Highly selective toxic and proapoptotic effects of two dimeric ribonucleases on thyroid cancer cells compared to the effects of doxorubicin

The lack of selectivity of conventional antitumour drugs against cancer cells is responsible for their high toxicity. The development of new tumour-specific drugs is therefore highly needed. We tested the cytotoxic effects and the nature of cell death induced by a naturally dimeric bovine RNase and a newly engineered dimeric human RNase upon three genetically well-defined normal and malignant thyroid cell systems. RNases effects were compared with those of doxorubicin, a conventional antineoplastic drug. Our results show significant and selective proapoptotic effects exerted on tumour cells by both RNases, the strength of their cytotoxic and apoptotic activity being directly related to the degree of cell malignancy. No toxic effects were observed upon normal cells. Doxorubicin showed, instead, cytotoxic and apoptotic effects also against normal cells. The in vitro results were corroborated by the antitumour action of both dimeric RNases towards a malignant human thyroid tumour grown in nude mice. These results indicate a selective action of dimeric RNases against cancer cells and suggest the potential application of these molecules or their derivatives to the treatment of aggressive subtypes of thyroid cancer

Inhibition of MAPK activity ,cell proliferation and anchorage-independent growth by N-ras antisense in an N-ras transformed human cell line.

Mammalian ras genes encode a family of plasma membrane-bound proteins that function as intermediates in signal transduction pathways involved in cell growth and differentiation. Ras oncogene is frequently involved in neoplastic transformation of different cellular histotypes. In this study, we tested the ability of antisense oligodeoxyribonucleotides (AS-ODN) that have mixed phosphodiester/phosphorothioate backbone, targeted against human N-Ras, to inhibit N-ras gene expression and to specifically interfere with the Ras-dependent activity of mitogen-activated protein kinase (MAPK) in two human cell lines carrying an endogenous N-ras mutated allele at codon 61. Three AS-ODN that inhibit basal MAPK activity have been identified. Moreover, AS-ODN treatment resulted in potent antiproliferative effects in cell culture and great inhibition of N-ras mRNA levels in one of two cell lines. These studies suggest that antisense molecules, targeted against N-Ras, could be of considerable value as a tool to study the N-Ras-specific transduction pathway

Seminal ribonuclease inhibits tumor growth and reduces the metastatic potential of Lewis lung carcinoma.

The role of some RNases as antitumoral agents has been recently emphasized. We have previously demonstrated a striking inhibitory effect of bovine seminal RNase on the in vitro growth of tumor cells of metastatic origin. This has prompted us to test the effects of this protein in vivo on the induction of metastatic foci in mice lungs after i.m. injection of a highly metastatic Lewis lung carcinoma cell line. The results presented here, while confirming and expanding upon those previously reported on the antitumor effects of bovine seminal RNase in vivo on primary thyroid epithelial tumors, indicate for the first time that bovine seminal RNase can also be regarded as a potent antimetastatic agent on in vivo spontaneous metastases

Verapamil reverts resistance to drug-induced apoptosis in Ki-ras-transformed cells by altering the cell membrane and the mitochondrial transmembrane potentials.

We have previously shown that in vivo ras-transformed cell lines display natural doxorubicin resistance compared with the normal cells and that such resistance is accompanied by a plasma membrane depolarization. In this article we first extend the analysis of doxorubicin effect to other ras-transformed cell lines, which are characterized by an increasing degree of malignant phenotype. Rat thyroid ras-transformed cells are markedly resistant to doxorubicin and the degree of drug resistance correlates with the degree of cell malignancy. The lower amount of drug accumulated inside the malignant and resistant cells is a consequence of their constitutive depolarized membrane potential and may account for their lack of drug-induced apoptosis. Verapamil, a known modulator of drug resistance, is able to decrease the resistance of all the malignant cell lines, initially causing a higher incorporation of doxorubicin as a consequence of its ability to hyperpolarize the membrane potential. In resistant cells, verapamil is also able to alter the mitochondrial membrane potential allowing apoptosis. In conclusion, these studies demonstrate that ras transformation induces the natural resistance to doxorubicin of the malignant cells. We suggest that the most malignant and resistant cells, of metastatic origin, could be preferentially destroyed by manipulation of their membrane properties, and we confirm the possibility of overcoming drug resistance by the administration of verapamil also in P-gp170-nonexpressing cells