title: Bone metastasis in prostate cancer: Recurring mitochondrial DNA mutation reveals selective pressure exerted by the bone microenvironment.
abstract: BACKGROUND
  Cancer progression and metastasis occur such that cells with acquired mutations enhancing growth and survival (or inhibiting cell death) increase in number, a concept that has been recognized as analogous to Darwinian evolution of species since Peter C. Nowell's description in 1976. Selective forces include those intrinsic to the host (including metastatic site) as well as those resulting from anti-cancer therapies. By examining the mutational status of multiple tumor sites within an individual patient some insight may be gained into those genetic variants that enhance site-specific metastasis. By comparing these data across multiple individuals, recurrent patterns may identify alterations that are fundamental to successful site-specific metastasis.
  
  
  METHODS
  We sequenced the mitochondrial genome in 10 prostate cancer patients with bone metastases enrolled in a rapid autopsy program. Patients had late stage disease and received androgen ablation and frequently other systemic therapies. For each of 9 patients, 4 separate tissues were sequenced: the primary prostate cancer, a soft tissue metastasis, a bone metastasis and an uninvolved normal tissue that served as the non-cancerous control. An additional (10th) patient had no primary prostate available for sequencing but had both metastatic sites (and control DNA) sequenced. We then examined the number and location of somatically acquired mitochondrial DNA (mtDNA) mutations in the primary tumor and two metastatic sites in each individual patient. Finally, we compared patients with each other to determine any common patterns of somatic mutation.
  
  
  RESULTS
  Somatic mutations were significantly more numerous in the bone compared to either the primary tumor or soft tissue metastases. A missense mutation at nucleotide position (n.p.) 10398 (A10398G; Thr114Ala) in the respiratory complex I gene ND3 was the most common (7 of 10 patients) and was detected only in the bone. Other notable somatic mutations that occurred in more than one patient include a tRNA Arg mutation at n.p. 10436 and a tRNA Thr mutation at n.p. 15928. The tRNA Arg mutation was restricted to bone metastases and occurred in three of 10 patients (30%). Somatic mutation at 15928 was not restricted to the bone and also occurred in three patients.
  
  
  CONCLUSIONS
  Mitochondrial genomic variation was greater in metastatic sites than in the primary tumor and bone metastases had statistically significantly greater numbers of somatic mutations than either the primary or the soft tissue metastases. The genome was not mutated randomly. At least one mutational "hot-spot" was identified at the individual base level (nucleotide position 10398 in bone metastases) indicating a pervasive selective pressure for bone metastatic cells that had acquired the 10398 mtDNA mutation. Two additional recurrent mutations (tRNA Arg and tRNA Thr) support the concept of bone site-specific "survival of the fittest" as revealed by variation in the mitochondrial genome and selective pressure exerted by the metastatic site.
authors.affiliation: Department of Urology, Emory University School of Medicine, Atlanta, GA 30322, USA; The Atlanta VA Medical Center, Decatur, GA 30033, USA.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Arnold
authors.affiliation: Emory University School of Public Health, Department of Epidemiology, Atlanta, GA 30322, USA.
authors.forename: Stacey A
authors.initials: SA
authors.lastname: Fedewa
authors.affiliation: Emory University School of Public Health, Department of Epidemiology, Atlanta, GA 30322, USA; Emory University Winship Cancer Institute, Atlanta, GA 30322, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Goodman
authors.affiliation: Department of Urology, Emory University School of Medicine, Atlanta, GA 30322, USA; The Atlanta VA Medical Center, Decatur, GA 30033, USA; Emory University Winship Cancer Institute, Atlanta, GA 30322, USA; Department of Pathology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Adeboye O
authors.initials: AO
authors.lastname: Osunkoya
authors.affiliation: Department of Urology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Haydn T
authors.initials: HT
authors.lastname: Kissick
authors.affiliation: Department of Urology, University of Washington, Seattle, WA 98195, USA.
authors.forename: Colm
authors.initials: C
authors.lastname: Morrissey
authors.affiliation: Department of Pathology, University of Washington Medical Center, Seattle, WA 98195, USA.
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: True
authors.affiliation: Department of Urology, Emory University School of Medicine, Atlanta, GA 30322, USA; The Atlanta VA Medical Center, Decatur, GA 30033, USA; Emory University Winship Cancer Institute, Atlanta, GA 30322, USA; Department of Pathology, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Hematology and Medical Oncology, Emory University School of Medicine, Atlanta, GA 30322, USA. Electronic address: jpetros@emory.edu.
authors.forename: John A
authors.initials: JA
authors.lastname: Petros
mesh_terms: D000368:Aged; D001483:Base Sequence; D001859:Bone Neoplasms / Q000235:genetics* / Q000556:secondary*; D001842:Bone and Bones / Q000473:pathology*; D001943:Breast Neoplasms / Q000473:pathology; D004252:DNA Mutational Analysis; D004272:DNA, Mitochondrial / Q000235:genetics*; D018450:Disease Progression; D042967:Electron Transport Complex I / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D009362:Neoplasm Metastasis; D010641:Phenotype; D016012:Poisson Distribution; D020641:Polymorphism, Single Nucleotide; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000473:pathology*; D059016:Tumor Microenvironment
chemical_list: D004272:DNA, Mitochondrial; D042967:Electron Transport Complex I; C114961:MT-ND3 protein, human
keywords: Bone metastases; Cancer evolution; Mitochondrial DNA; Prostate cancer