Over 50% of the flavonoids significantly inhibited aromatase activity, with greatest activity being demonstrated with apigenin (IC50: 0.9 microg/mL), chrysin (IC50: 1.1 microg/mL), and hesperetin (IC50: 1.0 microg/mL)
Vitamin C was ~10 times more potent than 2-DG for the targeting of CSCs
Cancer stem-like cells (CSCs) are thought to be the root cause of chemotherapy-resistance and radio-resistance
ultimately leading to treatment failure in patients with advanced disease [1-3]. They have been directly implicated mechanistically in tumor recurrence and metastasis, resulting in poor patient survival
mitochondrial biogenesis may be a key driver of the CSC phenotype
Our results indicate that increased mitochondrial oxidative stress and high NADH levels are both key characteristics of the CSC metabolic phenotype
high levels of NAD(P)H auto-fluorescence are known to be a surrogate marker for mitochondrial “power”, high OXPHOS capacity and increased ATP production
CSCs may be strictly dependent on NAD(P)H to maintain their enhanced mitochondrial function
an intact NAD+ salvage pathway is strictly required for mammosphere formation, supporting our results using NAD(P)H auto-fluorescence, which enriched CSC activity by more than 5-fold.
Since glycolysis is especially critical for maintaining the TCA cycle, OXPHOS and overall mitochondrial function, we next assessed the effects of known glycolytic inhibitors
we show that two other natural products that function as effective glycolysis inhibitors, also inhibited mammosphere formation. More specifically, vitamin C (ascorbic acid), which induces oxidative stress and inhibits the activity of GAPDH (a key glycolytic enzyme) [17], also inhibited mammosphere formation, with an IC-50 of 1 mM (Figure 7B). Therefore, vitamin C was ~10 times more potent than 2-DG at targeting CSC propagation
silibinin (the major active constituent of silymarin, an extract of milk thistle seeds) [18], which specifically functions as an inhibitor of glucose uptake, blocked mammosphere formation, with an IC-50 between 200 and 400 µM
caffeic acid phenyl ester (CAPE), a key component of honey-bee propolis, has potent anti-cancer properties
Propolis has a strong history of medicinal use, dating back more than 2,000 years
Because of it aromatic ring structure (Figure 8), we speculated that CAPE might function as a potent inhibitor of oxidative mitochondrial metabolism
CAPE quantitatively inhibits the mitochondrial oxygen consumption rate (OCR) and, in turn, induces the onset of aerobic glycolysis (ECAR)
CAPE shows a clear selectivity for targeting CSCs and adherent cancer cells, relative to normal fibroblasts.
CAPE functions as a “natural” mitochondrial OXPHOS inhibitor, that preferentially targets the CSC sub-population. This could explain CAPE’s known anti-cancer properties
Our data directly shows that a small fraction of the total cell population, characterized by increased PGC1α activity, high mitochondrial ROS/H2O2 and high NADH levels, has the ability to survive and grow under anchorage-independent conditions, driving mammosphere formation
We highlight the utility of certain natural products, such as Silibinin, Vitamin C and CAPE, that could be used to therapeutically target CSCs. Silibinin is the major active component of silymarin, which is an extract prepared from milk thistle seeds.
high NADH is a property that is conserved between normal and cancerous stem cells
Previous studies have also shown that when non-CSCs and CSCs are both fed mitochondrial fuels (such as L-lactate or ketone bodies), that CSCs quantitatively produce more NADH in response to this stimulus
CSCs may be strictly dependent on NADH to maintain their enhanced mitochondrial function
The Noble Prize winner, Linus Pauling, was among the first to describe and clinically test the efficacy of Vitamin C, as a relatively non-toxic anti-cancer agent
Vitamin C has two mechanisms of action. First, it is a potent pro-oxidant, that actively depletes the reduced glutathione pool, leading to cellular oxidative stress and apoptosis in cancer cells. Moreover, it also behaves as an inhibitor of glycolysis, by targeting the activity of GAPDH, a key glycolytic enzyme.
Here, we show that Vitamin C can also be used to target the CSC population, as it is an inhibitor of energy metabolism that feeds into the mitochondrial TCA cycle and OXPHOS
Vitamin C may prove to be promising agent for new clinical trials, aimed at testing its ability to reduce CSC activity in cancer patients, as an add-on to more conventional therapies, to prevent tumor recurrence, further disease progression and metastasis
Interestingly, a breast cancer based clinical study has already shown that the use of Vitamin C, concurrent with or within 6 months of chemotherapy, significantly reduces both tumor recurrence and patient mortality
CAPE quantitatively reduces mitochondrial oxygen consumption (OCR), while inducing a reactive increase in glycolysis (ECAR). As such, it potently inhibits mammosphere formation with an IC-50 of ~2.5 µM. Similarly, it also significantly inhibits cell migration
we also demonstrate that 7 different inhibitors of key energetic pathways can be used to effectively block CSC propagation, including three natural products (silibinin, ascorbic acid and CAPE). Future studies will be necessary to test their potential for clinical benefit in cancer patients.
