R. T. MacFarland

AMD-3100, a bicyclam, is a novel agent that uniquely inhibits the entry of human immunodeficiency virus type 1 (HIV-1) into CD4(+) T cells via selective blockade of the chemokine CXCR-4 receptor. Twelve healthy volunteers were given AMD-3100 as a single 15-min intravenous infusion at 10, 20, 40, or 80 microg/kg. Five subjects also received a single subcutaneous injection of AMD-3100 (40 or 80 microg/kg). Three subjects received two escalating oral doses each (80 and 160 microg/kg). All subjects tolerated their dose(s) well without any grade 2 toxicity or dose adjustment. Six subjects experienced mild, transient symptoms, primarily gastrointestinal in nature and not dose related. All subjects experienced a dose-related elevation of the white blood cell count, from 1.5 to 3.1 times the baseline, which returned to the baseline 24 h after dosing. AMD-3100 demonstrated dose proportionality for the maximum drug concentration in serum (C(max)) and the area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)) over the entire dose range. At the highest intravenous dose (80 microg/kg), the median C(max) was 515 (range, 470 to 521) ng/ml and the AUC(0-infinity) was 1,044 (range, 980 to 1,403) ng-h/ml. The median systemic absorption after subcutaneous dosing was 87% (range, 67 to 106%). No drug was detectable in the blood following oral dosing. Using a two-compartment model, the median pharmacokinetic parameter estimates (ranges) were as follows: volume of distribution, 0.34 (0. 27 to 0.36) liter/kg; clearance, 1.30 (0.97 to 1.34) liters/h; elimination half-life, 3.6 (3.5 to 4.9) h. After a single, well-tolerated intravenous dose of AMD-3100, concentrations were sustained for 12 h above the in vitro antiretroviral 90% inhibitory concentrations and for 8 h above antiviral concentrations identified in the SCID-hu Thy/Liv mouse model of HIV infection.

AMD3100 is a CXCR4 receptor inhibitor with anti-HIV-1 activity in vitro. We tested the safety, pharmacokinetics, and antiviral effect of AMD3100 administered for 10 days by continuous intravenous infusion in an open-label dose escalation study from 2.5 to 160 microg/kg/h. Forty HIV-infected patients with an HIV RNA level >5000 copies/mL on stable antiretroviral (ARV) regimens or off therapy were enrolled. Syncytium-inducing (SI) phenotype in an MT-2 cell assay was required in higher dose cohorts. Most subjects were black (55%), male (98%), and off ARV therapy. HIV phenotype was SI (30%), non-SI (45%), or not tested (25%). One patient (5 microg/kg/h) had serious and possibly drug-related thrombocytopenia. Two patients (40 and 160 microg/kg/h) had unexpected, although not serious, premature ventricular contractions. Most patients in the 80- and 160-microg/kg/h cohorts had paresthesias. Steady-state blood concentration and area under the concentration-time curve were dose proportional across all dose levels; the median terminal elimination half-life was 8.6 hours (range: 8.1-11.1 hours). Leukocytosis was observed in all patients, with an estimated maximum effect of 3.4 times baseline (95% confidence interval: 2.9-3.9). Only 1 patient, the patient whose virus was confirmed to use purely CXCR4 and who also received the highest dose (160 microg/kg/h), had a significant 0.9-log10 copies/mL HIV RNA drop at day 11. Overall, however, the average change in viral load across all patients was +0.03 log10 HIV RNA. Given these results, AMD3100 is not being further developed for ARV therapy, but development continues for stem cell mobilization.

