The bone ecosystem facilitates multiple myeloma relapse and the evolution of heterogeneous drug resistant disease

Multiple myeloma (MM) is an osteolytic malignancy that is incurable due to the emergence of treatment resistant disease. Defining how, when and where myeloma cell intrinsic and extrinsic bone microenvironmental mechanisms cause relapse is challenging with current biological approaches. Here, we report a biology-driven spatiotemporal hybrid agent-based model of the MM-bone microenvironment. Results indicate MM intrinsic mechanisms drive the evolution of treatment resistant disease but that the protective effects of bone microenvironment mediated drug resistance (EMDR) significantly enhances the probability and heterogeneity of resistant clones arising under treatment. Further, the model predicts that targeting of EMDR deepens therapy response by eliminating sensitive clones proximal to stroma and bone, a finding supported by in vivo studies. Altogether, our model allows for the study of MM clonal evolution over time in the bone microenvironment and will be beneficial for optimizing treatment efficacy so as to significantly delay disease relapse.

γδ-Enriched CAR-T cell therapy for bone metastatic castrate-resistant prostate cancer

Immune checkpoint blockade has been largely unsuccessful for the treatment of bone metastatic castrate-resistant prostate cancer (mCRPC). Here, we report a combinatorial strategy to treat mCRPC using γδ-enriched chimeric antigen receptor (CAR) T cells and zoledronate (ZOL). In a preclinical murine model of bone mCRPC, γδ CAR-T cells targeting prostate stem cell antigen (PSCA) induced a rapid and significant regression of established tumors, combined with increased survival and reduced cancer-associated bone disease. Pretreatment with ZOL, a U.S. Food and Drug Administration-approved bisphosphonate prescribed to mitigate pathological fracture in mCRPC patients, resulted in CAR-independent activation of γδ CAR-T cells, increased cytokine secretion, and enhanced antitumor efficacy. These data show that the activity of the endogenous Vγ9Vδ2 T cell receptor is preserved in CAR-T cells, allowing for dual-receptor recognition of tumor cells. Collectively, our findings support the use of γδ CAR-T cell therapy for mCRPC treatment.

Abstract 82: Role of MSC-derived CXCL1 in bone-metastatic prostate cancer

In 2022, the American Cancer Society estimates that over 34,000 men will die of PCa, largely due to metastatic PCa. Up to 90% of advanced prostate cancers metastasize to bone, and there are currently no curative therapies for bone metastatic prostate cancer (BM-PCa). BM-PCa cells interact with bone-forming osteoblasts and bone-resorbing osteoclasts to induce aberrant bone remodeling, which leads to skeletal related adverse events such as increased risk of fractures, bone pain, and poor quality of life. Mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into osteoblasts. Cook lab data show BM-PCa cells interact with MSCs and promote MSC differentiation into osteoblasts. Microarray analysis of MSC gene expression changes in response to BM-PCa show significant upregulation of CXCL8. To determine the importance of MSC-derived CXCL8 to BM-PCa, CXCL1 (the murine homolog of CXCL8) was genetically deleted in murine MSCs. While CXCL1 knock out (KO) had no significant impact on MSC proliferation, loss of CXCL1 decreased MSC migration, which suggests upregulation of MSC CXCL1 by BM-PCa cells functions to increase MSC migration into the tumor microenvironment. Additionally, CXCL1 KO MSCs have altered osteoblastic differentiation, whereas adipogenic differentiation was unchanged. RNA sequencing of MSCs stably expressing CXCL1-targeted shRNAs compared to scrambled controls show extensive gene expression changes, including altered expression of multiple osteogenic genes. In vivo data show intratibial co-injection of CXCL1 KO MSCs with murine RM1 BM-PCa cells in an immunocompetent mouse model increases tumor burden compared with co-injection of wildtype MSCs and BM-PCa cells, indicating a role for MSC-derived CXCL1 in suppressing BM-PCa tumor growth in bone. This project shows for the first time the importance of CXCL1 in MSC migration, osteogenesis, gene expression, suppression of BM-PCa progression in bone and tumor-induced bone remodeling.

Citation Format: Catherine S. Johnson, Diane Costanzo-Garvey, Massar Alsamraae, Jeremy S. Frieling, Leah M. Cook. Role of MSC-derived CXCL1 in bone-metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 82.

