Dendrimers as Non-Viral Vectors in Gene-Directed Enzyme Prodrug Therapy

Abstract

Gene-directed enzyme prodrug therapy (GDEPT) has been intensively studied as a promising new strategy of prodrug delivery, with its main advantages being represented by an enhanced efficacy and a reduced off-target toxicity of the active drug. In recent years, numerous therapeutic systems based on GDEPT strategy have entered clinical trials. In order to deliver the desired gene at a specific site of action, this therapeutic approach uses vectors divided in two major categories, viral vectors and non-viral vectors, with the latter being represented by chemical delivery agents. There is considerable interest in the development of non-viral vectors due to their decreased immunogenicity, higher specificity, ease of synthesis and greater flexibility for subsequent modulations. Dendrimers used as delivery vehicles offer many advantages, such as: nanoscale size, precise molecular weight, increased solubility, high load capacity, high bioavailability and low immunogenicity. The aim of the present work was to provide a comprehensive overview of the recent advances regarding the use of dendrimers as non-viral carriers in the GDEPT therapy.

Keywords: GDEP therapy; GDEPT; delivery vehicles; dendrimer; gene delivery system; non-viral vector; targeted therapy; transgene.

Figure 1

Diagram of ADEPT, VDEPT and GDEPT therapeutic strategies. 1−The gene encoding an enzyme that is delivered at the target site; 2−The triggering of the intracellular expression of the enzyme; 3−Systemic administration of a prodrug; 4−The activation of an inactive prodrug into an active cytotoxic agent; 5−The death of the transduced tumor cells; 1’−Viral vectors providing the gene encoding an enzyme; 1”−The enzyme that is vectorized or catalyzed directly by antibodies, towards antigens expressed on tumor cells, activating the prodrug; 2”−The cytotoxic effect of the active drug that entered into the cells; 3”− The death of tumor cells.

Figure 2

General representation of the GDEPT strategy involving the occurrence of the bystander effect. 1−The gene encoding an enzyme, that is delivered at the target site; 2−The triggering of the intracellular expression of the enzyme; 3−Systemic administration of a prodrug; 4− The activation of an inactive prodrug into an active cytotoxic agent, that leads to the transduced tumor cell death; 5a, 5b−The transfer of active metabolites to non-transduced neighboring cells; 6−The destruction of distant cells.

Figure 3

Examples of nVV systems for gene delivery in GDEPT.

Figure 4

The basic mechanism of nVV gene release through polyplex and lipoplex. (1) condensation; (2) endocytosis; (3) endosome escape; (4) degradation of DNA; (5) cytosolic migration; (6) transcription; (7) translation; (8) nuclear translocation. Adapted from [66], published J Transl Med, 2018.

Figure 5

General structure of dendrimers. Adapted from [139], published by Int. J. Nanomed, 2009.

Figure 6

Schematic history of dendrimers [132,133,134,140,141,142,143].

Figure 7

Mechanism of gene transfection through cationic dendriplexes. (1) nucleic acid condensation with dendrimers forming stable dendriplexes; (2) cellular uptake of dendriplex; (3) endosome escape of dendriplex; (4) the release of the dendriplex components; (5) the entrance of the nucleic acid in the nucleus. Adapted from [13], published by Elsevier, 2020.

Figure 8

General structures of some G2 dendrimers: (a) carbosilane dendrimers; (b) polypropylene-imine dendrimers; (c) cationic poly(amidoamine) dendrimers, most commonly used to provide therapeutic nucleic acids. Adapted from [184], published by Pharmaceutics, 2018.

Figure 9

Dendrimer 6-G4, used as a support for the delivery and release of therapeutic genes (a) 6-G4 dendrimer; (b) active dendrimer; (c) dendrimer as drug carrier; (d) dendriplex; (e) active dendrimer as drug carrier. Adapted from [33], published by Molecules 2020.

Figure 10

PAMAM dendrimers with a central structure consisting of diaminoethane (a), diaminohexane (b) and diaminododecane (c) radicals; PAMAM dendrimers obtained by modulating the surface structures of diaminoethane derivatives with triazine (d), diaminohexane derivatives with arginine (e) and diaminododecane derivatives with fluoroalkyls (f). Adapted from [223], published by Acta Biomaterialia, 2016.

Figure 11

Conjugated PAMAM dendrimer with arginine to enhance siRNA delivery. Adapted from [225], published by Bioconjug Chem, 2014.

Figure 12

Obtaining fluorinated PAMAM dendrimers (a)-reaction of G5-PAMAM dendrimers with perfluoro anhydrides of carboxylic acids, (b)-reaction of G5-PAMAM dendrimers with perfluoro anhydrides of sulphonic acids. Adapted from [227], published by Nat Commun, 2014.