Summit Therapeutics : Reports Financial Results for the Fourth Quarter and Fiscal Year Ended 31 January 2019 and Operational Progress

Summit Therapeutics plc

('Summit', the 'Company' or the 'Group')

Summit Therapeutics Reports Financial Results for the Fourth Quarter and Fiscal Year Ended 31 January 2019 and Operational Progress

•Focus on Improving Patient Outcomes for Serious Infectious Diseases

•Conference Call Today at 12:00pm GMT / 8:00am EDT

Oxford, UK, and Cambridge, MA, US, 27 March 2019 - Summit Therapeutics plc (NASDAQ: SMMT, AIM: SUMM), a leader in new mechanism antibiotic innovation, today reports its financial results for the fourth quarter and fiscal year ended 31 January 2019 and provides an update on its operational progress.

"The initiation of our global Phase 3 clinical trials of ridinilazole brings us closer to becoming a fully-integrated antibiotics company. Our capabilities span discovery through late-stage clinical development with an eye towards building a focussed commercial team," said Mr Glyn Edwards, Chief Executive Officer of Summit. "We believe our differentiated portfolio alongside our development plans aimed at demonstrating meaningful benefits to patients, physicians and payors have the potential to counter the current trends in the antibiotic sector.

"Ridinilazole has already shown clinical superiority against the standard of care in a Phase 2 clinical trial for C. difficile infection. If we were to achieve similar results in the ongoing Phase 3 clinical trials, we believe that would provide us with a compelling data package supporting the front-line use of ridinilazole in C. difficile infection. With approximately one third of patients with CDI currently experiencing unsatisfactory outcomes with the standard of care, ridinilazole has the potential to significantly improve patient outcomes.

"Further back in our pipeline are important programmes addressing other high priority targets of gonorrhoea and the ESKAPE pathogens. The unmet need here is clear, as antimicrobial resistance is having a major impact on the ability of patients to achieve cures. Our programmes aim to provide a potential treatment option that is potent across non-resistant and resistant infections due to their new mechanisms of action. Together, our pipeline comprises new mechanism antibiotics that are being developed to be the most appropriate antibiotic for the patient in question, which would support good antibiotic stewardship and potentially reduce the threat of antimicrobial resistance."

Programme Highlights

Antibiotics Focussed Strategy

•Summit is focussed on the development of new antibiotics that will meaningfully improve patient outcomes.

•Strategy realigned after the discontinuation of ezutromid for the treatment of Duchenne muscular dystrophy in June 2018 following the report of top-line data from the Phase 2 proof of concept clinical trial, where ezutromid missed its primary and secondary endpoints.

Ridinilazole for C. difficile Infection ('CDI')

•Phase 3 clinical trials of ridinilazole initiated in February 2019. The trials are expected to support the front-line use of ridinilazole for the treatment of CDI. The primary endpoint for both Phase 3 clinical trials tests for superiority of ridinilazole compared to the standard of care in the treatment of CDI. Additional endpoints include ridinilazole's impact on reducing disease recurrence and in preserving

the gut microbiome, as well as health economic outcomes measures that are intended to help support commercialisation efforts.

•$12 million option exercised by BARDA in August 2018 under existing contract to support clinical and regulatory development of ridinilazole, bringing total committed BARDA non-dilutive funding to $44 million.

•PLOS One publication highlighted microbiome-preserving activity of ridinilazole over standard of care in the CoDIFy Phase 2 clinical trial.

SMT-571 for Gonorrhoea

•SMT-571nominated to progress into IND-enabling studies for the treatment of gonorrhoea in September 2018.

•Preclinical data presented at various conferences highlighted SMT-571 as a selective and potent antibiotic with characteristics that could support its front-line use. Further data published in Journal of Antimicrobial Chemotherapy showed SMT-571 had consistently high potency across over 200 clinically relevant strains of N. gonorrhoeae, including numerous multi- and extensively-drug resistant strains.

•Up to $4.5 million of non-dilutive funding awarded by CARB-X in July 2018 to support the preclinical and Phase 1 clinical development of SMT-571.

ESKAPE Programme

•Novel targets against ESKAPE pathogens identified using the Discuva Platform.

•Discovery further highlights the power of Summit's proprietary Discuva Platform as a potential source of new mechanism antibiotics to treat serious infectious diseases.

Financial Highlights

•Net proceeds of $24.4 million (£19.2 million) received from the sale of American Depositary Shares in a private placement that completed in January 2019.

•Profit for the year ended 31 January 2019 of £7.5 million compared to a loss of £20.2 million for the

year ended 31 January 2018.

• Cash and cash equivalents at 31 January 2019 of £26.9 million compared to £20.1 million at 31 January 2018.

