Communications
doi.org/10.1002/ejoc.202100241
Synthesis and Biological Evaluation of an isoDGR-Paclitaxel
Conjugate Containing a Cell-Penetrating Peptide to
Promote Cellular Uptake
[
a]
[a]
[a]
[b]
[b]
[a]
[a]
Dedicated to Prof. Franco Cozzi on the occasion of his 70th Birthday.
Two new Drug Delivery Systems (DDS) cyclo[DKP-isoDGR]-PEG-
most successful strategies used for reducing unwanted side
[2]
[3]
4
-Val-Ala-PTX (2) and cyclo[DKP-isoDGR]-PEG-4-sC18-Val-Ala-PTX
effects. Among the high number of developed systems,
antibody-drug conjugates (ADCs) have become a successful
(
3), containing the cyclo[DKP-isoDGR] integrin ligand and the
[
4]
cytotoxic agent Paclitaxel (PTX), were synthesized to investigate
the influence of a PEG-4 chain and of the sC18 cell-penetrating
peptide (CPP) on the cellular uptake and the cytotoxicity of the
constructs. A “double click-reaction strategy” was planned, to
realize the connection of cyclo[DKP-isoDGR] and PTX to the CPP
moiety. Anti-proliferative bioassays were performed on the
α β -positive U87 human glioblastoma cell line using a short
approach for the treatment of many neoplastic conditions. In
these systems, a potent antitumor drug is linked through a
cleavable linker to an antibody that selectively binds a surface
receptor overexpressed in cancer cells. Upon the ligand-
receptor binding and the cleavage of the linker through
external stimulus, the cytotoxic compound is released and
accumulated at the tumor site, preventing its distribution into
V
3
[5]
contact time (15 min) followed by draining, washing of the cells,
and re-incubation for 72 h. Compound 3 was significantly more
potent (IC =27.6 μM) than compound 2 (IC >100 μM), and
healthy tissues. Subsequently, low-molecular-weight com-
pounds were also exploited as ligands to improve some
drawbacks of ADCs, such as costs of antibody production, poor
pharmacokinetics, and immunogenicity, giving rise to the so-
50
50
showed a reduced potency loss with respect to PTX (IC =
5
0
[6]
7
1 nM).
called small-molecule drug conjugates (SMDCs).
Among the suitable receptors for targeted drug-delivery,
integrins, a class of transmembrane proteins, have received
special attention because of their overexpression on the cell
surface of many types of tumor, such as glioblastoma, renal cell
Safety and efficacy are the fundamental features that a drug
candidate requires to be approved by regulatory systems. In the
quest of new treatments, scientists often encounter very potent
and promising new compounds that unfortunately present very
high toxicity towards healthy tissues, and low in vivo efficacy
due to poor pharmacokinetics. Drug-delivery technologies play
[7]
carcinoma, melanoma, and others.
These heterodimeric
proteins, especially α β , and α β , are involved in several
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3
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biological pathways including cell cycle and angiogenesis, and
they exploit their signaling pathways after internalization into
endosomes upon binding to endogenous ligands. The fact that
integrins recognize their natural ligands by the Arg-Gly-Asp
[1]
a pivotal role in overcoming these obstacles, and the selective
delivery of drugs to the target pathological cells is one of the
[8]
[9]
(
RGD) and isoAsp-Gly-Arg (isoDGR) sequences opened the
way to the design and development of high-affinity integrin
ligands containing these motifs for selective targeting of cancer
[
a] Dr. L. Bodero, Dr. S. Parente, F. Arrigoni, Dr. S. Gazzola, Prof. Dr. U. Piarulli
Dipartimento di Scienza e Alta Tecnologia,
Università degli Studi dell’Insubria,
Via Valleggio 11, 22100 Como, Italy
E-mail: s.gazzola@uninsubria.it
[10]
cells. Later on, several SMDCs bearing those ligands bound to
[11]
cytotoxic agents were reported in the literature. However, the
integrin-mediated endocytosis, which would allow the effective
delivery of such compounds inside the cells, has not been
completely elucidated as different mechanisms of internal-
ization have been proposed. For instance, monomeric integrin
ligands would enter the cell through a fluid phase endocytic
pathway independent of the α β receptor, while multimeric
b] Dr. A. Klimpel, Prof. Dr. I. Neundorf
University of Cologne, Department of Chemistry,
Institute for Biochemistry
Zuelpicher Str. 47a, 50674 Cologne, Germany
[
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3
ligands can cross-link multiple receptors and are internalized via
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clathrin-mediated endocytosis.
Recently, our group has
[13]
[14]
developed cyclic RGD and isoDGR peptidomimetics con-
taining a diketopiperazine (DKP) scaffold as low nanomolar and
selective αVβ3 integrin ligands, which were subsequently
©
2021 The Authors. European Journal of Organic Chemistry published by
Wiley-VCH GmbH. This is an open access article under the terms of the
Creative Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly cited.
,
[15,16]
[17]
conjugated to paclitaxel (PTX)
, α-amanitin and auristatin
[18]
derivatives through the lysosomally cleavable linker Val-Ala.
Eur. J. Org. Chem. 2021, 2383–2387
2383
© 2021 The Authors. European Journal of Organic Chemistry
published by Wiley-VCH GmbH