Research Progress on the Bone Metastasis Mechanism of Prostate Cancer and Bone-Targeted Drugs

Prostate cancer is a common male malignant tumor,and bone metastasis is one of the common complications in the late stage of prostate cancer.The mechanism of prostate cancer bone metastasis is a complex process involving multiple factors and steps.In recent years,with in-depth research on the mechanism of prostate cancer bone metastasis and the development of new drugs,important progress has been made in the treatment of prostate cancer bone metastasis.Based on this,this article introduces the mechanism of prostate cancer bone metastasis and the research progress of several bone-targeted drugs to provide reference and inspiration for future research.

Exosome-guided bone targeted delivery of Antagomir-188 as an anabolic therapy for bone loss

The differentiation shift from osteogenesis to adipogenesis of bone marrow mesenchymal stem cells(BMSCs)characterizes many pathological bone loss conditions.Stromal cell-derived factor-1(SDF1)is highly enriched in the bone marrow for C-X-C motif chemokine receptor 4(CXCR4)-positive hematopoietic stem cell(HSC)homing and tumor bone metastasis.In this study,we displayed CXCR4 on the surface of exosomes derived from genetically engineered NIH-3T3 cells.CXCR4+exosomes selectively accumulated in the bone marrow.Then,we fused CXCR4+exosomes with liposomes carrying antagomir-188 to produce hybrid nanoparticles(NPs).The hybrid NPs specifically gathered in the bone marrow and released antagomir-188,which promoted osteogenesis and inhibited adipogenesis of BMSCs and thereby reversed age-related trabecular bone loss and decreased cortical bone porosity in mice.Taken together,this study presents a novel way to obtain bone-targeted exosomes via surface display of CXCR4 and a promising anabolic therapeutic approach for age-related bone loss.

Clinical use of bone-targeting radiopharmaceuticals with focus on alpha-emitters

Various single or multi-modality therapeutic options are available to treat pain of bone metastasis in patients with prostate cancer.Different radionuclides that emitβ-rays such as 153Samarium and 89Strontium and achieve palliation are commercially available.In contrast toβ-emitters,223Radium as a a-emitter has a short path-length.The advantage of the a-emitter is thus a highly localized biological effect that is caused by radiation induced DNA double-strand breaks and subsequent cell killing and/or limited effectiveness of cellular repair mechanisms.Due to the limited range of the a-particles the bone surface to red bone marrow dose ratio is also lower for 223Radium which is expressed in a lower myelotoxicity.The a emitter 223Radium dichloride is the first radiopharmaceutical that significantly prolongslife in castrate resistant prostate cancer patients with wide-spread bone metastatic disease.In a phaseⅢ,randomized,double-blind,placebo-controlled study 921patients with castration-resistant prostate cancer and bone metastases were randomly assigned.The analysis confirmed the 223Radium survival benefit compared to the placebo(median,14.9 mo vs 11.3 mo;P<0.001).In addition,the treatment results in pain palliation and thus,improved quality of life and a delay of skeletal related events.At the same time the toxicity profile of223Radium was favourable.Since May 2013,223Radium dichloride(Xofigo?)is approved by the US Food and Drug Administration.

Bone morphogenetic protein signaling：a promising target for white matter protection in perinatal brain injury

Prematurely born newborns,as well as those born at term,may suffer from several types of brain injury including hypoxic-ischemic injury,intracranial hemorrhage,both intraventricular and parenchymal,and injury that is the consequence of intrauterine growth restriction（IUGR）.Injury of all types can impact the motor and cognitive abilities of survivors.The mechanisms leading to disability are not completely understood.

