A Phase 1b Dose Escalation Trial of PSK®/Placebo With Docetaxel to Treat Metastatic Castration-resistant Prostate Cancer

Inclusion Criteria: * Male patients 18 years or older * Histologically confirmed diagnosis of adenocarcinoma of the prostate * Evidence of metastatic disease by standard imaging studies (bone scan, Computerized Tomography Scan (CT) or Magnetic Resonance Imaging (MRI)) * Testosterone levels \<50 ng/dL * Confirmed progressive disease defined by one or more of the following: * an increase in PSA, \> 2ng/dL x 2 or more values at least 1 week apart in the setting of metastatic disease * appearance of new bone lesions on bone scan * progression of soft tissue lesion defined by the Response Evaluation Criteria In Solid Tumors \[RECIST\] 1.1 criteria * Concurrent use of an agent for testosterone suppression (e.g., Luteinizing Hormone Releasing Hormone \[LHRH\] agonist) if the patient is not surgically castrate * Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2 determined within 28 days before enrollment * Recovery to CTCAE grade ≤ 1 toxicity, to patient's baseline status (except alopecia), or toxicities deemed irreversible from the effects of prior cancer therapy (CTCAEs grade \> 1 that are not considered a safety risk by the investigator will be allowed) * Adequate bone marrow function defined as: * absolute neutrophil count (ANC) \> 1500 cells/mm³ without growth factor support * platelet count \> 100,000 cells/mm³ without transfusion or growth factor support * hemoglobin \> 9g/dL without transfusion or growth factor support * Adequate liver function defined as: * total bilirubin \< upper limit of normal (ULN) * alanine aminotransferase (ALT) \< 1.5 x ULN * aspartate aminotransferase (AST) \< 1.5 x ULN * Adequate renal function defined as serum creatinine level within normal limits (WNL) * At least a 6-month or greater life expectancy * Ability to understand and sign a written informed consent, which will be obtained from study participants before undergoing any study-specific procedures * Willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other trial procedures * Suitable venous access for the study-required blood sampling (i.e., including PK sampling) Exclusion Criteria: * Prior treatment with antineoplastic chemotherapy or radioisotopes for metastatic disease * Prior adjuvant or neo-adjuvant chemotherapy within 12 months of study entry * Last dose of sipuleucel-T therapy within 4 weeks of enrollment * Any investigational therapies within 4 weeks of study entry * Radiotherapy within 4 weeks of study entry * Major surgery within 4 weeks of study entry, and not fully recovered to baseline or a stable clinical status * Uncontrolled high blood pressure (systolic blood pressure \> 160mmHg, diastolic blood pressure \> 95mmHg) * Receiving chronic steroid therapy. Topical and inhaled steroids are permitted * Known severe hypersensitivity reactions to docetaxel or other drugs formulated in polysorbate 80, or to mushroom products * Any comorbid condition or unresolved toxicity that would preclude administration of docetaxel * Medical contraindication to any docetaxel pre-medications * History of \> grade 2 neurotoxicity or any toxicity from any cause that has not resolved to \< grade 1 * Brain or other CNS metastasis * The need for chronic daily immunosuppressive therapy, including concurrent use of prednisone * Evidence of active second malignancy, except non-melanoma skin cancer * Infection requiring intravenous antibiotic therapy or other severe infection within 14 days preceding first dose of study drug * Inability to swallow oral medication or maintain a fast, as required 2 hours before and 1 hour after PSK administration * Uncontrolled pain at baseline, impending complication from bone metastasis and/or presence of urinary obstruction * Other medical or psychiatric condition that may increase the risk associated with trial participation or any other condition in the judgment of the investigator that may interfere with the interpretation of trial results or would make the patient inappropriate for enrollment in this trial