K_i = 1.8 nM

IC₅₀ = 1 nM (Cell)

Average Selectivity

BACE1 > 50-fold

BACE1 > 50-fold

GRL-8234

      In proof-of-concept experiments using GRL-8234, we demonstrated that the test inhibitor entered rat brain (i.p. injection) and reduced the interstitial fluid Aβ40  by about 65% over 12 h. Young Tg2576 mice (5.5 month old) were implanted with osmotic pumps to deliver either a GRL-8234 solution (33.4 μg/g/day) or a control solvent over the experiment time of 220 days. Plasma Aβ40 and Aβ42 of the treated group were about 65% lower than the control group. Cognitive tests with a Morris Water Maze at 1.5 and 4.6 months of treatment showed no difference between the two groups. However, at 6.7 months, the cognitive performance of the treated group was clearly superior to the control groups in time latency, annulus crossing index, and time in quadrant. Furthermore, we observed a decrease of plaques and amyloid load with only slightly changed Aβ oligomer patterns in the brains of treated mice as compared to the controls. These results represent the first direct experimental evidence that the treatment of Tg2576 mice with a b-secretase inhibitor GRL-8234, rescued age-related cognitive decline.

X-Ray structure of GRL-8234-bound b-Secretase

Ghosh, Tang  et al.  Bioorg. Med. Chem. Lett. 2008, 18, 1031; Curr. Alz. Res.  2008, 5, 121-131; Neurotherapeutics, 2008, 5, 399-408.

Our Structure-based Design of Potent and Selective

b-Secretase (Memapsin 2) Inhibitors

          Memapsin 2 (b-secretase) is one of two proteases that cleave the b-amyloid precursor protein (APP) to produce the 40-42 residue amyloid-b peptide (Ab) in the human brain, a key event in the progression of Alzheimer’s disease. In a collaborative effort with Jordan Tang, at the Oklahoma Medical Research Foundation, we have designed and synthesized two potent transition-state inhibitors with K_i values of 6.8 nM and 1.6 nM respectively. This work represents the first case of designed potent inhibitors for this important pharmaceutical target related to Alzheimer’s disease. Subsequently, the crystal structure of the protease domain of human memapsin 2 complexed with an inhibitor was determined by at 1.9 Å resolution.    This   crystal   structure   provided critical information  regarding the specific ligand-binding site interactions in the active site of b-secretase (memapsin 2).

       Based upon this X-ray crystal structure bound to memapsin,  we have reduced the molecular weight and designed potent and selective memapsin inhibitors. Furthermore, we have designed and synthesized a series of novel macrocyclic amide-urethanes based upon the X-ray crystal structure of our lead inhibitor bound to memapsin 2.  Ring size and substituent effects have been investigated.  Cycloamide-urethanes containing a 16-membered ring exhibited low nanomolar inhibitory potencies against memapsin 2.

^{Ghosh, Tang et al. J. Med. Chem. 2001, 44, 2865-68; Biochemistry 2001, 40, 10001-06; Curr. Med. Chem. 2002, 9, 1135-44; J.  Mol.  Neuroscience  2003,  20,  299-304; Curr. Med. Chem. 2005, 16, 1609-22; Bioorg. Med. Chem. Lett.  2005, 15, 15-20.}

        From the therapeutic point of view, the selectivity of memapsin 2 inhibitors over other human aspartic proteases is expected to   be  important,  especially  memapsin 1 (BACE2) and cathepsin D. Memapsin 1, which has specificity similarities with   memapsin 2, has independent physiological functions. Cathepsin D, which is abundant in all cells, plays an important role in cellular protein catabolism.  Its inhibition would likely consume inhibitor drugs as well as lead to probable toxicity.  Our structure-based design   led to the development of very potent and highly selective memapsin 2 inhibitors.  Furthermore, our X-ray structural analysis of protein-inhibitor complexes has uncovered potentially important molecular interactions useful in the design of selectivity over other aspartyl proteases. Additional studies to further elucidate the role of these and other interactions important for selectivity are in progress.

X-ray Crystal Structure of Pyrazole-bound b-Secretase

Other key references:

  Ghosh, A. K., Brindisi, M., Tang, J.    2011. ASAP.

  Tang, J., Hong, L., Ghosh, A. K. in Aspartic Acid Proteases as Therapeutic Targets, Edited by Ghosh, A. K. Willey-VCH, 2010, 413-438.

 Ghosh, Tang  et al.  Bioorg. Med. Chem. Lett. 2008, 18, 1031.

 Ghosh, A. K., Tang, J. et. al. Curr. Alzheimer Res. 2008,  4,  418-422

 Ghosh, A. K., Tang, J. et. al. J. Med. Chem.  2007, 50, 2399-2407.

 Ghosh, A. K., Tang, J. et. al. J. Am. Chem. Soc. 2006, 128, 5310-11.

 Ghosh, A. K., Nagaswamy, K., Tang, J.  Curr. Med. Chem. 2005, 16, 1609-22.

 Ghosh, A. K., Tang, J. et. al.   Bioorg. Med. Chem. Lett.  2005, 15, 15-20.