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Urology. 2011 Sep;78(3):626-30. doi: 10.1016/j.urology.2011.04.041. Epub 2011 Jul 18.

Multicenter phase II trial of the heat shock protein 90 inhibitor, retaspimycin hydrochloride (IPI-504), in patients with castration-resistant prostate cancer.

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Mount Sinai School of Medicine, New York, New York 10029, USA.



To evaluate clinical activity and safety of retaspimycin hydrochloride (IPI-504) in patients with castration-resistant prostate cancer (CRPC).


A single-arm trial was conducted in 2 cohorts: group 1, chemotherapy naive; group 2, docetaxel-treated. IPI-504 was administered intravenously at 400 mg/m2 on days 1, 4, 8, and 11 of a 21-day cycle. Trial expansion was planned if ≥1 prostate-specific antigen (PSA) or radiographic response was noted per cohort. Pharmacokinetic samples were collected after the first dose; safety was assessed throughout.


A total of 19 patients were enrolled (4 in group 1; 15 in group 2), with a median age of 66 years (range 49-78). Group 2 had received a median of 2 previous chemotherapy regimens. All group 2 patients had bone metastases; 66% had measurable soft tissue or visceral metastases. One group 1 patient remained on-trial for 9 cycles; his PSA level declined 48% from baseline. No PSA response was observed in the other patients. Adverse events reported in >25% of the study population included nausea (47%), diarrhea (42%), fatigue (32%), anorexia (26%), and arthralgia (26%). Two patients in group 2 died on-trial, involving study drug-related events of hepatic failure and ketoacidosis, respectively.


Heat shock protein 90 inhibition with IPI-504 administered as a single agent had a minimal effect on the PSA level or tumor burden and was associated with unacceptable toxicity in several patients. Therefore, additional evaluation in CRPC patients is not warranted. IPI-504 is being investigated at less-intensive doses and schedules in other tumor types.

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