Phase I Dose-Escalation Study of the Safety and Pharmacokinetics of Atrasentan: an Endothelin Receptor Antagonist for Refractory Prostate Cancer1

$Phase I Dose-Escalation Study of the Safety and Pharmacokinetics of Atrasentan: an Endothelin Receptor Antagonist for Refractory Prostate Cancer1$

Vol. 9, 2965–2972, August 1, 2003 Clinical Cancer Research 2965

Phase I Dose-Escalation Study of the Safety and Pharmacokinetics of Atrasentan: An Endothelin Receptor Antagonist for Refractory Prostate Cancer1

Bernard A. Zonnenberg,2 Gerard Groenewegen, Conclusions: Atrasentan is well tolerated, with no dose- Todd J. Janus, Terri W. Leahy, limiting adverse events observed up to 95 mg. Adverse events are consistent with the vasodilatory effect of the drug. Rod A. Humerickhouse, Jeffrey D. Isaacson, PK are linear and dose-proportional; the half-life is appro- Robert A. Carr, and Emile Voest, priate for once-daily dosing. Department of Internal Medicine, University Hospital, 3584 CX Utrecht, the Netherlands [B. A. Z., G. G., E. V.], and Abbott INTRODUCTION Laboratories, Abbott Park, Illinois [T. J. J., R. A. H., J. D. I., R. A. C., 3 T. W. L.] The ETs, a family of three 21-amino acid isopeptides (ET-1, ET-2, and ET-3), were first identified in 1988 as secre- tory products of vascular endothelial cells with potent, sustained ABSTRACT vasoconstrictor activity (1). ET-1, the main isoform, is produced Purpose: Evidence suggests that endothelin (ET)-1 and by endothelial and epithelial cells and has been recognized as a mediator of growth and survival signal in both normal physiol- its primary receptor, the ETA receptor, may contribute to the progression of prostate and other cancers. Atrasentan ogy and tumor growth (2–4). ET-1 is also produced by many epithelial-derived human tumors (3, 5) and is considered to be a (ABT-627) is a highly potent, selective ETA receptor antagonist. This study assessed safety, maximum tolerated dose, mediator and an autocrine and a paracrine growth factor for and pharmacokinetics (PK) in patients with refractory ad- local cancer and stromal cells (6, 7). enocarcinomas, primarily prostate cancer. The action of ET-1 is thought to be mediated via two Experimental Design: This 28-day, single-center Phase I G-protein-coupled receptors, ETA and ETB, which are distin- guished by different binding affinities for the ETs. The ET trial evaluated the safety and PK of escalating oral atrasen- B receptor binds the three isotypes with equal affinity and func- tan doses (2.5–95 mg) given daily (except day 2) to eligible tions primarily as both a clearance receptor and a modulator of patients >18 years old with an adenocarcinoma proven ET-1 expression (8). In contrast, the ET receptor binds ET-1 resistant to standard therapy. Priority was given to patients A with a higher affinity than the other isoforms. Binding of ET-1 with hormone-refractory prostate cancer. After 28 days, to the ET receptor stimulates vasoconstriction in normal vas- patients without objective signs of tumor progression were A cular endothelium, stimulates proliferative responses in normal eligible to continue atrasentan in an extension study. and neoplastic cells, and potentiates other growth factors in Results: Thirty-nine patients (30 of whom had prostate malignant growth (2, 8–10). Recently, ET-1 has also been found cancer) were treated in cohorts of three patients each with to prevent apoptosis (11). escalating atrasentan doses (2.5, 5, 10, 20, 30, 45, 60, 75, and Secreted by normal prostate epithelial cells (12), ET-1 is 95 mg). The most common adverse events were rhinitis, found in human semen in the highest concentrations thus far headache, and peripheral edema. Anemia consistent with a observed in any body fluid (13). A dysregulation of the ET axis reversible hemodilution effect was observed. No maximum leading to increased ET-1 production was first reported in tolerated dose was found in the dose range studied. Atra- prostate cancer; ET-1 concentrations were found to be signifi- sentan PK were characterized by rapid absorption (mean cantly elevated in patients with metastatic hormone-refractory ؎ ؎ ؍ Tmax 0.9 h), mean SD oral clearance of 24 15 liters/h, disease (14). The tumor-promoting effects of ET-1 in prostate -and volume distribution of 726 ؎ 477 liters. PK were ap cancer were observed to occur via ETA receptors (15), with ETA proximately dose-proportional and time independent across receptors predominating (10). Tumor growth was shown to be doses. promoted by increased production of ET-1, decreased ET-1

clearance, and ETA overexpression (10, 16). ET-1 expression correlates well with the stage and grade of human prostatic cancer (10, 14, 17).

