Parathyroid hormone‐related protein inhibition blocks triple‐negative breast cancer expansion in bone through epithelial to mesenchymal transition reversal

Parathyroid hormone‐related protein (PTHrP) plays a major role in skeletal metastasis but its action mechanism has not been fully defined. We previously demonstrated the crucial importance of PTHrP in promoting mammary tumor initiation, growth, and metastasis in a mouse model with a mammary epithelium‐targeted Pthlh gene ablation. We demonstrate here a novel mechanism for bone invasion involving PTHrP induction of epithelial to mesenchymal transition (EMT) and cancer stem cells (CSCs) regulation. Clustered regularly interspaced short palindromic repeats (CRISPR)‐mediated Pthlh gene ablation was used to study EMT markers, phenotype, and invasiveness in two triple‐negative breast cancer (TNBC) cell types (established MDA‐MB‐231 and patient‐derived PT‐TNBC cells). In vitro, Pthlh ablation in TNBC cells reduced EMT markers, mammosphere‐forming ability, and CD44^high/CD24^low cells ratio. In vivo, cells were injected intratibially into athymic nude mice, and therapeutic treatment with our anti‐PTHrP blocking antibody was started 2 weeks after skeletal tumors were established. In vivo, compared to control, lytic bone lesion from Pthlh ‐ablated cells decreased significantly over 2 weeks by 27% for MDA‐MB‐231 and by 75% for PT‐TNBC‐injected mice (p < 0.001). Micro‐CT (μCT) analyses also showed that antibody therapy reduced bone lytic volume loss by 52% and 48% for non‐ablated MDA‐MB‐231 and PT‐TNBC, respectively (p < 0.05). Antibody therapy reduced skeletal tumor burden by 45% and 87% for non‐ablated MDA‐MB‐231 and PT‐TNBC, respectively (p < 0.002) and caused a significant decrease of CSC/EMT markers ALDH1, vimentin, and Slug, and an increase in E‐cadherin in bone lesions. We conclude that PTHrP is a targetable EMT molecular driver and suggest that its pharmacological blockade can provide a potential therapeutic approach against established TNBC‐derived skeletal lesions. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

PTHrP Drives Pancreatic Cancer Growth and Metastasis and Reveals a New Therapeutic Vulnerability

Pancreatic cancer metastasis is a leading cause of cancer-related deaths, yet very little is understood regarding the underlying biology. As a result, targeted therapies to inhibit metastasis are lacking. Here, we report that the parathyroid hormone-related protein (PTHrP encoded by PTHLH) is frequently amplified as part of the KRAS amplicon in patients with pancreatic cancer. PTHrP upregulation drives the growth of both primary and metastatic tumors in mice and is highly enriched in pancreatic ductal adenocarcinoma metastases. Loss of PTHrP-either genetically or pharmacologically-dramatically reduces tumor burden, eliminates metastasis, and enhances overall survival. These effects are mediated in part through a reduction in epithelial-to-mesenchymal transition, which reduces the ability of tumor cells to initiate metastatic cascade. Spp1, which encodes osteopontin, is revealed to be a downstream effector of PTHrP. Our results establish a new paradigm in pancreatic cancer whereby PTHrP is a driver of disease progression and emerges as a novel therapeutic vulnerability. SIGNIFICANCE: Pancreatic cancer often presents with metastases, yet no strategies exist to pharmacologically inhibit this process. Herein, we establish the oncogenic and prometastatic roles of PTHLH, a novel amplified gene in pancreatic ductal adenocarcinoma. We demonstrate that blocking PTHrP activity reduces primary tumor growth, prevents metastasis, and prolongs survival in mice.This article is highlighted in the In This Issue feature, p. 1601.

