The HGR motif is the antiangiogenic determinant of vasoinhibin: implications for a therapeutic orally active oligopeptide

Abstract

The hormone prolactin acquires antiangiogenic and antivasopermeability properties after undergoing proteolytic cleavage to vasoinhibin, an endogenous prolactin fragment of 123 or more amino acids that inhibits the action of multiple proangiogenic factors. Preclinical and clinical evidence supports the therapeutic potential of vasoinhibin against angiogenesis-related diseases including diabetic retinopathy, peripartum cardiomyopathy, rheumatoid arthritis, and cancer. However, the use of vasoinhibin in the clinic has been limited by difficulties in its production. Here, we removed this barrier to using vasoinhibin as a therapeutic agent by showing that a short linear motif of just three residues (His46-Gly47-Arg48) (HGR) is the functional determinant of vasoinhibin. The HGR motif is conserved throughout evolution, its mutation led to vasoinhibin loss of function, and oligopeptides containing this sequence inhibited angiogenesis and vasopermeability with the same potency as whole vasoinhibin. Furthermore, the oral administration of an optimized cyclic retro-inverse vasoinhibin heptapeptide containing HGR inhibited melanoma tumor growth and vascularization in mice and exhibited equal or higher antiangiogenic potency than other antiangiogenic molecules currently used as anti-cancer drugs in the clinic. Finally, by unveiling the mechanism that obscures the HGR motif in prolactin, we anticipate the development of vasoinhibin-specific antibodies to solve the on-going challenge of measuring endogenous vasoinhibin levels for diagnostic and interventional purposes, the design of vasoinhibin antagonists for managing insufficient angiogenesis, and the identification of putative therapeutic proteins containing HGR.

Dual Roles of Prolactin and Vasoinhibin in Inflammatory Arthritis

“…Because opposing actions reside within the PRL molecule, proteolytic cleavage represents an efficient mechanism for balancing functions. Recent work showed that a short linear motif of just three residues (His46-Gly47-Arg48) is the functional antiangiogenic determinant of vasoinhibin and that such motif is concealed in PRL by salt-bridges between Arg48 and Glu161 and 162 located in PRL fourth alfa-helix, a part of PRL removed during vasoinhibin generation ( 37 ).…”

“…Translation of vasoinhibin into the clinic has been hampered by difficulties in its recombinant production ( 58 ). However, the barrier of using vasoinhibin as therapeutic agent was recently removed by showing that seven amino acid peptides containing the anti-angiogenic motif (HGR) of vasoinhibin inhibit angiogenesis and vasopermeability with the same potency as the whole protein ( 37 ). Oligopeptide optimization to target vascular and not non-vascular actions in arthritis represents a promising therapeutic approach and an important tool for guiding future research.…”

Human Placental Tissue Contains A Placental Lactogen–Derived Vasoinhibin

“…The 9-kDa immunoreactive protein is also present in placental extracts and corresponds to vasoinhibin, as it contains the N-terminal region of PL defining vasoinhibin (see Fig. 1A and 1B ) [ 7 , 9 ]. In addition, the anti–N-terminal PL antibody reacted with a 28-kDa protein in placental tissue lysates (see Fig.…”

“…This short communication unveils a novel, 9-kDa, PL-derived vasoinhibin isoform in placental tissue. This vasoinhibin isoform contains the QK motif, which has recently been identified as the antiangiogenic motif of vasoinhibin derived from PL [ 9 ]. The placental vasoinhibin may fulfil physiological functions in the control of blood vessel growth and function in the placenta but may also contribute to placental pathology in PE.…”

“…Vasoinhibin is generated by the proteolytic cleavage of prolactin (PRL), but also, owing to the phylogenetic relationship between these hormones, by cleavage of placental lactogen (PL) and growth hormone [ 6-8 ]. The bioactive site of vasoinhibin resides in the loop connecting α helices 1 and 2 and is defined by a short HGR-motif at positions 74 to 76 in PRL, and residues QK at positions 66 to 67 in PL [ 9 ]. Based on the fundamental importance of factors regulating angiogenesis in the normal placenta in the etiopathology of PE, the present study aimed to investigate the presence of PL-derived vasoinhibin in the placenta.…”