Mitochondrial dysfunction-mediated apoptosis resistance associates with defective heat shock protein response in African-American men with prostate cancer

Targeting mitochondria and programmed cell death as potential interventions for metastatic castration-resistant prostate cancer

Prostate cancer is one of the major causes of morbidity and mortality in men worldwide. Most patients with prostate cancer will turn into end-of-life stage when those tumor cells become metastatic castration-resistant prostate cancer (mCRPC). The mCRPC subsequently developed a resistance to androgen signaling. The current regimens for mCRPC therapy are still ineffective. Much evidence from in vitro and in vivo studies explored the roles of therapeutic interventions targeted at the mitochondria and programmed cell death for prostate cancer therapy. The present review will focus on the recent medications which targeted at mitochondria and programmed cell death in mCRPC and the significant findings from each study will be summarized and discussed. Development of therapeutic interventions, particularly at mitochondrial and cytotoxic targets for treatment of mCRPC without inducing cellular toxicity of normal tissues will be considered as the novel therapeutic strategy for mCRPC.

Dichloroacetate for Cancer Treatment: Some Facts and Many Doubts

Rarely has a chemical elicited as much controversy as dichloroacetate (DCA). DCA was initially considered a dangerous toxic industrial waste product, then a potential treatment for lactic acidosis. However, the main controversies started in 2008 when DCA was found to have anti-cancer effects on experimental animals. These publications showed contradictory results in vivo and in vitro such that a thorough consideration of this compound's in cancer is merited. Despite 50 years of experimentation, DCA's future in therapeutics is uncertain. Without adequate clinical trials and health authorities' approval, DCA has been introduced in off-label cancer treatments in alternative medicine clinics in Canada, Germany, and other European countries. The lack of well-planned clinical trials and its use by people without medical training has discouraged consideration by the scientific community. There are few thorough clinical studies of DCA, and many publications are individual case reports. Case reports of DCA's benefits against cancer have been increasing recently. Furthermore, it has been shown that DCA synergizes with conventional treatments and other repurposable drugs. Beyond the classic DCA target, pyruvate dehydrogenase kinase, new target molecules have also been recently discovered. These findings have renewed interest in DCA. This paper explores whether existing evidence justifies further research on DCA for cancer treatment and it explores the role DCA may play in it.

The association between methylmalonic acid, a biomarker of mitochondrial dysfunction, and risk of prostate cancer

BACKGROUND

The aim of the study was to investigate the association between methylmalonic acid (MMA), a biomarker of mitochondrial dysfunction, and the risk of prostate cancer (PCa).

METHODS AND MATERIALS

The relevant data were collected from the National Health and Nutrition Examination Survey (NHANES). Weighted univariable and multivariable logistic regression analyses were performed to investigate the association between MMA and risk of PCa. A stratified analysis was also carried out. The dose-response relationship was elucidated by conducting a restricted cubic spline function.

RESULTS

A total of 2451 participants were included, of which 95 were PCa participants. The fully-adjusted model 2 constructed by weighted multivariable logistic regression analysis showed that the risk of PCa decreased by 53% when every MMA unit was added [OR: 0.47 (0.22-1.00), P = 0.049]. And a decrease in PCa risk was associated with a higher MMA level in MMA subgroups [OR: 0.34 (0.15-0.82), P = 0.02]. The results from a stratified analysis showed that participants in subgroups of other race, BMI (> 30 kg/m2), smoking (former and now), and hypertension (yes), an increase in every MMA unit was linked to a decrease in PCa risk. MMA and the risk of PCa were negatively correlated in a linear manner.

CONCLUSION

It was discovered in the study that an increase in MMA level is connected to a decrease in PCa risk. The serum MMA level may be helpful in assessing PCa risk.

Genetic and biological drivers of prostate cancer disparities in Black men

Black men with prostate cancer have historically had worse outcomes than white men with prostate cancer. The causes of this disparity in outcomes are multi-factorial, but a potential basis is that prostate cancers in Black men are biologically distinct from prostate cancers in white men. Evidence suggests that genetic and ancestral factors, molecular pathways involving androgen and non-androgen receptor signalling, inflammation, epigenetics, the tumour microenvironment and tumour metabolism are contributing factors to the racial disparities observed. Key genetic and molecular pathways linked to prostate cancer risk and aggressiveness have potential clinical relevance. Describing biological drivers of prostate cancer disparities could inform efforts to improve outcomes for Black men with prostate cancer.

