Release Of PTX Research Articles

Well-Defined Redox-Sensitive Polyethene Glycol–Paclitaxel Prodrug Conjugate for Tumor-Specific Delivery of Paclitaxel Using Octreotide for Tumor Targeting

A redox-sensitive prodrug, octreotide(Phe)-polyethene glycol-disulfide bond-paclitaxel [OCT(Phe)-PEG-ss-PTX], was successfully developed for targeted intracellular delivery of PTX. The formulation emphasizes long-circulation-time polymer-drug conjugates, combined targeting based on EPR and OCT-receptor mediated endocytosis, sharp redox response, and programmed drug release. The nontargeted redox-sensitive prodrug, mPEG-ss-PTX, and the targeted insensitive prodrug, OCT(Phe)-PEG-PTX, were also synthesized as controls. These polymer-PTX conjugates, structurally confirmed by 1H NMR, exhibited approximately 23,000-fold increase in water solubility over parent PTX and possessed drug contents ranging from 11% to 14%. The redox-sensitivity of the objective OCT(Phe)-PEG-ss-PTX prodrug was verified by in vitro PTX release profile in simulated reducing conditions, and the SSTRs-mediated endocytosis was demonstrated by flow cytometry and confocal laser scanning microscopy analyses. Consequently, compared with mPEG-PTX and OCT(Phe)-PEG-PTX, the OCT(Phe)-PEG-ss-PTX exhibited much stronger cyotoxicity and apoptosis-inducing ability against NCI-H446 tumor cells (SSTRs overexpression), whereas a comparable cytotoxicity of these prodrugs was obtained against WI-38 normal cells (no SSTRs expression). Finally, the in vivo studies on NCI-H466 tumor-bearing nude mice demonstrated that the OCT(Phe)-PEG-ss-PTX possessed superior tumor-targeting ability and antitumor activity over mPEG-PTX, OCT(Phe)-PEG-PTX and Taxol, as well as minimal collateral damage. This targeted redox-sensitive polymer-PTX prodrug system is promising in tumor therapy.

Somatostatin Receptor–Mediated Specific Delivery of Paclitaxel Prodrugs for Efficient Cancer Therapy

In this study, a novel PTX prodrug, octreotide(Phe)-polyethene glycol-paclitaxel [OCT(Phe)-PEG-PTX], was successfully synthesized and used for targeted cancer therapy. A nontargeting conjugate, mPEG-PTX, was also synthesized and used as a control. Chemical structures of OCT(Phe)-PEG-PTX and mPEG-PTX were confirmed using (1) H nuclear magnetic resonance and circular dichroism. The drug contents in both the conjugates were 12.0% and 14.0%, respectively. Compared with the parent drug (PTX), OCT(Phe)-PEG-PTX, and mPEG-PTX prodrugs showed a 20,000- and 30,000-fold increase in water solubility, respectively. PTX release from mPEG-PTX and OCT(Phe)-PEG-PTX exhibited a pH-dependent profile. Moreover, compared with mPEG-PTX, OCT(Phe)-PEG-PTX exhibited significantly stronger cytotoxicity against NCI-H446 cells (SSTR overexpression) but comparable cytotoxicity against WI-38 cells (no SSTR expression). Results of confocal laser scanning microscopy revealed that the targeting prodrug labeled with fluorescence probe was selectively taken into tumor cells via SSTR-mediated endocytosis. In vivo investigation of prodrugs in nude mice bearing NCI-H446 cancer xenografts confirmed that OCT(Phe)-PEG-PTX prodrug exhibited stronger antitumor efficacy and lower systemic toxicity than mPEG-PTX and commercial Taxol. These results suggested that OCT(Phe)-PEG-PTX is a promising anticancer drug delivery system for targeted cancer therapy.

