Docetaxel-based therapy has been shown to prolong survival as first-line therapy for patients with hormone refractory prostate cancer (HRPC), and has become the standard of care. The beneficial effects of any therapy in HRPC may be diverse and include reduction in tumor bulk (when measurable), reduction in prostate-specific antigen PSA, reduction in symptoms (particularly pain), or stabilization of disease. Clear reductions in tumor bulk or PSA may provide objective evidence of a treatment effect, and stabilization of disease may be just as clinically meaningful in patients who are actively progressing prior to starting therapy. Pemetrexed has shown a broad array of activity in many diseases that until now were thought to be non-responsive to chemotherapy in the second-line setting.

This trial is designed to further assess the efficacy, safety, tolerability, and pharmacogenetics of pemetrexed as a single agent in subjects with HRPC whose disease has progressed following one prior taxane-based chemotherapy regimen for HRPC.

OUTLINE: This is a multi-center study.

• Pemetrexed 500mg/m2 will be administered intravenously over approximately 10-minutes on Day 1 of a 21-day cycle.
• Folic Acid (350-1000 mcg. PO daily) will be taken by patients to reduce toxicity. At least 5 daily doses of folic acid must be taken during the 7-day period preceding the first dose of pemetrexed, and dosing should continue during the full course of therapy and for 21 days after the last dose of pemetrexed.
• Vitamin B12 (1000 µg) will be administered as an intramuscular injection during the week preceding the first dose of pemetrexed and every 3 cycles thereafter. Subsequent vitamin B12 injections may be given the same day as pemetrexed.

Performance Status: Karnofsky Performance Status 70-100

Life expectancy > 12 weeks

Hematopoietic:

• Absolute Neutrophil Count (ANC) > 1500/mm3
• Platelet count > 100,000/mm3
• Hemoglobin > 9 g/dL

Hepatic:

• Bilirubin < 1.5 X upper limit of normal (unless due to Gilbert's disease)
• Alkaline phosphatase and Alanine Transanimase (ALT) (SGPT) < 3 X upper limit of normal (ULN); may be < 5 X ULN for patients with liver metastases. Alkaline phosphatase may be any value for patients with bone metastases.

Renal:

• Calculated creatinine clearance >45 mL/min based on the standard Cockroft and Gault formula

Cardiovascular:

• No congestive heart failure requiring therapy or New York Heart Association (NYHA) class II or greater or active angina or known myocardial infarction within 12 months prior to study
• No unstable angina, uncontrolled congestive heart failure, or unstable symptomatic arrhythmia requiring medication within 6 months prior to being registered for protocol therapy
• Subjects with chronic atrial arrhythmia, i.e., atrial fibrillation, paroxysmal supraventricular tachycardia, or controlled hypertension are eligible

Pulmonary:

• Not specified

Inclusion Criteria:

• Histologically documented adenocarcinoma of the prostate
• Clinically refractory or resistant to hormone therapy as assessed by progression following at least one hormonal therapy (orchiectomy or luteinizing hormone-releasing hormone (LHRH) agonist)
• One prior taxane based chemotherapy regimen for HRPC
• Documented progression of disease after one taxane based prior chemotherapy regimen for HRPC. Progression is defined as at least one of the following:
• An increase in PSA > 50% over nadir value on prior Taxane-based therapy
• Progression of measurable disease as defined by RECIST
• Progression of bone disease as defined by the appearance of one or more new bone lesions or worsening symptoms
• Orchiectomy or testosterone levels < 50 ng/dL maintained by LHRH agonist
• Prior chemotherapy, or other experimental anticancer agents must be completed > 4 weeks prior to being registered for protocol therapy
• Palliative radiotherapy must be completed at least 14 days prior to registration.

Exclusion Criteria:

• Intravenous radio-isotopes therapy must be completed at least 6 weeks prior to registration
• No brain metastasis that are untreated and/or not controlled and/or still requiring corticosteroids
• No history of other malignancies within 5 years prior to being registered for protocol therapy, except for adequately treated basal or squamous cell skin cancer
• No history of uncontrolled psychiatric illness or serious systemic disease, including active infection, uncontrolled hypertension
• No surgery or significant traumatic injury within 21 days prior to being registered for protocol therapy
• Patients must be willing to interrupt aspirin or other non-steroidal anti-inflammatory agents for a 5-day period (8 day period for long acting agents such as piroxicam)
• Patients must be willing to take folic acid or vitamin B12 supplementation