Tumor pH-responsive flower-like micelles of poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(l-histidine)

Abstract

Polymeric micelles were constructed from poly(L-lactic acid) (PLA; M n 3K)-b-poly(ethylene glycol) (PEG; M n 2K)-b-poly(L-histidine) (polyHis; M n 5K) as a tumor pH-specific anticancer drug carrier. Micelles (particle diameter: ~ 80 nm; critical micelle concentration (CMC): 2 µg/ml) formed by dialysis of the polymer solution in dimethylsulfoxide (DMSO) against pH 8.0 aqueous solution, are assumed to have a flower-like assembly of PLA and polyHis blocks in the core and PEG block as the shell. The pH-sensitivity of the micelles originates from the deformation of the micellar core due to the ionization of polyHis at a slightly acidic pH. However, the co-presence of pH-insensitive lipophilic PLA block in the core prevented disintegration of the micelles and caused swelling/ aggregation. A fluorescence probe study showed that the polarity of pyrene retained in the micelles increased as pH was decreased from 7.4 to 6.6, indicating a change to a more hydrophilic environment in the micelles. Considering that the size increased up to 580 nm at pH 6.6 from 80 nm at pH 7.4 and that the transmittance of micellar solution increased with decreasing pH, the micelles were not dissociated but rather swollen/aggregated. Interestingly, the subsequent decline of pyrene polarity below pH 6.6 suggested re-self-assembly of the block copolymers, most likely forming a PLA block core while polyHis block relocation to the surface. Consequently, these pH-dependent physical changes of the PLA-b-PEG-b-polyHis micelles provide a mechanism for triggered drug release from the micelles triggered by the small change in pH (pH 7.2-6.5).

Super pH-sensitive multifunctional polymeric micelle for tumor pHe specific TAT exposure and multidrug resistance

“…Next, the protecting (benzyl) group of polyHis was deprotected using sodium and liquid ammonia as described before [21]. [24,25]. The micellar solution was lyophilized.…”

“…/min) at 37 °C. The measurement of DOX concentration in micelles was performed with a UV/visible spectrophotometer as described previously [24,25].…”

“…Fluorescein uptake (% FITC uptake) was measured by assaying the cell lysate using static fluorescence measurements (excitation and emission wavelengths of 488 and 520 nm, respectively), based upon a standard curve of fluorescence intensity of free TAT (FITC) with concentration. All fluorescence intensities were normalized to total cell protein (g) calculated from a standard BCA protein assay kit (Gibco) [24,25]. Furthermore, PHSM without TAT was investigated as a control group.…”

“…The pH of the culture medium was adjusted to each corresponding pH during the assay as described before [24,25]. Cell cytotoxicity as measured using the MTT assay [24,25].…”

“…The pH of the culture medium was adjusted to each corresponding pH during the assay as described before [24,25]. Cell cytotoxicity as measured using the MTT assay [24,25]. Cell viability (%) was calculated by dividing number of live cells (after being treated with DOX or DOX-loaded micelles) with number of live cells (existing in drug-free culture medium) at each pH after 48-hour incubation.…”