Breast Cancer Bone Metastasis Research Articles

Abstract PO5-05-13: Clinical utility of whole body low dose computed tomography for detecting bone metastasis in breast cancer patients: A cross sectional study

Abstract Clinical utility of Whole Body Low Dose CT scan for detecting bone metastasis in Breast cancer patients: A cross sectional study Background: Skeletal scintigraphy (Bone scan) is the imaging of choice to detect bone metastasis in locally advanced and metastatic breast cancer patients. Nuclear medicine facilities are however limited in their availability. As an alternative diagnostic modality to bone scan, we studied the diagnostic capability of Whole-Body Low Dose CT (WBLDCT) scan for detection of bone metastasis in these patients. Materials and Method: This cross-sectional study was conducted from November 2021 to May 2023 at a tertiary healthcare center in India with an aim to study the clinical applicability of whole-body low dose computed tomography scan for detecting bone metastasis in patients with breast cancer. Breast cancer patients with primary tumor measuring 5cm or more, pathologically proven axillary lymph node metastasis, Stage III/IV disease, symptoms attributable to metastasis and suspected disease recurrence were included. All patients underwent WBLDCT and Bone scan within a period of about 2 weeks. WBLDCT was done during the same time as conventional dose CT scan was being done as part of metastatic workup. WBLDCT acquisition protocol was set in CT scan machine by modulating the technical parameters like Care dose 4D-automated, Care kV semi, rotation time & noise index. The image analysis was performed by Radiologist and Nuclear medicine experts in a blinded fashion. Data was recorded in MS Excel sheet. Sensitivity, specificity, positive and negative predicative value, and concordance rates were calculated using SPSS software ver 25.0. Agreement amongst WBLDCT and Bone scan was calculated using Inter-rater agreement. p value < 0.05 was taken as significant. Results: 110 patients were enrolled in this study. The mean age of participants was 48.5 years and three fourth had stage III disease at presentation. Estrogen receptor positive disease was seen in 43.64% participants while 30% were triple negative. Her2neu positive disease was seen in 27.27% patients. Bone scan couldn’t be done in 03 patients who deferred treatment (these had no bone metastasis on WBLDCT). Both bone scan and WBLDCT detected bone metastasis in 19 patients. Bone scan picked up additional metastasis in three patients which were missed on WBLDCT. WBLDCT detected bone metastasis additionally in three patients which were not detected on Bone scan. Multiple lesions were most seen in vertebrae in 38.5% and 28.6% on bone scan and WBLDCT respectively. The sensitivity and specificity of WBLDCT for detection of bone metastasis was 86.36% and 96.47% respectively. The concordance rate between Bone scan and WBLDCT scan was 94.39% with an Inter-rater Kappa(k) quotient for agreement of 0.828 (p< 0.0001). Conclusion: WBLDCT scan has comparable diagnostic capability to skeletal scintigraphy in detecting bone metastasis in breast cancer and may be a useful alternative specially in resource limited settings. Table 1: Sensitivity, specificity, positive predictive value and negative predictive value of WBLDCT for detection of metastasis Variables Values Sensitivity (95% CI) 86.36% Specificity (95% CI) 96.47% AUC (95% CI) 0.91 Positive Predictive Value (95% CI) 86.36% Negative Predictive Value (95% CI) 96.47% Diagnostic accuracy 94.39% Inter-rater agreement (kappa) 0.828 Citation Format: Lipton Mitra, Suhani Suhani, Ankur Goyal, Rakesh Kumar, Mohit Joshi, Hemanga Bhattacharjee, Haresh KP, Raju Sharma, Rajinder Parshad. Clinical utility of whole body low dose computed tomography for detecting bone metastasis in breast cancer patients: A cross sectional study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-13.

