KISS1 in metastatic cancer research and treatment: potential and paradoxes

The significance of KISS1 goes beyond its original discovery as a metastasis suppressor. Its function as a neuropeptide involved in diverse physiologic processes is more well studied. Enthusiasm regarding KISS1 has cumulated in clinical trials in multiple fields related to reproduction and metabolism. But its cancer therapeutic space is unsettled. This review focuses on collating data from cancer and non-cancer fields in order to understand shared and disparate signaling that might inform clinical development in the cancer therapeutic and biomarker space. Research has focused on amino acid residues 68-121 (kisspeptin 54), binding to the KISS1 receptor and cellular responses. Evidence and counterevidence regarding this canonical pathway require closer look at the covariates so that the incredible potential of KISS1 can be realized.

Abstract 2662: Mitochondrial genetics appear to alter immune cell development/trafficking

Background Metastatic burden is the leading cause of cancer deaths; however, it remains unclear why some patients are more susceptible to metastatic disease. While the nuclear genome's role in tumor progression and metastasis is known, the role of mitochondrial DNA (mtDNA) polymorphisms (SNP) has only recently been explored. Using mitochondrial nuclear exchange (MNX) mice, we previously showed that mtDNA strongly influences mammary carcinoma progression and metastasis both intrinsically and via non-cell autonomous mechanisms. We hypothesized that mtDNA SNP alter immune cell development/trafficking which, in turn, could influence metastasis efficiency.

Methods Peritoneal exudate, and splenocytes were collected from male and female wild-type C57BL/6J (CC) and C3H/HeN (HH), and MNX mice - C57BL/6-mtMNX(C3H/HeN) (CH) and C3H/HeN-mtMNX(C57BL/6J) (HC) mice [first letter=nuclear; second letter=mitochondrial]. Lung metastases were established from tail-vein injection of E0771 (CC/CH) or K1735-M2 (HH/HC) cell lines.

Results Lung metastases derived from histocompatible (i.e. nDNA matched) tumor cell injection into wild-type or MNX mice increased in C3H/HeN mtDNA backgrounds (HH and CH). No significant differences were observed in seeding, suggesting that mtDNA mediated differences in metastatic microenvironments likely impact metastatic outgrowth. No significant changes in broad immune cell populations were observed in naïve animals, but selective changes in differentiation markers were observed. The most significant change was lower CD11c+ peritoneal macrophages in HH (3%) versus CC (16%) mice (p < 0.001). C57BL/6 mtDNA (HC) increased the percentage of macrophages (9%) compared to wild-type (HH) (p < 0.001). We next confirmed a role for mitochondrial derived ROS mediating immune microenvironmental regulation of metastasis, as mtDNA mediated metastatic differences are abrogated upon treatment with the anti-oxidant MitoTEMPO. Tumor infiltrating CD8+ lymphocytes (TIL) increased 1.5-fold in CH (1.7%) compared to wild-type CC (1.2%) (p = 0.07) while no differences were observed between HH and HC mice. Consistent with changes in metastasis in the HH background, MitoTempo treatment reduced CD4+ TIL >1.5-fold (1.5%), compared to the vehicle control (2.8%) (p = 0.029).

Discussion Our data support the hypothesis that mitochondrial SNP modulate immune cell development and/or trafficking, providing a plausible explanation for how metastatic potentials of syngeneic tumor cells injected into MNX mice are altered. That is, mtDNA contributions to immune function affect metastasis and may provide insight as to why some immune therapies succeed/fail.

Support: DOD BCRP BC171381 and Kansas INBRE P20 GM103418 (TCB); Susan G. Komen for the Cure SAC110037; National Foundation for Cancer Research and NIH CA168524 (DRW)

Citation Format: Thomas C. Beadnell, Amanda E. Brinker, Cori Fain, Carolyn J. Vivian, Danny R. Welch. Mitochondrial genetics appear to alter immune cell development/trafficking [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2662.

Abstract IA30: Intrinsic and extrinsic contributions of mitochondrial DNA to metastatic efficiency: A genetic explanation for disparities in metastasis efficiency?