Conference Call and Webcast Information

Summit will host a conference call and webcast to review the financial results for the fiscal year ended 31 January 2019 today at 12:00pm GMT / 8:00am EDT. To participate in the conference call, please dial [phone] (UK and international participants) or [phone] (US local number) and use the conference confirmation code 3179239. Investors may also access a live audio webcast of the call via the investors section of the Company's website, www.summitplc.com. A replay of the webcast will be available shortly after the presentation finishes.

About Summit Therapeutics

Summit Therapeutics is a leader in antibiotic innovation. Our new mechanism antibiotics are designed to become the new standards of care for the benefit of patients and create value for payors and healthcare providers. We are currently developing new mechanism antibiotics to treat infections caused by C. difficile, N. gonorrhoeae and ESKAPE pathogens and are using our proprietary Discuva Platform to expand our pipeline. For more information, visit www.summitplc.com and follow us on Twitter @summitplc.

This announcement contains inside information for the purposes of Article 7 of EU Regulation 596/2014 (MAR).

For more information:
Summit
Glyn Edwards / Richard Pye (UK office)	Tel: [phone]
Michelle Avery (US office)	[phone]
Cairn Financial Advisers LLP (Nominated Adviser)	Tel: [phone]
Liam Murray / Tony Rawlinson
N+1 Singer (Joint Broker)	Tel: [phone]
Aubrey Powell / Jen Boorer, Corporate Finance
Tom Salvesen, Corporate Broking
Bryan Garnier & Co Limited (Joint Broker)	Tel: [phone]
Phil Walker / Dominic Wilson
MSL Group (US)	Tel: [phone]
Jon Siegal	[e-mail]
Consilium Strategic Communications (UK)	Tel: [phone]
Mary-Jane Elliott / Sue Stuart / Jessica Hodgson /	[e-mail]
Lindsey Neville

Forward Looking Statements

Any statements in this press release about the Company's future expectations, plans and prospects, including but not limited to, statements about the potential benefits and future operation of the BARDA or CARB-X contract, including any potential future payments thereunder, the clinical and preclinical development of the Company's product candidates, the therapeutic potential of the Company's product candidates, the potential of the Discuva Platform, the potential commercialisation of the Company's product candidates, the sufficiency of the Company's cash resources, the timing of initiation, completion and availability of data from clinical trials, the potential submission of applications for marketing approvals and other statements containing the words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "plan," "potential," "predict," "project," "should," "target," "would," and similar expressions, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Actual results may differ materially from those indicated by such forward-looking statements as a result of various important factors, including: the ability of BARDA or CARB-X to terminate our contract for convenience at any time, the uncertainties inherent in the initiation of future clinical trials, availability and timing of data from ongoing and future clinical trials and the results of such trials, whether preliminary results from a clinical trial will be predictive of the final results of that trial or whether results of early clinical trials or preclinical studies will be indicative of the results of later clinical trials, expectations for regulatory approvals, laws and regulations affecting government contracts, availability of funding sufficient for the Company's foreseeable and unforeseeable operating expenses and capital expenditure requirements and other factors discussed in the "Risk Factors" section of filings that the Company makes with the Securities and Exchange Commission, including the Company's Annual Report on Form 20-F for the fiscal year ended 31 January 2018. Accordingly, readers should not place undue reliance on forward- looking statements or information. In addition, any forward-looking statements included in this press release represent the Company's views only as of the date of this release and should not be relied upon as representing the Company's views as of any subsequent date. The Company specifically disclaims any obligation to update any forward-looking statements included in this press release.

CHAIRMAN'S STATEMENT

Over the past year, Summit gained a new identity as an antibiotics company. Antibiotics have always been a part of our core strategy. Ridinilazole is our lead programme now in Phase 3 clinical trials, and the Discuva Platform is bolstering our pipeline. However, in the past, Summit was well known for its programme in Duchenne muscular dystrophy ('DMD').

While we were disappointed to announce negative results from our Phase 2 clinical trial in DMD in June 2018, they allowed us to align the entire company's efforts towards delivering new antibiotics that meaningfully improve patient outcomes. The Phase 2 DMD trial generated a high-quality data set that enabled us to come to the definitive conclusion that ezutromid was not providing a benefit to patients. What followed was a swift, strategic pivot to become a leading antibiotics company with what we believe are the capabilities to radically change the current antibiotic paradigm through a single focus: innovation.

It is abundantly clear that the world needs new antibiotics. Too many patients with serious bacterial infections have unsatisfactory outcomes with today's armamentarium of decades-old classes of antibiotics.

We aim to change that. Our goal is to bring innovation into the discovery, development and commercialisation of new mechanism antibiotics for serious infectious diseases.

