Proteasome inhibitor PS-341 inhibits human myeloma cell growth in vivo and prolongs survival in a murine model.

The proteasome is a ubiquitous and essential intracellular enzyme that degrades many proteins regulating cell cycle, apoptosis, transcription, cell adhesion,angiogenesis, and antigen presentation. We have shown recently that the proteasome inhibitor PS-341 inhibits growth, induces apoptosis, and overcomes drug resistance in human myeloma cells in vitro. In this study, we examined the efficacy, toxicity, and in vivo mechanism of action of PS-341 using a human plasmacytoma xenograft mouse model. One hundred immunodeficient (beige-nude-xid) mice were used in two independent experiments. The mice were injected s.c. with 3 x 10(7) RPMI-8226 myeloma cells. When tumors became measurable (9.2 days; range, 6-13 days after tumor injection), mice were assigned to treatment groups receiving PS-341 0.05 mg/kg (n = 13), 0.1 mg/kg (n = 15), 0.5 mg/kg (n = 14), or 1.0 mg/kg (n = 14) twice weekly via tail vein, or to control groups (n = 13) receiving the vehicle only. Significant inhibition of tumor growth, even with some complete tumor regression, was observed in PS-341-treated mice. The median overall survival was also significantly prolonged compared with controls (30 and 34 days for high dose-treated mice versus 14 days for controls; P < 0.0001). PS-341 was well tolerated up to 0.5 mg/kg, but some mice treated at 1.0 mg/kg became moribund and lost weight. Analysis of tumors harvested from treated animals showed that PS-341 induced apoptosis and decreased angiogenesis in vivo. These studies therefore demonstrate that PS-341 has significant in vivo antimyeloma activity at doses that are well tolerated in a murine model, confirming our in vitro data and further supporting the early clinical promise of PS-341 to overcome drug resistance and improve patient outcome.

Phase I trial of the proteasome inhibitor bortezomib in patients with advanced solid tumors with observations in androgen-independent prostate cancer.

PURPOSE: To determine the dose-limiting toxicity and maximum-tolerated dose of the proteasome inhibitor bortezomib administered intravenously weekly for 4 every 5 weeks; to determine the bortezomib pharmacokinetics and pharmacodynamics using plasma levels and an assay for 20S proteasome inhibition (PI) in whole blood; to correlate toxicity with bortezomib dose and degree of 20S PI; and to conduct a preliminary determination of the antitumor activity of bortezomib in patients with androgen independent prostate cancer (AIPCa). PATIENTS AND METHODS: Fifty-three patients (48 with AIPCa) received 128 cycles of bortezomib in doses ranging from 0.13 to 2.0 mg/m(2)/dose, utilizing a careful escalation scheme with a continuous reassessment method. Pharmacokinetic and pharmacodynamic studies were performed in 24 patients (at 1.45 to 2.0 mg/m(2)). RESULTS: A dose-related 20S PI was seen, with dose-limiting toxicity at 2.0 mg/m(2) (diarrhea, hypotension) occurring at an average 1-hour post-dose of >/= 75% 20S PI. Other side effects were fatigue, hypertension, constipation, nausea, and vomiting. No relationship was seen between body-surface area and bortezomib clearance over the narrow dose range tested. There was evidence of biologic activity (decline in serum prostate-specific antigen and interleukin-6 levels) at >/= 50% 20S PI. Two patients with AIPCa had prostate-specific antigen response and two patients had partial response in lymph nodes. CONCLUSION: The maximum-tolerated dose and recommended phase II dose of bortezomib in this schedule is 1.6 mg/m(2). Biologic activity (inhibition of nuclear factor-kappa B-related markers) and antitumor activity is seen in AIPCa at tolerated doses of bortezomib. This agent should be further explored with chemotherapy agents in advanced prostate cancer.

Phase I trial of the proteasome inhibitor PS-341 in patients with refractory hematologic malignancies.

