Osteoclast-independent mechanisms of early-stage bone colonization of breast canc

描述（由申请人提供）：转移几乎是所有乳腺癌相关死亡的原因。骨骼是最常受乳腺癌影响的器官。在临床显著阶段，骨转移由癌细胞和破骨细胞（骨吸收细胞）之间的恶性循环驱动。近年来，我们对这种恶性循环的认识大大增加，针对破骨细胞的治疗通常可以显着延缓疾病的进展。然而，骨转移仍然无法治愈。另一方面，在临床上可检测到骨转移之前通常存在数年至数十年的潜伏期，这表明残留的癌细胞可以在骨或骨髓中存在很长一段时间而不激活破骨细胞。我们开始发现破骨细胞独立的机制，在早期骨定植的恶性循环开始之前。我们的初步数据表明，成骨细胞（造骨细胞）和它们的前体细胞构成了显微骨转移的微环境生态位。癌细胞和“成骨细胞龛”之间的直接细胞-细胞接触对于它们的增殖至关重要。进一步的研究表明，mTOR通路的重新激活是骨转移起始的标志。我们还获得了初步证据，表明mTOR的激活是由癌细胞和小生境细胞之间的粘附连接（AJs）的形成介导的。基于这些发现，我们假设成骨细胞龛通过增强mTOR通路的活性，可能通过AJ复合物下游的信号传导，促进乳腺癌从单细胞到多细胞微转移的骨转移进展。为了验证这一假设，我们将追求两个具体目标：1）确定介导癌细胞与成骨细胞龛之间串扰的机制，这需要直接的细胞-细胞接触并导致mTOR信号传导的激活，以及2）鉴定驱动转移起始的mTOR下游效应物。我们的工作是创新和可行的，因为它采用了一种新的技术，通过循环选择性地将癌细胞输送到后肢骨中。这种方法能够以单细胞分辨率快速检查和稳健定量骨微转移，但避免了其他传统方法的警告。将该技术应用于几种癌症模型导致模拟人类疾病的惰性或休眠骨转移。我们将使用这种方法分别用于人类和小鼠癌细胞的异种移植和同基因移植，并研究AJs，mTOR复合物及其相关信号分子在骨转移启动中的作用。此外，我们还发明了一种3D共培养系统，忠实地概括了癌症-生态位相互作用的许多特征，这将有助于分子机制的解剖，并加速我们对候选介质的检查。这些目标的实现将使靶向治疗的设计能够抑制或根除潜伏的肿瘤细胞，并降低明显的骨转移相关症状的发生率和死亡率。

DESCRIPTION (provided by applicant): Metastasis accounts for nearly all breast cancer-related deaths. Bone is the organ most frequently affected by breast cancer. In the clinically significant stage, bone metastasis is driven by a vicious cycle between cancer cells and osteoclasts (bone-resorbing cells). Our knowledge of this vicious cycle has vastly increased in recent years, and therapies targeting osteoclasts can often significantly delay the progression of disease. However, bone metastases still remain incurable. On the other hand, there is often a latency of years to decades before bone metastases become clinically detectable, suggesting that residual cancer cells can exist in bone or bone marrow for a protracted period of time without activating osteoclasts. We set out to discover osteoclast-independent mechanisms in early-stage bone colonization before the onset of the vicious cycle. Our preliminary data demonstrated that osteoblasts (bone-making cells) and their precursor cells constitute the microenvironment niche of microscopic bone metastases. The direct cell-cell contact between cancer cells and the "osteoblastic niche" is crucial for their proliferation. Further studies indicated that the re-activation of the mTOR pathway is a hallmark of bone metastasis initiation. We also obtained preliminary evidence suggesting that the activation of mTOR is mediated by the formation of adhesion junctions (AJs) between cancer cells and niche cells. Based on these findings, we hypothesize that the osteoblastic niche facilitates bone metastasis progression of breast cancer from single cells to multi-cell micrometastases by augmenting the activity of the mTOR pathway, possibly through signaling downstream of AJ complexes. To test this hypothesis, we will pursue two specific aims: 1) to determine the mechanism mediating the crosstalk between cancer cells and the osteo-blastic niche, which entails direct cell-cell contact and leads to the activation of mTOR signaling, and 2) to identify the downstream effectors of mTOR that drive metastasis initiation. Our work is innovative and feasible because it employs a novel technique that selectively delivers cancer cells into hind limb bones via the circulation. This approach enables swift inspection and robust quantification of bone micrometastases at a single-cell resolution, yet avoids caveats of other conventional approaches. Application of this technique to several cancer models resulted in indolent or dormant bone metastases that mimic human diseases. We will use this approach for xenograft and syngeneic transplantation of human and mouse cancer cells, respectively, and investigate the roles of AJs, the mTOR complexes, and their related signaling molecules in bone metastasis initiation. In addition, we also invented a 3D co-culture system that faithfully recapitulates many features of cancer-niche interaction, which will facilitate the dissection of molecular mechanisms and accelerate our examination of candidate mediators. The fulfillment of these aims will enable the design of targeted therapies to suppress or eradicate latent tumor cells, and reduce the incidence of overt bone metastasis-related symptoms and mortality.