stromal cell - derived factor-1 ( sdf-1 or cxcl12 ) is a multifunctional cytokine that is 
 constitutively expressed and secreted by several tissues , including endothelium and stromal cells [ 1 , 2 ] . it has a single open reading frame of 282 nucleotides encoding a 
 polypeptide of 93 amino acids . sdf-1 arises in two forms , sdf-1 ( amino acids 2488 ) and sdf-1 ( amino acids 
 2493 ) , by differential splicing [ 35 ] . sdf-1 is so 
 far the only proven chemoattractant for primitive hematopoietic 
 progenitor cells ( hpc ) [ 68 ] . accordingly , sdf-1 is 
 considered as one of the key regulators for hematopoietic 
 progenitor cell trafficking between the peripheral circulation and 
 bone marrow . our group and others have demonstrated that 
 sdf-1 induces polarization and podia formation of hpc and 
 leukemic cells [ 9 , 10 ] , two properties that represent prerequisites for directed locomotion . sdf-1 alone showed a moderate effect on cell proliferation in cd34 cells 
 , and its effect on survival or apoptosis of hpc has remained controversial [ 1215 ] . furthermore the 
 sdf-1/cxcr4 axis plays a crucial role in regulation of 
 homing and adhesion to the supportive cellular microenvironment in 
 the stem cell niche . the receptor for sdf-1 has been identified as the 
 7-transmembrane receptor cxcr4 which is also a coreceptor for the 
 hiv type 1 virus [ 17 , 18 ] . sdf-1/cxcr4 interaction was 
 reported to play an important role during embryonic development , 
 especially in hematopoiesis , vascular development , and 
 cardiogenesis . cxcr4 expression on bone marrow endothelial cells 
 is important for internalization of circulating sdf-1 , 
 resulting in its translocation into the bone marrow . signal transduction pathways initiated by the binding of sdf-1 to cxcr4 are not fully understood . mechanisms involved in cxcr4 signaling include gi - protein - mediated activation 
 of pi3k and the phospholipase c cascade [ 6 , 19 , 20 ] . such molecules have several advantages over the natural one such as the ease of manufacturing and that they 
 can be more resistant to serum modification and inactivation 
 . ctce-0214 , for example , is an analog in which the c - terminal of sdf-1 is connected to the n - terminal region by a short bifunctional linker . a recent publication suggested 
 that ctce-0214 might improve ex vivo expansion and 
 engraftment of hpc in a mouse model . ctce-0214 has also been reported to increase circulating hpc concentrations when 
 administered to a murine model , indicating that this sdf-1 
 peptide agonist could be used for mobilization . ctce-9908 is another small peptide analog that comprises a 
 dimerized sequence of the disordered n - terminal region of 
 sdf-1 and was designed to block the cxcr4 receptor . amd3100 , for example , is a bicyclam 
 in which the two cyclam rings are tethered by an aromatic bridge . it was first designed as an inhibitor of virus replication of 
 hiv-1 and hiv-2 . however , amd3100 has been shown to be a very potent and selective inhibitor of cxcr4 and both experimental 
 and clinical data suggest that amd3100 might mobilize a more 
 primitive and hence multipotent hpc population than g - csf 
 [ 26 , 27 ] . the different peptide and nonpeptide analogs might have a more 
 selective effect with respect to the different functions of the 
