New opportunities in the management of prostate cancer–related bone complications

Improving bone health in prostate cancer patients starting androgen deprivation therapy: does Fracture Risk Assessment Tool (FRAX®) enhance stratification and targeted management?

Androgen deprivation therapy for prostate cancer can lead to osteoporosis and increased fracture risk. The Fracture Risk Assessment Tool (FRAX®) questionnaire can be used for risk stratification, and our study has demonstrated that the majority of men (91%) in our cohort commencing ADT for prostate cancer were considered low risk for future osteoporotic fracture.

PURPOSE/INTRODUCTION

Long-term use of androgen deprivation therapy (ADT) in prostate cancer patients results in increased bone turnover and decreased bone mineral density (BMD). Proper assessment of any existing osteoporotic fracture risk is crucial prior to starting treatment. However, this risk assessment is poorly performed in these patients in spite of available validated tools including the Fracture Risk Assessment Tool (FRAX®). The objective of this study was to assess the distribution of osteoporotic fracture risk in a cohort of men commencing ADT for prostate cancer using the FRAX® algorithm.

METHODS

Between July 2020 and May 2022, 200 men filled in the FRAX® questionnaire just before ADT. They were stratified into the high-risk (> 20% probability of a MOF over the next 10 years), intermediate-, and low-risk categories for fragility fractures. We also measured their serum vitamin D and calcium levels.

RESULTS

The average age was 73.5 years (54-89). It took less than 10 min to complete the assessment. Only six patients were at high-risk, were started on bisphosphonates immediately, and referred for a dual energy X-ray absorptiometry (DEXA) scan. Twelve patients in the intermediate-risk category were referred for DEXA scans for bone mineral density measurements. A total of 182 patients (91%), were in the low-risk category and given lifestyle advice only. All had normal calcium levels but 134 (67%) patients, mostly in the low-risk category, had reduced vitamin D levels (< 50 nmol/L).

CONCLUSION

The FRAX® questionnaire is simple and immediately identifies patients who are at risk of fragility fractures. Our study has demonstrated that the majority of men (91%) in our cohort commencing ADT for prostate cancer were considered low risk for future osteoporotic fracture. We were surprised that more than half of our patients had low vitamin D levels.

Extracellular Vesicle-Mediated Bone Remodeling and Bone Metastasis: Implications in Prostate Cancer

Bone metastasis is the tendency of certain primary tumors to spawn and dictate secondary neoplasia in the bone. The process of bone metastasis is regulated by the dynamic crosstalk between metastatic cancer cells, cellular components of the bone marrow microenvironment (osteoblasts, osteoclasts, and osteocytes), and the bone matrix. The feed-forward loop mechanisms governs the co-option of homeostatic bone remodeling by cancer cells in bone. Recent developments have highlighted the discovery of extracellular vesicles (EVs) and their diverse roles in distant outgrowths. Several studies have implicated EV-mediated interactions between cancer cells and the bone microenvironment in synergistically promoting pathological skeletal metabolism in the metastatic site. Nevertheless, the potential role that EVs serve in arbitrating intricate sequences of coordinated events within the bone microenvironment remains an emerging field. In this chapter, we review the role of cellular participants and molecular mechanisms in regulating normal bone physiology and explore the progress of current research into bone-derived EVs in directly triggering and coordinating the processes of physiological bone remodeling. In view of the emerging role of EVs in interorgan crosstalk, this review also highlights the multiple systemic pathophysiological processes orchestrated by the EVs to direct organotropism in bone in prostate cancer. Given the deleterious consequences of bone metastasis and its clinical importance, in-depth knowledge of the multifarious role of EVs in distant organ metastasis is expected to open new possibilities for prognostic evaluation and therapeutic intervention for advanced bone metastatic prostate cancer.

A novel patient-derived intra-femoral xenograft model of bone metastatic prostate cancer that recapitulates mixed osteolytic and osteoblastic lesions

Prostate cancer metastasizes to bone in the majority of patients with advanced disease leading to painfully debilitating fractures, spinal compression and rapid decline. In addition, prostate cancer bone metastases often become resistant to standard therapies including androgen deprivation, radiation and chemotherapy. There are currently few models to elucidate mechanisms of interaction between the bone microenvironment and prostate cancer. It is, thus, essential to develop new patient-derived, orthotopic models. Here we report the development and characterization of PCSD1 (Prostate Cancer San Diego 1), a novel patient-derived intra-femoral xenograft model of prostate bone metastatic cancer that recapitulates mixed osteolytic and osteoblastic lesions.

Methods

A femoral bone metastasis of prostate cancer was removed during hemiarthroplasty and transplanted into Rag2^-/-;γ_c^-/- mice either intra-femorally or sub-cutaneously. Xenograft tumors that developed were analyzed for prostate cancer biomarker expression using RT-PCR and immunohistochemistry. Osteoblastic, osteolytic and mixed lesion formation was measured using micro-computed tomography (microCT).

Results

PCSD1 cells isolated directly from the patient formed tumors in all mice that were transplanted intra-femorally or sub-cutaneously into Rag2^-/-;γ_c^-/- mice. Xenograft tumors expressed human prostate specific antigen (PSA) in RT-PCR and immunohistochemical analyses. PCSD1 tumors also expressed AR, NKX3.1, Keratins 8 and 18, and AMACR. Histologic and microCT analyses revealed that intra-femoral PCSD1 xenograft tumors formed mixed osteolytic and osteoblastic lesions. PCSD1 tumors have been serially passaged in mice as xenografts intra-femorally or sub-cutaneously as well as grown in culture.

Conclusions

PCSD1 xenografts tumors were characterized as advanced, luminal epithelial prostate cancer from a bone metastasis using RT-PCR and immunohistochemical biomarker analyses. PCSD1 intra-femoral xenografts formed mixed osteoblastic/osteolytic lesions that closely resembled the bone lesions in the patient. PCSD1 is a new primary prostate cancer bone metastasis-derived xenograft model to study metastatic disease in the bone and to develop novel therapies for inhibiting prostate cancer growth in the bone-niche.