Single-nucleotide polymorphisms (SNP) in nuclear and mitochondrial DNA are used to define clades (or races) in people, as well as different strains in mice (PMID: 27383787). Previous studies showed that nuclear SNP determine metastasis efficiency; we hypothesized that mtDNA SNP could also play roles in tumorigenicity and metastasis. Mitochondrial Nuclear Exchange (MNX) mice, created by transferring an oocyte nucleus from strainx into an enucleated oocyte from strainy (PMID: 27840835), show that mammary tumor formation and metastasis are regulated by inherited mitochondrial polymorphisms when MNX mice were bred to MMTV-PyMT or MMTV-HER2 mice (PMID: 26471915; 29070615). Since stromal compartments also possess changed mitochondria in MNX mice, we hypothesized that mitochondrial SNP in noncancer compartments could exert effects on tumor formation or metastasis in addition to genetic (cell autonomous) changes. Syngeneic tumor cells were injected into MNX mice with the same nuclear (and, therefore, same histocompatibility) background. Experimental metastasis was compared between wild-type and MNX mice (i.e., with same or different mtDNA backgrounds, respectively). E0771 mammary carcinoma and B16-F10 melanoma cells (both syngeneic to C57BL/6J), formed significantly (P<0.01) more lung metastases in C57BL/6J-mtMNX(C3H/HeN). K1735-M2 melanoma cells (syngeneic to C3H/HeN) formed significantly (P<0.05) fewer lung metastases in C3H/HeNmtMNX(C57BL/6J) mice. These results have been replicated ≥3 times using >10 mice per experiment. C57BL/6J mitochondria confer resistance to metastasis in both cell autonomous and non-cell autonomous experiments. Basal metabolic and ROS differences comparing mouse embryonic fibroblasts isolated from wild-type and MNX mice exist and may be responsible for the stromal effects. Likewise, significant and statistically significant differences in MNX mice for nuclear DNA methylation (PMID: 28663334) and epigenetic marks (J. McGuire & D.R. Welch, in preparation), immune (T.C. Beadnell & D.R. Welch, in preparation) and microbota (S.J. Manley & D.R. Welch, in preparation) profiles are observed. Together, our findings highlight the striking influences that mitochondrial haplotypes can exert on tumorigenicity and metastasis via both intrinsic and extrinsic mechanisms. These findings also suggest that mitochondrial SNP could serve, in part, as a genetic basis to explain racial disparities with regard to cancer aggressiveness.

Support: Susan G. Komen for the Cure (SAC11037), Natl. Fndn. Cancer Res., CA168524, W81XWH-18-1-0450, GM103418.

Citation Format: Danny R. Welch. Intrinsic and extrinsic contributions of mitochondrial DNA to metastatic efficiency: A genetic explanation for disparities in metastasis efficiency? [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr IA30.

Role of the tumor microenvironment in regulating the anti-metastatic effect of KISS1

KISS1, a metastasis suppressor gene, has been shown to block metastasis without affecting primary tumor formation. Loss of KISS1 leads to invasion and metastasis in multiple cancers, which is the leading cause of cancer morbidity and mortality. The discovery of KISS1 has provided a ray of hope for early clinical diagnosis and for designing effective treatments targeting metastatic cancer. However, this goal requires greater holistic understanding of its mechanism of action. In this review, we go back into history and highlight some key developments, from the discovery of KISS1 to its role in regulating multiple physiological processes including cancer. We discuss key emerging roles for KISS1, specifically interactions with tissue microenvironment to promote dormancy and regulation of tumor cell metabolism, acknowledged as some of the key players in tumor progression and metastasis. We finally discuss strategies whereby KISS1 might be exploited clinically to treat metastasis.

Mitochondrial Haplotype of the Host Stromal Microenvironment Alters Metastasis in a Non-cell Autonomous Manner

Mitochondria contribute to tumor growth through multiple metabolic pathways, regulation of extracellular pH, calcium signaling, and apoptosis. Using the Mitochondrial Nuclear Exchange (MNX) mouse models, which pair nuclear genomes with different mitochondrial genomes, we previously showed that mitochondrial SNPs regulate mammary carcinoma tumorigenicity and metastatic potential in genetic crosses. Here, we tested the hypothesis that polymorphisms in stroma significantly affect tumorigenicity and experimental lung metastasis. Using syngeneic cancer cells (EO771 mammary carcinoma and B16-F10 melanoma cells) injected into wild-type and MNX mice (i.e., same nuclear DNA but different mitochondrial DNA), we showed mt-SNP-dependent increases (C3H/HeN) or decreases (C57BL/6J) in experimental metastasis. Superoxide scavenging reduced experimental metastasis. In addition, expression of lung nuclear-encoded genes changed specifically with mt-SNP. Thus, mitochondrial-nuclear cross-talk alters nuclear-encoded signaling pathways that mediate metastasis via both intrinsic and extrinsic mechanisms. SIGNIFICANCE: Stromal mitochondrial polymorphisms affect metastatic colonization through reactive oxygen species and mitochondrial-nuclear cross-talk.

Abstract P5-05-09: Chemo-sensitization of triple negative breast cancer by targeting RNA-binding protein HuR

