A Novel Step-Up Dosage Regimen for Enhancing the Benefit-to-Risk Ratio of Mosunetuzumab in Relapsed or Refractory Follicular Lymphoma.

Mosunetuzumab, a T-cell engaging bispecific antibody targeting CD20xCD3, is approved for treating relapsed/refractory follicular lymphoma. This research supports the approved intravenous clinical dose regimen, summarizing the exposure-response relationships for clinical safety and efficacy. A population pharmacokinetic model and Emax logistic regression exposure-response models for safety and efficacy were developed using data from 439 patients with relapsed/refractory non-Hodgkin lymphoma and 159 patients with relapsed/refractory follicular lymphoma, respectively, from a Phase I/II study (NCT02500407). Data from 0.2 to 60 mg across fixed dosing (Cohort A) and Cycle 1 step-up dosing (Cohort B) were used. Exposure-response models, using two-cycle area-under-the-concentration curve (AUC0-42) as the primary exposure endpoint, accurately depicted the complete response and objective response rate data across a 600-fold AUC0-42 range. The approved clinical dose regimen of 1/2/60/30 mg achieved near-maximal efficacy, with model-estimated CR and ORR (90% confidence interval) of 63.1% (49.7-75.0) and 79.1% (69.1-87.7), respectively. The exposure-response analysis for Grade ≥ 2 cytokine release syndrome identified receptor occupancy (%) within the first two cycles as a driver, with CRS dissipating beyond the first dosing cycle. No exposure-dependent increases were observed for other serious adverse events, including neutropenia and infections. The approved intravenous step-up dose regimen (i.e., step doses of 1 and 2 mg on Day 1 and 8, respectively) mitigated severe CRS risk, allowing safe administration of loading (60 mg) and target doses (30 mg every 3 weeks) to achieve a favorable benefit-risk profile.

Mosunetuzumab with polatuzumab vedotin in relapsed or refractory aggressive large B cell lymphoma: a phase 1b/2 trial.

Relapsed/refractory aggressive large B cell lymphoma (LBCL) remains an area of unmet need. Here we report the primary analysis of a phase 1b/2 trial of outpatient mosunetuzumab (a CD20xCD3 T-cell-engaging bispecific antibody) plus polatuzumab vedotin (an anti-CD79B antibody-drug conjugate) in relapsed/refractory LBCL. The phase 2 component is a single arm of an ongoing multi-arm trial. The primary endpoint during dose expansion was independent review committee (IRC)-assessed best overall response rate. Secondary endpoints included investigator-assessed overall response rate, complete response, duration of response, progression-free survival and overall survival. At data cutoff, 120 patients were enrolled (22 dose escalation, 98 dose expansion). The primary endpoint was met during dose expansion, with IRC-assessed best overall response rate and complete response rates of 59.2% (58/98; 95% confidence interval (CI): 48.8-69.0) and 45.9% (45/98; 95% CI: 35.8-56.3), respectively (median follow-up, 23.9 months). Median duration of complete was not reached (95% CI: 20.5-not estimable (NE)). Median progression-free survival was 11.4 months (95% CI: 6.2-18.7). Median overall survival was 23.3 months (95% CI: 14.8-NE). Across dose escalation and expansion, the most common grade 3 or higher adverse events were neutropenia (25.0%, 30/120) and fatigue (6.7%, 8/120). Any-grade cytokine release syndrome occurred in 16.7% of patients. These data demonstrate that mosunetuzumab plus polatuzumab vedotin has a favorable safety profile with highly durable responses suitable as second-line therapy in transplant-ineligible relapsed/refractory LBCL. ClinicalTrials.gov identifier: NCT03671018 .

Loss of CD20 expression as a mechanism of resistance to mosunetuzumab in relapsed/refractory B-cell lymphomas.