Received 7/29/02; revised 4/1/03; accepted 4/2/03. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to 3 The abbreviations used are: ET, endothelin; AUC, area under the indicate this fact. curve; Cmax, maximum observed plasma concentration; Cmin, minimum 1 Supported by a grant from Abbott Laboratories. observed plasma concentration; DLT, dose-limiting toxicity; ECG, elec- 2 To whom requests for reprints should be addressed, at Department of trocardiogram; iET, immunoreactive endothelin-1; MTD, maximum Medical Oncology, University Medical Centre, Heidelberglaan 100, tolerated dose; NCI, National Cancer Institute; PK, pharmacokinetics;

3584 CX Utrecht, the Netherlands. Phone: 31-30-250-6680; Fax: 31- Tmax, time to maximum observed plasma concentration; t1/2, terminal 30-254-2531; E-mail: [email protected]. elimination half-life.

A dysregulation of the ET-1/ETA receptor system similar written informed consent before undergoing any study-related to that in prostatic cancer has been reported for ovarian and procedures. human papilloma virus-associated cervical carcinomas (18–20), Study Design. This dose-escalation study was designed

in which functional ETA receptors are overexpressed. Selective to enroll successive cohorts of patients (3 patients/cohort), each

antagonism of ETA receptors, but not ETB receptors, has been to be started on a fixed dose of atrasentan. The initial protocol found to inhibit ET-1-mediated growth effects in various tumor specified 10 mg/day for the first cohort. Planned dose levels for models (18–20). Additional evidence in support of ET-1 and/or subsequent cohorts were 20, 30, 45, 60, 75, and 95 mg/day. The protocol was later amended to include 2.5- and 5-mg doses so ETA receptor expression in human cancers suggests a wider participation of the ET axis in both human tumor cells and that more safety and pharmacokinetic data could be collected at normal stromal cells (21, 22). these lower doses. Atrasentan was administered once daily on Selective blockade of the ET-1 receptor represents a day 1 and days 3–28; the drug was withheld on day 2 to allow targeted approach to abrogating the pathophysiological ef- for pharmacokinetic analyses over a 48-h period. The drug was fects of ET in cancer (14). Atrasentan, a p.o. bioavailable supplied as capsules (2.5, 5, 10, and 25 mg) for oral adminis- ϭ ϭ tration. The patients took the capsules under fasting conditions drug, is a potent (Ki 0.034 nM) and selective (KiETB on study days 1, 7, 14, and 28. 63.3 nM)ETA receptor antagonist (23, 24). This Phase I dose-escalation study was designed to evaluate the safety and Dose escalation was to be halted when the MTD was tolerability of atrasentan (ABT-627), estimate the MTD, and reached; MTD was defined as one dose level below that at characterize the PK of the drug after once-daily oral admin- which DLT was observed in one-third or more of the patients. If one of the three patients in a dose cohort experienced a DLT, istration in patients with refractory adenocarcinomas, partic- three more patients were added to the cohort. If no further DLTs ularly those with hormone-refractory prostate cancer requir- were observed in the group after 28 days, an additional cohort of ing pain relief with opioids. three patients was enrolled at the next higher dose. Toxicities were graded using the NCI Common Toxicity PATIENTS AND METHODS Criteria (version 2). If a NCI grade did not apply, the adverse Patients. Patients selected for this single-center open- event was graded as mild, moderate, or severe. DLT was defined label Phase I study had an adenocarcinoma (documented cyto- as any atrasentan-related adverse event qualifying as NCI grade logically or histologically) refractory to standard therapy, with 3or4. preferred enrollment offered to patients with hormone-refrac- Health status assessments, conducted weekly, included physical examination, 12-lead ECG (days 7 and 28), blood tory prostate cancer requiring pain relief with opioid analgesics. chemistry, hematology, and urinalysis. Participants had to be at least 18 years old, have an Eastern Pharmacokinetic Analyses. Blood samples were col- Cooperative Oncology Group performance status of 0–2, and lected for pharmacokinetic analysis of atrasentan concentra- have a life expectancy of at least 3 months. Women with tions before the initial dose on days 1 and 28 and at the child-bearing potential were required to have a negative preg- following intervals thereafter: 15, 30, and 45 min and 1, 1.5, nancy test. Patients were excluded from the study if they had 2, 4, 6, 8, 12, 16, 24, 30, 36, and 48 h. Blood samples were brain metastases, severe left ventricular dysfunction (assessed collected over a dosing interval on days 1 and 28 for deter- by ECG or multigated acquisition), clinically significant ECG mination of the plasma concentrations of iET. In addition, a Ն abnormalities, history of migraines, total bilirubin 25.6 mM, predose sample was collected on day 14. Patients were re- Ն ϫ aspartate transaminase or alanine transaminase 1.5 the quired to fast for 8 h before dosing and, on days 1 and 28, for upper limit of the reference range, calculated creatinine clear- at least 2 h afterward. Ͻ Յ 3 ance 50 ml/min, WBC count 2,000/mm , absolute neutro- Atrasentan plasma concentrations were determined using a Յ 3 Յ 3 phil count 1,000/mm , platelet count 100,000/mm ,or validated liquid chromatography method with fluorescence de- Յ hemoglobin 1.4 nM. tection (25). iET plasma concentrations were measured using a Before enrollment, patients must have discontinued stron- validated enzyme-linked immunoassay (26). Measurements in- tium or suramin therapy for 3 months, rhenium-186-etidronate cluded Cmax,Cmin,Tmax, and AUC. The AUC of atrasentan was for 8 weeks, antiandrogen treatment with biclutamide or nilut- determined from zero to infinite time (AUCϱ) after dosing on amide for 8 weeks, antiandrogen treatment with flutamide for 4 day 1, with extrapolation after the last measurable concentra- weeks, and corticosteroids, radiotherapy, or chemotherapy for 4 tion. The terminal-phase elimination rate constant (␤) was ob- weeks. Due to potential blood pressure response with atrasentan, tained using a least squares linear regression analysis of the antihypertensive agents such as beta blockers, angiotensin- terminal log-linear portion of the plasma concentration-time converting enzyme inhibitors, calcium channel blockers, or al- profile. At least three concentration-time data points were used ␤ ␤ pha blockers were discontinued at least 7 days before the first to determine .t1/2 was calculated using ln(2)/ . Apparent oral atrasentan dose, and diuretic agents were tapered off. To begin clearance (CL/F, where F ϭ bioavailability) was calculated by treatment in the study, patients’ blood pressure had to be under dividing the dose by the corresponding AUC. Volume of dis-

