# DNA CROSSLINK REPAIR ENZYMES IN HUMAN CELLS

> **NIH NIH R01** · ST. JUDE CHILDREN'S RESEARCH HOSPITAL · 1992 · $138,967

## Abstract

There is compelling evidence that the response of human malignant
tumors to chemotherapy with bifunctional alkylating agents is
related to the extent of formation or rate of removal of DNA
interstrand crosslinks.  The hypothesis to be tested in the
proposed research is that reduction of crosslinking is mediated by
enzymic DNA repair processes.  The goal is to identify, isolate
and characterize the human-cell enzymes that may repair DNA
crosslinks or their precursors Immediate aims focus on crosslink
prevention by 06-alkylguanine-DNA alkyltransferase (GATase) in DNA
treated with the chloroethylnitrosoureas (CENUs).  GATase, purified
further from cultured human lymphoblasts or human liver, will be
used as a probe to define the molecular mechanism for crosslink
formation in DNA treated with CENUs and other classes of drug that
produce adducts at 06-guanine in DNA (e.g., clomesome,
mitozolomide, procarbazine, mitomycin C and cisplatin):  We shall
determine GATase activity in a variety of human tumor lines, in-
cluding tumors of the central nervous system, to establish the
relationship between cellular GATase levels and drug resistance.
Development of GATase-specific antibodies and cDNA probes should
eventually permit GATase levels to be readily determined in
clinical biopsy specimens. The in vitro methodologies that we have
developed for studying the CENUs and related drugs will be applied
to investigation of crosslink formation
and enzymic repair induced by other bifunctional alkylating agents
(e.g., cyclophosphamide, ifosfamide, mitomycin C and cisplatin).
Where necessary activated derivatives will be used.  DNA
interstrand crosslinking will be determined in vitro by measuring
the renaturability of isolated DNA with fluorometric, filter-
binding or electrophoretic methods.  Both purified human DNA repair
enzymes, such as alkylpurine-DNA glycosylase or GATase, and cruder
extracts from human cells will be assayed for activities that 1)
repair monoadduct precursors of crosslinks and 2) cleave existing
crosslinks. The ultimate goal of this research is to establish
correlations of repair enzyme activity, crosslink formation and
crosslink persistence with cytotoxicity and clinical response to
chemotherapy.  Such information should enable prediction of thera-
peutic response based on direct biochemical assay of repair enzyme
levels in tumor and normal tissues.  Intervention in these repair
processes by enzyme inhibition could provide a strategy for
overcoming drug resistance in cancer patients.

## Key facts

- **NIH application ID:** 3174492
- **Project number:** 5R01CA036888-08
- **Recipient organization:** ST. JUDE CHILDREN'S RESEARCH HOSPITAL
- **SAM.gov UEI:** JL4JHE9SDRR3
- **Principal Investigator:** THOMAS P BRENT
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1992
- **Award amount:** $138,967
- **Award type:** 5
- **Project period:** 1984-12-01 → 1993-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3174492

## Citation

> US National Institutes of Health, RePORTER application 3174492, DNA CROSSLINK REPAIR ENZYMES IN HUMAN CELLS (5R01CA036888-08). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/3174492. Licensed CC0.

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