Intravenous Infusion of High Dose Selenite in End-Stage Cancer Patients: Analysis of Systemic Exposure to Selenite and Seleno-Metabolites.

Cancer is one of the main causes of human death globally and novel chemotherapeutics are desperately required. As a simple selenium oxide, selenite is a very promising chemotherapeutic because of pronounced its dose-dependent tumor-specific cytotoxicity. We previously published a first-in-man systematic phase I clinical trial in patients with cancer (from IV to end-stage) (the SECAR trial) showing that selenite is safe and tolerable with an unexpectable high maximum tolerated dose (MTD) and short half-life. In the present study, we analyzed the selenium species in plasma samples, from the patients participating in the SECAR trial and from various time points and dose cohorts using LC-ICP-MS. In conclusion, selenite, selenosugars, and 1-2 unidentified peaks that did not correspond to any standard, herein denoted ui-selenium, were detected in the plasma. However, trimethylated selenium (trimethylselenonoium) was not detected. The unidentified ui-selenium was eluting close to the selenium-containing amino acids (selenomethionine and selenocysteine) but was not part of a protein fraction. Our data demonstrate that the major metabolite detected was selenosugar. Furthermore, the identification of selenite even long after the administration is remarkable and unexpected. The kinetic analysis did not support that dosing per the body surface area would reduce interindividual variability of the systemic exposure in terms of trough concentrations.

Selenoprotein P as Biomarker of Selenium Status in Clinical Trials with Therapeutic Dosages of Selenite.

Selenoprotein P (SELENOP) is an established biomarker of selenium (Se) status. Serum SELENOP becomes saturated with increasing Se intake, reaching maximal concentrations of 5-7 mg SELENOP/L at intakes of ca. 100-150 µg Se/d. A biomarker for higher Se intake is missing. We hypothesized that SELENOP may also reflect Se status in clinical applications of therapeutic dosages of selenite. To this end, blood samples from two supplementation studies employing intravenous application of selenite at dosages >1 mg/d were analyzed. Total Se was quantified by spectroscopy, and SELENOP by a validated ELISA. The high dosage selenite infusions increased SELENOP in parallel to elevated Se concentrations relatively fast to final values partly exceeding 10 mg SELENOP/L. Age or sex were not related to the SELENOP increase. Western blot analyses of SELENOP verified the results obtained by ELISA, and indicated an unchanged pattern of immunoreactive protein isoforms. We conclude that the saturation of SELENOP concentrations observed in prior studies with moderate Se dosages (<400 µg/d) may reflect an intermediate plateau of expression, rather than an absolute upper limit. Circulating SELENOP seems to be a suitable biomarker for therapeutic applications of selenite exceeding the recommended upper intake levels. Whether SELENOP is also capable of reflecting other supplemental selenocompounds in high dosage therapeutic applications remains to be investigated.

Pharmacokinetics and Toxicity of Sodium Selenite in the Treatment of Patients with Carcinoma in a Phase I Clinical Trial: The SECAR Study.

BACKGROUND: Sodium selenite at high dose exerts antitumor effects and increases efficacy of cytostatic drugs in multiple preclinical malignancy models. We assessed the safety and efficacy of intravenous administered sodium selenite in cancer patients' refractory to cytostatic drugs in a phase I trial. Patients received first line of chemotherapy following selenite treatment to investigate altered sensitivity to these drugs and preliminary assessment of any clinical benefits. MATERIALS AND METHODS: Thirty-four patients with different therapy resistant tumors received iv sodium selenite daily for consecutive five days either for two weeks or four weeks. Each cohort consisted of at least three patients who received the same daily dose of selenite throughout the whole treatment. If 0/3 patients had dose-limiting toxicities (DLTs), the study proceeded to the next dose-level. If 2/3 had DLT, the dose was considered too high and if 1/3 had DLT, three more patients were included. Dose-escalation continued until the maximum tolerated dose (MTD) was reached. MTD was defined as the highest dose-level on which 0/3 or 1/6 patients experienced DLT. The primary endpoint was safety, dose-limiting toxic effects and the MTD of sodium selenite. The secondary endpoint was primary response evaluation. RESULTS AND CONCLUSION: MTD was defined as 10.2 mg/m(2), with a calculated median plasma half-life of 18.25 h. The maximum plasma concentration of selenium from a single dose of selenite increased in a nonlinear pattern. The most common adverse events were fatigue, nausea, and cramps in fingers and legs. DLTs were acute, of short duration and reversible. Biomarkers for organ functions indicated no major systemic toxicity. In conclusion, sodium selenite is safe and tolerable when administered up to 10.2 mg/m(2) under current protocol. Further development of the study is underway to determine if prolonged infusions might be a more effective treatment strategy.

HER-2, EGFR, COX-2 expression status correlated to microvessel density and survival in resected non-small cell lung cancer.

The incidence of lung cancer is increasing throughout the world and is the most common cause of cancer-related death. Early detection followed by surgery has a reasonable, curative potential, but 30-50% of patients experience relapses. The immunohistochemical expressions of HER-2, EGFR and COX-2 were investigated in 53 resected non-small cell lung carcinomas and correlated to microvessel density and clinical data. HER-2, EGFR and COX-2 overexpressions were demonstrated in 15%, 30% and 40% of the tumours, respectively. In adenocarcinomas, HER-2 and COX-2 overexpression were more common, whereas in squamous cell carcinomas, EGFR overexpression was more common. COX-2 expression correlated with HER-2 expression (p = 0.002), and demonstrated a trend towards a correlation with microvessel density (p = 0.10). None of the markers alone had any impact on survival. However, HER-2+/EGFR- tumours proved to have a poor prognosis. In conclusion, adjuvant treatment with HER-2 antagonists might be a future treatment option in resected non-small cell lung cancer patients, especially when HER-2 is overexpressed without a concomitant overexpression of EGFR.