BAT6026, a novel anti-OX40 antibody with enhanced antibody dependent cellular cytotoxicity effect for cancer immunotherapy.

OX40 (CD134), a member of the TNF receptor superfamily, is a widely studied costimulatory immune checkpoint. Several OX40 agonistic antibodies are in the clinical stage for cancer treatment, among which PF-04518600 is the leader and currently in phase II trial. It has been recognized that one potential mode of action for anti-OX40 antibodies is the deletion of intratumoral Tregs. Thus, a novel human anti-OX40 antibody, BAT6026, was generated with enhanced antibody dependent cellular cytotoxicity (ADCC) via fucose deletion to strengthen its Treg depletion activity. This characteristic of BAT6026 differentiates it from other previously reported anti-OX40 antibodies in the field of tumor therapy. The affinity of BT6026 to OX40 was 0.28nM, approximately 8 times stronger than that of PF-04518600. BAT6026 effectively competed for the binding of ligand OX40L to OX40, whereas PF-04518600 only partially competed. Moreover, compared to PF-04518600, BAT6026 activated T cells more effectively when clustered by FcγRs engagement and stimulated SEB-pretreated PBMCs to secrete IL-2 cytokines in vitro. In addition, BAT6026 demonstrated stronger anti-tumor activity than PF-04518600 in an OX40-humanized mouse MC38 tumor model. BAT6026 also showed a significantly synergistic effect on tumor inhibition when combined treatment with PD-1 antibody. Analysis of tumor-infiltrating T cells revealed that BAT6026 treatment significantly reduced Treg cells and increased CD8+ T cells in tumor. Preclinical safety assessment in non-human primates demonstrated a good safety profile for BAT6026. Together these data warrant further development of BAT6026 into clinical trials for patients with cancer.

Comparison of Pharmacokinetic Similarity, Immunogenicity, and Safety of Ustekinumab and BAT2206 in Healthy Chinese Male Subjects in a Double-Blind, Randomized, Single-Dose, Parallel-Group Phase I Trial.

OBJECTIVE: We aimed to evaluate the similarity of BAT2206 to its originator, ustekinumab, including pharmacokinetic profiles, immunogenicity, and safety in healthy Chinese male subjects. METHODS: This was a double-blinded, randomized, single-dose, parallel-group clinical trial, in which 270 healthy male subjects were enrolled to receive a single subcutaneous injection (45 mg) of either BAT2206 or ustekinumab (European Union or USA) at a 1:1:1 ratio. The pairwise pharmacokinetic similarities and the safety and immunogenicity of both drugs were evaluated and compared. RESULTS: The results showed that the 90% confidence interval of the geometric mean ratio for primary pharmacokinetic parameters (maximum plasma concentration and area under the plasma concentration-time curve from time zero to infinity) among BAT2206 and ustekinumab (USA or European Union sourced) groups were all within the predefined equivalent interval of 80-125%. Furthermore, all the groups had similar incidences of treatment-emergent adverse events, in which the majority of cases belonged to Common Terminology Criteria for the Classification of Adverse Events Grade 1 or 2. Anti-drug antibodies were detected in 54 (20.1%) subjects, namely 24 (26.7%), 13 (14.8%), and 17 (18.9%) patients in the BAT2206, ustekinumab (European Union), and ustekinumab (USA) groups, respectively. In contrast, the incidences of positive neutralizing antibodies were similar among the three groups. CONCLUSIONS: Pharmacokinetic similarity between BAT2206 and ustekinumab (USA or European Union sourced) was confirmed. The three groups had similar safety profiles, and the investigational drugs were well tolerated by subjects. CLINICAL TRIAL REGISTRATION: This study was registered with ClinicalTrials.gov (NCT04371185).

Efficacy and safety of the proposed bevacizumab biosimilar BAT1706 compared with reference bevacizumab in patients with advanced nonsquamous non-small cell lung cancer: A randomized, double-blind, phase III study.

