Synthesis and Antitumor Activity of Ester-Modified Analogues of Bengamide B

Abstract

Bengamide B, a novel sponge-derived marine natural product with broad spectrum antitumor activity, was not suitable for further preclinical development because of its difficult synthesis and very poor water solubility. Bengamide B produced a 31% T/C at its solubility-limited maximum intravenous dose of 33 micromol/kg in MDA-MB-435 breast carcinoma implanted subcutaneously as a xenograft in nude mice. Compound 8a, a bengamide B analogue with three structural changes (t-Bu alkene substituent, unsubstituted lactam nitrogen, and inverted lactam 5'-myristoyloxy group), was as potent as bengamide B in vitro and more efficacious than bengamide B in vivo. A series of ester-modified analogues based on 8a were synthesized and tested in vitro and in vivo (MDA-MB-435). The cyclohexyl- and phenethyl-substituted esters, 8c and 8g, respectively, had in vitro and in vivo activities similar to that of 8a and enhanced water solubility (ca. 1 mg/mL). Consequently, 8c and 8g were tested in the MDA-MB-435 xenograft model at 100 micromol/kg and produced 29% and 57% tumor regression, respectively.

Proteomics-based Target Identification

“…Purification and Synthesis of Bengamide Analogues-The syntheses of bengamide E, LAF153, and LAF389 have been reported previously (3,7). Structures of the compounds are given in Fig.…”

“…All maintenance media contained 100 units/ml penicillin and 100 g/ml streptomycin. Antiproliferative effects of LAF389 in vitro were measured as described previously (3).…”

“…Confirmation of the assignment of the N-terminal sequences was performed by nano-ESMS/MS sequencing. Direct selection of the triply charged parent ion at m/z 421.22 from the Lys-C digest of the induced 14-3-3␥ isoform and subsequent fragmentation produced sufficient y and b type fragment ions to identify unambiguously the sequence of the peptide as M(oxi)-VDREQLVQK (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). A similar analysis of the aminoterminal peptide of the tryptic digest of the constitutive 14-3-3␥ confirmed the complete sequence as acetyl-VDREQLVQK (2-10) (data not shown).…”

“…Bengamide B is one of the most potent members of the family; it causes growth inhibition in vitro at low nM concentrations on all human tumor cell lines tested (2). In vivo, it significantly inhibits growth of MDA-MB435 human breast cancer xenografts at well tolerated doses (3). In vitro studies of bengamide B suggested its activity might be due to inhibition of a novel target, because its pattern of activity in the NCI 60 cell line screening panel was unique compared with that of other chemotherapeutic agents (2).…”

“…Therefore, a synthetic chemistry program was initiated to develop analogues of bengamide B with enhanced solubility and ease of synthesis. LAF389 was selected from a number of analogues because of its equivalent activity in vitro against a broad panel of human tumor cell lines and its improved activity in human tumor xenograft models (3).…”