Targeting the Metabolic Paradigms in Cancer and Diabetes

Dysregulated metabolic dynamics are evident in both cancer and diabetes, with metabolic alterations representing a facet of the myriad changes observed in these conditions. This review delves into the commonalities in metabolism between cancer and type 2 diabetes (T2D), focusing specifically on the contrasting roles of oxidative phosphorylation (OXPHOS) and glycolysis as primary energy-generating pathways within cells. Building on earlier research, we explore how a shift towards one pathway over the other serves as a foundational aspect in the development of cancer and T2D. Unlike previous reviews, we posit that this shift may occur in seemingly opposing yet complementary directions, akin to the Yin and Yang concept. These metabolic fluctuations reveal an intricate network of underlying defective signaling pathways, orchestrating the pathogenesis and progression of each disease. The Warburg phenomenon, characterized by the prevalence of aerobic glycolysis over minimal to no OXPHOS, emerges as the predominant metabolic phenotype in cancer. Conversely, in T2D, the prevailing metabolic paradigm has traditionally been perceived in terms of discrete irregularities rather than an OXPHOS-to-glycolysis shift. Throughout T2D pathogenesis, OXPHOS remains consistently heightened due to chronic hyperglycemia or hyperinsulinemia. In advanced insulin resistance and T2D, the metabolic landscape becomes more complex, featuring differential tissue-specific alterations that affect OXPHOS. Recent findings suggest that addressing the metabolic imbalance in both cancer and diabetes could offer an effective treatment strategy. Numerous pharmaceutical and nutritional modalities exhibiting therapeutic effects in both conditions ultimately modulate the OXPHOS-glycolysis axis. Noteworthy nutritional adjuncts, such as alpha-lipoic acid, flavonoids, and glutamine, demonstrate the ability to reprogram metabolism, exerting anti-tumor and anti-diabetic effects. Similarly, pharmacological agents like metformin exhibit therapeutic efficacy in both T2D and cancer. This review discusses the molecular mechanisms underlying these metabolic shifts and explores promising therapeutic strategies aimed at reversing the metabolic imbalance in both disease scenarios.

Mitochondrial Alterations in Prostate Cancer: Roles in Pathobiology and Racial Disparities

Prostate cancer (PCa) affects millions of men worldwide and is a major cause of cancer-related mortality. Race-associated PCa health disparities are also common and are of both social and clinical concern. Most PCa is diagnosed early due to PSA-based screening, but it fails to discern between indolent and aggressive PCa. Androgen or androgen receptor-targeted therapies are standard care of treatment for locally advanced and metastatic disease, but therapy resistance is common. Mitochondria, the powerhouse of cells, are unique subcellular organelles that have their own genome. A large majority of mitochondrial proteins are, however, nuclear-encoded and imported after cytoplasmic translation. Mitochondrial alterations are common in cancer, including PCa, leading to their altered functions. Aberrant mitochondrial function affects nuclear gene expression in retrograde signaling and promotes tumor-supportive stromal remodeling. In this article, we discuss mitochondrial alterations that have been reported in PCa and review the literature related to their roles in PCa pathobiology, therapy resistance, and racial disparities. We also discuss the translational potential of mitochondrial alterations as prognostic biomarkers and as effective targets for PCa therapy.

Racial disparity in prostate cancer in the African American population with actionable ideas and novel immunotherapies

BACKGROUND

African Americans (AAs) in the United States are known to have a higher incidence and mortality for Prostate Cancer (PCa). The drivers of this epidemiological disparity are multifactorial, including socioeconomic factors leading to lifestyle and dietary issues, healthcare access problems, and potentially tumor biology.

RECENT FINDINGS

Although recent evidence suggests once access is equal, AA men have equal outcomes to Caucasian American (CA) men, differences in PCa incidence remain, and there is much to do to reverse disparities in mortality across the USA. A deeper understanding of these issues, both at the clinical and molecular level, can facilitate improved outcomes in the AA population. This review first discusses PCa oncogenesis in the context of its diverse hallmarks before benchmarking key molecular and genomic differences for PCa in AA men that have emerged in the recent literature. Studies have emphasized the importance of tumor microenvironment that contributes to both the unequal cancer burden and differences in clinical outcome between the races. Management of comorbidities like obesity, hypertension, and diabetes will provide an essential means of reducing prostate cancer incidence in AA men. Although requiring further AA specific research, several new treatment strategies such as immune checkpoint inhibitors used in combination PARP inhibitors and other emerging vaccines, including Sipuleucel-T, have demonstrated some proven efficacy.

