Targeted NF1 cancer therapeutics with multiple modes of action: small molecule hormone-like agents resembling the natural anticancer metabolite, 2-methoxyoestradiol

Abstract

Background:Both the number and size of tumours in NF1 patients increase in response to the rise in steroid hormones seen at puberty and during pregnancy. The size of tumours decreases after delivery, suggesting that hormone-targeting therapy might provide a viable new NF1 treatment approach. Our earlier studies demonstrated that human NF1 tumour cell lines either went through apoptosis or ceased growth in the presence of 2-methoxyoestradiol (2ME2), a naturally occurring anticancer metabolite of 17-β estradiol. Previous reports of treatment with sulfamoylated steroidal and non-steroidal derivatives of 2ME2 showed promising reductions in tumour burden in hormone-responsive cancers other than NF1. Here we present the first studies indicating that 2ME2 derivatives could also provide an avenue for treating NF1, for which few treatment options are available.Methods:STX3451, (2-(3-Bromo-4,5-dimethoxybenzyl)-7-methoxy-6-sulfamoyloxy-1,2,3,4-tetrahydroisoquinoline), a non-steroidal sulphamate analogue of 2ME2, was tested in dose-dependent studies of malignant and benign NF1 human tumour cell lines and cell lines with variable controlled neurofibromin expression. The mechanisms of action of STX3451 were also analysed.Results:We found that STX3451-induced apoptosis in human malignant peripheral nerve sheath tumour (MPNST) cell lines, even in the presence of elevated oestrogen and progesterone. It inhibits both PI3 kinase and mTOR signalling pathways. It disrupts actin- and microtubule-based cytoskeletal structures in cell lines derived from human MPNSTs and in cells derived from benign plexiform neurofibromas. STX3451 selectively kills MPNST-derived cells, but also halts growth of other tumour-derived NF1 cell lines.Conclusion:STX3451 provides a new approach for inducing cell death and lowering tumour burden in NF1 and other hormone-responsive cancers with limited treatment options.

Modes of cell death induced by tetrahydroisoquinoline-based analogs in MDA-MB-231 breast and A549 lung cancer cell lines

“…Derivatives of 2-ME such as STX 3451 and STX 2895 are nonsteroidal chimeric microtubule disruptors which bind to the colchicine binding site leading to microtubule disruption by inhibiting tubulin assembly, which contributes to the compounds’ anti-proliferative effects. 21 , 24 Shen et al 21 demonstrated that both STX 3451 and STX 2895 reduced cell viability in ST88 human malignant peripheral nerve sheath tumor cells (MPNST) and induced cell death at a 10-fold lower concentration than 2-ME. Furthermore, STX 3451 treatment not only caused microtubule disruption but also affected the actin-based cytoskeleton through disruption of the long microfilaments and reorganization of actin molecules through depolymerization.…”

“…STX 3451 exposure increased the activation of caspase-3 in ST88 cells which indicated the induction of the apoptotic cell death pathway. 21 In addition, STX 3451 affected the phosphorylation of PI3K and mTOR pathways through inhibiting Akt phosphorylation, a pathway implicated in the induction of apoptosis as well as in the regulation of autophagy. 21 …”

“…STX 3451 has a disruptive effect on both the actin and tubulin cytoskeleton leading to the rounding of cells, fragmentation of chromatin and multilobed nucleoli and actin filament disruption. 21 , 32 During this in vitro study, A549 and MDA-MB-231 cells were exposed to the determined GI 50 values of 2-ME, STX 2895, STX 3329, STX 3451 and STX 3450 for 24 h and thereafter stained with anti-tubulin antibodies. Fluorescent microscopy indicated that the compounds resulted in microtubule abrogation and DNA fragmentation.…”

“… 57 This, however, is contradicted in the reported decrease in mTOR/Akt phosphorylation in a previous publication. 21 Thus, the increase in autophagic vacuoles may have a twofold origin, namely increased formation and decreased trafficking. Autophagic protein degradation assays could add value to the current hypothesis together with DNA expression and protein microarrays.…”

“…Furthermore, the early promise of these nonsteroidal microtubule-disrupting analogs was confirmed through recent studies in NF1 tumor cell lines and their inhibition of tumor growth in vivo in a xenograft model of multiple myeloma and breast cancer. 17 , 21 , 22 However, extensive exploration of the mechanism of action of these THIQ-based analogs is still lacking.…”