The isolation of new molecules from marine sources opens the door to their possible therapeutic use against tumors and other pathological conditions. Indeed, we recently defined the cytotoxicity of ES 285, obtained from the clam Mactromeris polynima, and its affects on the cells microfilament but not the microtubule network. Considering the analogy between ES 285 and sphingosine-related lipids, we wondered whether ES 285 might affect the activity of PKC at the intracellular level. While we anticipated that ES 285 might inhibit PKC, it turns out that in contrast it serves to activate PKC at the cellular level. Indeed, like other sphingosine-related lipids, ES 285 induces the phosphorylation of MARCKS. Additionally, we further examined the cytotoxicity of ES 285 to elucidate the molecular mechanisms through which this compound triggers apoptosis. When the influence of ES 285 on "cell death markers" was assessed, it became clear that ES285 activates caspase 3 and 12, and that it modified the phosphorylation of p53. In contrast, ES 285 does not affect other pathways widely implicated in regulating cell survival/apoptosis, such as JNK, Erks or Akt. Thus, these data suggest that ES 285-triggers an atypical cell death program when compared to other sphingosine-dependent apoptosis pathways.

The HIF signaling pathway is a crucial way in which tumors can circumvent the constraints of regions of low oxygen (hypoxia) to induce angiogenesis and maintain proliferation. The oxygen regulated subunit of the transcription factor hypoxia-inducible factor 1 (HIF1), HIF1αlpha, is a positive factor in tumor growth and its expression has been correlated with poor patient prognosis in a number of settings. We here present in vitro and in vivo data for a novel series of orally available small-molecule HIF signaling modulators that show nanomolar inhibition of the HIF signaling pathway in addition to potent anti-proliferative activity against a large number of cell lines derived from solid and blood tumors (EC50 in the range 1-100nM). Phenotypically, the compounds elicit an initial G2/M arrest, followed by the induction of caspase-3/7 and the onset of apoptosis. The in vitro results also translate into in vivo animal models. The lead compounds from the series show efficacy in tumor xenograft mouse models, with dose-dependent tumor growth inhibition of 60-70% after oral dosing (MDA-MB-231 xenograft). Structural optimisation has additionally allowed us to improve the PK and physicochemical characteristics of the compounds, with a lead candidate currently in formal pre-clinical development with the aim of entering a Phase 1 clinical trial in multiple myeloma at the end of 2010. In conclusion, we believe that the development towards clinical Proof-of-Concept of this new class of dual-mechanism inhibitors of HIF signaling and cell proliferation presents a promising new option for cancer therapeutics. 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 LB-294.

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