Preclinical antitumor activity, pharmacokinetics and pharmacodynamics of imexon in mice

Identification of iron metabolism-related predictive markers of endometriosis and endometriosis-relevant ovarian cancer

Endometriosis is associated with ovarian cancers, mainly endometrioid and clear-cell carcinomas. Iron metabolism has been shown to play a role in endometriosis. Therefore, it is vital to explore the relationship between iron metabolism and ovarian cancer and to identify novel markers for diagnostics and therapeutics. The endometriosis dataset GSE51981 and the ovarian cancer dataset GSE26712 were obtained from the gene expression omnibus database, and differentially expressed genes were identified. Iron metabolism genes were obtained from molecular signatures database, and hub genes from the 3 datasets were obtained. Seven hub genes were identified by bioinformatic analysis, and 3 hub genes (NCOA4, ETFDH, and TYW1) were further selected by logistic regression, which were verified in an independent endometriosis dataset (GSE25628) and ovarian cancer dataset (GSE14407), showing good predictive diagnostic value (area under the receiver operating characteristic curve of 0.88 and 0.9, respectively). Gene Ontology, gene set enrichment analysis, and immune infiltration analysis further confirmed the related functions, pathways, and immune relationship between iron metabolism and ovarian cancer. This study highlights the potential of targeting iron metabolism in the prevention of potential ovarian cancer and in the further exploration of endometriosis and endometriosis-relevant ovarian cancer therapeutics.

Magnetic Resonance Imaging Identifies Differential Response to Pro-Oxidant Chemotherapy in a Xenograft Model

Induction of oxidative stress is a key component of cancer therapy. Pro-oxidant drugs have been demonstrated to enhance the efficacy of radiotherapy and chemotherapy. An emerging concept is that therapeutic outcomes are dictated by the differential redox buffering reserve in subpopulations of malignant cells, indicating the need for noninvasive biomarkers of tumor redox that can be used for dose identification and response assessment in a longitudinal setting. Magnetic resonance imaging (MRI) enhanced with the thiol-binding contrast agent Gd-LC6-SH, and hemodynamic response imaging (HRI) in combination with hypercapnia and hyperoxia were investigated as biomarkers of the pharmacodynamics of the small molecule pro-oxidant imexon (IMX). Human multiple myeloma cell lines 8226/S and an IMX-resistant variant, 8226/IM10, were established as contralateral tumors in SCID mice. T1slope, an MRI measure of the washout rate of Gd-LC6-SH, was significantly lower post-IMX therapy in 8226/S tumors compared with vehicle controls, indicating treatment-related oxidization of the tumor microenvironment, which was confirmed by analysis of tumor tissue for thiols. T1slope and ex vivo assays for thiols both indicated a more reduced microenvironment in 8226/IM10 tumors following IMX therapy. HRI with hypercapnia challenge revealed IMX inhibition of vascular dilation in 8226/S tumors but not 8226/IM10 tumors, consistent with decreased immunohistochemical staining for smooth muscle actin in treated 8226/S tumors. MRI enhanced with Gd-LC6-SH, and HRI coupled with a hypercapnic challenge provide noninvasive biomarkers of tumor response to the redox modulator imexon.

Phase 2 study of imexon, a prooxidant molecule, in relapsed and refractory B-cell non-Hodgkin lymphoma

Lymphoma cells are subject to higher levels of oxidative stress compared with their normal counterparts and may be vulnerable to manipulations of the cellular redox balance. We therefore designed a phase 2 study of imexon (Amplimexon/NSC-714597), a prooxidant molecule, in patients with relapsed/refractory B-cell non-Hodgkin lymphoma (NHL). Imexon was administered at 1000 mg/m(2) IV daily for 5 days in 21-day cycles. Gene expression analysis performed on pretreatment tumor specimens included 13 transcripts used to generate a redox signature score, previously demonstrated to correlate with lymphoma prognosis. Twenty-two patients were enrolled having follicular (n = 9), diffuse large B-cell (DLBCL) (n = 5), mantle cell (n = 3), transformed follicular (n = 2), small lymphocytic (n = 2), and Burkitt (n = 1) lymphoma. The most common grade 3/4 adverse events were anemia (14%) and neutropenia (9%). The overall response rate was 30%, including responses in follicular lymphoma (4 of 9) and DLBCL (2 of 5). Gene expression analyses revealed CD68 and the redox-related genes, GPX1 and SOD2, as well as a higher redox score to correlate with clinical responses. Therefore, pretreatment markers of oxidative stress may identify patients likely to respond to this therapeutic approach. This trial was registered at www.clinicaltrials.gov as #NCT01314014.