 native molecule sdf-1 ( figure 1 ) . here , we have compared effects of sdf-1 , ctce-0214 , ctce-9908 , and amd3100 on polarization , migration , adhesion , proliferation , and 
 cxcr4 receptor internalization in human cd34 cells . hpcs were collected from fresh umbilical cord blood after informed 
 consent using guidelines approved by the ethic committee on the 
 use of human subjects at the university of heidelberg . mononuclear 
 cells ( mncs ) were isolated after density gradient centrifugation 
 on ficoll - hypaque technique ( biochrom kg , berlin , germany ) . cd34 cells were enriched by labeling with a monoclonal anti - cd34 antibody conjugated with magnetic microbeads in an 
 automacs system ( miltenyi biotec , bergisch - gladbach , germany ) . further purification was achieved using the automatic cell 
 depositing unit on an facs - vantage - se flow cytometry sorting 
 system after additional staining with anti - cd34-phycoerythrin ( pe ) 
 ( becton dickinson ( bd ) , san jose , calif , usa ) . staining with 
 propidium iodide ( pi ) the following analogs of sdf-1 were used : sdf-1 ( sigma - aldrich , st . louis , mo , usa ) ; ctce-0214 , peptide agonist 
 of cxcr4 ( amino acid sequence : kpvslsyrapfrff - linker - lkwiqeylekaln ) [ 23 , 24 ] ; 
 ctce-9908 , peptide antagonist of cxcr4 ( amino acid sequence : 
 kgvslsyr - x - ryslsvgk ; both compounds were kindly donated by 
 chemokine therapeutics corporation , vancouver , canada ) ; and 
 amd3100 , nonpeptide antagonist of cxcr4 ( courtesy of anormed , 
 langley , canada ) . iscove 's 
 modified dulbecco 's medium ( imdm ; cambrex , walkersville , md , usa ) 
 with 20% fcs and different concentrations of cxcr4 agonists or 
 antagonists as mentioned above were added to the lower chamber of 
 a falcon transwell ( 3 m pore size , becton dickinson ) . equal cell numbers were seeded in the upper chamber in medium 
 without cxcr4 agonists or antagonists . after 2 hours , the 
 transwells were removed and cells that had migrated through the 
 micropores into the lower chamber were counted in a counting 
 chamber . as the cell numbers of available cd34 cells varied between experiments , the fold - increase of migrating cells 
 was calculated relative to the corresponding control without 
 cytokines . cd34 cells were seeded in imdm medium with 20% fcs with sdf-1 , cxcr4 agonists or antagonists for 4 hours . cell 
 morphology was assessed with an olympus ix70 fluorescence 
 microscope ( olympus optical , hamburg , germany ) . phase contrast 
 pictures were taken from at least 3 regions in each well in each 
 of five independent experiments . the ratio of round cells compared 
 to polarized cells with a prominent uropod was determined . cd34 cells were labeled with carboxyfluorescein diacetate n - succinimidyl ester ( cfse ; sigma - aldrich , steinheim , 
 germany ) to monitor cell division . in brief , cells were washed in 
 pbs with 0.1% fcs and then stained with cfse at a final 
 concentration of 0.3 m for 10 minutes at 
 37c . staining reaction was stopped with ice cold rpmi with 20% fcs for 
 5 minutes with three subsequent washes . the labelled cells were 
 cultured for 7 days in rpmi-1640 medium with 20% fcs with cxcr4 
 agonists or antagonists ( 500 ng / ml ) as mentioned above . 
