2.5 Drug assay and release of DOX-loaded beta-CD nanocage
A series of standard DOX stock solutions were prepared, and a standard
curve was obtained by measuring the absorbance using a plate reader with
a 485 nm excitation filter and a 538 nm emission filter (Thermo
Scientific Fluoroskan Ascent FL). Based on the standard curve equation y
= 0.04464*x + 0.02131, the drug loading capacity of the beta-CD
nanocages was determined to be 37.5% using the formula: the beta-CD
nancage drug loading capacity=the loaded DOX content/( the loaded DOX
content+beta-CD nanocage content)*100%.
pH 4.5 PBS solution was used to mimic the acidic tumor microenvironment,
while a 5 mM GSH solution simulated the reductive tumor
microenvironment. pH 7.4 PBS solution was used to represent the normal
physiological environment. DOX-loaded beta-CD nanocages (20 mg) were
dissolved in each of these three types of solutions (1 ml) and poured
into separate Amicon centrifuge tubes. These tubes were then immersed in
larger tubes containing the respective release medium (5 ml) and placed
in an incubator shaker at 100 rpm at 37 °C. Aliquots were taken from the
release medium at predetermined time intervals, and an equal volume of
fresh buffer was added each time. The samples were measured using a
plate reader with a 96-well plate.