• Subject has signed an Informed Consent Form (ICF) prior to any study-specific procedures being performed

• ≥ 18 years old, irrespective of their race and ethnicity.

• Body Mass Index (BMI) 18.0-35.0 kg/m2, inclusive, at screening.

• Participants are willing and able to adhere to study protocol requirements including but not limited to scheduled outpatient visits, inpatient hospital stay, laboratory tests, and 12-lead ECGs.

• A. Diagnosis of RA and meeting the 2010 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria for RA at least 3 months prior to screening AND Active disease defined by ≥ 6 tender out of 68 joints and ≥ 6 swollen out of 66 swollen joint count at both screening and Day 1.

• AND Participants received conventional synthetic disease-modifying antirheumatic drug (csDMARD) therapy for ≥ 3 months and on a stable dose for ≥ 4 weeks prior to the first dose of study drug. The csDMARD allowed include methotrexate (MTX) (≤ 25mg/week), sulfasalazine (3 grams a day), hydroxychloroquine (≤400mg/day), chloroquine (≤250mg/day), and leflunomide (≤ 20mg/day) or intolerance to csDMARD as assessed by the investigator OR B. PsA diagnosis of at least 3 months duration prior to the date of first screening with Classification of Psoriatic Arthritis (CASPAR) confirmed diagnosis at Screening. Have active psoriasis defined by at least 1 psoriasis lesion \>= 2 cm diameter in areas other than the axilla or groin.

• AND Active disease defined by ≥ 3 tender out of 68 joints and ≥ 3 swollen out of 66 swollen joint count at both screening and Day 1.

• AND Participants received standard doses of NSAIDS for ≥4 weeks or csDMARDS (MTX ≤ 25mg/week), sulfasalazine (3 grams a day), and leflunomide (≤ 20mg/day), administered for ≥ 3 months and on a stable dose for ≥ 4 weeks prior to the first dose of study drug or intolerance to NSAIDS or DMARDs as assessed by the investigator. Other traditional DMARDS not listed as a prohibited concomitant medication may be considered after discussion with the Study physician.

• The subject must be judged to be in good health by the investigator to participate in the study, based on clinical evaluations, including laboratory safety tests, medical history, physical examination, vital signs and 12-lead ECG competed at the screening visit and prior to the first dose of study drug.

• Female subject is postmenopausal (at least 1 year; to be confirmed by follicle stimulating hormone (FSH) if less than 2 years since last menstrual period), permanently sterilized (e.g. tubal occlusion, hysterectomy, bilateral salpingectomy or if of childbearing potential and engaged in sexual activity that can result in pregnancy must agree to use any two of the highly effective contraception methods listed below. Male participants with a partner of childbearing potential must also agree to use any two of the highly effective contraception methods listed below between the both of them. This criterion must be followed from screening visit to 6 weeks after the last dose in females and for 90 days after the last dose for males.

• a. The following applies to all female participants with childbearing potential and female partners of male volunteers enrolled in the study.

• i. Implantable progestogen-only hormone contraception associated with inhibition of ovulation.

• ii. Intrauterine device. iii. Intrauterine hormone-releasing system. iv. Bilateral tubal occlusion. v. Combined (estrogen- and progestogen-containing) hormonal contraception associated with inhibition of ovulation:

⁃ Oral

⁃ Intravaginal

⁃ Transdermal

⁃ Injectable vi. Progestogen-only hormone contraception (oral or injectable) is associated with inhibition of ovulation.

• vii. Vasectomized partner viii. Sexual abstinence -this is considered a highly effective method only if defined as refraining from heterosexual intercourse during the entire period of risk associated with the study intervention. The reliability of sexual abstinence needs to be evaluated about the duration of the study and the preferred and usual lifestyle of the participant.

• ix. A combination of male condoms with either cervical cap, diaphragm, or sponge with spermicide (double-barrier methods) b. The following applies to all male participants in the study: i. Sexual abstinence- this is considered a highly effective method only if defined as refraining from heterosexual intercourse during the entire period of risk associated with the study intervention. The reliability of sexual abstinence must be evaluated for the study and the participant\'s preferred and usual lifestyle.

• ii. A combination of male condoms with either cervical cap, diaphragm, or sponge with spermicide (double-barrier methods).

• iii. Vasectomy

• Negative serum B-human chorionic gonadotropin test at screening (for all females) and negative urine pregnancy at randomization (Day 1) (females of childbearing potential) prior to administration of investigational product.