Research in the Casero Laboratory is focused on the role of polyamines in cancer cell proliferation and ways to exploit their metabolism and function as antiproliferative and chemopreventive targets. Polyamines are naturally occurring polycationic alkylamines that are absolutely required for eukaryotic cell growth and differentiation. Their intracellular concentrations (millimolar) are maintained in a narrow range through the actions of a highly regulated and specific transport system and a rapidly responding metabolic pathway. The first rate-limiting step in the production of polyamines is the decarboxylation of ornithine by the highly inducible and short-lived enzyme, ornithine decarboxylase (ODC). Increased ODC activity and new polyamine synthesis have frequently been associated with the neoplastic phenotype. The catabolism of the polyamines is controlled by the rate limiting enzyme spermidine/spermine N1-acetyltransferase (SSAT) that my laboratory has cloned and continues to study. This enzyme is highly controlled at the level of transcription, translation and is stabilized by the natural polyamines and antitumor polyamine analogues. We have also demonstrated that the phenotype-specific antitumor activity of specific polyamine analogues is associated with a superinduction of this enzyme in response to treatment.
Another enzyme discovered by my laboratory is the inducible FAD-dependent, spermine oxidase (SMOX), a polyamine catabolic enzyme that produces H2O2. SMOX is induced by many inflammatory stimuli including bacterial infection and inflammatory cytokines. As an example, Helicobacter pylori, a causative agent of gastric cancer, highly induces SMOX resulting in sufficient H2O2 production to produce oxidative DNA damage. We have also demonstrated that SMOX is induced by Bacteriodes fragilis, a bacterium that is associated with colon cancer. In an animal models of cancer induced, we have demonstrated inhibiting SMOX significantly reduced tumor formation. Importantly, SMOX-produced H2O2 and subsequent DNA damage have been implicated in epigenetic changes common in the early stages of cancer development. Thus it appears that SMOX may be one of the molecular links between inflammation, DNA damage, epigenetic changes, and carcinogenesis and a represents a promising target for chemopreventive intervention.
During the studies that lead to the discovery of SMOX, we also identified the sequence of a related FAD-dependent oxidase that was later identified as lysine specific demethylase 1 (LSD1). LSD1 is an important chromatin-remodeling enzyme that demethylates mono- and dimethyl lysine 4 of histone 3 (H3K4me1 & H3K4me2). As these histone marks are associated with active transcription, LSD1 has the ability to broadly repress gene transcription. LSD1 activity is involved with the inappropriate silencing of several tumor suppressor gene involved in the etiology and progression of cancer. As LSD1 is structurally and functionally homologous to SMOX, we hypothesized that certain polyamine analogues would inhibit LSD1 and lead to the re-expression of inappropriately silenced genes. We have now demonstrated that this is, in fact, the case and are pursuing this strategy to develop agents that may be useful in the treatment of neoplastic disease.
Consequently, polyamine metabolism and function, and related pathways present a target rich environment against which therapeutic and chemopreventive strategies may be developed.
Murray-Stewart T, Ferrari E, Xie Y, Yu F, Marton LJ, Oupicky D, Casero RA Jr. Biochemical evaluation of the anticancer potential of the polyamine-based nanocarrier Nano11047. PLoS One. 2017 PMID: 28423064.
Casero RA Jr, Murray Stewart T, Pegg AE. Polyamine metabolism and cancer: treatments, challenges and opportunities. Nat Rev Cancer. 2018 PubMed PMID: 30181570.
Murray-Stewart T, Sierra JC, Piazuelo MB, Mera RM, Chaturvedi R, Bravo LE, Correa P, Schneider BG, Wilson KT, Casero RA. Epigenetic silencing of miR-124 prevents spermine oxidase regulation: implications for Helicobacter pylori-induced gastric cancer. Oncogene 2016 PMID: 27041578.
Goodwin AC, Destefano Shields CE, Wu S, Huso DL, Wu X, Murray-Stewart TR, Hacker-Prietz A, Rabizadeh S, Woster PM, Sears CL, Casero RA Jr. Polyamine catabolism contributes to enterotoxigenic Bacteroides fragilis-induced colon tumorigenesis. Proc Natl Acad Sci U S A. 2011 PMID: 21876161.
Murray-Stewart T, Dunworth M, Lui Y, Giardiello FM, Woster PM, Casero RA Jr. Curcumin mediates polyamine metabolism and sensitizes gastrointestinal cancer cells to antitumor polyamine-targeted therapies. PLoS One. 2018 PubMed PMID: 30138353.