An adrenal cGMP-stimulated phosphodiesterase (cGS-PDE) has been shown to mediate atrial natriuretic peptide (ANP)-induced reductions in aldosterone secretion and cAMP levels in primary bovine glomerulosa cells. High concentrations of cGS-PDE have been localized to the zona glomerulosa cell layer of the adrenal cortex using biochemical and immunological techniques. Immunoblot analysis using an affinity-purified, isozyme-specific antiserum revealed a single band that comigrated with a purified cGS-PDE (105 kDa) (1) and that was most highly concentrated in the outermost 1-2 mm of the cortex, representing the capsule and zona glomerulosa regions. Greater than 90% of the overall phosphodiesterase activity present in tissue extracts prepared from these regions was immunoprecipitated using a solid-phase monoclonal antibody reagent, indicating the cGS-PDE as the predominant phosphodiesterase isozyme. Immunohistochemical staining experiments of frozen thin sections of intact adrenal tissue revealed that the cGS-PDE present in this region was localized in the glomerulosa cells themselves. The role of this isozyme as a mediator of ANP-induced decreases in intracellular cAMP concentrations and aldosterone production was tested in primary cultures of bovine adrenal glomerulosa cells. In cells stimulated by ACTH, ANP treatment produced dose-dependent reductions in aldosterone secretion and cellular cAMP content over the same concentration range. Increases in aldosterone production elicited by three cell-permeable cAMP derivatives (8-bromo-cAMP, 8-p-chlorophenylthio-cAMP, and N6-2'-O-dibutyryl-cAMP) were antagonized by ANP, indicating a site of action distal to adenylate cyclase for this hormone. Because the relative magnitude of the ANP effect differed depending upon the derivative used, the three derivatives were compared with respect to their relative rates of in vitro hydrolysis by adrenal cGS-PDE. A positive correlation between their rates of hydrolysis and the degree to which the steroidogenic response produced by these derivatives was antagonized by ANP was demonstrated, further suggesting an ANP-induced activation of the cGS-PDE as being responsible for this effect. The possible contribution of an additional pathway mediated by an inhibitory guanine nucleotide binding regulatory protein (Gi) acting on adenylate cyclase was tested by pretreatment of primary glomerulosa cells with pertussis toxin. Levels of pertussis toxin sufficient to inhibit subsequent in vitro ribosylation did not significantly alter the ANP effect on aldosterone production, although a partial reduction in the ANP effect on cAMP levels was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

BACKGROUND: AMD3100 is a small-molecule CXCR4 antagonist that has been shown to induce the mobilization of CD34 + hematopoietic progenitor cells from bone marrow to peripheral blood. AMD3100 has also been shown to augment the mobilization of CD34 + cells in cancer patients when administered in combination with granulocyte colony-stimulating factor (G-CSF) (filgrastim). The purpose of this study was to characterize the exposure-response relationship of AMD3100 in mobilizing CD34 + cells when administered as a single agent in healthy volunteers. METHODS: AMD3100 concentrations and CD34 + cell counts obtained from 29 healthy subjects in a single-dose, intensively sampled pharmacokinetic/pharmacodynamic (PK-PD) study were analyzed by use of nonlinear mixed effects regression with the software NONMEM. FOCE (first order conditional estimation) with interaction was the estimation method, and simultaneous PK-PD fitting was adopted. RESULTS: The pharmacokinetics of AMD3100 was described by a 2-compartment model with first-order absorption. The population estimates (+/-SE) for clearance and central volume of distribution were 5.17 +/- 0.49 L/h and 16.9 +/- 3.79 L, respectively. CD34 + cell mobilization was best described by an indirect effect model that stimulates the entry process of CD34 + from bone marrow to peripheral blood in the form of a sigmoid maximum effect model. The population estimates (+/-SE) of maximum effect, concentration causing 50% of maximum response, and equilibration time were 12.6 +/- 4.89, 53.6 +/- 11.9 mug/L, and 5.37 +/- 1.31 hours, respectively. CONCLUSIONS: This study characterizes the exposure-response relationship of AMD3100 in mobilizing CD34 + cells after subcutaneous administration. This PK-PD model will be useful in assessing relevant covariates and for optimizing the use of AMD3100 in various patient populations.

We examined whether antagonism of the CXCR₄receptor ameliorates the loss of renal function following ischemia-reperfusion. CXCR₄is ubiquitously expressed on leukocytes, known mediators of renal injury, and on bone marrow hematopoietic stem cells (HSCs). Plerixafor (AMD3100, Mozobil) is a small-molecule CXCR₄antagonist that mobilizes HSCs into the peripheral blood and also modulates the immune response in in vivo rodent models of asthma and rheumatoid arthritis. Treatment with plerixafor before and after ischemic clamping ameliorated kidney injury in a rat model of bilateral renal ischemia-reperfusion. Serum creatinine and blood urea nitrogen were significantly reduced 24 h after reperfusion, as were tissue injury and cell death. Plerixafor prevented the renal increase in the proinflammatory chemokines CXCL1 and CXCL5 and the cytokine IL-6. Flow cytometry of kidney homogenates confirmed the presence of significantly fewer leukocytes with plerixafor treatment; additionally, myeloperoxidase activity was reduced. AMD3465, a monocyclam analog of plerixafor, was similarly renoprotective. Four weeks postreperfusion, long-term effects included diminished fibrosis, inflammation, and ongoing renal injury. The mechanism by which CXCR₄inhibition ameliorates AKI is due to modulation of leukocyte infiltration and expression of proinflammatory chemokines/cytokines, rather than a HSC-mediated effect. The data suggest that CXCR₄antagonism with plerixafor may be a potential option to prevent AKI.