Cabozantinib Reverses Renal Cell Carcinoma-mediated Osteoblast Inhibition in Three-dimensional Coculture In Vitro and Reduces Bone Osteolysis In Vivo

BIGH3 mediates apoptosis and gap junction failure in osteocytes during renal cell carcinoma bone metastasis progression

Renal cell carcinoma (RCC) bone metastatis progression is driven by crosstalk between tumor cells and the bone microenvironment, which includes osteoblasts, osteoclasts, and osteocytes. RCC bone metastases (RCCBM) are predominantly osteolytic and resistant to antiresorptive therapy. The molecular mechanisms underlying pathologic osteolysis and disruption of bone homeostasis remain incompletely understood. We previously reported that BIGH3/TGFBI (transforming growth factor-beta-induced protein ig-h3, shortened to BIGH3 henceforth) secreted by colonizing RCC cells drives osteolysis by inhibiting osteoblast differentiation, impairing healing of osteolytic lesions, which is reversible with osteoanabolic agents. Here, we report that BIGH3 induces osteocyte apoptosis in both human RCCBM tissue specimens and in a preclinical mouse model. We also demonstrate that BIGH3 reduces Cx43 expression, blocking gap junction (GJ) function and osteocyte network communication. BIGH3-mediated GJ inhibition is blocked by the lysosomal inhibitor hydroxychloroquine (HCQ), but not osteoanabolic agents. Our results broaden the understanding of pathologic osteolysis in RCCBM and indicate that targeting the BIGH3 mechanism could be a combinational strategy for the treatment of RCCBM-induced bone disease that overcomes the limited efficacy of antiresorptives that target osteoclasts.

An Exploration of The Role of Osteoclast Lineage Cells in Bone Tissue Engineering

Bone defects due to age, trauma, and surgery, which are exacerbated by medication side effects and common diseases like osteoporosis, diabetes, and rheumatoid arthritis, are a problem of epidemic scale. The present clinical standard for treating these defects includes autografts and allografts. While both treatments can promote robust regenerative outcomes, they fail to strike a desirable balance of availability, side effect profile, consistent regenerative efficacy, and affordability. This difficulty has contributed to the rise of bone tissue engineering (BTE) as a potential avenue through which enhanced bone regeneration could be delivered. BTE is founded upon a paradigm of using biomaterials, bioactive factors, osteoblast lineage cells (ObLCs), and vascularization to cue deficient bone tissue into a state of regeneration. Despite promising preclinical results, BTE has had modest success in being translated into the clinical setting. One barrier has been the simplicity of its paradigm relative to the complexity of biological bone. Therefore, this paradigm must be critically examined and expanded to better account for this complexity. One potential avenue for this is a more detailed consideration of osteoclast lineage cells (OcLCs). While these cells ostensibly oppose ObLCs and bone regeneration through their resorptive functions, myriad investigations have shed light on their potential to influence bone equilibrium in more complex ways through their interactions with both ObLCs and bone matrix. Most BTE research has not systematically evaluated their influence. Yet contrary to expectations associated with the paradigm, a selection of BTE investigations have demonstrated that this influence can enhance bone regeneration in certain contexts. Additionally, much work has elucidated the role of many controllable scaffold parameters in both inhibiting and stimulating the activity of OcLCs in parallel to bone regeneration. Therefore, this review aims to detail and explore the implications of OcLCs in BTE, and how they can be leveraged to improve upon the existing BTE paradigm.

TGFBI: A novel therapeutic target for cancer

TGFBI, an extracellular matrix protein induced by transforming growth factor β, has been found to exhibit aberrant expression in various types of cancer. TGFBI plays a crucial role in tumor cell proliferation, angiogenesis, and apoptosis. It also facilitates invasion and metastasis in various types of cancer, including colon, head and neck squamous, renal, and prostate cancers. TGFBI, a prominent p-EMT marker, strongly correlates with lymph node metastasis. TGFBI demonstrates immunosuppressive effects within the tumor immune microenvironment. Targeted therapy directed at TGFBI shows promise as a potential strategy to combat cancer. Hence, a comprehensive review was conducted to examine the impact of TGFBI on various aspects of tumor biology, including cell proliferation, angiogenesis, invasion, metastasis, apoptosis, and the immune microenvironment. This review also delved into the underlying biochemical mechanisms to enhance our understanding of the research advancements related to TGFBI in the context of tumors.