Folate-polyethyleneimine functionalized mesoporous carbon nanoparticles for enhancing oral bioavailability of paclitaxel

Polymer-functionalized carbon nanoparticles hold great promise for their use in enhancing the oral absorption of drugs with poor oral bioavailability. And since the abundant expression of folate receptors in intestinal tract, folic acid (FA) modified uniform mesoporous carbon spheres (UMCS) was used to improve oral absorption of paclitaxel, a chemotherapeutic drug with poor oral bioavailability. In this research, folate-polyethyleneimine (FA-PEI) was grafted onto acid-treated uniform mesoporous carbon spheres through one-step electrostatic attraction. PTX was loaded into mesopores of nanoparticles through solvent evaporation, present as amorphous. The release of PTX from the FA-PEI-UMCS nanoparticles exhibited an initial rapid release, followed by a sustained release. And release rate could be regulated by changing amount of FA-PEI complex on the UMCS. The uptake of PTX-encapsulated nanoparticles was studied exploiting Caco-2 cells as an in vitro model. The results of confocal microscopy and flow cytometry demonstrated that folate functionalization enhanced internalization of nanoparticles by the cells. Moreover, PTX loaded in FA-PEI-UMCS nanoparticles resulted in a 5.37-fold increase in apparent permeability (Papp) across Caco-2 cell monolayers compared to Taxol®. And the in vivo results showed that FA-PEI-UMCS nanoparticles did not only improve the oral bioavailability of PTX, but also decrease the gastrointestinal toxicity of PTX. In conclusion, the FA-PEI-UMCS nanoparticles might be a potentially applicable system to improve oral absorption of drugs with poor oral bioavailability.

Paclitaxel/gelatin coated magnetic mesoporous silica nanoparticles: Preparation and antitumor efficacy in vivo

We reported a magnetic targeted drug delivery system based on core/shell structural magnetic mesoporous silica nanoparticles (MMSNs) and the surface of MMSNs was coated by gelatin layer. In this system, the gelatin layer retarded the diffusion of paclitaxel (PTX, model drug) from quickly moving into the bulk solution to achieve sustained release of PTX. In addition, glutaraldehyde (GA) was used as crosslinking agent to crosslink the coating layer and the release of PTX could be regulated by adjusting the degree of crosslinking of the gelatin layer. The gelatin coated MMSNs (MMSN@GELs) had a saturated magnetization of 5.53emu/g and could facilely response to an external magnet. To confirm our hypothesis that the carriers could be guided by an external magnetic field in vivo, the ex vivo imaging study and quantitative analysis were conducted. The results reflected that the external magnet altered the biodistribution of the magnetic carriers, so that more magnetic carriers were found to accumulate in tumors rather than to accumulate in normal tissues. Moreover, tumor reduction study reflected that the tumor growth of the group treated with PTX/MMSN@GELs in the presence of an external magnetic field were significantly delayed without an obvious body weight loss compared with PTX/MMSN@GELs in the absence of the magnet and with the commercial Taxol® at the same dose. All the results suggested that MMSNs coated by gelatin would be promising drug carriers for effective delivery of chemotherapeutic agents.

Multi-drug delivery system based on alginate/calcium carbonate hybrid nanoparticles for combination chemotherapy

A facile strategy to prepare nano-sized drug carriers for co-delivery of multiple types of drugs in combination chemotherapy was developed. Inorganic/organic hybrid alginate/CaCO3 nanoparticles were prepared by co-precipitation in an aqueous solution under very mild conditions. A hydrophilic drug (doxorubicin hydrochloride, DOX) and a hydrophobic drug (paclitaxel, PTX) were co-encapsulated in the hybrid nanoparticles. For comparison, PTX loaded nanoparticles and DOX loaded nanoparticles were also prepared. The measurement based on dynamic light scattering indicated all nanoparticles had a mean size less than 200nm with a relatively narrow size distribution. The morphology of the nanoparticles was observed by TEM. The in vitro drug release study showed that the release of DOX and PTX from the dual drug loaded nanoparticles could be effectively sustained. The tumor cell inhibitory effect of the drug loaded nanoparticles was evaluated in HeLa cells and MCF-7/ADR cells. The dual drug loaded nanoparticles exhibited significantly enhanced cell uptake and nuclear localization as compared with the single drug loaded nanoparticles. As a result, the dual drug loaded nanoparticles had a significantly enhanced cell inhibitory effect, especially for drug resistant tumor cells. These results indicated that alginate/CaCO3 hybrid nanoparticles have promising applications for the co-delivery of drugs with different physicochemical properties in combination chemotherapy to overcome multidrug resistance.

