. 2021 Mar 16;11(3):746. doi: 10.3390/nano11030746

Table 4.

Summary of enzyme-induced response mechanisms used in stimuli-responsive drug delivery systems.

Mechanism	Enzyme and Substrate	Reference
Cleavage by hydrolases		[124] ^c
		[120] ^c,***
		[534] ^c,**
		[535] ^b,c,**
		[160] ^b,c,* [329] ^b,c, [536] ^b,d [537] ^a,b,c,**
		[157] ^a,b,c,***
		[261] ^a,b,c [242] ^c [243] ^a,b,c [265] ^a,b,c,* [330] ^b,c,* [538] ^b,c,* [539] ^a,c,* [540] ^a,b,c,*** [541] ^a,b,c
		[525] ^a,b,c,*
		[19] ^a,b,c,* [212] ^b,c,*** [542] ^a,b [543] ^a,b,c,* [544] ^b,c,**
		[205] ^b,c,* [530] ^a,b,c,* [531] ^a,b,c,***
Cleavage by reductases		[545] ^c
Cleavage by reductases		[529] ^a,b,c,***
Cleavage by other enzymes		[190] ^b
		[182] ^c,***
		[47] [328] ^a,b,c,* [532] ^b,c, [533]

^a Evaluation included in vivo tests on mice.; ^b Evaluation included in vitro tests on cells.; ^c Small molecules, such as antitumor drugs and dyes, were used as payloads.; ^d Large molecules, such as proteins and plasmid DNA, were used as payloads.; * Premature payload leakage was >20%.; ** Premature payload leakage was between 10% and 20%.; *** Premature payload leakage was $\leq$ 10%.