 alternatively , the cells were cultured for 5 days in myelocult 
 ( stem cell technology , vancouver , canada ) supplemented with a 
 cytokine cocktail ( 2.5 u / ml erythropoietin , 10 ng / ml 
 interleukin-3 , 500 u / ml interleukin-6 , 10 ng / ml 
 granulocyte - macrophage colony - stimulating factor , 2.5 ng / ml 
 basic fibroblast growth factor , 10 ng / ml insulin - like growth 
 factor-1 , 50 ng / ml stem cell factor , and 2.5 ng / ml 
 fibroblast growth factor - beta ) as described previously 
 [ 28 , 29 ] . the number of cell divisions could be estimated by the 
 periodical dilution of residual cfse dye to daughter cells . adhesive cell - cell interaction was analyzed on a feeder layer of 
  human mesenchymal stromal cells ( mscs ) from human bone marrow ( bm ) , which were isolated in the culture medium described by reyes et al .   and wagner et al . [ 31 , 32 ] . negative control adhesion was 
 analyzed on glass surface upon coating for 15 minutes with 
 10 ng / ml fibronectin ( sigma - aldrich ) or 2.5 g / dl bovine 
 serum albumin ( bsa ; paa , clbe , germany ) . the percentage of 
 adherent cells was quantified with our novel adhesion assay 
 . in brief , adhesive press - to - seal silicone isolators with eight wells , 9 mm diameter , 1.0 mm deep ( invitrogen , 
 karlsruhe , germany ) feeder layer cells 
 were seeded in these wells in a density of about 
 10 cells / cm and were grown for 2472 hours at 
 37c and 5% co2 until they formed a confluent cell layer . all adhesion experiments were performed in imdm 
 supplemented with 20% fcs , penicillin 1000 u / ml , and 
 streptomycin 100 u / ml . hpcs were stained with the fluorescent 
 membrane dye pkh26 ( sigma - aldrich ) before use [ 3437 ] . about 10 000 hpc were seeded per well and were allowed to settle 
 for 15 minutes . a cover slide was sealed airtight on the silicone 
 spacer and cells were allowed to adhere for additional 45 minutes . hpcs were then analyzed on the feeder layer cells with an olympus 
 ix70 fluorescence microscope ( olympus optical , hamburg , germany ) 
 using a dual - band fluorescence filter set fitc / cy3 ( ahf 
 analysetechnik , tbingen , germany ) . the microscope was 
 equipped with an incubation box to keep a constant temperature of 
 37c and 5% co2 . the experimental setting was then inverted 180. adherent cells remained attached to feeder layer cells , whereas nonadherent cells dropped down and 
 could be observed on the focus level of the cover slide . fluorescent images were always taken from the same region before 
 the inversion ( all cells on the feeder layer = all ) as 
 well as after the inversion in the focus level of feeder layer 
 cells ( adherent cells = adh ) , and on the lower glass 
 slide level ( nonadherent cells = non - adh ) . three independent 
 experiments were performed in duplicate with each of the 
 sdf-1 analogs , and a control without these compounds was 
 always analyzed in parallel . percentage of adherent cells was 
 always calculated by two methods : ( 1 ) adh / all ; 
 ( 2 ) adh/(adh + non - adh ) , and these 
 results were always consistent . auto - macs enriched cd34 cells or bm - msc were incubated with sdf-1 analogs ( 500 ng / ml ) for 30 minutes at 37c . cells were then either washed twice with ice - cold pbs before antibody staining or the antibodies were incubated 
 together with the sdf-1 analogs . cells were stained with 
 anti - cxcr4-phycoerythrin ( pe ; clone 12g5 ) and anti - cd34-allophycocyanin ( apc ) ( both bd biosciences ) for additional 30 minutes at 4c , washed in pbs 4c , and immediately analyzed by flow cytometry to determine surface 
 expression of cxcr4 . all results are expressed as mean  standard deviation . to 
 estimate the probability of differences , we have adopted the 
 paired student t test . chemotaxis of cd34 cells towards a gradient of sdf-1 and cxcr4 agonists or antagonists was assessed in a transwell migration assay . the number of migratory cells increased 
 continuously with the sdf-1 concentration of up to 
