Screening cultured marine microalgae for anticancer-type activity

Marine Cyanophyceae, and to a lesser extent other marine microalgae, are a promising source of new anticancer-type natural products. Microscopic forms that do not form mats or tufts in nature must be cultured in order to obtain sufficiently sized samples. Field collections of microalgae in intertidal and shallow subtidal tropical environments utilize hand collection and manipulation techniques into small-volume wide-mouth jars. Acclimation times in the laboratory environment are important in bringing new cultures into cultivation. Manipulation on agar plates has given the best success rate for obtaining unialgal cultures; sometimes these are obtained directly as axenic clones. These pure strains are cultured in an initial volume of 3 L to give sufficient material for pharmacological screening. The extracts are evaluated in a series of mechanism-based anticancer screens, including protein kinase C (PKC), protein tryosine kinase (PTK) and inosine monophosphate dehydrogenase (IMPDH). More that 501 extracts have been screened in these three assay areas, and have yielded 23 active to IMPDH, 9 to PKC, and 9 to PTK. The extract of one cultured microalga which was active to PTK,Poteriochromonas malhamensis, has yielded a novel chlorosulfolipid, whose structure is discussed. Future efforts will (a) target less well explored groups of microalgae including several orders of cyanophyceae as well as field collections of cryptophytes and chrysophytes, and (b) complement mechanism-based screening with cancer cell cytotoxicity screening.