Enhanced gene transfection of macrophages by photochemical internalization: Potential for gene-directed enzyme prodrug therapy of gliomas

•Transfected macrophages (NR8383) can act as converter cells in gene-directed enzyme prodrug therapy.•Compared to glioma cells, macrophages demonstrated increased resistance to the effects of the produced active drug.•PCI greatly increased non-viral transfection efficiency of prodrug converter gene cytosine deaminase (CD) into macrophages.•Reduced glioma cell viability by co-culture with NR8383 when prodrug 5-fluorocytosine (5-FC) was present, but not absent. Drawn by tumor synthesis of chemo-attractive factors, macrophages are frequently found in and around glioblastomas and play an important role both in augmenting as well as inhibiting tumor growth. Patient-derived macrophages have the potential, therefore, to act as targeted delivery vectors for a variety of anti-cancer treatments. Among these is ex vivo gene transfection and re-injection back into the patient of macrophages to target residual tumors. In this study, photochemical internalization (PCI) is investigated as a technique for the non-viral transfection of the cytosine deaminase (CD) prodrug activating gene into macrophages. The CD gene encodes an enzyme that converts the nontoxic antifungal agent, 5-fluorocytosine (5-FC), into 5-fluorouracil (5-FU) – a potent chemotherapeutic agent. PCI (photosensitizer + light treatment) mediated CD gene transfection of rat alveolar Ma cells was carried out in vitro. CD gene transfected NR8383 macrophages were co-cultured with F98 rat glioma cells in the presence or absence of 5-FC. Cell viability was assayed using the MTS colorimetric assay. Compared to the glioma cells, NR8383 demonstrated enhanced resistance to the toxic effects of 5-FU. PCI greatly increased the transfection efficiency of the CD gene in NR8383 cells. The viability of F98 cells was significantly inhibited by coculture with CD transfected NR8383 macrophages and 5-FC. Although gene insertion into macrophages has proven difficult, the results presented here show that non-viral transfection of the CD gene into these immune cells can be enhanced via PCI. CD transfected NR8383 cells could efficiently convert 5-FC to 5-FU and export the drug, producing a pronounced bystander toxic effect on adjacent non-transfected glioma cells. Compared to single treatment, repetitive PCI-induced transfection was more efficient at low CD plasmid concentration.