Genetic insight into the putative causal proteins and druggable targets of osteoporosis: a large-scale proteome-wide mendelian randomization study

Background: Osteoporosis is a major causative factor of the global burden of disease and disability, characterized by low bone mineral density (BMD) and high risks of fracture. We aimed to identify putative causal proteins and druggable targets of osteoporosis. Methods: This study utilized the largest GWAS summary statistics on plasma proteins and estimated heel BMD (eBMD) to identify causal proteins of osteoporosis by mendelian randomization (MR) analysis. Different GWAS datasets were used to validate the results. Multiple sensitivity analyses were conducted to evaluate the robustness of primary MR findings. We have also performed an enrichment analysis for the identified causal proteins and evaluated their druggability. Results: After Bonferroni correction, 67 proteins were identified to be causally associated with estimated BMD (eBMD) (p < 4 × 10^-5). We further replicated 38 of the 67 proteins to be associated with total body BMD, lumbar spine BMD, femoral neck BMD as well as fractures, such as RSPO3, IDUA, SMOC2, and LRP4. The findings were supported by sensitivity analyses. Enrichment analysis identified multiple Gene Ontology items, including collagen-containing extracellular matrix (GO:0062023, p = 1.6 × 10^-10), collagen binding (GO:0005518, p = 8.6 × 10^-5), and extracellular matrix structural constituent (GO:0005201, p = 2.7 × 10^-5). Conclusion: The study identified novel putative causal proteins for osteoporosis which may serve as potential early screening biomarkers and druggable targets. Furthermore, the role of plasma proteins involved in collagen binding and extracellular matrix in the development of osteoporosis was highlighted. Further studies are warranted to validate our findings and investigate the underlying mechanism.

An In Vitro Analysis of TKI-Based Sequence Therapy in Renal Cell Carcinoma Cell Lines

The tyrosine kinase inhibitor (TKI) cabozantinib might impede the growth of the sunitinib-resistant cell lines by targeting MET and AXL overexpression in metastatic renal cell carcinoma (mRCC). We studied the role of MET and AXL in the response to cabozantinib, particularly following long-term administration with sunitinib. Two sunitinib-resistant cell lines, 786-O/S and Caki-2/S, and the matching 786-O/WT and Caki-2/WT cells were exposed to cabozantinib. The drug response was cell-line-specific. The 786-O/S cells were less growth-inhibited by cabozantinib than 786-O/WT cells (p-value = 0.02). In 786-O/S cells, the high level of phosphorylation of MET and AXL was not affected by cabozantinib. Despite cabozantinib hampering the high constitutive phosphorylation of MET, the Caki-2 cells showed low sensitivity to cabozantinib, and this was independent of sunitinib pretreatment. In both sunitinib-resistant cell lines, cabozantinib increased Src-FAK activation and impeded mTOR expression. The modulation of ERK and AKT was cell-line-specific, mirroring the heterogeneity among the patients. Overall, the MET- and AXL-driven status did not affect cell responsiveness to cabozantinib in the second-line treatment. The activation of Src-FAK might counteract cabozantinib activity and contribute to tumor survival and may be considered an early indicator of therapy response.

Retinoic Acid Receptor Activation Reduces Metastatic Prostate Cancer Bone Lesions by Blocking the Endothelial-to-Osteoblast Transition

Metastatic prostate cancer in the bone induces bone-forming lesions that contribute to progression and therapy resistance. Prostate cancer-induced bone formation originates from endothelial cells (EC) that have undergone endothelial-to-osteoblast (EC-to-OSB) transition in response to tumor-secreted BMP4. Current strategies targeting prostate cancer-induced bone formation are lacking. Here, we show that activation of retinoic acid receptor (RAR) inhibits EC-to-OSB transition and reduces prostate cancer-induced bone formation. Treatment with palovarotene, an RARγ agonist being tested for heterotopic ossification in fibrodysplasia ossificans progressiva, inhibited EC-to-OSB transition and osteoblast mineralization in vitro and decreased tumor-induced bone formation and tumor growth in several osteogenic prostate cancer models, and similar effects were observed with the pan-RAR agonist all-trans-retinoic acid (ATRA). Knockdown of RARα, β, or γ isoforms in ECs blocked BMP4-induced EC-to-OSB transition and osteoblast mineralization, indicating a role for all three isoforms in prostate cancer-induced bone formation. Furthermore, treatment with palovarotene or ATRA reduced plasma Tenascin C, a factor secreted from EC-OSB cells, which may be used to monitor treatment response. Mechanistically, BMP4-activated pSmad1 formed a complex with RAR in the nucleus of ECs to activate EC-to-OSB transition. RAR activation by palovarotene or ATRA caused pSmad1 degradation by recruiting the E3-ubiquitin ligase Smad ubiquitination regulatory factor1 (Smurf1) to the nuclear pSmad1/RARγ complex, thus blocking EC-to-OSB transition. Collectively, these findings suggest that palovarotene can be repurposed to target prostate cancer-induced bone formation to improve clinical outcomes for patients with bone metastasis.

SIGNIFICANCE

This study provides mechanistic insights into how RAR agonists suppress prostate cancer-induced bone formation and offers a rationale for developing RAR agonists for prostate cancer bone metastasis therapy. See related commentary by Bhowmick and Bhowmick, p. 2975.

