**2.1 The sipuleucel-T (PROVENGE®) approach**

The history of this new treatment option began with phase I and phase II clinical trials in the academic field back in the 1990th. In the early 2000th the first phase III accrual of patients started and first data published in 2006 and FDA approval was asked for. But the FDA concluded that further confirmation would be obligatory prior to approval. This judgment sparked protests from patients and advocates who urged the FDA to repeal its decision. In 2009 preliminary results of that phase III pivotal trial, named Imunotherapy for Prostate

2. Immunisation against specified antigen(s)

used: "peptide cocktail" diff. epitopes from prostate

2.4.2 Single peptide used: e.g. HER2/neu epitope

Ref. (e.g.)

(Feyerabend et al.,

(Perez et al., 2010)

2009)

Ref. (e.g.)

2.4.1 Multiple peptides

stem cell antigen; TAA = tumor associated antigen; VV = Vaccinia virus

adaptive immune response and breaking peripheral tolerance.

**2.1 The sipuleucel-T (PROVENGE®) approach** 

2.4 Peptide based

TAAs

(776-790)

Table 1. Systematic list of vaccine-delivering systems in PCa vaccine approaches

in mCRPC patients (Antonarakis & Drake, 2010; Antonarakis & Eisenberger, 2011).

AdV = Adenovirus; DCs = dendritic cells; diff. = different; FV = Fowl pox virus; mRNA = messenger RNA; PAP = prostatic acid phosphatase; PSMA = prostate-specific membrane antigen; PSCA = prostate

Novel therapeutic options for patients of this stage of disease have been stated as an urgent medical need. Thus besides vaccine therapies a number of agents (e. g. endothelin receptor antagonists, receptor activator of nuclear factor κB ligand inhibitors, anti-angiogenic drugs, cytochrome P17 enzyme inhibitors, vitamin D analogues) are now tested in phase III registration trials either alone or in combination with docetaxel for first- or second-line use

Clinical trails that have engrossed most interest include i) Dendritic Cell (DC)-based vaccines (with clinically meaningful outcome for sipuleucel-T), ii) DNA vaccines (e.g. viral vector-based Prostvac-VF) together with recombinant peptide vaccines, and iii) whole-

Since cancer in fact develops and evolves in the presence of an intact immune system TAAs are by definition inadequately immunogenic. This results in a suboptimal T-cell activation, induction of immune tolerance and thus an ineffective immune reaction. Cancer vaccines are intended to break this immune tolerance. Strong presentation of antigen by antigenpresenting cells (APCs) is essential. Dendritic cells (DCs), which are the most powerful APCs, are known to be deficient in number and function in cancer patients. Activating APCs that are able to appropriately process and present the TAA is pivotal to activating an

The history of this new treatment option began with phase I and phase II clinical trials in the academic field back in the 1990th. In the early 2000th the first phase III accrual of patients started and first data published in 2006 and FDA approval was asked for. But the FDA concluded that further confirmation would be obligatory prior to approval. This judgment sparked protests from patients and advocates who urged the FDA to repeal its decision. In 2009 preliminary results of that phase III pivotal trial, named Imunotherapy for Prostate

1. Immunisation against multiple (not specified) antigens

tumor cell vaccines (e.g. GVAX).

**2. DC-based vaccines** 

Adenocarcinoma Treatment (IMPACT) study, were presented to the community at an AUA national conference and to the FDA (Schellhammer et al., 2009). After re-analysis of these facts the FDA finally permitted sipuleucel-T end of April 2010, so it is worth to have a closer look into the prescription information (FDA, 2010a) and the approval letter (FDA, 2010b) as this product is not just another in a row of existing PCa vaccines but – as the first active immune therapy granted with approval for use in human subjects – opens an entire new entity for curative intervention. Finally in July 2010 the IMPACT trial data were presented in a peer reviewed journal (Kanthoff et al., 2010b) and as a result the prostate panel of the National Comprehensive Cancer Network (NCCN) has changed its guidelines how to treat mCRPC patients by adding sipuleucel-T as a category 1 treatment recommendation (NCCN, 2010).

