Pulmonary delivery of cationic liposomal hydroxycamptothecin and 5-aminolevulinic acid for chemo-sonodynamic therapy of metastatic lung cancer

Sonodynamic therapy (SDT) has been tried for cancer treatment; however, sonosensitizers are usually administered by injection, leading to low distribution in the tumor tissue and compromised therapeutic effect, even serious side effect. Here, we combined cationic liposomal hydroxycamptothecin (CLH) and 5-aminolevulinic acid (5-ALA) via intratracheal (i.t.) administration for the chemo-sonodynamic (Chemo-SDT) therapy of metastatic lung cancer. CLH was prepared from HCPT and the lipid mixture of soybean lecithin/cholesterol/octadecylamine with a film method. The optimal pre-incubation time of 5-ALA with tumor cells before ultrasound exposure was 4 h, for sake of sonosensitizer accumulation, i.e., protoporphyrin IX, the metabolite of 5-ALA. In vitro studies showed the higher cytotoxicity of Chemo-SDT compared to the other treatments, including i.t. CLH, intravenous (i.v.) CLH, and SDT alone. The combination of pulmonary delivery and Chemo-SDT showed the highest anticancer effect among the treatments on the metastatic lung tumor-bearing mice, which was judged according to the tumor appearance and pathological sections. The major anticancer mechanism of Chemo-SDT included the improved apoptosis of cancer cells and the enhanced production of reactive oxygen species, and more importantly, the synergy of chemotherapy and SDT. Pulmonary delivery of chemotherapeutics and sonosensitizers is a promising strategy for the treatment of lung cancer.