Vitamin C and Doxycycline: A synthetic lethal combination therapy targeting metabolic flexibility in cancer stem cells (CSCs)

Abstract

Here, we developed a new synthetic lethal strategy for further optimizing the eradication of cancer stem cells (CSCs). Briefly, we show that chronic treatment with the FDA-approved antibiotic Doxycycline effectively reduces cellular respiration, by targeting mitochondrial protein translation. The expression of four mitochondrial DNA encoded proteins (MT-ND3, MT-CO2, MT-ATP6 and MT-ATP8) is suppressed, by up to 35-fold. This high selection pressure metabolically synchronizes the surviving cancer cell sub-population towards a predominantly glycolytic phenotype, resulting in metabolic inflexibility. We directly validated this Doxycycline-induced glycolytic phenotype, by using metabolic flux analysis and label-free unbiased proteomics.Next, we identified two natural products (Vitamin C and Berberine) and six clinically-approved drugs, for metabolically targeting the Doxycycline-resistant CSC population (Atovaquone, Irinotecan, Sorafenib, Niclosamide, Chloroquine, and Stiripentol). This new combination strategy allows for the more efficacious eradication of CSCs with Doxycycline, and provides a simple pragmatic solution to the possible development of Doxycycline-resistance in cancer cells. In summary, we propose the combined use of i) Doxycycline (Hit-1: targeting mitochondria) and ii) Vitamin C (Hit-2: targeting glycolysis), which represents a new synthetic-lethal metabolic strategy for eradicating CSCs.This type of metabolic Achilles’ heel will allow us and others to more effectively “starve” the CSC population.

A mitochondrial based oncology platform for targeting cancer stem cells (CSCs): MITO-ONC-RX

“…Remarkably, what we observed is that DoxyR-CSCs show a dramatic shift towards aerobic glycolysis, due to a loss of mitochondrial function, ultimately resulting in metabolic inflexibility [22]. As expected, they showed an up to 35-fold loss of mitochondrial-DNA encoded proteins (mt-DNA) that are absolutely required for OXPHOS activity, such as MT-ND3, MT-CO2, MT-ATP6 and MT-ATP8 [22]. Also, DoxyR-CSCs appeared to be more “quiescent”, with > 50% reductions in proliferation and cell migration, as well as a significantly impaired ability to form 3D spheroids.…”

“…Regarding therapy with Doxycycline, one possible concern that arises is the potential for the development of drug-resistance in CSCs [22]. To address this issue directly, we developed and characterized the phenotypic behavior of Doxy-resistant (DoxyR)-MCF7 cells [22].…”

“…To address this issue directly, we developed and characterized the phenotypic behavior of Doxy-resistant (DoxyR)-MCF7 cells [22]. Remarkably, what we observed is that DoxyR-CSCs show a dramatic shift towards aerobic glycolysis, due to a loss of mitochondrial function, ultimately resulting in metabolic inflexibility [22].…”

“…To address this issue directly, we developed and characterized the phenotypic behavior of Doxy-resistant (DoxyR)-MCF7 cells [22]. Remarkably, what we observed is that DoxyR-CSCs show a dramatic shift towards aerobic glycolysis, due to a loss of mitochondrial function, ultimately resulting in metabolic inflexibility [22]. As expected, they showed an up to 35-fold loss of mitochondrial-DNA encoded proteins (mt-DNA) that are absolutely required for OXPHOS activity, such as MT-ND3, MT-CO2, MT-ATP6 and MT-ATP8 [22].…”

“…Therefore, the efficacy of Doxycycline could be potentially improved, by developing combination therapies with these other metabolic inhibitors, based on the concepts of metabolic inflexibility and synthetic lethality in cancer cells [22]. …”