A self-contained enzyme activating prodrug cytotherapy for preclinical melanoma

Abstract

Gene-directed enzyme prodrug therapy (GDEPT) has been investigated as a means of cancer treatment without affecting normal tissues. This system is based on the delivery of a suicide gene, a gene encoding an enzyme which is able to convert its substrate from non-toxic prodrug to cytotoxin. In this experiment, we have developed a targeted suicide gene therapeutic system that is completely contained within tumor-tropic cells and have tested this system for melanoma therapy in a preclinical model. First, we established double stable RAW264.7 monocyte/macrophage-like cells (Mo/Ma) containing a Tet-On® Advanced system for intracellular carboxylesterase (InCE) expression. Second, we loaded a prodrug into the delivery cells, double stable Mo/Ma. Third, we activated the enzyme system to convert the prodrug, irinotecan, to the cytotoxin, SN-38. Our double stable Mo/Ma homed to the lung melanomas after 1 day and successfully delivered the prodrug-activating enzyme/prodrug package to the tumors. We observed that our system significantly reduced tumor weights and numbers as targeted tumor therapy after activation of the InCE. Therefore, we propose that this system may be a useful targeted melanoma therapy system for pulmonary metastatic tumors with minimal side effects, particularly if it is combined with other treatments.

Challenges in SN38 drug delivery: current success and future directions

“…Basel et al (2012) used engineered Raw264.7 cells (mouse monocyte/-macrophage-like cells, Mo/Ma) to express intracellular rabbit carboxylesterase (InCE) [24,69]. Dextran (70 kDa)-SN38 conjugate was prepared by reacting succinic acid-modified dextran with SN38 using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) coupling reaction.…”

Prodrug and nanomedicine approaches for the delivery of the camptothecin analogue SN38

“…Bioengineered and tumour-homing cells have been utilised as targeted delivery carriers of both SN38 prodrugs and the prodrugactivating enzyme [107][108][109]. For example, RAW 264.7 cells (mouse monocytes/macrophage-like cells, Mo/Ma) for inducible expression of carboxylesterase have been engineered.…”

“…For example, RAW 264.7 cells (mouse monocytes/macrophage-like cells, Mo/Ma) for inducible expression of carboxylesterase have been engineered. CPT-11 (0.45 nmol) was loaded into Mo/Ma cells, which was stable for 24 h [107]. The Tet-On® advanced system was used to activate the self-contained carboxylesterase within the cells which eventually regenerate the parent drug SN38 in the presence of external stimulation (i.e.…”

Cells As Delivery Vehicles for Cancer Therapeutics

“…The cells were loaded with irinotecan and injected intravenously into mice with metastatic melanoma. When treated with both the loaded cells and doxycycline the treatment decreased the number, weight and size of melanoma tumors in the lungs as compared to controls [84].…”