Suicide gene and cytokines combined nonviral gene therapy for spontaneous canine melanoma

Canine spontaneous melanoma is a highly aggressive tumor resistant to current therapies. We evaluated the safety, efficacy and antitumor effects of direct intratumor injections of lipoplexes encoding herpes simplex thymidine kinase coadministrated with ganciclovir, and irradiated transgenic xenogeneic cells secreting 20-30 mg day(-1) of human granulocyte-macrophage colony-stimulating factor and interleukin-2. Toxicity was minimal or absent in all patients. This combined treatment (CT) induced tumor regression and a pronounced immune cell infiltration. The objective responses (47%: 21/45) averaged 80% of tumor mass loss. Local CT also induced systemic antitumor response evidenced by complete remission of one pulmonary metastasis and by the significantly higher percentage of metastasis-free patients (76: 34/45)) until the study ending compared to untreated (UC: 29%, 5/17), surgery-treated (CX: 48%, 11/23) or suicide gene-treated controls (SG: 56%, 9/16) (Fisher's exact test). CT significantly improved median survival time: 160 (57-509) days compared to UC (69 (10-169)), CX (82 (43-216)) or SG (94 (46-159)). CT also increased (P<0.00001, Kaplan-Meier analysis) metastasis-free survival: 4509 (57-509) days with respect to UC: 41 (10-169), CX: 133 (43-216) and SG: 4159 (41-159). Therefore, CT controlled tumor growth by delaying or preventing distant metastasis, thereby significantly extending survival and recovering the quality of life.