Systemic transduction of p16INK4a antitumor peptide inhibits lung metastasis of the MBT‑2 bladder tumor cell line in mice

p16INK4a (p16) is a key molecule in bladder tumor (BT) development. We previously reported that a p16 antitumor peptide inhibited the growth of subcutaneous BT grafts in mice through restoration of p16 function using a Wr-T peptide transporter system. In the present study, the efficacy of mouse p16 peptide administration in a mouse lung metastasis model for BT and also the toxicity of peptides by cardiac peptide injection were evaluated. Mouse lung metastases were developed by tail vein injection of a p16-deficient MBT-2 cell line. Six-week-old C3H/He female mice were divided into three groups: A control group (n=12) receiving no treatment; a group treated once on the 3rd experimental day (n=12); and a group treated three times on the 3rd, 5th and 7th experimental days (n=10) with an injection of a mixture of 80 nmol mouse p16 peptide and 50 nmol Wr-T into the tail vein. At the 14th experimental day, the lung metastases were histologically evaluated. Lung metastases were observed in 100% (12/12), 41.7% (5/12) and 30% (3/10) of the aforementioned three groups, respectively. The number and area of metastatic lung tumors were significantly different between control and treatment groups (control vs. triple treatment group for the number and area, P=0.0029 and P=0.0296, respectively). Immunohistochemistry demonstrated that phosphorylated retinoblastoma (Rb) protein was decreased in lung tumors of the treatment groups, compared with the control group. The toxicity of p16 peptide transduction was evaluated by using low-dose treatment (three dosages) and high-dose treatment (two dosages) on three male and three female C3H/He mice in early and late experimental phases. In low and high dose groups, no notable change was determined in body weight or blood analyses in early or late phases following mouse p16 peptide administration. In addition, no notable change was observed histologically in bone marrow of treatment groups. To conclude, systemic p16 peptide administration decreased lung tumor development in a mouse metastatic BT model without severe adverse events, as assessed by blood analyses and histological evaluation.