Intensely Potent Doxorubicin Analogues:  Structure−Activity Relationship

Abstract

N-(5,5-Diacetoxypent-1-yl)doxorubicin (1b) is an intensely cytotoxic doxorubicin analogue that retains full potency against tumor cells that express elevated levels of P-glycoprotein and are resistant to doxorubicin. 1b was designed to be hydrolyzed in the presence of carboxylate esterases to N-(5-oxypent-1-yl)doxorubicin, an aldehyde capable of existing in equilibrium with a cyclic carbinolamine. To investigate the structural determinants of potency for 1b, we have prepared a series of chemically related compounds in which various omega-[bis(acetoxy)]alkyl or omega-[bis(acetoxy)]alkoxyalkyl groups are substituted at the 3'-amino position of the daunosamine sugar. These groups were selected to assess the effect of chain length, oxygen substitution, and carbinolamine ring size on analogue potency. The compounds were evaluated for their ability to inhibit the in vitro growth of the following cell lines: (a) Chinese hamster ovary (CHO) cells, (b) a CHO cell mutant 100-fold resistant to doxorubicin that expresses elevated levels of P-glycoprotein, (c) a murine ductal cell pancreatic adenocarcinoma (Panc 02), and (d) a murine mammary carcinoma (CA 755). The most potent members of the series were those that could form a straight chain aldehyde intermediate after esterase-mediated hydrolysis of the omega-bis(acetoxy) groups and give rise to 5- or 6-membered ring carbinolamines. Analogues capable of forming 7-, 8-, or 9-membered carbinolamines were markedly less active. The N-methyl derivative of 1b, which cannot give rise to a cyclic carbinolamine, was 2 orders of magnitude less potent than 1b. A branched chain analogue, 1f, which contained a tertiary carbon atom adjacent to the omega-bis(acetoxy) groups, was also substantially less active than its nonbranched counterpart, 1a. These findings suggest that the chain length of the 3'-amino substituents and the ability of the derived aldehydes to form 5- or 6-membered carbinolamines are critical determinants of biologic potency.

Recent Advances in Understanding and Exploiting the Activation of Anthracyclines by Formaldehyde

“…However, these adducts appear to have a high thermal stability and are essentially irreversible at 37°C [74]. Furthermore, 2-pyrrolinodoxorubicin is a semisynthetic derivative of doxorubicin with 500-1000 times greater potency that is anticipated to form DNA adducts similar to CMA [75] while N-(5, 5-diacetoxypentyl)doxorubicin, a doxorubicin analog, is 100-fold more potent and functions by inducing interstrand crosslinks at low drug doses [76][77][78].…”

Modifications of human carboxylesterase for improved prodrug activation

“…However, since these drugs have not been assayed against the purified human enzymes, it is unclear whether hCE1 or hiCE can activate these compounds. These doxorubicin prodrugs demonstrated good activity in cell culture models, but it is not clear if these drugs have been tested in in vivo models [68]. However given the widespread use of doxorubicin in the clinic, it is likely that prodrugs based on this compound are likely to be useful against human tumors.…”

Manipulation of gene expression by an ecdysone-inducible gene switch in tumor xenografts

“…[12] The murine ductal cell pancreatic adenocarcinoma cell line, Panc02 [19], was kindly provided by Dr. James Nelson, MD Anderson Cancer Center. Plasmid DNA was prepared by the "EndoFree Plasmid Maxi kit" from Qiagen (Valencia, CA) using the manufacturer's procedure.…”