The purpose of the study is to evaluate the safety of administering repeated doses of CTX-100 (formerly ETX-100) to subjects with smoking-related chronic obstructive pulmonary disease.

The study primarily aims to establish safety and evaluate biochemical activity of CTX-100 (formerly ETX-100) with respect to elastin breakdown, but will also concurrently gather data that may point to efficacy. The preliminary efficacy results will be used to assist in the design of subsequent phase 2b clinical studies of longer duration to examine both efficacy and safety of CTX-100 as a therapy for chronic obstructive pulmonary disease.

Inclusion Criteria:

• Able and willing to provide written informed consent and comply with study requirements.
• Men or women aged 40 through 75 years at the time of consent.
• At least 10-pack years (average packs/day x number of years) of cigarette use, and either current smoker or ex-smoker.
• Diagnosis of COPD at screening consistent with National Institutes of Health guidelines.
• Evidence of emphysema on chest x-ray.
• A ratio of prebronchodilator FEV1 to forced vital capacity (FVC) of ≤ 70% at screening.
• FEV1 ≥ 50% (prebronchodilator) and ≤ 79% (postbronchodilator) of predicted normal at screening.
• Clinical laboratory tests (complete blood count, serum chemistry, and urinalysis) within normal limits or clinically acceptable to the PI/sponsor at screening.
• Women of childbearing potential and men who are sexually active must agree to use an adequate method of contraception (oral contraceptives, depot progesterone, condom plus spermicide, or IUD) during the study and for 1 month after the final dose of study drug.

Exclusion Criteria:

• Subjects with a measured DLCO of ≤ 50%, or unable to perform a reproducible DLCO.
• Subjects unable to perform 3 reproducible spirometry tests after 5 attempts.
• Upper or lower respiratory tract infection within 2 weeks prior to screening and baseline (day 1).
• Presence of clinically relevant abnormality on chest x-ray (other than evidence of emphysema) at screening or within the previous 12 months.
• Use of supplemental oxygen therapy.
• Requirement for ventilatory support within the last year.
• Exacerbation requiring treatment with systemic corticosteroids within the last 3 months.
• History of lung transplant.
• Presence of clinically relevant abnormality on electrocardiogram (ECG).
• Any medical condition that, in the investigator's judgment, would compromise study participation or the evaluation of the study drug.
• Women who are pregnant or breastfeeding.
• Receipt of an investigational drug within 30 days prior to screening (including subjects who participated in the first phase of this study).