Triple negative breast cancer (TNBC) has a lower 5-year survival rate and higher recurrence rate compared to other types of breast cancer, which is partially due to the acquired resistance to current treatment regimens. The RNA-binding protein Hu antigen R (HuR) is overexpressed in breast cancer. Cytoplasmic HuR accumulation correlates with high-grade malignancy, poor distant disease-free survival and serves as a prognostic factor for poor clinical outcome in breast cancer. HuR promotes tumorigenesis by promoting mRNA stability and translation of proteins implicated in proliferation, survival, angiogenesis, invasion, and metastasis. HuR also modulates sensitivity of breast cancer cells to chemotherapy. HuR knockout in TNBC cells with high HuR sensitizes them to chemotherapy while HuR overexpression induces chemo-resistance. Meanwhile, chemotherapy promotes cytoplasmic HuR accumulation and increases expression of HuR target encoding proteins in TNBC cells. Therefore, there is a positive feedback loop between HuR and chemo-resistance. These findings suggest that HuR plays a critical role in promoting a drug-resistance mechanism and HuR is a potential target for developing a novel therapy to overcome chemo-resistance in TNBC. RNA-binding proteins such as HuR had previously been considered to be “undruggable” due to the lack of a well-defined binding pocket for target RNAs. Nevertheless, using high throughput screening followed by structure-based rational design and lead optimization, we have identified small molecules that potently inhibit HuR-mRNA interaction with nM to sub-µM potency. Our top HuR inhibitor, KH-3, inhibits TNBC cell growth in vitro and in vivo. KH-3 also sensitizes TNBC cells to docetaxel and doxorubicin treatment in vitro. Furthermore, acquired docetaxel-resistant MDA-MB-231 cells and doxorubicin-resistant MDA-MB-231 cells display similar sensitivity to KH-3 to their parental cells. In the study of mechanism of action, several HuR direct targets are found to be involved in acquired docetaxel and doxorubicin resistance. KH-3 can disrupt the interaction of HuR with those target mRNAs. In animal efficacy studies, the combination of KH-3 and chemotherapy shows synergistic effect in both parental and acquired resistant cell xenograft models. Our data provide a proof-of-principle that HuR inhibition by KH-3 may be developed as a promising molecular therapy to overcome chemo-resistance of TNBC with high HuR.

Citation Format: Xiaoqing Wu, Lanjing Wei, Gulhumay Gardashova, Cuncong Zhong, Lan Lan, Qi Zhang, Dan A Dixon, Danny R Welch, Jeffrey Aubé, Liang Xu. Chemo-sensitization of triple negative breast cancer by targeting RNA-binding protein HuR [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-05-09.

KISS1 in breast cancer progression and autophagy

Tumor suppressors are cellular proteins typically expressed in normal (non-cancer) cells that not only regulate such cellular functions as proliferation, migration and adhesion, but can also be secreted into extracellular space and serve as biomarkers for pathological conditions or tumor progression. KISS1, a precursor for several shorter peptides, known as metastin (Kisspeptin-54), Kisspeptin-14, Kisspeptin-13 and Kisspeptin-10, is one of those metastasis suppressor proteins, whose expression is commonly downregulated in the metastatic tumors of various origins. The commonly accepted role of KISS1 in metastatic tumor progression mechanism is the ability of this protein to suppress colonization of disseminated cancer cells in distant organs critical for the formation of the secondary tumor foci. Besides, recent evidence suggests involvement of KISS1 in the mechanisms of tumor angiogenesis, autophagy and apoptosis regulation, suggesting a possible role in both restricting and promoting cancer cell invasion. Here, we discuss the role of KISS1 in regulating metastases, the link between KISS1 expression and the autophagy-related biology of cancer cells and the perspectives of using KISS1 as a potential diagnostic marker for cancer progression as well as a new anti-cancer therapeutics.

Mitochondrial genetics cooperate with nuclear genetics to selectively alter immune cell development/trafficking

The nuclear genome drives differences in immune cell populations and differentiation potentials, in part regulated by changes in metabolism. Despite this connection, the role of mitochondrial DNA (mtDNA) polymorphisms (SNP) in this process has not been examined. Using mitochondrial nuclear exchange (MNX) mice, we and others have shown that mtDNA strongly influences varying aspects of cell biology and disease. Based upon an established connection between mitochondria and immune cell polarization, we hypothesized that mtDNA SNP alter immune cell development, trafficking, and/or differentiation. Innate and adaptive immune cell populations were isolated and characterizated from the peritoneum and spleen. While most differences between mouse strains are regulated by nuclear DNA (nDNA), there are selective changes that are mediated by mtDNA differences (e.g., macrophage (CD11c) differentiation), These findings highlight how nuclear-mitochondrial crosstalk may alter pathology and physiology via regulation of specific components of the immune system.

The Histone Demethylase KDM3A, Increased in Human Pancreatic Tumors, Regulates Expression of DCLK1 and Promotes Tumorigenesis in Mice

BACKGROUND & AIMS

The histone lysine demethylase 3A (KDM3A) demethylates H3K9me1 and H3K9Me2 to increase gene transcription and is upregulated in tumors, including pancreatic tumors. We investigated its activities in pancreatic cancer cell lines and its regulation of the gene encoding doublecortin calmodulin-like kinase 1 (DCLK1), a marker of cancer stem cells.

METHODS

We knocked down KDM3A in MiaPaCa-2 and S2-007 pancreatic cancer cell lines and overexpressed KDM3A in HPNE cells (human noncancerous pancreatic ductal cell line); we evaluated cell migration, invasion, and spheroid formation under hypoxic and normoxic conditions. Nude mice were given orthotopic injections of S2-007 cells, with or without (control) knockdown of KDM3A, and HPNE cells, with or without (control) overexpression of KDM3A; tumor growth was assessed. We analyzed pancreatic tumor tissues from mice and pancreatic cancer cell lines by immunohistochemistry and immunoblotting. We performed RNA-sequencing analysis of MiaPaCa-2 and S2-007 cells with knockdown of KDM3A and evaluated localization of DCLK1 and KDM3A by immunofluorescence. We analyzed the cancer genome atlas for levels of KDM3A and DCLK1 messenger RNA in human pancreatic ductal adenocarcinoma (PDAC) tissues and association with patient survival time.

