Page 47 - Read Online

Dave et al. J Cancer Metastasis Treat 2020;6:46 I http://dx.doi.org/10.20517/2394-4722.2020.106 Page 9 of 36

Sulforaphane demonstrates inhibition of phase I and phase II enzymes, induces cell-cycle arrest and
inhibits angiogenesis. At 15 µmol/L, sulforaphane promotes apoptosis and cell-cycle arrest in prostate
cancer cells (LNCaP and PC3) by decreasing histone deacetylase (HDAC) enzymes [115] .

Carcinogen-treated Wistar rats at 10 weeks of age were treated with 150 µmol of sulforaphane by oral
gavage, mammary glands were extracted, and sulforaphane concentration after 12 h was 22 µmol/L. In
addition, there was an increase of NQO1 and HO-1 levels observed in rat mammary gland. Subsequently,
healthy women were placed on a cruciferous-free diet and administered 200 µmol of sulforaphane. The
amount of sulforaphane distributed in breast tissue was found to be 0.92 ± 0.72 µmol/L [116] .

It is documented in various epidemiological studies that the consumption of isothiocyanates from
cruciferous vegetables is inversely proportional to the incidence of lung cancer cases [117] . This inverse
correlation was even stronger in a study conducted in female patients who do not smoke cigarettes [118] .
There is also substantial evidence based on studies conducted with cisplatin-resistant cancer stem
cells [such as human non-small cell lung cancer (NSCLC)] that up-regulation of miR-214 induced by
sulforaphane may lead to anti-cancer activity [119] .

Chemopreventive mechanisms of sulforaphane
KEAP-nrf2 signaling
Genetic deletion of nrf2 can lead to detrimental effects on the survival of mice; they are more prone to
brain injury and lung injury and other pathological conditions involving inflammation. To the contrary,
the activation of KEAP1-nrf2 leads to protective effects in various animal models [120,121] . Nrf2 is important
for the regulation of antioxidant genes such as enzymes that produce glutathione (GSH) and NADPH [122] .
Sulforaphane, on entering cells, reacts with Kelch-like ECH associated protein, which functions as a sensor
protein complex. Under basal conditions, KEAP1 binding to nrf1 leads to ubiquitination and proteasomal
degradation. Sulforaphane protects nrf2 from degradation [Figure 4], allowing escape and the regulation
of downstream target genes capable of mediating anti-inflammatory and antioxidant activities [123] . NQO1
-/-
+/+
and GST levels are significantly elevated in sulforaphane-treated wild-type mice (nrf2 ) whereas nrf2
deficient mice exhibited no changes in NQO1 [124] .
Activity of cyclin dependent kinase and reduced cyclin D1
Cyclin D1 is a cell-cycle regulator and a transcriptional modulator for histone deacetylase 3. Overexpression
of these factors has been linked to cancer progression. Therefore, reduction of cyclin D is considered
as a potential strategy for chemoprevention [125] . In this context, sulforaphane-treated A549 cells showed
concentration-dependent reduction of cyclin D1 as well as increased expression of the p21 [126] . In DU-
145 prostate cancer cells, sulforaphane reduced CDK4 activity and cyclin D1 levels when treated with 9
and 50 μmol/L, respectively. CDK4 activity was also affected by a concentration of less than 1 μmol/L,
but not significantly [127] . In an in vivo study, sulforaphane reduced tumor promotion and polyp formation
in an ApcMin/+ mouse small intestine cancer model in a dose-dependent manner. However, biomarkers
including cyclin D1 remained unaffected [128] .

Inhibition of HDAC activity in human prostate and colorectal cancer cells
Increased HDAC expression has been associated with the deregulation of cell-cycle and apoptotic
processes. HDAC inhibitors have shown potential in clinical studies for chemoprevention. Sulforaphane has
demonstrated potential to reduce HDAC activity in prostate and colorectal cancer cells [129] . Sulforaphane
(15 μmol/L) reduced HDAC activity by 30%, 40%, and 40% in LNCaP, BPH-1, and PC-3 cell lines,
respectively. Expression of p21 associated with histone H4 was increased in all three cells lines leading to
apoptosis [130] . In 4-6 week-old NOD/SCID mice inoculated with A549 lung cancer cells, administration
of 9 μmol sulforaphane by oral gavage for 4 weeks attenuated the increase of tumor volume, significantly