Enzyme-Responsive Theranostic FRET Probe Based on l-Aspartic Amphiphilic Polyester Nanoassemblies for Intracellular Bioimaging in Cancer Cells

Abstract

The present study reports one of the first attempts on the design and development of an enzymatic-biodegradable theranostic fluorescence resonance energy transfer (FRET) probe constructed on l-amino acid polymer nanoassemblies and demonstrates the proof-of-concept in live cell bioimaging. l-Aspartic acid was converted into amide or carbamate pendants containing bis-carboxylic acid ester monomers, and they were subjected to melt polymerization along with commercial diols to produce amphiphilic aliphatic polyesters. Nanoparticles of size <200 nm were obtained because of self-assembly of these amphiphilic polyesters in an aqueous medium. These nanoparticles exhibited excellent encapsulation capability for green-fluorescent anti-inflammatory drug curcumin (CUR) and highly luminescent red-fluorophore Nile red (NR) to yield a CUR-NR theranostic FRET probe. Detailed photophysical studies were carried out to demonstrate photoexcitation energy transfer from CUR to NR for the occurrence of the FRET phenomena. The theranostic FRET probe was found to be very stable at extracellular environment and underwent biodegradation at the intracellular regions for delivery of the loaded cargoes. As a result, the theranostic FRET probe functioned as turn-on at the extracellular level and became turn-off at the intracellular level under lysosomal enzyme-responsiveness. The polymer nanoparticle was nontoxic to cells, whereas its CUR encapsulated nanoparticle showed relatively good cytotoxicity in breast cancer cell lines. Live cell confocal microscopy studies using lysotracker staining confirmed the colocalization of CUR as well as NR within the polymer nanoparticles in the lysosomes for enzymatic-biodegradation. Selective photoexcitation experiments in the confocal microscope were carried out to study the FRET probe action in cancer cells. Time-dependent FRET imaging directly supported the occurrence of FRET at the intracellular level and enabled the real-time drug release studies. The present approach opens natural resource-based biodegradable theranostic FRET probes for bioimaging application.

Magnetoliposomes Incorporated in Peptide-Based Hydrogels: Towards Development of Magnetolipogels

“…The Förster resonance energy transfer (FRET) process between curcumin (energy donor) and Nile Red (energy acceptor) that has been used in different works as the spectral overlap between the Nile Red absorption and curcumin fluorescence is significant [ 9 , 11 , 30 ]. Figure 3 B–D display the FRET process between curcumin and Nile Red, as evidenced by the strong fluorescence emission of Nile Red, while exciting the curcumin dye (λ exc = 420 nm).…”

An AIE-driven fluorescent polysaccharide polymersome as an enzyme-responsive FRET nanoprobe to study the real-time delivery aspects in live cells

“…To elucidate the FRET phenomena in the P TPE+RB and P TPE+NR polymersomes, time-resolved fluorescence decay measurements were carried out by the time-correlated single photon counting (TCSPC) method to determine the Förster distance and FRET efficiencies following the reported procedures. [49][50][51][52] TCSPC decay profiles for P TPE+RB and P TPE+NR are shown in Fig. S9 in the ESI † (excitation LED source 340 nm).…”

“…A similar observation was reported by us recently in the FRET probes and DOX release kinetics of the biodegradable L-aspartic acid based polyester nano-assemblies. 52,53 Therefore, the decrease in the TPE emission with increasing incubation time is attributed to the above-mentioned enzymatic-disassembly of polymersomes followed by the clearance of the individual chains by the cell machinery. In Fig.…”

Smart materials for drug delivery and cancer therapy

“…Esters of carboxylic ester, phospholipids, 168 and acetylcholine 169 are vulnerable to specific enzymatic digestion and have been applied for fabricating materials sensitive to hydrolytic esterase. In the work of Saxena et al, self‐assembly nanoparticles of the L‑Aspartic amphiphilic polyester containing bis‐carboxylic acid ester monomers exhibited excellent encapsulation capability for curcumin and Nile red 170 . These curcumin and Nile red‐loaded nanoparticles performed the turn‐on theranostic fluorescence resonance energy transfer (FRET) probe function at the extracellular areas, but the turn‐off theranostic FRET probe function under the intracellular carboxylic ester hydrolase (CES) hydrolyzation.…”