Targeted therapy for breast cancer with osteolytic bone damage

描述（由申请人提供）：骨是乳腺癌（BCa）最常见的转移部位，在晚期患者中引起显著的发病率和死亡率。BCa细胞和骨微环境细胞的恶性循环导致破骨细胞的激活和骨破坏的增加。联合化疗和双膦酸盐治疗骨病变对发病率和生存率的影响很小。因此，需要开发既能改善骨破坏又能提高转移性乳腺癌患者生存率的新疗法。对BCa骨病理分子事件的更好理解表明，核因子κ b配体受体激活因子（RANKL）通过与RANK结合刺激破骨细胞的募集、分化和活化。骨保护素（OPG）是一种“诱饵”受体，与RANK竞争RANKL，从而调节RANKL的作用。然而，在转移过程中，内源性OPG水平显著降低。因此，OPG仍然是未来治疗骨转移的有效分子。骨内播散性肿瘤的生长通过骨髓源性抑制细胞（MDSCs）的浸润进一步改变免疫环境，抑制宿主抗肿瘤免疫反应。此外，我们发现在小鼠和人类骨内的恶性转移级联过程中，MDSCs直接作为破骨细胞祖细胞起作用，从而增强骨破坏。目前的提案将涉及三个主要方面，即：溶骨性骨损伤、肿瘤生长和使用靶向破骨细胞激活的基因修饰干细胞方法的免疫抑制、使用tnf相关凋亡诱导配体（TRAIL）诱导肿瘤细胞凋亡，以及分别联合使用吉西他滨进行MDSC消融。本研究的中心假设是，在保留RANKL结合而取消TRAIL结合的情况下，将基因工程OPG靶向骨递送，与TRAIL治疗结合，靶向MDSC群体，将显著减少骨溶解性骨损伤，重塑受损骨骼，诱导肿瘤细胞凋亡，提高生存率。这一假设将通过免疫能力、骨弥散性BCa的临床前小鼠模型进行检验，以寻找可能的临床转化。为了实现这一目标，我们最近建立了：a)间充质干细胞（MSC）利用OPG靶向RANK信号的潜力，b)一种独特的体内靶向策略来增强基因工程MSC的骨特异性归巢，c) MDSCs在直接形成破骨细胞中的作用，d) MDSCs的消耗增强了骨转移BCa模型中抗肿瘤Th1活性。此外，由于OPG也与TRAIL结合从而增加肿瘤细胞的存活率，我们已经：e)通过同源建模确定了OPG上假定的TRAIL结合域(s), f)开发了一种突变OPG (OPGm)，保留了RANKL结合，但消除了TRAIL结合，并在体外和体内证实了其在骨中的生物活性

DESCRIPTION (provided by applicant): Bone is the most common site of metastasis for breast cancer (BCa), which causes significant morbidity and mortality in patients with advanced disease. A vicious cycle involving BCa cells and cells in the bone microenvironment results in the activation of osteoclasts and increased bone destruction. Combination chemotherapy and bisphosphonate use for bone lesions provide very little effect on morbidity and survival. Thus, development of newer therapies that can both ameliorate bone destruction and improve survival of patients with metastatic breast disease is needed. A better understanding of the molecular events in BCa bone pathology indicates that receptor activator of nuclear factor kappa-B ligand (RANKL) stimulates the recruitment, differentiation, and activation of osteoclasts by binding to RANK. Osteoprotegerin (OPG) is a "decoy" receptor that competes with RANK for RANKL, thereby modulating the effects of RANKL. However, during metastases, endogenous OPG levels are markedly reduced. Thus, OPG remains as an effective molecule for future therapies for bone metastasis. The growth of disseminated tumor in the bone further alters the immune milieu through infiltration of myeloid-derived suppressor cells (MDSCs) that dampen the host anti-tumor immune responses. Further, we identified that MDSCs function as osteoclast progenitors directly during this vicious metastatic cascade within the bone both in mouse and in humans, enhancing bone destruction. The current proposal will address three major aspects, namely: osteolytic bone damage, tumor growth and immunosuppression using a genetically-modified stem cell approach targeting osteoclast activation, induction of tumor cell apoptosis using TNF-related apoptosis-inducing ligand (TRAIL), and using gemcitabine for MDSC ablation, respectively, in combination. The central hypothesis of the proposed study is bone-targeted delivery of genetically-engineered OPG, while retaining RANKL binding but abolishing TRAIL binding, in combination with TRAIL therapy together with targeting the MDSC population will significantly decrease osteolytic bone damage, remodel the damaged skeleton, and induce tumor cell apoptosis to improve survival. This hypothesis will be tested using an immunocompetent, preclinical mouse model of bone-disseminated BCa for possible clinical translation. Towards achieving this goal, we have recently established: a) the potential of mesenchymal stem cells (MSC) targeting RANK signaling by using OPG, b) a unique in vivo targeting strategy to enhance bone-specific homing of genetically-engineered MSC, c) the role of MDSCs in forming osteoclasts directly, and d) that depletion of MDSCs enhances anti-tumor Th1 activity in a bone metastatic BCa model. Further, since OPG also binds to TRAIL thereby increasing tumor cells survival, we have: e) identified putative TRAIL binding domain(s) on OPG by homology modeling, and f) developed a mutant OPG (OPGm) that retains RANKL binding but abolishes TRAIL binding and confirmed its biological activity both in vitro and in vivo in bone remodeling. These advances are anticipated to result in a novel treatment option for bone-disseminated BCa.