 500 ng / ml sdf-1 . in contrast , neither the agonist ctce-0214 nor the antagonists ctce-9908 or amd3100 induced 
 any significant migration under these conditions ( figure 2(a ) ) . however , a further increase in the concentration of ctce-0214 ( 100 g / ml ) resulted in a moderate increase in migration of cd34 cells . polarization and podia formation are prerequisites for directed 
 locomotion of hpc . we have analyzed the podia formation of 
 cd34 cells upon 4-hour treatment with sdf-1 , cxcr4 agonists or cxcr4 antagonists . consistent with our previous report 15% ( 2% ) of the cells demonstrated an elongated morphology with a prominent uropod in the control experiments 
 . the percentage of polarized cells with a prominent uropod increased under treatment with sdf-1 in a 
 concentration - dependent manner ( up to 40%  10% in sdf-1 500 ng / ml ) . surprisingly , a significant increase 
 in podia - forming cells was also achieved by the agonist ctce-0214 
 or the antagonist ctce-9908 . thus , these compounds might induce 
 podia formation , probably via cytoskeletal rearrangements , but did 
 not induce directed migration in concentrations between 
 10 ng / ml to 500 ng / ml . cd34 cells were cultured in a culture 
 medium supplemented with a cytokine cocktail ( epo , il-3 , il-6 , 
 gm - csf , scf , bfgf , and igf-1 ) as described before [ 28 , 29 ] . a high cell viability was observed and less than 1% of the cell population was pi positive upon treatment with any of the cxcr4 agonists or antagonists . most of the cells divided up to six times 
 after five days and cell division kinetics were not affected by 
 the compounds ( figures 3(a ) and 3(b ) ) . thus , we reasoned that a cytokine deprived culture condition might be more suitable for analysis of survival and proliferation . culturing of enriched cd34 cells in rpmi-1640 medium with 20% fcs for seven days without any supplements resulted in a reduced cell viability . according to forward scatter ( fsc ) and 
 side scatter ( ssc ) , the cell population could be clearly 
 distinguished and represented about 30% of the counted events . about 3.1%  0.9% of these cells were positive for propidium 
 iodide ( figure 3(a ) ) . the addition of sdf-1 , ctce-0214 , ctce-9908 , or amd3100 ( 500 ng / ml each ) did not have 
 any significant impact on the cell number according to counted 
 events , nor on the percentage of pi positive cells ( 3.9%  
 0.7% ; 3.0%  0.4% ; 2.0%  1.3% ; 3.4%  1.2% ; 
 3.3%  0.5% , resp . ) . of the remaining cells approximately 
 50% have divided as determined by dilution of cfse dye . sdf-1 and its analogs did not have any significant effect 
 on proliferation of cd34 cells although there was a tendency towards more cell divisions with ctce-0214 
 ( figure 3(c ) ) . the sdf-1/cxcr4 pathway plays a significant role in homing 
 and mobilization of hematopoietic stem cells . human mesenchymal 
 stromal cells from bone marrow ( bm - msc ) represent a surrogate 
 model for studying molecular mechanisms of adhesion of human hpc 
 towards the cellular determinants of the niche . this heterotypic 
 cell - cell adhesion was analyzed using a novel adhesion assay 
 . by means of gravitational force , hpcs were separated into those adherent to the feeder layer and those that dropped to 
 the original covering glass upon inversion of the culture 
 preparations . furthermore , we have analyzed adhesion of hpc to a 
 protein coated glass surface without feeder layer cells . about 
 20%  1% of the cells demonstrated unspecific binding to bsa 
 and 28%  6% remained attached to fibronectin coated surfaces 
 . in contrast , 74%  10% of the cd34 adhered 
 to bm - msc under control conditions without addition of 
 sdf-1 analogs . as demonstrated in figure 4 , there was a significant reduction in cell adhesion upon treatment 
 with sdf-1 ( 55%  13% ; p = .014 ) , ctce-0214 ( 46%  16% ; p = .7 ) and amd3100 ( 32%  11% ; 
 p = 7  10 ) . the peptide 
 antagonist ctce-9908 did not have an effect on cell adhesion 
 ( 74%  8% ) . various reports demonstrated that sdf-1 induced 
