Bone Marrow Microenvironment as a Regulator and Therapeutic Target for Prostate Cancer Bone Metastasis

Bone is the most common site of prostate cancer metastasis. Once prostate cancer cells metastasize to bone, the mortality rate of prostate cancer patients increases significantly. Furthermore, bone metastases produce multiple skeletal complications, including bone pain that impairs the patients' quality of life. Effective therapies for bone metastatic disease are underdeveloped with most current therapies being primarily palliative with modest survival benefit. Although the exact mechanisms through which prostate cancer metastasizes to bone are unclear, growing evidence suggests that the bone marrow microenvironment, particularly its hematopoietic activity, is a significant mediator of prostate cancer bone tropism. Moreover, the bone microenvironment may regulate metastatic prostate cancer cells between dormant and proliferative states. In this review, we discuss (1) how prostate cancer cells interact with the bone microenvironment to establish bone metastases and (2) current and future potential treatments for prostate cancer patients with bone metastases.

Optimal usage of radium-223 in metastatic castration-resistant prostate cancer

Radium-223 is a first-in-class α-emitting radiopharmaceutical that targets bone metastases associated with metastatic castration-resistant prostate cancer (mCRPC). In the pivotal phase III trial ALSYMPCA, radium-223 significantly increased overall survival (OS), compared with placebo (median 14.9 vs 11.3 months; hazard ratio 0.70; 95% CI 0.58-0.83; p < 0.001), in patients with mCRPC and symptomatic bone metastases-with a comparable safety profile. To optimize treatment outcomes, selection of appropriate patients is important. As well as osteoblastic bone metastases, mCRPC patients should be well enough to receive six doses of radium-223 as this treatment duration has been shown to greatly improve OS outcomes compared with administration of four or fewer doses. Additionally, alkaline phosphatase and lactate dehydrogenase are emerging as important biomarkers during radium-223 treatment. Optimal concomitant standard-of-care therapies (such as abiraterone or enzalutamide) to be administered with radium-223 have yet to be defined as does the most efficacious dose and duration of radium-223 treatment. In conclusion, radium-223 is an important addition to the mCRPC treatment landscape and marks a paradigm shift in the treatment of bone metastases.

Management of metastatic castration-resistant prostate cancer: A focus on radium-223: Opinions and suggestions from an expert multidisciplinary panel

Radium-223, a calcium mimetic bone-seeking radionuclide that selectively targets bone metastases with alpha particles, is approved for the treatment of men with metastatic castration-resistant prostate cancer (mCRPC) and symptomatic bone metastases. In patients with mCRPC, treatment with radium-223 has been associated with survival benefit, regardless of prior docetaxel use, and also has a positive impact on symptomatic skeletal events and quality of life. Radium-223 is best suited for patients with symptomatic mCRPC and bone-predominant disease and no visceral metastases, and may lead to better outcomes when given early in the course of the disease. An expert multidisciplinary panel convened in Milan, Italy to review the current best-evidence literature on radium-223 and to convey their personal expertise with the use of radium-223 and identify possible strategies for best practice. This article summarizes the best available evidence for the use of radium-223, discusses the essential role of the multidisciplinary team in delivering effective treatment for mCRPC, clarifies pre- and post-treatment evaluation and monitoring, and outlines future scenarios for radium-223 in the treatment of men with MCRPC.