Table 2.

Examples of CPP-siRNA delivery.

CPP	Interactions	Proposed mechanism	Target gene	Results	References
MPG&MPGΔNLS	Non-covalent	Non-endocytotic	Luciferase	Effective up to 80%-95%	(Simeoni et al., 2003)
Tat-LK15	Non-covalent	Endocytic	nNOS	Improving the stability of siRNA in serum, and downregulating the expression of nNOS effectively and specifically	(Peng et al., 2017)
pH responsive ACPP	Non-covalent	Endocytic	PLK-1	Selectivity towards tumor cells	(Xiang et al., 2017)
RICK	Non-covalent	Non-endocytotic	Luciferase & CyclinB1	Knockdown of the expression of luciferase ∼75% and 80% of endogenous CyclinB1	(Vaissière et al., 2017)
LMWP	Covalent	Non-endocytotic	EGFP	Improving siRNA delivery with high gene-silencing efficacy and low cytotoxicity	(Ye et al., 2017; Ye et al., 2018).
Modified Octa-arginine	Non-covalent	Endocytic	Survivin	Reduction of the gene expression up to ∼60%, and strong siRNA binding and delivery efficiency	(Li et al., 2015)
PF & NF (analogs of Transportan 10)	Non-covalent	Endocytic	Luciferase	Effective up to 65%-85%	(Veiman et al., 2013)
SPACE	Non-covalent	Endocytic	IL-10& GAPDH	Improving penetration of siRNA into skin, and enhanced internalization into epidermal keratinocytes	(Hsu & Mitragotri, 2011)
SHRss	Non-covalent	Endocytic	Luciferase	High efficacy, and low toxicity	(Tai et al., 2015)
gH625	Non-covalent	Non-endocytic	GFP	High efficacy, and limited cell toxicity	(Ben Djemaa et al., 2018)
RVG9R3LC	Non-covalent	Endocytic	Murine superoxide dismutase-1	Enhanced endosomal escape, high efficacy, and no significant cell toxicity	(Ullah et al., 2018)
BR2	Non-covalent	Endocytic	GFP	High transfection efficiency, specificity towards target cells, and no significant cytotoxicity	(Lee et al., 2018)
LKH-stEK	Non-covalent	Endocytic	CTGF	High gene knockdown efficiency, and enhanced endosomal escape	(Hyun et al., 2018)