Cleave Biosciences Initiates Phase 1 Clinical Trial of CB5083 in Patients with Advanced Solid Tumors Burlingame, Calif. – January 8, 2015 – Cleave Biosciences today announced that it has begun a Phase 1 clinical trial to evaluate its lead drug candidate, CB5083, in patients with advanced solid tumors. CB 5083 is a firstinclass, oral inhibitor of p97, a critical enzyme that controls various aspects of protein homeostasis. P97 inhibition is a novel approach that has the potential to treat a wide range of cancers, including both solid tumors and hematologic malignancies. CB5083 is also being studied in a Phase 1 trial in patients with relapsed and refractory multiple myeloma. In the dose escalation part of the Phase 1 openlabel trial, the safety, pharmacokinetics and pharmacodynamics of CB5083 will be evaluated in patients with advanced solid tumors who have progressed, are nonresponsive to available therapies or for whom no standard therapy exists. In the dose expansion part of the study, antitumor activity will be assessed in two parallel arms, one focusing on patients with advanced pancreatic neuroendocrine tumors (pNETs) and a second focusing on patients with tumors carrying KRAS mutations. Preclinical and clinical data suggest that a subset of K RAS mutated tumors and pNETs are particularly sensitive to inhibitors of protein homeostasis pathways including CB5083. Cleave expects to enroll up to 75 patients in the whole study at multiple U.S. cancer centers. More information about the trial, including enrolling centers, is available by visiting www.clinicaltrials.gov (identifier NCT02243917) or www.cleavebio.com. “Targeting protein homeostasis has been validated by the clinical and commercial success of VELCADE® (bortezomib) and KYPROLIS® (carfilzomib) in multiple myeloma; however these agents are generally not effective in solid tumors owing to both chemistry and pharmacology limitations. Cleave has demonstrated impressive activity with CB5083 in a wide range of solid tumor xenograft models where the ‘omibs have little to no activity. This Phase 1 study will enable us to hone in on the solid tumors that are dependent on the p97 pathway for growth and survival and therefore will be more likely to respond to CB5083 treatment,” said Laura Shawver, Ph.D., Chief Executive Officer of Cleave Biosciences. CB5083 is derived from a compound initially synthesized by the Specialized Chemistry Center at the University of Kansas, which is part of the National Institutes of Health’s Molecular Libraries Program. Cleave’s discovery partners also include TsuiFen Chou, Ph.D. from the laboratory of Raymond J. Deshaies, Ph.D., who is Professor of Biology, California Institute of Technology, a Howard Hughes Medical Institute Investigator and a Scientific Founder of Cleave Biosciences; and The Scripps Research Institute, also a member of the Molecular Libraries Program. About Cleave Biosciences Biopharmaceutical company Cleave Biosciences is a pioneer in the discovery and development of drugs that target protein homeostasis systems and have the potential to transform the treatment of people