Activation of liver myofibroblasts (LMF) of different origins is responsible for the development of liver fibrosis in chronic liver diseases of all causes and remarkably, LMF clearance by apoptosis may prevent development of liver fibrosis and liver injury, and possibly allow recovery from reversal of liver fibrosis. Inhibiting o reversing myofibroblast activation (the therapeutic cellular target) is critical for the treatment of liver fibrosis. Both preventing progression of liver fibrosis as well as possibly, regression of liver fibrosis despite continued liver injury, as we documented in our pre-clinical studies, are considered important clinical targets for patients with advanced liver fibrosis and cirrhosis. Finally, blocking the progression of liver fibrosis would decrease development of primary liver cancer since most hepatocellular carcinomas arise in cirrhotic livers. The basis for our Research and Development is the development of a novel ‘humanized’ therapeutic peptide (XFB-19). We created a library using analog synthesis to improve potential pitfalls for human therapy. We have performed in a step-wise manner assays to select the safest and most efficient ‘humanized’ peptide (including medicinal chemistry, stability assays in human plasma and human liver microsomes, apoptosis assays in activated primary human liver myofibroblasts, cell-free caspase 8 activation assays, liver injury/fibrogenesis models, pharmacokinetics, bioassay, CYP-450 inhibition studies, immunogenicity assays in human T-cells and in mice, cardiotoxicity assays in human stem cell-derived cardiomyocytes, and toxicology assays in HCV-infected primary human hepatocytes and in normal and cirrhotic mice). In an animal model of decompensated cirrhosis, the XFB-19 peptide rescues hepatocyte cell death and liver failure, and remarkably prevents by 45 % animal mortality from week-16 to week-32. We have developed a novel (first-in-class inhibitor of a site-specific phosphorylation) and highly effective anti- fibrotic peptide in animal models, with no evidences of immunogenicity, and with exceptional stability in human microsomal systems and human plasma. XFB-19 has excellent solubility in water. These features should facilitate administration by subcutaneous injection with excellent bioavailability during clinical trials judging by the steady-state release in plasma of XFB-19 from the PEG-XFB-19. The PEG-XFB-19 was not toxic to mice at 100-fold the therapeutic dose. There was no evidence of cardiotoxicity or inhibition of CYP-450 isoenzymes. The aims that are proposed for this SBIR are to complete IND-enabling, FDA-mandated studies. There is no FDA-approved medication for the treatment of liver fibrosis, and none of the drugs currently in Clinical Studies target directly activated myofibroblasts.