Activatable cell-penetrating peptides (ACPPs) based on linkage of an inhibitory domain. Amino acids are indicated via the single letter code, in which d-amino acids are noted in lower case. Cy5 = cyanine5 red dye; PpIX = protoporphyrin IX; Dox = doxorubicin; PLK-1 = polo-like kinase 1; PSA = protease specific antigen; NE = neutrophil elastase; FITC = fluorescein; NA = not available; CPT = camptothecin; EGFR = epidermal growth factor; QDs = quantum dots.

		CPP			Trigger	Ref.
Enzyme sensitive linkers
1	PLGLAG	r9	e6,8	Cy5	MMP-2 and -9	19 and 21
		R9	E8	PpIX		23
		R9	E9	Dox		24
		Poly(M-block-K)	PEG	Dox		25
2	PVGLIG	R9	(EGG)3	CsA-LMNC	MMP-9	26
3	PGFK	Tat	E6	Dox	Cathepsin B	28
4	HSSKYQ	R8	(DGG)4	PLK-1 siRNA	PSA	29
5	RLQLK(Ac)L	r9	e9	Cy5	NE	32
6	DPRSFL	r9	e8	Cy5 Rhodamine	Thrombin	33
pH sensitive linkers
7		R8	(ehG)4	PLK-1 siRNA	pH < 6.8	37
ROS sensitive linkers
8		R9	E9	FITC Cy5	H2O2	43
Light sensitive linkers
9		Tat	PEG	Liposomes loaded with Atto655	λ = 254 nm, 2 min	47
10		R7	E7	FITC CPT	λ = 365 nm, 10 min	48
11		Penetratin	E4R4	EGFR siRNA	λ = 740 nm, 30 min and pH < 6.4	53
12		R7	E7	QDs	Two-photon, λ = 740 nm, 3 h	48