PURPOSE: To determine the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacodynamics (PD) of the proteasome inhibitor bortezomib (previously known as PS-341) in patients with refractory hematologic malignancies. PATIENTS AND METHODS: Patients received PS-341 twice weekly for 4 weeks at either 0.40, 1.04, 1.20, or 1.38 mg/m(2), followed by a 2-week rest. The PD of PS-341 was evaluated by measurement of whole blood 20S proteasome activity. RESULTS: Twenty-seven patients received 293 doses of PS-341, including 24 complete cycles. DLTs at doses above the 1.04-mg/m(2) MTD attributed to PS-341 included thrombocytopenia, hyponatremia, hypokalemia, fatigue, and malaise. In three of 10 patients receiving additional therapy, serious reversible adverse events appeared during cycle 2, including one episode of postural hypotension, one systemic hypersensitivity reaction, and grade 4 transaminitis in a patient with hepatitis C and a substantial acetaminophen ingestion. PD studies revealed PS-341 induced 20S proteasome inhibition in a time-dependent manner, and this inhibition was also related to both the dose in milligrams per meter squared, and the absolute dose of PS-341. Among nine fully assessable patients with heavily pretreated plasma cell dyscrasias completing one cycle of therapy, there was one complete response and a reduction in paraprotein levels and/or marrow plasmacytosis in eight others. In addition, one patient with mantle cell lymphoma and another with follicular lymphoma had shrinkage of nodal disease. CONCLUSION: PS-341 was well tolerated at 1.04 mg/m(2) on this dose-intensive schedule, although patients need to be monitored for electrolyte abnormalities and late toxicities. Additional studies are indicated to determine whether incorporation of dose/body surface area yields a superior PD model to dosing without normalization. PS-341 showed activity against refractory multiple myeloma and possibly non-Hodgkin's lymphoma in this study, and merits further investigation in these populations.

A phase I trial of the novel proteasome inhibitor PS341 in advanced solid tumor malignancies.

PURPOSE: The purpose of this study was to evaluate the toxicity and pharmacodynamic behavior of the novel proteasome inhibitor PS341 administered as a twice weekly i.v. bolus for 2 weeks, followed by a 1-week recovery period in patients with advanced solid tumor malignancies. EXPERIMENTAL DESIGN: In this Phase I trial, 43 patients were treated with PS341 in doses ranging from 0.13 to 1.56 mg/m2/dose. A standard Phase I design was used. Pharmacodynamic studies were performed to access 20S proteasome activity. RESULTS: Forty-three patients were treated with 89 cycles of PS341. Patients were heavily pretreated. Dose-limiting toxicities on this schedule were diarrhea and sensory neurotoxicity. Other side effects seen were fatigue, fever, anorexia, nausea, vomiting, rash, pruritus, and headache. There was no dose-limiting hematological toxicity. A dose-related inhibition of 20S proteasome activity with increasing dose of PS341 was seen. There was one major response in a patient with refractory non-small cell lung carcinoma. CONCLUSIONS: Given the results of this trial, it is safe and reasonable to recommend treatment with PS341 on the schedule used in this trial at 1.56 mg/m2/dose in Phase II trials. Particular care should be taken with patients with preexisting neuropathy. Further testing in Phase II trials is warranted.

Development of 17-allylamino-17-demethoxygeldanamycin hydroquinone hydrochloride (IPI-504), an anti-cancer agent directed against Hsp90.

Heat shock protein 90 (Hsp90) is an emerging therapeutic target of interest for the treatment of cancer. Its role in protein homeostasis and the selective chaperoning of key signaling proteins in cancer survival and proliferation pathways has made it an attractive target of small molecule therapeutic intervention. 17-Allylamino-17-demethoxygeldanamycin (17-AAG), the most studied agent directed against Hsp90, suffers from poor physical-chemical properties that limit its clinical potential. Therefore, there exists a need for novel, patient-friendly Hsp90-directed agents for clinical investigation. IPI-504, the highly soluble hydroquinone hydrochloride derivative of 17-AAG, was synthesized as an Hsp90 inhibitor with favorable pharmaceutical properties. Its biochemical and biological activity was profiled in an Hsp90-binding assay, as well as in cancer-cell assays. Furthermore, the metabolic profile of IPI-504 was compared with that of 17-AAG, a geldanamycin analog currently in clinical trials. The anti-tumor activity of IPI-504 was tested as both a single agent as well as in combination with bortezomib in myeloma cell lines and in vivo xenograft models, and the retention of IPI-504 in tumor tissue was determined. In conclusion, IPI-504, a potent inhibitor of Hsp90, is efficacious in cellular and animal models of myeloma. It is synergistically efficacious with the proteasome inhibitor bortezomib and is preferentially retained in tumor tissues relative to plasma. Importantly, it was observed that IPI-504 interconverts with the known agent 17-AAG in vitro and in vivo via an oxidation-reduction equilibrium, and we demonstrate that IPI-504 is the slightly more potent inhibitor of Hsp90.