Could anti-cancer drugs be derived from sea-sponges?

Yes: Eribulin is a drug that works by interfering with proteins that form structures known as microtubules, vital for cell division and function. It is derived from sea sponges and it's currently used for patients with breast cancer.

Psammaplin: Many medicines, including those used against cancer, are naturally-occurring -- usually poisons that damage cancer cells more than good cells. Psammaplin A has been under study for over a decade and nothing much has come of it.