Tumor Xenograft Response to Redox-Active Therapies Assessed by Magnetic Resonance Imaging Using a Thiol-Bearing DOTA Complex of Gadolinium

Gd-LC6-SH is a thiol-bearing DOTA complex of gadolinium designed to bind plasma albumin at the conserved Cys(34) site. The binding of Gd-LC6-SH shows sensitivity to the presence of competing thiols. We hypothesized that Gd-LC6-SH could provide magnetic resonance imaging (MRI) enhancement that is sensitive to tumor redox state and that the prolonged retention of albumin-bound Gd-LC6-SH in vivo can be exploited to identify a saturating dose above which the shortening of MRI longitudinal relaxation time (T(1)) of tissue is insensitive to the injected gadolinium dose. In the Mia-PaCa-2 pancreatic tumor xenograft model in SCID mice, both the small-molecule Gd-DTPA-BMA and the macromolecule Galbumin MRI contrast agents produced dose-dependent decreases in tumor T(1). By contrast, the decreases in tumor T(1) provided by Gd-LC6-SH at 0.05 and 0.1 mmol/kg were not significantly different at longer times after injection. SCID mice bearing Mia-PaCa-2 or NCI-N87 tumor xenografts were treated with either the glutathione synthesis inhibitor buthionine sulfoximine or the thiol-oxidizing anticancer drug Imexon, respectively. In both models, there was a significantly greater increase in tumor R(1) (=1/T(1)) 60 minutes after injection of Gd-LC6-SH in drug-treated animals relative to saline-treated controls. In addition, Mercury Orange staining for nonprotein sulfhydryls was significantly decreased by drug treatment relative to controls in both tumor models. In summary, these studies show that thiol-bearing complexes of gadolinium such as Gd-LC6-SH can serve as redox-sensitive MRI contrast agents for detecting differences in tumor redox status and can be used to evaluate the effects of redox-active drugs.

Anti-tumor activity and mechanism of action for a cyanoaziridine-derivative, AMP423

PURPOSE

Preclinical studies evaluated the anti-tumor activity and mechanism of action of AMP423, a naphthyl derivative of 2-cyanoaziridine-1-carboxamide with structural similarity to the pro-oxidant anti-tumor agent imexon.

METHODS

The cytotoxic potency was evaluated in vitro against a variety of human cancer cell lines. Mechanism-of-action studies were performed in the human 8226/S myeloma cell line and its imexon-resistant variant, 8226/IM10. In vivo activity was evaluated against human myeloma and lymphoma xenografts in SCID mice. Pharmacokinetics and toxicology were investigated in non-tumor-bearing mice.

RESULTS

The 72-h IC(50)s for all cell types ranged from 2 to 36 μM, across a wide variety of human cancer cell lines. AMP423 was active in SCID mice bearing 8226/S myeloma and SU-DHL-6 B-cell lymphoma tumors, with a median tumor growth delay (T-C) of 21 days (P = 0.0002) and 5 days (P = 0.004), respectively, and a median tumor growth inhibition (T/C) of 33.3% (P = 0.03) and 82% (P = 0.01), respectively. In non-tumor-bearing mice, AMP423 was not myelosuppressive. Mechanistic studies show that AMP423's mode of cell death is a mixture of necrosis and apoptosis, with generation of reactive oxygen species, inhibition of protein synthesis, and a decrease in reduced sulfhydryl levels, but no alkylation of nucleophiles. Unlike its structural analog imexon, which causes cell cycle arrest in G(2)/M, AMP423 induces the accumulation of cells in S-phase.

CONCLUSIONS

AMP423 has pro-oxidant effects similar to imexon, has greater cytotoxic potency in vitro, and has anti-tumor activity in hematologic tumors in vivo.