RESULTS

Levels of KDM3A were increased in human pancreatic tumor tissues and cell lines, compared with adjacent nontumor pancreatic tissues, such as islet and acinar cells. Knockdown of KDM3A in S2-007 cells significantly reduced colony formation, invasion, migration, and spheroid formation, compared with control cells, and slowed growth of orthotopic tumors in mice. We identified KDM3A-binding sites in the DCLK1 promoter; S2-007 cells with knockdown of KDM3A had reduced levels of DCLK1. HPNE cells that overexpressed KDM3A formed foci and spheres in culture and formed tumors and metastases in mice, whereas control HPNE cells did not. Hypoxia induced sphere formation and increased levels of KDM3A in S2-007 cells and in HPNE cells that overexpressed DCLK1, but not control HPNE cells. Levels of KDM3A and DCLK1 messenger RNA were higher in human PDAC than nontumor pancreatic tissues and correlated with shorter survival times of patients.

CONCLUSIONS

We found human PDAC samples and pancreatic cancer cell lines to overexpress KDM3A. KDM3A increases expression of DCLK1, and levels of both proteins are increased in human PDAC samples. Knockdown of KDM3A in pancreatic cancer cell lines reduced their invasive and sphere-forming activities in culture and formation of orthotopic tumors in mice. Hypoxia increased expression of KDM3A in pancreatic cancer cells. Strategies to disrupt this pathway might be developed for treatment of pancreatic cancer.

Abstract 654: Dietary interventions ameliorate infectious colitis through differential regulation of Lgr5

Background: During inflammatory bowel disease (IBD), the disruption of the epithelial barrier and translocation of bacteria drive inappropriate immune responses and unresolved inflammation. Rapid wound healing responses orchestrated by intestinal stem cells (ISCs) are central to inflammatory resolution and normalization of the mucosal barrier. Commensal microbiota ferment fibers to produce short-chain-fatty-acids (SCFAs) such as butyrate and its decrease has been linked to IBD. However, the mechanism through which SCFAs promote wound healing is poorly understood.

Aims: The present study was designed to test the hypothesis that dietary fibers/butyrate ameliorate infectious colitis by differentially regulating Lgr5-dependent crypt regeneration and wound healing.

Methods: Lgr5CreERT2/+; Rosa26LacZ reporter (Lgr5-R) mice and wild-type littermates were infected with Citrobacter rodentium (CR; 108 CFUs) and fed with either 6% Pectin (Pec) or 6% Tributyrin (Tbt) diets followed by euthanasia at 12 days post-infection. To partially deplete microbiota, mice were also given a cocktail of vancomycin (500mg/L), metronidazole (1g/L) and Ciprofloxacin (0.2g/L) for 10 days starting 3-days post-CR infection. Fresh feces pre- and post-infection/treatments were taken for 16S rDNA sequencing. Lineage tracing post-tamoxifen and Lgr5 promoter reporter activity assays were performed.

Results: Both Pec and Tbt reduced the severity of CR-induced colitis as was evidenced by increased body weight and colon length, reduced immune cell infiltration and increased mucus production compared with CR-infected but untreated mice. 16s rDNA sequencing revealed significant dysbiosis during CR infection with the dominance of Proteobacteria and loss of Firmicutes and Bacteroidetes. Both Pec and Tbt diets reduced the levels of Proteobacteria and restored Firmicutes and Bacteroidetes phyla to pre-infection levels. X-gal staining revealed that there was an expansion of LacZ-labeled Lgr5(+) stem cells in the colons of CR infected Lgr5-R mice when subjected to dietary intervention via Pectin and Tributyrin as sources of butyrate compared with controls. Interestingly, Pec-induced Lgr5 regulation was dependent upon the presence of gut microbiota as antibiotics treatment reduced Pec-induced Lgr5 expansion and the extent of crypt regeneration. Tbt-treatment, on the other hand, regulated Lgr5 independently of the microbiota. Butyrate, in a dose-dependent (1-10mM) manner, increased Lgr5 promoter reporter activity. Docking studies further revealed butyrate’s ability to efficiently bind Lgr5 with a -4.0 Kcal/mol binding energy. The cellular thermal shift assay showed that butyrate was indeed able to bind Lgr5.

Conclusions: Thus, dietary interventions, by altering the gut microbiota, can differentially regulate Lgr5’s ability to orchestrate crypt regeneration and wound healing to ameliorate colitis.

Citation Format: Ishfaq Ahmed, Badal C. Roy, Rita-Marie T. Raach, Sharon J. Manley, Pugazhendhi Srinivasan, Prasad Dandawate, Afreen Sayed, Danny R. Welch, Shrikant Anant, Venkatesh Sampath, Shahid Umar. Dietary interventions ameliorate infectious colitis through differential regulation of Lgr5 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 654.