CONCLUSION

Genomic profiling to integrate clinical and genomic data for diagnosis, prognosis, and treatment will allow physicians to plan a "Precision Medicine" approach to AA men. There is a pressing need for further research for risk stratification, which may allow early identification of AA men with higher risk disease based on their unique clinical, genomic, and immunological profiles, which can then be mapped to appropriate clinical trials. Treatment options are outlined, with a concise description of recent work in AA specific populations, detailing several targeted therapies, including immunotherapy. Also, a summary of current clinical trials involving AA men is presented, and it is important that policies are adopted to ensure that AA men are actively recruited. Although it is encouraging that many of these explore the lifestyle and educational initiatives and therapeutic interventions, there is much still work to be done to reduce incidence and mortality in AA men and equalize current racial disparities.

HSP60 in cancer: a promising biomarker for diagnosis and a potentially useful target for treatment

Heat shock proteins (HSPs), most of which are molecular chaperones, are highly conserved proteins produced by cells under physiological stress or pathological conditions. HSP60 (57-69 kDa) can promote or inhibit cell apoptosis through different mechanisms, and its abnormal expression is also related to tumour cell metastasis and drug resistance. In recent years, HSP60 has received increasing attention in the field of cancer research due to its potential as a diagnostic and prognostic biomarker or therapeutic target. However, in different types of cancer, the specific mechanisms of abnormally expressed HSP60 in tumour carcinogenesis and drug resistance are complicated and still require further study. In this article, we comprehensively review the regulative mechanisms of HSP60 on apoptosis, its applications as a cancer diagnostic biomarker and a therapeutic target, evidence of involvement in tumour resistance and the applications of exosomal HSP60 in liquid biopsy. By evaluating the current findings of HSP60 in cancer research, we highlight some core issues that need to be addressed for the use of HSP60 as a diagnostic or prognostic biomarker and therapeutic target in certain types of cancer.

Dichloroacetate and PX-478 exhibit strong synergistic effects in a various number of cancer cell lines

Background

One key approach for anticancer therapy is drug combination. Drug combinations can help reduce doses and thereby decrease side effects. Furthermore, the likelihood of drug resistance is reduced. Distinct alterations in tumor metabolism have been described in past decades, but metabolism has yet to be targeted in clinical cancer therapy. Recently, we found evidence for synergism between dichloroacetate (DCA), a pyruvate dehydrogenase kinase inhibitor, and the HIF-1α inhibitor PX-478. In this study, we aimed to analyse this synergism in cell lines of different cancer types and to identify the underlying biochemical mechanisms.

Methods

The dose-dependent antiproliferative effects of the single drugs and their combination were assessed using SRB assays. FACS, Western blot and HPLC analyses were performed to investigate changes in reactive oxygen species levels, apoptosis and the cell cycle. Additionally, real-time metabolic analyses (Seahorse) were performed with DCA-treated MCF-7 cells.

Results

The combination of DCA and PX-478 produced synergistic effects in all eight cancer cell lines tested, including colorectal, lung, breast, cervical, liver and brain cancer. Reactive oxygen species generation and apoptosis played important roles in this synergism. Furthermore, cell proliferation was inhibited by the combination treatment.

Conclusions

Here, we found that these tumor metabolism-targeting compounds exhibited a potent synergism across all tested cancer cell lines. Thus, we highly recommend the combination of these two compounds for progression to in vivo translational and clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08186-9.

Synergistic effect of dichloroacetate on talaporfin sodium-based photodynamic therapy on U251 human astrocytoma cells

BACKGROUND

Talaporfin sodium (TS) is an authorized photosensitizer for photodynamic therapy (PDT) against some tumors in Japan; however, the drawbacks of the drug include its high cost and side effects. Thus, reducing the dose of TS in each round of TS-PDT against tumors is important for reducing treatment costs and improving patients' quality of life. Dichloroacetate (DCA) is approved for treating lactic acidosis and hereditary mitochondrial diseases, and it is known to enhance reactive oxygen species production and induce apoptosis in cancer cells. Therefore, DCA has the potential to enhance the effects of TS-PDT and permit the use of lower TS doses without reducing the anti-cancer effect.