ABSTRACT: CD20 is an established therapeutic target in B-cell malignancies. The CD20 × CD3 bispecific antibody mosunetuzumab has significant efficacy in B-cell non-Hodgkin lymphomas (NHLs). Because target antigen loss is a recognized mechanism of resistance, we evaluated CD20 expression relative to clinical response in patients with relapsed and/or refractory NHL in the phase 1/2 GO29781 trial investigating mosunetuzumab monotherapy. CD20 was studied using immunohistochemistry (IHC), RNA sequencing, and whole-exome sequencing performed centrally in biopsy specimens collected before treatment at predose, during treatment, or upon progression. Before treatment, most patients exhibited a high proportion of tumor cells expressing CD20; however, in 16 of 293 patients (5.5%) the proportion was <10%. Analyses of paired biopsy specimens from patients on treatment revealed that CD20 levels were maintained in 29 of 30 patients (97%) vs at progression, where CD20 loss was observed in 11 of 32 patients (34%). Reduced transcription or acquisition of truncating mutations explained most but not all cases of CD20 loss. In vitro modeling confirmed the effects of CD20 variants identified in clinical samples on reduction of CD20 expression and missense mutations in the extracellular domain that could block mosunetuzumab binding. This study expands the knowledge about the occurrence of target antigen loss after anti-CD20 therapeutics to include CD20-targeting bispecific antibodies and elucidates mechanisms of reduced CD20 expression at disease progression that may be generalizable to other anti-CD20 targeting agents. These results also confirm the utility of readily available IHC staining for CD20 as a tool to inform clinical decisions. This trial was registered at www.ClinicalTrials.gov as #NCT02500407.

Systems-based digital twins to help characterize clinical dose-response and propose predictive biomarkers in a Phase I study of bispecific antibody, mosunetuzumab, in NHL.

Phase I oncology clinical trials often comprise a limited number of patients representing different disease subtypes who are divided into cohorts receiving treatment(s) at different dosing levels and schedules. Here, we leverage a previously developed quantitative systems pharmacology model of the anti-CD20/CD3 T-cell engaging bispecific antibody, mosunetuzumab, to account for different dosing regimens and patient heterogeneity in the phase I study to inform clinical dose/exposure-response relationships and to identify biological determinants of clinical response. We developed a novel workflow to generate digital twins for each patient, which together form a virtual population (VPOP) that represented variability in biological, pharmacological, and tumor-related parameters from the phase I trial. Simulations based on the VPOP predict that an increase in mosunetuzumab exposure increases the proportion of digital twins with at least a 50% reduction in tumor size by day 42. Simulations also predict a left-shift of the exposure-response in patients diagnosed with indolent compared to aggressive non-Hodgkin's lymphoma (NHL) subtype; this increased sensitivity in indolent NHL was attributed to the lower inferred values of tumor proliferation rate and baseline T-cell infiltration in the corresponding digital twins. Notably, the inferred digital twin parameters from clinical responders and nonresponders show that the potential biological difference that can influence response include tumor parameters (tumor size, proliferation rate, and baseline T-cell infiltration) and parameters defining the effect of mosunetuzumab on T-cell activation and B-cell killing. Finally, the model simulations suggest intratumor expansion of pre-existing T-cells, rather than an influx of systemically expanded T-cells, underlies the antitumor activity of mosunetuzumab.

ARID1A mutations confer intrinsic and acquired resistance to cetuximab treatment in colorectal cancer.

Most colorectal (CRC) tumors are dependent on EGFR/KRAS/BRAF/MAPK signaling activation. ARID1A is an epigenetic regulator mutated in approximately 5% of non-hypermutated CRC tumors. Here we show that anti-EGFR but not anti-VEGF treatment enriches for emerging ARID1A mutations in CRC patients. In addition, we find that patients with ARID1A mutations, at baseline, are associated with worse outcome when treated with cetuximab- but not bevacizumab-containing therapies; thus, this suggests that ARID1A mutations may provide both an acquired and intrinsic mechanism of resistance to anti-EGFR therapies. We find that, ARID1A and EGFR-pathway genetic alterations are mutually exclusive across lung and colorectal cancers, further supporting a functional connection between these pathways. Our results not only suggest that ARID1A could be potentially used as a predictive biomarker for cetuximab treatment decisions but also provide a rationale for exploring therapeutic MAPK inhibition in an unexpected but genetically defined segment of CRC patients.

Combination of Atezolizumab and Tazemetostat in Patients With Relapsed/Refractory Diffuse Large B-Cell Lymphoma: Results From a Phase Ib Study.