Abstract 1235: Targeting RNA-binding protein HuR to inhibit human breast cancer invasion and metastasis

The majority of breast cancer-related mortality is due to metastasis. Patients diagnosed with metastatic breast cancer have a dismal 5-year survival rate of only 24%. The RNA-binding protein Hu antigen R (HuR) is overexpressed in breast cancer. Cytoplasmic HuR accumulation correlates with high-grade malignancy, poor distant disease-free survival and serves as a prognostic factor for poor clinical outcome in breast cancer. HuR promotes tumorigenesis by regulating numerous proto-oncogenes, growth factors and cytokines that implicate major tumor hallmarks including invasion and metastasis. Knocking out HuR by CRISPR/CAS9 technology inhibits cell invasion in breast cancer cells. Therefore, HuR is an emerging target for breast cancer therapy, especially the lethal metastatic breast cancer. RNA-binding proteins had previously been considered “undruggable” due to lack of a well-defined binding pocket for target RNAs. Using high throughput screening followed by structure-based rational design and lead optimization, we have identified small molecules that inhibit HuR-mRNA interaction at nM to sub-µM potency. Our lead compound, KH-3, potently inhibits breast cancer cell growth and decreases cell invasion in vitro similar to HuR knockout, as well as increasing the expression of epithelial marker E-cadherin. In the study of mechanism of action, a transcription factor, FOXQ1, which is recently revealed to implicate in breast cancer invasion and metastasis processes, is found for the first time to be a direct mRNA target of HuR and one of the top genes that are reduced by KH-3 treatment. Exogenous introduction of FOXQ1 can rescue cell invasive capability impaired by HuR knockout and abolish the effect of KH-3 on inhibiting cell invasion in breast cancer cells. Moreover, KH-3 disrupts HuR-FOXQ1 interaction in RNP-IP, RNA pull down and FOXQ1 3′-UTR luciferase reporter assays. In vivo efficacy studies show that KH-3 not only exhibits potent antitumor efficacy in an orthotopic xenograft model of breast cancer, but also efficiently inhibits lung metastasis and improves mouse survival in an experimental metastasis model. Our data provide a proof-of-principle that HuR inhibition by KH-3 may be developed as a promising molecular therapy for inhibiting progression and metastasis of breast cancer with high HuR.

Citation Format: Xiaoqing Wu, Gulhumay Gardashova, Lan Lan, Shuang Han, Cuncong Zhong, Ragul Gowthaman, John Karanicolas, Dan A. Dixon, Danny R. Welch, Ling Li, Min Ji, Jeffrey Aubé, Liang Xu. Targeting RNA-binding protein HuR to inhibit human breast cancer invasion and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1235.

Defining the Hallmarks of Metastasis

Metastasis is the primary cause of cancer morbidity and mortality. The process involves a complex interplay between intrinsic tumor cell properties as well as interactions between cancer cells and multiple microenvironments. The outcome is the development of a nearby or distant discontiguous secondary mass. To successfully disseminate, metastatic cells acquire properties in addition to those necessary to become neoplastic. Heterogeneity in mechanisms involved, routes of dissemination, redundancy of molecular pathways that can be utilized, and the ability to piggyback on the actions of surrounding stromal cells makes defining the hallmarks of metastasis extraordinarily challenging. Nonetheless, this review identifies four distinguishing features that are required: motility and invasion, ability to modulate the secondary site or local microenvironments, plasticity, and ability to colonize secondary tissues. By defining these first principles of metastasis, we provide the means for focusing efforts on the aspects of metastasis that will improve patient outcomes.

Mitochondrial polymorphisms contribute to aging phenotypes in MNX mouse models

Many inbred strains of mice develop spontaneous tumors as they age. Recent awareness of the impacts of mitochondrial DNA (mtDNA) on cancer and aging has inspired developing a mitochondrial-nuclear exchange (MNX) mouse model in which nuclear DNA is paired with mitochondrial genomes from other strains of mouse. MNX mice exhibit mtDNA influences on tumorigenicity and metastasis upon mating with transgenic mice. However, we also wanted to investigate spontaneous tumor phenotypes as MNX mice age. Utilizing FVB/NJ, C57BL/6J, C3H/HeN, and BALB/cJ wild-type inbred strains, previously documented phenotypes were observed as expected in MNX mice with the same nuclear background. However, aging nuclear matched MNX mice exhibited decreased occurrence of mammary tumors in C3H/HeN mice containing C57BL/6J mitochondria compared to wild-type C3H/HeN mice. Although aging tumor phenotypes appear to be driven by nuclear genes, evidence suggesting that some differences are modified by the mitochondrial genome is presented.

The second genome: Effects of the mitochondrial genome on cancer progression

The role of genetics in cancer has been recognized for centuries, but most studies elucidating genetic contributions to cancer have understandably focused on the nuclear genome. Mitochondrial contributions to cancer pathogenesis have been documented for decades, but how mitochondrial DNA (mtDNA) influences cancer progression and metastasis remains poorly understood. This lack of understanding stems from difficulty isolating the nuclear and mitochondrial genomes as experimental variables, which is critical for investigating direct mtDNA contributions to disease given extensive crosstalk exists between both genomes. Several in vitro and in vivo models have isolated mtDNA as an independent variable from the nuclear genome. This review compares and contrasts different models, their advantages and disadvantages for studying mtDNA contributions to cancer, focusing on the mitochondrial-nuclear exchange (MNX) mouse model and findings regarding tumor progression, metastasis, and other complex cancer-related phenotypes.

