300 microg/d days 8 to 14; (4) 300 microg/d days 8, 10, 12, and 14; and (5) 300 microg/d days 8 and 12.

RESULTS

All of the G-CSF schedules covered the neutrophil nadir time. Schedule 5 was equivalent to the daily schedules (schedules 1 and 3) and to the alternate day schedules (schedules 2 and 4) with respect to incidence of grade 3 and 4 neutropenia (P = .79 and P = .89, respectively), rate of fever episodes (P = .84 and P = .77, respectively), incidence of neutropenic fever (P = .74 and P = .56, respectively), need of antibiotics (P = .77 and P = .88, respectively), and percentage of delayed cycles (P = .43 and P = .42, respectively). G-CSF had no significant impact on the delivered dose-intensity compared with the non-G-CSF arms.

CONCLUSION

In the adjuvant setting, the frequency of prophylactic G-CSF administration during EC could be curtailed to only two administrations (days 8 and 12) without altering outcome. This nonrandomized trial design provides support for evaluating alternative, less intense G-CSF schedules for women with early breast cancer.

The biphasic effects of cyclopentenone prostaglandins, prostaglandin J2 and 15-deoxy-Δ12,14-prostaglandin J2 on proliferation and apoptosis in rat basophilic leukemia (RBL-2H3) cells

Mast cells produce chemical mediators, including histamine and arachidonate metabolites such as prostaglandin D(2) (PGD(2)) after antigen stimulation. Cyclopentenone prostaglandins of the J series, prostaglandin J(2) (PGJ(2)) and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), are thought to be derivatives of PGD(2). In this study, the biphasic effects of the PGJ(2) and 15d-PGJ(2) on proliferation and apoptosis in rat basophilic leukemia cells (RBL-2H3), a tumor analog of mast cells, were examined. At low concentrations, 1 or 3 microM PGJ(2) and 15d-PGJ(2) induced cell proliferation, respectively. At high concentrations (10-30 microM) both the inhibition of viability and decrease in histamine content in RBL-2H3 cells were dose dependent. These effects were independent of the nuclear hormone receptor, peroxisome proliferator-activated receptor gamma (PPARgamma), since troglitazone, an agonist of PPARgamma did not cause any effects in RBL-2H3 cells. Cell death induced by PGJ(2) and 15d-PGJ(2) was the result of apoptotic processes, since RBL-2H3 cells treated with 30 microM of the prostaglandins had condensed nuclei, DNA fragmentation and increase in activities of caspase-3 and -9. Moreover, PGJ(2) or 15d-PGJ(2)-induced apoptotic effects were prevented by the caspase inhibitor, z-VAD-fmk. In conclusion, the PGJ(2) or 15d-PGJ(2)-induced apoptosis in RBL-2H3 cells occurs mainly via mitochondrial pathways instead of by PPARgamma-dependent mechanisms.

Leridistim, a chimeric dual G-CSF and IL-3 receptor agonist, enhances multilineage hematopoietic recovery in a nonhuman primate model of radiation-induced myelosuppression: effect of schedule, dose, and route of administration

Leridistim is from the myelopoietin family of proteins, which are dual receptor agonists of the human interleukin-3 and G-CSF receptor complexes. This study investigated the effect of dosage, administration route, and schedule of leridistim to stimulate multilineage hematopoietic recovery in total body irradiated rhesus monkeys. Animals were x-irradiated on day 0 (600 cGy, 250 kVp) and then received, on day 1, leridistim s.c. in an abbreviated, every-other-day schedule at 200 microg/kg, or daily at 50 microg/kg, or i.v. daily or every-other-day schedules at 200 microg/kg dose. Other cohorts received G-CSF (Neupogen((R)) [Filgrastim]) in an every-other-day schedule at 100 microg/kg/day, or autologous serum (0.1%) s.c. daily. Hematopoietic recovery was assessed by bone marrow clonogenic activity, peripheral blood cell nadirs, duration of cytopenias, time to recovery to cellular thresholds, and requirements for clinical support. Leridistim, administered s.c. every other day, or i.v. daily, significantly improved neutrophil, platelet, and lymphocyte nadirs, shortened the respective durations of cytopenia, hastened trilineage hematopoietic recovery, and reduced antibiotic and transfusion requirements. A lower dose of leridistim administered daily s.c. enhanced recovery of neutrophil and platelet parameters but did not affect lymphocyte recovery relative to controls. Leridistim, a novel engineered hematopoietic growth factor administered at the appropriate dose, route and schedule, stimulates multilineage hematopoietic reconstitution in radiation-myelosuppressed nonhuman primates.

