Bone metastatic breast cancer is currently incurable and will be evident in more than 70% of patients that succumb to the disease. Understanding the factors that contribute to the progression and metastasis of breast cancer can reveal therapeutic opportunities. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes whose role in cancer has been widely documented. They are capable of contributing to every step of the metastatic cascade, but enthusiasm for the use of MMP inhibition as a therapeutic approach has been dampened by the disappointing results of clinical trials conducted more than 20 years ago. Since the trials, our knowledge of MMP biology has expanded greatly. Combined with advances in the selective targeting of individual MMPs and the specific delivery of therapeutics to the tumor microenvironment, we may be on the verge of finally realizing the promise of MMP inhibition as a treatment strategy. Here, as a case in point, we focus specifically on MMP-2 as an example to show how it can contribute to each stage of breast-cancer-to-bone metastasis and also discuss novel approaches for the selective targeting of MMP-2 in the setting of the bone-cancer microenvironment.

Matrix metalloproteinases (MMPs) are a family of enzymes involved at different stages of cancer progression and metastasis. We previously identified a novel class of bisphosphonic inhibitors, selective for MMPs crucial for bone remodeling, such as MMP-2. Due to the increasing relevance of specific MMPs at various stages of tumor malignancy, we focused on improving potency towards certain isoforms. Here, we tackled MMP-9 because of its confirmed role in tumor invasion, metastasis, angiogenesis, and immuno-response, making it an ideal target for cancer therapy. Using a computational analysis, we designed and characterized potent MMP-2/MMP-9 inhibitors. This is a promising approach to develop and clinically translate inhibitors that could be used in combination with standard care therapy for the treatment of skeletal malignancies.

Understanding dormancy in prostate cancer is challenging because of model availability. In this study, using murine and human prostate cancer cell lines, we generated a stress-induced model of dormancy in vitro and demonstrated that the phenotype could be sustained upon intrailiac artery delivery into the bone marrow microenvironment. RNA sequencing analysis revealed that the transcription factor positive regulatory domain–containing 16 (PRDM16) was commonly upregulated in dormant prostate cancer cells compared with controls. Furthermore, bone marrow–disseminated prostate cancer cells from primary orthotopic tumors were largely positive for PRDM16. Genetic ablation and forced ectopic expression supported a role for PRDM16 in maintaining prostate cancer dormancy in vitro and in vivo. Clinically, PRDM16 negatively correlated with disease recurrence and with the E2F cell-cycle program in disseminated tumor cells derived from the bone marrow of patients with prostate cancer. Gene enrichment and characterization studies implicated PRDM16 as a regulator of metabolic and cell-cycle pathways. Chromatin immunoprecipitation–qPCR further revealed that PRDM16 binds upstream of the promoter of RB1, a potent repressor of E2F activity. Overall, this study developed a straightforward method for inducing cancer cell dormancy and applied this approach to find that PRDM16 governs an intrinsic dormancy program in prostate cancer. Significance: PRDM16 initiates a dormancy program in prostate cancer cells that is sustained in the bone marrow microenvironment, highlighting PRDM16 as a potential biomarker for relapse and target for eliminating dormant cancer cells.

Understanding dormancy in prostate cancer is challenging because of model availability. In this study, using murine and human prostate cancer cell lines, we generated a stress-induced model of dormancy in vitro and demonstrated that the phenotype could be sustained upon intrailiac artery delivery into the bone marrow microenvironment. RNA sequencing analysis revealed that the transcription factor positive regulatory domain–containing 16 (PRDM16) was commonly upregulated in dormant prostate cancer cells compared with controls. Furthermore, bone marrow–disseminated prostate cancer cells from primary orthotopic tumors were largely positive for PRDM16. Genetic ablation and forced ectopic expression supported a role for PRDM16 in maintaining prostate cancer dormancy in vitro and in vivo. Clinically, PRDM16 negatively correlated with disease recurrence and with the E2F cell-cycle program in disseminated tumor cells derived from the bone marrow of patients with prostate cancer. Gene enrichment and characterization studies implicated PRDM16 as a regulator of metabolic and cell-cycle pathways. Chromatin immunoprecipitation–qPCR further revealed that PRDM16 binds upstream of the promoter of RB1, a potent repressor of E2F activity. Overall, this study developed a straightforward method for inducing cancer cell dormancy and applied this approach to find that PRDM16 governs an intrinsic dormancy program in prostate cancer.Significance:PRDM16 initiates a dormancy program in prostate cancer cells that is sustained in the bone marrow microenvironment, highlighting PRDM16 as a potential biomarker for relapse and target for eliminating dormant cancer cells.

Enrichment and correlation values used in the study