We describe and characterize a complex reaction that catalyzes DNA supercoiling and chromatin assembly in vitro. A Xenopus oocyte extract supplemented with ATP and Mg++ converts DNA circles into minichromosomes that display a native, 200 bp periodicity. When supercoiled DNA is added to this extract it undergoes a time-dependent series of topological changes, which precisely mimic those found when the DNA is microinjected into oocytes. As judged by the conformation of the subsequently deproteinized DNA, the supercoiled DNA is first relaxed, in a reaction that takes 4 min, and then it is resupercoiled in a slower process that takes 4 hr. The relaxation is partially inhibited by EDTA, to an extent that suggests that that it is catalyzed by a type I DNA topoisomerase. The resupercoiling , on the other hand, requires ATP and Mg++, is completely inhibited by EDTA, and is inhibited by novobiocin in a manner that suggests it is catalyzed by a type II DNA topoisomerase. These findings, and the ones reported in the preceding paper ( Ryoji and Worcel , 1984), lead us to propose that chromatin assembly is an active, ATP-driven process.

We evaluated the safety, efficacy and anti-tumor effects of a surgery adjuvant treatment on canine patients with malignant melanoma. This approach combined suicide gene therapy with a subcutaneous vaccine composed by formolized tumor cells and irradiated xenogeneic cells producing human interleukin-2 and granulocyte-macrophage colony-stimulating factor. The post-surgical margin of the cavity was infiltrated with lipid-complexed thymidine kinase suicide gene coadministrated with ganciclovir. Toxicity was minimal or absent in all patients. With respect to surgery-treated controls (SC), this combined treatment (CT) significantly increased the fraction of patients local disease-free from 6 to 58% and distant metastases-free from 43 to 78% (Fisher's Exact test).In addition, CT significantly improved both SC overall 78 (23-540) and metastasis-free survival 112 (0-467) days to more than 1312 days (respective ranges: 43-1312 and 0-1312) (Kaplan-Meier analysis). In those patients subjected to partial surgery or presenting local recurrence, the efficacy of CT was verified by a 49% of objective responses that averaged 85% of tumor mass loss, while 22% displayed tumor progression as 94% of SC did. Therefore, surgery adjuvant CT controlled tumor growth, delaying or preventing post-surgical recurrence and distant metastasis, significantly extending survival and recovering the quality of life.

We present here the updated results after 9 years of the beginning of a trial on canine patients with malignant melanoma. This surgery adjuvant approach combined local suicide gene therapy with a subcutaneous vaccine composed by tumor cells extracts and xenogeneic cells producing human interleukin-2 and granulocyte-macrophage colony-stimulating factor. Toxicity was absent or minimal in all patients (0pVCOG-CTCAE gradep1). With respect to surgery-treated controls (ST), the complete surgery (CS) arm of this combined treatment (CT) significantly increased the fraction of local disease-free patients from 13 to 81% and distant metastases free from 32 to 84%. Even though less effective than the CS arm, the partial surgery (PS) arm of this CT was significantly better controlling the disease than only surgery (14% while PS-ST: 0%, Po0.01 and CS-ST: 5%, Po0.05). In addition, CT produced a significant sevenfold (CS) and threefold (PS) increase in overall survival. The CS-CT arm significantly improved both CS-ST metastasis-free-and melanoma overall survival from 99 days (respective ranges: 11-563 and 10-568) to 42848 days (81-2848 and 35-2848). Thus, more of 50% of our CT patients died of melanoma unrelated causes, transforming a lethal disease into a chronic one. Finally, surgery adjuvant CT delayed or prevented post-surgical recurrence and distant metastasis, significantly improved disease-free and overall survival maintaining the quality of life. Long-term safety and efficacy of this treatment are supported by the high number of CT patients (283) and extensive follow-up (49 years). The successful clinical outcome encourages the further translation of similar approaches to human gene therapy trials.

To validate the use of multicellular spheroids to predict the efficacy of herpes simplex thymidine kinase/ganciclovir (HSVtk/GCV) suicide gene therapy in the respective in vivo tumors, we established and characterized 15 melanomaderived cell lines from surgically excised melanoma tumors. Three HSVtk-lipofected cell lines were not sensitive to GCV in any culture configuration, other five displayed similar sensitivity as monolayers or spheroids, and only one resulted more sensitive when grown as spheroids. Other six cell lines manifested a relative multicellular resistance (MCR) phenotype growing as spheroids, compared with the same cells growing as monolayers. The reverse correlation between the MCR and the monolayers survival to HSVtk/GCV suggests that one of the main causes of MCR would be the rapid cell repopulation after suicide gene treatment. The high correlation of MCR with the spheroids radial growth and with the mitotic index of the respective originary tumors supported this re-growth involvement. A remarkable finding was the high correlation in HSVtk/GCV sensitivity between in vivo tumor and the corresponding derived cell lines growing as spheroids (R 2 ¼ 0.85). This strongly encourages the implementation of spheroids as highly realistic experimental model for optimizing and predicting the in vivo response of the respective tumors to therapeutic strategies.

We present here a nonviral immunogene therapy trial for canine malignant melanoma, an aggressive disease displaying significant clinical and histopathological overlapping with human melanoma. As a surgery adjuvant approach, it comprised the co-injection of lipoplexes bearing herpes simplex virus thymidine kinase and canine interferon-b genes at the time of surgery, combined with the periodic administration of a subcutaneous genetic vaccine composed of tumor extracts and lipoplexes carrying the genes of human interleukin-2 and human granulocyte-macrophage colony-stimulating factor. Following complete surgery (CS), the combined treatment (CT) significantly raised the portion of local disease-free canine patients from 11% to 83% and distant metastases-free (M0) from 44% to 89%, as compared with surgery-only-treated controls (ST). Even after partial surgery (PS), CT better controlled the systemic disease (M0: 82%) than ST (M0: 48%). Moreover, compared with ST, CT caused a significant 7-fold (CS) and 4-fold (PS) rise of overall survival, and > 17-fold (CS) and > 13-fold (PS) rise of metastasis-free survival. The dramatic increase of PS metastasis-free survival ( > 1321 days) and CS recurrence-and metastasis-free survival (both > 2251 days) demonstrated that CT was shifting a rapidly lethal disease into a chronic one. In conclusion, this surgery adjuvant CT was able of significantly delaying or preventing postsurgical recurrence and distant metastasis, increasing disease-free and overall survival, and maintaining the quality of life. The high number of canine patients involved in CT (301) and the extensive follow-up ( > 6 years) with minimal or absent toxicity warrant the long-term safety and efficacy of this treatment. This successful clinical outcome justifies attempting a similar scheme for human melanoma.