A Clinical Trial to Study the Effects of GRC 17536 in Patients With Painful Diabetic Neuropathy (Painful Extremities Due to Peripheral Nerve Damage in Diabetic Patients)

Inclusion Criteria: 1. Patients willing to provide voluntary written informed consent 2. Male and female (women of non child-bearing potential) patients ≥18 yrs and ≤ 75 yrs 3. Patients with diabetes mellitus with painful peripheral neuropathy for at least 6 months 4. A baseline 24-hour average daily pain intensity score ≥5 5. Women must be of non child-bearing potential, defined as post menopausal or surgically sterile. Exclusion Criteria: 1. Other chronic pain conditions not associated with DPN, that may confound the assessment of neuropathic pain 2. Other causes of neuropathy or lower extremity pain 3. Complex regional pain syndrome or trigeminal neuralgia 4. Lower extremity amputations other than toes 5. Participation in another study with an investigational compound within the previous 90 days prior to study medication administration, or concurrent participation in another clinical study 6. Major depression. 7. Presence or history of cancer within the past 5 years with the exception of adequately treated localized basal cell skin cancer or in situ uterine cervical cancer. 8. Patients with clinically significant or uncontrolled hepatic, gastrointestinal, cardiovascular, respiratory, neurological (other than neuropathy), psychiatric, hematological, renal, or dermatological disease, or any other medical condition that according to Investigator's medical judgment: Could interfere with the accurate assessment of safety or efficacy, or, Could potentially affect a patient's safety or study outcome