METHODS

U251 human astrocytoma cells were simultaneously incubated with TS and DCA using different concentrations, administration schedules, and treatment durations, followed by laser irradiation. Cell viability was determined using the CCK-8 assay.

RESULTS

The combinational use of DCA and TS resulted in synergistically enhanced TS-PDT effects in U251 cells. The duration of DCA treatment before TS-PDT slightly enhanced the efficacy of TS-PDT. The intensity of laser irradiation was not associated with the synergistic effect of DCA on TS-PDT. In addition, the relationship between the elapsed time after TS/DCA combination treatment and PDT ineffectiveness was identical to that of TS monotherapy.

CONCLUSIONS

DCA synergistically enhanced the anti-cancer effect of TS-PDT, illustrating its potential for drug repositioning in cancer therapy in combination with PDT.

Pyruvate dehydrogenase kinase 1 interferes with glucose metabolism reprogramming and mitochondrial quality control to aggravate stress damage in cancer

Pyruvate dehydrogenase kinase 1 (PDK1) is a key factor in the connection between glycolysis and the tricarboxylic acid cycle. Restoring the mitochondrial OXPHOS function by inhibiting glycolysis through targeting PDK1 has become a hot spot for tumor therapy. However, the specific mechanism by which metabolic changes affect mitochondrial function remains unclear. Recent studies have found that mitochondrial quality control such as mitochondrial protein homeostasis plays an important role in maintaining mitochondrial function. Here, we focused on PDK1 and explored the specific mechanism by which metabolic changes affect mitochondrial OXPHOS function. We showed that glucose metabolism in HepG2 and HepG3B cells switched from anaerobic glycolysis to the mitochondrial tricarboxylic acid cycle under different concentrations of dichloroacetate (DCA) or short hairpin PDK1. After DCA treatment or knockdown of PDK1, the mitochondrial morphology was gradually condensed and exhibited shorter and more fragmented filaments. Additionally, expression of the mitochondrial autophagy proteins parkin and PTEN-induced kinase was down-regulated, and the biosynthetic protein peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1α) and its regulated complex I, III, IV, and V protein were down-regulated. This indicated that PDK1 inhibition affected the level of mitochondrial quality control. Analysis of mitochondrial function revealed significantly increased mitochondrial reactive oxygen species and decreased membrane potential. Therefore, glucose metabolism reprogramming by PDK1 inhibition could induce mitochondrial quality control disorders to aggravate mitochondrial stress damage.

Hsp60 and IL-8 axis promotes apoptosis resistance in cancer

Background

Interleukin-8 (IL-8) and heat shock protein 60 (Hsp60) play crucial roles in cell survival and maintenance of cellular homoeostasis. However, cross talks between these two proteins are not defined.

Methods

IL-8 expression in tumour tissue sections was analysed by immunohistochemistry. IL-8 expression and release in cancer cells was quantified using enzyme-linked immunosorbent assay (ELISA). Apoptosis was quantified using caspase activity and Annexin-V/PI staining.

Results

We observed IL-8 release from cancer cells in response to histone deacetylase inhibitor, apicidin (Api), and non-competitive inhibitor of the sarco/endoplasmic reticulum Ca²⁺ ATPase, thapsigargin (TG). IL-8 release was increased upon TG-treatment. TG-induced IL-8 expression was reduced in the presence of Api in Bax-dependent manner. Increased apoptosis was associated with decreased IL-8 expression in response to combined treatment of TG and Api. TG and Api combination induced caspase-8 and caspase-9 dependent apoptosis. Hsp60 knockdown abrogated IL-8 expression induced by Api, TG, and their combination. The level of TGF-β, an upstream regulator of IL-8, was decreased upon Hsp60-silencing. Knocking down Hsp60 decreased IL-8 expression and its release in prostate cancer cell xenograft tumours in SCID mice.

Conclusion

This study describes the underlying mechanism associated with apoptosis resistance mediated via Hsp60-IL-8 axis in cancer.