The future of cancer therapy is cancer stem cells. Study finds that Vitamin C, silymarin, and bee propolis blocks mitochondrial energy pathways in cancer stem cells. Vitamin C is a known glycolytic inhbitor. Vitamin C was found to inhibit glycolysis via GAPDH targeting to inhibit the energy pathways of the mitochondria in CSCs. The authors propse that Vitamin C can be used as add on therapies for conventional therapies to specifically attack the CSCs and their contribution to recrurence, treatment resistance, and metastasis potential all in addition to the ability of vitamin C to reduce the side effects of chemotherapy.
The five most common adult malignancies (colorectal, breast, prostate, melanoma and lung cancer)
n breast cancer, the optimal regimen(s) for cytotoxicchemotherapy in recurrent/metastatic disease are still notdefined, despite over 30 years of ‘research’ and a plethora of RCTs since the original Cooper regimen was published in1969
The five most ‘chemo-sensitive’ cancers,namely testis, Hodgkin’s disease and non-Hodgkin’s lym- phoma, cervix and ovary
only 13 out of the 22 malignancies evaluated showed any improvement in 5-year survival, and theimprovement was greater than 10% in only three of those13 malignancies
the contribution of curative and adjuvant cytotoxic chemotherapy to 5-year survival in adults is 2.3% in Australia and 2.1% in the USA
a benefit of less than 2.5% is likely to be applicable in other developed countries
Overview
The Contribution o
the benefit of cytotoxic chemotherapy may have been overestimated for cancers of oesophagus, stomach,rectum and brain.
this reflects the presentation of results as a ‘reduction in risk’ rather than asan absolute survival benefit[89,90]and by exaggerating theresponse rates by including ‘stable disease’
recent
studies have documented impaired cognitive function inwomen receiving adjuvant treatment for breast cancer
the 5-year survival rate due solely to cytotoxicchemotherapy was 1.6%
the value of palliative chemotherapy has beenquestioned
Incredibly low impact of cytotoxic chemotherapy despite its wide spread utilization. This article referenced cost yet did not evaluate the cost of cytotoxic side effect. The question to answer: is Cytotoxic chemotherapy a valid treatment, at all, for the majority of cancers.
Mast cells contribute/cause the pro inflammatory response that results in pain in people with interstitial cystitis. This is mediated via Histamine type I and type II receptors.
Avemar exhibits about a 50-fold higher IC(50) (10.02 mg/ml) for peripheral blood lymphocytes to induce a biological response, which provides the broad therapeutic window for this supplemental cancer treatment modality with no toxic effects.
These eight distinct cancer types included: DCIS, breast (ER(+) and ER(-)), ovarian, prostate, lung, and pancreatic carcinomas, as well as melanoma and glioblastoma. Doxycycline was also effective in halting the propagation of primary cultures of CSCs from breast cancer patients, with advanced metastatic disease (isolated from ascites fluid and/or pleural effusions)
Doxycycline behaves as a strong radio-sensitizer, successfully overcoming radio-resistance in breast CSCs
cancer cells can indeed escape the effects of Doxycycline, by reverting to a purely glycolytic phenotype. Fortunately, the metabolic inflexibility conferred by this escape mechanism allows Doxycycline-resistant (DoxyR) CSCs to be more effectively targeted with many other metabolic inhibitors, including Vitamin C, which functionally blocks aerobic glycolysis
Vitamin C inhibits GAPDH (a glycolytic enzyme) and depletes the cellular pool of glutathione, resulting in high ROS production and oxidative stress
DoxyR CSCs are between 4- to 10-fold more susceptible to the effects of Vitamin C
Doxycycline and Vitamin C may represent a new synthetic lethal drug combination for eradicating CSCs, by ultimately targeting both mitochondrial and glycolytic metabolism
inhibiting their propagation in the range of 100 to 250 µM
metabolic flexibility in cancer cells allows them to escape therapeutic eradication, leading to chemo- and radio-resistance
used doxycycline to pharmacologically induce metabolic inflexibility in CSCs, by chronically inhibiting mitochondrial biogenesis
This treatment resulted in a purely glycolytic population of surviving cancer cells
DoxyR cells are mainly glycolytic
MCF7 cells survive and develop Doxycycline-resistance, by adopting a purely glycolytic phenotype
Cancer stem cells (CSCs) are thought to be the “root cause” of tumor recurrence, distant metastasis and therapy-resistance
the conserved evolutionary similarities between aerobic bacteria and mitochondria, certain classes of antibiotics inhibit mitochondrial protein translation, as an off-target side-effect
Vitamin C was more potent than 2-DG; it inhibited DoxyR CSC propagation by > 90% at 250 µM and 100% at 500 µM
IC-50
DoxyR CSCs are between 4- to 10-fold more sensitive to Vitamin C than control MCF7 CSCs
Berberine, which is a naturally occurring antibiotic that also behaves as an OXPHOS inhibitor
treatment with Berberine effectively inhibited the propagation of the DoxyR CSCs by > 50% at 1 µM and > 80% at 10 µM.
