Abstract 755: Repression of tumor survival pathways by novel and selective inhibitors of MNK1 and MNK2 kinases in glioblastoma and colorectal cancer

Herewith, we report development of small molecule inhibitors of MNK1 and MNK2 kinases and their cellular activity. MNK1 and 2 are MAP kinase-interacting kinases that are activated by RAS and MAPK signaling pathways and are involved in regulation of translation. Both kinases phosphorylate translation initiation factor eIF4e on a conserved serine 209 residue. eIF4E can contribute to the oncogenic transformation both in vitro and in vivo and is highly expressed in various tumor types. Interestingly, mice that lack both MNK1 and MNK2 do not have any apparent phenotype, which is promising for the therapeutic window of MNK1/2 inhibitors. SEL201 is a series of small molecule inhibitors which inhibit activity of both MNK1 and MNK2 in a low nM range. Selected compounds were tested on the kinome panels and indicated MNK1 and MNK2 as primary kinase targets. SEL201 compounds caused dose dependent inhibition of phosphorylation of eIF4e at Ser209 in various cancer cell lines at concentrations <100nM, which were lower when compared with other reported MNK1/2 inhibitors such as Cercosporamid and CGP57380. Consistently, potent inhibition of eIF4e Ser209 was observed also in vivo after oral administration of the inhibitors in xenograft models. High potency, selectivity and favorable ADME/PK profile indicates that SEL201 inhibitors would be useful tools in probing molecular consequences of eIF4e Ser209 inhibition in cancer cells alone and in combination with other inhibitors targeting PI3K/mTOR or RAS/MEK pathway. SEL201 in vitro and in vivo activities on viability and metastasis will be presented in cellular and in vivo models of colorectal cancer and glioblastoma. SEL201 series is further developed as a promising anticancer therapy with potentially wide therapeutic window.

Citation Format: Tomasz Rzymski, Malgorzata Szajewska-Skuta, Adrian Zarebski, Kamil Sitarz, Lukasz Sapala, Malgorzata Zurawska, Magdalena Salwinska, Renata Windak, Ewa Trebacz, Joanna Daniel-Wojcik, Radoslaw Obuchowicz, Bozena Winnik, Ewelina Wincza, Urszula Kulesza, Katarzyna Kucwaj-Borysz, Mariusz Milik, Agnieszka Dreas, Krzysztof Brzozka. Repression of tumor survival pathways by novel and selective inhibitors of MNK1 and MNK2 kinases in glioblastoma and colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 755. doi:10.1158/1538-7445.AM2014-755

Abstract 696: Development of selective CDK8 inhibitors for colorectal cancer and mantle cell lymphoma treatment

CDK8 is a kinase component of the mediator complex which functions as a bridge between a basal transcriptional machinery and specific transcription factors. CDK8 is amplified and differentially expressed in colorectal cancer and in certain hematological malignancies such as mantle cell lymphomas. Cells that express elevated CDK8 levels are highly dependent on its expression for proliferation. Here we report development of first-in-class selective inhibitors CDK8. Compounds from the SEL120 series have binding affinities towards CDK8 in the low nM range. Results from the kinome panel indicated that selectivity of SEL120 compounds was comparable with some of the most selective clinical kinase inhibitors. SEL120 compounds reduced viability of mantle cell lymphoma and colorectal cancer cell lines, with particularly good activity in cell lines overexpressing CDK8 and with G13D mutation in KRAS. Slightly lower sensitivity was observed for cells with mutated P53 and other mutations in KRAS/BRAF pathway. In contrast to pan-CDK inhibitors with main target activity on CDK9, treatment with SEL120 compounds did not repress phosphorylation of PolII and did not cause global transcriptional shutdown. Selective inhibition of CDK8 was sufficient to inhibit both paracrine and autocrine activities of cancer cells and stimulated normal cells. Production of proinflammatory cytokines, such as IL6 was repressed by SEL120 compounds in normal and cancer cells stimulated by sub-optimal doses of chemotherapeutics. SEL120 also reduced both murine and human IL6 in blood of mice bearing human xenograft models. Oral administration of SEL120 revealed favorable pharmacokinetics profile and strong, dose dependent potency in colon cancer mouse xenograft models. Presented data validate inhibition of CDK8 as a promising strategy for anticancer treatment, particularly for CRC and mantle cell lymphomas resistant to current treatments.