Race-associated expression of MHC class I polypeptide-related sequence A (MICA) in prostate cancer

Despite the lack of a complete understanding of the disparities involved, prostate cancer (PCa) has both higher incidence and death rates in African American Men (AAM) relative to those of Caucasian American Men (CAM). MHC class I polypeptide related sequence A (MICA) is an innate immunity protein involved in tumor immunoevasion. Due to a lack of reports of race-specific expression of MICA in PCa, we evaluated MICA expression in patients' tumors and in cell lines from a racially diverse origin. Immunohistochemistry was done on a tissue microarray (TMA) with antibodies against MICA. Tumor MICA mRNA was assessed by data mining using Oncomine and PROGeneV2. Surface MICA and release rate of soluble (s) MICA was evaluated in PCa cell lines originally derived from African American (MDA-PCa-2b) or Caucasian (LNCaP and DU-145) PCa patients. Prostate tumor tissue had a 1.7-fold higher MICA expression relative to normal tissue (p < .0001). MICA immunoreactivity in PCa tissue from AAM was 24% lower (p = .002) compared to CAM. Survival analysis revealed a marginal association of low MICA with poor overall survival (OS) (p = .058). By data mining analysis, a 2.9-fold higher level of MICA mRNA was evidenced in tumor compared to normal tissue (p < .0001). Tumors from AAM had 24% lower levels of MICA mRNA compared to tumors from CAM (p = .038), and poor prognosis was found for patients with lower MICA mRNA (p = .028). By flow cytometry analysis, cell fraction positive for surface MICA was of 3% in MDA-PCa-2b cells, 54% in DU-145 cells, and 67% in LNCaP cells (p < .0001). sMICA was detected in DU-145 and LNCaP cells, but was not detected in MDA-PCa-2b cells. Both LNCaP and DU-145 cells were sensitive to cytolysis mediated by Natural killer (NK) cells. MDA-PCa-2b cells, however were between 1.3-fold at 10:1 Effector:Target (E:T) ratio (p < .0001) and 2-fold at 50:1 E:T ratio (p < .0001) more resistant to NK-mediated cytolysis relative to cells from Caucasian origin. These results suggest that MICA expression may be related to the aggressive nature of PCa. Our findings also demonstrate for the first time that there are variations in MICA expression in the context of racial differences. This study establishes a rationale for further investigation of MICA as a potential race-specific prognostic marker in PCa.

Reactive oxygen species and cancer: A complex interaction

Elevated levels of Reactive Oxygen Species (ROS), increased antioxidant ability and the maintenance of redox homeostasis can cumulatively contribute to tumor progression and metastasis. The sources and the role of ROS in a heterogeneous tumor microenvironment can vary at different stages of tumor: initiation, development, and progression, thus making it a complex subject. In this review, we have summarized the sources of ROS generation in cancer cells, its role in the tumor microenvironment, the possible functions of ROS and its important scavenger systems in tumor progression with special emphasis on solid tumors.

Dichloroacetic acid upregulates apoptosis of ovarian cancer cells by regulating mitochondrial function

Background

Metabolic reprogramming is a characteristic of tumor cells and is considered a potential therapeutic target. Even under aerobic conditions, tumor cells use glycolysis to produce energy, a phenomenon called the “Warburg effect”. Pyruvate dehydrogenase kinase 1 (PDK1) is a key factor linking glycolysis and the tricarboxylic acid cycle. Dichloroacetic acid (DCA) reverses the Warburg effect by inhibition of PDK1 to switch cytoplasmic glucose metabolism to mitochondrial oxidative phosphorylation (OXPHOS).

Methods

Cell viability was examined using a standard MTT assay. Glucose consumption and l-lactate production were measured using commercial colorimetric kits, and intracellular lactate dehydrogenase (LDH) activity was evaluated using cell lysates and an LDH Quantification Kit. Real-time PCR was used to detect the expression of related genes. The production of total ROS was evaluated by staining with dichlorofluorescin diacetate.

Results

Comparison of various aspects of glucose metabolism, such as expression of key enzymes in glycolysis, lactate production, glucose consumption, mitochondrial oxygen consumption rate, and citric acid production, revealed that A2780/DDP cells were primarily dependent on glycolysis whereas A2780 cells were primarily dependent on mitochondrial OXPHOS. Mitochondrial uncoupling protein 2 (UCP2) protects against mitochondrial ROS while allowing energy metabolism to switch to glycolysis. Treatment of A2780 cells with various concentrations of DCA resulted in decreased expression of UCP2, a metabolic switch from glycolysis to mitochondrial OXPHOS, and an increase in oxidative stress induced by ROS. These effects were not observed in A2780/DDP cells with higher UCP2 expression suggesting that UCP2 might induce changes in mitochondrial functions that result in different sensitivities to DCA.