adequate control. tribution (V␤/F) was calculated by dividing CL/F by ␤. For The study was approved by the hospital review board for iET, AUC was determined over 24 h on both days 1 and 28

studies on human subjects at The University Hospital Utrecht (AUC0–24). (Utrecht, the Netherlands) and conformed to the guidelines of To test for linearity and dose-proportionality of pharmaco- ␤ the Declaration of Helsinki. All patients were required to give kinetic parameters of ,Tmax, and dose-normalized Cmax,Cmin,

Table 1 Patient characteristics Dose cohort 2.5 mg 5mg 10 mg 20 mg 30 mg 45 mg 60 mg 75 mg 95 mg Total Characteristic (n ϭ 3) (n ϭ 3) (n ϭ 3) (n ϭ 3) (n ϭ 3) (n ϭ 7) (n ϭ 7) (n ϭ 6) (n ϭ 4) (n ϭ 39) Gender (M:F) 3:0 3:0 3:0 3:0 3:0 5:2 6:1 6:0 4:0 36:3 Age (mean, yr) 65.3 75.7 75.0 79.0 72.0 70.4 65.7 63.5 66.3 69.2 Range 56–71 68–80 70–84 78–80 68–75 56–82 54–77 55–76 60–73 54–84 Carcinoma Prostate 3 3 332454330(77%) Renal cell 0 0 00112217(18%) Ovarian 0 0 00010001(3%) Thyroid 0 0 00010001(3%)

