Angewandte
Chemie
DOI: 10.1002/anie.201406577
Cancer Sensitization
Hot Paper
A Small Molecule Inhibits Protein Disulfide Isomerase and Triggers the
Chemosensitization of Cancer Cells**
Jꢀrgen Eirich, Simone Braig, Liliana Schyschka, Phil Servatius, Judith Hoffmann,
Sabrina Hecht, Simone Fulda, Stefan Zahler, Iris Antes, Uli Kazmaier, Stephan A. Sieber,* and
Angelika M. Vollmar*
Abstract: Resistance to chemotherapeutic agents represents
a major challenge in cancer research. One approach to this
problem is combination therapy, the application of a toxic
chemotherapeutic drug together with a sensitizing compound
that addresses the vulnerability of cancer cells to induce
apoptosis. Here we report the discovery of a new compound
class (T8) that sensitizes various cancer cells towards etoposide
treatment at subtoxic concentrations. Proteomic analysis
revealed protein disulfide isomerase (PDI) as the target of
the T8 class. In-depth chemical and biological studies such as
the synthesis of optimized compounds, molecular docking
analyses, cellular imaging, and apoptosis assays confirmed the
unique mode of action through reversible PDI inhibition.
significant homology. PDI catalyzes thiol–disulfide exchange
reactions of both intra- and intermolecular disulfides.[4] The
role of this enzyme in diseases reaches far beyond cancer and
was recently reviewed in detail.[5] Although several inhibitors
were published in recent years[6–12] the most specific com-
pounds—16F16, RB-11-ca, PACMA 31, and P1—exhibit
a pharmacologically less desired irreversible mode of action.
Here we introduce reversible and highly specific PDI
inhibitors that sensitize tumor cells towards classical chemo-
therapeutic agents.
The screening of a commercial compound library for the
chemosensitization of etoposide-induced apoptosis in various
cancer cell lines revealed T8 as a promising candidate. The
combination of subtoxic concentrations of etoposide (500 nm)
and T8 dose-dependently led to pronounced apoptosis rates
with a minimal concentration of 25 mm T8 in a leukemic
(Jurkat) as well as in a breast cancer cell line (MDA-MB-231)
(Figure 1A). In addition, the long-term survival of Jurkat cells
was synergistically inhibited after treatment with a combina-
tion of etoposide and T8 (Figure 1B). Growth of various
carcinoma cell lines such as LNCAP (prostate cancer),
PancTu1, and L3.6pl (pancreas cancer) was also strongly
affected by the combined treatment with other chemother-
apeutic drugs such as doxorubicin or TRAIL and T8
(Figures S1 and S2). In contrast, noncancerous human
endothelial cells (HUVEC) did not respond to T8 in
combination with etoposide or doxorubicin (Figure S3).
T
he resistance of tumor cells to drugs results from numerous
genetic and epigenetic changes.[1] Cancer cells by nature
require increased protein synthesis and thus respond to
endoplasmic reticulum (ER) stress by activating the unfolded
protein response (UPR) which is mediated by ER chaperones
such as protein disulfide isomerase (PDI).[1c,2]
As ER chaperones maintain ER homeostasis and support
cancer cell survival, interest has emerged in targeting these
proteins to fight chemoresistance. In this respect PDI has
received increasing attention and the crystal structures of the
human full-length protein have recently been published.[3]
The isomerase is organized in four distinct domains (a, a’ and
b, b’). The a and a’ domains are catalytically active and share
[*] Dr. J. Eirich,[$] [+] Prof. Dr. I. Antes, Prof. Dr. S. A. Sieber
Center for Integrated Protein Science Munich CIPSM
Department of Chemistry, Institute of Advanced Studies IAS
Technische Universitꢀt Mꢁnchen
S. Hecht, Prof. Dr. I. Antes
Department of Life Sciences, Technische Universitꢀt Mꢁnchen
Emil-Erlenmeyer-Forum 8, 85354 Freising-Weihenstephan
(Germany)
[$] Current address: Department of Oncology/Pathology
Lichtenbergstrasse 4, 85747 Garching (Germany)
E-mail: stephan.sieber@tum.de
Dr. S. Braig,[+] Dr. L. Schyschka, Prof. Dr. S. Zahler,
Prof. Dr. A. M. Vollmar
Cancer Proteomics Mass Spectrometry
SciLifeLab Stockholm, Karolinska Institutet
Tomtebodavꢀgen 23, 17165 Solna (Sweden)
[+] These authors contributed equally to this work.
Department of Pharmacy, Center for Drug Research
Pharmaceutical Biology, Ludwig-Maximilians-Universitꢀt Mꢁnchen
Butenandtstrasse 5–13, 81377 Mꢁnchen (Germany)
E-mail: angelika.vollmar@cup.uni-muenchen.de
[**] We thank Mona Wolff, Katja Bꢀuml, and Burghard Cordes for
excellent scientific support, Dr. Stuppner and Dr. Langner (Univer-
sity of Innsbruck) for collaboration. S.A.S. was supported by the
Deutsche Forschungsgemeinschaft (SFB749, SFB1035, and
FOR1406), an ERC starting grant, and the Center for Integrated
Protein Science Munich CIPSM, J.E. thanks the TUM Graduate
School and A.M.V. thanks the DFG and the Wilhelm Sander
Foundation.
P. Servatius, J. Hoffmann, Prof. Dr. U. Kazmaier
Institute for Organic Chemistry, Saarland University
Im Stadtwald, Geb. C4.2, 66123 Saarbrꢁcken (Germany)
Prof. Dr. S. Fulda
Institute for Experimental Cancer Research in Pediatrics
University Hospital Frankfurt
Supporting information for this article (synthesis and character-
ization of compounds, bioassays, cell biology as well as proteome
preparation, labeling, and mass spectrometry) is available on the
Komturstrasse 3a, 60528 Frankfurt a. M. (Germany)
Angew. Chem. Int. Ed. 2014, 53, 1 – 7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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