**6.4 Shishijimicins A-C**

A class of beta-carboline alkaloids, isolated from the ascidian *Didemnum proliferum.* These peptides are potent antitumorigenic agents [46]. Three classes of alkaloids isolated from the Guinea sea squirt *Eudistoma* species consists of Rigidin, RigidinE and 1-methylherbiproline. These three alkaloids were reported to contain moderate inhibitory potential towards human P53 colon carcinoma cell lines and A431 epidermal carcinoma cell lines [47].

An alkaloid Fascaplysin isolated from the sponge *Fascaplysinopsis Bergquist* species, contained an excellent cytotoxic activity against murine C38 CFU cell lines and human H116 cell lines [48]. Meridianins, are brominated 3-(2-aminopyrimidine) indole alkaloids isolated from the ascidian *Aplidium meridianum.* It is shown to have anti-proliferative effects, inducing apoptosis and inhibiting various cyclin dependent protein kinases, casein kinase-1 and glycogen synthase kinase-3 in NT2 teratocarcinoma cells [49].