The isolated C-terminal nuclear localization sequence of the breast cancer metastasis suppressor 1 is disordered

BRMS1 is a 246-residue-long protein belonging to the family of metastasis suppressors. It is a predominantly nuclear protein, although it can also function in the cytoplasm. At its C terminus, it has a region that is predicted to be a nuclear localization sequence (NLS); this region, NLS2, is necessary for metastasis suppression. We have studied in vitro and in silico the conformational preferences in aqueous solution of a peptide (NLS2-pep) that comprises the NLS2 of BRMS1, to test whether it has a preferred conformation that could be responsible for its function. Our spectroscopic (far-UV circular dichroism, DOSY-NMR and 2D-NMR) and computational (all-atom molecular dynamics) results indicate that NLS2-pep was disordered in aqueous solution. Furthermore, it did not acquire a structure even when experiments were performed in a more hydrophobic environment, such as the one provided by 2,2,2-trifluoroethanol (TFE). The hydrodynamic radius of the peptide in water was identical to that of a random-coil sequence, in agreement with both our molecular simulations and other theoretical predictions. Thus, we suggest that NLS2 is a disordered region, with non pre-formed structure, that participates in metastasis suppression.

Roles of the mitochondrial genetics in cancer metastasis: not to be ignored any longer

Mitochondrial DNA (mtDNA) encodes for only a fraction of the proteins that are encoded within the nucleus, and therefore has typically been regarded as a lesser player in cancer biology and metastasis. Accumulating evidence, however, supports an increased role for mtDNA impacting tumor progression and metastatic susceptibility. Unfortunately, due to this delay, there is a dearth of data defining the relative contributions of specific mtDNA polymorphisms (SNP), which leads to an inability to effectively use these polymorphisms to guide and enhance therapeutic strategies and diagnosis. In addition, evidence also suggests that differences in mtDNA impact not only the cancer cells but also the cells within the surrounding tumor microenvironment, suggesting a broad encompassing role for mtDNA polymorphisms in regulating the disease progression. mtDNA may have profound implications in the regulation of cancer biology and metastasis. However, there are still great lengths to go to understand fully its contributions. Thus, herein, we discuss the recent advances in our understanding of mtDNA in cancer and metastasis, providing a framework for future functional validation and discovery.

Zeeman spectroscopy as a method for determining the magnetic field distribution in self-magnetic-pinch diodes (invited)

In the self-magnetic-pinch diode, the electron beam, produced through explosive field emission, focuses on the anode surface due to its own magnetic field. This process results in dense plasma formation on the anode surface, consisting primarily of hydrocarbons. Direct measurements of the beam's current profile are necessary in order to understand the pinch dynamics and to determine x-ray source sizes, which should be minimized in radiographic applications. In this paper, the analysis of the C IV doublet (580.1 and 581.2 nm) line shapes will be discussed. The technique yields estimates of the electron density and electron temperature profiles, and the method can be highly beneficial in providing the current density distribution in such diodes.

Abstract 431: Mitochondrial-nuclear crosstalk influences accumulation of mitochondrial DNA mutations in mammary tumor progression

Introduction: Previous studies demonstrated that mitochondrial inheritance may contribute to aggressiveness of metastatic disease. Accumulating evidence suggests the mitochondrial genetic background may influence how certain cancers behave. We utilized Mitochondrial-Nuclear eXchange (MNX) female mice crossed with transgenic mice over-expressing the Her-2 gene and showed mitochondrial DNA (mtDNA)-dependent differences in tumor latency, lung metastasis number and lung metastasis size. We hypothesized that mtDNA mutations accumulate as mammary tumors progress and that the evolution is associated with mtDNA-nuclear DNA cross-talk. To test this hypothesis, we conducted next generation sequencing analyses to examine the spectra of mutations in the mitochondrial genome.

Methods: Normal mammary gland, primary tumor and lung metastases [n=5 each] were obtained from FVB/NJ mice with FVB/NJ (designated FF), C57BL/6J (designated FC) or BALB/cJ mtDNA (designated FB). Epithelial cells from mammary gland or tumor cells were carefully isolated by laser capture microdissection in order to minimize contamination from surrounding stromal cell mtDNA. mtDNA was deep sequenced using three pools totaling 182 overlapping primers spanning the whole mitochondrial genome using the Ion TorrentTM PGM System. Sequences were compared to an FVB mtDNA reference sequence to detect variants.

Results: Significant differences in the total number of mtDNA mutations were observed between the wild-type and MNX mice. Both FB and FC MNX cohorts exhibited increased mtDNA mutations compared to the wild-type (FF). As tumor progressed, the numbers of and distribution of mutations across the mitochondrial genome increased. ‘Hotspots' were observed in FB mice (S12 rRNA, COX I, ND4, CYTB) that were distinct from common mutations in the FC mice (16S rRNA, COX I).

