RANKL inhibition: clinical implications for the management of patients with multiple myeloma and solid tumors with bone metastases

BACKGROUND

Receptor activator of NF-kappaB ligand (RANKL) binds to RANK on the surface of osteoclast precursors and enhances their differentiation, survival and fusion, activates mature osteoclasts and inhibits their apoptosis. Osteoprotegerin (OPG) is the decoy receptor of RANKL. Disruption of the RANK/RANKL/OPG axis is implicated in bone metastases.

OBJECTIVE/METHODS

A review of the role of RANKL signaling in bone development and the rationale for targeting RANKL in treatment of bone metastases and myeloma bone disease.

RESULTS/CONCLUSIONS

In preclinical models of solid tumors and myeloma, RANKL inhibition reduced osteoclast numbers and subsequent bone resorption, prevented development of osteolytic lesions and decreased tumor burden. Preliminary clinical studies with denosumab, an anti-RANKL fully human monoclonal antibody, in patients with solid tumors with bone metastases and myeloma showed that targeting RANKL reduces osteoclastogenesis, bone resorption markers and skeletal-related events, supporting further study of this molecule and others with anti-RANKL activity.

Castration-resistant prostate cancer: locking up the molecular escape routes

The understanding of the key role that androgens play on the normal and pathological physiology of the prostate guided the development of different therapies for the treatment of locally advanced or metastatic prostate cancer (PCa). These so-called androgen deprivation therapies include surgical or chemical castration, achieved by the administration of gonadotropin-releasing hormone analogs; inhibition of steroidogenic enzymes; and finally, blocking of the binding of androgens to their receptor (AR) by the use of antiandrogens. Despite an excellent initial response, in approximately 2 to 3 years, most of these patients will succumb to the castration resistant form of the disease. Remarkably, even in the presence of castration levels of circulating androgens, these tumors are still dependent on a functional AR, and several molecular mechanisms have been proposed to explain this phenomenon. These include: (1) gene amplification and increased expression of the AR mRNA and protein, (2) selection of mutations in the AR that confer broader ligand specificity, (3) changes in the ratios or expression between the AR and its coregulators, (4) increased expression of steroidogenic enzymes, and (5) up-regulation of cross-talk signal transduction pathways that can activate the AR in a ligand-independent manner. We will summarize how these molecular hypotheses are being tested in the clinic by the latest therapeutic modalities.