A novel agent, ABT-627, appears to delay the progression of cancer in patients with hormone-refractory prostate cancer and produces few side effects, according to results from preliminary clinical trials.

The prostate is a male sex gland located between the bladder and rectum. It is comprised of muscular and glandular tissue and is approximately the size of a chestnut. The prostate produces a secretion that liquefies coagulated semen. Prostate cancer is a common occurrence among older men and, when caught early, is considered curable with radiation and surgery. However, many patients experience a cancer recurrence following initial treatment. Standard therapy for prostate cancer may consist of watchful waiting, radiation therapy, chemotherapy, surgery, cryotherapy, and/or hormonal therapy alone or in combination. Once prostate cancer reaches an advanced stage, it often spreads to the patient’s bones, which causes debilitating pain and bone fractures. Typically, radiation therapy is used to treat the bone cancer, but is associated with significant side effects. When patients have reached this stage of disease, they have often exhausted most of their treatment options and are left with few choices.

Hormone therapy is a common treatment for prostate cancer that has recurred. Prostate cancer cells are stimulated to grow by male hormones, particularly testosterone. Hormone therapy is a type of therapy that either blocks male hormones from being produced in the body or blocks male hormones from entering cancer cells, thus inhibiting their growth. Once patients stop responding to hormone therapy, they are referred to as “hormone-refractory” and are left with few treatment options. Therefore, researchers continue to investigate new treatments for men with hormone-refractory prostate cancer.

ABT-627 is a novel agent still in clinical trials that appears to delay the spread of prostate cancer. ABT-627 works by blocking endothelin, a protein known for its vasoconstrictive properties. Endothelin is produced in excess amounts by prostate cancer cells and is speculated to act as a cellular growth enhancer and promoter of cancer spread to the bone. However, the exact mechanism by which endothelin contributes to the progression of prostate cancer is unknown.

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One clinical trial evaluating ABT-627 involved 244 patients with hormone-refractory prostate cancer whose disease was progressing. One group of patients received ABT-627 and the other group received a placebo (inactive substitute). Those taking ABT-627 had the progression of their disease delayed by nearly 70 days compared to those taking a placebo. In addition, the group of patients who received ABT-627 took twice as long for a rise in their prostate specific antigen (PSA) levels (a protein secreted by prostate cancer cells used as an indicator for cancer progression). Few patients experienced mild side effects.

A second clinical trial evaluated ABT-627 and its effects on cancer progression, specifically to the bone in hormone-refractory prostate cancer patients. During this trial, patients who received ABT-627 maintained stable levels of blood “markers”, which are used as an indicator of cancer spread to the bones. Conversely, patients receiving a placebo demonstrated a continued elevation in these markers, indicating a continual progression of cancer spread to the bones.

A third study involving ABT-627 evaluated the effects of this agent on a patient’s quality of life. Patients receiving ABT-627 reported a 30% improvement in quality of life issues over patients who received a placebo.

The results from these combined studies indicate that ABT-627 may help delay the progression of prostate cancer and improve quality of life for patients with hormone-refractory disease. Researchers report that ABT-627 may be used for patients who have no treatment options left or for patients who choose to receive less toxic therapies before resorting to chemotherapy or radiation and their associated side effects. Researchers are launching an important trial designed to evaluate the effectiveness of ABT-627 in slowing disease progression of hormone-refractory prostate cancer. Previous clinical trials have indicated the efficacy of ABT-627 in delaying the progression of hormone-refractory prostate cancer, which has led to the initiation of the final phase of clinical trials prior to FDA review. Patients with localized and metastatic (spread to distant sites in the body) hormone-refractory prostate cancer can learn more about the ongoing phase III trial evaluating ABT-627. Patients interested in participating in this trial can enroll at eCancerTrials.com.

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