The purpose of the study is to assess the tolerability and safety of a range of repeated inhaled doses of MDT-637. This includes monitoring effects on pulmonary function and determination of blood levels of MDT-637 following inhalation.

Inclusion Criteria:

• Males and/or surgically sterile or post-menopausal females (confirmed by FSH test); males must agree to practice barrier contraception until they are discharged from the study
• Willing to give written informed consent
• 18 to 50 years of age
• BMI of 19-30 kg/m2
• Non-smoker (for at least 90 days prior to screening) and willing to abstain from smoking during the course of the study
• Good general health as determined by medical history, physical examination, spirometry, ECG and clinical laboratory tests
• Willing to abstain from alcohol, caffeine, and xanthine-containing beverages for 24 hours prior to and 24 hours after dosing

Exclusion Criteria:

• Uncontrolled, clinically significant disease which in the opinion of the Principal Investigator and Sponsor (MDTx) would place the subject at risk through study participation or would confound the assessment of the safety of MDT-637
• Evidence of current or history of respiratory disease; for instance asthma, emphysema, chronic bronchitis or cystic fibrosis.
• Upper respiratory tract infection within 6 weeks of Visit 1
• Symptoms of rhinitis (stuffy nose, rhinorrhea, sneezing, nasal discharge) within 2 weeks of Visit 1
• Current symptoms of cough, dyspnea, wheezing or nocturnal awakenings due to respiratory symptoms
• History of significant nasal irritation from nasal inhalation of medication
• History of malignancy
• History of clinically significant alcohol or drug abuse
• Positive drug screen for drugs of abuse
• Positive test for HIV, Hepatitis B or Hepatitis C
• Allergy to lactose, or lactose intolerance
• Use of prescription medication within 14 days of Visit 2 or over-the-counter preparations, including dietary and herbal supplements, within 5 days of Visit 2
• Positive urine pregnancy test at Visit 1
• Inability to perform reproducible spirometry in accordance with American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines
• Abnormal QTc interval at Visit 1(>450 msec in males or > 470 msec in females)
• Significant blood donation (or testing) in previous 8 weeks