Novel biodegradable heparin-coated nanocomposite system for targeted drug delivery

HP–SPIO NPs (42 nm) were formulated by co-precipitation. Doxorubicin and paclitaxel were loaded into the SPIO NP core. HP–SPIO NPs had sustained release of DOX (87%) and PTX (75%) at pH 6.0. Drug loaded HP–SPIO NPs caused 95 and 84%, and 85 and 77% apoptosis in A2780 and OVCAR-3 cells, respectively. DOX–HP–SPIO NPs and PTX–HP–SPIO NPs caused a sharp decrease in bcl-2 and survivin proteins.

Novel Multifunctional Biocompatible Gelatin-Oleic Acid Conjugate: Self-Assembled Nanoparticles for Drug Delivery

In this work, a novel, biocompatible conjugates of gelatin and oleic acid (GOC) were synthesized by a novel aqueous solvent-based method that overcame challenges of completely contrary solubility between gelatin and oleic acid (OA). The GO nanoparticles (GONs) and Paclitaxel encapsulated nanoparticles (PTX-GON) were prepared by self-assembly in water. These nanoparticles (NPs) were then conjugated with folic acid (FA) for targeting cervical cancer cells (Hela cells) and were characterized for their various physicochemical and pharmaceutical properties. Fourier transform infrared spectroscopy (FT-IR) and 1H NMR studies indicated the successful synthesis of GOC which showed low critical aggregation concentration in water (0.015 mg/ml). All NPs were stable in human blood serum and their mean diameters were below 300 nm suitable for passive targeting. Powder X-ray diffraction (PXRD) diffractograms showed the reduction in drug crystallinity and hence, leading to the solubility enhancement of PTX. The release of PTX from both PTX-GON and FA conjugated PTX-GON (PTX-FA-GON) was controlled for a long time. The cytotoxicity results demonstrated great advantages of PTX-FA-GON and PTX-GON over the conventional dosage form of pacliaxel (Taxol). These results, therefore, indicate that GOC is a promising material to prepare drug encapsulated NP as a controlled delivery system and PTX-FA-GON is a potential targeted delivery system for cancer therapy.

Abstract P6-11-11: Multistage Delivery of Paclitaxel: Increased Drug Stability and Sustained Release Results in Enhanced Efficacy in Breast Cancer

Abstract Background: A significant challenge for effectively treating cancer is overcoming biological barriers that reduce circulation times and increase degradation of possible treatments. We established an innovative approach to address this issue by embedding drug-containing nanoparticles within the pores of a larger mesoporous silicon particle (MSP) in order to optimize site-specific localization and release of therapeutic agents. The objective is to develop a nanotherapeutic-based multistage platform for breast cancer treatment, wherein paclitaxel, a mitotic inhibitor used in the treatment of breast tumors, will be loaded into polymeric micelles, which in turn will be loaded within MSPs. We hypothesize that this nested incorporation of drugs within MSPs, combined with enhanced tumor transport, will result in a more pronounced and sustained antitumor effect. Materials and Methods: Micelles were assembled from amphiphilic block copolymers consisting of poly(ethylene glycol)-poly(∈-caprolactone) (PEG-PCL, MW = 5k-5k). Nanoparticle size, zeta potential, and morphology was determined, and PTX loading and release kinetics from micelles analyzed. Drug-containing micelles were incorporated into MSPs by a previously established dry-loading method, wherein nanoparticles were incorporated into pores via capillary action. Loading of fluorescent micelles was used to verify loading within MSPs via fluorescence microscopy and flow cytometry analysis. Sulforhodamine B assays were used to evaluate the in vitro antitumor efficacy of the platform in MCF-7 and MDA-MB-468 breast cancer cells. In vivo efficacy was evaluated in MDA-MB-468 breast tumors in female nu/nu mice. Results: Resulting micelles had an average size of 20 nm, as confirmed through TEM, with paclitaxel loaded into micelles very effectively. Release kinetics showed that 50% of the drug was released within 4 hours and 80% released within 24 hours. Loading of micelles into MSPs depended largely on electrostatic interactions, with micelles loading better within pores of MSPs displaying increased positive charge. Micelle loading into MSPs was successful as demonstrated by flow cytometry, and release was significantly retarded (< 30% of drug released over 4 d). Incubation of micelle-containing MSPs with breast cancer cells in vitro showed that MSPs could be internalized by cells, after which a sustained and delayed release of the payload was observed in cells. Breast tumors treated with MSPs demonstrated sustained tumor suppression (169 mm3 compared to initial starting volume of 200 mm3) at day 35 following a single injection. It is important to note that sustained tumor efficacy was achieved with nanoparticle and free drug formulations, however, with the caveat of repeated administrations. Discussion: A novel multistage approach to chemotherapy effectively allows a secondary payload to be loaded and preserved within the MSPs until reaching the tumor site. This prevents premature release of the drug and allows for a sustained release which may potentially result in fewer patient side effects. Future studies will involve loading of multiple nanoparticle types into MSPs and addition of targeting and diagnostic components. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-11-11.