 internalization of the cxcr4 receptor [ 3840 ] . in this 
 study , we have analyzed surface expression of cxcr4 and cd34 
 either under treatment with cxcr4 agonists and antagonist ( n = 
 4 ) or after two additional washing steps upon treatment with 
 cxcr4 agonists and antagonists ( n = 4 ) . in four individual 
 experiments without additional washing steps , 41.6%  7.9% of 
 the cells within the cd34 fraction expressed cxcr4 on the cell surface and this proportion was even higher in the 
 residual cd34 cells ( 61.4%  14.9% , p = .07 ) . pretreatment with sdf-1 reduced the cxcr4 expression 
 within the cd34 cells ( 30.0%  13.9% , p = .13 ) . detection of cxcr4 was significantly reduced upon pretreatment 
 with amd3100 ( 6.5%  0.8% , p = .002 ) . the peptide agonist ctce-0214 did not show any effect on cxcr4 expression ( 43.9%  12.9% ) , whereas the peptide antagonist ctce-9908 enhanced the 
 proportion of cxcr4 cells ( 47.0%  6.1% , p = .02 ) . additional washing steps with ice - cold pbs to remove sdf-1 agonists and antagonists prior to antibody staining revealed the same tendency , although cxcr4 detection was 
 higher upon removal of amd3100 ( control 32.8%  3.3% ; 
 sdf-1 20.7%  5.2% , p = .06 ; ctce-0214 31.2%  5.2% ; ctce-9908 33.9%  4.7% ; amd3100 22.5%  6.1% , 
 p = .02 ) . in addition , cells were permeabilized upon treatment 
 with the sdf-1 agonists and antagonists . in the control , nearly all cells ( 98.45% ) were positive for cxcr4 and no decrease 
 in cxcr4 detection was observed after cytokine stimulation . to examine the potentials of agonists and antagonists of cxcr4 , we 
 have monitored directed migration , podia formation , adhesion 
 behavior , and proliferation of human hpc under the influence of 
 sdf-1 , a peptide agonist of cxcr4 ( ctce-0214 ) , a peptide 
 antagonist ( ctce-9908 ) , and a nonpeptide antagonist ( amd3100 ) . 
 despite the rationale that all of the sdf-1 analogs act 
 on the same cxcr4 receptor , we have demonstrated that these 
 compounds might have differential effects on different functional 
 properties of sdf-1. it might be speculated that the 
 sdf-1 analogs induce different conformational changes of 
 the cxcr4 receptor or that other coreceptors are involved . these 
 results suggest that the signal cascade induced by sdf-1 
 is not a monocausal succession ( sdf-1 binding to cxcr4 
 activating g - proteins further activating downstream mediators ) but 
 rather a complex network [ 6 , 20 ] . analysis of the downstream targets in signal cascades such as 
 calcium flux or mapkp42/42 activation is concurrently under way 
 and might help to clarify some of the effects of cxcr4 agonists 
 and antagonists . sdf-1 is a powerful chemoattactant for primitive human 
 hematopoietic progenitor cells [ 20 , 41 , 42 ] . chemotaxis of 
 cd34 cells can be enhanced by sdf-1 in a dose - dependent manner in concentrations ranging from 0.01 
 g / ml to 0.5 g / ml [ 9 , 41 ] . have 
 previously reported that the peptide agonist ctce-0214 can also enhance migration of cd34 cells in a transwell 
 migration assay . these authors used concentrations of ctce-0214 up to 100 g / ml and they described a six - fold increase in migration of cd34 cells from mobilized peripheral blood as compared to unstimulated cells . in analogy , we observed a moderate increase in cell migration using 100 g / ml ctce-0214 . however , using the same concentration range as 
 for sdf-1 ( 0.01 g / ml0.5 g / ml ) , we demonstrated that neither ctce-0214 nor ctce-9908 or amd3100 exerted significant effects on migration of cd34 cells from umbilical cord blood . thus , in comparison to sdf-1 and on a g to g basis , none of the agonists and antagonists were a potent chemoattractant . we have previously demonstrated that the primitive fraction of 
 slow dividing cells has a higher proportion of elongated cells 
 with a prominent uropod . furthermore , hpcs adhere to supportive feeder layer cells with their uropod at the trailing 
 edge . we and others have previously demonstrated that sdf-1 affects podia formation in various aml cell lines [ 9 , 10 ] . in this study , we have shown that polarization and 
