PTD-mediated Loading of Tumor-Seeking Lymphocytes with Prodrug-Activating Enzymes

Abstract

Abstract. Using the approach of peptide transduction domain (PTD)-mediated loading of interleukin-2 (IL-2)-activated natural killer (A-NK) cells, tumor-seeking lymphocytes, with prodrug-activating enzymes, we primarily aim to generate a cytotoxic drug selectively within tumors and minimize damage to normal tissues. A-NK cells are able to accumulate selectively at tumor sites. While these cells by themselves possess significant antitumor effect in vivo, we suggest that they can also serve as Trojan horses, by bringing anticancer agents, such as prodrug-activating enzymes, selectively to tumors. We have successfully demonstrated in a mouse model that A-NK cells can be rapidly loaded with prodrugactivating enzymes, such as alkaline phosphatase (AP) and beta-galactosidase (beta-gal), in vitro using enzyme-conjugated peptide PTD5. Upon adoptive transfer into lung-tumor-bearing animals, the loaded A-NK cells are able to bring their cargo of the prodrug-activating enzymes selectively to pulmonary metastases. The targeting of the AP to the tumor tissues is highly specific, since more than a fivefold higher concentration of AP was found in the tumor tissues compared to the surrounding normal lung tissue at 24 h after injection. The approach of transporting prodrug-activating enzymes selectively into tumors clearly shows potential for future targeted chemotherapy. Ongoing studies in our laboratory are evaluating the antitumor efficacy of cellular-dependent enzyme prodrug therapy.KEY WORDS: activated natural killer cells; delivery; metastases in vivo; prodrug enzymes; protein transduction domain.

Phosphatase‐Triggered Fusogenic Liposomes for Cytoplasmic Delivery of Cell‐Impermeable Compounds

“…A metastatic cell line, B16F10, was selected for this assay because of its high phosphatase expression and because it has previously been used to evaluate the cytotoxic effects of phosphate prodrugs. [31][32][33] No significant difference in cell toxicity, as compared to resulted in greater cellular accumulation. Furthermore, the significant reduction in uptake and accumulation of liposomes containing FP-2Sul-Chems provides further evidence that dephosphorylation is required for PTP internalization.…”

Phosphatase‐Triggered Fusogenic Liposomes for Cytoplasmic Delivery of Cell‐Impermeable Compounds

“…The metastatic B16F10 cell line was selected for the assay because of its phosphatase expression and its previous use to evaluate the cytotoxic effects of phosphate pro-drugs. [31][32][33] No significant difference in cell toxicity, as compared to POPC, was observed with FP-2Sul-Chems and FP-2PT-Chems liposomes at concentrations relevant for cellular uptake studies (10 μM Figure S.3c-d). This suggests that the anchored phosphopeptide on the PTP was dephosphorylated, which resulted in greater cellular accumulation.…”