Abstract 1767: Biodistribution of zoledronate and effects on gd PSCA-CAR T cells in a model of bone metastatic prostate cancer

Background: Metastatic castrate resistant prostate cancer (mCRPC) is frequently manifested in the bone, leading to increased morbidity and mortality. We have previously demonstrated that γδ Chimeric Antigen Receptor (CAR) T cells targeting prostate stem cell antigen (PSCA) led to significant regression of established prostate cancer cells in the bone. Regression was further increased by combination with the bisphosphonate zoledronate (ZOL), routinely administered to mCRPC patients to prevent bone loss. To further optimize the use of γδ CAR T cells for mCRPC, we aimed to determine the kinetics of γδ CAR T cell in a mouse model of bone metastatic prostate cancer, either as single treatment or in combination with ZOL. In addition, we identified the sites of systemic ZOL accumulation in an immune competent model that could potentially induce off-target effects of γδ CAR T cells.

Methods: Male NSG mice were injected with C4-2B prostate cancer cells expressing PSCA and luciferase in the left tibia, while the right tibia received PBS. ZOL (25 μg/kg) was injected every other day subcutaneously in half of the mice and was discontinued one day prior to administering T cells. When tumors were established, mice received γδ PSCA-CAR T cells, γδ untransduced (UT) T cells or were left untreated. Bone marrow from tumor-bearing tibia, tumor-naive tibia, femur, spleen and blood were recovered at multiple time points, and the number of γδ T cells was analyzed by flow cytometry. To determine systemic ZOL uptake, C57BL/6 mice were injected with PTE-82 prostate cell line in both tibias. One week after injection, mice received ZOL-AF647 every other day for 2 weeks. Bone marrow, liver, kidney, peritoneal lavage, skin-draining lymph nodes, Peyer’s patches and spleen were recovered and analyzed by flow cytometry.

Results: γδ CAR T cells showed a rapid accumulation in the bone marrow recovered from tumor-bearing tibias, with 3 times more cells than those from mice treated with γδ UT cells (p=0.0002). The number of γδ T cells peaked at 5 days post infusion and were still detected after 21 days. Increased γδ CAR T cell accumulation was not observed in tumor-free bones or in spleen or blood, suggesting a preferential localization of γδ CAR T cells at tumor sites. Treatment with ZOL did not significantly affect the number or phenotype of γδ T cells accumulated in bone. Analysis of ZOL distribution showed significant uptake by macrophages, specially from liver and peritoneal lavage (p<0.0001), with an average of 30% and 70% of macrophages showing positive staining for ZOL-AF647, respectively (p<0.0001).

Conclusion: γδ PSCA-CAR T cells accumulate and get activated at tumor sites with limited distribution outside the bone, while their kinetics is not affected by ZOL treatment in the NSG xenograft model. Additional studies will be necessary to determine the impact of ZOL uptake by myeloid cells on γδ CAR T cells migration.

Citation Format: Leticia Tordesillas, Junior Cianne, Jeremy S. Frieling, Xiomar Bustos, Conor C. Lynch, Daniel Abate-Daga. Biodistribution of zoledronate and effects on gd PSCA-CAR T cells in a model of bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1767.

Quantification and Optimization of Standard-of-Care Therapy to Delay the Emergence of Resistant Bone Metastatic Prostate Cancer

BACKGROUND

Bone metastatic prostate cancer (BMPCa), despite the initial responsiveness to androgen deprivation therapy (ADT), inevitably becomes resistant. Recent clinical trials with upfront treatment of ADT combined with chemotherapy or novel hormonal therapies (NHTs) have extended overall patient survival. These results indicate that there is significant potential for the optimization of standard-of-care therapies to delay the emergence of progressive metastatic disease.

METHODS

Here, we used data extracted from human bone metastatic biopsies pre- and post-abiraterone acetate/prednisone to generate a mathematical model of bone metastatic prostate cancer that can unravel the treatment impact on disease progression. Intra-tumor heterogeneity in regard to ADT and chemotherapy resistance was derived from biopsy data at a cellular level, permitting the model to track the dynamics of resistant phenotypes in response to treatment from biological first-principles without relying on data fitting. These cellular data were mathematically correlated with a clinical proxy for tumor burden, utilizing prostate-specific antigen (PSA) production as an example.

RESULTS

Using this correlation, our model recapitulated the individual patient response to applied treatments in a separate and independent cohort of patients (n = 24), and was able to estimate the initial resistance to the ADT of each patient. Combined with an intervention-decision algorithm informed by patient-specific prediction of initial resistance, we propose to optimize the sequence of treatments for each patient with the goal of delaying the evolution of resistant disease and limit cancer cell growth, offering evidence for an improvement against retrospective data.

