Targeting RAF1 with C-Type Natriuretic Peptide to Promote Bone Union in NF1
Abstract
Children with NF1 can present with tibia bowing shortly after birth. There is currently no sensitive method to predict whether a child born from a parent with NF1 will develop tibia bowing and possibly progress to fracture. Not only do parents of a child with NF1 have the constant worry of this risk, they face the possibility of frequent, painful surgeries with amputation looming over their child s life as the final outcome. The other skeletal abnormalities associated with NF1, including scoliosis, low bone density, short stature, facial disfigurement, are also very real quality of life, as well as health, issues. A significant proportion of the NF1 population has one or more of these problems, and solutions are desperately needed. One area of emphasis of the Fiscal Year 2014 Neurofibromatosis Research Program is target identification and drug discovery for the treatment of NF. In this application, we propose to use C-type Natriuretic Peptide (CNP) to inhibit RAF1 activity and block the constitutive activation of the RAF1-MEK-ERK pathway induced by NF1 loss of function in bone forming cells, with the goal of promoting bone healing and union in children with NF1. Why CNP? First, MEK inhibitors have been trialed in the setting of NF1 mouse models of impaired bone healing, but so far results weakly support efficacy. First, one study reported that one of these inhibitors was effective in promoting bone healing, but we have since then gathered data indicating that the mouse model used in this study is not appropriate to model NF1 pseudarthrosis and the clinically relevant response of osteoprogenitors to this drug. Second, inhibition of RAF1, a kinase upstream of MEK, has never been trialed in the setting of NF1. Our data show that targeting this specific kinase with CNP can block pERK activation in both Nf1-/- chondrocytes and osteoblasts and ameliorate growth plate parameters in mice lacking Nf1 in osteochondroprogenitors. Third, because CNP is an endogenous peptide acting via a specific receptor and signaling pathway, its use as exogenous peptide in the setting of NF1-deficient bones might increase the benefit:risk ratio compared to MEK inhibitors that can target virtually any cell of the body and lead to significant side effects. Fourth, and perhaps most importantly, CNP is already Food and Drug Administration-approved for a current clinical trial for enhancement of growth in children with dwarfism (BMN111, Biomarin). The advanced development of this recombinant form of CNP compared to other experimental drugs thus could shorten time to a NF clinical trial, with the goal of augmenting bone healing in children with NF1 presenting with tibia fracture and pseudarthrosis. Our plan is to use our expertise in preclinical model development and RAS/ERK signaling in bone cells to understand what parameters CNP can correct in Nf1-deficient chondrocytes and osteoblasts, two cell lineages critical for the formation of the soft and calcified callus, respectively. This part of the study will be performed in vitro in order to be able to dissociate all of these functions and effect of Nf1-deficiency and treatment. In the second part of the study, we will use what we believe is one of the most relevant models of NF1 pseudarthrosis to assess the potential of CNP/BMN111 to promote bone healing. Mice are not humans, but the use of such preclinical models is necessary if we want to progress in our goal of discovering potent therapeutic options for children with hard to heal broken bones because the relatively low number of patients affected in the general population and the variability of their orthopaedic management make it difficult to use human data to understand this condition. Importantly, CNP will be compared to a MEK inhibitor with clinical potential (already approved for the treatment of skin cancer), and its efficacy will also be compared to a dual treatment with BMP2 because our preliminary data indicate that MEK i
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 04, 2016
- Source ID
- W81XWH1510714
Entities
People
- Florent Elefteriou
Organizations
- Baylor College of Medicine
- United States Army