A phase 1-2 study of imexon plus dacarbazine in patients with unresectable metastatic melanoma

BACKGROUND

Imexon (Amplimexon) is an aziridine compound that increases reactive oxygen species, disrupts mitochondrial membranes, and induces apoptosis. Preclinical studies showed activity against melanoma cell lines and models in mice, and synergy with dacarbazine. The authors evaluated standard doses of dacarbazine combined with increasing doses of imexon to determine the maximal tolerated dose (MTD), toxicities, pharmacokinetics, and efficacy.

METHODS

Sixty-eight chemotherapy-naive melanoma patients (1 inoperable stage III and 67 stage IV) were treated with dacarbazine (250 mg/m2) and imexon (570-1300 mg/m2), both daily for 5 days every 3 weeks.

RESULTS

There were 18 patients in the phase 1, and 50 in the phase 2 component of the study. The MTD of imexon with dacarbazine was 1000 mg/m2. Dose-limiting toxicities were pulmonary edema and hepatorenal failure. At the MTD, therapy was well tolerated. The most common toxicities (any grade) were vomiting, diarrhea, anemia, thrombocytopenia, anorexia, fever, and constipation. Among 68 patients, there were 7 treatment-related serious adverse events. Partial response and stable disease rates were 5.9% and 25% for all subjects and 2% and 30% for the phase 2 patients, respectively. Median progression-free and overall survival of all patients were 2.0 and 11.7 months and 2 and 7.5 months for the phase 2 patients, respectively. Overall survival of the 31 patients with normal lactate dehydrogenase levels was >22.5 months. Pharmacokinetics of both drugs were similar to previous reports.

CONCLUSIONS

Imexon plus dacarbazine was well tolerated. The survival data suggest further evaluation in a randomized phase 2 study.

Redox-directed cancer therapeutics: molecular mechanisms and opportunities

Redox dysregulation originating from metabolic alterations and dependence on mitogenic and survival signaling through reactive oxygen species represents a specific vulnerability of malignant cells that can be selectively targeted by redox chemotherapeutics. This review will present an update on drug discovery, target identification, and mechanisms of action of experimental redox chemotherapeutics with a focus on pro- and antioxidant redox modulators now in advanced phases of preclinal and clinical development. Recent research indicates that numerous oncogenes and tumor suppressor genes exert their functions in part through redox mechanisms amenable to pharmacological intervention by redox chemotherapeutics. The pleiotropic action of many redox chemotherapeutics that involves simultaneous modulation of multiple redox sensitive targets can overcome cancer cell drug resistance originating from redundancy of oncogenic signaling and rapid mutation.Moreover, some redox chemotherapeutics may function according to the concept of synthetic lethality (i.e., drug cytotoxicity is confined to cancer cells that display loss of function mutations in tumor suppressor genes or upregulation of oncogene expression). The impressive number of ongoing clinical trials that examine therapeutic performance of novel redox drugs in cancer patients demonstrates that redox chemotherapy has made the crucial transition from bench to bedside.

A phase I study of imexon plus gemcitabine as first-line therapy for advanced pancreatic cancer

PURPOSE

Imexon is an aziridine-derived iminopyrrolidone which has synergy with gemcitabine in pancreatic cancer cell lines. Gemcitabine is a standard therapy for pancreatic cancer. We performed a phase I trial of imexon and gemcitabine to evaluate safety, dose-limiting toxicity (DLT), and maximum tolerated dose (MTD) in patients with advanced pancreatic cancer.

METHODS

Patients with untreated locally advanced or metastatic pancreatic adenocarcinoma received therapy in sequential cohorts on regimen A (n = 19; imexon 200 or 280 mg/m(2) intravenously (IV) over 30 min days 1-5, 15-19 and gemcitabine 800 or 1,000 mg/m(2) IV over 30 min on days 1,8,15 every 28 days) or regimen B (n = 86; imexon 280-1,300 mg/m(2) IV over 30-60 min days 1, 8, and 15 and gemcitabine 1,000 mg/m(2) IV over 30 min on days 1, 8, and 15 every 28 days).

RESULTS

One hundred five patients received 340 treatment cycles (median 2, range 1-16).

