From the cancer facts and figures of 2016 American Cancer Society, we can define cancer as: “a group of diseases characterized by the uncontrolled growth and an abnormal spread of cells. Indeed, if this growth is not controlled, it can lead to death. Cancer can be caused by external factors, such as smoking, infectious organisms, and an unhealthy diet, and by internal factors, inherited genetic mutations, hormones and immune conditions. These factors can act together or sequentially to generate cancer. Ten or more years can pass from exposure to external factors before detecting the presence of cancer. Cancer treatments include surgery, radiation therapy, chemotherapy, hormone therapy, immunological therapy and targeted therapy (when the drug specifically acts on the growth of cancer cells) “. The secondary metabolites of terrestrial plants and microbes have always been considered invaluable for the discovery of new drugs. Only in recent decades, however, has the gaze been turned towards what is the 70% component of the earth: the sea.

Today more and more experimentation on marine organisms is becoming a source of curiosity but also of effective discovery of drugs, some of which have already been approved. By now we look to the sea as a new source of molecules capable of improving human life. We, therefore, indicate with the abbreviation MNPs the natural products of marine origin, many of which have shown incredible capabilities as antineoplastic drugs. Among the molecules of marine origin with anticancer activity we can distinguish:

• alkaloids: “cyclic organic compounds containing nitrogen in a negative oxidation state of limited distribution among living organisms.” Alkaloids have been isolated from marine organisms such as sponges, tunicates, anemones and molluscs, all of which are characterized by bright colors and patterns, which are often linked to the presence of alkaloids. Alkaloids are attributed to a wide range of biological activities, including antifouling, cytotoxic, antileukemic, antimalarial and antimicrobial;

• polyketides: natural metabolites which comprise a highly diverse class of chemical structures. The compounds of this class include macrolides, polyethers, polyols and aromatic compounds. These metabolites are isolated from sponges, sea squirts, soft corals and bryozoans and can be produced by commensal or symbiotic bacteria. Polyketides have broad spectrum biological activities, including antibiotic, anticancer, antifungal, antiparasitic and neurotoxic effects;

• terpenes: they involve a five-carbon isoprene structure. Different groups of marine organisms produce terpenes that exhibit biological activities such as cytotoxic, antiproliferative, antifouling, antifungal and antimicrobial activities;

• peptides: nitrogen and amino acid sources varying in size from 2 to 20 amino acid residues and are related to numerous potential physiological functions such as: neurotoxic, cardiotonic, antiviral and anticancer, cardiotoxic and antimicrobial. Peptides are characterized by low off-target toxicity and high stability, which makes them excellent molecules usable in the therapeutic field. Peptides are present in many marine species and the extensive research that has been carried out on them has shown that they are more often found in sponges, as for polyketides; peptides can also be produced by commensal or symbiotic bacteria or fungi;

• carbohydrates: the main class of which can be isolated from marine organisms are polysaccharides, but it is also possible to obtain low molecular weight glycosylated oligosaccharides, usually from sponges and tunicates. Polysaccharides are a different class of macromolecules comprising monosaccharide polymers bound with glycosidic residues and which present a wide structural diversity. These have shown functions such as antimutational, antitumoral, cholesterol lowering and anticoagulant. Marine oligosaccharides are generated by the hydrolysis of marine polysaccharides. Normally, oligosaccharides contain 10 to 12 monosaccharide units;

• glycosides: class of carbohydrates. These molecules have a sugar linked to another functional group through a glycosidic bond. They have two parts, sugar and the aglycone chemical group;

• glycosaminoglycans: they are molecules with a linear and complex carbohydrate structure.

Since ancient times, natural compounds have been used for the care of man in general, but almost never have marine organisms, as possible producers of useful molecules to improve human life, been considered.

The marine ecosystem offers unlimited sources of new bioactive compounds that with the improvement of technologies (such as scuba diving or marine prospecting) and the development of new analytical technologies, spectroscopy and high-performance screening methods, can be more easily isolated. Today these molecules are the center of new developing antineoplastic research.

As it has been possible to see from this excursus of MNPs, the most promising organisms are, certainly, Porifera (sponges), highly diversified both in the structure and in the production of molecules.

Maria Bruno