BACKGROUND: BAT1706 is a proposed biosimilar of bevacizumab (Avastin®). We aimed to compare the efficacy and safety of BAT1706 with that of EU-sourced reference bevacizumab (EU-bevacizumab) in patients with advanced nonsquamous non-small cell lung cancer (NSCLC). METHODS: Patients were randomized 1:1 to BAT1706 plus paclitaxel and carboplatin (BAT1706 arm) or EU-bevacizumab plus paclitaxel and carboplatin (EU-bevacizumab arm) given every 3 weeks for six cycles, followed by maintenance therapy with BAT1706 or EU-bevacizumab. The primary endpoint was overall response rate at week 18 (ORR18 ). Clinical equivalence was demonstrated if the 90% confidence interval (CI) of the BAT1706:EU-bevacizumab ORR18 risk ratio was contained within the predefined equivalence margins of 0.75-1.33 (China National Medical Products Administration requirements), or 0.73-1.36 (US Food and Drug Administration), or if the 95% CI of the ORR18 risk difference between treatments was contained within the predefined equivalence margin of -0.12 to 0.15 (EMA requirements). RESULTS: In total, 649 randomized patients (BAT1706, n = 325; EU-bevacizumab, n = 324) received at least one cycle of combination treatment. The ORR18 was comparable between the BAT1706 and EU-bevacizumab arms (48.0% and 44.5%, respectively). The ORR18 risk ratio of 1.08 (90% CI: 0.94-1.24) and the ORR18 risk difference of 0.03 (95% CI: -0.04 to 0.11) were within the predefined equivalence margins, demonstrating the biosimilarity of BAT1706 and EU-bevacizumab. The safety profile of BAT1706 was consistent with that of EU-bevacizumab and no new safety signals were observed. CONCLUSION: In patients with advanced nonsquamous NSCLC, BAT1706 demonstrated clinical equivalence to EU-bevacizumab in terms of efficacy, safety, pharmacokinetics, and immunogenicity.

CT53518, a novel selective FLT3 antagonist for the treatment of acute myelogenous leukemia (AML).

Up to 30% of acute myelogenous leukemia (AML) patients harbor an activating internal tandem duplication (ITD) within the juxtamembrane domain of the FLT3 receptor, suggesting that it may be a target for kinase inhibitor therapy. For this purpose we have developed CT53518, a potent antagonist that inhibits FLT3, platelet-derived growth factor receptor (PDGFR), and c-Kit (IC(50) approximately 200 nM), while other tyrosine or serine/threonine kinases were not significantly inhibited. In Ba/F3 cells expressing different FLT3-ITD mutants, CT53518 inhibited IL-3-independent cell growth and FLT3-ITD autophosphorylation with an IC(50) of 10-100 nM. In human FLT3-ITD-positive AML cell lines, CT53518 induced apoptosis and inhibited FLT3-ITD phosphorylation, cellular proliferation, and signaling through the MAP kinase and PI3 kinase pathways. Therapeutic efficacy of CT53518 was demonstrated both in a nude mouse model and in a murine bone marrow transplant model of FLT3-ITD-induced disease.

Discovery and development of a novel N-(3-bromophenyl)-{[(phenylcarbamoyl)amino]methyl}-N-hydroxythiophene-2-carboximidamide indoleamine 2,3-dioxygenase inhibitor using knowledge-based drug design.

Indoleamine 2,3-dioxygenase-1 (IDO1) is a potential target for the next generation of cancer immunotherapies. We describe the development of two series of IDO1 inhibitors incorporating a N-hydroxy-thiophene-carboximidamide core generated by knowledge-based drug design. Structural modifications to improve the cellular activity and pharmacokinetic (PK) properties of the compounds synthesized, including extension of the side chain of the N-hydroxythiophene-2-carboximidamide core, resulted in compound 27a, a potent IDO1 inhibitor which demonstrated significant (51%) in vivo target inhibition on IDO1 in a human SK-OV-3 ovarian xenograft tumor mouse model. This strategy is expected to be applicable to the discovery of additional IDO1 inhibitors for the treatment of other diseases susceptible to modulation of IDO1.

Large-scale production, purification, and function of a tumor multi-epitope vaccine: Peptibody with bFGF/VEGFA.