Citation Format: Tomasz Rzymski, Adrian Zarebski, Renata Windak, Karolina Krawczynska, Ewa Trebacz, Agnieszka Dreas, Katarzyna Kucwaj, Karolina Osowska, Marek Cholody, Paulina Szczepanska, Jakub Woyciechowski, Radosław Obuchowicz, Magdalena Salwińska, Joanna Fogt, Malgorzata Zurawska, Arkadiusz Białas, Katarzyna Wiklik, Mariusz Milik, Angelo Sanzone, Adam Radzimierski, Krzysztof Brzózka. Development of selective CDK8 inhibitors for colorectal cancer and mantle cell lymphoma treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 696. doi:10.1158/1538-7445.AM2013-696

Abstract 2160: Development of selective MELK kinase inhibitors for cancer treatments

Maternal embryonic leucine zipper kinase (MELK) is an atypical member of the AMPK family of serine-threonine kinases that has been implicated in stem cell renewal, cell cycle progression, cytokinesis, mRNA splicing and apoptosis. MELK activity is correlated with its phosphorylation level, is cell cycle dependent and maximal during mitosis although direct upstream regulators of MELK kinase activity are unknown. This kinase is highly expressed in several types of solid cancers: colon, breast, ovary, lung, and brain and shows relatively low expression levels in normal tissues. MELK overexpression in patient-derived tumors strongly correlates with poor prognosis in glioblastoma and breast cancer. Moreover, siRNA mediated knockdown of MELK kinase significantly inhibits growth of tumor cell lines both in vitro and in vivo. Therefore, MELK kinase is an emerging and interesting target of significant potential for therapeutic intervention in cancer. In this study, we are reporting results for a series of new MELK kinase inhibitors that were developed at Selvita. Newly synthesized derivatives exert good selectivity and potency in MELK inhibitions with the low sub-micromolar range. Anticancer effects of these compounds were investigated in several cancer cell lines of solid tumor origin where the compounds were shown to induce cell death with low micromolar ED50 values. Compounds were also analyzed for their effects on cell death, proliferation, apoptosis, cell cycle parameters and ADME properties. Taken altogether, the presented data supports our rationale of using inhibitors of MELK kinases as a novel approach for the cancer therapy, especially for the treatment of glioblastoma and breast cancer.

Citation Format: Piotr Kowalczyk, Paulina Wegrzyn, Przemyslaw Zawadzki, Edyta Palacz, Ewa Trebacz, Katarzyna Wiklik, Mariusz Milik, Adrian Zarebski, Karolina Krawczynska, Krzysztof Brzózka. Development of selective MELK kinase inhibitors for cancer treatments. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2160. doi:10.1158/1538-7445.AM2013-2160

Abstract 3245: Identification of potent, dual PIM/FLT3 kinase inhibitors for AML treatment

Acute myeloid leukemia (AML) is a highly heterogeneous disease with numerous signaling pathways that contribute to its pathogenesis. Advances in our understanding of molecular mechanisms of AML pathogenesis and prognosis so far did not translate into significant clinical improvements. AML is still the highest unmet medical need within hematological malignancies area, particularly in case of the elderly patients. FLT3 inhibitors were investigated in the recent years as possible therapeutic agents, however to date the clinical trials of FLT3 inhibitors have yielded disappointing results. On the other hand, PIM kinases have been identified in the last years as critical downstream components of FLT3 signaling, especially in the case of oncogenic FLT3 mutants. PIM kinases are being overexpressed in a range of hematopoietic malignancies and solid cancers and the overexpression of PIMs is associated with a poor prognosis and decreased survival of patients suffering from cancer. In many cases also, PIM overexpression was associated with development of drug resistance. As dual and simultaneous inhibition of various pathway components is an emerging therapeutic idea, exemplified by several compounds in development for cancer treatment, we have developed a series of dual PIM/FLT3 small molecule inhibitors to investigate this concept. Similarly to examples of small molecule inhibitors from the JAK/STAT or PI3K/AKT pathways, where compounds are being developed as a way to improve efficacy, resistance development and overcoming the negative feedback loops, often seen after single target inhibition, we have observed increased potency of compounds developed in this series of dual PIM/FLT3 inhibitors. Synthesized inhibitors showed higher activity towards mutated FLT3 (FLT3-ITD and other FLT3 mutants) than wild type kinase and the selectivity profile on a panel of 450 kinases was comparable to best clinical examples of kinase inhibitors. In contrast to selective PIM inhibitors, the treatment with dual PIM/FLT3 inhibitors showed potent apoptosis induction as a results of Erk and S6 phosphorylation inhibition. The in vitro activity in FTL3-ITD positive cells was also confirmed in vivo in a PK/PD xenograft experiment, where sustained biomarker inhibition was observed already after single compounds administration. Oral administration of dual PIM/FLT3 inhibitors led to potent effect in vivo and in certain cases also to remissions in subcutaneous xenograft models. Observed activity profile and synergistic effects observed with other targeted therapies and standard of care compounds, makes dual PIM/FLT3 inhibitors an exciting approach for treatment of FLT3-mutant positive AML patients with high chances of clinical success.