CONCLUSIONS

Our results show how minimal but widely available patient information can be used to model and track the progression of BMPCa in real time, offering a clinically relevant insight into the patient-specific evolutionary dynamics of the disease and suggesting new therapeutic options for intervention.

TRIAL REGISTRATION

NCT # 01953640.

FUNDING

Funded by an NCI U01 (NCI) U01CA202958-01 and a Moffitt Team Science Award. CCL and DB were partly funded by an NCI PSON U01 (U01CA244101). AA was partly funded by a Department of Defense Prostate Cancer Research Program (W81XWH-15-1-0184) fellowship. LC was partly funded by a postdoctoral fellowship (PF-13-175-01-CSM) from the American Cancer Society.

Mesenchymal stem cell-derived interleukin-28 drives the selection of apoptosis resistant bone metastatic prostate cancer

Bone metastatic prostate cancer (PCa) promotes mesenchymal stem cell (MSC) recruitment and their differentiation into osteoblasts. However, the effects of bone-marrow derived MSCs on PCa cells are less explored. Here, we report MSC-derived interleukin-28 (IL-28) triggers prostate cancer cell apoptosis via IL-28 receptor alpha (IL-28Rα)-STAT1 signaling. However, chronic exposure to MSCs drives the selection of prostate cancer cells that are resistant to IL-28-induced apoptosis and therapeutics such as docetaxel. Further, MSC-selected/IL-28-resistant prostate cancer cells grow at accelerated rates in bone. Acquired resistance to apoptosis is PCa cell intrinsic, and is associated with a shift in IL-28Rα signaling via STAT1 to STAT3. Notably, STAT3 ablation or inhibition impairs MSC-selected prostate cancer cell growth and survival. Thus, bone marrow MSCs drive the emergence of therapy-resistant bone metastatic prostate cancer yet this can be disabled by targeting STAT3.

Neutrophils are mediators of metastatic prostate cancer progression in bone

Bone metastatic prostate cancer (BM-PCa) significantly reduces overall patient survival and is currently incurable. Current standard immunotherapy showed promising results for PCa patients with metastatic, but less advanced, disease (i.e., fewer than 20 bone lesions) suggesting that PCa growth in bone contributes to response to immunotherapy. We found that: (1) PCa stimulates recruitment of neutrophils, the most abundant immune cell in bone, and (2) that neutrophils heavily infiltrate regions of prostate tumor in bone of BM-PCa patients. Based on these findings, we examined the impact of direct neutrophil-prostate cancer interactions on prostate cancer growth. Bone marrow neutrophils directly induced apoptosis of PCa in vitro and in vivo, such that neutrophil depletion in bone metastasis models enhanced BM-PCa growth. Neutrophil-mediated PCa killing was found to be mediated by suppression of STAT5, a transcription factor shown to promote PCa progression. However, as the tumor progressed in bone over time, neutrophils from late-stage bone tumors failed to elicit cytotoxic effector responses to PCa. These findings are the first to demonstrate that bone-resident neutrophils inhibit PCa and that BM-PCa are able to progress via evasion of neutrophil-mediated killing. Enhancing neutrophil cytotoxicity in bone may present a novel therapeutic option for bone metastatic prostate cancer.

CAR-T Engineering: Optimizing Signal Transduction and Effector Mechanisms

The adoptive transfer of genetically engineered T cells expressing a chimeric antigen receptor (CAR) has shown remarkable results against B cell malignancies. This immunotherapeutic approach has advanced and expanded rapidly from preclinical models to the recent approval of CAR-T cells to treat lymphomas and leukemia by the Food and Drug Administration (FDA). Ongoing research efforts are focused on employing CAR-T cells as a therapy for other cancers, and enhancing their efficacy and safety by optimizing their design. Here we summarize modifications in the intracellular domain of the CAR that gave rise to first-, second-, third- and next-generation CAR-T cells, together with the impact that these different designs have on CAR-T cell biology and function. Further, we describe how the structure of the antigen-sensing ectodomain can be enhanced, leading to superior CAR-T cell signaling and/or function. Finally we discuss how tissue-specific factors may impact the clinical efficacy of CAR-T cells for bone and the central nervous system, as examples of specific indications that may require further CAR signaling optimization to perform in such inhospitable microenvironments.