Conclusion

Our results show that a drug targeting tumor metabolic changes affects almost the entire process of glucose metabolism. Thus, it is necessary to comprehensively determine tumor metabolic functions to facilitate individualized antitumor therapy.

Cytochrome c Deficiency Confers Apoptosome and Mitochondrial Dysfunction in African-American Men with Prostate Cancer

Although African-American (AA) patients with prostate cancer tend to develop greater therapeutic resistance and faster prostate cancer recurrence compared with Caucasian-American (CA) men, the molecular mechanisms of this racial prostate cancer disparity remain undefined. In this study, we provide the first comprehensive evidence that cytochrome c deficiency in AA primary tumors and cancer cells abrogates apoptosome-mediated caspase activation and contributes to mitochondrial dysfunction, thereby promoting therapeutic resistance and prostate cancer aggressiveness in AA men. In AA prostate cancer cells, decreased nuclear accumulation of nuclear respiration factor 1 (Nrf1) and its subsequent loss of binding to the cytochrome c promoter mediated cytochrome c deficiency. The activation of cellular Myc (c-Myc) and NF-κB or inhibition of AKT prevented nuclear translocation of Nrf1. Genetic and pharmacologic inhibition of c-Myc and NF-κB or activation of AKT promoted Nrf1 binding to cytochrome c promoter, cytochrome c expression, caspase activation, and cell death. The lack of p-Drp1^S616 in AA prostate cancer cells contributed to defective cytochrome c release and increased resistance to apoptosis, indicating that restoration of cytochrome c alone may be insufficient to induce effective apoptosis. Cytochrome c deficiency promoted the acquisition of glycolytic phenotypes and mitochondrial dysfunction, whereas cytochrome c restoration via inhibition of c-Myc and NF-κB or activation of AKT attenuated glycolysis in AA prostate cancer cells. Inhibition of c-Myc and NF-κB enhanced the efficacy of docetaxel in tumor xenografts. Therefore, restoring cytochrome c may overcome therapeutic resistance and prostate cancer aggressiveness in AA men. Overall, this study provides the first comprehensive experimental, mechanistic, and clinical evidence for apoptosome and mitochondrial dysfunction in prostate cancer racial disparity. SIGNIFICANCE: Mechanistic insights on prostate cancer health disparity among American men provide novel approaches to restore mitochondrial function, which can address therapeutic resistance and aggressiveness in African-American men with prostate cancer.

Mitochondrial biology and prostate cancer ethnic disparity

Prostate cancer remains the second most prevalent cancer in men. Its incidence, progression and mortality profiles vary significantly by race and ethnicity, with African-American men having the highest incidence rate and mortality rate in the world. Although these disparities can be partially explained by socioeconomic factors, the underlying molecular causes are complex and require careful research. A considerable amount of literature exists, supporting the association between mitochondrial health and the incidence, aggression and risk of prostate cancer. Genetic alterations in mitochondrial DNA are frequent in prostate cancer; therefore, the resulting mitochondrial dysfunction and metabolic dysregulation may contribute to or indicate oncogenesis. Many of the prominent features of cancer cells are also closely related to mitochondrial functions, such as resistance to apoptosis, excess reactive oxygen species production and altered oxidative phosphorylation. In addition, prostate cancer ethnic disparity is influenced by environmental and lifestyle factors, which involves differences in mitochondrial metabolism and retrograde signaling events.