Citation Format: Wojciech Czardybon, Michal Galezowski, Renata Windak, Magdalena Salwińska, Izabela Dolata, Ewa Trebacz, Radosław Obuchowicz, Pawel Guzik, Magdalena Zawadzka, Ewelina Wincza, Katarzyna Wiklik, Mariusz Milik, Malgorzata Zurawska, Karolina Krawczynska, Krzysztof Brzózka. Identification of potent, dual PIM/FLT3 kinase inhibitors for AML treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3245. doi:10.1158/1538-7445.AM2013-3245

Abstract 3845: Antitumor activity of SEL120: An orally available dual inhibitors of Haspin/CDK9, for standalone and combination therapy with AuroraB inhibitors in solid tumors and hematopoietic malignancies

The mitotic machinery is a validated target for potential drug therapies in cancer. However, anti-mitotic agents are not without complications from various side effects, notably neurological and hematological toxicities. There is much interest in identifying new drug targets in mitosis which could lead to safer and more efficacious treatments of cancer. Recently, Haspin has been identified as another important kinase involved in mitosis. Similar to other mitotic kinases such as Polo-like kinase-1 and the Aurora kinases, inhibition of Haspin represents a novel approach in anti-mitotic cancer therapeutics. In this study we report the development of SEL120, series of novel ATP competitive inhibitors of Haspin kinase. These compounds have binding affinities towards Haspin kinase in the low nM range. Several compounds in the series exerted significant activity on CDK9 (selectively over other CDK kinases), a part of positive transcription elongation factor b (P-TEFb) involved in the expression of survival proteins during progression of cancer. SEL120 inhibited proliferation and clonogenic survival of a number of tumor cell lines with particularly good cytostatic activity in colon, lung (NSCLS) and B cell lymphoma cell lines. The only substrate of Haspin reported in literature to date is histone H3. During mitosis Haspin targets a single site in this protein, namely threonine at position T3 (H3T3ph). By using siRNA, we have confirmed that Thr3 phosphorylation of histone H3 could be completely repressed by the knockdown of Haspin in HCT116 colon and A549 (NSCLC) lung cancer cell lines. We also consistently observed decreased phosphorylation of histone H3 (Thr3) in both synchronized and asynchronous cell lines treated with SEL120 inhibitor. In addition SEL120-1 treatment decreased levels of CDK9 biomarkers- phosphorylation of pol II CTD (Ser2) and expression of the pro-survival protein Mcl-1 Treatment with SEL120 consistently resulted in mitotic cell cycle arrest in A549 cell line confirming inhibition of Haspin as the mechanism of action. Remarkably, inhibitory activity on CDK9 correlated with levels of cell death. Furthermore, co-administration of SEL120 with an AuroraB inhibitors, resulted in strong synergistic cytostatic effects. Treatment with both compounds increased the number of cells arrested in mitosis, notably without any signs of polyploidy typically observed after inhibition of AuroraB. Oral administration of SEL120 (25mg/kg BID) revealed excellent potency in colon and B-cell lymphoma xenograft models. Analysis of pharamcokinetic, ADMET and histopathological parameters afforded encouraging results towards potential development of new therapeutics emerging from our SEL120 program.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3845. doi:1538-7445.AM2012-3845