and AUC, analyses of covariance were performed with body adverse events were rated as mild or as NCI grade 2 or lower. weight as the covariate. In these analyses, the primary test was The 29 cases of rhinitis and nasal congestion were mild in 28 a linear contrast orthogonal to the dose. To test for time inde- cases and moderate in 1 case; symptoms were tolerated without pendence, analyses of variance with dose as the only factor were treatment or relieved with over-the-counter medications such as performed on the difference between day 1 and day 28 pharma- antihistamines or oxymetazoline nasal spray. Headaches were cokinetic parameters. The same analyses were performed for the mild in 17 cases and moderate in 7 cases and were tolerated iET parameters. All analyses used the procedures of the General without treatment or controlled with paracetamol analgesic ther- Linear Model of SAS/STAT version 6.12 (SAS Institute, Gary, apy. Six of the seven patients with moderate headaches received Ͻ NC). P 0.05 was considered to be statistically significant. atrasentan doses of 60 mg or higher. No patient discontinued treatment as a result of rhinitis or headaches. Peripheral edema RESULTS was mild in 14 cases, moderate in 7 cases, and severe in 1 case. Study Population. This clinical trial (excluding the ex- Six of the seven patients with grade 1 edema received atrasentan tension study) was conducted between April 1997 and April at doses of 45 mg or higher. A 77-year-old patient with grade 2 1999. The demographic characteristics of patients, types of edema of the lower legs (rated as severe) had his dose reduced cancer, and assignment to cohorts are shown in Table 1. Of the from 45 to 30 mg and went on to complete the study at this dose 39 patients enrolled, 3 were female (8%), and 36 were male level. (92%); all were Caucasian. Their ages ranged from 54 to 84 Patients exhibited an overall mean decrease in blood pres- years (mean age, 69.2 years), and their mean baseline Eastern sure during the study. Systolic pressure decreased by –2.9 mm Cooperative Oncology Group score was 0.54; the median score Hg during week 1 (P ϭ 0.233), reaching an overall reduction of was 0. Ϫ9.7 mm Hg at week 4 (P ϭ 0.002). Diastolic pressure de- Of the 39 patients, 36 completed the study; 3 patients creased –6.44 mm Hg during week 1 (P ϭ 0.002) and Ϫ6.0 mm were withdrawn before day 28 due to disease progression (1 Hg by week 4 (P ϭ 0.006). Pressures returned to baseline levels patient each from the 45-, 60-, and 95-mg cohorts). A 56- within 1 week after dosing. year-old woman with ovarian cancer discontinued the study Laboratory Evaluations. Within 1 week after atra- drug (45 mg) after 7 days due to NCI grade 3 nausea and sentan administration was begun, a mean decrease in hemo- vomiting that the investigator attributed to disease progression. A 59-year-old man with prostate cancer discontinued 60 globin of 1 g/dl (0.67 mM) was observed across all dose mg of atrasentan on day 26 because of hematuria attributed to groups. This was accompanied by a 3% mean decrease in ϫ 12 disease progression. A 73-year-old man with prostate cancer hematocrit and a 0.35 10 /liter mean decrease in RBC discontinued 95 mg of atrasentan after 18 days due to in- count across all dose groups. The changes did not appear to creased pain from spinal cord compression secondary to be progressive over time. Many patients had pretreatment tumor progression. anemia due to their underlying disease. Four patients re- Safety. Atrasentan was generally well tolerated in all ceived transfusions for anemia. In all cases, the anemia was patients; there were no deaths during the study. A 62-year-old considered by the investigator to be unrelated to study drug man receiving 75 mg of atrasentan experienced supraventricular administration. There was also a decrease in WBC count tachycardia 28 h after his last dose of the study drug; his pulse from baseline over the 4 weeks of the study. The mean was 212 beats/min, and blood pressure was 95/45 mm Hg. After decrease in total protein for all dose groups combined ranged carotid massage and administration of i.v. verapamil and a from – 0.22 g/dl at week 2 to – 0.48 g/dl at week 4. Recovery plasma volume expander, the patient made a complete recovery to the baseline values was observed for all laboratory tests as and had no further episodes. early as 1 week after dosing. Except for the blood samples The most commonly reported adverse events were rhinitis collected for pharmacokinetic analyses, there was no evi- or nasal congestion (29 patients, 74%), headache (24 patients, dence of blood loss, i.e., no evidence of change in bilirubin 62%), peripheral edema (22 patients, 56%), nausea (12 patients, level, platelet number, peripheral blood smears, or urinalysis 31%), and dyspnea (12 patients, 31%; Table 2). The majority of values.