PATIENT CHARACTERISTICS

median age 63, 61% male, ECOG PS 0/1 50%/50%, 93% metastatic. DLT was abdominal cramping and pain, often with transient, acute diarrhea. Best response was confirmed partial response (PR) in 11.4%, 8.9% unconfirmed PR, and 48.1% with stable disease. There was a dose proportional increase in imexon AUC across the doses tested with terminal half life 69 min at the MTD and no alteration of gemcitabine pharmacokinetics.

CONCLUSIONS

The recommended phase II dose of imexon is 875 mg/m(2) with gemcitabine 1,000 mg/m(2). DLT was acute abdominal pain and cramping. Encouraging antitumor responses support further evaluation of this combination in advanced pancreatic cancer.

A phase I trial of imexon, a pro-oxidant, in combination with docetaxel for the treatment of patients with advanced breast, non-small cell lung and prostate cancer

PURPOSE

Imexon is an iminopyrrolidone that induces apoptosis and has synergistic activity with docetaxel in preclinical models. This trial was designed to establish the maximum tolerated dose (MTD) of imexon given with docetaxel in breast, prostate and non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

34 patients received protocol therapy. 26 patients received escalating doses of imexon given intravenously over 60 min on days 1-5 every 21 days. Docetaxel was administered intravenously at a fixed dose of 75 mg/m(2) immediately following imexon on day 1 every 21 days. A 3+3 design was used with eight additional patients treated at MTD. Response was measured using RECIST.

RESULTS

Seven dose levels of imexon were evaluated (390 mg/m(2) to 1,700 mg/m(2)). The MTD was imexon 1,300 mg/m(2) IV on days 1-5 in combination with docetaxel. Dose limiting toxicities were grade 3 non-cardiac chest pain and grade 3 diarrhea. Activity was seen in 4 patients [2 partial responses (NSCLC (PR=1), prostate cancer (PR=1)), 2 minor responses (MR=breast, NSCLC)]. Eleven patients had stable disease by RECIST (including the patients with MR; prostate cancer=6, NSCLC=3). Six (one with breast cancer, two with prostate cancer and three with NSCLC) demonstrated stable disease (SD) for > or = 3 months.

CONCLUSION

The MTD of combination therapy is imexon 1,300 mg/m(2) IV on days 1-5 with docetaxel 75 mg/m(2) IV on day 1 of a 21 day treatment cycle. Demonstrated responses warrant further investigation in phase II trials of which a phase II trial in NSCLC is planned.

Phase I trial of imexon in patients with advanced malignancy

PURPOSE

Imexon, a pro-oxidant small molecule, has antitumor activity in preclinical models. The drug induces apoptosis through accumulation of reactive oxygen species. The purpose of this trial was to define the maximum-tolerated dose (MTD), toxicities, pharmacokinetics, and pharmacodynamics of imexon in patients with advanced cancers.

PATIENTS AND METHODS

Forty-nine patients with metastatic cancer received intravenous imexon over 30 to 45 minutes for 5 consecutive days (one course) every other week (days 1 through 5 and 15 through 19) monthly. Doses were initially escalated using an accelerated trial design and then a modified Fibonacci method. Plasma imexon levels and six different thiols were measured by high-performance liquid chromatography assays.

RESULTS

There were 13 dose levels evaluated, from 20 mg/m2/d to 1,000 mg/m2/d. The MTD recommended for phase II studies was 875 mg/m2/d for 5 days every 2 weeks (n = 9 patients). The two dose-limiting toxicities at 1,000 mg/m2/d involved grade 3 abdominal pain and fatigue and grade 4 neutropenia, which occurred in one patient each. Other common toxicities included nausea and vomiting (58%) and constipation (63%); both were managed well with prophylactic medications. One partial response was obtained in a heavily pretreated patient with non-Hodgkin's lymphoma. Pharmacokinetic studies showed dose-independent clearance, with a 95-minute mean half-life. Plasma thiol studies showed a dose- and area under the curve-dependent decrease in cystine levels 8 hours after dosing at 750 mg/m2/d.

CONCLUSION

The phase II recommended dose of imexon is 875 mg/m2/d for 5 days every other week. A decrease in plasma thiols did correlate with imexon exposure.