Evolving cancer-niche interactions and therapeutic targets during bone metastasis

Many cancer types metastasize to bone. This propensity may be a product of genetic traits of the primary tumour in some cancers. Upon arrival, cancer cells establish interactions with various bone-resident cells during the process of colonization. These interactions, to a large degree, dictate cancer cell fates at multiple steps of the metastatic cascade, from single cells to overt metastases. The bone microenvironment may even influence cancer cells to subsequently spread to multiple other organs. Therefore, it is imperative to spatiotemporally delineate the evolving cancer-bone crosstalk during bone colonization. In this Review, we provide a summary of the bone microenvironment and its impact on bone metastasis. On the basis of the microscopic anatomy, we tentatively define a roadmap of the journey of cancer cells through bone relative to various microenvironment components, including the potential of bone to function as a launch pad for secondary metastasis. Finally, we examine common and distinct features of bone metastasis from various cancer types. Our goal is to stimulate future studies leading to the development of a broader scope of potent therapies.

All bone metastases are not created equal: Revisiting treatment resistance in renal cell carcinoma

Renal cell carcinoma (RCC) is the most common malignancy of the kidney, representing 80-90% of renal neoplasms, and is associated with a five-year overall survival rate of approximately 74%. The second most common site of metastasis is bone. As patients are living longer due to new RCC targeting agents and immunotherapy, RCC bone metastases (RCCBM) treatment failure is more prevalent. Bone metastasis formation in RCC is indicative of a more aggressive disease and worse prognosis. Osteolysis is a prominent feature and causes SRE, including pathologic fractures. Bone metastasis from other tumors such as lung, breast, and prostate cancer, are more effectively treated with bisphosphonates and denosumab, thereby decreasing the need for palliative surgical intervention. Resistance to these antiresportives in RCCBM reflects unique cellular and molecular mechanisms in the bone microenvironment that promote progression via inhibition of the anabolic reparative response. Identification of critical mechanisms underlying RCCBM induced anabolic impairment could provide needed insight into how to improve treatment outcomes for patients with RCCBM, with the goals of minimizing progression that necessitates palliative surgery and improving survival.

Antitumor Effect of Cabozantinib in Bone Metastatic Models of Renal Cell Carcinoma

BACKGROUND

The presence of bone metastases in renal cell carcinoma (RCC) negatively affects patients' survival. Data from clinical trials has highlighted a significant benefit of cabozantinib in bone metastatic RCC patients. Here, we evaluated the antitumor effect of cabozantinib in coculture models of renal cell carcinoma (RCC) and osteoblasts (OBs) to investigate whether and how its antiproliferative activity is influenced by OBs.

METHODS

Bone/RCC models were generated, coculturing green fluorescent protein (GFP)-tagged Caki-1 and 786-O cells with human primary OBs in a "cell-cell contact" system. RCC proliferation and the OB molecular profile were evaluated after the cabozantinib treatment.

RESULTS

The Caki-1 cell proliferation increased in the presence of OBs (p < 0.0001), while the 786-O cell growth did not change in the coculture with the OBs. The cabozantinib treatment reduced the proliferation of both the Caki-1 (p < 0.0001) and 786-O (p = 0.03) cells cocultured with OBs. Intriguingly, the inhibitory potency of cabozantinib was higher when Caki-1 cells grew in presence of OBs compared to a monoculture (p < 0.001), and this was similar in 786-O cells alone or cocultured with OBs. Moreover, the OB pretreatment with cabozantinib "indirectly" inhibited Caki-1 cell proliferation (p = 0.040) without affecting 786-O cell growth. Finally, we found that cabozantinib was able to modulate the OB gene and molecular profile inhibiting specific proliferative signals that, in turn, could affect RCC cell growth.

CONCLUSIONS

Overall, the "direct" effect of cabozantinib on OBs "indirectly" increased its antitumor activity in metastatic RCC Caki-1 cells but not in the primary 786-O model.

Accumulation of CD45RO+CD8+ T cells is a diagnostic and prognostic biomarker for clear cell renal cell carcinoma

Renal cell carcinoma is characterized by high immunogenicity and infiltration of immune cells. CD45RO+CD8+ T cells are well known as a critical role in host defense of the immune environment. However, their role in clear cell renal carcinoma (ccRCC) remains unknown. To elucidate the clinical importance of CD45RO+CD8+ T cells in ccRCC as well as its underlying mechanism, we analyzed several types of peripheral immune cells from 274 patients with ccRCC who have received radical or partial nephrectomy and 350 healthy people. Flow cytomety assays showed there was no significant difference in the proportions of CD8+ T cells and its subtypes other than CD45RO+/CD45RA+CD8+ cells. Both gene and protein expression levels of CD45RO in ccRCC tissues were decreased. CD45RO+CD8+ T cells showed increased proliferative abilities but decreased apoptotic abilities through MAPK signaling activation in ccRCC. High expression level of CD45RO+CD8+ T cells inhibited ccRCC progression, including proliferation, invasion, as well as autophagy of ccRCC through many signaling pathways. Bioinformatics and immunohistochemical chip analysis measured gene and protein levels of CD45RO and other related proteins. The combination of UCHL1, HMGB3, and CD36 has diagnostic value in ccRCC and is able to predict prognosis. Collectively, CD45RO+CD8+ T cells play a critical role in ccRCC progression and may be regarded as clinical indicators.