pr-104 and Hypoxia

We previously demonstrated vast expansion of hypoxic areas in the leukemic microenvironment and provided a rationale for using hypoxia-activated prodrugs. PR104 is a phosphate ester that is rapidly hydrolyzed in vivo to the corresponding alcohol PR-104A and further reduced to the amine and hydroxyl-amine nitrogen mustards that induce DNA cross-linking in hypoxic cells under low oxygen concentrations. In this phase I/II study, patients with relapsed/refractory acute myeloid leukemia (n=40) after 1 or 2 prior treatments or acute lymphoblastic leukemia (n=10) after any number of prior treatments received PR104; dose ranged from 1.1 to 4 g/m(2). The most common treatment-related grade 3/4 adverse events were myelosuppression (anemia 62%, neutropenia 50%, thrombocytopenia 46%), febrile neutropenia (40%), infection (24%), and enterocolitis (14%). Ten of 31 patients with acute myeloid leukemia (32%) and 2 of 10 patients with acute lymphoblastic leukemia (20%) who received 3 g/m(2) or 4 g/m(2) had a response (complete response, n=1; complete response without platelet recovery, n=5; morphological leukemia-free state, n=6). The extent of hypoxia was evaluated by the hypoxia tracer pimonidazole administered prior to a bone marrow biopsy and by immunohistochemical assessments of hypoxia-inducible factor alpha and carbonic anhydrase IX. A high fraction of leukemic cells expressed these markers, and PR104 administration resulted in measurable decrease of the proportions of hypoxic cells. These findings indicate that hypoxia is a prevalent feature of the leukemic microenvironment and that targeting hypoxia with hypoxia-activated prodrugs warrants further evaluation in acute leukemia. The trial is registered at clinicaltrials.gov identifier: 01037556.

Topics: Adult; Aged; Anemia; Antigens, Neoplasm; Antineoplastic Agents, Alkylating; Biomarkers; Bone Marrow; Carbonic Anhydrase IX; Carbonic Anhydrases; Enterocolitis; Female; Gene Expression; Humans; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Leukemia, Myeloid, Acute; Male; Middle Aged; Neutropenia; Nitrogen Mustard Compounds; Nitroimidazoles; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Prodrugs; Recurrence; Remission Induction; Thrombocytopenia

PR-104 is a "pre-prodrug" designed to be activated to a dinitrobenzamide nitrogen mustard cytotoxin by nitroreduction in hypoxic regions of tumors. This study was conducted to establish the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), safety, and pharmacokinetics (PK) of PR-104 in patients with advanced solid tumors.. Patients with solid tumors refractory or not amenable to conventional treatment were evaluated in a dose-escalation trial of PR-104 administered as a 1-h intravenous (IV) infusion every 3 weeks. The plasma PK of PR-104 and its primary metabolite, PR-104A, were evaluated.. Twenty-seven patients received a median of two cycles of PR-104 in doses ranging from 135 to 1,400 mg/m(2). The MTD of PR-104 as a single-dose infusion every 3 weeks was established as 1,100 mg/m(2). One of six patients treated at 1,100 mg/m(2) experienced DLT of grade 3 fatigue. Above the MTD, the DLTs at 1,400 mg/m(2) were febrile neutropenia and infection with normal absolute neutrophil count. No objective responses were observed, although reductions in tumor size were observed in patients treated at doses > or = 550 mg/m(2). The plasma PK of PR-104 demonstrated rapid conversion to PR-104A, with approximately dose-linear PK of both species.. PR-104 was well tolerated at a dose of 1,100 mg/m(2) administered as an IV infusion every 3 weeks. The area under the PR-104A plasma concentration-time curve at this dose exceeded that required for activity in human tumor cell cultures and xenograft models. The recommended dose of PR-104 as a single agent for phase II trials is 1,100 mg/m(2) and further trials are underway.

Topics: Adult; Aged; Anemia; Area Under Curve; Fatigue; Female; Humans; Hypoxia; Infusions, Intravenous; Male; Metabolic Clearance Rate; Middle Aged; Molecular Structure; Multienzyme Complexes; Neoplasms; Neutropenia; Nitrogen Mustard Compounds; Prodrugs; Treatment Outcome

Hypoxia is a characteristic of solid tumors and a potentially important therapeutic target. Here, we characterize the mechanism of action and preclinical antitumor activity of a novel hypoxia-activated prodrug, the 3,5-dinitrobenzamide nitrogen mustard PR-104, which has recently entered clinical trials.. Cytotoxicity in vitro was evaluated using 10 human tumor cell lines. SiHa cells were used to characterize metabolism under hypoxia, by liquid chromatography-mass spectrometry, and DNA damage by comet assay and gammaH2AX formation. Antitumor activity was evaluated in multiple xenograft models (PR-104 +/- radiation or chemotherapy) by clonogenic assay 18 h after treatment or by tumor growth delay.. The phosphate ester "pre-prodrug" PR-104 was well tolerated in mice and converted rapidly to the corresponding prodrug PR-104A. The cytotoxicity of PR-104A was increased 10- to 100-fold by hypoxia in vitro. Reduction to the major intracellular metabolite, hydroxylamine PR-104H, resulted in DNA cross-linking selectively under hypoxia. Reaction of PR-104H with chloride ion gave lipophilic cytotoxic metabolites potentially able to provide bystander effects. In tumor excision assays, PR-104 provided greater killing of hypoxic (radioresistant) and aerobic cells in xenografts (HT29, SiHa, and H460) than tirapazamine or conventional mustards at equivalent host toxicity. PR-104 showed single-agent activity in six of eight xenograft models and greater than additive antitumor activity in combination with drugs likely to spare hypoxic cells (gemcitabine with Panc-01 pancreatic tumors and docetaxel with 22RV1 prostate tumors).. PR-104 is a novel hypoxia-activated DNA cross-linking agent with marked activity against human tumor xenografts, both as monotherapy and combined with radiotherapy and chemotherapy.

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Comet Assay; Cross-Linking Reagents; DNA; DNA Damage; Drug Screening Assays, Antitumor; Histones; Humans; Hypoxia; Mice; Neoplasm Transplantation; Neoplasms; Nitrogen Mustard Compounds; Phosphates

PR-104 is a dinitrobenzamide mustard pre-prodrug that is activated by reduction to a cytotoxic hydroxylamine metabolite in hypoxic tumour cells; it has recently commenced Phase I clinical trial. Here, we report two validated methods for the determination of PR-104 and its alcohol hydrolysis product, PR-104A in plasma and tissues across species. A high pH LC/MS/MS method was optimised for rapid and sensitive analysis of both analytes in rat, dog and human plasma. This assay was linear over the concentration range 0.005-2.5 microg/ml for PR-104 and 0.05-25 microg/ml for PR-104A (0.005-2.5 microg/ml for rat). A second method, using a low pH LC separation, was designed to provide higher chromatographic resolution, facilitating identification of metabolites. Both methods were successfully applied to the plasma pharmacokinetics of PR-104 and PR-104A in rats. In addition, cytotoxic reduced metabolites of PR-104A were identified in human tumour xenografts by the higher chromatographic resolution method.

Topics: Animals; Calibration; Chromatography, High Pressure Liquid; Female; Humans; Hypoxia; Mice; Nitrogen Mustard Compounds; Rats; Rats, Sprague-Dawley; Reference Standards; Reproducibility of Results; Sensitivity and Specificity; Tandem Mass Spectrometry