Table 2 Treatment emergent adverse effects reported by 10% or more of patients Dose cohort 2.5 mg 5mg 10 mg 20 mg 30 mg 45 mg 60 mg 75 mg 95 mg Total Body system/COSTART terma (n ϭ 3) (n ϭ 3) (n ϭ 3) (n ϭ 3) (n ϭ 3) (n ϭ 7) (n ϭ 7) (n ϭ 6) (n ϭ 4) (n ϭ 39) Body as a whole Headache 1 1 3 1 1 6 3 5 3 24 (62%) Asthenia 0 0 0 0 0 3 3 0 0 6 (15%) Face edema 0 0 0 0 0 2 2 0 1 5 (13%) Pain 1 0 1 0 1 1 1 0 0 5 (13%) Abdominal pain 0 0 2b 1 0 0 1 0 0 4 (10%) Back pain 0 0 1 0 0 1 0 1 1 4 (10%) Infection 0 1 0 0 0 1 1 1 0 4 (10%) Cardiovascular system Vasodilatation 1 0 2 1 0 1 0 1 1 7 (18%) Vascular disorder 1 0 0 0 0 1 1 1 0 4 (10%) Digestive system Nausea 1 0 3 1 1 2 2 1 1 12 (31%) Nausea/vomiting 0 0 1 0 0 1c 1 1 1 5 (13%) Vomiting 0 0 1 0 0 2 0 0 1 4 (10%) Hemic and lymphatic system Anemia 0 1 1 0 0 1 1 1 0 5 (13%) Metabolic and nutritional disorders Peripheral edema 1 2 0 1 2 3c 5 6 2 22 (56%) Nervous system Dizziness 1 0 0 1 2 0 0 2 0 6 (15%) Respiratory system Rhinitis (nasal congestion) 3 2 0 1 1 6 6 6 4 29 (74%) Dyspnea 0 1 0 1 0 2 3 4 1 12 (31%) Cough increased 1 0 0 0 1 1 2 2 0 7 (18%) Urogenital system Hematuria 0 1 0 0 1 0 1d 0 1 4 (10%) a Treatment emergent events reported by at least four patients overall. Each patient was counted only once for each COSTART term, regardless of the number of times the event was experienced. b One event reported as “severe.” Note: Other severe events not experienced by 10% or more of patients were carcinoma, supraventricular tachycardia, neuropathy, and paraplegia. c One event reported as severe. d Event was reported as severe.

Pharmacokinetics. In general, the PK of atrasentan were After peak levels of atrasentan were reached, plasma con- linear (dose-proportional) and time independent (Table 3). centrations declined biexponentially, with a terminal phase half- Dose-normalized AUC did not vary with dose on either day 1 or life averaging 21 h. No consistent trend with dose was observed Ͼ ␤ day 28 (P 0.67). Dose-normalized AUC0–24 on day 28 did not for the elimination rate constant ( ), which increased with differ from dose-normalized AUCϱ on day 1 (P ϭ 0.66). Atra- increasing dose on day 1 (P Ͻ 0.01), but not on day 28 sentan PK were characterized by a global mean Ϯ SD CL/F and (P ϭ 0.40). There was no difference between days 1 and

V␤/F of 24 Ϯ 15 liters/h and 726 Ϯ 477 liters, respectively. PK 28 (P ϭ 0.84). Atrasentan concentrations accumulated with varied considerably among individuals. On day 1, percent co- multiple dosing; on day 28, they were about double the levels

efficient of radiation values for CL/F and V␤/F were 46% and observed on day 1, which is the expected accumulation for a 45%, respectively; on day 28, these values were 73% and 83%, compound with a 21-h half-life dosed once daily (Figs. 1 and 2). respectively. Steady-state plasma concentrations of atrasentan would be ex-

Atrasentan was rapidly absorbed, with mean Tmax values pected after 5 days of dosing (five half-lives). Predose concen- ranging from 0.3 to 1.6 h. No consistent trend with dose was trations of atrasentan on days 14 and 28 were similar (P ϭ 0.08).

observed with Tmax, which increased with increasing dose on Body weight was not a statistically significant covariate in the ϭ ϭ ϭ day1(P 0.02), but not on day 28 (P 0.54). There was no analysis of any parameter except Tmax on day 1 (P 0.04). ϭ difference in Tmax between days 1 and day 28 (P 0.89). A iET concentrations increased over time with atrasentan statistically significant increase in dose-normalized atrasentan dosing and were about 40% greater on day 28 than on day 1

