**5. Bioactivity of colchicine and its derivatives**

**Figure 6.** Thiocolchicines with modified ring A: **60** 1,4-quinone and **61** quinomethane.

have been tested against cancer cell lines [55] (**Figure 7**).

50 Cytotoxicity

esters of 1-*O*-demethyl, 2-*O*-demethyl and 3-*O*-demethylthiocolchicine were also obtained **53**– **57** (**Figure 5**) [49]. 10-methylthiocolchicine has been demethylated to 1-demethyl-10-methylthiocolchicine **58**, 2-demethyl-10-methylthiocolchicine **59**, and 1,2-*O*-didemethylthiocolchicine **52** then **58** and **59** have been oxidized to quinine (**Figure 6**) [50]. Complex ethers of 3-demethyl-10-methylthiocolchicine **62**–**65** have been prepared as potential pharmaceuticals [51]. The C-7 amide group of ring B with (*R*)-configuration [15] is also one of the crucial factors which decide of molecule's anticancer activity. Eight synthetic derivatives of *N*-deacetylthiocolchicine have been obtained and tested against cancer cell lines and 3 of them showed good activity **66**, **67**, **68** [52]. Thiocolchicine derivative **69** has been modified at C-2 carbon atom and then converted into salt **70** [53]. Among 37 thiocolchicine derivatives tested, compound **71** showed good activity as inhibitor of topoisomerases *in vitro* [54]. *N*-substituted thiocolchicine derivatives and their water-soluble phosphate salts **72–78** (and 5 others) have been obtained and their activity

**Figure 7.** Thiocolchicines modified on ring B.

Colchicine **1** has been known and used from ancient times, despite its toxicity to cure acute gout attacks because of its anti-inflammatory properties. After administration of colchicine **1,** it is mainly metabolized in liver *via* demethylation by cytochrome P450 system (isoform CYP 3A4) to 2-demethylcolchicine **2** and 3-demethylcolchicine **3** [11]. Colchiceine **12** was described as a metabolite in rats produced by cytochrome P450 3A4 isoform [60], but it does not occur in humans *in vivo* [61]. Colchicine's most common toxicity is gastrointestinal (nausea, vomiting, diarrhea, abdominal pain) which occurs during first 24 hours after overdose. Toxic effect of colchicine appears after oral administration of 7–60 mg of colchicine and is fatal, symptoms occur in about 4 h and death in about 4 days. Severe colchicine overdose may be treated with a colchicine-specific antigen-binding immunoglobulin [11].

Beside colchicine **1** has many naturally occurring derivatives many attempts have been made to discover more effective and less toxic analogs by modifying the substituents of its basic structure.

Colchicine blocks mitosis metaphase due to different anti-mitotic effects: disruption of mitotic spindle formation and second disruption of the sol-gel formation. Colchicine can also interact with lipid membranes. The interaction between colchicine and membrane results with significant alternations of both the properties of the lipid membrane and alkaloid [39]. Tubulin is an α and β heterodimer initially identified as the cellular colchicine-tubulin protein [10, 62]. Colchicine can interact with human serum albumin, which has been studied by spectroscopic method [63, 64]. Study of colchicine-tubulin complex showed that colchicine binds at the location where it prevents curved tubulin from adopting a straight structure, which inhibits assembly. Microtubules are cytoskeletal polymers of tubulin involved in many cellular functions [65]. Their dynamic instability is controlled by many proteins and compounds such as colchicine.

Colchicine and its biologically active derivatives, especially thiocolchicine and its derivatives, have been extensively tested on cancer cell lines for *in vitro* cytotoxicity, in mice, evaluated for inhibition of tubulin polymerization [66], on axonal cytoskeleton of rat peroneus nerve [67]. Thiocolchicine has been studied as a potent compound to treat Peyronie's disease [68]. Derivatives of thiocolchicine have been tested ex vivo to human T-lymphoblastoid (CEM) cells [69].