The efficiency of tumor-specific pH-responsive peptide-modified polymeric micelles containing paclitaxel

The acidic pH in tumor tissues could be used for targeting solid tumors. In the present study, we designed a tumor-specific pH-responsive peptide H 7K(R 2) 2, which could respond to the acidic pH in tumor tissues, and prepared H 7K(R 2) 2-modified polymeric micelles containing paclitaxel (PTX-PM-H 7K(R 2) 2) in order to evaluate their potential targeting of tumor cells and tumor endothelial cells and their anti-tumor activity in mice with tumor cells. PTX-PM-H 7K(R 2) 2 was prepared by a thin-film hydration method. The in vitro release of PTX from PTX-PM-H 7K(R 2) 2 was tested. The in vitro targeting characteristics of H 7K(R 2) 2-modified polymeric micelles on HUVEC (human umbilical vein endothelial cells) and MCF-7 (human breast adenocarcinoma cells) were evaluated. The in vivo targeting activity of H 7K(R 2) 2-modified polymeric micelles and the in vivo anti-tumor activity of PTX-PM-H 7K(R 2) 2 were also investigated in MCF-7 tumor-bearing mice. The released PTX from the PTX-PM-H 7K(R 2) 2 was not affected by the pH. The targeting activity of the H 7K(R 2) 2-modified polymeric micelles was demonstrated by in vitro flow cytometry and confocal microscopy as well as in vivo biodistribution. PTX-PM-H 7K(R 2) 2 produced very marked anti-tumor and anti-angiogenic activity in MCF-7 tumor-bearing mice in vivo.

In vivo efficacy of paclitaxel-loaded injectable in situ-forming gel against subcutaneous tumor growth

Injectable in situ-forming gels have received considerable attention as localized drug delivery systems. Here, we examined a poly(ethylene glycol)–b-polycaprolactone (MPEG–PCL) diblock copolymer gel as an injectable drug depot for paclitaxel (Ptx). The copolymer solution remained liquid at room temperature and rapidly gelled in vivo at body temperature. In vitro experiments showed that Ptx was released from MPEG–PCL copolymer gels over the course of more than 14 days. Experiments employing intratumoral injection of saline (control), gel-only, Taxol, or Ptx-loaded gel into mice bearing B16F10 tumor xenografts showed that Ptx-loaded gel inhibited the growth of B16F10 tumors more effectively than did saline or gel alone. Further, intratumoral injection of Ptx-loaded gel was more efficacious in inhibiting the growth of B16F10 tumor over 10 days than was injection of Taxol. A histological analysis demonstrated an increase in necrotic tissue in tumors treated with Ptx-loaded gel. In conclusion, our data show that intratumoral injection of Ptx-loaded MPEG–PCL diblock copolymer yielded an in situ-forming gel that exhibited controlled Ptx release profile, and that was effective in treating localized solid tumors.

A novel size-tunable nanocarrier system for targeted anticancer drug delivery

We have developed a nanocarrier drug-delivery system based on micelles formed by a new class of well-defined linear PEGylated two-arm oligomer of cholic acids in aqueous solution. By varying the length of the linear PEG chains and the configuration of cholic acid oligomer, one can easily fine-tune the physicochemical properties of the amphiphilic polymers and the resulting micelles. These include particle size, critical micelle concentration, and drug-loading capacity. High level of hydrophobic anticancer drugs such as PTX, etoposide and SN-38 can be readily loaded into such nanocarriers. The loading capacity of the nanocarrier for PTX (PTX) is extremely high (12.0 mg/mL), which is equivalent to 37.5% (w/w) of the total mass of the micelle. PTX-loaded nanocarriers are much more stable than Abraxane ® (PTX/human serum albumin nanoaggregate) when stored in bovine serum albumin solution or dog plasma. PTX release profile from the micelles is burst-free and sustained over a period of seven days. The anti-tumor activity of PTX-loaded nanocarriers against ovarian cancer cell line in vitro, with continuous drug exposure, is similar to Taxol ® (formulation of PTX dissolved in Cremophor EL and ethanol) or Abraxane ®. Targeted drug delivery to tumor site with these novel micelles was demonstrated by near infrared fluorescence (NIRF) imaging in nude mice bearing ovarian cancer xenograft. Furthermore, PTX-loaded nanocarriers demonstrated superior anti-tumor efficacy compared to Taxol ® at equivalent PTX dose in ovarian cancer xenograft model.

