DENVER – A series of three vaccine injections delivered over three months may benefit men with nonmetastatic recurrent prostate cancer after local therapy and men with androgen-independent prostate cancer with minimal burden of metastatic disease, according to preliminary data presented here at the 2009 American Association for Cancer Research 100th Annual Meeting.

Researchers at the University of Iowa are administering an adenovirus/PSA vaccine to men with biochemical recurrence and negative results on bone scans and abdominal and pelvic CT following surgery or radiation. The vaccine uses a replication-deficient adenovirus that has been transformed with the gene for human PSA. This vaccine product previously has been shown to induce strong anti-PSA immune responses in preclinical studies.

The investigators say the incorporation of Gelfoam, a collagen matrix, appears to enhance the ability of the vaccine to induce strong anti-PSA immune responses. Results from a prior phase 1 study showed this vaccine to be safe and to induce anti-PSA immune response in 68% of patients.

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At the time of the meeting, the current phase 2 trials had enrolled 10 patients. The researchers assigned four patients to protocol 1 and six to protocol 2. In protocol 1, which is randomized, half of the patients received three injections of the vaccine alone (arm A) and half of the patients received 14 days of a luteinizing hormone releasing hormone (LHRH) agonist and anti-androgen therapy, followed by three vaccine injections four weeks apart (arm B). All the patients in LHRH group had received androgen deprivation therapy for a minimum of six months. In protocol 2, patients receive three injections of the vaccine alone every four weeks.

Positive T cell responses developed in all four patients in protocol 1 and five of six patients in protocol 2. One patient in protocol 1 and three in protocol 2 had an increased PSA doubling time.

“We are, to my knowledge, the only ones conducting a trial with this vaccine product using adenovirus,” said investigator Daniel A. Vaena, MD, Clinical Assistant Professor of Medicine at the University of Iowa, in Iowa City. Noting that the vaccine uses a replication-deficient adenovirus, he related: “We didn’t expect to see much pathogenicity with it, and so far, that has been the case.”

He added: “So far, we have seen very minimal side effects. Most have been grade 1 or grade 2, with mild headaches or very few low-grade fevers. Otherwise, we are not seeing any significant side effects. This vaccine appears to be safe and promising, but we need more data. We are encouraged by these preliminary results.”

The protocols continue to accrue patients, he said, with a goal of enrolling 25 patients in each arm of protocol 1 and 32 in protocol 2.