Rhizoma Drynariae-derived nanovesicles reverse osteoporosis by potentiating osteogenic differentiation of human bone marrow mesenchymal stem cells via targeting ERα signaling

Although various anti-osteoporosis drugs are available,the limitations of these therapies,including drug resistance and collateral responses,require the development of novel anti-osteoporosis agents.Rhizoma Drynariae displays a promising anti-osteoporosis effect,while the effective component and mechanism remain unclear.Here,we revealed the therapeutic potential of Rhizoma Drynariae-derived nanovesicles(RDNVs)for postmenopausal osteoporosis and demonstrated that RDNVs potentiated osteogenic differentiation of human bone marrow mesenchymal stem cells(hBMSCs)by targeting estrogen receptor-alpha(ERα).RDNVs,a natural product isolated from fresh Rhizoma Drynariae root juice by differential ultracentrifugation,exhibited potent bone tissue-targeting activity and anti-osteoporosis efficacy in an ovariectomized mouse model.RDNVs,effectively internalized by hBMSCs,enhanced proliferation and ERαexpression levels of hBMSC,and promoted osteogenic differentiation and bone formation.Mechanistically,via the ERαsignaling pathway,RDNVs facilitated mRNA and protein expression of bone morphogenetic protein 2 and runt-related transcription factor 2 in hBMSCs,which are involved in regulating osteogenic differentiation.Further analysis revealed that naringin,existing in RDNVs,was the active component targeting ERαin the osteogenic effect.Taken together,our study identified that naringin in RDNVs displays exciting bone tissue-targeting activity to reverse osteoporosis by promoting hBMSCs proliferation and osteogenic differentiation through estrogen-like effects.

Management of bone metastases in renal cell carcinoma: bone-targeted treatments, systemic therapies, and radiotherapy

Metastatic renal cell carcinoma(mRCC)presents with bone metastases in around 20%-30%of patients enrolled in the most recent first-line clinical trials.Emergence of several new agents in first line,in both monotherapy and combination,has significantly improved patient outcomes.However,the activity of such agents on bone metastases is unclear and management of these patients is complex,due to potential complications that can significantly impair quality of life.This review addresses mRCC diagnosis and monitoring and summarizes the current evidence on systemic therapy,ablative therapies such as stereotactic ablative radiotherapy and surgery,and supportive therapy with bone-targeting agents for these patients,with the goal of improving their outcomes.

A bone-targeted engineered exosome platform delivering siRNA to treat osteoporosis

The complex pathogenesis of osteoporosis includes excessive bone resorption,insufficient bone formation and inadequate vascularization,a combination which is difficult to completely address with conventional therapies.Engineered exosomes carrying curative molecules show promise as alternative osteoporosis therapies,but depend on specifically-functionalized vesicles and appropriate engineering strategies.Here,we developed an exosome delivery system based on exosomes secreted by mesenchymal stem cells(MSCs)derived from human induced pluripotent stem cells(iPSCs).The engineered exosomes BT-Exo-siShn3,took advantage of the intrinsic anti-osteoporosis function of these special MSC-derived exosomes and collaborated with the loaded siRNA of the Shn3 gene to enhance the therapeutic effects.Modification of a bone-targeting peptide endowed the BT-Exo-siShn3 an ability to deliver siRNA to osteoblasts specifically.Silencing of the osteoblastic Shn3 gene enhanced osteogenic differentiation,decreased autologous RANKL expression and thereby inhibited osteoclast formation.Furthermore,Shn3 gene silencing increased production of SLIT3 and consequently facilitated vascularization,especially formation of type H vessels.Our study demonstrated that BT-Exo-siShn3 could serve as a promising therapy to kill three birds with one stone and implement comprehensive anti-osteoporosis effects.