The acquisition of our Discuva Platform in December 2017 strengthened our capabilities in antibiotics by incorporating discovery efforts into Summit. This Platform, alongside our team of scientists, has the potential to disrupt the field of antibiotic discovery. Over the past year, we have added three new programmes to our pipeline, all of which originated from the Discuva Platform, an encouraging early sign of how prolific we believe our proprietary platform can be.

Two of the programmes we added to our pipeline are for the treatment of gonorrhoea. We are entering a world of super gonorrhoea, infections that are extensively drug resistant. One such case of super gonorrhoea arrived in the UK just last year, with further cases reported since. Neisseria gonorrhoeae is particularly clever when it comes to evading antibiotics. It has consistently gained resistance to the antibiotics used to treat it and keeps this resistance over time. The only recommended treatment is failing in many cases, and there are no other recommended drugs available to treat gonorrhoea. In order to gain the upper hand against N. gonorrhoeae, society desperately needs new mechanism antibiotics.

Through the Discuva Platform, we have identified two new targets for N. gonorrhoeae. Our focus in gonorrhoea is on our lead clinical candidate, SMT-571, which was nominated in September 2018. In preclinical studies, SMT-571 has demonstrated potent activity across hundreds of clinically relevant N. gonorrhoeae strains, including numerous multi- and extensively-drug resistant strains. Our opportunity in gonorrhoea is to be the next treatment option recommended for the 78 million estimated annual cases worldwide.

Our third programme added in 2018 addresses serious hospital-acquired infections caused by the ESKAPE pathogens. These infections are plagued by resistance, which result in poor patient outcomes and substantial medical costs. As is the case with all of our programmes, we believe that developing new mechanism antibiotics that are designed to target a specific infection or pathogen could result in significantly improved patient outcomes and reduced healthcare costs. We look forward to providing an update on this programme in 2019. Our late-stage antibiotic ridinilazole for the treatment of C. difficile infection has made a strong start to 2019 following the progress made in our manufacturing processes during 2018. We dosed the first patient in our much-anticipated Phase 3 clinical trials in February. These Phase 3 clinical trials of ridinilazole truly exemplify our innovation in development and planning for commercial success.

Our goal is to send a clear message to physicians and payors that ridinilazole is a superior product clinically and economically and should be used as a front-line treatment of CDI. We have designed the Phase 3 clinical trials to support this goal. The primary endpoint for the Phase 3 clinical trials aims to show superiority of ridinilazole over the standard of care, vancomycin, in sustained clinical response. In other words, the trials are designed to provide evidence that patients are being cured and remaining free of CDI, something which doesn't happen in approximately one-third of CDI patients treated with vancomycin. There are over a million cases of CDI in the US and Europe every year, representing unacceptably high number of patients who are not receiving a satisfactory clinical outcome.

Our Phase 3 clinical programme also is designed to support commercialisation through the inclusion of health economic outcomes measures. Unsatisfactory patient outcomes lead to higher healthcare costs. If treatment with ridinilazole improves patient outcomes, it could reduce those healthcare costs and potentially support its uptake by healthcare providers.

We believe the clinical and economic outcomes will both play a key role in ensuring ridinilazole's potential commercial success. Superior clinical and positive health economic outcomes could provide healthcare providers with the information to encourage use, guideline writers to change their recommendations and payors to provide reimbursement. We are bold in this endeavour, but the positive results from our Phase 2 clinical trial of ridinilazole and lessons from past antibiotic launches provide us with confidence that this is the right path to achieve success.

Our differentiated approach to antibiotic development continues to be endorsed by third parties. In 2018, BARDA exercised one of its options in our award of up to $62 million for the clinical and regulatory development of ridinilazole. The total committed capital from BARDA is now $44 million. Also in 2018, we received a grant worth up to $4.5 million from the public-private partnership, CARB-X, to support the development of SMT-571 through the end of a Phase 1 clinical trial. These awards are further endorsement of Summit's strategy and innovation in new mechanism antibiotics. In addition to these non-dilutive capital sources, we believe our singular focus as an antibiotics company and clear mission to bring new mechanism antibiotics to patients are increasingly resonating with the investment community, including new and existing shareholders.

Our people are central to being successful in antibiotic research. We have a team with deep expertise and experience in infectious diseases from conducting early stage research to running global clinical trials and successfully launching new antibiotics.

Our ambitious goals in the discovery of new mechanism antibiotics through to commercialisation of these products ourselves in key territories rely on having the support of our shareholders and the right team in place to do so. We thank our shareholders for supporting us in this vision and our employees, who are dedicated to bringing potentially life-saving treatments to patients. Together, we are redefining antibiotic development and bringing much needed innovation to this crucial area of medicine.

Frank Armstrong, FRCPE, FFPM

Non-Executive Chairman