Abstract PO3-22-01: Characterization of peripheral T-cell dynamics in the patients with bone metastasis from breast cancer following stereotactic body radiotherapy

Abstract Purpose: Preclinical studies suggest that radiotherapy (RT) elicits various effects on antitumor T-cell responses. However, systemic T-cell responses upon RT in real-world cancer patients, including those with metastatic breast cancer, are poorly characterized. This study aims to investigate the detailed dynamics of peripheral T cells upon stereotactic body radiotherapy (SBRT) in metastatic breast cancer patients. Methods: Peripheral blood samples of 32 prospectively recruited patients who received SBRT to bone metastasis of breast cancer, which were acquired at pre-SBRT (W0), 1 week after SBRT (W1), and 4 weeks after SBRT (W4), were analyzed using multi-color flow cytometry and cytometric bead array. Most patients (n = 30) received SBRT of 1 fraction (n = 16) or 3 fractions (n = 14). We also performed a subgroup analysis of 22 patients who did not start a new systemic therapy within 1 month before SBRT (new systemic Tx >1mo) to exclude the effects of systemic therapies. Results: Peripheral PD-1+ CD8+ T cells, which are enriched for tumor-specific clonotypes, were activated with increased expression of Ki-67 at W1 compared to W0. Expression of Ki-67 on PD-1+ CD8+ T cells remained higher at W4 than W0, although it was not statistically significant. Moreover, expressions of Ki-67 and CTLA-4 on circulating regulatory T (TREG) cells were increased at W1 compared to W0. The suppressive (Foxp3hiCD45RA–) TREG cells also exhibited enhanced expressions of Ki-67 and CTLA-4 at W1. We defined immunologic responders (ImmRs) as patients with Ki-67 expression on PD-1+ CD8+ T cells at W1 greater than 1.5-times of W0, and otherwise immunologic non-responders (ImmNRs). Notably, fold changes in expressions of Ki-67 and CTLA-4 on TREG cells and proportion of suppressive TREG cells among total TREG cells at W1 over W0 were higher in ImmRs than ImmNRs. Similar phenotypical changes of T cells were observed in the subgroup analysis of the patients with new systemic Tx >1mo. The peripheral T-cell changes were not significantly different between the dose-fractionation schedules (1 fraction vs. 3 fractions) nor molecular subtypes of cancer. In patients with new systemic Tx >1mo, plasma level changes of TGF-β1, sCTLA-4, and s4-1BB at W1 compared to W0 were significantly higher in ImmRs compared to ImmNRs, while only change of s4-1BB was associated with the immunologic response. Conclusions: Our results suggest that circulating PD-1+ CD8+ T cells are activated upon SBRT. However, SBRT also results in the activation of circulating TREG cells, which was more prominent in patients with a significant activation of circulating PD-1+ CD8+ T cells. Alterations in plasma levels of TGF-β1, sCTLA-4, and s4-1BB are associated with the peripheral T-cell responses. Dose-fractionation schedule is not associated with the peripheral T-cell responses. Work supported by grants from the National Research Foundation of Korea (NRF-2023R1A2C3003782) Citation Format: Seung Hyuck Jeon, Eui-Cheol Shin, In Ah Kim. Characterization of peripheral T-cell dynamics in the patients with bone metastasis from breast cancer following stereotactic body radiotherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-22-01.

Abstract PO5-05-05: Clinical outcomes of CDK4/6 inhibitors in patients with bone only metastatic breast cancer