Cmax with increasing dose was observed on both days 1 and 28, (Figs. 3 and 4). This increase appeared to be consistent across in part due to relatively low Cmax values for the lowest dose (2.5 dose groups. iET Cmax,Cmin, and AUC0–24 were all greater on Ͻ mg). Mean Cmin values on day 28 increased roughly dose- day 28 than on day 1 (P 0.01; Table 3). Predose iET proportionally for the dose range 2.5–45 mg (slope ϭ 1.0; R2 ϭ concentrations on days 14 and 28 were similar (P ϭ 0.79). On 0.94) and somewhat less than dose-proportionally at higher either day 1 or day 28, iET AUC was independent of atrasentan Ͼ ϭ doses. Across all dose groups, a statistically significant trend dose (P 0.67), as was Cmin on day 28 (P 0.96). As ϭ with dose in dose-normalized Cmin was observed (P 0.02). expected, iET Cmin was also independent of atrasentan dose on

Table 3 Estimates of pharmacokinetic parameters (mean Ϯ SD) for atrasentan and iET A. Atrasentan parameter estimates

Cmax AUC CL/F a b ⅐ Dose (mg) N (ng/ml) Tmax (h) Cmin (ng/ml) t1/2 (h) (ng h/ml) (liters/h) V␤/F (liters) Day 1 2.5 3 7 Ϯ 2 0.50 Ϯ 0.25 NA 23.3 Ϯ 7.5 112 Ϯ 25 23.1 Ϯ 5.9 824 Ϯ 264 5327Ϯ 8 0.58 Ϯ 0.14 NA 30.6 Ϯ 7.8 285 Ϯ 134 20.5 Ϯ 9.6 873 Ϯ 218 10 3 53 Ϯ 41 0.92 Ϯ 0.95 NA 25.3 Ϯ 3.5 428 Ϯ 190 28.4 Ϯ 17.0 1045 Ϯ 614 20 3 168 Ϯ 103 0.33 Ϯ 0.14 NA 21.7 Ϯ 2.7 969 Ϯ 85 20.7 Ϯ 1.9 653 Ϯ 78 30 3 182 Ϯ 51 0.67 Ϯ 0.14 NA 18.6 Ϯ 1.1 1221 Ϯ 337 26.2 Ϯ 8.6 712 Ϯ 281 45 7 391 Ϯ 152 1.07 Ϯ 1.31 NA 20.8 Ϯ 6.0 2654 Ϯ 1629 23.4 Ϯ 14.4 689 Ϯ 325 60 7 439 Ϯ 247 0.86 Ϯ 0.50 NA 16.4 Ϯ 3.1 2442 Ϯ 1190 29.8 Ϯ 13.3 718 Ϯ 335 75 5 638 Ϯ 360 1.10 Ϯ 0.65 NA 14.7 Ϯ 2.9 3769 Ϯ 2183 27.7 Ϯ 18.7 566 Ϯ 301 95 4 854 Ϯ 472 1.56 Ϯ 0.59 NA 19.8 Ϯ 4.0 5975 Ϯ 2387 18.5 Ϯ 8.9 564 Ϯ 311 Day 28 2.5 3 13 Ϯ 4 0.50 Ϯ 0.00 4 Ϯ 1 23.9 Ϯ 7.4 155 Ϯ 44 16.9 Ϯ 4.4 668 Ϯ 395 5332Ϯ 6 1.00 Ϯ 0.87 8 Ϯ 5 34.4 Ϯ 4.1 293 Ϯ 152 20.4 Ϯ 10.0 1086 Ϯ 830 10 3 64 Ϯ 16 0.33 Ϯ 0.14 12 Ϯ 6 22.0 Ϯ 5.3 590 Ϯ 363 22.7 Ϯ 15.0 855 Ϯ 799 20 3 185 Ϯ 119 1.50 Ϯ 2.17 26 Ϯ 11 17.4 Ϯ 3.3 1153 Ϯ 545 20.0 Ϯ 8.7 505 Ϯ 196 30 3 310 Ϯ 63 0.50 Ϯ 0.00 25 Ϯ 2 18.0 Ϯ 4.5 1604 Ϯ 344 19.3 Ϯ 3.9 531 Ϯ 222 45 5 550 Ϯ 309 0.75 Ϯ 0.43 48 Ϯ 29 21.1 Ϯ 3.8 2614 Ϯ 1235 25.4 Ϯ 23.0 754 Ϯ 638 60 6 530 Ϯ 167 0.88 Ϯ 0.61 38 Ϯ 19 15.1 Ϯ 3.2 2654 Ϯ 919 26.5 Ϯ 14.1 587 Ϯ 307 75 6 916 Ϯ 710 1.17 Ϯ 0.52 63 Ϯ 45 19.6 Ϯ 4.7 4256 Ϯ 3056 32.3 Ϯ 32.1 990 Ϯ 1116 95 3 1562 Ϯ 893 1.00 Ϯ 0.50 69 Ϯ 26 19.8 Ϯ 13.3 5868 Ϯ 1974 17.8 Ϯ 7.1 639 Ϯ 475 B. iET parameter estimates

