Summit Therapeutics plc ( Summit or the Company ) SUMMIT THERAPEUTICS GRANTED KEY PATENT FOR NOVEL ANTIBIOTIC SMT19969 FOR THE TREATMENT OF C. DIFFICILE INFECTION Oxford, UK, 30 April 2015 Summit Therapeutics plc (AIM: S

Summit Therapeutics plc

( Summit or the Company )

SUMMIT THERAPEUTICS GRANTED KEY PATENT FOR NOVEL ANTIBIOTIC SMT19969 FOR THE TREATMENT OF C. DIFFICILE INFECTION

Oxford, UK, 30 April 2015 Summit Therapeutics plc (AIM: SUMM, NASDAQ: SMMT), the drug discovery and development company advancing therapies

for Duchenne muscular dystrophy and Clostridium difficile infection ( CDI ) announces that the United States Patent and Trademark Office has issued a patent that protects the use of SMT19969 in the treatment of CDI.

United States Patent number 8,975,416 is entitled Antibacterial Compounds and will provide a period of exclusivity for the use in the United

States of the small molecule antibiotic SMT19969 in the treatment of CDI through until at least 1 December 2029. Patent protection has previously been granted for SMT19969 in the treatment of CDI in a number of other countries including Japan.

The grant of this key patent for SMT19969 in one of the major commercial markets represents a critical component in our strategy for advancing this

highly selective antibiotic for the treatment of CDI. SMT19969 has the potential to treat initial infection and reduce rates of disease recurrence by being highly sparing of healthy gut flora, commented Glyn Edwards, Chief Executive Officer

of Summit. Through the grant of this patent the intellectual property estate protecting SMT19969 has been significantly strengthened as we continue to evaluate this promising antibiotic in Phase 2 proof of concept patient clinical trials.

Data are expected from the trial in the second half of this year.

C. difficile infection is a serious healthcare threat in hospitals, long-term care homes and increasingly the

wider community. It is a serious illness caused by infection of the colon by the bacteria C. difficile, which produces toxins that cause inflammation, severe diarrhoea and in the most serious cases can be fatal. Patients typically develop CDI

following the use of broad-spectrum antibiotics that disrupt the natural balance of the gastrointestinal (gut) flora allowing C. difficile to flourish. Existing CDI antibiotics cause further damage to the gut flora and are associated with

high rates of recurrent disease. This is the key clinical issue as repeat episodes are typically more severe and associated with an increase in mortality rates and healthcare costs. The economic impact of CDI is significant with acute care costs

estimated at $4.8 billion in the US alone.

SMT19969 is a novel, oral small molecule antibiotic that is being developed specifically for the treatment of CDI. Results from non-clinical efficacy studies

show that SMT19969 combines potent bactericidal activity against C. difficile with high levels of antibacterial selectivity. A Phase 1 trial conducted in healthy volunteers showed SMT19969 to be well tolerated at all doses tested. In

addition, a significant reduction in total clostridia but not in other bacterial groups was reported which demonstrated that SMT19969 was highly sparing of gut flora. The Phase 2 proof of concept trial (CoDIFy) is currently being conducted in North

About Summit Therapeutics

biopharmaceutical company focused on the discovery, development and commercialization of novel medicines for indications for which there are no existing or only inadequate therapies. Summit is conducting clinical programs focused on the genetic

disease Duchenne muscular dystrophy and the infectious disease C. difficile infection. Further information is available at www.summitplc.com and Summit can be followed on Twitter (@summitplc).

For more information, please contact:

Forward Looking Statements

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