Abstract B242: Antitumor activity of SEL120: An orally available small-molecule inhibitor of Haspin kinase for standalone and combination therapy with AuroraB inhibitors in colorectal cancer

The mitotic machinery is a validated target for potential drug therapies in cancer. Anti-mitotic drugs like vinca alkaloids and taxanes interfering with microtubules are important classes of chemotherapeutical agents. However, these agents are not without complications from various side effects, notably neurological and hematological toxicities. There is much interest in identifying new drug targets in mitosis which could lead to safer and more efficacious treatments of cancer. Recently, Haspin has been identified as another important kinase involved in mitosis. Similar to other mitotic kinases such as Polo-like kinase-1 and the Aurora kinases, inhibition of Haspin represents a novel approach in anti-mitotic cancer therapeutics.

In this study we report the development of SEL120, a novel ATP competitive inhibitor of Haspin kinase. These small-molecule compounds have binding affinities towards Haspin kinase in the low nM range. SEL120 inhibited proliferation and clonogenic survival of a number of tumor cell lines with particularly good cytostatic activity in colon, lung (NSCLS) and B cell lymphoma cell lines.

The only substrate of Haspin reported in literature to date is histone H3. During mitosis Haspin targets a single site in this protein, namely threonine at position T3 (H3T3ph). By using siRNA, we have confirmed that Thr3 phosphorylation of histone H3 could be completely repressed by the knockdown of Haspin in HCT116 colon and A549 (NSCLC) lung cancer cell lines. We also consistently observed decreased phosphorylation of histone H3 (Thr3) in both synchronized and asynchronous cell lines treated with SEL120 inhibitor. Haspin-depleted cells were arrested in the prometaphase as a result of chromosome alignment defects and activation of the mitotic checkpoint. Treatment with SEL120 consistently resulted in mitotic cell cycle arrest in HCT116 and A549 cell lines confirming inhibition of Haspin as the mechanism of action. Furthermore, co-administration of SEL120 with an AuroraB inhibitor, AZD1152, resulted in strong synergistic cytostatic effects. Treatment with both compounds increased the number of cells arrested in mitosis, notably without any signs of polyploidy (cells with >4n) typically observed after inhibition of AuroraB.

Oral administration of SEL120 (25mg/kg BID) revealed excellent potency in the HCT116 xenograft model; observed tumor growth inhibition was over 80%. Analysis of pharamcokinetic, ADMET and histopathological parameters afforded encouraging results towards potential development of new therapeutics emerging from our SEL120 program. Presented data validates Haspin as a promising target for anticancer treatments, particularly for colon cancer, lung cancer and lymphomas.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B242.

Abstract A243: Novel Pim kinase inhibitors for treatment of hematological malignancies and solid tumors

The family of Pim kinases emerged as a novel and interesting target with significant potential for therapeutic intervention in cancer. All three members of the family Pim-1, Pim-2 and Pim-3 were shown to be prevent apoptosis, promote protein translation and cell survival thereby enhancing proliferation of malignant cells. Pim kinases seem to be crucial downstream effectors various important oncogenes like Jak, Flt3 or Ras kinases. Multiple targets phosphorylated by Pim kinases play important roles in intracellular signaling and contribute to pathways involved in cell survival, proliferation, stress response and cellular motility. Moreover, the significance and relevance of Pim kinases as valid therapeutic targets is further confirmed by their expression levels in variety of cancer types of both hematological origin. For example Pim kinase overexpression contributes to the development of diffuse B cell lymphoma, mantle cell lymphoma, B-cell chronic lymphocytic leukemia and Flt3-mediated acute myelogenous leukemia. Interestingly, accumulating literature data point towards emerging role of Pim kinases also in development of malignancies that originate from epithelial cells, especially gastric, colon and hepatocellular cancers, but also prostate and pancreatic cancers.