Discussion: As predicted, tumor cells accumulated more mutations in mtDNA as neoplastic cells from the primary tumor progressed to metastasis. Surprisingly, wild-type (FF) mice, even though more clinically aggressive (i.e., more metastases), accumulated fewer mtDNA mutations than tumors arising in the MNX mice. The mutations appear to occur in different sites, depending upon the nuclear-mitochondrial combination. Whether the mtDNA mutations function as contributors to metastatic efficiency has not yet been determined. Nonetheless, the data imply that nuclear-mitochondrial cross-talk influences mtDNA mutational spectra and metastasis and that defining the critical mtDNA genes most commonly involved may eventually be used to predict patient prognosis.

Citation Format: Takae M. Brewer, Amanda E. Brinker, Sharon Manley, Carolyn J. Vivian, Danny R. Welch. Mitochondrial-nuclear crosstalk influences accumulation of mitochondrial DNA mutations in mammary tumor progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 431.

Abstract SY37-03: Mitochondrial genetic contributions to metastatic efficiency

Complex phenotypes, like tumorigenicity or metastasis, require coordinated expression of multiple genes. Additionally, the contributions of some of those genes can be affected by polymorphisms in the protein coding or regulatory sequences (PMID: 22257951). The pathobiology of metastasis remains poorly understood because both intrinsic (i.e., genetic) and extrinsic (i.e., tumor-microenvironment interactions) are involved. A growing body of data indicates demonstrate that there are underlying genetic components that govern the processes involved in cancer spread and colonization. To assess the contributions of mitochondrial genetics in metastasis, we created Mitochondrial Nuclear Exchange (MNX) mice by transferring an oocyte nucleus from strainx into an enucleated oocyte from strainy, and showed that mammary tumor formation and metastasis are regulated by inherited mitochondrial polymorphisms in an oncogenic driver-dependent manner (PMID: 26471915; PMID: 29070615). Since stromal compartments also possess changed mitochondria in the MNX mice, we hypothesized that mitochondrial polymorphisms in non-cancer cell compartments could exert effects on tumor formation and/or metastasis in addition to genetic (cell autonomous) changes. Syngeneic tumor cells were injected into MNX mice with the same nuclear, and therefore same MHC, background. Experimental metastasis was compared between wild-type and MNX mice (i.e., with same or different mtDNA backgrounds, respectively). E0771 mammary carcinoma and B16-F10 melanoma cells (both syngeneic to C57BL/6J), formed significantly (P<0.01) more lung metastases in C57BL/6J-mtMNX(C3H/HeN). K1735-M2 melanoma cells (syngeneic to C3H/HeN) formed significantly (P<0.05) fewer lung metastases in C3H/HeNmtMNXC57BL/6J. These results have been replicated ≥3 times using >10 mice per experiment. C57BL/6J mitochondria confer resistance to metastasis in both cell autonomous and non-cell autonomous experiments. Basal metabolic and ROS differences comparing mouse embryonic fibroblasts isolated from wild-type and MNX mice are among mechanisms being explored. Differential gene expression occurred in tissues isolated from wild-type and MNX mice (PMID: 28663334). Additionally, altered immune and microbiota profiles have been observed. Together, our findings highlight striking influences that mitochondrial haplotypes can exert on tumorigenicity and metastasis via both intrinsic and extrinsic mechanisms.

Support: Susan G. Komen for the Cure (SAC11037), Natl Fndn Cancer Res. and CA168524.

Citation Format: Danny R. Welch. Mitochondrial genetic contributions to metastatic efficiency [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr SY37-03.

Abstract 867: Blocking breast cancer metastasis by targeting HuR-FOXQ1 signaling axis

As most of treatment options do not work very well for metastatic cancer. Patients with metastatic cancer have a greatly lower survival rate compared with patients with local cancer. Metastasis remains a life-threat to cancer patients and an unmet medical need. The RBP Hu antigen R (HuR) is overexpressed in virtually all malignancies tested, including breast cancer. Cytoplasmic HuR accumulation correlates with high-grade malignancy, poor distant disease-free survival and serves as a prognostic factor for poor clinical outcome in breast cancer. HuR promotes tumorigenesis by promoting mRNA stability and translation of proteins implicated in proliferation, survival, angiogenesis, invasion, and metastasis. We found that silencing of HuR inhibited cell invasion in vitro in breast cancer. Using RIP-seq (ribonucleoprotein immunoprecipitation-sequencing), a transcription factor FOXQ1, which is recently revealed to implicate in breast cancer invasion and metastasis processes, is found to be a direct HuR target. Furthermore, exogenous introduction of FOXQ1 can rescue cell invasive ability inhibited by HuR knockout. Taken together, HuR-FOXQ1 signaling axis is a potential target for blocking breast cancer metastasis. RNA-binding proteins had previously been considered “undruggable” due to lack of a well-defined binding pocket for target RNAs. Using high throughput screening followed by structure-based rational design and lead optimization, we have identified small molecules that inhibit HuR-mRNA interaction at nM to sub-µM potency. Our lead compound, KH-3, potently inhibits breast cancer cell growth and decreases cell invasion in vitro similar to HuR knockout, as well as increasing the expression of epithelial marker E-cadherin. FOXQ1 overexpression abolishes the effect of KH-3 on blocking metastasis in breast cancer cells, demonstrating that the HuR inhibitor KH-3 inhibits cell metastasis by blocking FOXQ1 function. Moreover, KH-3 treatment disrupts HuR-FOXQ1 interaction in RNP-IP and FOXQ1 3′-UTR luciferase reporter assays. In vivo efficacy studies show that KH-3 not only exhibits potent antitumor efficacy in orthotopic xenograft models of breast cancer, but also efficiently blocks lung metastasis in experimental metastatic cancer model. In conclusion, we identified a potent and specific small molecule disrupter of HuR-FOXQ1 interaction for potential novel anti-metastatic therapy of breast cancer with HuR overexpression.