Breaking the vicious cycle between tumor cell proliferation and bone resorption by chloroquine-loaded and bone-targeted polydopamine nanoparticles

The vicious cycle between tumor cell proliferation and bone resorption remarkably elevates the progression and metastasis of bone tumors.Here,we fabricated polyethylene glycol-conjugated alendronate-functionalized and chloroquine(CQ)-loaded polydopamine nanoparticles(PPA/CQ)for efficient treatment of bone tumors via breaking the vicious cycle.The nanoparticles were efficiently accumulated to the bone tissues,especially the osteolytic lesions around tumors.CQ released from PPA/CQ inhibited osteoclastogenesis via preventing the degradation of tumor necrosis factor(TNF)receptor-associated receptor 3 to attenuate the osteolysis in bone tumors.On the other hand,CQ blocked the autophagy in cancer cells,resulting in improved photothermal killing of cancer cells.Finally,the in vivo experiment revealed that PPA/CQ-associated treatment efficiently inhibited both tumor growth and osteolysis.This work suggests that autophagy inhibition-associated photothermal therapy could be a promising strategy for treating malignant bone tumors.

Targeted and intracellular delivery of protein therapeutics by a boronated polymer for the treatment of bone tumors

The treatment of malignant bone tumors by chemotherapeutics often receives poor therapeutic response due to the specific physiological bone environment,and thus calls for the development of new therapeutic options.Here,we reported a bone-targeted protein nanomedicine for this purpose.Saporin,a toxin protein,was co-assembled with a boronated polymer for intracellular protein delivery,and the formed nanoparticles were further coated with an anionic polymer poly(aspartic acid)to shield the positive charges on nanoparticles and provide the bone targeting function.The prepared ternary complex nanoparticles showed high bone accumulation both in vitro and in vivo,and could reverse the surface charge property from negative to positive after locating at tumor site triggered by tumor extracellular acidity.The boronated polymer in the de-shielded nanoparticles further promote intracellular delivery of saporin into tumor cells,exerting the anticancer activity of saporin by inactivation of ribosomes.As a result,the bone-targeted and saporin-loaded nanomedicine could kill cancer cells at a low saporin dose,and efficiently prevented the progression of osteosarcoma xenograft tumors and bone metastatic breast cancer in vivo.This study provides a facile and promising strategy to develop protein-based nanomedicines for the treatment of malignant bone tumors.

Bone-targeting melphalan prodrug with tumor-microenvironment sensitivity： Synthesis, in vitro and in vivo evaluation

Bone tumor is a refractory neoplastic growth of tissue in bone. According to the unique environment and phys-chemical characteristics of bone tissues, the chemotherapeutic agents are unlikely to prolong the survival of patients and often associated with systemic side effects. The bone targeting drug delivery via systemic administration may provide both better treatment efficacy and less frequent administration. In this study, we describe the synthesis, in vitro and in vivo evaluation of novel melphalan-bisphosphonate hybrids, with a tumor microenvironment sensitive linkage, which could be enzymatic activation under tumor microenvironment conditions. We have also evaluated the in vitro targeting efficiency of these prodrugs via the affinity of hydroxyapatite （HA） and cellular proliferation. The in vivo distribution suggested the bisphosphonate conjugated prodrugs with high bone selectivity.

Bone targeting antioxidative nano-iron oxide for treating postmenopausal osteoporosis

Osteoporosis is the most common degenerative orthopedic disease in the elderly.Recently,the therapeutic methods for osteoporosis have shifted towards the regulation of local immunity in bone tissues,which could provide a suitable environment for the positive regulation of bone metabolism,promoting osteogenic differentiation and inhibiting osteoclast differentiation.Our previous work demonstrated that iron oxide nanoparticles(IONPs)could positively regulate bone metabolism in vitro.In this study,we further demonstrated that daily administration of IONPs relieved estrogen deficiency-induced osteoporosis via scavenging reactive oxygen species in vivo.Meanwhile,IONPs promoted the osteogenic differentiation of bone marrow mesenchymal stem cells and inhibited the osteoclast differentiation of monocytes from IONPs treated mice.Besides,alendronate,a clinically used anti-osteoporosis bisphosphate,was employed to precisely deliver the IONPs to the bone tissues and played a synergically therapeutic role.Eventually,we verified the bone targeting ability,therapeutic efficiency,and biocompatibility of the novel bone target iron oxides in ovariectomy-induced osteoporotic mice.By applying BTNPs,the OVX-induced osteoporosis was significantly revised in mice models via the positive regulation of bone metabolism.