BACKGROUND: The combination of atezolizumab, a monoclonal antibody that targets programmed death-ligand 1 (PD-L1) and inhibits the interaction between PD-L1 and its receptors, and tazemetostat, an EZH2 inhibitor, may lead to selective epigenetic reprogramming, alter the tumor microenvironment, and provide additive or synergistic response to patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL). MATERIALS AND METHODS: This was an open-label, phase Ib study assessing the safety, tolerability, and preliminary efficacy of atezolizumab plustazemetostat in patients with R/R DLBCL. Atezolizumab (1200 mg) was administered via intravenous (IV) infusion on day 1 of each cycle and tazemetostat (800 mg) was given orally twice daily (BID) on days 1 to 21. Primary endpoints were safety and tolerability, and to identify a recommended phase II dose (RP2D) for atezolizumab. Secondary efficacy endpoints included response rate and duration of response. RESULTS: A total of 43 patients were enrolled, receiving a median of 3 prior lines of treatment (range: 1-9). The RP2D for atezolizumab was 1200 mg IV infusion every 3 weeks in combination with tazemetostat 800 mg BID. At the RP2D, adverse events reported in ≥20% patients were anemia(11 patients [26%]), fatigue (10 patients [23%]), and nausea (10 patients [23%]). Overall response rate was 16% (complete response rate: 7%). Median progression-free survival was 2 months (range: 0-24) and median overall survival was 13 months (range: 1-29). CONCLUSIONS: The combination of atezolizumab and tazemetostat was determined to be safe and tolerable. However, anti-tumor activity of the combination was modest.

The MDM2 antagonist idasanutlin in patients with polycythemia vera: results from a single-arm phase 2 study.

Idasanutlin, an MDM2 antagonist, showed clinical activity and a rapid reduction in JAK2 V617F allele burden in patients with polycythemia vera (PV) in a phase 1 study. This open-label phase 2 study evaluated idasanutlin in patients with hydroxyurea (HU)-resistant/-intolerant PV, per the European LeukemiaNet criteria, and phlebotomy dependence; prior ruxolitinib exposure was permitted. Idasanutlin was administered once daily on days 1 through 5 of each 28-day cycle. The primary end point was composite response (hematocrit control and spleen volume reduction > 35%) in patients with splenomegaly and hematocrit control in patients without splenomegaly at week 32. Key secondary end points included safety, complete hematologic response (CHR), patient-reported outcomes, and molecular responses. All patients (n = 27) received idasanutlin; 16 had response assessment (week 32). Among responders with baseline splenomegaly (n = 13), 9 (69%) attained any spleen volume reduction, and 1 achieved composite response. Nine patients (56%) achieved hematocrit control, and 8 patients (50%) achieved CHR. Overall, 43% of evaluable patients (6/14) showed a ≥50% reduction in the Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score (week 32). Nausea (93%), diarrhea (78%), and vomiting (41%) were the most common adverse events, with grade ≥ 3 nausea or vomiting experienced by 3 patients (11%) and 1 patient (4%), respectively. Reduced JAK2 V617F allele burden occurred early (after 3 cycles), with a median reduction of 76%, and was associated with achieving CHR and hematocrit control. Overall, the idasanutlin dosing regimen showed clinical activity and rapidly reduced JAK2 allele burden in patients with HU-resistant/- intolerant PV but was associated with low-grade gastrointestinal toxicity, leading to poor long-term tolerability. This trial was registered at www.clinincaltrials.gov as #NCT03287245.

Low-pass Whole-genome Sequencing of Circulating Cell-free DNA Demonstrates Dynamic Changes in Genomic Copy Number in a Squamous Lung Cancer Clinical Cohort.

PURPOSE: We developed a method to monitor copy number variations (CNV) in plasma cell-free DNA (cfDNA) from patients with metastatic squamous non-small cell lung cancer (NSCLC). We aimed to explore the association between tumor-derived cfDNA and clinical outcomes, and sought CNVs that may suggest potential resistance mechanisms. EXPERIMENTAL DESIGN: Sensitivity and specificity of low-pass whole-genome sequencing (LP-WGS) were first determined using cell line DNA and cfDNA. LP-WGS was performed on baseline and longitudinal cfDNA of 152 patients with squamous NSCLC treated with chemotherapy, or in combination with pictilisib, a pan-PI3K inhibitor. cfDNA tumor fraction and detected CNVs were analyzed in association with clinical outcomes. RESULTS: LP-WGS successfully detected CNVs in cfDNA with tumor fraction ≥10%, which represented approximately 30% of the first-line NSCLC patients in this study. The most frequent CNVs were gains in chromosome 3q, which harbors the PIK3CA and SOX2 oncogenes. The CNV landscape in cfDNA with a high tumor fraction generally matched that of corresponding tumor tissue. Tumor fraction in cfDNA was dynamic during treatment, and increases in tumor fraction and corresponding CNVs could be detected before radiographic progression in 7 of 12 patients. Recurrent CNVs, such as MYC amplification, were enriched in cfDNA from posttreatment samples compared with the baseline, suggesting a potential resistance mechanism to pictilisib. CONCLUSIONS: LP-WGS offers an unbiased and high-throughput way to investigate CNVs and tumor fraction in cfDNA of patients with cancer. It may also be valuable for monitoring treatment response, detecting disease progression early, and identifying emergent clones associated with therapeutic resistance.

