Combretastatin A4-β-Galactosyl Conjugates for Ovarian Cancer Prodrug Monotherapy

Abstract

Chemotherapy for ovarian cancer often causes severe side effects. As candidates for combretastatin A4 (CA4) prodrug for ovarian cancer prodrug monotherapy (PMT), we designed and synthesized two β-galactose-conjugated CA4s (CA4-βGals), CA4-βGal-1 and CA4-βGal-2. CA4 was liberated from CA4-βGals by β-galactosidase, an enzyme more strongly expressed in ovarian cancer cells than normal cells. CA4-βGal-2, which has a self-immolative benzyl linker between CA4 and the β-galactose moiety, was more cytotoxic to ovarian cancer cell lines than CA4-βGal-1 without a linker. Therefore, CA4-βGal-2 can serve as a platform for the design and manufacture of prodrugs for ovarian cancer PMT. KEYWORDS: Antitumor agent, prodrug monotherapy, ovarian cancer, tubulin polymerization inhibitor, β-galactosidase, combretastatin A4 O varian cancer is called a "silent killer", and its late diagnosis reduces the overall cure rate.1 Metastasis of ovarian cancer cells to the peritoneal cavity occurs easily because no anatomical barrier exists between them.2 Chemotherapy for stage 3 patients (in whom ovarian cancer cells have metastasized to the abdomen) revealed that intraperitoneal delivery of cisplatin and paclitaxel is more effective than intravenous delivery of those drugs. However, the intraperitoneal delivery method causes more side effects than the intravenous delivery method.3 This indicates that chemotherapy for advanced-stage ovarian cancer patients requires antitumor agents that exhibit selective cytotoxicity to cancer cells.In prodrug monotherapy (PMT), a nontoxic prodrug is administered, which releases a cytotoxic drug in response to enzymatic activity enhanced in tumor tissues, realizing cancer cell selective chemotherapy. 4 It is known that β-galactosidase activity is enhanced in some cancer cell lines, such as ovarian, 5 breast, 6 colon, 6 and larynx 7 cancers and gliomas. 8 Utilizing this characteristic, Asanuma et al. developed a fluorescence probe that is transformable into a fluorescent dye by β-galactosidase and applied it to the visualization of small peritoneal metastases in mouse models of ovarian cancer.9 Based on this result, we hypothesized that noncytotoxic molecules that are transformed into cytotoxic molecules by β-galactosidase are suitable prodrugs for ovarian cancer PMT.We focused on combretastatin A4 (CA4), a potent tubulin polymerization inhibitor, because microtubule disrupting agents, such as paclitaxel, are used for ovarian cancer chemotherapy. CA4 is a natural product isolated from the bark of the African willow tree Combretum caf f rum. 10Structure−activity relationship studies of CA4 revealed that the three methoxy substituents on ring A, the cis-stilbene moiety, and hydrogen bond donors, such as the hydroxy group on ring B, are necessary for CA4 to exert potent cytotoxicity (Figure 1a). 11 Based on this knowledge, we speculated that the cytotoxicity of CA4 would be weakened by substituting a β-

Application of Mono‐ and Disaccharides in Drug Targeting and Efficacy

“…Although there is much research to support the antitumor activity and aqueous solubility of α‐isomers of glycosylated drugs being superior to those of the β‐isomers, two isomers showed little significant difference in the uptake of glucose by GLUT3 . We hypothesize that the advantageous uptake of α‐anomers of glycoconjugates into cancer cells may be ascribed to their entire topological configuration being recognized preferentially by GLUTs to a certain degree, as release of the parent drug occurred readily because the α‐glycosides were found to be very unstable under some conditions …”

“…As expected, the monosaccharide–NO‐donor conjugates were stable, and release of NO from them was regulated by glycosidase activity (Figure ). In fact, the strategy of enzyme‐activated NO donors in biomedical research has been widely carried out in the design of NO prodrugs …”

“…In fact, the strategy of enzyme-activated NO donors in biomedical research has been widely carried out in the design of NO prodrugs. [57] As eries of galactosylated prodrugs were designeda nd shown to be efficient in the treatment of ovarian cancer. [58] Glycosylated platinum conjugates showed significant efficacy againstc ancerc ells, as well as lower toxicity towardn ormal cells after glycosylation.…”

“…[5] We hypothesize that the advantageous uptake of aanomerso fg lycoconjugates into cancerc ells may be ascribed to their entire topological configurationb eing recognized preferentially by GLUTst oac ertain degree, as releaseo ft he parentd rug occurred readily because the a-glycosides were found to be very unstable under some conditions. [57] Table 1. Aqueoussolubility and in vitro cytotoxicity of glycosylated paclitaxel and docetaxel derivatives.…”

More Than Resveratrol: New Insights into Stilbene-Based Compounds

“…Etherification, esterification, and substitution may be the most basic methods of modifying this group. For example, the conversion of a hydroxyl group into an ether bond has been used by Doura et al to create innovative prodrugs for ovarian cancer therapy [120]. A molecule glycoside was hydrolyzed by galactosidase, an enzyme strongly induced in cancer cells.…”