Sipuleucel-T is an antigen specific cellular immunotherapy based on autologoues DCs (see Tab. 1) and indicated in metastatic but asymptomatic or minimally symptomatic patients who are in a hormone refractory and disease progressive stage. Sipuleucel-T consists of APCs and other cells of the peripheral blood mononuclear cells (PBMC) compartment, that have been activated during a defined ex vivo period with a recombinant human fusion protein combining PAP and GM-CSF. To obtain patient's PBMCs a standard leukapheresis procedure approximately 72 hours prior to the infusion date has to be performed. During ex vivo culture period the PAP protein can bind to and be processed by APCs into smaller TAA fragments, so the recombinant antigen should target the DCs, and is thought to direct the immune response to PAP (Kanthoff et al., 2010a).

Due to the autologoues nature of sipuleucel-T and the individuality of this approach its final cellular composition (T-, B-, NK-, and other cells) depends on the cells obtained from the patient's leukapheresis and will vary from patient to patient and from dose to dose, but the ex vivo procedure is regulated in that a minimum of 50 million PAP-GM-CSF activated CD54+ cells are included, suspended in 250 mL of Lactated Ringer's solution, and reinfused intravenously to the patient (FDA, 2010a; Kanthoff et al., 2010a).

The IMPACT trial was randomized, placebo-controlled, double-blind, multicentered. A total of 512 patients were randomized (2:1 ratio) to receive sipuleucel-T (n = 341) or control (n = 171). The placebo material used in control subjects was peripheral blood mononuclear cells that had not been PAP-activated, but given back to the patients under equal clinical conditions. In case of disease progression control subjects were allowed to cross over to an open-label use of the vaccine. The effectiveness of sipuleucel-T showed an increase in OS of 4.1 months in the pivotal phase III trial (25.8 vs 21.7 months) and OS benefit (3-year OS of 31.7 % vs 23.0 %). Sipuleucel-T successfully reached the prespecified level of statistical significance and reduced the overall risk of death by 22 % compared to control (p < 0.05) (Kanthoff et al., 2010b). Analyses of time to disease progression did not differ between verum and placebo patients and thus not meet statistical significance.

As sipuleucel-T is intended and produced solely for personalized use in a central laboratory there is no routine testing for transmissible infectious diseases so general precautions for handling blood products has to be employed. Due to the expiration time being as short as 18 h the product safety testing is challenging and sipuleucel-T has to be released for use based on the sterility and microbial results from a number of tests. If the sterility results show positive for microbial contamination after the use of sipuleucel-T, the manufacturer will inform the treating doctor. As, due to the character of the product, no cell filter can be used during the i.v. re-infusion of the ex vivo stimulated blood compounds, acute infusion reactions are the most common solely adverse event (AE) in patients receiving sipuleucel-T but also in control

Entering a New Era – Prostate Cancer

disease (Fioretti et al., 2010).

**3.1 Prostvac-VF approach** 

Immuno-Therapy After the FDA Approval for Sipuleucel-T 299

PSCA and PSA) rather than tumor-specific antigens. The major advantages of DNA vaccines is, at least compared with DC-based vaccines, that they are easy and inexpensive to produce and that with some viral vectors used in this attempt there is a huge body of experience as they have been used in millions of persons for preventive vaccinations against infective

This approach has been tested clinically in a number of phase I studies demonstrating safety of the vectors (Sanda et al., 1999; DiPaola et al., 2006; Arlen et al., 2007), and three phase II studies. Prostvac-VF consists of two genetically engineered viruses (recombinant Vaccinia (V) virus and Fowl pox (F) virus) administered in a sequential regimen. The virus strain used in Prostvac-V is a to some extent attenuated version of the virus used for smallpox immunization. Fowl pox viruses are unable to replicate in human cells but have been shown to be an effective way of boosting cellular immune responses primarily initiated using Vaccinia virus. The viral vectors are engineered to contain a gene encoding human PSA which contains an alteration in the HLA-A2 specific epitope that is planned to enhance the immunogenicity of the expressed antigen. In addition, these viruses both contain the genes encoding three co-stimulatory molecules, B7.1, ICAM-1 and LFA-3 (together named TRICOM). The academic work to establish this vaccine platform was done in cooperation with industrial sponsorship initially with Therion Biologics Cambridge, MA and subsequently with BN ImmunoTherapeutics, Garcia Ave, CA (Madan et al., 2009). The first phase II trial conducted by the Eastern Cooperative Oncology group enrolled 64 eligible patients and assigned them randomly to receive i) four vaccinations with fowl pox-PSA (rF-PSA), ii) three rF-PSA vaccines followed by one vaccinia-PSA (rV-PSA) vaccine, or iii) one rV-PSA vaccine followed by three rF-PSA vaccines. In this trial the TRICOM-component was not included. The prime/boost schedule was well tolerated with a small amount of adverse events. Of the eligible patients, 45.3% of men remained free of PSA progression at 19.1 months and 78.1 % demonstrated clinical progression free survival. There was a trend favouring the

