Arnold Rebecca S, Fedewa Stacey A, Goodman Michael, Osunkoya Adeboye O, Kissick Haydn T, Morrissey Colm, True Lawrence D, Petros John A
Department of Urology, Emory University School of Medicine, Atlanta, GA 30322, USA; The Atlanta VA Medical Center, Decatur, GA 30033, USA.
Emory University School of Public Health, Department of Epidemiology, Atlanta, GA 30322, USA.
Bone. 2015 Sep;78:81-6. doi: 10.1016/j.bone.2015.04.046. Epub 2015 May 5.
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.
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.
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.
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.
癌症进展和转移的发生机制是，具有获得性突变从而增强生长和存活能力（或抑制细胞死亡）的细胞数量增加，自1976年彼得·C·诺韦尔对此进行描述以来，这一概念被认为类似于物种的达尔文进化。选择压力包括宿主内在的因素（包括转移部位）以及抗癌治疗所产生的因素。通过检查个体患者体内多个肿瘤部位的突变状态，可能会对那些增强特定部位转移的基因变异有所了解。通过比较多个个体的这些数据，反复出现的模式可能会识别出对成功的特定部位转移至关重要的改变。
我们对10名参加快速尸检项目的骨转移前列腺癌患者的线粒体基因组进行了测序。患者处于疾病晚期，接受了雄激素剥夺治疗，并且经常接受其他全身治疗。对于9名患者中的每一位，对4个不同的组织进行了测序：原发性前列腺癌、软组织转移灶、骨转移灶以及作为非癌对照的未受累正常组织。另外一名（第10名）患者没有可用于测序的原发性前列腺组织，但对两个转移部位（以及对照DNA）进行了测序。然后，我们检查了每位患者原发性肿瘤和两个转移部位中体细胞获得的线粒体DNA（mtDNA）突变的数量和位置。最后，我们对患者进行相互比较，以确定体细胞突变的任何共同模式。
与原发性肿瘤或软组织转移灶相比，骨中的体细胞突变明显更多。呼吸复合体I基因ND3中核苷酸位置（n.p.）10398处的错义突变（A10398G；Thr114Ala）最为常见（10名患者中有7名），并且仅在骨中检测到。在不止一名患者中出现的其他显著体细胞突变包括n.p. 10436处的tRNA Arg突变和n.p. 15928处的tRNA Thr突变。tRNA Arg突变仅限于骨转移灶，在10名患者中有3名（30%）出现。15928处的体细胞突变并不局限于骨，也在3名患者中出现。
转移部位的线粒体基因组变异大于原发性肿瘤，并且骨转移灶的体细胞突变数量在统计学上显著多于原发性肿瘤或软组织转移灶。基因组并非随机突变。在单个碱基水平（骨转移灶中的核苷酸位置10398）至少鉴定出一个突变“热点”，这表明对获得10398 mtDNA突变的骨转移细胞存在普遍的选择压力。另外两个反复出现的突变（tRNA Arg和tRNA Thr）支持了骨特定部位“适者生存”的概念，这一概念通过线粒体基因组变异和转移部位施加的选择压力得以揭示。