Enhancement of mast cell survival: a novel function of some secretory phospholipase A(2) isotypes

This study tested the hypothesis that certain secretory phospholipase A(2) (sPLA(2)) isotypes act in a cytokine-like fashion through cell surface receptors to influence mast cell survival. Initial experiments revealed that sPLA(2) activity and sPLA(2) receptor expression are increased, and mast cells lost their capacity to maintain membrane asymmetry upon cytokine depletion. Groups IB and III, but not group IIA PLA(2), prevented the loss of membrane asymmetry. Similarly, group IB prevented nucleosomal DNA fragmentation in mast cells. Providing putative products of sPLA(2) hydrolysis to cytokine-depleted mast cells did not influence survival. Furthermore, catalytic inactivation of sPLA(2) did not alter its capacity to prevent apoptosis. Inhibition of protein synthesis using cycloheximide or actinomycin reversed the antiapoptotic effect of sPLA(2). Additionally, both wild-type and catalytically inactive group IB PLA(2) induced IL-3 synthesis in mast cells. However, adding IL-3-neutralizing Ab did not change Annexin V(FITC) binding and only partially inhibited thymidine incorporation in sPLA(2)-supplemented mast cells. In contrast, IL-3-neutralizing Ab inhibited both Annexin V(FITC) binding and thymidine incorporation in mast cells maintained with IL-3. sPLA(2) enhanced phosphoinositide 3'-kinase activity, and a specific inhibitor of phosphoinositide 3'-kinase reversed the antiapoptotic effects of sPLA(2). Likewise, sPLA(2) increased the degradation of I-kappaBalpha, and specific inhibitors of nuclear factor kappa activation (NF-kappaB) reversed the antiapoptotic effects of sPLA(2). Together, these experiments reveal that certain isotypes of sPLA(2) enhance the survival of mast cells in a cytokine-like fashion by activating antiapoptotic signaling pathways independent of IL-3 and probably via sPLA(2) receptors rather than sPLA(2) catalytic products.

Role of Bax in apoptosis of IL-3-dependent cells

IL-3 removal was reported to induce membrane association of the apoptotic effector Bax. This report demonstrates that IL-3-dependent cells from Bax-null mice failed to activate caspases after IL-3 removal and survived in an 10-fold lower concentration of IL-3. As IL-3 removal also down-regulates expression of Bcl-X, we examined the relationship between Bcl-X decrease and Bax membrane association. IL-3 removal from BAF-3 cells, followed by sorting caspase-active and caspase-inactive populations, showed that both expressed similar levels of Bcl-X. Inhibition of IL-3 signalling via PI-3 kinase and MEK1/2 resulted in cells with minimal Bcl-X, which remained viable with soluble Bax. However BAF-3-derived cells, which maintained Bcl-X expression without IL-3, also remained viable with soluble Bax on IL-3 removal. Therefore a decrease in Bcl-X is necessary, though not sufficient, for Bax membrane association on IL-3 removal. In contrast, treatment of BAF-3 cells with hydroxyurea induced apoptosis in the absence of a Bcl-X decrease. Furthermore, IL-3-dependent cells from Bax-null mice activated caspases after hydroxyurea treatment and show the same sensitivity to a variety of cytotoxic drugs. Thus, apoptosis after IL-3 removal requires a decrease in Bcl-X and Bax membrane association, whereas that induced by cytotoxic drugs does not.

Src family kinases are required for prolactin induction of cell proliferation

Prolactin (PRL) is a pleiotropic cytokine promoting cellular proliferation and differentiation. Because PRL activates the Src family of tyrosine kinases (SFK), we have studied the role of these kinases in PRL cell proliferation signaling. PRL induced [(3)H]thymidine incorporation upon transient transfection of BaF-3 cells with the PRL receptor. This effect was inhibited by cotransfection with the dominant negative mutant of c-Src (K>A295/Y>F527, SrcDM). The role of SFK in PRL-induced proliferation was confirmed in the BaF-3 PRL receptor-stable transfectant, W53 cells, where PRL induced Fyn and Lyn activation. The SFK-selective inhibitors PP1/PP2 and herbimycin A blocked PRL-dependent cell proliferation by arresting the W53 cells in G1, with no evident apoptosis. In parallel, PP1/PP2 inhibited PRL induction of cell growth-related genes c-fos, c-jun, c-myc, and odc. These inhibitors have no effect on PRL-mediated activation of Ras/Mapk and Jak/Start pathways. In contrast, they inhibited the PRL-dependent stimulation of the SFKs substrate Sam68, the phosphorylation of the tyrosine phosphatase Shp2, and the PI3K-dependent Akt and p70S6k serine kinases. Consistently, transient expression of SrcDM in W53 cells also blocked PRL activation of Akt. These results demonstrate that activation of SFKs is required for cell proliferation induced by PRL.