 formation of an prominent uropod can be increased in 
 cd34 cells in a dose - dependent manner by sdf-1. this effect can probably be attributed to cytoskeleton 
 rearrangements of actin - containing protrusions . surprisingly the peptide agonist and the peptide antagonist also 
 had a significant impact on podia formation although they did not 
 induce directed migration . survival of cd34 cells in culture could be maintained to a limited extent by cytokines such as thrombopoietin ( tpo ) , 
 stem cell factor ( scf ) , or flt-3 ligand alone or in combination . some studies have indicated that sdf-1 also might have a 
 moderate effect on survival of cd34 cells and this effect was significantly enhanced in combination with other 
 cytokines [ 1113 , 15 ] . in analogy , it has been shown that ctce-0214 alone did not increase the viability of cd34 cells , whereas a synergistic activity of ctce-0214 in conjunction 
 with other growth factors has been described . in this study , we have demonstrated that neither the native molecule 
 sdf-1 nor the agonist nor the antagonists alone had a 
 significant impact on proliferation or survival of cd34 cells . we can not exclude the possibility that sdf-1 
 agonists or antagonists might induce proliferation when applied in 
 conjunction with other chemokines as described before . it has been 
 reported that amd3100 was able to mobilize a cd34 population with higher proliferative potential than upon 
 mobilization with g - csf . these observations are most likely due to different subfractions of cd34 cells mobilized by amd3100 as we did not observe a significant effect of 
 this compound on proliferation . human bm - msc represents a surrogate in vitro model for 
 studying the specific molecular mechanisms of adhesion of hpc 
 towards the cellular niche . the adhesion assay described here was used to test different compounds in parallel and it might 
 be suitable for testing new chemical compounds that play a role on 
 heterotypic cell - cell adhesion . we have demonstrated in this study 
 that adhesion of cd34 cells to bm - msc was significantly reduced upon treatment with sdf-1 , ctce-0214 , or amd3100 . other authors demonstrated that cell adhesion is 
 increased by sdf-1 [ 43 , 45 , 46 ] . however , in these studies adhesion was usually analyzed upon interaction with 
 extracellular matrix components such as fibronectin , and 
 nonadherent cells were separated by a washing step at one time 
 point . in contrast , in our standardized adhesion assay without 
 shear stress , gravitational force is affecting cell - cell 
 interaction over a time course of one hour . an explanation for the 
 increased migratory activity upon treatment with sdf-1 is 
 that cell adhesion is temporarily loosened and these cells would 
 then detach and add to the no - adherent fraction . furthermore , it 
 has been reported that cxcr4 activation is also important for 
 mediating specific migration of bone marrow stromal cells although 
 this receptor seems to be only present at very low levels at the 
 surface of msc [ 4749 ] . thus , in contrast to previous 
 studies that analyzed adhesion of hsc to fibronectin , we have 
 analyzed adhesion to msc with and without the addition of 
 sdf-1 , its agonists , and antagonists . our results are 
 compatible with the observation that both agonist and antagonists 
 of the sdf-1/cxcr4 axis have been shown to effectively 
 mobilize primitive hpc to the peripheral blood . elevated plasma 
 levels of sdf-1 induce mobilization of hpc to the 
 peripheral blood . in the murine system , injection of ctce-0214 led to an increase of primitive hpc in the peripheral 
 blood . amd3100 has been reported to mobilize hsc from the bone marrow to peripheral blood efficiently . the increase of hpc is rapid after a single injection and the 
 corresponding clinical trials have been conducted successfully in 
 patients who have failed to respond to granulocyte colony 
