**15. Anticancer activity**

The urgency of brand-new anticancer medications is an important issue provided the increasing resistance against currently available drugs (such as taxanes) and the outbreak of new types of cancer subjected to chemotherapeutic treatment failure [29]. A considerable number of highly active cyanobacterial compounds target tubulin or actin filaments in eukaryotic cells and have exhibited potent antimitotic properties, which makes them a noteworthy source of potential anticancer agents [4]. Several of them have gone through Phase I and II clinical trials such as the third generation dolastatin15 and TZT-1027 (soblidotin), a synthetic derivative of dolastatin-10 [136, 137]. They generally act by blocking cell division at the M-phase by targeting tubulin with efficacy equivalent to clinical drugs, such as vinblastine, vincristine, or paclitaxel. Some of these highly cytotoxic compounds are described below in **Figure 1** [138].

#### **Figure 1.**

*Potential of cyanobacterial extract as anticancer activity.*

*Cyanobacteria Natural Products as Sources for Future Directions in* Antibiotic *Drug Discovery DOI: http://dx.doi.org/10.5772/intechopen.106364*

#### **15.1 Coibamide A – An anticancer agent with a novel action mechanism**

Coibamide A, extracted from a Leptolyngbya strain, shows a novedous action mechanism targeting tubulin or actin filaments. Notable cytotoxical properties against breast, central nervous system, colon, and ovary cancers have been observed [41].

#### **15.2 Cryptophycins**

Cryptophycins are examples of cyanobacteria-derived tubulin-binding compounds with potent anticancer activity. Cryptophycin A was first isolated by Schwartz and coworkers in 1990 from Nostoc sp. strains ATCC 53789 and GSV224 [22]. Microtubule dynamics suppression and blocking of G2/M phases are features making this molecule a potent anti-carcinoma metabolite [29]. Cryptophycin-52 (LY 355073), a chemical analog of cryptophycin-1, was developed to improve its hydrolytic stability but produced very slight activity in the clinical trial. The second-generation analog, cryptophycins-249 and -309, show better water solubility and stability [139]. According to a study by [140], the thioesterase derived from the cryptophycin biosynthetic pathway through the macrocyclization of a series of linear synthetic forerunners generate 16-membered cyclic depsipeptides, showed significant efficiency as anticancer agents.

#### **15.3 Largazole- a histone deacetylase inhibitor**

Largazole, an ant proliferating compound with an unusual chemical scaffold, is extracted from *Symploca sp.* [141], and shows a considerable histone deacetylase (HDAC) inhibitory activity [142], together with a great selectivity in human mammary epithelial and fibroblastic osteosarcoma cells. The FDA ratification of HDAC inhibitor suberoylanilide hydroxamic acid as a treatment for dermal T-cell lymphomas, besides its mood stability properties and anti-epileptic characteristics, confirms this compound for cancer treatment.

#### **15.4 Apratoxins – signal transduction inhibitors**

Apratoxins, a notable class of potent cytotoxic cyclic depsipeptides, was initially isolated from a chemically rich *Lyngbya boulloni* strain and, according to NCI's Developmental Therapeutics Branch, demonstrated a unique action pattern against a panel of 60 cancer cell lines [143]. Limited findings until now indicate that the induction of G1-phase cell-cycle arrest and apoptosis is how apratoxins function as anticancer agents [39]. Apratoxin A showed moderate cytotoxicity in multiple human tumor cell lines (e.g., LoVo cell lines and KB cancer cells), although this compound is acid sensitive and decomposes when exposed to the HCl present in CDCl3. Other analogs, especially apratoxin D, have been studied in order to develop a lead structure [4].

#### **15.5 Polypeptides- Hassallidins**

Polypeptides, mostly with microbial origins, have long been used for pharmaceutical applications either as antimicrobial agents or for disinfection. A group of cyclic glycosylated lipopeptide Cyanobacteria metabolites are the hassallidins A [52] and B [144], which are purified from *Hassallia*; these compounds are a type of comprehensive with action against human pathogenic fungi [1].
