Inclusion Criteria:

- histologically-confirmed adenocarcinoma of the prostate

- radiographic evidence of metastatic prostate cancer (stage M1 or D2)

- has prostate cancer unresponsive or refractory to medical or surgical castration with
a serum testosterone level of < 50 ng/mL

- has had disease progression or intolerance on docetaxel-based therapy

- PSA ≥ 10 ng/mL

- all clinically significant toxic effects of prior surgery, radiotherapy, chemotherapy
or hormonal therapy have resolved to ≤ Grade 1, based on NCI CTCAE v 4.02

- patient has an ECOG Performance Status 0-2

- adequate hematologic function

- adequate hepatic function

- adequate renal function

- urinary protein is ≤ 1 on dipstick or routine analysis

- life expectancy of more than 3 months

- fertile man with partners that are women of childbearing potential must use an
adequate method of contraception during the study

- signed Informed Consent document

Exclusion Criteria:

- concurrent active malignancy other than adequately treated nonmelanomatous skin
cancer or other noninvasive or in situ neoplasms

- The patient has received more than 1 prior cytotoxic chemotherapy regimen for
metastatic disease

- prior therapy with mitoxantrone for advanced prostate cancer

- The patient has a history of symptomatic congestive heart failure or has a pre study
echocardiogram or multigated acquisition scan with left ventricular ejection fraction
that is ≥ 10% below the lower limit of normal institutional range

- history of prior treatment with other agents that directly inhibit PDGF or
platelet-derived growth factor receptors

- known allergy to any of the treatment components: IMC 3G3, mitoxantrone, and/or
prednisone

- radiotherapy within 21 days prior to first dose of IMC-3G3

- any investigational therapy within 30 days of randomization

- is receiving corticosteroids at a dose > 5 mg prednisone orally (PO) 2 times per day
(BID) or equivalent

- received prior strontium-89, rhenium-186, rhenium-188, or samarium-153
radionucleotide therapy and has either ongoing evidence of bone marrow dysfunction or
poorly controlled bone pain

- has any ongoing or active infection, symptomatic congestive heart failure, unstable
angina pectoris, serious cardiac arrhythmia, psychiatric illness, active bleeding or
pathological condition that carries a high risk of bleeding, or any other serious
uncontrolled medical disorders

- known or suspected brain or leptomeningeal metastases

- known human immunodeficiency virus infection or acquired immunodeficiency
syndrome-related illness