Main text
Introduction
Nasopharyngeal
carcinoma (NPC) is endemic in Southern China
(Chang & Adami, 2006). Patients with NPC
are uniformly treated with high-dose radiation therapy, with additional
(concurrent chemoradiation) or adjunct chemotherapy for locally advanced
diseases (Blanchard et al., 2015;
Shield et al., 2017). Unfortunately,
30-50% of patients still relapse within 5 years despite this radical
intensive treatment (Sun et al., 2014).
The main characteristic of this cancer is the high association between
Epstein-Barr virus (EBV) infection and NPC risk, especially type III.
Moreover, a hallmark of undifferentiated NPC (the commonest histological
type in endemic regions) is substantial infiltration of immune cells
into the tumor microenvironment (TME).
Consumption of soy is associated with many health benefits, including a
modest reduction in the risk of developing certain cancers
(Trock, Hilakivi-Clarke & Clarke, 2006;
Yan & Spitznagel, 2005). Soy products
provide the main sources of soy phytochemicals, including
soy isoflavones which comprise
predominately genistein, daidzein and glycitein. Idronoxil (IDX, also
known as phenoxodiol) is a synthetic derivative of genistein
(Joannou, Kelly, Reeder, Waring & Nelson,
1995). Preclinical studies have shown that IDX causes apoptosis in a
wide range of cancer cell lines and is 5-20 times more effective than
genistein. IDX is also active in murine cancer models which can
sensitize certain types of cancer to chemotherapy
(Alvero et al., 2008). The activity of IDX
is likely related to its inhibition of enzymes including sphingosine
kinase and PI3 kinase which are over-expressed in cancer cells and
responsible for regulating cell pro-survival mechanisms
(Porter, Fairlie, Laczka, Delebecque &
Wilkinson, 2020; Yao et al., 2012).
Another target of IDX is a protein found on the outer membrane of all
cancer cells known as Ecto-Nicotinamide adenine dinucleotide oxidase
disulfide-thiol exchanger type 2 (ENOX2)
(Morre, Chueh, Yagiz, Balicki, Kim &
Morre, 2007). The binding of IDX to respective receptors can induce
cell cycle arrest and promote DNA damage in cancer cells
(Aguero, Facchinetti, Sheleg &
Senderowicz, 2005).
Whilst clinically tested in the past, IDX’s journey was discontinued as
a result of its low bioavailability in humans when administered either
intravenously or orally, though strategies to overcome this issue are
currently being explored. Strikingly, IDX has previously been reported
to inhibit the proliferation and migration of human endothelial cells,
thereby inhibiting angiogenesis (Gamble et
al., 2006). Moreover, IDX can induce a range of interferon
(IFN)-stimulated genes in immortalised mouse embryonic fibroblasts
(Yagiz, Wu, Kuntz, James Morre & Morre,
2007). These findings illustrate that IDX may be targeting the
apoptotic machinery itself. Indeed, one report described activated T
cells (Herst, Davis, Neeson, Berridge &
Ritchie, 2009) as a target for IDX and Georgaki et al. have also
classified IDX as an immunomodulator through its capacity to stimulate
the innate arm of the immune system, specifically the
CD56+ natural killer (NK) cell population
(Georgaki et al., 2009). Despite the
augmentation of NK cell activity and T cells proliferation being
critical for the treatment of tumors, the exact mechanisms by which IDX
controls the TME and cancer progression remain unclear.
Here we determined the IC50 of IDX on NPC cell lines and
showed that it could further sensitize the cells to apoptosis and
inhibit the proliferation and migration in conjunction with cisplatin
(cis) treatment. Our results also demonstrated a purported ability of
IDX to re-educate the TME and elicit anti-tumorigenic effects. In this
capacity, IDX itself could induce T-cell migration with augmented
cytotoxic functions and proliferative capacity. While IDX treatment did
not show significant impact alone, combination of both IDX and cis
targeting was synergistic in regulating CD8+ T cell
expansion. We next developed spheroid cocultures of NPC cells and immune
cells to study the infiltration, activation and functions of these cells
towards human tumors. Increased immune cell infiltrates in IDX-treated
spheroids were enriched for double-positive (DP)
CD4+CD8+ cells, mediated by the
up-regulated expression of IFNα/CXCL10. Particularly, the infiltrated DP
cells demonstrated downregulated expression of both lymphoid node homing
and dysfunctional markers, CD62L and PD-1. Thus,
IDX kills cancer cells both
directly and also indirectly, by evoking antitumor immunity by
modulating T-cell infiltration into and migration within tumors.
Additionally, IDX may be a tool to gather further insights concerning
TME and the poor response of NPC cells to conventional chemotherapy.