Provenge (Sipuleucel-T) - Description and Clinical Pharmacology

DESCRIPTION

PROVENGE consists of autologous peripheral blood mononuclear cells, including antigen presenting cells (APCs), that have been activated during a defined culture period with a recombinant human protein, PAP-GM-CSF, consisting of prostatic acid phosphatase (PAP), an antigen expressed in prostate cancer tissue, linked to granulocyte-macrophage colony-stimulating factor (GM-CSF), an immune cell activator. The patient's peripheral blood mononuclear cells are obtained via a standard leukapheresis procedure approximately 3 days prior to the infusion date. Due to the autologous nature of PROVENGE, it is important that the patient and physician adhere to the personalized leukapheresis and infusion schedules.

The active components of PROVENGE are autologous APCs and PAP-GM-CSF. During culture, the recombinant antigen can bind to and be processed by APCs into smaller protein fragments. The recombinant antigen is designed to target APCs, and may help direct the immune response to PAP. Minimal residual levels of the intact PAP-GM-CSF are detectable in the final PROVENGE product.

The cellular composition of PROVENGE is dependent on the composition of cells obtained from the patient's leukapheresis. In addition to APCs, the final product contains T cells, B cells, natural killer (NK) cells, and other cells. The number of cells present and the cellular composition of each PROVENGE dose will vary. Each dose of PROVENGE contains a minimum of 50 million autologous CD54⁺ cells activated with PAP-GM-CSF, suspended in 250 mL of Lactated Ringer's Injection, USP.

The potency of PROVENGE is in part determined by measuring the increased expression of the CD54 molecule, also known as ICAM-1, on the surface of APCs after culture with PAP-GM-CSF. CD54 is a cell surface molecule that plays a role in the immunologic interactions between APCs and T cells, and is considered a marker of immune cell activation.

CLINICAL PHARMACOLOGY

Mechanism of Action

PROVENGE is classified as an autologous cellular immunotherapy. While the precise mechanism of action is unknown, PROVENGE is designed to induce an immune response targeted against PAP, an antigen expressed in most prostate cancers. During ex vivo culture with PAP-GM-CSF, APCs take up and process the recombinant target antigen into small peptides that are then displayed on the APC surface.

In Study 1, 237 out of the 512 patients randomized were evaluated for the development of humoral and T cell immune responses (proliferative and gamma-interferon (γIFN) ELISPOT) to the target antigens at Baseline, and at Weeks 6, 14, and 26. Antibody (IgM and IgG) responses against PAP-GM-CSF and PAP antigen alone were observed through the follow-up period in the PROVENGE group. Neutralizing antibody responses to GM-CSF were transient. T cell proliferative and γIFN ELISPOT responses to PAP-GM-CSF fusion protein were observed in cells collected from peripheral blood of patients through the follow-up period in the PROVENGE treatment group but not in controls. In some patients a response to PAP antigen alone was observed. No conclusions could be made regarding the clinical significance of the observed immune responses.

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

No carcinogenicity or mutagenicity studies of PROVENGE in animals were conducted. No studies on the effects of PROVENGE on fertility have been conducted.

CLINICAL STUDIES

The effect of PROVENGE on patients with metastatic castrate resistant (hormone refractory) prostate cancer was studied in three similar randomized, double-blind, placebo-controlled, multicenter trials. Following randomization, patients from both treatment groups underwent a series of 3 leukapheresis procedures (at approximately Weeks 0, 2, and 4). Each leukapheresis was followed approximately 3 days later by infusion of PROVENGE or control. The control was autologous peripheral blood mononuclear cells that had not been activated [ see Description (11 )]. Following disease progression, patients were treated at the physician's discretion with other anti-cancer interventions.

Study 1

Study 1 was a randomized, double-blind, placebo-controlled, multicenter trial in patients with asymptomatic or minimally symptomatic metastatic castrate resistant (hormone refractory) prostate cancer. Eligible patients had metastatic disease in the soft tissue and/or bone with evidence of progression either at these sites or by serial Prostate Specific Antigen (PSA) measurements. Exclusion criteria included visceral (liver, lung, or brain) metastases, moderate to severe prostate cancer-related pain, and use of narcotics for cancer-related pain.

A total of 512 patients were randomized in a 2:1 ratio to receive PROVENGE (n=341) or control (n=171). The median age was 71, and 90% of the patients were Caucasian. Thirty-five percent of patients had undergone radical prostatectomy, 54% had received local radiotherapy, and 82% had received combined androgen blockade. All patients had baseline testosterone levels < 50 ng/mL. Forty-eight percent of patients were receiving bisphosphonates and 18% had received prior chemotherapy, including docetaxel. Eighty-two percent of patients had an ECOG performance status of 0; 58% had primary Gleason scores of four or more; 44% had bone and soft tissue disease; 48% had bone-only disease; 7% had soft tissue-only disease; and 43% had greater than ten bony metastases.

Supportive Studies

Study 2 was a randomized, double-blind, placebo-controlled, multicenter trial in patients with metastatic castrate resistant prostate cancer and no cancer-related pain. The primary endpoint was time to disease progression; analysis of the primary endpoint did not reach statistical significance. All patients were to be followed for survival; however, the survival analysis was not pre-specified. A third study, similar in design to Study 2, was terminated prior to completion of planned accrual.

Summary of Study Results

Figure 1 and Table 2 present overall survival results observed in two randomized, Phase 3 studies of PROVENGE in men with metastatic castrate resistant prostate cancer. The survival findings were consistent across multiple subgroups. Analyses of time to disease progression did not meet statistical significance in any Phase 3 study of PROVENGE.

Figure 1 Kaplan-Meier Overall Survival Curve for Study 1