Establishment of biological and pharmacokinetic assays of telomerase-specific replication-selective adenovirus

The use of replication-selective tumor-specific viruses represents a novel approach for the treatment of neoplastic disease. We constructed an attenuated adenovirus, telomerase-specific replication-selective adenovirus (TRAD), in which the human telomerase reverse transcriptase promoter element drives the expression of the E1A and E1B genes linked with an internal ribosome entry site (IRES). Forty-eight hours after TRAD infection at a multiplicity of infection of 1.0, the cell viability of H1299 human lung cancer cells was consistently less than 50% and therefore this procedure could be used as a potency assay to assess the biological activity of TRAD. We also established a quantitative real-time polymerase chain reaction (PCR) analysis with consensus primers for either the adenovirus E1A or IRES sequence. The linear ranges of quantitation with E1A and IRES primers were 10³ -10⁸ and 10²-10⁸ plaque-forming units/ mL in the plasma, respectively. The PCR analysis demonstrated that the levels of E1A in normal tissues were more than 10³ lower than in the tumors of A549 human lung tumor xenografts in nu/nμ mice at 28 days after intratumoral injection. Our results suggest that the cell-killing assay against H1299 cells and real-time PCR can be used to assess the biological activity and biodistribution of TRAD in clinical trials.