In tumor tissue, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor A (VEGFA) promote tumorigenesis by activating angiogenesis, but targeting single factor may produce drug resistance and compensatory angiogenesis. The Peptibody with bFGF/VEGFA was designed to simultaneously blockade these two factors. We were aiming to produce this Fc fusion protein in a large scale. The biological characterizations of Peptibody strains were identified as Escherichia coli and the fermentation mode was optimized in the shake flasks and 10-L bioreactor. The fermentation was scaled up to 100 L, with wet cell weight (WCW) 126 g/L, production 1.41 g/L, and productivity 0.35 g/(L·h) of IPTG induction. The target protein was isolated by cation-exchange, hydrophobic and Protein A chromatography, with total recovery of 60.28% and HPLC purity of 86.71%. The host cells protein, DNA, and endotoxin residues were within the threshold. In mouse model, immunization of Peptibody vaccine could significantly suppressed the tumor growth and angiogenesis, with inhibition rate of 57.73 and 39.34%. The Peptibody vaccine could elicit high-titer anti-bFGF and anti-VEGFA antibodies, which inhibited the proliferation and migration of Lewis lung cancer cell cells by decreasing the Akt/MAPK signal pathways. Therefore, the Peptibody with bFGF/VEGFA might be used as a therapeutic tumor vaccine. The large-scale process we developed could support its industrial production and pre-clinical study in the future.

Synthesis of pochoxime prodrugs as potent HSP90 inhibitors.

Pochoximes are potent inhibitors of heat shock protein 90 (HSP90) based on the radicicol pharmacophores. Herein we present a pharmacokinetics and pharmacodynamics evaluation of this compound series as well as a phosphate prodrug strategy to facilitate formulation and improve oral bioavailability.

A Global Phase I Clinical Study Comparing the Safety and Pharmacokinetics of Proposed Biosimilar BAT1706 and Bevacizumab (Avastin®) in Healthy Male Subjects.

OBJECTIVE: BAT1706 is a proposed biosimilar of bevacizumab (BEV). The objective of this phase I clinical trial was to establish pairwise similarity between BAT1706, US-sourced BEV (US-BEV), and EU-sourced BEV (EU-BEV) after a single intravenous (IV) infusion in healthy male subjects. METHODS: This phase I clinical trial was a randomized, double-blinded, three-arm study in 128 healthy adult male subjects. Every subject received a single IV infusion of 1 mg/kg of study drug and was subsequently monitored for 14 weeks. Pharmacokinetic, safety, and immunogenicity data were collected from each patient. The primary pharmacokinetic endpoint of this clinical study was area under the concentration curve from time zero to infinity (AUC0-inf). Biosimilarity of the study drugs was confirmed if the two-sided 90% confidence interval (CI) ratios of the geometric means for the three pairwise comparisons were contained within the range 80-125%. Other pharmacokinetic parameters including area under the concentration curve to time t (AUC0-t), maximum concentration of drug in plasma (Cmax), half-life (t½), and time to Cmax (tmax) were also measured. RESULTS: The pharmacokinetic parameters were comparable for the three drug products evaluated. The 90% CI for the AUC0-inf was 99-112% for BAT1706 versus EU-BEV, 97-110% for BAT1706 vs US-BEV and 92-104% for EU-BEV versus US-BEV comparisons, respectively, demonstrating biosimilarity. There were no significant adverse events attributable to BAT1706, as compared to EU-BEV and US-BEV. BAT1706 demonstrated a similar safety profile to EU-BEV and US-BEV. In addition, no anti-drug antibody positive result was reported for any subject included in the study. CONCLUSION: In this study, BAT1706, a proposed biosimilar of BEV, was shown to be highly similar to EU-BEV and US-BEV in terms of pharmacokinetic equivalence, safety, and immunogenicity in healthy subjects after a single IV infusion. TRIAL REGISTRATION: NCT03030430.

Potent and selective inhibitors of PDGF receptor phosphorylation. 2. Synthesis, structure activity relationship, improvement of aqueous solubility, and biological effects of 4-[4-(N-substituted (thio)carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives.

