Cell‐Mediated Assembly of Phototherapeutics

Abstract

Light-activatable drugs offer the promise of controlled release with exquisite temporal and spatial resolution. However, light sensitive pro-drugs are typically converted to their active forms using short wavelengths, which display poor tissue penetrance. We report herein erythrocyte-mediated assembly of long wavelength-sensitive phototherapeutics. The activating wavelength of the constructs is readily pre-assigned by using fluorophores with the desired λ ex . Drug release from the erythrocyte carrier was 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; dexamethasone, induced nuclear migration of the glucocorticoid receptor. KeywordsPhotochemistry; Drug Delivery; Cobalamins; Pro-drugs The 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 of a photosensitizer to the tissue of interest. [1] 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 socalled "optical window of tissue", the wavelength of light that enjoys maximal tissue penetration, which lies in the range of 600 -900 nm. [2] Wavelengths less than <600 nm are absorbed by hemoglobin in the circulatory system and melanin in the skin whereas water interferes with light penetrance >900 nm. Unfortunately, nearly all light-activatable prodrugs described to date respond to short wavelengths <450 nm. [3] This limitation is responsible for the intense interest in two-photon [4] and up converting [5] technologies. However, as discussed in recent reviews, [4][5] both technologies must overcome daunting challenges before potential therapeutic applications are realized. We recently described the long wavelength (>600 nm) photolysis of alkylcobalamins (alkyl-Cbl). [6] We now report the cell-mediated assembly of lipid-Cbl-drug and lipid-fluorophore conjugates in which the latter serve as long wavelength-capturing antennas that promote drug release.Erythrocytes have been called the "champions of drug delivery" due to their biocompatibility, their long life span (120 days), and their size, which allows large quantities of drug to be conveyed relative to other carriers. [7] However, "practically useful controlled release from carrier RBC (red blo...

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“…By contrast, we found that photohomolysis of RCH 2 -Co(III)Cbl primarily generates the alkyl, RCH 3 , product under cell culture conditions. 44 It struck us as unlikely that attaching Cbl to “essential” methyl groups in biologically active compounds would serve as a general method for preparing light-activatable species. Initially, we wondered whether the steric bulk of the corrin ring might be sufficient to provide biological camouflage, precluding the interaction of inhibitors, activators, or sensors with their biological targets.…”

“…44 We decided to focus on anti-inflammatory drugs based on their role in treating arthritis. Long-term use of anti-inflammatory agents can and does result in moderate to severe side effects.…”

“…44 Lipidated fluorophores serve as antennas, capturing the desired wavelength, which is then used to mediate drug release. The mechanism of “energy transfer” from antenna to drug–Cbl is currently under investigation.…”

“…The mechanism of “energy transfer” from antenna to drug–Cbl is currently under investigation. Reproduced with permission from ref 44. Copyright 2014 John Wiley & Sons, Inc.…”

“…44 (a) HeLa cells incubated (in the dark) in the presence of erythrocytes containing the Dex conjugate 18 and the Cy5 antenna 19 . HeLa cells are stained for the Dex receptor, GRα, which is cytoplasmic in the absence of Dex.…”