Angewandte
Chemie
DOI: 10.1002/anie.201406216
Drug Delivery
Cell-Mediated Assembly of Phototherapeutics**
Weston J. Smith, Nathan P. Oien, Robert M. Hughes, Christina M. Marvin, Zachary L. Rodgers,
Junghyun Lee, and David S. Lawrence*
[
4]
Abstract: Light-activatable drugs offer the promise of con-
trolled release with exquisite temporal and spatial resolution.
However, light-sensitive prodrugs are typically converted to
their active forms using short-wavelength irradiation, which
displays poor tissue penetrance. We report herein erythrocyte-
mediated assembly of long-wavelength-sensitive photothera-
peutics. The activating wavelength of the constructs is readily
preassigned by using fluorophores with the desired excitation
sible for the intense interest in two-photon and up-convert-
[
5]
ing
reviews,
technologies. However, as discussed in recent
both technologies must overcome daunting chal-
lenges before potential therapeutic applications are realized.
[
4,5]
We recently described the long-wavelength (> 600 nm) pho-
[
6]
tolysis of alkylcobalamins (alkyl-Cbl). We now report the
cell-mediated assembly of lipid-Cbl-drug and lipid-fluoro-
phore conjugates in which the latter serve as long-wave-
length-capturing antennas that promote drug release.
wavelength l . Drug release from the erythrocyte carrier was
ex
confirmed by standard analytical tools and by the expected
biological consequences of the liberated drugs in cell culture:
methotrexate, binding to intracellular dihydrofolate reductase;
colchicine, inhibition of microtubule polymerization; dexame-
thasone, induced nuclear migration of the glucocorticoid
receptor.
Erythrocytes have been called the “champions of drug
delivery” due to their biocompatibility, their long lifespan
(120 days), and their size, which allows large quantities of
[7]
drug to be conveyed relative to other carriers. However,
“practically useful controlled release from carrier RBC (red
[
7]
blood cells) remains an elusive goal”. Our strategy to
address this issue is depicted in Figure 1. Based on a previ-
T
he use of light to activate therapeutic agents at disease sites
offers the advantage of aggressive treatment with exquisite
spatial control, thereby reducing potential deleterious side
effects at unintended sites. An excellent example of this
concept is photodynamic therapy, which employs the delivery
[
1]
of a photosensitizer to the tissue of interest. Upon excitation
with the appropriate wavelength of light and, in the presence
of oxygen, cytotoxic reactive oxygen species are generated,
resulting in destruction of the target cells. This minimally
invasive procedure furnishes control over where and when the
reactive oxygen species are produced. However, a more
general strategy that can control the delivery of any drug
could profoundly influence the treatment of a variety of
disorders, including cancer, diabetes, and autoimmune and
vascular diseases. A major challenge in this regard is the so-
called “optical window of tissue”, the wavelength of light with
maximal tissue penetration, which lies in the range of 600–
Figure 1. A wavelength-encoded drug-release strategy. Anti-inflamma-
tory drugs are covalently appended to Cbl by means of a photolabile
CoÀC bond. Lipidated-Cbl and fluorophore constructs assemble on the
[
2]
plasma membrane of human erythrocytes. The fluorophore serves as
an antenna, capturing long-wavelength light and transmitting the
energy to the Cbl-drug conjugate, resulting in drug release from the
erythrocyte carrier.
9
00 nm. Wavelengths less than 600 nm are absorbed by
hemoglobin in the circulatory system and melanin in the skin,
whereas water interferes with light penetration for wave-
lengths greater than 900 nm. Unfortunately, nearly all light-
activatable prodrugs described to date respond to short-
[3]
wavelength irradiation < 450 nm. This limitation is respon-
ously demonstrated energy transfer between fluorophores
and Cbls in covalently appended Cbl-fluorophore conju-
[
6]
gates, we decided to explore the premise that the cell-
mediated assembly of C -Cbl-drug and C -fluorophore
[*] W. J. Smith, N. P. Oien, Dr. R. M. Hughes, C. M. Marvin,
1
8
18
Z. L. Rodgers, J. Lee, Prof. D. S. Lawrence
conjugates could act in concert as a photoresponsive drug-
delivery system. Illumination of the fluorophore antenna at its
lmax and subsequent energy transfer to the Cbl-drug moiety
Department of Chemistry, Division of Chemical Biology and
Medicinal Chemistry, and Department of Pharmacology
University of North Carolina, Chapel Hill, NC 27599 (USA)
E-mail: lawrencd@email.unc.edu
[
6,8]
should result in cleavage of the weak CoÀC bond,
thereby
liberating the drug.
[
**] We thank the NIH for financial support (R01 CA79954) and Prof.
Melanie Priestman for assistance with the imaging experiment in
the Supporting Information, Figure S8.
A series of lipidated Cbl (C -Cbl) and C -fluorophore
18
18
derivatives were prepared (Figure 2; Figures S1–S4,
Tables S3–S6, and Scheme S1 in the Supporting Information
(SI)). In the case of the Cbl derivatives, the C18 moiety was
Angew. Chem. Int. Ed. 2014, 53, 10945 –10948
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
10945