Inclusion Criteria:

1. Men > 18 years of age.

2. Histologically proven adenocarcinoma of the prostate.

3. Presence of radiographic bone metastasis with at least one which is amenable to
serial imaging using MRI/PET imaging.

4. Patients must have evidence of progressive disease by either radiographic progression
or a rising PSA within 4 weeks prior to registration.

5. Patients must have had prior treatment with bilateral orchiectomy or other primary
androgen-deprivation therapy.

6. For patients previously treated with flutamide (Eulexin), Nilutamide (Nilandron), or
bicalutamide (Casodex): Patients must have discontinued flutamide > 4 weeks prior to
registration with continued evidence of progressive disease. For bicalutamide or
nilutamide, patients must have discontinued the drug > 6 weeks prior to registration
with evidence of progressive disease.

7. Prior therapy is permitted as long as it was given > 4 weeks prior to registration,
and evidence for disease progression is met.

8. Patients must not have had prior radiotherapy < 4 weeks prior to registration.

9. Prior use of bisphosphonates allowed only if started at least 12 or more weeks prior
to registration (can continue current dose/schedule while on study).

10. Patient cannot have had prior Strontium 89, Samarium 153, or other radioisotope.

11. No concurrent use of estrogen, or estrogen-like agents

12. Patients must have adequate organ function

13. ECOG performance status 0-2.

Exclusion Criteria:

1. Use of potent CYP450 inducers (such as phenytoin, rifampicin, carbamazepine and
phenobarbitone, St. John's Wort) within 2 weeks prior to start of study treatment.

2. Prior therapy with endothelin receptor antagonists or family history of
hypersensitivity to endothelin antagonists.

3. History of past or current epilepsy, epilepsy syndrome, or other seizure disorder.

4. Stage II, III or IV cardiac failure (classified according to New York Heart
Association (NYHA) classification), myocardial infarction within 6 months prior to
study entry, or have left ventricular function (LVEF) below the institutional normal
limit.

5. QT interval corrected for heart rate (by Bazett's correction) (QTcB) >470 msec.

6. Previous history or presence of another cancer, other than prostate cancer or treated
squamous/basal cell carcinoma of the skin, within the last 5 years.

7. Major surgery within 6 weeks of registration.

8. Hemoglobin (Hb) <9 g/dL. Concomitant use of erythropoietin or blood transfusions is
allowed.

9. Inability to take or absorb oral medications.