In this study we are reporting the results for novel small molecule Pim kinase inhibitors that were developed by Selvita. in Currently, we are performing a lead optimization program of novel, small molecule pan-Pim kinase inhibitors. Compounds developed within the SEL24 series exert high potency in vitro both on all three Pim kinases as well as on a large panel of cancer cell lines. Among synthesized compounds we have identified most selective Pim kinase inhibitors described so far with selectivity scores on a panel of 290 kinases inhibited over 90% at 1 μM concentration was equal to 1.8%. Mechanism of action for selected compounds was confirmed both in vitro in variety of cell lines and in vivo in xenograft models by downregulation of c-Myc and 4EBP1 phosphorylation inhibition. Further experiments indicated that our compounds induced both apoptotic cell death and cell cycle arrest at G0/G1, consistently with the predicted Pim kinase inhibition phenotype. SEL24 compounds showed mostly synergistic effects in a range of combinations with standard anti-cancer therapeutics in both leukemias and solid tumor cell lines. Strong synergies were observed not only for cytotoxic agents like docetaxel, gemcitabine or cyratabine, but also for targeted therapies like the PI3K/Akt pathway inhibitors or Jak kinase inhibitors. Data will be presented on in vivo efficacy of SEL24 lead compounds examined in xenograft models of leukemias, lymphomas and solid tumors (lung and colon cancer). Apart from excellent efficacy in in vivo xenograft models, SEL24 compounds show preferable safety profile with no effect on ion channel mediated cardiotoxicity and favorable pharmacokinetic profile. Taken together, presented data supports the rationale of using Pim kinase inhibition as a novel approach to standalone cancer therapy, and in combination with other targeted and cytotoxic therapies, especially to overcome developing drug resistance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A243.

Abstract 4499: In vitro and in vivo evaluation of novel Pim kinase inhibitors with potent anticancer activity

The Pim serine-threonine kinase family is composed of three members that play an important role in intracellular signaling and contribute to pathways involved in cell survival, proliferation, stress response and cellular motility. Out the three family members, Pim-1 has been studied most extensively and was shown to be a crucial downstream effector of several oncogenes such as Jak2 and FLT3 kinases. Pim-1 overexpression has been also reported in a variety of cancers such as diffuse B cell lymphoma, chronic lymphocytic leukemia, Flt3-mediated acute myelogenous leukemia and solid tumors including prostate and pancreatic cancers. For this reason, Pim-1 kinase emerged as a novel and interesting target of significant potential for therapeutic intervention.

In the current study, the optimization of the initial lead compound - which presented moderate potency in Pim kinase inhibition, low solubility and bioavailability - led to the identification of a group of new compounds. Among the newly synthesized compounds several derivatives exerted increased potency in Pim kinase inhibition with IC50 values below 5 nM. Profiling of best inhibitors on a KINOMEscanTM Max kinase panel revealed superior selectivity towards Pim kinases.

Anticancer activity of these new derivatives was investigated in various neoplastic cell lines of hematological and solid tumor origin where the compounds were shown to induce apoptosis both as a single agent, but also synergistically with standard therapies, such as docetaxel and cytarabine. FACS analyses revealed accumulation of subG0 phase, indicating apoptosis in time and concentration dependant manner. In the living cells, two phenotypes could be observed, namely a cell cycle arrest of the cells either in the G0/G1 or G2/M phases, depending on the cell line.

In order to confirm that the observed cytotoxic and cell cycle effects were due to inhibition of the Pim kinases, we performed analyses of direct downstream substrates of these kinases. Pim kinases were shown to phosphorylate p27KIP1, 4E-BP1 and Bad proteins, and treatment of cells in vitro with our new compounds caused a dramatic reduction in the phosphorylation levels of these targets. Best performing compounds were then chosen for an efficacy screen in a mouse xenograft model, proving their anticancer activity. Treatment of the animals also led to in vivo biomarker inhibition after single administration of the compounds.

Results of Selvita's Pim kinase inhibitor optimization efforts are shown and discussed, supporting further development of this class of inhibitors in oncology indications.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4499.

