- Reata is developing a novel class of C-terminal Hsp90 inhibitors. Inhibition of Hsp90 may result in activation of Hsp70, a molecular chaperone that plays a critical role in the process through which a protein assumes its functional shape and that serves as a central gatekeeper for mitochondrial protein import. Mitochondria rely on Hsp70-dependent protein import mechanisms for almost all of their activity, including the production of ATP1. There are also indications that Hsp70 activation may play a profound role in neuroprotection since nerve cells are high consumers of ATP and rely on Hsp70-dependent protein import for proper mitochondrial function2.
- Our lead compound in this class, RTA 901, has shown favorable activity in a range of preclinical models of neurodegeneration and neuroprotection, including diabetic neuropathy and neural inflammation, as well as positive effects on mitochondrial bioenergetics.
- RTA 901 is currently being studied in a Phase 1 trial in healthy volunteers.
Heat shock proteins (Hsps), organized into several families based on molecular weight (Hsp90, Hsp70, Hsp60, etc.) and function, play important roles in multiple aspects of the cellular stress response. The expression of Hsps can be induced by a variety of stimuli, including thermal, oxidative, mechanical, chemical, and pathophysiological stresses. One important function of Hsps, under both normal and stressful conditions, is to act as molecular chaperones, promoting proper folding of client proteins that would otherwise misfold and lose function3. Hsps also appear to play significant roles in antigen processing and inflammatory signaling4, and Hsp70 has been shown to have a critical function in promoting mitochondrial importation of proteins that are essential for efficient energy production1. Inducing the expression of Hsp70 is recognized as a promising strategy for treating neurodegenerative diseases, chronic inflammatory diseases, and other pathologies, and the development of selective Hsp modulators has been an area of significant interest. Reata has licensed multiple classes of novel Hsp modulators that overcome mechanistic limitations of previous compounds in this category. The lead compound, RTA 901, has shown profound activity in animal models of the insensate form of diabetic neuropathy, a condition that affects millions of Americans and has no effective therapy.
Neuroprotective and Neuroregeneration Potential
Reata’s Hsp90 inhibitors, including RTA 901, are highly potent and selective C-terminal inhibitors of Hsp90. Inhibition of Hsp90 may result in activation of Hsp70, a molecular chaperone that plays a critical role in the process through which a protein assumes its functional shape and that serves as a central gatekeeper for mitochondrial protein import. Mitochondria rely on Hsp70-dependent protein import mechanisms for almost all of their activity, including the production of ATP1. Recent insights have indicated a potentially profound role of Hsp70 activation in neuroprotection and neuronal regeneration, since nerve cells are particularly high consumers of ATP and rely heavily on Hsp70-dependent protein import for proper mitochondrial function2. The role of Hsp70 in quality control of protein expression is also significant in the context of many neurodegenerative diseases, which involve toxic aggregation of misfolded proteins.
Reata’s lead molecules from this program have demonstrated nonclinical activity in a range of models of neurodegeneration and neuroprotection, including diabetic neuropathy and neural inflammation. These agents have shown significant rescue of nerve function, restoration of thermal and mechanical sensitivity, improvement in nerve conductance velocity, and increases in mitochondrial function of relevant neuronal tissues in rodent disease models5. The effects with RTA 901 are achieved with once-daily oral dosing in these preclinical models6. RTA 901 also has demonstrated acceptable tolerability in early GLP toxicology studies. Reata’s Hsp90 inhibitors also have shown significant neuroprotective activity in models of Alzheimer’s disease7 and demyelinating motor nerve diseases8.
Clinical Development Program
Reata initiated a Phase 1 clinical trial in January 2017 to evaluate the safety, tolerability, and pharmacokinetic profile of RTA 901 in healthy adult volunteers. The trial is designed in two parts, part one with single ascending doses and part two with multiple ascending doses. Part one is enrolling up to 56 healthy subjects randomized in a 3:1 ratio to receive a single dose of RTA 901 or placebo, respectively. Part two will enroll approximately 30 healthy subjects to be randomized in a 4:1 ratio to receive RTA 901 or placebo, respectively. Reata plans to complete the trial and report data in the second half of 2017. If the Phase 1 clinical trial of RTA 901 supports further development, the company plans to follow it with a Phase 2 clinical trial of RTA 901 for the treatment of an orphan neurological indication or diabetic neuropathy.
- Fan et al. Function of cytosolic chaperones in Tom70-mediated mitochondrial import. Protein Pept Lett; 18(2) 122-31.
- Brown. Heat shock proteins and protection of the nervous system. Ann N Y Acad Sci. 2007; 1113:147-58.
- Santoro et al. Heat shock factors and control of the stress response. Biochem Pharmacol. 2000; 59(1):55-63.
- Turturici et al. Hsp70 and its molecular role in nervous system diseases. Biochem Res Int. 2011; 2011: 618127.
- Ma et al. Heat shock protein 70 is necessary to improve mitochondrial bioenergetics and reverse diabetic sensory neuropathy following KU-32 therapy. J Pharmacol Exp Ther. 2014; 348(2):281-92.
- Reata Pharmaceuticals, Inc., internal data.
- Menchen et al. Neuronal protection by a novel C-terminal Hsp90 modulator. KU ScholarWorks Dissertation. 2012.
- Li et al. Induction of heat shock protein 70 (Hsp70) prevents neuregulin-induced demyelination by enhancing the proteasomal clearance of c-Jun. ASN Neuro. 2012; 4(7): e00102.