4-[4-(N-Substituted (thio)carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives such as KN1022 are potent inhibitors of the phosphorylation of platelet derived growth factor receptor (PDGFR). Structure activity relationships in the (thio)urea moiety, the phenyl ring itself, the linker between these two moieties, and the piperazine moiety were investigated. The role of the linker was found to be quite different, where ureas yielded decreasing activity, while thioureas provided increasing activity. Cyanoguanidine as a bioisostere of thiourea and related dicyanovinyl or nitrovinyl groups were not suitable for potent activity. A hydrogen atom on the (thio)urea moiety was essential for activity. Stereochemistry was also important for inhibition of PDGFR phosphorylation. Through the modification of these moieties, benzylthiourea analogues with a small substituent on the 4-position and the 3,4-methylenedioxy group (KN734/CT52923) were found to be optimal for selective and potent activity. Replacement of the phenyl ring by heterocycles improved aqueous solubility without loss of activity and kinase selectivity. Introduction of a methyl group on 5-position of the piperazine ring and replacement by homopiperazine reduced inhibitory activity. An efficient synthetic method was also developed for 2-pyridylurea-containing analogues, via carbonylation of 2-aminopyridine with N,N'-carbonyldiimidazole. A potent analogue, KN734, inhibited smooth muscle cell proliferation and migration induced by platelet derived growth factor-BB (PDGF-BB) and suppressed neointima formation following balloon injury in rat carotid artery by oral administration. Therefore, 4-[4-(N-substituted (thio)carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives may be expected to have potential as therapeutic agents for the treatment of restenosis.

Potent and selective inhibitors of platelet-derived growth factor receptor phosphorylation. 3. Replacement of quinazoline moiety and improvement of metabolic polymorphism of 4-[4-(N-substituted (thio)carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives.

We have previously reported that a series of 4-[4-(N-substituted (thio)carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives were potent and selective inhibitors of platelet-derived growth factor receptor (PDGFR) phosphorylation and demonstrated several biological effects such as suppression of neointima formation following balloon injury in rat carotid artery by oral administration. Here, we investigated structure-activity relationships of the 6,7-dimethoxyquinazolinyl moiety. In regard to 6,7-dimethoxy groups, ethoxy analogues showed potent activity (IC(50) of 16b is 0.04 microM; IC(50) of 17a is 0.01 microM) and further extension of the alkyl group reduced activity. Interestingly, methoxyethoxy (IC(50) of 16j is 0.02 microM; IC(50) of 17h is 0.01 microM) and ethoxyethoxy (IC(50) of 17j is 0.02 micro M) analogues showed the most potent activity, suggesting that the inserted oxygen atom significantly interacts with beta-PDGFR. Among tricyclic quinazoline derivatives, the 2-oxoimidazo[4,5-e]quinazoline derivative 21a showed potent activity (IC(50) = 0.10 microM). Regarding replacements of quinazoline by other heterocyclic rings, pyrazolo[3,4-d]pyrimidine (39a, IC(50) = 0.17 microM) and quinoline (IC(50) of 40a is 0.18 microM; IC(50) of 40b is 0.09 microM) derivatives showed potent activity. Isoquinoline and some pyridopyrimidine derivatives were completely inactive; therefore, 1-aza has an important role. Also 7-aza and 8-aza substitution on the parent quinazoline ring has a detrimental effect on the interaction with beta-PDGFR. We also demonstrated that the substituents on the quinazoline ring possess major consequences for metabolic polymorphism. Although there existed extensive metabolizers and poor metabolizers in Sprague-Dawley rats administrated 6,7-dimethoxyquinazoline derivatives (1b and 1c), 6-(2-methoxy)ethoxy-7-methoxyquinazoline analogue 16k showed no metabolic polymorphism.

Identification of orally active, potent, and selective 4-piperazinylquinazolines as antagonists of the platelet-derived growth factor receptor tyrosine kinase family.

We have previously found that the 4-[4-(N-substituted carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazolines can function as potent and selective inhibitors of platelet-derived growth factor receptor (PDGFR) phosphorylation. A series of highly potent, specific, orally active, small molecule kinase inhibitors directed against members of PDGFR receptor have been developed through modifications of the novel quinazoline template I. Systematic modifications in the A-bicyclic ring and D-rings of protype I were carried out to afford potent analogues, which display IC(50) values of <250 nM in cellular betaPDGFR phosphorylation assays. An optimized analogue in this series, 75 (CT53518), inhibits Flt-3, betaPDGFR, and c-Kit receptor phosphorylation with IC(50) values of 50-200 nM, whereas 15-20-fold less potent activity against CSF-1R was observed. This analogue also inhibits autophosphorylation of Flt-3 ligand-stimulated wild-type Flt-3 and a constitutively activated Flt-3/internal tandem duplication (ITD) with IC(50) values of 30-100 nM. Through this optimization process, 75 was found to be metabolically stable and has desirable pharmacokinetic properties in all animal species studied (F% > 50%, T(1/2) > 8 h). Oral administration of 75 promotes mice survival and significantly delayed disease progression in a Flt-3/ITD-mediated leukemia mouse model and shows efficacy in a nude mouse model of chronic myelomonocytic leukemia.