Role of p53-dependent activation of caspases in chronic obstructive uropathy: evidence from p53 null mutant mice

Chronic obstructive uropathy (COU) created by unilateral ureteric ligation is associated with increased renal cell apoptosis and p53 expression. Genetically engineered mice were used to examine the role of p53 in renal cell apoptosis in COU and the involved molecular pathways. Obstructed kidneys in p53+/+, p53+/-, and p53-/- mice were examined at days 4, 7, 15, 20, and 30 for apoptosis, and mRNA were examined for p53, members of the bcl-2 family, the death receptor family, and the common effectors of apoptosis. Obstructed kidneys in p53+/- and p53-/- mice exhibited equal attenuation of tubular and interstitial cell apoptosis (70 and 50%, respectively), compared with p53+/+ mice. However, p53 gene deficiency did not confer complete protection from apoptosis. Obstructed kidneys from p53-/- mice did not express p53 mRNA, whereas those from p53+/- and p53+/+ mice displayed mild and marked increase in their expression, respectively. Obstructed kidneys in p53+/+, p53+/-, and p53-/- mice displayed upregulation of mRNA for members of the bcl-2 family and most of the death receptor family, except for a lower level of tumor necrosis factor receptor-1, TRAIL, and FAP in p53+/+ mice. Obstructed kidneys in p53-/- and p53+/- mice showed virtual absence of caspase 11 and marked attenuation of caspases 1 and 12, contrasted with their strong expression in p53+/+ kidneys. These data suggest that apoptosis in obstructed kidneys involves p53-dependent as well as p53-independent pathways. The p53-dependent pathway may involve activation of caspases 1, 11, and 12, whereas the p53-independent pathway may involve activation of members of the bcl-2 and death receptor families.

Activation of the phosphatidylinositol 3-kinase/Akt pathway protects against interleukin-3 starvation but not DNA damage-induced apoptosis

Baf-3 cells are dependent on interleukin-3 (IL-3) for their survival and proliferation in culture. To identify anti-apoptotic pathways, we performed a retroviral-insertion mutagenesis on Baf-3 cells and selected mutants that have acquired a long term survival capacity. The phenotype of one mutant, which does not overexpress bcl-x and proliferates in the absence of IL-3, is described. We show that, in this mutant, Akt is constitutively activated leading to FKHRL1 phosphorylation and constitutive glycolytic activity. This pathway is necessary for the mutant to survive following IL-3 starvation but is not sufficient or necessary to protect cells from DNA damage-induced cell death. Indeed, inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in Baf-3 cells does not prevent the ability of IL-3 to protect cells against gamma-irradiation-induced DNA damage. This protective effect of IL-3 rather correlates with the expression of the anti-apoptotic Bcl-x protein. Taken together, these data demonstrate that the PI3K/Akt pathway is sufficient to protect cells from growth factor starvation-induced apoptosis but is not required for IL-3 inhibition of DNA damage-induced cell death.

The combined administration of daniplestim and Mpl ligand augments the hematopoietic reconstitution observed with single cytokine administration in a nonhuman primate model of myelosuppression

