Sosei Provides an Update on Its Immuno-Oncology Clinical Program with AstraZeneca

Sosei Group Corporation ("Sosei” or the "Company”) (TOKYO: 4565), the world leader in GPCR medicine design and development, announces that its immuno-oncology collaboration with AstraZeneca is progressing well. The first patient has been dosed in an expansion cohort in the Phase 1b segment of the Phase 1 study in advanced solid tumours. Furthermore, a new clinical study including AZD4635 to investigate novel combination therapies in EGFRm non-small cell lung cancer is expected to begin in the first quarter 2018.

AZD4635 is a potent and selective, orally available, small molecule adenosine A_2A receptor (A_2AR) antagonist discovered by Sosei subsidiary Heptares Therapeutics and licensed to AstraZeneca in 2015.

AZD4635 is currently in a Phase 1 clinical trial for patients with advanced solid malignancies, the primary objective of which is to determine maximum tolerated dose (MTD) of AZD4635 alone and in combination with AstraZeneca’s anti-PD-L1 antibody durvalumab. Phase 1b expansion cohorts in advanced solid tumours, are now open and the first patient has been dosed. The trial, sponsored by AstraZeneca, is expected to complete in the second half of 2019. For information on this study please refer to clinicaltrials.gov, trial # NCT02740985.

AstraZeneca, with its global biologics research and development affiliate, MedImmune, is also planning a new clinical study to assess safety, tolerability and anti-tumour activity of novel combination therapies in subjects with advanced epidermal growth factor receptor (EGFRm) mutated non-small cell lung cancer (NSCLC). This Phase 1b/2^* study will evaluate the combination of MEDI9447 (an anti-CD73 antibody developed by MedImmune) with AZD4635 or TAGRISSO® (osimertinib), an EGFR tyrosine kinase inhibitor for NSCLC developed by AstraZeneca. For information on this study please refer to clinicaltrials.gov, trial #NCT03381274.

"We are pleased with the progress made with AZD4635 in the Phase 1 clinical study under our partnered immuno-oncology program with AstraZeneca. We are also delighted that AstraZeneca and MedImmune are evaluating AZD4635 in a new clinical study in combination with the anti-CD73 antibody, MEDI9447 in EGFRm non-small cell lung cancer,” commented Dr. Tim Tasker, Sosei’s Chief Medical Officer. "Blocking adenosine-mediated immune suppression is an attractive new mechanism for treating a range of cancers and development of this novel candidate could result in a potential new treatment as a monotherapy or in combination to improve the efficacy of checkpoint inhibitors and other drug classes.”

^* Entry into initial new Phase 1b study does not trigger a milestone payment

Notes to Editors

About AZD4635

AZD4635 is a potent and selective, orally available, small molecule adenosine A_2A receptor (A_2AR) antagonist discovered by Sosei subsidiary Heptares Therapeutics and licensed to AstraZeneca in 2015. AZD4635 blocks A_2A receptor signalling and prevents an evolved survival mechanism of tumours from being effective at the level of the immune cell. By stimulating A_2A receptors, adenosine, a natural anti-inflammatory molecule, is released preventing T-cells within the immune system from being activated and reduces their ability to destroy cancer cells. A_2A receptor antagonism can therefore promote the anti-cancer response of T-cells within the tumour microenvironment, offering a novel mechanism of action as a mono- or combination therapy.

About Sosei

Sosei is an international biopharmaceutical company focused on the design and development of new medicines originating from its proprietary GPCR-targeted StaR® technology and structure-based drug design platform capabilities. The Company is advancing a broad and deep pipeline of partnered and wholly owned product candidates in multiple therapeutic areas, including CNS, cancer, metabolic diseases and other rare/specialty indications. The Company’s leading clinical programs include a proprietary Phase 2 candidate for dementia with Lewy bodies (DLB) in Japan, together with partnered candidates aimed at the symptomatic treatment of Alzheimer’s disease (with Allergan) and immuno-oncology approaches to treat cancer (with AstraZeneca). Sosei’s additional partners and collaborators include Novartis, Teva, Pfizer, Daiichi-Sankyo, PeptiDream, Kymab and MorphoSys. The Company is headquartered in Japan with R&D facilities in the UK.

Sosei is listed on the Mothers Index of the Tokyo Stock Exchange (TOKYO: 4565). For more information, please visit http://www.sosei.com/en/.

Forward-looking statements

This press release contains forward-looking statements, including statements about the discovery, development and commercialisation of products. Various risks may cause Sosei’s actual results to differ materially from those expressed or implied by the forward-looking statements, including: adverse results in clinical development programs; failure to obtain patent protection for inventions; commercial limitations imposed by patents owned or controlled by third parties; dependence upon strategic alliance partners to develop and commercialise products and services; difficulties or delays in obtaining regulatory approvals to market products and services resulting from development efforts; the requirement for substantial funding to conduct research and development and to expand commercialisation activities; and product initiatives by competitors. As a result of these factors, prospective investors are cautioned not to rely on any forward-looking statements. We disclaim any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

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