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 λex. 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.

B12-Mediated, Long Wavelength Photopolymerization of Hydrogels

“…33 For our initial studies, we chose ethyl-cobalamin (EtCbl) due to its reported high quantum yield of photohomolysis (~0.3), 32 but it may be possible to use other primary alkyl ligands, such as aminopropyl, for dual photopolymerization and functionalization of hydrogels. 30,31 The EtCbl-ethylenediamine 5 intermediate is derived from Zn-mediated reduction of 4 to a supernucleophilic Co I species and subsequent alkylation with ethyl bromide. 34 Photoinitiator 1 ( ε ~ 8500 M −1 cm −1 , λ max ~ 510 nm, Figure 1) was prepared by reacting the free amine of 4 with acetic anhydride.…”

“…29 Recently, we reported the NIR induced scission of weak cobalt–carbon bonds present in vitamin B 12 -derived alkyl-cobalamins (Co–C; bond dissociation energy ~ 30 kcal/mol). 30,31 Normally, excitation of unmodified alkyl-cobalamins ( λ ex ~ 510 nm) induces a metal-to-ligand charge transfer that decays to a dissociative alkyl radical and cobalt(II) species with high quantum yields (Φ ~ 20–40%). 32 However, despite lacking absorption longer than 600 nm, alkyl-cobalamin photolysis in the red, far red, and NIR can be achieved by excitation of covalently linked or noncovalently associated fluorophores.…”

Phototriggered Secretion of Membrane Compartmentalized Bioactive Agents

“…[6] B12 is not membrane permeable, but rather is transported into cells via a sophisticated protein carrier, receptor-mediated, endosome-dependent mechanism. [7] We wondered whether Cbl-bioagent conjugates might retain the membrane impermeability properties of the parent B12 and thus could be ensconced within lipid-enclosed compartments until needed.…”

“…Previously, we’ve shown that the light responsiveness of Cbl conjugates can be tuned to specific wavelengths deep into the red, far red, and near IR. [6b] These wavelengths penetrate tissue more effectively than UV and short visible wavelengths, a decided advantage under in vivo conditions. [8] With these features in mind, we chose the interior of erythrocytes as a membrane enclosed environment to explore the conjecture that illumination can be used to control the secretion of biologically active compounds (Figure 1).…”

“…We’ve previously shown that Co-C photolysis can be induced by red, far red, or near IR light using Cbl derivatives possessing appended long wavelength, light-harvesting fluorophores. [6b] Given the unique excitation wavelengths of individual fluorophores, we investigated whether specific agents could be released from erythrocytes in a wavelength-designated fashion.…”