A multicenter, single-arm, open-label, phase 2 study of apitolisib (GDC-0980) for the treatment of recurrent or persistent endometrial carcinoma (MAGGIE study).

BACKGROUND: The current single-arm, open-label trial was designed to evaluate the activity of apitolisib (GDC-0980), a dual phosphoinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) inhibitor, in patients with advanced endometrial cancer (EC). METHODS: Patients with recurrent or persistent EC who were treated with 1 to 2 prior lines of chemotherapy but no prior PI3K/mTOR inhibitor received oral apitolisib at a dose of 40 mg daily during 28-day cycles until disease progression or intolerable toxicity occurred. Patients with type I/II diabetes who required insulin were excluded. The primary endpoints were progression-free survival (PFS) at 6 months and objective response rate. RESULTS: A total of 56 women were enrolled, including 13 (23%) with well-controlled diabetes. Reasons for discontinuation were disease progression (24 patients; 43%), adverse events (13 patients; 23%), and withdrawal by subject (12 patients; 21%). Grade 3/4 apitolisib-related adverse events were hyperglycemia (46%), rash (30%), colitis (5%), and pneumonitis (4%) (toxicities were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events [version 4.0]). The PFS rate at 6 months was 20% (Kaplan-Meier estimate; 95% confidence interval [95% CI], 7%-33%). The objective response rate was 6% (confirmed). The median PFS was 3.5 months (95% CI, 2.7-3.7 months) and the median overall survival was 15.7 months (95% CI, 9.2-17.0 months). Nineteen patients discontinued the study before the first tumor assessment. Dose reductions were required for 4 diabetic (31%) and 18 nondiabetic (42%) patients. Comprehensive molecular profiling of 46 evaluable archival tumor samples demonstrated that 57% of patients had at least 1 alteration in phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), phosphatase and tensin homolog (PTEN), or AKT1. All 3 patients with a confirmed response had at least 1 alteration in a PI3K pathway gene. CONCLUSIONS: The antitumor activity noted with the use of a dose of 40 mg of apitolisib daily was limited by tolerability, especially in diabetic patients. Patients with PI3K pathway mutations may have derived enhanced benefit from apitolisib. Cancer 2016;122:3519-28. © 2016 American Cancer Society.

Randomized Open-Label Phase II Trial of Apitolisib (GDC-0980), a Novel Inhibitor of the PI3K/Mammalian Target of Rapamycin Pathway, Versus Everolimus in Patients With Metastatic Renal Cell Carcinoma.