Abstract 520: Therapeutic antibodies against parathyroid hormone-related peptide (PTHrP) inhibit the growth of established skeletal metastasis in mice transplanted with human triple negative breast cancer cell lines

Parathyroid Hormone-related Peptide (PTHrP)is a potent regulator of bone turnover and is thought to play a major role in the progression of skeletal metastasis through its activation of growth factors in the bone microenvironment. Our previous studies using genetically engineered mouse models in which PTHrP was ablated in the mammary epithelium have demonstrated that PTHrP also plays a direct role on tumor progression by enhancing tumor initiation, growth and metastasis outside the skeleton. We therefore proposed a novel mechanism of PTHrP driven bone metastasis by which PTHrP controls both the seed (tumor cells) and the soil (the bone microenvironment). We tested our hypothesis in triple negative breast cancer cell line (TNBC)models which are not responsive to either tamoxifen or Herceptin. Monoclonal antibodies against PTHrP were generated with strong in vitro anti-proliferative and anti-invasive potency in two human PTHrP expressing cell lines: the widely used TNBC MDAMB231 cell line and a patient derived TNBC cell line. Ablation of PTHrP or treatment with anti-PTHrP monoclonal antibodies induced major changes in the phenotype of these cells as determined by flow cytometry with stem cells and EMT markers, invasion assays and mammosphere assays indicating a reversal of their metastatic/invasive phenotype. Next we transplanted these cell lines into 8 weeks old female athymic nude mice to examine the efficacy of the therapeutic monoclonal antibodies on the progression of established bone metastasis.104 tumor cells were injected intra-tibially and animals examined at timed intervals(14, 21, 28, 25 and 42 days) with X-rays and high resolution CTs.At 14 days animals were administered intra-peritoneally with 200 micrograms of therapeutic anti-PTHrP antibodies or non-immune IgG(10 animals per group) and every 3 days thereafter til sacrifice(42 days). At sacrifice PET scan was performed to measure tumor volume and activity and bone were collected for histomorphometry analysis of tumor size and bone turnover activity. A significant reduction in bone lesions (P&lt;0.05) was observed over time by imaging in animals treated with the therapeutic antibodies. At sacrifice PET scan indicates a strong reduction in tumor activity in treated animals (P&lt;0.05). Histomorphometry analysis showed greater than 50% reduction in tumor volume associated with a significant inhibition of bone turnover in treated animals (P&lt;0.05). In summary our data demonstrate that, in two TNBC models, PTHrP blockade can reprogram cancer cells to a reduced tumorigenicity and block the progression of established bone metastasis by targeting both the tumor cell and the bone microenvironment. Our data lend support to the “seed and soil” hypothesis proposed by Paget and the rational of anti-PTHrP therapeutic strategies alone or in combination with bone targeting agents in order to eradicate the development of skeletal metastasis.

Citation Format: Jiarong Li, Anne Camirand, Mahvash Zakikhani, Karine Sellin, Richard Kremer. Therapeutic antibodies against parathyroid hormone-related peptide (PTHrP) inhibit the growth of established skeletal metastasis in mice transplanted with human triple negative breast cancer cell lines [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 520.

Abstract 3062: Ablation of parathyroid hormone-related protein in the triple negative human breast cancer line MDA-MB-231 inhibits its cancer stem cell phenotype

Parathyroid hormone-related protein (PTHrP) is a pleiotropic hormone involved in a wide range of developmental & physiological processes. It is also dysregulated in advanced cancers where it causes malignancy-associated hypercalcemia & plays a major role in the progression of bone metastases. We have shown previously that PTHrP ablation delays tumor initiation & that it is preferentially expressed in triple negative breast cancer (TNBC).Here we investigated how PTHrP can influence the phenotype of the human TNBC cell line MDA-MB231 using CRISPR/cas 9 knockout technology. We used U6G RNA-Cas9-2A-red fluorescence protein (RFP) vector with a human PTHrP specific guide RNA directed to exon 4(knockout/KO) or an empty vector as control. PTHrP KO cells (RFP+) were isolated using AutoMacs Pro Separator & single cells were exp&ed in 96 well plates. Positive clones were confirmed by DNA sequencing. Real time PCR & immunofluorescence staining confirmed that 5/96 KO clones had between 95-99% decrease in PTHrP expression compared to control cells. We then assessed cancer stem cell (CSC) characteristics of both KO & control cell lines. Mammosphere formation was reduced by over 60% in KO cells. Stem cell phenotype assessed by ALDH1 & CD44+/CD24 low using FACS analysis were significantly reduced by over 30% in KO cells. Cell morphology analysis showed a shift from a mesenchymal phenotype towards an epithelial phenotype. Overall our data show that PTHrP regulates TNBC towards a more aggressive phenotype & suggest that it could be targeted therapeutically.

