Oligoamine analogues in combination with 2-difluoromethylornithine synergistically induce re-expression of aberrantly silenced tumour-suppressor genes

Abstract

Epigenetic gene silencing is an important mechanism in the initiation and progression of cancer. Abnormal DNA CpG island hypermethylation and histone modifications are involved in aberrant silencing of tumour-suppressor genes. LSD1 (lysine-specific demethylase 1) was the first enzyme identified to specifically demethylate H3K4 (Lys4 of histone H3). Methylated H3K4 is an important mark associated with transcriptional activation. The flavin adenine dinucleotide-binding amine oxidase domain of LSD1 is homologous with two polyamine oxidases, SMO (spermine oxidase) and APAO (N1-acetylpolyamine oxidase). We have demonstrated previously that long-chain polyamine analogues, the oligoamines, are inhibitors of LSD1. In the present paper we report the synergistic effects of specific oligoamines in combination with DFMO (2-difluoromethylornithine), an inhibitor of ornithine decarboxylase, in human colorectal cancer cells. DFMO treatment depletes natural polyamines and increases the uptake of exogenous polyamines. The combination of oligoamines and DFMO results in a synergistic re-expression of aberrantly silenced tumour-suppressor genes, including SFRP2 (secreted frizzled-related protein 2), which encodes a Wnt signalling pathway antagonist and plays an anti-tumorigenic role in colorectal cancer. The treatment-induced re-expression of SFRP2 is associated with increased H3K4me2 (di-methyl H3K4) in the gene promoter. The combination of LSD1-inhibiting oligoamines and DFMO represents a novel approach to epigenetic therapy of cancer.

Structure–activity study for (bis)ureidopropyl- and (bis)thioureidopropyldiamine LSD1 inhibitors with 3-5-3 and 3-6-3 carbon backbone architectures

“…8, 18, 30 Thus, we tested the ability of compounds 6b – 6d to promote re-expression of silenced tumor suppressor genes in the Calu-6 cell line. The secreted frizzle-related protein 2 (SFRP2), a modulator of the Wnt signaling pathway, H-cadherin (HCAD), a membrane bound mediator of calcium-dependent cell to cell adhesion, GATA4, a zinc finger transcription factor, and p16, a cell cycle-regulating protein were chosen as candidate genes for these expression studies because it has been hypothesized that their silencing promotes tumorigenesis 8, 18, 30–32 . In the present study, Calu-6 cells were treated for 24 or 48h in the presence of 10 μM of compound 6b , 6c or 6d and the mRNA levels of SFRP2, HCAD, GATA4 , and p16 expression were subsequently determined by qRT-PCR analysis (Figure 5).…”

Polyamines and cancer: implications for chemotherapy and chemoprevention

“…The data from studies with these compounds demonstrate that minor structural modifications can result in significantly altered biological responses to the individual polyamine analogues. Additionally, these studies have validated the strategy that reactive functional groups can be added to the polyamine backbone to facilitate the entry of such conjugates into the cell through the polyamine transport system, leading to the synthesis of multiple compounds exploiting this strategy (Refs 121, 122, 123, 124). …”

“…Interestingly, a very recent study has demonstrated a synergistic effect on gene expression when CGC-11144 and DFMO were used in combination in HCT116 cells (Ref. 123). …”

Epigenetic therapy: use of agents targeting deacetylation and methylation in cancer management

“…By targeting H3K4me1 and H3K4me2, LSD1 selectively mediates repression and has been found to be overexpressed in a significant number of cancers, including tumors of the brain, breast, and prostate, thereby making it an attractive target for drug therapy 92–94. Small molecules such as SL11144 and tranylcypromine appear to be potent inhibitors of LSD1,95,96 and have been shown in cancer cell lines to restore expression of multiple aberrantly silenced tumor suppressors, including secreted frizzled-related protein and GATA transcription factors. Research with neuroblastoma xenografts also demonstrates antitumor activity 94.…”