Rhodamine-123 is widely used to make dynamic measurements of mitochondrial membrane potential both in vitro and in situ. Yet data interpretation is difficult due to a lack of quantitative understanding of how membrane potential and measured fluorescence are related. To develop such understanding, a model for dye transport across the mitochondrial inner membrane and partition into the membrane was developed. The model accounts for experimentally measured dye selfquenching and was integrated into a model of mitochondrial electrophysiology to estimate transients in mitochondrial membrane potential from kinetic fluorescence measurements. Our analysis indicates that (i) R123 fluorescence peaks at concentrations near 50 μM due to selfquenching; (ii) measured fluorescence intensity and membrane potential are related by a nonlinear calibration curve sensitive to certain experimental details, including total concentration of dye and mitochondria in suspensions; and (iii) the time courses of membrane potential and electron transport fluxes following a perturbation (i.e. addition of ADP) significantly differ from observed transients in fluorescence intensity. These findings are consistent with the model predictions that mitochondria display a characteristic time of response to changes in substrate concentration of less than 0.1 s, corresponding to the time scale over which the rate of ATP synthesis changes to meet changes in ADP concentration.

Cancer chemoprevention is the most effective approach to control cancer in the population. Despite significant progress, chemoprevention has not been widely adopted because agents that are safe tend to be less effective and those that are highly effective tend to be toxic. Thus, there is an urgent need to develop novel and effective chemopreventive agents, such as mitochondria-targeted agents, that can prevent cancer and prolong survival. Mitochondria, the central site for cellular energy production, have important functions in cell survival and death. Several studies have revealed a significant role for mitochondrial metabolism in promoting cancer development and progression, making mitochondria a promising new target for cancer prevention. Conjugating delocalized lipophilic cations, such as triphenylphosphonium cation (TPP+), to compounds of interest is an effective approach for mitochondrial targeting. The hyperpolarized tumor cell membrane and mitochondrial membrane potential allow for selective accumulation of TPP+ conjugates in tumor cell mitochondria versus those in normal cells. This could enhance direct killing of precancerous, dysplastic, and tumor cells while minimizing potential toxicities to normal cells.

Lung cancer is the leading cause of cancer death worldwide. Vaccination against EGFR can be one of the venues to prevent lung cancer. Blocking glutamine metabolism has been shown to improve anticancer immunity. Here, the authors report that JHU083, an orally active glutamine antagonist prodrug designed to be preferentially activated in the tumor microenvironment, has potent anticancer effects on EGFR‐driven mouse lung tumorigenesis. Lung tumor development is significantly suppressed when treatment with JHU083 is combined with an EGFR peptide vaccine (EVax) than either single treatment. Flow cytometry and single‐cell RNA sequencing of the lung tumors reveal that JHU083 increases CD8+ T cell and CD4+ Th1 cell infiltration, while EVax elicits robust Th1 cell‐mediated immune responses and protects mice against EGFRL858R mutation‐driven lung tumorigenesis. JHU083 treatment decreases immune suppressive cells, including both monocytic‐ and granulocytic‐myeloid‐derived suppressor cells, regulatory T cells, and pro‐tumor CD4+ Th17 cells in mouse models. Interestingly, Th1 cells are found to robustly upregulate oxidative metabolism and adopt a highly activated and memory‐like phenotype upon glutamine inhibition. These results suggest that JHU083 is highly effective against EGFR‐driven lung tumorigenesis and promotes an adaptive T cell‐mediated tumor‐specific immune response that enhances the efficacy of EVax.

Cancer is one of the most serious threats to public health around the world. Efforts in developing new therapies and prevention strategies are clearly insufficient in the face of a dramatically rising disease burden worldwide. New evaluation of alternate strategies, including those based on traditional medicine, is increasingly needed. These therapeutic or prevention approaches could prove complementary to current medical practice or could potentially aid in the development of new classes of pharmaceutical drugs with anti-cancer properties. Prunella vulgaris, a perennial herb, is a representative Chinese herb that has been put into practice to treat various types of diseases, including cancer. The triterpenoid, flavonoids, and phenylpropanoids in P. vulgaris have shown a collective therapeutic effect against cancer mediated through multiple pathways. This review discusses the chemical constituents of P. vulgaris, summarizes all of the known formulas that contain P. vulgaris, and also discusses in vitro, in vivo, and clinical studies on the anti-tumor properties of P. vulgaris. The aim is to bring better insights regarding P. vulgaris as an effective complementary method for treating cancer. Highlighted throughout this review is the necessity for additional prospective clinical trials on anti-tumor properties of P. vulgaris.

Atovaquone, an FDA‐approved drug for malaria, is known to inhibit mitochondrial electron transport. A recently synthesized mitochondria‐targeted atovaquone increased mitochondrial accumulation and antitumor activity in vitro. Using an in situ vaccination approach, local injection of mitochondria‐targeted atovaquone into primary tumors triggered potent T cell immune responses locally and in distant tumor sites. Mitochondria‐targeted atovaquone treatment led to significant reductions of both granulocytic myeloid‐derived suppressor cells and regulatory T cells in the tumor microenvironment. Mitochondria‐targeted atovaquone treatment blocks the expression of genes involved in oxidative phosphorylation and glycolysis in granulocytic‐myeloid‐derived suppressor cells and regulatory T cells, which may lead to death of granulocytic‐myeloid‐derived suppressor cells and regulatory T cells. Mitochondria‐targeted atovaquone inhibits expression of genes for mitochondrial complex components, oxidative phosphorylation, and glycolysis in both granulocytic‐myeloid‐derived suppressor cells and regulatory T cells. The resulting decreases in intratumoral granulocytic‐myeloid‐derived suppressor cells and regulatory T cells could facilitate the observed increase in tumor‐infiltrating CD4 + T cells. Mitochondria‐targeted atovaquone also improves the anti‐tumor activity of PD‐1 blockade immunotherapy. The results implicate granulocytic‐myeloid‐derived suppressor cells and regulatory T cells as novel targets of mitochondria‐targeted atovaquone that facilitate its antitumor efficacy.