CStone and IMPACT Therapeutics' clinical collaboration progresses to IND filing acceptance for CS1001+IMP4297 combination therapy

SUZHOU,China,Feb. 8,2019 -- CStone Pharmaceutical ("CStone") and IMPACT Therapeutics,Inc. ("IMPACT") today jointly announced that an Investigational New Drug (IND) filing has been accepted by the National Medical Products Administration (NMPA) for the combination of CStone's fully-human anti-PD-L1 monoclonal antibody (mAb) CS1001 with IMPACT's PARP inhibitor IMP4297 for multiple tumor types. CStone and IMPACT entered into a worldwide clinical collaboration for the two products in 2018,and the acceptance of the IND filing marks a major milestone in the global clinical collaboration.

Upon IND approval,CStone and IMPACT plan to initiate a joint clinical study that will assess the safety,tolerability,pharmacokinetics,and anti-tumor efficacy of the anti-PD-L1 antibody CS1001 paired with PARP inhibitor IMP4297 as a combination therapy for patients with advanced solid tumors.

Both preclinical and clinical data suggest that the combination of a PD-L1 antibody with PARP inhibition has the potential to produce a synergistic anti-tumor effect. The pairing of CS1001 and IMP4297 is expected to prolong the survival of advanced cancer sufferers and potentially expand the scope of indications of each drug,leading to significant benefits to cancer patients as a result.

CStone's Chairman and CEO Dr. Frank Jiang commented: "Combination therapy is CStone's core R&D strategy. CS1001 is one of our backbone IO pipeline candidates,while IMP4297 has the potential to be the best-in-class. We are thrilled that IMPACT chose us as a strategic partner in 2018 and happy to see our collaboration moving forward. We look forward to achieving positive results in clinical studies and benefiting more Chinese patients."

IMPACT's CEO Dr. Bao Jun said: "We are delighted to be collaborating with one of China's leading biopharmaceutical companies. The successful filing of the IND for the combination of IMP4297 and CS1001 to begin Phase I studies demonstrates the close cooperation between both companies. We look forward to bringing improved treatment options for cancer patients through this partnership."

About CStone

CStone Pharmaceuticals is a biopharma company focused on developing and commercializing innovative immuno-oncology and molecularly targeted drugs to address significant unmet medical needs for cancer patients in China and worldwide. Since the company's inception three years ago,CStone has assembled a world-class management team that has a full spectrum of complementary skillsets from preclinical research to clinical development and commercialization. Through a dual source of innovation,comprised of internal research and external partnership,the company has built a rich oncology pipeline of 14 drug candidates with significant mono- and combination-therapy potential and synergies,including 4 assets exclusively in-licensed from Agios and Blueprint Medicines. Among CStone's portfolio,4 late-stage drug candidates are at or near registrational trials. CStone's business model has a clear focus on clinical development,while at the same time,the company is rapidly developing its commercial and manufacturing capabilities. The company is backed by prestigious VC and PE funds with record-breaking amounts of equity investment,raising a combined total ofUSD 412 million in two financing rounds to date. With an experienced team,a rich pipeline,a robust clinical development-driven business model,and substantial funding,CStone's vision is to become globally recognized as a leading biopharma company by bringing innovative and differentiated oncology therapies to cancer patients in China and worldwide.

For more information about CStone Pharmaceuticals,please visit: www.cstonepharma.com.

About IMPACT Therapeutics

IMPACT Therapeutics,Inc. is dedicated to the discovery,development and commercialization of novel and "best-in-class" therapeutics to treat cancer and other life-threatening diseases. Founded by a highly experienced team with a strong background in pharmaceutical R&D at multinational companies,IMPACT has applied its unique DNA damage response (DDR) small-molecule drug discovery and development platform to establish a pipeline of anti-tumor drugs in preclinical and clinical stages,including PARP,Hedgehog pathway,DDR,and microtubule inhibitors. The firm's PARP inhibitor IMP4297 is the subject of ongoing clinical trials in China and Australia. IMPACT's technical research capabilities have been recognized with national and regional awards in China,while the firm has received strong venture capital backing from prestigious investors that will underpin its ongoing work towards breakthrough innovations.

About CS1001

CS1001,developed by CStone Pharmaceuticals,is an investigational mAb directed against PD-L1 . Authorized by the U.S.-based Ligand Corporation,CS1001 is generated by the OMT transgenic animal platform,which can produce fully human antibodies in one step. As a fully human,full-length anti-PD-L1 monoclonal antibody,CS1001 mirrors natural G-type immune globulin 4 (IgG4) human antibodies,potentially reducing the risk of immunogenicity and potential toxicities in patients,a unique advantage over similar drugs.

Currently,CS1001 has completed a Phase I dose-escalation study in China,which showed the drug to be well-tolerated and produced sustained clinical benefit during the Phase Ia stage of development. In addition,two pivotal Phase II studies have been initiated in China: for natural killer cell/T-cell lymphoma (CS1001-201) and classical Hodgkin's lymphoma (CS1001-202). Meanwhile,Phase III studies are under way or being prepared both in China and globally for various solid tumor indications.

About IMP4297

Developed by IMPACT Therapeutics with independent intellectual property rights,IMP4297 is a high potency PARP inhibitor that has already been selected for support as a Major National Science and Technology Project in China. In comparison with similar drugs,IMP4297 has demonstrated not only greater potency in CTX (cell-line derived xenograph) and PDX (patient-derived xenograph) mouse models,but also improved efficacy and a longer therapeutic window. Early data from Phase I clinical studies indicate IMP4297 has a good rate of oral absorption. Low doses of IMP4297 produced clear signs of efficacy in BRCA-mutated tumor patients,while the blood toxicity associated with PARP inhibition was only evident at very high doses. Pre-clinical and clinical data show that IMP4297 may offer improved efficacy and/or lower toxicity than drugs of the same class,and has the potential to be a best-in-class PARP inhibitor. IMPACT is developing IMP4297 for the treatment of BRCA-mutated or DNA repair-deficient cancer,including breast cancer,ovarian cancer and prostate cancer.

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