Abstract Background: CDK4/6 inhibitors (CDK 4/6i) have significantly advanced the treatment of hormone receptor-positive (HR+) metastatic breast cancer in the last decade. Several clinical trials including PALOMA, MONALEESA, and MONARCH have shown improved progression-free survival (PFS) rates when CDK4/6i were combined with endocrine therapy (ET). These results led to recommending their use in combination with ET as the first line of therapy in the metastatic settings. Bone metastasis is the most common site of disease in patients with HR+ metastatic breast cancer, about 40% of whom have bone as the only site of metastasis (bone-only disease [BoD]). While previous studies have shown that BoD can have a unique clinical course and a more favorable prognosis compared to non-BoD metastasis, most of the aforementioned CDK 4/6i clinical trials have not shown significant improvements in PFS in BoD subset of patients. Here we aimed to investigate the survival outcomes of BoD patients at a single institution center and evaluate CDK 4/6i activity in preclinical models of bone metastasis in breast cancer. Patients and methods: Patients with HR+, HER2-negative metastatic breast cancer from a retrospective CDK4/6i study at Washington University School of Medicine were included in this analysis. We selected all the patients who received CDK4/6i in the first- or second-line settings from June 2014 to March 2020. Outcomes were collected through June 10, 2023. The Kaplan-Meier method with log rank test and multivariable cox model were used for survival analysis. Results: 114 female patients (n=75 first line, n=39 second line, n=20 African American, n=94 Caucasian) were included in this study. All patients received Palbociclib as the first exposure to CDK4/6 inhibitor in combination with ET for at least two months. Median age was 60 years (range, 28-87) and forty-seven patients (41%) were in the BoD group. Survival outcomes for BoD group were compared to the rest of patients who had either bone and visceral or visceral only metastatic lesions (BV group). Our results demonstrated a significantly reduced median PFS in BoD group compared to BV group (13.1 months [95%CI:8-18.2] vs 19.6 months [95%CI:6.8-32.4], p=0.01) respectively. There was no significant difference in overall survival between BoD and BV groups (36.6 months [95%CI:32.2-41] vs 41.7 months [95%CI 36.1-47.2] p=0.74) respectively. In multivariate analysis regarding the associated risk factors with PFS, after adjusting for age and race, BoD had a HR of 1.62 (95%CI:1.04-2.54) for PFS. Among the 75 patients who received CDK4/6i as their first line of therapy, BoD (n=32 patients [42.7%]) also showed an inferior (p=0.05) median PFS (20 months [95%CI 12.9-27]) compared to BV group (n=43 patients [57.3%], median PFS=28.4 months [95%CI: 16.3-40.4]). To investigate potential treatment resistance mechanisms in bone metastases, we used the triple negative 4T1 and the ER+ luminal B PyMT Bo1 breast tumor cell line derived mammary gland models in immunocompetent mice. Single agent CDK4/6i, ribociclib, decreased primary mammary gland tumor burden. This effect was abrogated when CD8+ T-cells were depleted. In the bone colonization model using these cell lines, ribociclib had little effect on bone tumor burden. Arg1+ immune suppressive macrophages were significantly decreased in the primary mammary tumor but not in the bone tumor after ribociclib administration, suggesting a relative treatment resistance and immune suppression in the bone tumor microenvironment compared to the primary mammary gland. Conclusion: CDK4/6i play a significant role in the treatment of patients with HR+ metastatic breast cancer. Our single institution, retrospective study and preclinical data suggests that CDK4/6i may not be as effective for the treatment of tumors residing in the bone microenvironment, warranting future studies to understand the mechanisms of CDK4/6 inhibitors action in bone versus visceral metastases. Citation Format: Mahta Mardani, Suleyman Noordeen, Katherine Clifton, Cynthia Ma, Jingqin Luo, Jing Xi, Nusayba Bagegni, Foluso Ademuyiwa, Rama Suresh, Ashley Frith, Andrew Davis, Ron Bose, Lindsay Peterson, Shana Thomas, Yu Tao, Takayuki Kobayashi, Jingyu Xiang, Yalin Xu, Xinming Su, Katherine Weilbaecher. Clinical outcomes of CDK4/6 inhibitors in patients with bone only metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-05.

Abstract PO2-27-02: Re-sensitizing the Refractory Breast Cancer Bone Metastasis to Endocrine Therapies