PH-Sensitive degradable polymersomes for triggered release of anticancer drugs: A comparative study with micelles

pH-Sensitive degradable polymersomes and micelles were prepared based on diblock copolymer of poly(ethylene glycol) (PEG) and an acid-labile polycarbonate, poly(2,4,6-trimethoxybenzylidenepentaerythritol carbonate) (PTMBPEC). Polymersomes of PEG(1.9k)–PTMBPEC(6k) revealed average sizes of 100–200 nm. The acetals of polymersomes, similar to those of PEG(5k)–PTMBPEC(5.8k) micelles, though stable at pH 7.4 were prone to fast hydrolysis at mildly acidic pH of 4.0 and 5.0, with half lives of 0.5 and 3 d, respectively. The acetal hydrolysis resulted in significant size increase of polymersomes, to over 1000 nm in 24 h at pH 4.0. Drug encapsulation studies revealed that polymersomes were able to simultaneously load paclitaxel (PTX, hydrophobic) and doxorubicin hydrochloride (DOX·HCl, hydrophilic), whereas micelles loaded PTX only. Notably, polymersomes showed lower drug loading efficiencies for PTX than micelles (30.0–37.7% versus 61.4–65.2%). The in vitro release studies demonstrated that release of PTX and DOX·HCl from polymersomes was highly pH-dependent, i.e. significantly faster drug release at mildly acidic pH of 4.0 and 5.0 compared to physiological pH. Furthermore, much higher release rates were observed for PTX release from the polymersomes compared to that from the micelles under otherwise the same conditions. These pH-sensitive nano-sized degradable polymersomes hold great promise for combination therapy for cancers.

Thermosensitive poly(organophosphazene)–paclitaxel conjugate gels for antitumor applications

A poly(organophosphazene)–PTX conjugate was synthesized by a covalent ester linkage between PTX and carboxylic acid-terminated poly(organophosphazene), which can be readily modified by various hydrophobic, hydrophilic, and other functional substitutes. The physicochemical properties, hydrolytic degradation and PTX release behaviors of the polymer–PTX conjugate were characterized, in addition to the in vitro and in vivo antitumor activities. The aqueous solutions of these conjugates showed a sol–gel transition behavior that depended on temperature changes. The in vitro antitumor activity of the polymer–PTX conjugate was investigated by an MTT assay against human tumor cell lines. From the in vivo antitumor activity studies with tumor-induced (xenografted) nude mice, the polymer–paclitaxel conjugate hydrogels after local injection at the tumor site were shown to inhibit tumor growth more effectively and longer than paclitaxel and saline alone, indicating that the tumor-active paclitaxel from the polymer–PTX conjugate hydrogel is released slowly over a longer period of time and effectively accumulated locally in the tumor sites. These combined observations suggest that this poly(organophosphazene)–PTX conjugate holds promise for use in clinical studies as single and/or combination therapies.

Characterization and Biological Evaluation of Paclitaxel-Loaded Poly(l-lactic acid) Microparticles Prepared by Supercritical CO2