treatment group that received a priming dose of rV-PSA (Kaufman et al., 2004).

So in further trials using this approach rV-PSA priming was always followed by rF-PSA boostering. In the second phase II trial (n = 125 patients) it could be shown that at 3 years post study analysis, Prostvac-VF patients (n = 82) had a better OS with 25 (30 %) of 82 alive versus 7 (17 %) of 40 controls, longer median survival by 8.5 months (25.1 vs 16.6 months for controls), an estimated hazard ratio of 0.56 (95% CI, 0.37-0.85), and stratified log-rank p < 0.01. There was a minor imbalance in favour of the Prostvac-VF arm in mean and median of some laboratory values. But integration of these factors plus performance status in the Halabi nomogram revealed a 1-month mean and 2-month median difference in predicted survival (mean and median of 20.4 months for controls vs mean of 21.4 months and median of 22.5 months for Prostvac-VF). The observed survival difference of 8.5 months far exceeds that predicted by the Halabi nomogram. So these data are – despite of OS being not the primary end point – considered clinically meaningful and strongly suggests that Prostvac-VF immunotherapy may produce an OS benefit, but still regarded as hypothesis generating data as the authors state in the discussion of there recently published work (Kantoff et al., 2010b). The National Cancer Institute (NCI) has also recently completed a third phase II study in 32 PCa bearing men in whom immune and regulatory T-cell responses were

subjects receiving the non-activated peripheral blood mononuclear cells. Such events included, but were not limited to, vomiting, fatigue, fever, chills, respiratory events (dyspnea, hypoxia, and bronchospasm), nausea, hypertension, and tachycardia. To minimize potential acute infusion reactions e.g. chills and/or fever, it is recommended to premedicate patients orally with an antihistamine prior to infusion of sipuleucel-T (Kanthoff et al., 2010b).

The safety evaluation of sipuleucel-T, released by the FDA, is based on 601 PCa patients who received at least one dose of sipuleucel-T reported in four different clinical trials (Small et al., 2006; Harzstark et al., 2009; Higano et al., 2009a; Kanthoff et al., 2010a). Almost all (98.3 %) indivduals in the sipuleucel-T group and 96.0 % in the control group reported an adverse event. In 67.4 % of patients in the sipuleucel-T group, these adverse events were mild or moderate. Severe (grade 3) and life-threatening (grade 4) adverse events were reported in 23.6 % and 4.0 % of patients in the sipuleucel-T group compared with 25.1 % and 3.3 % of control group patients. Fatal (grade 5) adverse events were reported in 3.3 % of patients in the sipuleucel-T group compared with 3.6 % of patients in the control group. The FDA recommended the manufacturer to run a post-marketing study to assess the risk of cerebrovascular events in 1,500 PCa patients who receive sipuleucel-T and awaits completion of this study till December 31, 2015 (FDA, 2010b).

Each dose of sipuleucel-T requires a leukapheresis approximately three days prior to the infusion. AE´s that were reported within one day following the leukapheresis procedure included citrate toxicity (14.2 %), oral paresthesia (12.6 %), general paresthesia (11.4 %), and fatigue (8.3 %) (FDA, 2010a).

Due to its novelty in the market as if the pricey production process and due to the high research and development costs sipuleucel-T as a pharmaceutical product is quite expensive – more than 90.000 USD. So there is a discussion whether or not these costs should be covered by the public. In comparison to other recently introduced drugs in other tumor entities (e.g. lung cancer or breast cancer) and based on the calculation of the achievable duration in life time the costs of sipuleucel-T has been calculate as about 10 times higher (Longo, 2010).
