Development of ultra-sensitive single molecule immunoassays for the intracellular kinases Akt1/pAkt1 and Erk2/pErk2 for small tissue studies

e22068

Background: The Ras/Raf/MEK/ERK and PI3K/PTEN/AKT kinase cascades are critical pathways in malignant transformation, tumor progression and multi-drug resistance (MDR) in human cancers. Expression and genetic studies have contributed much to our understanding of this role, but further clinical investigations at the post-transcriptional level are necessary. Towards this end, Singulex has developed single molecule immunoassays for total Akt1, pAkt1, total Erk2 and pErk2 utilizing the Erenna Immunoassay System for use in small tissue studies and clinical trials. Methods: Analytical sensitivity, inter- assay precision, linearity and specificity were determined and compared to corresponding ELISA assays. Novel assays were tested on lysates from a variety of commonly utilized cell lines in cancer studies: MCF-7, PBMC, Jurkat, HeLa, and NIH3T3 cells. Results: All four novel assays were significantly more sensitive than the ELISA assay method based upon sample endpoint dilutions. Acceptable precision (<20%CV) was demonstrated for the Akt1/pAkt1 assays in PBMC lysates and for the Erk2/pErk2 assays in MCF-7, HeLa and NIH3T3 lysates. The LLoQ of the Akt1/pAkt1 assay in Jurkat lysates was sufficient to quantify Akt1/pAkt1 from as few as 10–20 cells. Based upon a typical 1mm needle biopsy, this is sufficient to quantify Akt1/pAkt1 from less than 1/1000th of that biopsy. Conclusions: We show that the Singulex Akt1, pAkt1, Erk2 and pErk2 assays are over 50 fold more sensitive than currently available ELISA assays, and specifically quantify analyte in a variety of cell lysates. We have further demonstrated that the Akt1/pAkt1 assay can quantify from as little as 1/1000th of a typical needle biopsy. Thus, these novel assays greatly improve upon pre- existing technology, providing a new tool for clinical trials investigating Ras/Raf/MEK/ERK and PI3K/PTEN/AKT pathways previously limited by ELISA sensitivity.

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In situ staining for poly(ADP-ribose) polymerase activity using an NAD analogue

Poly(ADP-ribose) polymerase (PARP) is a highly abundant nuclear enzyme which metabolizes NAD, in response to DNA strand breakage, to produce chains of poly(ADP-ribose) attached to nuclear proteins. PARP activation has been implicated in ischemia/reperfusion injury, but its biological significance is not fully understood. We have modified an existing in situ method for detection of PARP activity by using an NAD analogue in which adenine is modified by an "etheno" (vinyl) bridge. Etheno-NAD serves as a PARP substrate in an initial enzymatic reaction; a specific antibody to ethenoadenosine is then used in an immunohistochemical reaction to detect the production of modified poly(ADP-ribose). The method produces strong and specific labeling of nuclei in which PARP has been activated, i.e., those in which DNA strand breaks have been produced, and the results can be analyzed by microscopy, flow cytometry, or colorimetry. The method is applicable to cultured cells in several formats and to frozen tissue sections. The particular characteristics of the new method may assist in future in situ studies of PARP activation.