The chemopreventive potential of Spirulina is to a certain extent associated with its immune modulation and antioxidant properties. Human studies on anticancer effects of Spirulina or Spirulina extracts have shown complete regression of oral leukoplakia (a precancerous lesion) in pan tobacco chewers and the activation of the human innate immune system. Specific chemopreventive actions of Spirulina major components reported include: (1) The induction by phycocyanin of apoptotic death in histiocytic tumor AK-5 cells and in human chronic myeloid cell line K562 as well as the expression of CD59 protein in Hela cells which is accompanied by a decline of the multiplication activity of the cells, (2) The antiproliferative effects of Spirulina water extracts on human liver cancer cells HepG2 and the inhibition of tumor invasion and metastasis by spirulan, (3) Concerning GLA, it has been shown that it is the most promising polyunsaturated fatty acid in the treatment of human malignant gliomas and other advanced solid malignancies. Limited open label clinical studies showed that intratumoral injection/infusion of GLA is safe and effective against malignant gliomas, while a recent phase 2 GLA clinical trial demonstrated faster clinical response in patients with breast cancer receiving GLA in addition to the synthetic nonsteroidal antiestrogen tamoxifen. In the last case, GLA seems to function as a novel selective modulator of estrogen receptor.
The chemopreventive effect of Spirulina against animal liver cytotoxicity and carcinogenesis induced by nitrosamines has also been reported, suggesting the potential use of Spirulina in chemoprevention of cancer Another important promising application of phycocyanin and phycobilin constituents of Spirulina for cancer treatment is photodynamic therapy (PDT). PDT is a selective treatment modality that affects mainly the target tissue, in which, light, O2, and a photosensitizing drug are used in combination. The selectivity is based on a difference in the photosensitizer concentration between normal and tumour tissue and on the directing of light into the tumour tissue. After injection, the photosensitizer accumulates in the target tumour tissue and then the light directed to the tumour tissue (laser light can be directed through fiber optic cables) activates the photosensitizer molecules, which in turn produce reactive oxygen species, in the presence of oxygen. These reactive species are responsible for the damage of vital structures and functions of tumour cells with minimal damage of healthy tissue. Among photosensitizers used for PDT, the most important molecules are tetrapyrrole derivatives, which include phycocyanin, and phycocyanobilin derivatives.