Potent and selective inhibitors of platelet-derived growth factor receptor phosphorylation. 1. Synthesis, structure-activity relationship, and biological effects of a new class of quinazoline derivatives.

A new series of 4-[4-(N-substituted carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives were found to show potent and selective inhibition of platelet-dervied growth factor (PDGF) receptor phosphorylation. In this exploration of the structure-activity relationships (SARs) of the prototype inhibitor KN1022, the 4-nitrophenylurea moiety was probed. We found that 4-substitution on the phenyl ring was optimal and the introduction of more than two substituents on the phenyl ring decreased activities. Bulky substituents on the phenyl ring enhanced activities. Thiourea analogues were also prepared, and the SARs were found to be slightly different from those of the urea derivatives. Through this research, we obtained some potent KN1022 derivatives such as 4-(4-methylphenoxy)phenyl (36, IC(50) 0.02 micromol/L), 4-tert-butylphenyl (16, IC(50) 0.03 micromol/L), and 4-phenoxyphenyl (21, IC(50) 0.08 micromol/L) analogues, which had almost a 10-fold increase in activity against KN1022. These potent compounds retained their high selectivity against the PDGF receptor family similar to KN1022. We also observed that these compounds could inhibit the PDGF-BB-induced proliferation of porcine vascular smooth muscle cells without cell toxicity almost at the same IC(50) values observed for PDGF receptor phosphorylation. To evaluate the biological effects in vivo, we selected some analogues on the basis of the measurement of the plasma drug concentration after oral administration to rats. Oral administration of the 4-chlorophenyl (6), 4-bromophenyl (9), or 4-isopropoxyphenyl (20) analogue to Sprague-Dawley rats (30 mg/kg, twice daily) resulted in significant inhibition (24-38%) of neointima formation in the carotid artery of the balloon catheter deendothelialized vessel in the rats. Therefore, 4-[4-(N-substituted carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives, which are potent inhibitors of PDGFR phosphorylation, may be expected to represent a new therapeutic approach for the treatment of various aspects of atherosclerosis and other cellular proliferative disorders.

Roles of tyrosine 589 and 591 in STAT5 activation and transformation mediated by FLT3-ITD.

Acquired mutations in the FLT3 receptor tyrosine kinase are common in acute myeloid leukemia and result in constitutive activation. The most frequent mechanism of activation is disruption of the juxtamembrane autoregulatory domain by internal tandem duplications (ITDs). FLT3-ITDs confer factor-independent growth to hematopoietic cells and induce a myeloproliferative syndrome in murine bone marrow transplant models. We and others have observed that FLT3-ITD activates STAT5 and its downstream effectors, whereas ligand-stimulated wild-type FLT3 (FLT3WT) does not. In vitro mapping of tyrosine phosphorylation sites in FLT3-ITD identified 2 candidate STAT5 docking sites within the juxtamembrane domain that are disrupted by the ITD. Tyrosine to phenylalanine substitution of residues 589 and 591 in the context of the FLT3-ITD did not affect tyrosine kinase activity, but abrogated STAT5 activation. Furthermore, FLT3-ITD-Y589/591F was incapable of inducing a myeloproliferative phenotype when transduced into primary murine bone marrow cells, whereas FLT3-ITD induced myeloproliferative disease with a median latency of 50 days. Thus, the conformational change in the FLT3 juxtamembrane domain induced by the ITD activates the kinase through dysregulation of autoinhibition and results in qualitative differences in signal transduction through STAT5 that are essential for the transforming potential of FLT3-ITD in vivo.

Potent and selective inhibitors of platelet-derived growth factor receptor phosphorylation. Part 4: structure-activity relationships for substituents on the quinazoline moiety of 4-[4-(N-substituted(thio)carbamoyl)-1-piperazinyl]-6,7-dimethoxyquinazoline derivatives.