Proteolytic Regulation of Parathyroid Hormone-Related Protein: Functional Implications for Skeletal Malignancy

Parathyroid hormone-related protein (PTHrP), with isoforms ranging from 139 to 173 amino acids, has long been implicated in the development and regulation of multiple tissues, including that of the skeleton, via paracrine and autocrine signaling. PTHrP is also known as a potent mediator of cancer-induced bone disease, contributing to a vicious cycle between tumor cells and the bone microenvironment that drives the formation and progression of metastatic lesions. The abundance of roles ascribed to PTHrP have largely been attributed to the N-terminal 1-36 amino acid region, however, activities for mid-region and C-terminal products as well as additional shorter N-terminal species have also been described. Studies of the protein sequence have indicated that PTHrP is susceptible to post-translational proteolytic cleavage by multiple classes of proteases with emerging evidence pointing to novel functional roles for these PTHrP products in regulating cell behavior in homeostatic and pathological contexts. As a consequence, PTHrP products are also being explored as potential biomarkers of disease. Taken together, our enhanced understanding of the post-translational regulation of PTHrP bioactivity could assist in developing new therapeutic approaches that can effectively treat skeletal malignancies.

Matrix metalloproteinase processing of PTHrP yields a selective regulator of osteogenesis, PTHrP1-17

Parathyroid hormone-related protein (PTHrP) is a critical regulator of bone resorption and augments osteolysis in skeletal malignancies. Here we report that the mature PTHrP_1-36 hormone is processed by matrix metalloproteinases to yield a stable product, PTHrP_1-17. PTHrP_1-17 retains the ability to signal through PTH1R to induce calcium flux and ERK phosphorylation but not cyclic AMP production or CREB phosphorylation. Notably, PTHrP_1-17 promotes osteoblast migration and mineralization in vitro, and systemic administration of PTHrP_1-17 augments ectopic bone formation in vivo. Further, in contrast to PTHrP_1-36, PTHrP_1-17 does not affect osteoclast formation/function in vitro or in vivo. Finally, immunoprecipitation-mass spectrometry analyses using PTHrP_1-17-specific antibodies establish that PTHrP_1-17 is indeed generated by cancer cells. Thus, matrix metalloproteinase-directed processing of PTHrP disables the osteolytic functions of the mature hormone to promote osteogenesis, indicating important roles for this circuit in bone remodelling in normal and disease contexts.

Current and emerging therapies for bone metastatic castration-resistant prostate cancer

BACKGROUND

A paucity of therapeutic options is available to treat men with metastatic castration-resistant prostate cancer (mCRPC). However, recent developments in our understanding of the disease have resulted in several new therapies that show promise in improving overall survival rates in this patient population.

METHODS

Agents approved for use in the United States and those undergoing clinical trials for the treatment of mCRPC are reviewed. Recent contributions to the understanding of prostate biology and bone metastasis are discussed as well as how the underlying mechanisms may represent opportunities for therapeutic intervention. New challenges to delivering effective mCRPC treatment will also be examined.

RESULTS

New and emerging treatments that target androgen synthesis and utilization or the microenvironment may improve overall survival rates for men diagnosed with mCRPC. Determining how factors derived from the primary tumor can promote the development of premetastatic niches and how prostate cancer cells parasitize niches in the bone microenvironment, thus remaining dormant and protected from systemic therapy, could yield new therapies to treat mCRPC. Challenges such as intratumoral heterogeneity and patient selection can potentially be circumvented via computational biology approaches.

CONCLUSIONS

The emergence of novel treatments for mCRPC, combined with improved patient stratification and optimized therapy sequencing, suggests that significant gains may be made in terms of overall survival rates for men diagnosed with this form of cancer.

Abstract 5061: Roles for matrix metalloproteinase-3 (MMP-3) in the prostate tumor-bone microenvironment

Prostate cancer commonly metastasizes to bone, resulting in lesions hallmarked by a mixture of osteolysis and osteogenesis. The “vicious cycle” is the paradigm describing tumor-bone interaction, and MMPs have been implicated in regulating the bioavailability and activity of growth factors that control the cycle. We have found that MMP-3, also known as stromelysin-1 and typically generated by host/stromal cells, is differentially expressed in the prostate tumor-bone microenvironment. Based on our initial observations, we hypothesize that host derived MMP-3 expression contributes to prostate tumor growth in bone.