In this study, paclitaxel loaded poly( L-lactic acid) (PTX-PLLA) microparticles were prepared using solution enhanced dispersion by supercritical CO2(SEDS) technique. This supercritical antisolvent technique offers the advantage of negligible organic solvent residua in the drug loaded microparticles. Scanning electron microscopy (SEM) showed that microparticles exhibited rather spherical shape and small particle size with narrow particle size distribution. X-ray diffraction (XRD) and differential scanning calorimeter (DSC) indicated that PTX was amorphously dispersed in the PLLA matrix. The drug loading and encapsulation efficiency of PTX-PLLA microparticles were 14.33% and 62.68%, respectively. In vitro cytotoxicity evaluation of PTX-PLLA microparticles against nonsmall-cell lung cancer A549 and ovarian cancer SKOV3 cell lines indicated that PTX-PLLA had superior antiproliferation activity against the A549 and SKOV3 cell lines, compared with free PTX formulations. The cellular internalization of fluorescent microparticles was evidenced by fluorescence microscope and further confirmed by transmission electron microscopy (TEM). This was attributed to the efficient intracellular accumulation of PTX via cell phagocytosis and sustained release of PTX from PLLA matrix. The anticancer activity of PTX-PLLA was associated with PTX-induced cell apoptosis such as nuclear aberrations, condensation of chromatin and swelling damage in mitochondria. The cell apoptosis index detected by flow cytometry was higher in PTX-PLLA group than in free PTX. The PTX-PLLA formulation, which was obtained through micronization of PTX and encapsulation of micronized PTX into PLLA simultaneously in the SEDS process, significantly potentiated the anticancer activity of PTX.

A novel trans-lymphatic drug delivery system: Implantable gelatin sponge impregnated with PLGA–paclitaxel microspheres

A translymphatic drug delivery system which incorporates poly-lactide- co-glycolide–paclitaxel (PLGA–PTX) or PLGA–rhodamine microspheres into gelatin sponge matrix is described. The system combines the sustained release properties of PLGA–PTX with the structural advantages of gelatin matrix that can be implanted directly to the lymphatic site for both therapeutic and prophylactic purposes. The PLGA microspheres were prepared using spray drying technique. The particles were in the size range of 1–8 μm, suitable for intraperitoneal and intrapleural lymphatic targeting delivery. Scanning electron microscopy revealed the homogeneous distribution of PLGA microspheres in the porous sponge network. The release of PTX was mainly controlled by the degradation of the PLGA. Crosslinking gelatin using carbodiimide reduced the biodegradation of the sponge and thereby delayed the release of the PLGA in vitro. In vivo lymphatic delivery was assessed in both healthy rats and rats bearing orthotopic lung cancer. Intraperitoneal and intrapleural implantation of the sponge impregnated with PLGA microspheres resulted in spontaneous absorption of the particles in the lymphatic system. It is concluded that the system provides great potential for targeted delivery of therapeutic agent to the lymphatic system especially for the control of lymphatic metastasis in cancer.

The role of G-protein signaling in hematopoietic stem/progenitor cell mobilization

AbstractThe directed migration of mature leukocytes to inflammatory sites and the lymphocyte trafficking in vivo are dependent on G protein–coupled receptors and delivered through pertussis toxin (Ptx)–sensitive Gi-protein signaling. In the present study, we explored the in vivo role of G-protein signaling on the redistribution or mobilization of hematopoietic stem/progenitor cells (HPCs). A single injection of Ptx in mice elicits a long-lasting leukocytosis and a progressive increase in circulating colony-forming unit-culture (CFU-C) and colony-forming unit spleen (CFU-S). We found that the prolonged effect is sustained by a continuous slow release of Ptx bound to red blood cells or other cells and is potentially enhanced by an indirect influence on cell proliferation. Plasma levels of certain cytokines (interleukin 6 [IL-6], granulocyte colony-stimulating factor [G-CSF]) increase days after Ptx treatment, but these are unlikely initiators of mobilization. In addition to normal mice, mice genetically deficient in monocyte chemotactic protein 1 (MCP-1), matrix metalloproteinase 9 (MMP-9), G-CSF receptor, β2 integrins, or selectins responded to Ptx treatment, suggesting independence of Ptx-response from the expression of these molecules. Combined treatments of Ptx with anti–very late activation antigen (anti-VLA-4), uncovered potentially important insight in the interplay of chemokines/integrins, and the synergy of Ptx with G-CSF appeared to be dependent on MMP-9. As Ptx-mobilized kit+ cells display virtually no response to stromal-derived factor 1 (SDF-1) in vitro, our data suggest that disruption of CXCR4/SDF-1 signaling may be the underlying mechanism of Ptx-induced mobilization and indirectly reinforce the notion that active signaling through this pathway is required for continuous retention of cells within the bone marrow. Collectively, our data unveil a novel example of mobilization through pharmacologic modulation of signaling.