Citation Format: Xiaoqing Wu, Gulhumay Gardashova, Lan Lan, Yu Zhan, Jiajun Liu, Dan A. Dixon, Jeffrey Aubé, Danny R. Welch, Liang Xu. Blocking breast cancer metastasis by targeting HuR-FOXQ1 signaling axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 867.

NGF reprograms metastatic melanoma to a bipotent glial-melanocyte neural crest-like precursor

Melanoma pathogenesis from normal neural crest-derived melanocytes is often fatal due to aggressive cell invasion throughout the body. The identification of signals that reprogram de-differentiated, metastatic melanoma cells to a less aggressive and stable phenotype would provide a novel strategy to limit disease progression. In this study, we identify and test the function of developmental signals within the chick embryonic neural crest microenvironment to reprogram and sustain the transition of human metastatic melanoma to a neural crest cell-like phenotype. Results reveal that co-culture of the highly aggressive and metastatic human melanoma cell line C8161 upregulate a marker of melanosome formation (Mart-1) in the presence of embryonic day 3.5 chick trunk dorsal root ganglia. We identify nerve growth factor (NGF) as the signal within this tissue driving Mart-1 re-expression and show that NGF receptors trkA and p75 cooperate to induce Mart-1 re-expression. Furthermore, Mart-1 expressing C8161 cells acquire a gene signature of poorly aggressive C81-61 cells. These data suggest that targeting NGF signaling may yield a novel strategy to reprogram metastatic melanoma toward a benign cell type.

Summary: We identify and test the function of nerve growth factor to reprogram human metastatic melanoma cells to a less aggressive phenotype. This article has an associated First Person interview with the first author of the paper as part of the supplementary information.

Chloroquine-Inducible Par-4 Secretion Is Essential for Tumor Cell Apoptosis and Inhibition of Metastasis

The induction of tumor suppressor proteins capable of cancer cell apoptosis represents an attractive option for the re-purposing of existing drugs. We report that the anti-malarial drug, chloroquine (CQ), is a robust inducer of Par-4 secretion from normal cells in mice and cancer patients in a clinical trial. CQ-inducible Par-4 secretion triggers paracrine apoptosis of cancer cells and also inhibits metastatic tumor growth. CQ induces Par-4 secretion via the classical secretory pathway that requires the activation of p53. Mechanistically, p53 directly induces Rab8b, a GTPase essential for vesicle transport of Par-4 to the plasma membrane prior to secretion. Our findings indicate that CQ induces p53- and Rab8b-dependent Par-4 secretion from normal cells for Par-4-dependent inhibition of metastatic tumor growth.

Mitochondrial Haplotype Alters Mammary Cancer Tumorigenicity and Metastasis in an Oncogenic Driver-Dependent Manner

Using a novel mouse model, a mitochondrial-nuclear exchange model termed MNX, we tested the hypothesis that inherited mitochondrial haplotypes alter primary tumor latency and metastatic efficiency. Male FVB/N-Tg(MMTVneu)202Mul/J (Her2) transgenic mice were bred to female MNX mice having FVB/NJ nuclear DNA with either FVB/NJ, C57BL/6J, or BALB/cJ mtDNA. Pups receiving the C57BL/6J or BALB/cJ mitochondrial genome (i.e., females crossed with Her2 males) showed significantly (P < 0.001) longer tumor latency (262 vs. 293 vs. 225 days), fewer pulmonary metastases (5 vs. 7 vs. 15), and differences in size of lung metastases (1.2 vs. 1.4 vs. 1.0 mm diameter) compared with FVB/NJ mtDNA. Although polyoma virus middle T-driven tumors showed altered primary and metastatic profiles in previous studies, depending upon nuclear and mtDNA haplotype, the magnitude and direction of changes were not the same in the HER2-driven mammary carcinomas. Collectively, these results establish mitochondrial polymorphisms as quantitative trait loci in mammary carcinogenesis, and they implicate distinct interactions between tumor drivers and mitochondria as critical modifiers of tumorigenicity and metastasis. Cancer Res; 77(24); 6941-9. ©2017 AACR.