Inhibition of the fibroblast growth factor receptor (FGFR) pathway: the current landscape and barriers to clinical application.

The fibroblast growth factor/fibroblast growth factor receptor (FGF/FGFR) is a tyrosine kinase signaling pathway that has a fundamental role in many biologic processes including embryonic development, tissue regeneration, and angiogenesis. Increasing evidence indicates that this pathway plays a critical role in oncogenesis via gene amplification, activating mutations, or translocation in tumors of various histologies. With multiplex sequencing technology, the detection of FGFR aberrations has become more common and is tied to cancer cell proliferation, resistance to anticancer therapies, and neoangiogenesis. Inhibition of FGFR signaling appears promising in preclinical studies, suggesting a pathway of clinical interest in the development of targeted therapy. Phase I trials have demonstrated a manageable toxicity profile. Currently, there are multiple FGFR inhibitors under study with many non-selective (multi-kinase) inhibitors demonstrating limited clinical responses. As we progress from the first generation of non-selective drugs to the second generation of selective FGFR inhibitors, it is clear that FGFR aberrations do not behave uniformly across cancer types; thus, a deeper understanding of biomarker strategies is undoubtedly warranted. This review aims to consolidate data from recent clinical trials with a focus on selective FGFR inhibitors. As Phase II clinical trials emerge, concentration on patient selection as it pertains to predicting response to therapy, feasible methods for overcoming toxicity, and the likelihood of combination therapies should be utilized. We will also discuss qualities that may be desirable in future generations of FGFR inhibitors, with the hope that overcoming these current barriers will expedite the availability of this novel class of medications.

Preservation of cone photoreceptors after a rapid yet transient degeneration and remodeling in cone-only Nrl-/- mouse retina.

Cone photoreceptors are the primary initiator of visual transduction in the human retina. Dysfunction or death of rod photoreceptors precedes cone loss in many retinal and macular degenerative diseases, suggesting a rod-dependent trophic support for cone survival. Rod differentiation and homeostasis are dependent on the basic motif leucine zipper transcription factor neural retina leucine zipper (NRL). The loss of Nrl (Nrl(-/-)) in mice results in a retina with predominantly S-opsin-containing cones that exhibit molecular and functional characteristics of wild-type cones. Here, we report that Nrl(-/-) retina undergoes a rapid but transient period of degeneration in early adulthood, with cone apoptosis, retinal detachment, alterations in retinal vessel structure, and activation and translocation of retinal microglia. However, cone degeneration stabilizes by 4 months of age, resulting in a thinner but intact outer nuclear layer with residual cones expressing S- and M-opsins and a preserved photopic electroretinogram. At this stage, microglia translocate back to the inner retina and reacquire a quiescent morphology. Gene profiling analysis during the period of transient degeneration reveals misregulation of genes related to stress response and inflammation, implying their involvement in cone death. The Nrl(-/-) mouse illustrates the long-term viability of cones in the absence of rods and retinal pigment epithelium defects in a rodless retina. We propose that Nrl(-/-) retina may serve as a model for elucidating mechanisms of cone homeostasis and degeneration that would be relevant to understanding diseases of the cone-dominant human macula.

Angiotensin-converting enzyme 2: enhancing the degradation of angiotensin II as a potential therapy for diabetic nephropathy.

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that degrades angiotensin II with high efficiency leading to the formation of angiotensin-(1-7). ACE2 within the kidneys is largely localized in tubular epithelial cells and in glomerular epithelial cells. Decreased glomerular expression of this enzyme coupled with increased expression of ACE has been described in diabetic kidney disease, both in mice and humans with type 2 diabetes. Moreover, both ACE2 genetic ablation and pharmacological ACE2 inhibition have been shown to increase albuminuria and promote glomerular injury. Studies using recombinant ACE2 have shown the ability of ACE2 to rapidly metabolize Ang II in vivo and form the basis for future studies to examine the potential of ACE2 amplification in the therapy of diabetic kidney disease and cardiovascular disease.