Characterization of glycosylation and adherent properties of melanoma cell lines

The repertoire of oligosaccharide components of cellular glycoproteins significantly contributes to cell adhesion and communication. In tumor cells, alteration in cellular glycosylation may play a key role in giving rise to invasive and metastatic potential. Over 100 melanoma cell lines deposited in the ESTDAB Melanoma Cell Bank (Tubingen, Germany) were studied for the characteristic glycan composition related to tumor progression. Analysis of: (1) cell adhesion to extracellular matrix proteins--fibronectin, laminin, and collagen; (2) the expression of selected glycosyltransferases--alpha2,3(Gal beta1,3)- and alpha2,3(Gal beta1,4)-sialyltransferases, alpha1,2- and alpha1,3-fucosyltransferases, and N-acetylglucosaminyltransferase V; (3) characterization of N-glycans was carried out on uveal (4), primary cutaneous (6), and metastatic (96) melanoma cell lines. Results showed that uveal cells did not adhere to any of the substrates and, in general, possessed less glycans containing alpha-2,6- and alpha-2,3-linked sialic acid. The average number of polypeptides bearing beta-1,6-branched tri- and tetra antennary glycans (characteristic of the metastatic phenotype) were similar in uveal, primary cutaneous, and metastatic melanoma cell lines. Characterization of N-glycans may open a new perspective in the search for specific glycoproteins that could become targets for the therapeutic modulation of melanoma.

Mercury species in the liver of ringed seals

Four types of mercury species, namely, methylmercury, organic mercury other than methylmercury, inorganic mercury, and insoluble mercury, deemed to be mercuric selenide (HgSe), were found in the liver of 45 ringed seals from the Canadian Arctic. On average, methylmercury, at 2%, made up the smallest fraction of the total mercury in the liver of these animals. Of the total mercury concentration in seal liver, 53% was insoluble mercury, estimated to be largely mercuric selenide. Other workers have found this compound to be present in mammalian liver and identified it to be HgSe. Organic mercury other than methylmercury made up 4%, and inorganic mercury 42% of the total mercury in the liver. The sum of the independently determined mercury species agreed well with the total mercury concentration in the liver. Species other than mercuric selenide are known to be toxic. Mercuric selenide, considered to be a stable end product of the demethylation process of methylmercury, although not readily eliminated from the liver, is inert and apparently non-toxic. Only approximately half of the total mercury in the liver was potentially toxic mercury. All four mercury species were positively correlated with the age of animals, the regression slope on age being 20 times larger for insoluble Hg (HgSe) than for methylmercury. A number of reported observations, such as the long half-life of Hg in liver (> or = 10 years), the dependence of Hg on age, and the often-observed one-to-one relationship between Hg and Se (on a molar basis), are readily explained by the temporal accumulation of HgSe in the liver. In the future, a more accurate assessment of the health risk to animals and humans from the consumption of contaminated animal tissues will be possible, by measuring all mercury species rather than just total mercury or methylmercury. Total mercury alone in the liver is an inadequate indicator of toxicity to animals. Methylmercury was analyzed by capillary gas-liquid chromatography with ECD detection, and the other species were operationally/experimentally defined using physical/chemical methods.

Methylmercury and total mercury in tissues of arctic marine mammals

Concentrations of methylmercury, total mercury and selenium in marine mammal tissues were determined in liver, muscle, skin (muktuk) and blubber of belugas, ringed seals and narwhal, using atomic absorption and capillary gas chromatography with ECD detection. Mean MeHg levels in the types of tissues analysed, except blubber, generally exceeded the Canadian Federal Consumption Guideline for mercury in fish (0.5 micrograms/g wet wt.). A spatial trend of higher MeHg levels in western compared to eastern Arctic belugas and ringed seals was found which followed a similar trend observed for total mercury. Factors which could explain this trend are discussed. Robust linear regression of MeHg on total Hg and MeHg on age of animals was performed and a strong correlation between the two variables was found in each case. The ratio of MeHg to total mercury as indicated by the regression coefficients was close to one for muscle and skin (muktuk) while for liver it was < 1. The mean percentage of MeHg in the liver of marine mammals was 3-12% of the total Hg in this tissue depending on species and location. It is postulated that the formation and deposition of mercuric selenide in the liver is part of the demethylation process in this tissue. This is based on the relatively low fraction of MeHg in the liver not withstanding the fact that the predominant form of mercury taken up via food is MeHg. The long half-life for total mercury and the relatively short half-life for MeHg in this organ are in accord with this postulate as is the 1:1 stoichiometric relationship between mercury and selenium in the liver.