Inclusion Criteria:

- Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2

- Life expectancy of at least 12 weeks

- Histologic documentation of adenocarcinoma of the prostate

- Surgical castration or ongoing use of gonadotropin-releasing hormone agonists with
confirmed castrate levels of testosterone

- Metastatic progressive CRPC defined as progressive disease despite surgical
castration or ongoing use of gonadotropin-releasing hormone agonists with confirmed
castrate levels of testosterone

- For patients in the dose-expansion cohort of the study, not more than two prior lines
of cytotoxic chemotherapy in the metastatic setting

- Evaluable or measurable disease

- Documented willingness to use an effective means of contraception

Exclusion Criteria:

- Anti-tumor therapy, including chemotherapy, biologic, experimental, or hormonal
therapy, or radiotherapy within 4 weeks prior to Day 1, with the following
exceptions: maintenance hormonal therapy for metastatic prostate cancer and
palliative radiation to bone metastases within 2 weeks prior to Day 1

- Major surgical procedure within 4 weeks prior to Day 1

- Known active bacterial, viral, fungal, mycobacterial, or other infection (including
HIV and atypical mycobacterial disease, but excluding fungal infections of the nail
beds)

- Ongoing corticosteroid use with > 10 mg of daily prednisone or equivalent

- Symptomatic hypercalcemia requiring continued use of bisphosphonate therapy. Patients
who are receiving bisphosphonate therapy specifically to prevent skeletal events and
who do not have a history of clinically significant hypercalcemia are eligible.

- History of severe allergic or anaphylactic reactions to monoclonal antibody therapy
(or recombinant antibody-related fusion proteins)

- Clinically significant history of liver disease, including viral or other hepatitis,
current alcohol abuse, or cirrhosis

- Untreated or active central nervous system (CNS) metastases. Patients with a history
of treated CNS metastases are eligible, provided that they meet all of the following
criteria: evaluable or measurable disease outside the CNS, radiographic demonstration
of improvement upon the completion of CNS-directed therapy and no evidence of interim
progression between the completion of CNS-directed therapy and the screening
radiographic study, and screening CNS radiographic study is >/= 8 weeks since
completion of radiotherapy and >/= 4 weeks since the discontinuation of
corticosteroids and anticonvulsants