Mitochondrial determinants of cancer health disparities

Mitochondria, which are multi-functional, have been implicated in cancer initiation, progression, and metastasis due to metabolic alterations in transformed cells. Mitochondria are involved in the generation of energy, cell growth and differentiation, cellular signaling, cell cycle control, and cell death. To date, the mitochondrial basis of cancer disparities is unknown. The goal of this review is to provide an understanding and a framework of mitochondrial determinants that may contribute to cancer disparities in racially different populations. Due to maternal inheritance and ethnic-based diversity, the mitochondrial genome (mtDNA) contributes to inherited racial disparities. In people of African ancestry, several germline, population-specific haplotype variants in mtDNA as well as depletion of mtDNA have been linked to cancer predisposition and cancer disparities. Indeed, depletion of mtDNA and mutations in mtDNA or nuclear genome (nDNA)-encoded mitochondrial proteins lead to mitochondrial dysfunction and promote resistance to apoptosis, the epithelial-to-mesenchymal transition, and metastatic disease, all of which can contribute to cancer disparity and tumor aggressiveness related to racial disparities. Ethnic differences at the level of expression or genetic variations in nDNA encoding the mitochondrial proteome, including mitochondria-localized mtDNA replication and repair proteins, miRNA, transcription factors, kinases and phosphatases, and tumor suppressors and oncogenes may underlie susceptibility to high-risk and aggressive cancers found in African population and other ethnicities. The mitochondrial retrograde signaling that alters the expression profile of nuclear genes in response to dysfunctional mitochondria is a mechanism for tumorigenesis. In ethnic populations, differences in mitochondrial function may alter the cross talk between mitochondria and the nucleus at epigenetic and genetic levels, which can also contribute to cancer health disparities. Targeting mitochondrial determinants and mitochondrial retrograde signaling could provide a promising strategy for the development of selective anticancer therapy for dealing with cancer disparities. Further, agents that restore mitochondrial function to optimal levels should permit sensitivity to anticancer agents for the treatment of aggressive tumors that occur in racially diverse populations and hence help in reducing racial disparities.

Racial differences in the expression of inhibitors of apoptosis (IAP) proteins in extracellular vesicles (EV) from prostate cancer patients

African-American men with prostate cancer typically develop more aggressive tumors than men from other racial/ethnic groups, resulting in a disproportionately high mortality from this malignancy. This study evaluated differences in the expression of inhibitors of apoptosis proteins (IAPs), a known family of oncoproteins, in blood-derived exosomal vesicles (EV) between African-American and European-American men with prostate cancer. The ExoQuick™ method was used to isolate EV from both plasma and sera of African-American (n = 41) and European-American (n = 31) men with prostate cancer, as well as from controls with no cancer diagnosis (n = 10). EV preparations were quantified by acetylcholinesterase activity assays, and assessed for their IAP content by Western blotting and densitometric analysis. Circulating levels of the IAP Survivin were evaluated by ELISA. We detected a significant increase in the levels of circulating Survivin in prostate cancer patients compared to controls (P<0.01), with the highest levels in African-American patients (P<0.01). African-American patients with prostate cancer also contained significantly higher amounts of EVs in their plasma (P<0.01) and sera (P<0.05) than European-American patients. In addition, EVs from African-American patients with prostate cancer contained significantly higher amounts of the IAPs Survivin (P<0.05), XIAP (P<0.001), and cIAP-2 (P<0.01) than EVs from European-American patients. There was no significant correlation between expression of IAPs and clinicopathological parameters in the two patient groups. Increased expression of IAPs in EVs from African-American patients with prostate cancer may influence tumor aggressiveness and contribute to the mortality disparity observed in this patient population. EVs could serve as reservoirs of novel biomarkers and therapeutic targets that may have clinical utility in reducing prostate cancer health disparities.

Investigation of Mitochondrial Metabolic Response to Doxorubicin in Prostate Cancer Cells: An NADH, FAD and Tryptophan FLIM Assay

Prostate cancer (PCa) is one of the leading cancers in men in the USA. Lack of experimental tools that predict therapy response is one of the limitations of current therapeutic regimens. Mitochondrial dysfunctions including defective oxidative phosphorylation (OXPHOS) in cancer inhibit apoptosis by modulating ROS production and cellular signaling. Thus, correction of mitochondrial dysfunction and induction of apoptosis are promising strategies in cancer treatment. We have used Fluorescence Lifetime Imaging Microscopy (FLIM) to quantify mitochondrial metabolic response in PCa cells by tracking auto-fluorescent NAD(P)H, FAD and tryptophan (Trp) lifetimes and their enzyme-bound fractions as markers, before and after treatment with anti-cancer drug doxorubicin. A 3-channel FLIM assay and quantitative analysis of these markers for cellular metabolism show in response to doxorubicin, NAD(P)H mean fluorescence lifetime (τ_m) and enzyme-bound (a₂%) fraction increased, FAD enzyme-bound (a₁%) fraction was decreased, NAD(P)H-a₂%/FAD-a₁% FLIM-based redox ratio and ROS increased, followed by induction of apoptosis. For the first time, a FRET assay in PCa cells shows Trp-quenching due to Trp-NAD(P)H interactions, correlating energy transfer efficiencies (E%) vs NAD(P)H-a₂%/FAD-a₁% as sensitive parameters in predicting drug response. Applying this FLIM assay as early predictor of drug response would meet one of the important goals in cancer treatment.