Citation Format: Jiarong Li, Louis Doré-Savard, Karine Sellin, Anne Camirand, Richard Kremer. Ablation of parathyroid hormone-related protein in the triple negative human breast cancer line MDA-MB-231 inhibits its cancer stem cell phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3062.

Gene expression profiling and histomorphometric analyses of the early bone healing response around nanotextured implants

While in vitro studies have shown that nanoscale surface modifications influence cell fate and activity, there is little information on how they modulate healing at the bone-implant interface.

AIM

This study aims to investigate the effect of nanotopography at early time intervals when critical events for implant integration occur.

MATERIALS & METHODS

Untreated and sulfuric acid/hydrogen peroxide-treated machined-surface titanium alloy implants were placed in rat tibiae. Samples were processed for DNA microarray analysis and histomorphometry.

RESULTS

At both 3 and 5 days, the gene expression profile of the healing tissue around nanotextured implants differed from that around machined-surface implants or control empty holes, and were accompanied by an increase in bone-implant contact on day 5. While some standard pathways such as the immune response predominated, a number of unclassified genes were also implicated.

CONCLUSION

Nanotexture elicits an initial gene response that is more complex than suspected so far and favors healing at the bone-implant interface.

Ameloblastin is not implicated in bone remodelling and repair

Ameloblastin (AMBN) is an enamel matrix protein produced by ameloblasts. It has been suggested that AMBN might also be implicated in craniofacial bone formation. Our objective was to determine whether AMBN has an effect on osteogenic mineralisation and influences bone remodelling and repair. MC3T3-E1 cells were screened for endogenous expression of enamel proteins using real time PCR. Various osteogenic cells were infected with lentivirus encoding for AMBN and protein expression was verified using immunochemistry. Cultures were stained with alizarin red and mineralisation was quantified. Healing bone was probed for expression of AMBN by DNA microarray analysis. Tooth extraction, experimental tooth movement (ETM), and creation of a non-critical size bone defect in the tibia (BDT) were carried out in wild type and AMBN(Δ5-6) mutant mice. Tissues were processed for immunolabelling of AMBN and Bril, an osteoblast specific protein associated with active bone formation. MC3T3-E1 cells and healing bone showed no significant expression of AMBN. Overexpression of AMBN in osteogenic cultures induced no noticeable changes in mineralisation. In wild type mice, AMBN was immunodetected in ameloblasts and enamel, but not in normal bone, and at sites where bone remodelling and repair were induced. Bone remodelling during ETM and BDT repair in AMBN(Δ5-6) mice were not significantly different from that in wild type animals. Our results suggest that AMBN does not influence osteogenic activity in vitro under the conditions used, and does not participate in craniofacial bone remodelling under mechanical stress and in repair of non-critical size bone defects.

Osteocrin is a specific ligand of the natriuretic Peptide clearance receptor that modulates bone growth

Osteocrin (Ostn) is a recently discovered secreted protein produced by cells of the osteoblast lineage that shows a well conserved homology with members of the natriuretic peptide (NP) family. We hypothesized that Ostn could interact with the NP receptors, thereby modulating NP actions on the skeleton. Ostn binds specifically and saturably to the NP peptide receptor-C (NPR-C) receptor with a Kd of approximately 5 nM with no binding to the GC-A or GC-B receptors. Deletion of several of the residues deemed important for NP binding to NPR-C led to abolition of Ostn binding, confirming the presence of a "natriuretic motif." Functionally, Ostn was able to augment C-type natriuretic peptide-stimulated cGMP production in both pre-chondrocytic (ATDC5) and osteoblastic (UMR106) cells, suggesting increased NP levels due to attenuation of NPR-C associated NP clearance. Ostn-transgenic mice displayed elongated bones and a marked kyphosis associated with elevated bone cGMP levels, suggesting that elevated natriuretic peptide activity contributed to the increased bone length possibly through an increase in growth plate chondrocyte proliferation. Thus, we have demonstrated that Ostn is a naturally occurring ligand of the NPR-C clearance receptor and may act to locally modulate the actions of the natriuretic system in bone by blocking the clearance action of NPR-C, thus locally elevating levels of C-type natriuretic peptide.