Doxycycline, a clinically approved antibiotic, induces metabolic stress in cancer cells. This allows the remaining cancer cells to be synchronized towards a purely glycolytic phenotype, driving a form of metabolic inflexibility
Doxycycline-driven aerobic glycolysis
new synthetic lethal strategy for eradicating CSCs, by employing i) Doxycycline (to target mitochondria) and ii) Vitamin C (to target glycolysis)
Doxycycline inhibits mitochondrial biogenesis and OXPHOS,
hibits glycolytic metabolism by targeting and inhibiting the enzyme GAPDH
CSCs act as the main promoter of tumor recurrence and patient relapse
a metabolic shift from oxidative to glycolytic metabolism represents an escape mechanism for breast cancer cells chronically-treated with a mitochondrial stressor like Doxycycline, as mitochondrial dys-function leads to a stronger dependence on glucose
Vitamin C has been demonstrated to selectively kill cancer cells in vitro and to inhibit tumor growth in experimental mouse models
many of these actions have been attributed to the ability of Vitamin C to act as a glycolysis inhibitor, by targeting GAPDH and depleting the NAD pool
here we show that DoxyR CSCs are more vulnerable to the inhibitory effects of Vitamin C, at 4- to 10-fold lower concentrations, between 100 to 250 μM
concurrent use of Vitamin C, with standard chemotherapy, reduces tumor recurrence and patient mortality
after oral administration, Vitamin C plasma levels reach concentrations of ~70-220 μM
intravenous administration results in 30- to 70- fold higher plasma concentrations of Vitamin C
pro-oxidant activity results from Vitamin C’s action on metal ions, which generates free radicals and hydrogen peroxide, and is associated with cell toxicity
it has been shown that high-dose Vitamin C is more cytotoxic to cancer cells than to normal cells
This selectivity appears to be due to the higher catalase content observed in normal cells (~10-100 fold greater), as compared to tumor cells. Hence, Vitamin C may be regarded as a safe agent that selectively targets cancer cells
the concurrent use of Doxycycline and Vitamin C, in the context of this infectious disease, appeared to be highly synergistic in patients
Goc et al., 2016, showed that Doxycycline is synergistic in vitro with certain phytochemicals and micronutrients, including Vitamin C, in the in vitro killing of the vegetative spirochete form of Borrelia spp., the causative agent underlying Lyme disease
Doxycycline, an FDA-approved antibiotic, behaves as an inhibitor of mitochondrial protein translation
CSCs successfully escape from the anti-mitochondrial effects of Doxycycline, by assuming a purely glycolytic phenotype. Therefore, DoxyR CSCs are then more susceptible to other metabolic perturbations, because of their metabolic inflexibility
To date nearly half of known human tumors show a dysregulation of the WNT signaling pathway
It should be also noted that the WNT pathway is not exclusively employed during development or overactivated in cancer. In adults many healthy tissues rely on it for renewal and homeostasis maintenance, most notably the intestine, haematopoietic system, hair, bones and skin. Therefore one might expect adverse reactions in all these organ systems, which has indeed been observed for many WNT-targeting compounds upon attempts to push them into the clinics
The intestine seems to be the most vulnerable in this regard
Ivermectin inhibits proliferation of human colon cancer and lung cancer cells both in vitro and in vivo
The anti-proliferative action, affecting both the bulk tumor cells and CSCs, was linked in this study to inhibition of WNT signaling
the anti-WNT IC50 of ivermectin is 5–10 times (~1–2 µM vs. 10 µM) lower than that of its toxic effect against chloride channels
oral bioavailability of the drug, as for other antiparasitic drugs discussed in this section, is very low
Toxicity studies in vivo have also demonstrated a wide therapeutic index for ivermectin
Its anti-proliferative activity has been demonstrated in a wide array of cancer cell lines representative of WNT-dependent cancers: non-small lung carcinoma [96], multiple myeloma [97], hepatoma [98], adrenocortical carcinoma [99], ovarian cancer [100] and glioblastoma
Niclosamide inhibits the canonical WNT pathway
In addition to inhibiting the canonical WNT pathway, niclosamide may mediate its anticancer activities through several other signaling pathways such as NOTCH [107], MTOR [108], NF-κB [97] and STAT3 [96]
review article highlights older medications that have anti-Wnt pathway effects in cancer. Roughly, 50% of cancer involve upregulated Wnt pathway activity. Other drugs of note: metformin