 stimulating factors alone . in our previous work , we provided evidence that more primitive 
 fractions of hpc adhere significantly more than their more 
 differentiated counterparts ( cd34 versus 
 cd34 , cd34cd38 versus 
 cd34cd38 , slow dividing fraction versus fast dividing fraction of cd34cd38 cells ) . furthermore , there is evidence that amd3100 and g - csf 
 might mobilize a more primitive and hence multipotent hpc 
 population than g - csf alone [ 26 , 27 ] . thus , it could be speculated that 
 cxcr4 agonists and antagonists affect the specific interaction of 
 primitive hpcs and their cellular microenvironment . have previously demonstrated that sdf-1 induced redistribution and internalization of a cxcr4-fusion protein in kg1a cells 
 . dar et al . reported that cxcr4-dependent internalization of and resecretion of sdf-1 by endothelial and stromal cells played an essential role to establish an 
 sdf-1 gradient that assisted directed migration of 
 cd34 cells . multiple residues within the cxcr4 c - terminal tail appeared to mediate this receptor internalization . in this context , our data have provided evidence that cxcr4 is also internalized in cd34 cells upon stimulation with sdf-1. hatse et al . reported long - term interaction of amd3100 with cxcr4 that blocked binding of the same antibody ( clone 12g5 ) at the cell membrane . this is in line with 
 our observation that cxcr4 surface detection by the 12g5 antibody 
 is abolished by amd3100 , whereas additional washing steps 
 increased the detection of cxcr4 . thus , further analysis of 
 internalized receptor revealed no effect of amd3100 treatment on 
 intracellular cxcr4 detection . on the other hand , our results provide evidence that ctce-0214 does not affect receptor 
 internalization , whereas the peptide antagonist ctce-9908 enhanced 
 the proportion of cxcr4 cells , and this observation is compatible with reduced receptor internalization . the g - protein 
 coupled receptor cxcr4 is not an adhesion protein itself . however , 
 recently crosstalk between the cxcr4/sdf-1 axis and other 
 adhesion proteins such as vla-4 , vla-5 , and cd164 has been shown 
 , and hence internalization of cxcr4 upon stimulation with agonists and antagonists might be associated with 
 redistribution of these adhesion proteins , and thereby reducing 
 intercellular adhesion . the ease of synthesis , lower manufacturing 
 costs , improved bioavailability , and lower immunogenicity of 
 peptides or analogs may make them more accessible for clinical 
 applications . recent results have also suggested that the 
 sdf-1/cxcr4 axis is also used by cancer cells for 
 metastatic dissemination in many types of solid tumours 
 [ 52 , 53 ] . in addition to mobilization of hpc , cxcr4 agonists 
 and antagonists might have the potential for treatment of 
 metastatic diseases . if confirmed , precise knowledge of homing and 
 adhesion and their specific manipulation might have significant 
 therapeutic potentials and implications .
stromal cell - derived factor-1alpha ( sdf-1 ) has pleiotropic effects on hematopoietic progenitor cells ( hpcs ) . 
 we have monitored podia formation , migration , proliferation , and cell - cell adhesion of human hpc under the influence of sdf-1 , a peptide agonist of cxcr4 ( ctce-0214 ) , a peptide antagonist ( ctce-9908 ) , and a nonpeptide antagonist ( amd3100 ) . whereas sdf-1 induced migration of cd34 + cells in a dose - dependent manner , ctce-0214 , ctce-9908 , and amd3100 did not induce chemotaxis in this concentration range albeit the peptides ctce-0214 and ctce-9908 increased podia formation . 
 cell - cell adhesion of hpc to human mesenchymal stromal cells was impaired by the addition of sdf-1 , ctce-0214 , and amd3100 . 
 proliferation was not affected by sdf-1 or its analogs . 
 surface antigen detection of cxcr4 was reduced upon treatment with sdf-1 or amd3100 and it was enhanced by ctce-9908 . despite the fact that all these molecules target the same cxcr4 receptor , cxcr4 agonists and antagonists have selective effects on different functions of the natural molecule .