Inhibition of furin by bone targeting superparamagnetic iron oxide nanoparticles alleviated breast cancer bone metastasis

Breast cancer bone metastasis poses significant challenge for therapeutic strategies.Inside the metastatic environment,osteoclasts and tumor cells interact synergistically to promote cancer progression.In this study,the proprotein convertase furin is targeted due to its critical roles in both tumor cell invasion and osteoclast function.Importantly,the furin inhibitor is specifically delivered by bone targeting superparamagnetic iron oxide(SPIO)nanoparticles.Our in vitro and in vivo data demonstrate that this system can effectively inhibit both osteoclastic bone resorption and breast cancer invastion,leading to alleviated osteolysis.Therefore,the bone targeting&furin inhibition nanoparticle system is a promising therapeutic and diagnostic strategy for breast cancer bone metastasis.

Bone infection site targeting nanoparticle-antibiotics delivery vehicle to enhance treatment efficacy of orthopedic implant related infection

Orthopedic implants account for 99%of orthopedic surgeries,however,orthopedic implant-related infection is one of the most serious complications owing to the potential for limb-threatening sequelae and mortality.Current antibiotic treatments still lack the capacity to target bone infection sites,thereby resulting in unsatisfactory therapeutic effects.Here,the bone infection site targeting efficacy of D6 and UBI29-41 peptides was investigated,and bone-and-bacteria dual-targeted nanoparticles(NPs)with D6 and UBI29-41 peptides were first fabricated to target bone infection site and control the release of vancomycin in bone infection site.The results of this study demonstrated that the bone-and-bacteria dual-targeted mesoporous silica NPs exhibit excellent bone and bacteria targeting efficacy,excellent biocompatibility and effective antibacterial properties in vitro.Furthermore,in a rat model of orthopedic implant-related infection with methicillin-resistant Staphylococcus aureus,the growth of bacteria was evidently inhibited without cytotoxicity,thus realizing the early treatment of implant-related infection.Hence,the bone-and-bacteria dual-targeted molecule-modified NPs may target bacteria-infected bone sites and act as ideal candidates for the therapy of orthopedic implant-related infections.

Bone-seeking nanoplatform co-delivering cisplatin and zoledronate for synergistic therapy of breast cancer bone metastasis and bone resorption

The"vicious cycle"established between tumor growth and osteolysis aggravates the process of breast cancer bone metastasis,leading to life-threatening skeletal-related events that severely reduce survival and quality of life.To effectively interrupt the"vicious cycle",innovative therapeutic strategies that not only reduce osteolysis but also relieve tumor burden are urgently needed.Herein,a bone-seeking moiety,alendronate(ALN),functionalized coordination polymer nanoparticles(DZ@ALN)co-delivering cisplatin prodrug(DSP)and antiresorptive agent zoledronate(ZOL)via Zn2+crosslinking for combination therapy was reported.The versatile DZ@ALN with a diameter of about 40 nm can cross the fissure in the bone marrow sinus capillaries,and possesses an excellent bone-seeking ability both in vitro and in vivo.Additionally,DZ@ALN could synergistically inhibit the proliferation of cancer cells,suppress the formation of osteoclast-like cells and induce the apoptosis of osteoclasts in vitro.Importantly,it could preferentially accumulate in bone affected site,remarkably inhibit the proliferation of tumor cells,relieving bone pain,and significantly inhibit the activation of osteoclasts,protecting the bone from destruction in vivo,eventually leading to the breakdown of"vicious cycle"without inducing obvious systemic toxicity.This innovative nanoagent combines chemotherapy and osteolysis inhibition,exhibiting an inspiring strategy for effective treatment of bone metastasis.