AUC0–24 ⅐ Dose (mg) N Cmax (pg/ml) Tmax (h) Cmin (pg/ml) (pg h/ml) Day 1 2.5 3 4.77 Ϯ 0.14 14.7 Ϯ 8.3 3.24 Ϯ 0.79 100 Ϯ 14 5 3 5.52 Ϯ 2.02 18.7 Ϯ 9.2 3.65 Ϯ 0.71 108 Ϯ 27 10 3 4.64 Ϯ 1.75 4.0 Ϯ 6.9 3.24 Ϯ 0.98 97 Ϯ 36 20 3 6.38 Ϯ 1.35 18.7 Ϯ 9.2 4.40 Ϯ 0.78 127 Ϯ 27 30 3 4.20 Ϯ 1.10 8.3 Ϯ 6.4 2.90 Ϯ 0.66 89 Ϯ 21 45 7 6.90 Ϯ 2.29 15.7 Ϯ 11.0 3.28 Ϯ 1.35 127 Ϯ 46 60 7 5.05 Ϯ 1.19 6.3 Ϯ 8.5 2.91 Ϯ 0.59 90 Ϯ 21 75 6 5.57 Ϯ 2.15 6.0 Ϯ 9.3 2.85 Ϯ 1.06 109 Ϯ 42 95 4 6.43 Ϯ 1.91 3.8 Ϯ 5.5 3.06 Ϯ 0.49 108 Ϯ 25 Day 28 2.5 3 7.20 Ϯ 0.89 16.3 Ϯ 13.3 4.81 Ϯ 0.71 146 Ϯ 15 5 3 7.01 Ϯ 1.69 16.0 Ϯ 13.9 4.65 Ϯ 1.32 141 Ϯ 38 10 3 6.12 Ϯ 0.85 9.3 Ϯ 2.3 3.93 Ϯ 1.45 122 Ϯ 28 20 3 8.56 Ϯ 1.95 9.3 Ϯ 12.9 5.99 Ϯ 0.95 177 Ϯ 35 30 3 7.32 Ϯ 1.69 3.0 Ϯ 4.4 4.50 Ϯ 0.99 131 Ϯ 30 45 5 9.92 Ϯ 4.24 2.4 Ϯ 3.1 5.34 Ϯ 1.72 167 Ϯ 58 60 6 9.41 Ϯ 0.93 1.0 Ϯ 0.0 4.82 Ϯ 1.34 145 Ϯ 27 75 6 11.47 Ϯ 6.58 1.0 Ϯ 0.0 5.05 Ϯ 1.91 152 Ϯ 64 95 3 12.79 Ϯ 4.55 0.7 Ϯ 0.6 4.41 Ϯ 0.54 150 Ϯ 23 a Ϯ t1/2 is reported as harmonic mean pseudo-SD. On day 1, AUC was reported as AUCϱ and on day 28 it was reported as AUC0–24. b N, number of samples evaluated; Cmax, maximum observed plasma concentration; Tmax, time to maximum observed plasma concentration; Cmin, minimum observed plasma concentration; t1/2, terminal elimination half-life; NA, not applicable.

ϭ day1(P 0.21). iET Cmax increased somewhat with increasing defined MTD was not achieved in the study, and none of the dose on day 28 (P Ͻ 0.01), but not on day 1 (P ϭ 0.25). iET adverse effects was dose-limiting. The most frequently reported Յ Tmax decreased with increasing dose on both days 1 and 28 (P adverse effects of headache, rhinitis, and peripheral edema were 0.03). Body weight was not a statistically significant covariate attributable to the vasoactive pharmacology of this class of in the analysis of any iET parameter (P Ͼ 0.14). The iET results compound. These effects were mild to moderate in intensity, from this study were generally similar to those reported previ- reversible, and, when necessary, readily controlled with symp- ously for atrasentan doses of 10 to 75 mg once daily adminis- tomatic treatment. tered to adults with refractory adenocarcinoma (27). Most cases of headache and peripheral edema occurred in patients taking doses of 60 mg of atrasentan or higher. In DISCUSSION another Phase I study of atrasentan in oncology patients, head- Atrasentan was well tolerated in patients with refractory aches of moderate intensity occurred at the 75-mg dose; whereas adenocarcinomas at doses of up to 95 mg/day. The protocol- they were not considered dose-limiting events, they were of

Fig. 3 Mean iET plasma concentrations after a single dose of atrasen- Fig. 1 Mean plasma concentrations of atrasentan after a single dose on tan on day 1. day 1.

