XXII. BIOCHEMICKÝ ZJAZD - Jesseniova lekárska fakulta

Lectures
OrIGIN of aCQUIrED rESISTaNCE TO CYTOTOXIC aCYCLIC
NUCLEOSIDE PHOSPHONaTES
Helena Mertlíková-Kaiserová, Antonín Holý and Ivan Votruba
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech
Republic, Gilead Sciences & IOCB Research Center, 166 10 Prague, Czech Republic
Acquired resistance to chemotherapy upon repeated administration of the cytotoxic drugs
remains a serious clinical issue. Disclosing the mechanisms that lead to its development is
necessary for introduction of successful prevention/reversal strategies. In our laboratory,
we have prepared CCRF-CEM leukemic cells resistant to high concentrations of cytotoxic
nucleotide analogs PMEG and PMEDAP. Employing [8- 3 H] radiolabeled compounds we
aimed to describe changes in membrane transport and/or intracellular metabolism of
the compounds. We found that the uptake of both PMEG and PMEDAP was unaffected in
resistant cells. The resistance is therefore not due to decreased intracellular concentrations
of the parent compounds. However, their metabolites PMEG/PMEDAP phosphate
and PMEG/PMEDAP diphosphate were only present in sensitive but not resistant cells.
As only the latter two can be incorporated into the DNA and act as chain terminators it
is clear that the origin of resistance lies in the phosphorylation step catalyzed by relevant
nucleoside monophosphate kinases - guanylate kinase (GUK) for PMEG and mitochondrial
adenylate kinase (AK2) for PMEDAP. Expression of these proteins was indeed decreased
in resistant cells. It is possible that apart from lower amount of GUK and AK2 protein,
catalytic activity of these enzymes might also be affected. This will further be explored.
Acknowledgments: Research project of the IOCB #OZ40550506; Project #1M0508 by the
Ministry of Education, Youth and Sports of the Czech Republic.
XXII. Biochemistry Congress, Martin
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