Summit Therapeutics Reports Financial Results and Operational Progress for the First Quarter Ended 30 April 2019

Oxford, UK, and Cambridge, MA, US, 12 June 2019 - Summit Therapeutics plc (NASDAQ: SMMT, AIM: SUMM) today reports its financial results and provides an update on its operational progress for the first quarter ended 30 April 2019.

“As global leaders are sounding the alarm for new antibiotics, we are proud to be taking a leadership role in discovering and developing new classes of antibiotics with the potential to help combat the rising threat posed by antibiotic resistance,” said Mr Glyn Edwards, Chief Executive Officer of Summit. “We believe these new class antibiotics have the potential to transform patient lives and that it is possible to show clear advantages over standard of care treatments and cost effectiveness during development. With this differentiated approach, we believe we will have the opportunity to be commercially successful.

“Ridinilazole is the exemplar of this strategy. It is a precision, microbiome preserving antibiotic that aims to sustain cures of C. difficileinfection to improve outcomes for patients. We were excited to initiate our landmark Ri-CoDIFy Phase 3 clinical programme in February 2019. If successful, we believe our two Phase 3 clinical trials of ridinilazole will deliver clinical and economic data to support ridinilazole as the new standard of care for patients with C. difficile infection.

“Our Discuva Platform is enabling us to expand our leadership role as innovators in infectious disease. In April

2019, we announced the addition to our pipeline of another new class antibiotic programme targeting Enterobacteriaceae infections. With this new discovery-stage programme, our preclinical programme for N. gonorrhoeae and ridinilazole for C. difficile, our pipeline now targets the three most urgent bacterial threats as defined by the US Centers for Disease Control and Prevention with new classes of antibiotics.”

Programme Highlights

Strategy

• Through its scientific focus, Summit is discovering new classes of antibiotics to treat serious infectious diseases. Through creative development programmes, Summit aims to show its new classes of antibiotics offer significant advantages over current standards of care. Through demonstrating economic advantages, Summit aims to provide compelling value for payors and healthcare systems and achieve commercial success.

Ridinilazole for C. difficile Infection (‘CDI’)

• RiCoDIFy Phase 3 clinical trial programme initiated in February 2019, which aims to support adoption of ridinilazole as the new standard of care treatment for C. difficile infection.
• These landmark design clinical trials aim to: i) show superiority over the current standard of care, vancomycin, using a composite endpoint measuring sustained clinical response; ii) generate health economic data to help support the commercial launch, if approved; and iii) undertake deep microbiome analysis that aims to show ridinilazole’s preservation of the gut microbiome.
• Recruitment of patients into the two Phase 3 clinical trials is ongoing, and the programme remains on-track for expected reporting of top-line data in H2 2021.
• Clinical and regulatory development of ridinilazole is supported by a BARDA contract worth up to $62 million.

SMT-571 for Gonorrhoea

• SMT-571 is a new class antibiotic that is designed to treat infections caused by Neisseria gonorrhoeae.
• In February 2019, preclinical data was published in the Journal of Antimicrobial Chemotherapy that showed SMT-571 had consistently high potency across over 200 clinically relevant strains of N. gonorrhoeae, including numerous multi-drug resistant and extensively-drug resistant strains.
• IND-enabling studies are ongoing and expected to continue through the second half of the year. The Phase 1 clinical trial is no longer expected to initiate in H2 2019. Summit is evaluating the design of a clinical trial programme with the potential to shorten the overall clinical development timeline of SMT-571, subject to regulatory approvals. Further updates on the design and timelines for the start of the clinical programme to be provided when available.
• SMT-571 development is being supported by an award of up to $4.5 million from CARB-X.

DDS-04 for Enterobacteriaceae

• Identification of DDS-04 compound series, a new class of antibiotics that acts via the novel bacterial target LolCDE with the potential to treat infections caused by the gram-negative bacteria, Enterobacteriaceae.
• In vivo proof of concept demonstrated with a DDS-04 series compound cured infection in a translationally-relevant animal model of urinary tract infection, while therapeutic concentrations were also achieved in the lungs and bloodstream showing potential to treat other major Enterobacteriaceae infection sites. These data were presented at the 20^th European Congress of Clinical Microbiology & Infectious Diseases.

Financial Highlights

Cash and cash equivalents at 30 April 2019 of £28.3 million compared to £26.9 million at 31 January 2019.

Loss for the three months ended 30 April 2019 of £4.0 million compared to a loss of £5.8 million for the three months ended 30 April 2018.

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

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 Enterobacteriaceae and are using our proprietary Discuva Platform to expand our pipeline. For more information, visit www.summitplc.com and follow us on Twitter @summitplc.

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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 2019. 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.