Retaspimycin

Retaspimycin is a water-soluble hydroquinone hydrochloride salt inhibitor of Hsp90 [1].

Hsp90 is a member of the Hsp family. The other members of this protein family are Hsp40, Hsp70 and so on. These proteins act as molecule chaperons and participate in many cellular processes. When cells are exposed in stress, some proteins become unstable, accumulate to form aggregates and subsequently cause cell apoptosis. In this situation, Hsps will help their client proteins folding correctly, accompany them to be translocated to the correct location and thus prevent the cells from apoptosis. Hsps are required for cancer cells development. They are found to overexpress in a variety of cancer cells. Therefore, the inhibitors of Hsp are thought to be attractive therapy for cancer treatment. As an inhibitor of Hsp90, retaspimycin works through binding to the ATP-binding pocket of Hsp90 N-terminal [1].

In both RPMI-8826 and MM1.S cells, treatment of retaspimycin resulted in degradation of the Hsp90 client proteins, for instance, c-RAF and Her2. It also caused increased levels of Hsp70. Besides that, retaspimycin is found to prevent RPMI-8826 cells from secreting the immunoglobulin light chain. In breast cancer cells which are resistant to trastuzumab, treatment of retaspimycin potently caused Her2 degradation and resulted in tumor growth suppression and cell apoptosis [1].

Retaspimycin is often used as combination therapy with other drugs in cancer treatment. In mice bearing GIST-882 (gastrointestinal stromal tumor) xenografts, the administration of retaspimycin associated with imatinib showed a significant effect with a 66% tumor regression. In mice bearing GIST-PSW xenografts, both the combination treatment of retaspimycin and imatinib or sunitinib showed effective antitumor activities in reducing tumor burden. When used alone, retaspimycin reduced tumor volumes by 84% and 69% in GIST-PSW and GIST-882 mice models, respectively. Moreover, retaspimycin is found to decrease the mitotic activity in these two models. However, the antimitotic effects of retaspimycin were less significant than of imatinib or sunitinib or the combination treatment [2].

References:
[1].  Hanson B E, Vesole D H. Retaspimycin hydrochloride (IPI-504): a novel heat shock protein inhibitor as an anticancer agent. 2009.
[2].  Floris G, Debiec-Rychter M, Wozniak A, et al. The heat shock protein 90 inhibitor IPI-504 induces KIT degradation, tumor shrinkage, and cell proliferation arrest in xenograft models of gastrointestinal stromal tumors. Molecular cancer therapeutics, 2011, 10(10): 1897-1908.

Multicenter phase II trial of the heat shock protein 90 inhibitor, retaspimycin hydrochloride (IPI-504), in patients with castration-resistant prostate cancer.[Pubmed:21762967]

Urology. 2011 Sep;78(3):626-30.

OBJECTIVE: To evaluate clinical activity and safety of Retaspimycin hydrochloride (IPI-504) in patients with castration-resistant prostate cancer (CRPC). METHODS: 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. RESULTS: 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. CONCLUSION: 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.

A phase 1 study of IPI-504 (retaspimycin hydrochloride) in patients with relapsed or relapsed and refractory multiple myeloma.[Pubmed:21851215]

Leuk Lymphoma. 2011 Dec;52(12):2308-15.

Abstract A phase 1 study of IPI-504 (Retaspimycin hydrochloride) administered intravenously twice weekly for 2 weeks at 22.5, 45, 90, 150, 225, 300 or 400 mg/m(2) followed by 10 days off-treatment was conducted to determine the safety and maximum tolerated dose (MTD) of IPI-504 in patients with relapsed or relapsed/refractory multiple myeloma (MM). Anti-tumor activity and pharmacokinetics were also evaluated. Eighteen patients (mean age 60.5 years; median 9 prior therapies) were enrolled. No dose-limiting toxicities (DLTs) were reported for IPI-504 doses up to 400 mg/m(2). The most common treatment-related adverse event was grade 1 infusion site pain (four patients). All other treatment-related events were assessed as grade 1 or 2 in severity. The area under the curve (AUC) increased with increasing dose, and the mean half-life was approximately 2-4 h for IPI-504 and its metabolites. Four patients had stable disease, demonstrating modest single-agent activity in relapsed or relapsed/refractory MM.