Abstract Approximately 90% of Breast Cancer (BrCa) related deaths are caused by metastasis and bone is the first and most frequent site of breast cancer metastatic expansion, which can lead to severe pain, immobility, fractures, and nerve damage, as well as the development of metastases in other organs, hence; a poor quality of life in patients. Currently, treatment options for these bone metastases (BoM) are limited because most patients with BoM shows reduced ER dependency which leads to resistance to standard endocrine or hormonal therapies for estrogen receptor-positive (ER+) BrCa. The long-term goal of the proposed research is to develop a strategy where metastatic cancer cells in bone can be dependent on ER signaling again thereby restoring their sensitivity to endocrine therapies. We observed a transient loss of ER expression in concert with enhanced activity of the transcriptional coactivators YAP/TAZ - the downstream effectors of the Hippo pathway (responsible for regulating cell proliferation and death) during bone colonization by BrCa cells. We hypothesize that the interaction between cancer cells and osteoblasts in the bone microenvironment leads to the activation of calcium signaling in cancer cells, resulting in the de-phosphorylation and nuclear localization of YAP/TAZ which subsequently suppresses the transcription of the estrogen receptor gene (ESR). Our research strategy is as presented below. First, we will employ a combination of 2D/3D co-culture models of BoM along with a mechanical loading system and determine the molecular mechanism driving the dynamical activation of YAP/TAZ in BrCa BoM. Using a unique ex vivo BM model called Bone In Culture Array (BICA) which replicates the in-vivo conditions, we will determine if verteporfin, a YAP/TAZ antagonist, can synergize and possibly enhance the effects of Fulvestrant, an ER antagonist in current use for certain types of BrCa in preventing BoM outgrowths and treating established BoM in mice. This research could ultimately lead to a favorable combination strategy to treat endocrine-resistant BoM in BrCa patients and prolong their survival. Citation Format: Anindita Das, Cheyenne Ernst. Re-sensitizing the Refractory Breast Cancer Bone Metastasis to Endocrine Therapies [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-02.

The role of IL-1B in breast cancer bone metastasis

Interleukin-1B (IL-1B) is a potent pro-inflammatory cytokine that plays multiple, pivotal roles, in the complex interplay between breast cancer cells and the bone microenvironment. IL-1B is involved in the growth of the primary tumours, regulation of inflammation within the tumour microenvironment, promotion of epithelial to mesenchymal transition (EMT), migration and invasion. Moreover, when breast cancer cells arrive in the bone microenvironment there is an upregulation of IL-1B which promotes the creation of a conducive niche for metastatic breast cancer cells as well as stimulating initiation of the vicious cycle of bone metastasis. Pre-clinical studies have demonstrated that inhibition of IL-1 signalling reduces bone metastasis from oestrogen receptor positive/triple-negative breast cancers in various mouse models. However, effects on primary tumours and soft tissue metastasis remain controversial with some studies showing increased tumour growth in these sites, whilst others show no effects. Notably, combining anti-IL-1 therapy with standard-of-care treatments, such as chemotherapy and immunotherapy, has been demonstrated to reduce the growth of primary tumours, bone metastasis, as well as metastatic outgrowth in other organs. This review focuses on the mechanisms by which IL-1B promotes breast cancer bone metastasis.

Cryoprotective isoliquiritigenin-zein phosphatidylcholine nanoparticles inhibits breast cancer-bone metastasis by targeting JAK-STAT signaling pathways

Breast cancer (BC) is the most common cancer in women and is known for its tendency to spread to the bones, causing significant health issues and mortality. In this study, we aimed to investigate whether cryoprotective isoliquiritigenin-zein phosphatidylcholine nanoparticles (ISL@ZLH NPs) could inhibit BC-induced bone destruction and tumor metastasis in both in vitro and animal models. To evaluate the potential of ISL@ZLH NPs, we conducted various experiments. First, we assessed cell viability, colony formation, transwell migration, and wound healing assays to determine the impact of ISL@ZLH NPs on BC cell behavior. Western blotting, TRAP staining and ALP activity were performed to examine the effects of ISL@ZLH NPs on osteoclast formation induced by MDA-MB-231 cell-conditioned medium and RANKL treated RAW 264.7 cells. Furthermore, we assessed the therapeutic impact of ISL@ZLH NPs on tumor-induced bone destruction using a mouse model of BC bone metastasis. Treatment with ISL@ZLH NPs effectively suppressed BC cell proliferation, colony formation, and motility, reducing their ability to metastasize. ISL@ZLH NPs significantly inhibited osteoclast formation and the expression of factors associated with bone destruction in BC cells. Additionally, ISL@ZLH NPs suppressed JAK-STAT signaling in RAW264.7 cells. In the BCBM mouse model, ISL@ZLH NPs led to a significant reduction in osteolytic bone lesions compared to the control group. Histological analysis and TRAP staining confirmed that ISL@ZLH NPs preserved the integrity of bone structure, preventing invasive metastasis by confining tumor growth to the bone marrow cavity. Furthermore, ISL@ZLH NPs effectively suppressed tumor-induced osteoclastogenesis, a key process in BC-related bone destruction. Our findings demonstrate that ISL@ZLH NPs have the potential to inhibit BC-induced bone destruction and tumor metastasis by targeting JAK-STAT signaling pathways and suppressing tumor-induced osteoclastogenesis. These results underscore the therapeutic promise of ISL@ZLH NPs in managing BC metastasis to the bones.

