2 research outputs found
The Myeloablative Drug Busulfan Converts Cysteine to Dehydroalanine and Lanthionine in Redoxins
The myeloablative agent busulfan
(1,4-butanediol dimethanesulfonate)
is an old drug that is used routinely to eliminate cancerous bone
marrow prior to hematopoietic stem cell transplant. The myeloablative
activity and systemic toxicity of busulfan have been ascribed to its
ability to cross-link DNA. In contrast, here we demonstrate that incubation
of busulfan with the thiol redox proteins glutaredoxin or thioredoxin
at pH 7.4 and 37 °C results in the formation of putative <i>S</i>-tetrahydrothiophenium adducts at their catalytic Cys residues,
followed by β-elimination to yield dehydroalanine. Both proteins
contain a second Cys, in their catalytic C-X-X-C motif, which reacts
with the dehydroalanine, the initial Cys adduct with busulfan, or
the <i>S</i>-tetrahydrothiophenium, to form novel intramolecular
cross-links. The reactivity of the dehydroalanine (DHA) formed is
further demonstrated by adduction with glutathione to yield a lanthionine
and by a novel reaction with the reducing agent tris(2-carboxyethyl)phosphine
(TCEP), which yields a phosphine adduct via Michael addition to the
DHA. Formation of a second quaternary organophosphonium salt via nucleophilic
substitution with TCEP on the initial busulfan-protein adduct or on
the THT<sup>+</sup>-Redoxin species is also observed. These results
reveal a rich potential for reactions of busulfan with proteins <i>in vitro</i>, and likely <i>in vivo</i>. It is striking
that several of the chemically altered protein products retain none
of the atoms of busulfan, in contrast to typical drug-protein adducts
or traditional protein modification reagents. In particular, the ability
of a clinically used drug to convert Cys to dehydrolanine in intact
proteins, and its subsequent reaction with biological thiols, is unprecedented