# Novel Topoisomerase II alpha isoform as a drug resistance determinant

> **NIH NIH R01** · OHIO STATE UNIVERSITY · 2020 · $356,850

## Abstract

DNA Topoisomerase IIα (TOP2α; 170 kDa) is a prominent target for anticancer drugs whose clinical
efficacy is often compromised due to acquired chemoresistance. While mutant forms of TOP2α have been
reported in resistance models, evidence from patient samples strongly suggests that decreased levels of
TOP2α is the major determinant of drug resistance.
 We have reported that, in etoposide resistant human leukemia K/VP.5 cells, 170 kDa TOP2α (TOP2α/170)
was decreased compared to parental K562 cells, while a novel C-terminal truncated 90 kDa TOP2α isoform
(TOP2α/90) was dramatically increased. TOP2α/90 is the translation product of alternatively processed pre-
mRNA which retains intron 19; confirmed by 3'-rapid amplification of cDNA ends, PCR, and sequencing.
Intron 19 in TOP2α/90 mRNA harbors an in-frame stop codon, and two consensus poly(A) sites allowing for
the processed transcript to be polyadenylated. TOP2α/90 mRNA is translated to a protein missing the C-
terminal 770 amino acids of TOP2α/170 and lacks the active site Tyr805. TOP2α/90 contains 25 unique amino
acids through translation of the exon 19/intron 19 “read-through” allowing for antisera to be raised to detect
this isoform. Using this antisera and a C-terminal antibody to detect TOP2α/170, cellular experiments revealed
that TOP2α/90 co-immunoprecipitated with TOP2α/170. Forced expression of TOP2α/90 in K562 cells
suppressed while siRNA-mediated knockdown of TOP2α/90 in K/VP.5 cells enhanced etoposide-mediated
DNA strand breaks. Together, results strongly suggest that expression of TOP2α/90 is a determinant of
chemoresistance through a dominant negative effect related to heterodimerization with TOP2α/170.
 This background serves as the foundation for the hypothesis that a major mechanism of acquired
resistance to TOP2α-targeted drugs is due to alternative RNA processing/splicing. It is further hypothesized
that restoration of canonical RNA splicing will be capable of circumventing drug resistance. In order to test
these hypotheses two specific aims will be pursued to: 1) establish the role of TOP2α/90 as a determinant of
acquired resistance through its interaction with TOP2α/170; 2) determine the mechanism(s) of alternative RNA
processing of TOP2α pre-mRNA and develop tractable strategies to circumvent resistance.
 Successful completion of these Aims will have important impact in two areas. First, complete
characterization of alternative RNA processing of TOP2α will drive strategies to circumvent acquired drug
resistance. Results obtained may allow for tumor cell/biopsy evaluation of TOP2α/90 as a biomarker for drug
resistance, prognosis, and/or direct future TOP2α-targeted therapies. Second, our strategies will reveal
fundamental new information regarding spliceosome function as a process that may be utilized for regulating
the expression of TOP2α and/or other important anticancer drug targets known to be alternatively processed
as determinants of drug resistance.
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## Key facts

- **NIH application ID:** 9829545
- **Project number:** 5R01CA226906-02
- **Recipient organization:** OHIO STATE UNIVERSITY
- **Principal Investigator:** TERRY S ELTON
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $356,850
- **Award type:** 5
- **Project period:** 2018-12-01 → 2023-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9829545

## Citation

> US National Institutes of Health, RePORTER application 9829545, Novel Topoisomerase II alpha isoform as a drug resistance determinant (5R01CA226906-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9829545. Licensed CC0.

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