Fig. 2 Mean plasma concentrations of atrasentan on day 28 after Fig. 4 Mean iET plasma concentrations on day 28 after once-daily once-daily dosing from day 3 to day 28. atrasentan dosing from day 3 to day 28.

sufficient severity and duration to halt dose escalation at 75 mg aches, rhinitis, hemodilution effect, peripheral edema, and blood (27). Headaches were the DLT in healthy subjects receiving pressure changes seen in our patients. In two recent studies of atrasentan; healthy male volunteers were unable to tolerate nonselective ET antagonists in patients with heart failure, high headaches that occurred at the 40-mg dose (26, 28). In healthy doses of these agents sometimes exacerbated cardiac symptoms volunteers, the headaches were typically migrainous and were when administered without an appropriate dose titration sched- severe enough to necessitate bed rest and cause photophobia, ule (31, 32). Until more data are available on the administration nausea, and vomiting. Headaches of this severity were not of ET antagonists in patients with underlying cardiovascular observed in this study. Headaches have also been reported with conditions, these agents should be used with the same caution administration of other ET antagonists (29, 30). Changes in observed for calcium channel blockers in patients with a history laboratory values were consistent with a mild, self-limited he- of heart failure. modilution effect of atrasentan associated with increased body Pharmacokinetic parameters in oncology patients in this weight, a phenomenon that has also been noted in healthy study were linear, dose-proportional, and independent of time volunteers (28). No differences in atrasentan PK were found over the range of 2.5–95 mg/day. Steady-state plasma concen- between healthy volunteers and oncology patients to explain the trations consistent with biological activity in preclinical models

contrast in tolerability. were achieved; for example, the mean unbound Cmin for the The observed effects of atrasentan are consistent with the 10-mg regimen (accounting for 98.8% binding to plasma pro-

pharmacological activity of ETA receptor antagonists. The va- teins) was approximately 8-fold greater than the Ki for the ETA sodilatory activity of atrasentan could have caused the head- receptor (23). For this reason, dosing above 95 mg/day appeared

to be unwarranted, especially because the severity of the of production and isometric tension studies. J. Urol., 150: 495–499, headaches seemed to increase at the higher doses. Across 1993. atrasentan dose groups, plasma iET concentrations increased 13. Casey, M. L., Byrd, W., and MacDonald, P. C. Massive amounts of modestly (about 40%) during dosing. Whether the increases immunoreactive endothelin in human seminal fluid. J. Clin. Endocrinol. in iET concentrations over baseline were due to ligand dis- Metab., 74: 223–225, 1992. placement or antagonism of an inhibitory feedback pathway 14. Nelson, J. B., Hedican, S. P., George, D. J., Reddi, A. H., Pianta- dosi, S., Eisenberger, M. A., and Simons, J. W. Identification of endo- is not known. thelin-1 in the pathophysiology of metastatic adenocarcinoma of the ET-1, a peptide expressed by neoplastic cells and acting via prostate. Nat. Med., 1: 944–949, 1995. the ETA receptor, has been identified in prostate and other 15. Nelson, J. B., and Carducci, M. A. The role of the endothelin axis cancers (33). Atrasentan, a selective ETA receptor antagonist, in prostate cancer. Prostate J., 1: 126–130, 1999. has the potential to attenuate the progression and morbidity of 16. Le Brun, G., Aubin, P., Soliman, H., Ropiquet, F., Villette, J. M., numerous neoplastic diseases through its action on the ET Berthon, P., Creminon, C., Cussenot, O., and Fiet, J. Upregulation of system. With generally mild to moderate side effects for doses endothelin 1 and its precursor by IL-1-␤, TNF-␣, and TGF-␤ in the PC3 of up to 95 mg/day, predictable PK, and the advantage of human prostate cancer cell line. Cytokine, 11: 157–162, 1999. once-daily oral dosing, atrasentan is a targeted cytostatic agent 17. Gohji, K., Kitazawa, S., Tamada, H., Katsuoka, Y., and Nakajima, with significant therapeutic potential in patients with prostate M. Expression of endothelin receptor A associated with prostate cancer and other cancers. progression. J. 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