Using an in vivo intratibial model of prostate to bone metastases (PaIII), we found that that tumor growth and tumor induced bone remodeling were significantly mitigated (p<0.05) in MMP-3 null animals compared to wild type controls. Using a candidate approach to examine potential mechanisms, we focused on parathyroid hormone related protein (PTHrP), a powerful regulator of osteoblast behavior in the vicious cycle. We identified that MMP-3 processes mature PTHrP1-36 to yield PTHrP1-16, PTHrP17-26, and PTHrP27-36 fragments in vitro. The fragments did not impact osteoblast proliferation (MTT assay) or differentiation (Alizarin red staining), however, we observed a significant increase in migration of osteoblasts and osteoblast precursors in response to 10nM PTHrP1-16. The stimulation of migration by PTHrP1-16 was significantly greater than that induced by mature PTHrP1-36. Further analysis via confocal microscopy revealed a reduction in actin stress fibers as well as variations in lamellipodia and vinculin organization of osteoblasts treated with PTHrP1-16. In addition, western blots show a reduction of myosin light chain phosphorylation suggesting that PTHrP1-16 may mediate osteoblast migration by modulating Rho-associated protein kinase (ROCK) activity.

Our data demonstrate that host MMP-3 contributes to prostate tumor growth and tumor induced changes in bone remodeling in vivo. Further, we have identified that mature PTHrP1-36 is subject to cleavage by MMP-3 resulting in PTHrP1-16, PTHrP17-26, and PTHrP27-36 fragments of which PTHrP1-16 significantly stimulates migration of osteoblasts and osteoblast precursors. Collectively, these data indicate that specific inhibition of MMP-3 and/or targeting MMP generated neo-epitopes would be efficacious for the treatment of prostate to bone metastases.

Citation Format: Jeremy S. Frieling, Lizzie Atomi Pamen, Leah M. Cook, Shengyu Yang, Conor C. Lynch. Roles for matrix metalloproteinase-3 (MMP-3) in the prostate tumor-bone microenvironment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5061. doi:10.1158/1538-7445.AM2013-5061

Abstract 2464: Novel MMP-3 generated PTHrP peptides promote osteoblast proliferation: Implications for prostate to bone metastases

Up to 90% of patients that succumb to prostate cancer will have evidence of bone metastasis. Prostate to bone metastases generate mixed lesions hallmarked by areas of extensive bone resorption and formation mediated by osteoclasts and osteoblasts respectively. Tumor derived PTHrP has been defined as a major molecule facilitating tumor-osteoblast interaction. Mature PTHrP is comprised of 36 amino-acids and new data from our lab has identified that MMP-3, one of several MMPs we have found highly expressed in the prostate cancer-bone microenvironment, can process PTHrP to yield novel distinct peptides. We posit that MMP-3 generated PTHrP peptides can have distinct biological effects on osteoblasts. Our results to date demonstrate that MMP-3 processes mature PTHrP to yield PTHrP1-16, PTHrP17-26, and PTHrP27-36 amino acid peptides in vitro as determined by N-terminal amino acid sequencing and MALDI-TOF analysis. Next, we determined the biological activity of the MMP-3 generated PTHrP peptides by treating osteoblast cell lines and examining differentiation and proliferation. We found using alizarin red staining that the MMP-3 generated PTHrP peptides did not impact osteoblast differentiation. However, analysis of cell proliferation, using an MTT assay, identified that the PTHrP1-16 peptide stimulated osteoblast proliferation over a 24-hour period. Follow-up studies revealed that the MMP-3 generated PTHrP1-16 fragment significantly enhanced phosphorylation of MAPK 42/44 and CREB, presumably via the PTHrP receptor, PTH1R. In conclusion, our data identify for the first time that PTHrP is an MMP substrate and that MMP-3 generated PTHrP peptide PTHrP1-16, can promote osteoblast proliferation. These findings suggest that MMP-3 expression in the prostate tumor microenvironment can potentially impact osteoblast expansion and may play a role in the generation of osteoblastic lesions that are commonly associated with prostate to bone metastases.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2464. doi:1538-7445.AM2012-2464

Endogenous Aeromonas hydrophila endophthalmitis

Aeromonas hydrophila as the etiologic agent of endophthalmitis is rare, having only been reported in association with a perforating injury of the eye. We describe a case of isolated spontaneous, endogenous endophthalmitis due to this agent, with no apparent source.