Abstract 3508: A diazirine-based photoaffinity etoposide probe for labeling topoisomerase II
Bibliographic record
Abstract
Abstract Etoposide is a widely used anticancer drug that targets topoisomerase II, an essential nuclear enzyme. However, despite the fact that it has been in use and studied for more than 30 years the specific site on the enzyme to which it binds is unknown. In order to identify the etoposide binding site(s) on topoisomerase II, a diazirine-based photoaffinity etoposide analog probe has been synthesized and its photoreactivity and biological activities have been characterized. Upon UV irradiation, the diazirine probe rapidly produced a highly reactive carbene species that formed covalent adducts containing stable carbon-based bonds indicating that it should also be able to form stable covalent adducts with amino acid residues on topoisomerase II. The human leukemia K562 cell growth and topoisomerase II inhibitory properties of the diazirine probe suggest that it targets topoisomerase II in a manner similar to etoposide. The diazirine probe was also shown to act as a topoisomerase II poison through its ability to cause topoisomerase IIα-mediated double-strand cleavage of DNA. Additionally, the diazirine probe significantly increased protein-DNA covalent complex formation upon photoirradiation of diazirine probe-treated K562 cells, as compared to etoposide-treated cells. This result suggests that the photoactivated probe forms a covalent adduct with topoisomerase IIα. In conclusion, the present characterization of the chemical, biochemical, and biological properties of the newly synthesized diazirine-based photoaffinity etoposide analog indicates that use of a proteomics mass spectrometry approach will be a tractable strategy for future identification of the etoposide binding site(s) on topoisomerase II through covalent labeling of amino acid residues. This work was supported by institutional grants from the University of Manitoba, Canadian Institutes of Health Research, National Institutes of Health grant CA090787 to J.C.Y. and a Canada Research Chair for Drug Development for B.B.H 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 3508.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".