Investigation of the potential utility of a linomide analogue for treatment of choroidal neovascularization

Silibinin inhibits VEGF secretion and age-related macular degeneration in a hypoxia-dependent manner through the PI-3 kinase/Akt/mTOR pathway

BACKGROUND AND PURPOSE

Hypoxia-mediated neovascularization plays an important role in age-related macular degeneration (AMD). There are few animal models or effective treatments for AMD. Here, we investigated the effects of the flavonoid silibinin on hypoxia-induced angiogenesis in a rat AMD model.

EXPERIMENTAL APPROACH

Retinal pigmented epithelial (RPE) cells were subjected to hypoxia in vitro and the effects of silibinin on activation of key hypoxia-induced pathways were examined by elucidating the hypoxia-inducible factor-1 alpha (HIF-1α) protein level by Western blot. A rat model of AMD was developed by intravitreal injection of VEGF in Brown Norway rats, with or without concomitant exposure of animals to hypoxia. Animals were treated with oral silibinin starting at day 7 post-VEGF injection and AMD changes were followed by fluorescein angiography on days 14 and 28 post-injection.

KEY RESULTS

Silibinin pretreatment of RPE cells increased proline hydroxylase-2 expression, inhibited HIF-1α subunit accumulation, and inhibited VEGF secretion. Silibinin-induced HIF-1α and VEGF down-regulation required suppression of hypoxia-induced phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway. In the rat model of AMD, silibinin administration prevented VEGF- and VEGF plus hypoxia-induced retinal oedema and neovascularization.

CONCLUSION AND IMPLICATIONS

The effects of silibinin, both in vitro and in vivo, support its potential as a therapeutic for the prevention of neovascular AMD.

N-Phenyl-4-hydroxy-2-quinolone-3-carboxamides as selective inhibitors of mutant H1047R phosphoinositide-3-kinase (PI3Kα)

This work describes our efforts to optimize the lead PI3Kα inhibitor N-benzyl 4-hydroxy-2-quinolone-3-carboxamide using structure-based design and molecular docking. We identified a series of N-phenyl 4-hydroxy-2-quinolone-3-carboxamides as selective inhibitors of mutant H1047R versus wild-type PI3Kα and we also showed that the cell growth inhibition by these compounds likely occurs by inhibiting the formation of pAKT and induction of apoptosis.

Morpholino-mediated increase in soluble Flt-1 expression results in decreased ocular and tumor neovascularization

Background

Angiogenesis is a key process in several ocular disorders and cancers. Soluble Flt-1 is an alternatively spliced form of the Flt-1 gene that retains the ligand-binding domain, but lacks the membrane-spanning and intracellular kinase domains of the full-length membrane bound Flt-1 (mbFlt-1) protein. Thus, sFlt-1 is an endogenous inhibitor of VEGF-A mediated angiogenesis. Synthetic mopholino oligomers directed against splice site targets can modulate splice variant expression. We hypothesize that morpholino-induced upregulation of sFlt-1 will suppress angiogenesis in clinically relevant models of macular degeneration and breast cancer.

Methods and Findings

In vivo morpholino constructs were designed to target murine exon/intron 13 junction of the Flt-1 transcript denoted VEGFR1_MOe13; standard nonspecific morpholino was used as control. After nucleofection of endothelial and breast adenocarcinoma cell lines, total RNA was extracted and real-time RT-PCR performed for sFlt-1 and mbFlt-1. Intravitreal injections of VEGFR1_MOe13 or control were done in a model of laser-induced choroidal neovascularization and intratumoral injections were performed in MBA-MD-231 xenografts in nude mice. VEGFR1_MOe13 elevated sFlt-1 mRNA expression and suppressed mbFlt-1 mRNA expression in vitro in multiple cellular backgrounds (p<0.001). VEGFR1_MOe13 also elevated sFlt/mbFlt-1 ratio in vivo after laser choroidal injury 5.5 fold (p<0.001) and suppressed laser-induced CNV by 50% (p = 0.0179). This latter effect was reversed by RNAi of sFlt-1, confirming specificity of morpholino activity through up-regulation of sFlt-1. In the xenograft model, VEGFR1_MOe13 regressed tumor volume by 88.9%, increased sFlt-1 mRNA expression, and reduced vascular density by 50% relative to control morpholino treatment (p<0.05).

Conclusions

Morpholino oligomers targeting the VEGFR1 mRNA exon/intron 13 junction promote production of soluble FLT-1 over membrane bound FLT-1, resulting in suppression of lesional volume in laser induced CNV and breast adenocarcinoma. Thus, morpholino manipulation of alternative splicing offers translational potential for therapy of angiogenic disorders.