Safety, Pharmacokinetics and Efficacy of ARQ-151 Cream in Adults With Mild to Moderate Chronic Plaque Psoriasis

There are 2 cohorts of subjects. Cohort 1 is a single dose study of ARQ-151 0.5% cream
applied to 25 cm2 of psoriatic plaque(s) in up to 8 psoriasis subjects. Cohort 2 is a
parallel group, double blind, vehicle controlled study in which ARQ-151 cream 0.5%, ARQ-151
cream 0.15% or vehicle cream is applied once a day for 28 days to subjects with between 0.5%
to 5.0% BSA of chronic plaque psoriasis. Including both Cohorts, a total of up to 92 subjects
will be enrolled at 8 study sites in Canada and the US. Subjects will be adult (≥18 years
old) males or females with chronic plaque psoriasis.

Inclusion Criteria:

- Adult male and female subjects aged ≥18 years

- In Cohort 1, subjects must have at least 25 cm2 of chronic plaque psoriasis (excluding
the face, scalp, intertriginous areas, palms and soles).

- In Cohort 2, subjects must have 0.5% to 5.0% of total BSA of chronic plaque psoriasis
and at least one target plaque, of at least 9 cm2 in size with a TPSS ≥4 (excluding
the face, scalp, intertriginous areas, palms and soles).

- Women of childbearing potential must have a negative urine pregnancy test at Screening
and agree to use birth control throughout the trial.

- In good health as judged by the Investigator, based on medical history, physical
examination, 12-lead electrocardiogram (ECG), serum chemistry labs, hematology values,
and urinalysis.

- Subjects agree not to have prolonged sun exposure during the course of the study.
Tanning bed use is not allowed.

- Subjects are competent to sign and give informed consent and considered reliable and
capable of adhering to the Protocol and visit schedule.

Exclusion Criteria:

- Subjects with non-plaque forms of psoriasis (erythrodermic, guttate, pustular or
palmo-plantar psoriasis) or with drug-induced psoriasis

- Evidence of skin conditions other than psoriasis that would interfere with evaluation
of the effect of the study medication.

- Pregnant or lactating women or women planning to become pregnant during the study and
/ or within 28 days following the last dose of study medication

- Known allergies to excipients in ARQ-151 cream

- Subjects who cannot discontinue the use of strong P-450 cytochrome inducers or
inhibitors for two weeks prior to the baseline visit and during the study period.

- Subjects who are unwilling to refrain from using a tanning bed for 2 weeks before and
during the study.

- Subjects who cannot discontinue systemic therapies and/or topical therapies for the
treatment of psoriasis.

- Subjects with a history of chronic alcohol or drug abuse in past 6 months.

- History of and/or concurrent condition of serious hypersensitivity (anaphylactic shock
or anaphylactoid reaction) to phosphodiesterase type 4 (PDE-4) inhibitors.

- Current or a history of cancer within 5 years with the exception of fully excised skin
basal cell carcinoma, cutaneous squamous cell carcinoma or carcinoma in situ of the
cervix.

- Subjects with active infection that requires oral or intravenous administration of
antibiotics, antifungal or antiviral agents.

- Subjects who are unable to communicate, read or understand language, or who display
another condition which makes them unsuitable for clinical study participation.