Interrogating Estrogen Signaling Pathways in Human ER-Positive Breast Cancer Cells Forming Bone Metastases in Mice.

Breast cancer bone metastases (BMET) are incurable, primarily osteolytic, and occur most commonly in estrogen receptor-α positive (ER+) breast cancer. ER+ human breast cancer BMET modeling in mice has demonstrated an estrogen (E2)-dependent increase in tumor-associated osteolysis and bone-resorbing osteoclasts, independent of estrogenic effects on tumor proliferation or bone turnover, suggesting a possible mechanistic link between tumoral ERα-driven osteolysis and ER+ bone progression. To explore this question, inducible secretion of the osteolytic factor, parathyroid hormone-related protein (PTHrP), was utilized as an in vitro screening bioassay to query the osteolytic potential of estrogen receptor- and signaling pathway-specific ligands in BMET-forming ER+ human breast cancer cells expressing ERα, ERß, and G protein-coupled ER. After identifying genomic ERα signaling, also responsibility for estrogen's proliferative effects, as necessary and sufficient for osteolytic PTHrP secretion, in vivo effects of a genomic-only ER agonist, estetrol (E4), on osteolytic ER+ BMET progression were examined. Surprisingly, while pharmacologic effects of E4 on estrogen-dependent tissues, including bone, were evident, E4 did not support osteolytic BMET progression (vs robust E2 effects), suggesting an important role for nongenomic ER signaling in ER+ metastatic progression at this site. Because bone effects of E4 did not completely recapitulate those of E2, the relative importance of nongenomic ER signaling in tumor vs bone cannot be ascertained here. Nonetheless, these intriguing findings suggest that targeted manipulation of estrogen signaling to mitigate ER+ metastatic progression in bone may require a nuanced approach, considering genomic and nongenomic effects of ER signaling on both sides of the tumor/bone interface.

In Silico Discovery of Stapled Peptide Inhibitor Targeting the Nur77-PPARγ Interaction and Its Anti-Breast-Cancer Efficacy.

The binding of peroxisome proliferator-activated receptor γ (PPARγ) to the orphan nuclear receptor Nur77 facilitates the ubiquitination and degradation of Nur77, and leads to aberrant fatty acid uptake for breast cancer progression. Because of its crucial role in clinical prognosis, the interaction between Nur77 and PPARγ is an attractive target for anti-breast-cancer therapy. However, developing an inhibitor of the Nur77-PPARγ interaction poses a technical challenge due to the absence of the crystal structure of PPARγ and its corresponding interactive model with Nur77. Here, ST-CY14, a stapled peptide,is identified as a potent modulator of Nur77 with a KD value of 3.247×10-8M by in silico analysis, rational design, and structural modification. ST-CY14 effectively increases Nur77 protein levels by blocking the Nur77-PPARγ interaction, thereby inhibiting lipid metabolism in breast tumor cells. Notably, ST-CY14 significantly suppresses breast cancer growth and bone metastasis in mice. The findings demonstrate the feasibility of exploiting directly Nur77-PPARγ interaction in breast cancer, and generate what to the best knowledge is the first direct inhibitor of the Nur77-PPARγ interaction available for impeding fatty acid uptake and therapeutic development.

Combining TIGIT blockage with MDSC inhibition hinders breast cancer bone metastasis by activating anti-tumor immunity.