This study evaluated the ability of daniplestim, a high affinity interleukin 3 receptor agonist, to enhance the hematopoietic response of Mpl ligand (Mpl-L) administration in nonhuman primates following severe, radiation-induced myelosuppression. Rhesus monkeys were total body x-irradiated (TBI) to 600 cGy, midline tissue dose. Beginning on day 1 post-TBI, animals were s.c. administered daniplestim (100 microg/kg bid; n = 4), Mpl-L (10 microg/kg qd; n = 3), daniplestim (100 microg/kg bid) plus Mpl-L (10 microg/kg qd) (n = 4) or 0.1% autologous serum (AS) (n = 11) for 18 days. CBCs were monitored for 60 d after TBI. The duration of thrombocytopenia (platelet count; PLT <20,000/microl) was significantly decreased by the administration of daniplestim (6.5 d, p = .01), Mpl-L (3.0 d, p = .003) and the coadministered daniplestim/Mpl-L (1.3 d, p = .001) compared to controls (10.4 d). As monotherapy Mpl-L but not daniplestim significantly improved the PLT nadir (21,000/microl, p = .023 and 5,000/microl, p = .266, respectively) compared to the control (3,000/microl). The combined administration of daniplestim and Mpl-L significantly improved the PLT nadir (28,000/microl, p = .007) compared to both the control cohort (3,000/microl) and the daniplestim only cohort (5,000/microl, p = .043). Recovery of PLT to preirradiation values occurred earlier in the daniplestim only (d 21) or the daniplestim/Mpl-L cohorts (d 18) than in the Mpl-L only or control cohorts (d 28, d 29, respectively). The administration of daniplestim or Mpl-L alone neither shortened the duration of neutropenia (ANC<500/microl) compared to the controls (15.8 d, 16.0 d versus 16.2 d, respectively), nor improved the recovery time of neutrophils to baseline values (d 22, d 25, and d 23, respectively). The ANC nadir was significantly improved by daniplestim alone but not Mpl-L administration (76/microl, p = .001 and 50/microl, p = .093, respectively) compared to the controls (8/microl). Coadministration of daniplestim and Mpl-L significantly improved the ANC nadir (196/microl, p = .001) compared to either the AS- or the monotherapy-treated cohorts. Also the duration of neutropenia observed in the AS-controls (16.2 d) was significantly reduced in the daniplestim/Mpl-L cohort (10.8 d, p = .002). The combined administration of daniplestim and Mpl-L significantly improved hematopoietic recovery and further enhanced the stimulatory effect of cytokine monotherapy, as well as reducing clinical support requirements after radiation-induced bone marrow myelosuppression.

Transforming growth factor-beta 1 induces apoptosis independently of p53 and selectively reduces expression of Bcl-2 in multipotent hematopoietic cells

Transforming growth factor-beta1 (TGF-beta1) can inhibit cell proliferation or induce apoptosis in multipotent hematopoietic cells. To study the mechanisms of TGF-beta1 action on primitive hematopoietic cells, we used the interleukin-3 (IL-3)-dependent, multipotent FDCP-Mix cell line. TGF-beta1-mediated growth inhibition was observed in high concentrations of IL-3, while at lower IL-3 concentrations TGF-beta1 induced apoptosis. The proapoptotic effects of TGF-beta1 occur via a p53-independent pathway, since p53(null) FDCP-Mix demonstrated the same responses to TGF-beta1. IL-3 has been suggested to enhance survival via an increase in (antiapoptotic) Bcl-x(L) expression. In FDCP-Mix cells, neither IL-3 nor TGF-beta1 induced any change in Bcl-x(L) protein levels or the proapoptotic proteins Bad or Bax. However, TGF-beta1 had a major effect on Bcl-2 levels, reducing them in the presence of high and low concentrations of IL-3. Overexpression of Bcl-2 in FDCP-Mix cells rescued them from TGF-beta1-induced apoptosis but was incapable of inhibiting TGF-beta1-mediated growth arrest. We conclude that TGF-beta1-induced cell death is independent of p53 and inhibited by Bcl-2, with no effect on Bcl-x(L). The significance of these results for stem cell survival in bone marrow are discussed.

Involvement of p53 and interleukin 3 in the up-regulation of CD95 (APO-1/Fas) by X-ray irradiation

Interleukin 3-dependent bone marrow and Ba/F3 cells present constitutive Fas expression. A dose dependent increase in Fas surface expression was induced in these cells by X-ray irradiation. Using primary cell cultures and established cell lines derived from p53-null mice (p53-/-), we demonstrated that the increase in Fas expression upon X-ray irradiation is dependent on the presence of at least one wild-type p53 allele. Fas induction by X-ray irradiation was negatively modulated by IL-3; an earlier Fas induction was observed in the absence of IL-3 or at low IL-3 concentrations. However, IL-3 withdrawal in non-irradiated cells did not induce an increase in Fas expression. X-ray irradiation of Ba/F3 cells induced the expression of functional Fas receptors. Therefore, in IL-3-dependent cells, IL-3 regulates the rate of Fas expression, which is correlated with the degree of apoptosis observed in X-irradiated cells. Finally, we demonstrate that IL-3 controls the degree of Fas expression induced by irradiation through a p53-mediated pathway.