PURPOSE: To the best of our knowledge, this study is the first to compare dual inhibition of PI3K/mammalian target of rapamycin (mTOR) by apitolisib (GDC-0980) against single inhibition of mTORC1 by everolimus in metastatic renal cell carcinoma (mRCC). PATIENTS AND METHODS: Patients with clear-cell mRCC who progressed on or after vascular endothelial growth factor-targeted therapy were randomly assigned to apitolisib 40 mg once per day or to everolimus 10 mg once per day. End points included progression-free survival, safety, overall survival, and objective response rate. Biomarker assessments were conducted. RESULTS: Eighty-five patients were randomly assigned. After 67 events, stratified analysis revealed that median progression-free survival was significantly shorter for apitolisib than for everolimus (3.7 v 6.1 months; hazard ratio, 2.12 [95% CI, 1.23 to 3.63; P < .01]); apitolisib was not favored in any stratification subgroup. Median overall survival was not significantly different but trended in favor of everolimus (16.5 v 22.8 months; hazard ratio, 1.77 [95% CI, 0.97 to 3.24; P = .06]). The objective response rate was 7.1% for apitolisib and 11.6% for everolimus. Patients administered apitolisib with a greater incidence of grade 3 to 4 adverse events were more likely to discontinue treatment (31% v 12% for everolimus). No drug-related deaths were observed. Apitolisib in comparison with everolimus was associated with substantially more high-grade hyperglycemia (40% v 9%) and rash (24% v 2%). Apitolisib pharmacokinetics suggested a relationship between exposure, and rash and hyperglycemia. Retrospective biomarker analyses revealed a relationship between VHL mutation status and outcome with everolimus but not with apitolisib. High hypoxia-inducible factor 1α protein expression was associated with better outcome in both arms. CONCLUSION: This study demonstrated that dual PI3K/mTOR inhibition by apitolisib was less effective than was everolimus in mRCC, likely because full blockade of PI3K/mTOR signaling resulted in multiple on-target adverse events. VHL mutation and hypoxia-inducible factor 1α expression may be predictive of an mTOR inhibitor benefit, although prospective validation is required.

The molecular landscape of high-risk early breast cancer: comprehensive biomarker analysis of a phase III adjuvant population.

Breast cancer is a heterogeneous disease and patients are managed clinically based on ER, PR, HER2 expression, and key risk factors. We sought to characterize the molecular landscape of high-risk breast cancer patients enrolled onto an adjuvant chemotherapy study to understand how disease subsets and tumor immune status impact survival. DNA and RNA were extracted from 861 breast cancer samples from patients enrolled onto the United States Oncology trial 01062. Samples were characterized using multiplex gene expression, copy number, and qPCR mutation assays. HR+ patients with a PIK3CA mutant tumor had a favorable disease-free survival (DFS; HR 0.66, P=0.05), however, the prognostic effect was specific to luminal A patients (Luminal A: HR 0.67, P=0.1; Luminal B: HR 1.01, P=0.98). Molecular subtyping of triple-negative breast cancers (TNBCs) suggested that the mesenchymal subtype had the worst DFS, whereas the immunomodulatory subtype had the best DFS. Profiling of immunologic genes revealed that TNBC tumors (n=280) displaying an activated T-cell signature had a longer DFS following adjuvant chemotherapy (HR 0.59, P=0.04), while a distinct set of immune genes was associated with DFS in HR+ cancers. Utilizing a discovery approach, we identified genes associated with a high risk of recurrence in HR+ patients, which were validated in an independent data set. Molecular classification based on PAM50 and TNBC subtyping stratified clinical high-risk patients into distinct prognostic subsets. Patients with high expression of immune-related genes showed superior DFS in both HR+ and TNBC. These results may inform patient management and drug development in early breast cancer.

Upregulation of Periostin and Reactive Stroma Is Associated with Primary Chemoresistance and Predicts Clinical Outcomes in Epithelial Ovarian Cancer.

PURPOSE: Up to one third of ovarian cancer patients are intrinsically resistant to platinum-based treatment. However, predictive and therapeutic strategies are lacking due to a poor understanding of the underlying molecular mechanisms. This study aimed to identify key molecular characteristics that are associated with primary chemoresistance in epithelial ovarian cancers. EXPERIMENTAL DESIGN: Gene expression profiling was performed on a discovery set of 85 ovarian tumors with clinically well-defined response to chemotherapies as well as on an independent validation dataset containing 138 ovarian patients from the chemotreatment arm of the ICON7 trial. RESULTS: We identified a distinct "reactive stroma" gene signature that is specifically associated with primary chemoresistant tumors and was further upregulated in posttreatment recurrent tumors. Immunohistochemistry (IHC) and RNA in situ hybridization (RNA ISH) analyses on three of the highest-ranked signature genes (POSTN, LOX, and FAP) confirmed that modulation of the reactive stroma signature genes within the peritumoral stromal compartments was specifically associated with the clinical chemoresistance. Consistent with these findings, chemosensitive ovarian cells grown in the presence of recombinant POSTN promoted resistance to carboplatin and paclitaxel treatment in vitro. Finally, we validated the reactive stroma signature in an independent dataset and demonstrated that a high POSTN expression level predicts shorter progression-free survival following first-line chemotherapy. CONCLUSIONS: Our findings highlight the important interplay between cancer and the tumor microenvironment in ovarian cancer biology and treatment. The identified reactive stromal components in this study provide a molecular basis to the further development of novel diagnostic and therapeutic strategies for overcoming chemoresistance in ovarian cancer.