A multicenter trial evaluating retaspimycin HCL (IPI-504) plus trastuzumab in patients with advanced or metastatic HER2-positive breast cancer.[Pubmed:23580070]

Breast Cancer Res Treat. 2013 May;139(1):107-13.

Heat shock protein 90 (Hsp90) facilitates maturation and stability of HER2. Combining an Hsp90 inhibitor and trastuzumab has demonstrated anti-tumor effects in patients with HER2+ breast cancer. Adults with measurable, locally advanced or metastatic HER2+ breast cancer and prior trastuzumab treatment were enrolled in a phase 2 trial employing weekly 300 mg/m(2) Retaspimycin HCl, a potent Hsp90 inhibitor, with 6 mg/kg trastuzumab every 3 weeks. A Simon's two-stage design determined trial expansion by dose-limiting toxicity (DLT) and response rates. Pharmacokinetics and electrocardiograms were evaluated. Twenty-six patients with median age 52.5 years (range 33-72) enrolled with a median of six prior chemotherapeutic regimens (range 2-20). On study, patients received a median of three treatment cycles (range 1-12). No DLTs were observed. Most adverse events (AEs) were grade 1 or 2; common treatment-related AEs included fatigue (46 %), nausea (31 %), and diarrhea (23 %). One patient had treatment-related serious AEs of grade 1 diarrhea and grade 3 hypokalemia. grade 3 transaminase elevation occurred in one patient (4 %) who also had metastatic liver disease. Sixteen patients (62 %) had stable disease, with a median on-study duration of 2.4 months (range 1.1-8.2). No confirmed responses were observed. Retaspimycin HCl at 300 mg/m(2) weekly in combination with trastuzumab was well tolerated and without significant toxicities. Modest clinical activity was observed, but did not meet criteria for trial expansion. The safety profile for patients on study raises the possibility of Retaspimycin HCl underdosing that limited efficacy. Studies employing higher doses are ongoing.

A phase I study of the HSP90 inhibitor retaspimycin hydrochloride (IPI-504) in patients with gastrointestinal stromal tumors or soft-tissue sarcomas.[Pubmed:24045182]

Clin Cancer Res. 2013 Nov 1;19(21):6020-9.

PURPOSE: Heat shock protein 90 (HSP90) is required for the proper folding, function, and stability of various client proteins, two of which (KIT and PDGFRalpha) are critical in the pathogenesis and progression of gastrointestinal stromal tumors (GIST). This phase I study investigated the safety and maximum tolerated dose (MTD) of Retaspimycin hydrochloride (IPI-504), a novel potent and selective HSP90 inhibitor, in patients with metastatic and/or unresectable GIST or other soft-tissue sarcomas (STS). EXPERIMENTAL DESIGN: IPI-504 was administered intravenously at doses ranging from 90 to 500 mg/m(2) twice weekly for 2 weeks on/1 week off. Safety, pharmacokinetic, and pharmacodynamic profiles were determined. Response was assessed by Response Evaluation Criteria for Solid Tumors (RECIST) 1.0 and optionally via 18-fluorodeoxyglucose positron emission tomography (18-FDG-PET) imaging. RESULTS: Fifty-four patients received IPI-504; 37 with GIST and 17 with other STS. The MTD was 400 mg/m(2) twice weekly for 2 weeks on/1 week off. Common related adverse events were fatigue (59%), headache (44%), and nausea (43%). Exposure to IPI-504, 17-AAG, and 17-AG increased with IPI-504 dose. Stable disease (SD) was observed in 70% (26 of 37) of patients with GIST and 59% (10 of 17) of patients with STS. There was one confirmed partial response (PR) in a patient with GIST and one PR in a patient with liposarcoma. Metabolic partial responses occurred in 11 of 29 (38%) patients with GIST. CONCLUSIONS: In this study of advanced GIST or other STS, IPI-504 was generally well-tolerated with some evidence of antitumor activity, serving as a clinical proof-of-concept that HSP90 inhibition remains a promising strategy.