The role of p53 in death of IL-3-dependent cells in response to cytotoxic drugs

This report examines the cytotoxicity of chemotherapeutic agents to primary bone marrow-derived IL-3-dependent cells. Such cells derived from p53-null mice were resistant to almost 100-fold higher concentrations of the inhibitors of deoxyribonucleotide synthesis FUdR, methotrexate and hydroxyurea than cells with wild-type p53. In contrast, the cytotoxicity of the DNA damaging agents X-irradiation, cisplatin or bleomycin was p53-independent. The topoisomerase II inhibitor etoposide induced p53-dependent death, which suggests that DNA damage may not be its primary mechanism of cytotoxicity in this cell type. An IL-3-dependent cell line which expresses wild-type p53 was used to demonstrate that the ability of cytotoxic drugs to increase p53 expression level does not control their ability to induce p53-dependent loss of clonigenicity. Finally, comparison with a p53-null IL-3-dependent cell line was used to show that absence of p53 delays the rate of entry into apoptosis following treatment with either DNA damaging agents or inhibitors of deoxyribonucleotide synthesis. This distinguishes short-term effects of p53 on rate of entry into apoptosis from its role in controlling ultimate cell survival. Oncogene (2000) 19, 3556 - 3559

Myelopoietin, an engineered chimeric IL-3 and G-CSF receptor agonist, stimulates multilineage hematopoietic recovery in a nonhuman primate model of radiation-induced myelosuppression

Myelopoietins (MPOs) constitute a family of engineered, chimeric molecules that bind and activate the IL-3 and G-CSF receptors on hematopoietic cells. This study investigated the in vivo hematopoietic response of rhesus monkeys administered MPO after radiation-induced myelosuppression. Animals were total body irradiated (TBI) in 2 series, with biologically equivalent doses consisting of either a 700 cGy dose of Cobalt-60 (60Co) γ-radiation or 600 cGy, 250 kVp x-irradiation. First series: On day 1 after 700 cGy irradiation, cohorts of animals were subcutaneously (SC) administered MPO at 200 μg/kg/d (n = 4), or 50 μg/kg/d (n = 2), twice daily, or human serum albumin (HSA) (n = 10). Second series: The 600 cGy x-irradiated cohorts of animals were administered either MPO at 200 μg/kg/d, in a daily schedule (n = 4) or 0.1% autologous serum (AS) , daily, SC (n = 11) for 23 days. MPO regardless of administration schedule (twice a day or every day) significantly reduced the mean durations of neutropenia (absolute neutrophil count [ANC] &lt; 500/μL) and thrombocytopenia (platelet &lt; 20 000/μL) versus respective control-treated cohorts. Mean neutrophil and platelet nadirs were significantly improved and time to recovery for neutrophils (ANC to &lt; 500/μL) and platelets (PLT &lt; 20 000/μL) were significantly enhanced in the MPO-treated cohorts versus controls. Red cell recovery was further improved relative to control-treated cohorts that received whole blood transfusions. Significant increases in bone marrow-derived clonogenic activity was observed by day 14 after TBI in MPO-treated cohorts versus respective time-matched controls. Thus, MPO, administered daily was as effective as a twice daily schedule for multilineage recovery in nonhuman primates after high-dose, radiation-induced myelosuppression.

Deficiency of Trp53 rescues the male fertility defects of Kit(W-v) mice but has no effect on the survival of melanocytes and mast cells

Mutations of the receptor tyrosine kinase, Kit, or its ligand, mast growth factor (Mgf), affect three unrelated cell populations: melanocytes, germ cells, and mast cells. Kit signaling is required initially to prevent cell death in these lineages both in vitro and in vivo. Mgf appears to play a role in the survival of some hematopoietic cells in vitro by modulating the activity of p53. Signaling by Mgf inhibits p53-induced apoptosis of erythroleukemia cell lines and suppresses p53-dependent radiation-induced apoptosis of bone marrow cells. We tested the hypothesis that cell survival in Kit mutant mice would be enhanced by p53 deficiency in vivo. Double-mutant mice, which have greatly reduced Kit receptor tyrosine kinase activity and also lack Trp53, were generated and the affected cell lineages examined. Mast cell, melanoblast, and melanocyte survival in the double Kit(W-v/W-v):Trp53(-/-) mutants was not increased compared to the single Kit(W-v/W-v):Trp53(+/+) mutants. However, double-mutant males showed an increase in sperm viability and could father litters, in contrast to their homozygous Kit mutant, wild-type p53 littermates. This germ cell rescue appears to be male specific, as female ovaries were similar in mice homozygous for the Kit mutant allele with or without p53. We conclude that defective Kit signaling in vivo results in apoptosis by a p53-independent pathway in melanocyte and mast cell lineages but that in male germ cells apoptosis in the absence of Kit is p53-dependent.