Prodrugs and prodrug-activated systems in gene therapy

Abstract

The inclusion of genes that control cell fate (so-called suicide, or kill-switch, genes) into gene therapy vectors is based on a compelling rationale for the safe and selective elimination of aberrant transfected cells. Prodrug-activated systems were developed in the 1980s and 1990s and rely on the enzymatic conversion of non-active prodrugs to active metabolites that lead to cell death. Although considerable effort and ingenuity has gone into vector design for gene therapy, less attention has been directed at the efficacy or associated adverse effects of the prodrug systems employed. In this review, we discuss prodrug systems employed in clinical trials and consider their role in the field of gene therapy. We highlight potential drawbacks associated with the use of specific prodrugs, such as systemic toxicity of the activated compound, the paucity of data on biodistribution of prodrugs, bystander effects, and destruction of genetically modified cells, and how these can inform future advances in cell therapies. Prodrug-activated gene therapyEarly gene therapy trials carried out for monogenic diseases, such as severe combined immune deficiency (SCID) and alpha 1-antitypsin deficiency, initially focused on replacing a single deficient or mutated gene with a normal copy. However, the safety concerns inherent in cellular therapy were highlighted when 4 of 10 patients treated with gene therapy for SCID developed acute T cell lymphoblastic leukemia as the result of insertional mutagenesis into the host genome. 4 One strategy to mitigate potential adverse effects (AEs) caused by genetically modified cells is to include a cell-fate control system, such as a suicide gene, in the transfer vector; thus, a second transgene accompanies the gene of interest and acts as a suicide switch that allows transduced cells to be destroyed when exposed to a particular signal. 1,5 Several mechanisms can be used to control cell fate in this way (Figure 1). Prodrug-activated gene therapy (PAGT) strategies aim to enable the selective, on-demand destruction of transduced cells. A suicide transgene that encodes an enzyme is introduced into a target cell, and the transduced cell then becomes able to convert

GRP75-driven, cell-cycle-dependent macropinocytosis of Tat/pDNA-Ca2+ nanoparticles underlies distinct gene therapy effect in ovarian cancer

“…As a Pak1interacting substrate, dynein light chain phosphorylation controls macropinocytosis [54]. Therefore, phosphorylation-modified GRP75 may significantly modulate this process; (3) we have demonstrated that GRP75-KD or inhibition significantly reduced Rac1 activation [34]. Since Rac1 activation always induces membrane ruffling and macropinocytic cup formation [32], dynamic expression and phosphorylation of GRP75 from S-to M-phase modulate macropinocytosis is logical (Fig.…”

“…The cytotoxic action is localized inside tumor or, if applicable, in neighboring tumor cells that have not been transduced but undergo oncolysis due to the “bystander effect”. The most utilized suicide gene therapy is based on herpes simplex virus-thymidine kinase (HSV-TK) followed by treatment with antiviral drug ganciclovir (GCV), which is transformed to toxic metabolites by the TK action, causing failure of cancer cells in DNA replication and cell apoptosis [ 3 ]. Although suicide gene therapy is in progress, it is far from reaching OC patients.…”

Strategies to Improve the Safety of iPSC-Derived β Cells for β Cell Replacement in Diabetes

“…The most commonly used suicide genes perform their function via enzymatic drug conversion activity, apoptotic potential, or the ability to direct the immune response against a cell by the addition of a tag ( 126 ). In particular, enzyme prodrugs can enzymatically convert an innocuous prodrug into a toxic compound that can kill the target cell ( 127 ). The toxic molecule generated can act only towards the edited cell or can have a broader action killing also the surrounding cells, called the “bystander effect,” usually used to treat cancer ( 128 ).…”

Barnase-Barstar Pair: Contemporary Application in Cancer Research and Nanotechnology

“…Gene therapy relies on a cell-specific expression of the chosen protein genes or regulatory RNA either in cancer cells or in effector cells that can be used in therapy. In suicide gene therapy, the genes that encode toxins or prodrugconverting enzymes are used to transduce cancer cells [36]. Ribonucleases are promising agents for use in anticancer therapy, as the production of RNases in the cytoplasm of eukaryotic cells leads to cell death via an apoptosis-mediated pathway [37].…”