Molecular predictors of response to a humanized anti-insulin-like growth factor-I receptor monoclonal antibody in breast and colorectal cancer.

The insulin-like growth factor-I receptor (IGF-IR) pathway is required for the maintenance of the transformed phenotype in neoplastic cells and hence has been the subject of intensive drug discovery efforts. A key aspect of successful clinical development of targeted therapies directed against IGF-IR will be identification of responsive patient populations. Toward that end, we have endeavored to identify predictive biomarkers of response to an anti-IGF-IR-targeting monoclonal antibody in preclinical models of breast and colorectal cancer. We find that levels of the IGF-IR itself may have predictive value in these tumor types and identify other gene expression predictors of in vitro response. Studies in breast cancer models suggest that IGF-IR expression is both correlated and functionally linked with estrogen receptor signaling and provide a basis for both patient stratification and rational combination therapy with antiestrogen-targeting agents. In addition, we find that levels of other components of the signaling pathway such as the adaptor proteins IRS1 and IRS2, as well as the ligand IGF-II, have predictive value and report on the development of a pathway-focused panel of diagnostic biomarkers that could be used to test these hypotheses during clinical development of IGF-IR-targeting therapies.

Age-dependent acceleration of ischemic injury in endothelial nitric oxide synthase-deficient mice: potential role of impaired VEGF receptor 2 expression.

Morbidity and mortality of peripheral arterial occlusive disease significantly increases with age, often exhibiting more severe disease pathology and decreased treatment effectiveness. Therapeutic angiogenesis with angiogenic growth factors may represent a valuable treatment option for the severely ill, older adult patient population. Aging is considered an independent cardiovascular risk factor, but pathomechanistically it is not well understood. Diminished endothelial nitric oxide (EDNO) production has been considered as a major contributor to the aging process. To investigate the effect of age on postischemic revascularization independent of changes in EDNO, we used endothelial nitric oxide synthase-deficient (ecNOS-KO) mice. We found an age-dependent acceleration in ischemic injury following unilateral femoral artery ligation in these animals compared to C57BL/J6 mice. Postischemic revascularization, quantified by measuring von Willebrand factor expression, was significantly impaired, suggesting that factors other than progressive EDNO deterioration are also involved in the age-dependent severe disease phenotype. Ischemia led to an increase in the expression of vascular endothelial growth factor receptor-2, KDR, in younger ecNOS-KO; however, this increase in KDR expression was absent in the older animals. Lack of increased KDR expression may provide a mechanistic explanation for the severe ischemic injury and perhaps can be used as a clinical marker to identify severe, vascular endothelial growth factor refractory patient population.

Anti-atherosclerotic effect of simvastatin depends on the presence of apolipoprotein E.

Low density lipoprotein receptor deficient (LDLR-KO) and apolipoprotein E deficient (apo E-KO) mice both develop hyperlipidemia and atherosclerosis by different mechanisms. The aim of the present study was to compare the effects of simvastatin on cholesterol levels, endothelial dysfunction, and aortic lesions in these two models of experimental atherosclerosis. Male LDLR-KO mice fed a high cholesterol (HC; 1%) diet developed atherosclerosis at 8 months of age with hypercholesterolemia. The addition of simvastatin (300 mg/kg daily) to the HC diet for 2 more months lowered total cholesterol levels by approximately 57% and reduced aortic plaque area by approximately 15% compared with the LDLR-KO mice continued on HC diet alone, P<0.05. Simvastatin treatment also improved acetylcholine (ACh)-induced endothelium-dependent vasorelaxation in isolated aortic rings, which was associated with an increase in NOS-3 expression by approximately 88% in the aorta measured by real time polymerase chain reaction (PCR), P<0.05. In contrast, in age-matched male apo E-KO mice fed a normal diet, the same treatment of simvastatin elevated serum total cholesterol by approximately 35%, increased aortic plaque area by approximately 15%, and had no effect on endothelial function. These results suggest that the therapeutic effects of simvastatin may depend on the presence of a functional apolipoprotein E.