Inhibition of COX2 enhances the chemosensitivity of dichloroacetate in cervical cancer cells

Dichloroacetate (DCA), a traditional mitochondria-targeting agent, has shown promising prospect as a sensitizer in fighting against malignancies including cervical cancer. But it is unclear about the effect of DCA alone on cervical tumor. Moreover, previous reports have demonstrated that the increased cyclooxygenase-2 (COX2) expression is associated with chemoresistance and poor prognosis of cervical cancer. However, it is still unknown whether COX2 can affect the sensitivity of DCA in cervical cancer cells. In this study, we found that cervical cancer cells were insensitive to DCA. Furthermore, we for the first time revealed that DCA could upregulate COX2 which impeded the chemosensitivity of DCA in cervical cancer cells. Mechanistic study showed that DCA reduced the level of RNA binding protein quaking (QKI), leading to the decay suppression of COX2 mRNA and the subsequent elevation of COX2 protein. Inhibition of COX2 using celecoxib could sensitize DCA in repressing the growth of cervical cancer cells both in vitro and in vivo. These results indicate that COX2 is a novel resistance factor of DCA, and combination of celecoxib with DCA may be beneficial to the treatment of cervical cancer.

Differential expression of miR-34b and androgen receptor pathway regulate prostate cancer aggressiveness between African-Americans and Caucasians

African-Americans are diagnosed with more aggressive prostate cancers and have worse survival than Caucasians, however a comprehensive understanding of this health disparity remains unclear. To clarify the mechanisms leading to this disparity, we analyzed the potential involvement of miR-34b expression in African-Americans and Caucasians. miR-34b functions as a tumor suppressor and has a multi-functional role, through regulation of cell proliferation, cell cycle and apoptosis. We found that miR-34b expression is lower in human prostate cancer tissues from African-Americans compared to Caucasians. DNA hypermethylation of the miR-34b-3p promoter region showed significantly higher methylation in prostate cancer compared to normal samples. We then sequenced the promoter region of miR-34b-3p and found a chromosomal deletion in miR-34b in African-American prostate cancer cell line (MDA-PCA-2b) and not in Caucasian cell line (DU-145). We found that AR and ETV1 genes are differentially expressed in MDA-PCa-2b and DU-145 cells after overexpression of miR-34b. Direct interaction of miR-34b with the 3' untranslated region of AR and ETV1 was validated by luciferase reporter assay. We found that miR-34b downregulation in African-Americans is inversely correlated with high AR levels that lead to increased cell proliferation. Overexpression of miR-34b in cell lines showed higher inhibition of cell proliferation, apoptosis and G1 arrest in the African-American cells (MDA-PCa-2b) compared to Caucasian cell line (DU-145). Taken together, our results show that differential expression of miR-34b and AR are associated with prostate cancer aggressiveness in African-Americans.

Endoplasmic reticulum-mediated unfolded protein response and mitochondrial apoptosis in cancer

Abrogation of endoplasmic reticulum (ER) protein folding triggered by exogenous or endogenous factors, stimulates a cellular stress response, termed ER stress. ER stress re-establishes ER homeostasis through integrated signaling termed the ER-unfolded protein response (UPR^ER). In the presence of severe toxic or prolonged ER stress, the pro-survival function of UPR^ER is transformed into a lethal signal transmitted to and executed through mitochondria. Mitochondria are key for both apoptotic and autophagic cell death. Thus ER is vital in sensing and coordinating stress pathways to maintain overall physiological homeostasis. However, this function is deregulated in cancer, resulting in resistance to apoptosis induction in response to various stressors including therapeutic agents. Here we review the connections between ER stress and mitochondrial apoptosis, describing potential cancer therapeutic targets.