Bone is the most common site of breast cancer metastasis. Bone metastasis are incurable and are associated with severe morbidity. Utilizing an immunocompetent mouse model of spontaneous breast cancer bone metastasis, we profiled the immune transcriptome of bone metastatic lesions and peripheral bone marrow at distinct metastatic stages, revealing dynamic changes during the metastatic process. We show that crosstalk between granulocytes and T cells is central to shaping an immunosuppressive microenvironment. Specifically, we identified the PD-1 and TIGIT signaling axes and the pro-inflammatory cytokine IL1b as central players in the interactions between granulocytes and T cells. Targeting these pathways in vivo resulted in attenuated bone metastasis and improved survival, by reactivating anti-tumor immunity. Analysis of patient samples revealed that TIGIT and IL1b are prominent in human bone metastasis. Our findings suggest that co-targeting immunosuppressive granulocytes and dysfunctional T cells may be a promising novel therapeutic strategy to inhibit bone metastasis.

Abstract LB213: NF1 loss promotes bone metastasis in estrogen receptor positive breast cancer

Abstract Up to 80% of breast cancer (BCa) expresses estrogen receptor-α (ER). Over 60% ER+ BCa metastasizes to the bone and are challenging to treat. This study investigates what drives bone metastasis by focusing on a key tumor suppressor neurofibromin (NF1), a GTPase-activating protein that represses RAS signaling. Earlier, we reported that NF1 acts as a transcriptional corepressor for ER in BCa. Our group established that combination fulvestrant (selective ER degrader) and binimetinib (MEK-inhibitor) induces tumor regression in NF1lowER+ models. This combination is now in clinical trial, NCT05554354 (NCI ComboMATCH). Numerous studies indicate that the NF1 loss may impact bone health by altering the equilibrium between bone formation and resorption. Since, bone is the primary site of metastasis in 50-70% of ER+ BCa, understanding the role of NF1 loss in bone metastases becomes imperative. An osteolytic vicious cycle may drive bone metastasis, where cancer cells in the bone stimulate the bone-destructing osteoclasts (OC); leading to subsequent bone deterioration, which in turn, releases growth factors to further promote tumor growth. OCs and many cells in the bone are ER+. We thus hypothesize that deregulated RAS and ER signaling by NF1 loss can drive ER+ bone metastasis by promoting an osteolytic vicious cycle. To assess the clinical impact of NF1 loss on bone metastasis, we analyzed metastatic BCa patient data from cBioPortal and the MSK-EMC cohort. To define how NF1 loss affect bone metastasis, NF1 knockout (KO) ER+ BCa cells were tested in vitro and in vivo for bone tropism, growth in bone and effect on the vicious cycle. Analyses of clinical data suggest that NF1 copy number (CN) loss in ER+ tumors associates with accelerated metastasis to the bone. Additionally, NF1 CN loss and mutations are more prevalent in bone metastasis BCa patients. Lower levels of NF1 mRNA are correlated with shorter duration of bone metastasis-free survival.Our preclinical studies further supported the driver role of NF1 in bone metastasis. NF1KO ER+ BCa cells migrate more efficiently toward the bone in vitro compared to their NF1+ counterparts. When injected into the mammary fat pads of mice, NF1KO cells more frequently metastasized to the bone compared to NF1+ cells. When NF1KO cells were delivered to the mouse femur by intra-iliac injection, they grew more efficiently and induced more bone degradation. This is consistent with our in vitro results, which show that NF1KO ER+ BCa cells can more efficiently promote OC formation from progenitor cells. For this experiment, Mass-spectrometry based unbiased profiling of the conditioned medium showed that osteolytic factors, such as ICAM1 and OSTF1, were enriched in the NF1KO medium. Hence, we conclude that the loss of NF1 deregulates RAS and ER, leading to increased osteolytic factors, that drive bone metastasis. Co-targeting RAS and ER can be a potential treatment for NF1 loss-induced bone metastasis in ER+ BCa. Citation Format: Zifan Zhao, Ze-Yi Zheng, Jonathan Lei, Matthew J. Baik, Yi-Hsuan Wu, Junkai Wang, Igor Bado, Meenakshi Anurag, Bing Zhang, Xiang Zhang, Eric Chang. NF1 loss promotes bone metastasis in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB213.

