Summary The effects of several members of the family of lamellarins, polyaromatic alkaloids isolated from tunicates belonging to the genus Didemnwn, on the growth of several tumour cell lines and on P-glycoprotein (P-gp)-mediated multidrug resistance (MDR), were investigated. Cytotoxicity experiments of lamellarins were performed on a panel of tumour cell lines, including two multidrug-resistant cell lines. Some lamellarins showed good anti-tumour activity, with similar levels of cytotoxicity against both the resistant and their corresponding parental cell lines. Two lamellarins displayed a high potency against lung carcinoma cells. Studies of the resistance modifier activity of the different lamellarins at non-toxic concentrations were also carried out in cells exhibiting MDR, and lamellarin I was selected for the highest chemosensitising activity. At non-toxic doses, verapamil and lamellarin I effectively increased the cytotoxicity of doxorubicin, vinblastine and daunorubicin in a concentration-dependent manner in multidrug-resistant cells, but the potency of lamellarin I as a MDR modulator was 9-to 16-fold higher than that of verapamil. In vitro measurements of rhodamine 123 accumulation in the multidrug-resistant Lo Vo/Dx cells suggest that lamellarin I reverses MDR by directly inhibiting the P-gp-mediated drug efflux. This work underscores the possibility of using these marine-derived compounds as a potential new source of anti-tumoral drugs active on resistant cells as well as of non-toxic modulators of the MDR phenotype.

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Three cytotoxic triterpenes, sodwanones G [5], H [6], and I [7], have been isolated from a marine sponge. The three structures were determined by interpretation of nmr spectra, and in the case of 5, also on the basis of the X-ray diffraction analysis. The X-ray diffraction analysis of two other earlier reported sodwanones, E [3] and F [4] is also discussed. The cytotoxic activity against several cancer cell lines, has been tested. IC50 values between 20 and 0.02 microM were obtained. Compounds 5 and 6 were 10- and 500-fold, respectively, more cytotoxic to A-549 cells than to any of the other cell lines tested (HT-29, MEL-28, P-388).

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