Optimization of Marine Triterpene Sipholenols as Inhibitors of Breast Cancer Migration and Invasion

Abstract

Sipholenol A, a sipholane triterpene isolated from the Red Sea sponge Callyspongia siphonella, has the ability to reverse multidrug resistance in cancer cells that overexpress P-glycoprotein (P-gp). Here, the antimigratory activity of sipholenol A and analogues are reported against the highly metastatic human breast cancer cell line MDA-MB-231 in a wound-healing assay. Sipholenol A and sipholenone A were semisynthetically optimized using ligand-based strategies to generate structurally diverse analogues in an attempt to maximize their antimigratory activity. A total of 22 semisynthetic ester, ether, oxime, and carbamate analogues were generated and identified by extensive one- and two-dimensional NMR spectroscopy and high-resolution mass spectrometry analyses. Sipholenol A 4β-4-chlorobenzoate and 19,20-anhydrosipholenol A 4β-4-chlorobenzoate esters were the most potent of all tested analogues in the wound-healing assay, with IC(50) values of 5.3 and 5.9 μM, respectively. Generally, ester derivatives showed better antimigratory activities than the carbamate analogues. A KINOMEscan of 19,20-anhydrosipholenol A 4β-benzoate ester against 451 human protein kinases identified protein tyrosine kinase 6 (PTK6) as a potential target. In breast tumor cells, PTK6 promotes growth factor signaling and migration, and as such the semisynthetic sipholanes were evaluated for their ability to inhibit PTK6 phosphorylation in vitro. The two analogues with the highest antimigratory activities, sipholenol A 4β-4-chlorobenzoate and 19,20-anhydrosipholenol A 4β-4-chlorobenzoate esters, also exhibited the most potent inhibition of PTK6 phosphorylation inhibition. None of the compounds exhibited cytotoxicity in a normal epithelial breast cell line. These derivatives were evaluated in an in vitro invasion assay, where sipholenol A succinate potently inhibited MDA-MB-231 cell invasion at 10 μM. These results highlight sipholane triterpenoids as novel antimigratory marine natural products with potential for further development as agents for the control of metastatic breast malignancies.

Discovery and Computer-Aided Drug Design Studies of the Anticancer Marine Triterpene Sipholanes as Novel P-gp and Brk Modulators

“…Ester analogs of 1 were more active than ether, oxime and carbamate analogs. This illustrates the important role of the ester carbonyl group as well as the distance limit between the aromatic side chain and C-4 oxygen for optimal antimigratory activity [49]. Longer distances, as represented by oximes or carbamates, significantly decreased the antimigratory activity.…”

“…Aromatic esters showed a better activity profile than aliphatic esters; for example, the benzoate 28 was twice as active as the acetate 25 (Table 26.2). The aromatic ester was tolerant to bioisosteric substitution as evident from the comparable activity of isonicotinate ester (29) to the benzoate ester 28 (Table 26.2) [49]. In order to identify a potential target, KINOME scan profiling was performed to quantitatively measure interactions between the most active ester analog 34 and a diverse kinase panel [49].…”

“…The screening of an in-house marine-derived natural products library in the woundhealing assay (WHA) allowed for the identification of sipholanes 1 and 2 as inhibitors of the migration of the highly metastatic MDA-MB-231 breast cancer cells at mid-μM concentrations [49]. This finding encouraged the reinvestigation of other sipholanes from the source sponge C. siphonella (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), as well as a number of previously reported products of sipholenol A biocatalysis [3] (18-22), for antimigratory activity in order to establish a preliminary structure-activity relationship (SAR) profile.…”

“…The aromatic ester was tolerant to bioisosteric substitution as evident from the comparable activity of isonicotinate ester (29) to the benzoate ester 28 (Table 26.2) [49]. In order to identify a potential target, KINOME scan profiling was performed to quantitatively measure interactions between the most active ester analog 34 and a diverse kinase panel [49]. Analog 34 was screened against 451 human kinases using an ATP site competition-binding assay at a single concentration of 10 µM.…”

Untitled

“…In this study, the antimigratory activity of sipholenol A and analogues was reported against the highly metastatic human breast cancer cell line MDA-MB-231 in a wound-healing assay. 48 Neviotine-A (133) possessing a unique tetracyclic skeleton related to the sipholanes and siphonellanes, was isolated from the Red Sea sponge Siphonochalina siphonella. Its structure was elucidated mainly on the basis of NMR experiments and by chemical transformations and.…”