Trial to Evaluate Efficacy and Safety of Lenabasum in Dermatomyositis

Subjects will be randomized to receive lenabasum 20 mg twice per day, lenabasum 5 mg twice
per day, or placebo twice per day in a 2:1:2 ratio. The primary efficacy outcome at Week 52
will be Total Improvement Score (TIS), which is a weighted composite measure of improvement
from baseline in six endpoints: Physician Global Assessment of Disease Activity, Physician
Assessment of Extramuscular Disease Activity, Patient Global Assessment of Disease Activity,
Health Assessment Questionnaire (patient-reported disability), Manual Muscle Testing (MMT),
and muscle enzymes.

Inclusion Criteria:

- Fulfill one of the following criteria for dermatomyositis:

1. Bohan and Peter criteria (Bohan and Peter, 1975a; Bohan and Peter 1975b)

2. ACR/EULAR criteria (Lundberg et al, 2017)

- Disease activity/severity fulfills one of the following three criteria:

1. MDGA ≥ 3 cm (0 - 10 cm Visual Analog Scale [VAS]) and MMT-8 score ≤ 142 (out of
150 total possible)

2. Sum of MDGA, PtGA and EMGA VAS scores is ≥ 10 cm (0-10 cm VAS for each)

3. MDGA ≥ 3 cm (0-10 cm VAS) and CDASI activity score of > 14

- Stable doses of immunosuppressive medications for DM as defined by:

1. Unchanged dose of oral corticosteroids ≤ 20 mg per day prednisone or equivalent
for ≥ 4 weeks before Visit 1

2. Unchanged dose of immunosuppressive medications other than oral corticosteroids
for ≥ 8 weeks before Screening

Exclusion Criteria:

- Unstable DM or DM with end-stage organ involvement at Screening or Visit 1

- Significant diseases or conditions other than DM that may influence response to the
study drug or safety

- Any of the following values for laboratory tests at Screening:

1. A positive pregnancy test (or at Visit 1)

2. Hemoglobin < 9 g/dL in males and < 8 g/dL in females

3. Neutrophils < 1.0 × 10^9/L

4. Platelets < 75 × 10^9/L

5. Creatinine clearance < 50 mL/min on screening blood test, per the Modification of
Diet in Renal Disease Study or in 24 hour urine creatine clearance measurement