#41. Discovery of novel tubulin code in bone metastasis of breast cancer

#41. Discovery of novel tubulin code in bone metastasis of breast cancer

#35. Defining short-form RON mediated anti-tumor immunity in breast cancer bone metastasis

#35. Defining short-form RON mediated anti-tumor immunity in breast cancer bone metastasis

#22. Investigating the TGF-β/integrin β3 signaling axis as a mediator of chemoresistance in breast cancer bone metastasis

#22. Investigating the TGF-β/integrin β3 signaling axis as a mediator of chemoresistance in breast cancer bone metastasis

#50. Investigating the role of EphA2 in breast cancer bone metastasis

#50. Investigating the role of EphA2 in breast cancer bone metastasis

#3. IL-17A supports osteoblasts to become cancer-associated fibroblasts in breast cancer bone metastases

#3. IL-17A supports osteoblasts to become cancer-associated fibroblasts in breast cancer bone metastases

Germacrone alleviates breast cancer-associated osteolysis by inhibiting osteoclastogenesis via inhibition of MAPK/NF-κB signaling pathways.

Bone is one of the most frequent sites for metastasis in breast cancer patients. Bone metastasis significantly reduces the survival time and the life quality of breast cancer patients. Germacrone (GM) can serve humans as an anti-cancer and anti-inflammation agent, but its effect on breast cancer-induced osteolysis remains unclear. This study aims to investigate the functions and mechanisms of GM in alleviating breast cancer-induced osteolysis. The effects of GM on osteoclast differentiation, bone resorption, F-actin ring formation, and gene expression were examined in vitro. RNA-sequencing and Western Blot were conducted to explore the regulatory mechanisms of GM on osteoclastogenesis. The effects of GM on breast cancer-induced osteoclastogenesis, and breast cancer cell malignant behaviors were also evaluated. The in vivo efficacy of GM in the ovariectomy model and breast cancer bone metastasis model with micro-CT and histomorphometry. GM inhibited osteoclastogenesis, bone resorption and F-actin ring formation in vitro. Meanwhile, GM inhibited the expression of osteoclast-related genes. RNA-seq analysis and Western Blot confirmed that GM inhibited osteoclastogenesis via inhibition of MAPK/NF-κB signaling pathways. The in vivo mouse osteoporosis model further confirmed that GM inhibited osteolysis. In addition, GM suppressed the capability of proliferation, migration, and invasion and promoted the apoptosis of MDA-MB-231 cells. Furthermore, GM could inhibit MDA-MB-231 cell-induced osteoclastogenesis in vitro and alleviate breast cancer-associated osteolysis in vivo human MDA-MB-231 breast cancer bone metastasis-bearing mouse models. Our findings identify that GM can be a promising therapeutic agent for patients with breast cancer osteolytic bone metastasis.

CDK4/6 inhibitor and doxorubicin synergistically inhibit breast cancer bone metastasis and enhance T-cell targeted therapy

CDK4/6 inhibitor and doxorubicin synergistically inhibit breast cancer bone metastasis and enhance T-cell targeted therapy

Treatment of Bone Metastases of Breast Cancer With 177Lu-DOTA-IBA.

Bone metastasis of breast cancer often presents as osteolytic. 177Lu-DOTA-ibandronic acid (177Lu-DOTA-IBA) is a new radioactive drug for bone metastasis lesion. We report a case of recurrent intermittent pain due to bone metastasis, who demonstrated a satisfactory therapy response after 2 cycles of 177Lu-DOTA-IBA. In addition, the patient did not have any observable adverse effects.

Abstract 1490: Elucidating the effect of glutamine metabolism in breast to bone metastasis