Here, we investigated the structure-activity relationships of the 6,7-dimethoxyquinazoline moiety. With regard to exploration of positions and varieties of substituents on the quinazoline ring, 6,7-dialkoxy substitution was optimal. This study suggests the possibility of further modifications for this moiety.

Variable sensitivity of FLT3 activation loop mutations to the small molecule tyrosine kinase inhibitor MLN518.

FLT3 is constitutively activated by internal tandem duplications (ITDs) in the juxtamembrane domain or by activation loop mutations in acute myeloid leukemia (AML). We tested the sensitivity of 8 activation loop mutations to the small molecule FLT3 inhibitor, MLN518. Each FLT3 activation loop mutant, including D835Y, D835A, D835E, D835H, D835N, D835V, D835del, and I836del, transformed Ba/F3 cells to factor-independent proliferation and had constitutive tyrosine kinase activation, as assessed by FLT3 autophosphorylation and activation of downstream effectors, including STAT5 and ERK. MLN518 inhibited FLT3 autophosphorylation and phosphorylation of STAT5 and ERK in FLT3-ITD-transformed Ba/F3 cells with an IC(50) (50% inhibition of cell viability) of approximately 500 nM. However, there was a broad spectrum of sensitivity among the 8 activation loop mutants, with IC(50) ranging from approximately 500 nM to more than 10 microM for the inhibition of phosphorylation of FLT3, STAT5, and ERK. The relative sensitivity of the mutants to MLN518 in biochemical assays correlated with the cellular IC(50) for cytokine-independent proliferation of FLT3-transformed Ba/F3 cells in the presence of MLN518. Thus, certain activation loop mutations in FLT3 simultaneously confer resistance to small molecule inhibitors. These findings have implications for the evaluation of responses in clinical trials with FLT3 inhibitors and provide a strategy to screen for compounds that can overcome resistance.

Identification of 4-piperazin-1-yl-quinazoline template based aryl and benzyl thioureas as potent, selective, and orally bioavailable inhibitors of platelet-derived growth factor (PDGF) receptor.

4-[4-(N-Substituted-thio-carbamoyl)-1-piperazinyl]-6-methoxy-7-alkoxyamino-quinazoline derivatives such as 14 (CT53986) have been identified to be potent and selective inhibitors of the phosphorylation of PDGFR. SAR-investigations are described in the arylamine segment, C-7 appendage, and the thiourea moiety. Bioisosteres of thiourea (cyanoguanidine), and of quinazoline (quinoline-3-carbonitrile) were synthesized and are compared for their in vitro inhibitory activity. PK profiles of the optimized compounds in rat, dog, and cynomolgus monkey are described.

Blockade of platelet-derived growth factor or its receptors transiently delays but does not prevent fibrous cap formation in ApoE null mice.

Platelet-derived growth factor (PDGF) is a potent stimulant of smooth muscle cell migration and proliferation in culture. To test the role of PDGF in the accumulation of smooth muscle cells in vivo, we evaluated ApoE -/- mice that develop complex lesions of atherosclerosis. Fetal liver cells from PDGF-B-deficient embryos were used to replace the circulating cells of lethally irradiated ApoE -/- mice. One month after transplant, all monocytes in PDGF-B -/- chimeras are of donor origin (lack PDGF), and no PDGF-BB is detected in circulating platelets, primary sources of PDGF in lesions. Although lesion volumes are comparable in the PDGF-B +/+ and -/- chimeras at 35 weeks, lesions in PDGF-B -/- chimeras contain mostly macrophages, appear less mature, and have a reduced frequency of fibrous cap formation as compared with PDGF-B +/+ chimeras. However, after 45 weeks, smooth muscle cell accumulation in fibrous caps is indistinguishable in the two groups. Comparison of elicited peritoneal macrophages by RNase protection assay shows an altered cytokine and cytokine receptor profile in PDGF-B -/- chimeras. ApoE -/- mice were also treated for up to 50 weeks with a PDGF receptor antagonist that blocks all three PDGF receptor dimers. Blockade of the PDGF receptors similarly delays, but does not prevent, accumulation of smooth muscle and fibrous cap formation. Thus, elimination of PDGF-B from circulating cells or blockade of PDGF receptors does not appear sufficient to prevent smooth muscle accumulation in advanced lesions of atherosclerosis.