Abstract Bone-metastatic lesions will develop in approximately 65-75% of patients with metastatic breast cancer and are associated with high morbidity and mortality. Despite our limited understanding of how breast-to-bone metastases form, the recent emergence of metabolic adaptation as a critical factor in metastasis is a promising development. Breast cancer cells are particularly reliant on glutamine, a key amino acid that is metabolized by the enzyme glutaminase (GLS) to facilitate many downstream metabolic processes. Bone-tropic breast cancer cell lines significantly enhance their glutamine uptake, suggesting that glutamine metabolism may be a significant factor in bone metastasis. In addition to tumor cells, glutamine metabolism is critical for osteoblasts, important bone-resident cells that contribute to the “vicious cycle” of bone destruction during metastatic outgrowth in the bone niche. In this study, we sought to evaluate the role of glutamine metabolism in breast cancer bone metastasis by examining the effect of GLS function in metastasizing tumor cells and bone-native osteoblasts. Using an intracardiac inoculation model of bone metastasis, we found that breast cancer cells lacking GLS (GLS KO) failed to effectively form bone metastatic tumors. We also observed that GLS KO bone tumors show a reduction in osteolysis using a direct intratibial injection model. Mechanistically, we have found that GLS KO breast cancer cells develop a “senescence-like” phenotype that may limit metastatic outgrowth within the bone. To investigate the importance of glutamine metabolism in the bone niche, we developed a conditional genetic mouse model to delete GLS in osterix-expressing in osteoblast progenitors and mature osteoblasts (GLSOBKO). Remarkably, we observed reduced bone destruction in GLSOBKO mice after intratibial injection of syngeneic breast cancer cells. We also report a reduction in the number of osteoclasts at the bone/tumor interface in these mice, suggesting that loss of osteoblast GLS could temporarily halt the “vicious cycle” of bone metastasis. Together, this work suggests that glutamine metabolism may promote breast-to-bone metastasis via both intrinsic and extrinsic mechanisms. These findings raise the possibility of using pre-existing cancer therapies targeting glutamine metabolism to ameliorate bone metastatic burden in breast cancer. Citation Format: Breelyn A. Karno, Yoonha Hwang, Rachelle Johnson, Jin Chen, Deanna Edwards. Elucidating the effect of glutamine metabolism in breast to bone metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1490.

Abstract 2815: Immunotherapy development landscape for bone metastasis - need of predictive preclinical efficacy evaluation for de-risking clinical development

Abstract Most cancer deaths are due to metastases, and bone metastases are challenge especially in breast and prostate cancer, being developed in 70-90% of advanced-stage patients. Bone metastases remain incurable causing high mortality, skeletal-related effects and decreased quality of life. Currently used immunotherapies are ineffective in bone metastases. This creates a need to improve understanding immune microenvironment in bone metastases, namely interactions between tumor, immune and bone cells according to the osteoimmuno-oncology (OIO) concept, and ultimately to develop immunotherapies that primarily target bone metastases. We used 1stOncology database, a cancer drug development resource to identify novel immunotherapies in development for breast and prostate cancer bone metastasis. Twenty-four immunotherapies that included evaluation of effects on bone metastasis were identified. Efficacy of only three of the identified therapies had been evaluated in preclinical bone metastasis models, one reason being that such models have not been commonly available. The use of clinically relevant and predictive preclinical bone metastasis models would significantly de-risk decision making when moving to clinical development in bone metastasizing cancers. To support predictive preclinical evaluation of immunotherapies for bone metastatic cancers, we describe a preclinical bone metastasis technology platform for evaluating efficacy of immunotherapies. The platform utilizes tumors growing in bone microenvironment, mimicking growth of bone metastases in patients, and generates tumor-induced bone effects in a cancer-type specific manner. Syngeneic and/or humanized mouse models with tumor and immune cells of the same species are needed for development of immunotherapies, allowing interactions of tumor and immune cells in the bone metastatic microenvironment to support mode-of-action studies. The platform is clinically predictive, as demonstrated with observed effects that align with clinical findings. As an example, anti-PD-1 antibody had no effects on breast and prostate cancer bone metastases, predicting recent clinical findings that demonstrate lack of efficacy in clinical prostate cancer trials. We conclude that tumor microenvironment in bone metastases has unique characteristics and is understudied as a potential primary cause of lack of efficacy of many immunotherapies, especially in breast and prostate cancer. It is prime time to focus on bone metastases by increasing understanding of the immune landscape in the bone tumor microenvironment according to the OIO concept. The biologically relevant and clinically predictive preclinical bone metastasis technology platform should be routinely used to study the mechanism-of-action and efficacy of therapies before entering clinical development in bone metastasizing cancers. Citation Format: Tiina E. Kähkönen, Jussi M. Halleen, Gary MacRitchie, Ronnie M. Andersson, Jenni Bernoulli. Immunotherapy development landscape for bone metastasis - need of predictive preclinical efficacy evaluation for de-risking clinical development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2815.