A Study to Evaluate the Efficacy, Safety, and Tolerability of NDI-034858 in Participants With Active Psoriatic Arthritis

Inclusion Criteria

• Participant has PsA on the basis of the Classification Criteria for Psoriatic Arthritis with peripheral symptoms at the screening visit.
• Participant has a history of PsA symptoms for ≥ 6 months prior to the screening visit.
• Participant has ≥ 3 tender joints and ≥ 3 swollen joints at screening and Day 1 visits.
• Participant has at least one lesion of plaque psoriasis ≥ 2 cm in diameter, nail changes characteristic of psoriasis, or a documented history of plaque psoriasis.
• Participant has active PsA despite previous standard doses of non-steroidal anti-inflammatory drug (NSAIDs) administered for ≥ 4 weeks, or traditional disease-modifying anti-rheumatic drug (DMARDs) (including methotrexate and sulfasalazine) administered for ≥ 3 months, or tumor necrosis factor inhibitor (TNFi) agents administered for ≥ 3 months, or participants are intolerant to NSAIDs or DMARDs or TNFi agents.
• If participant is on concurrent PsA treatments, they must be on stable doses.
• All female participants should followed the protocol defined contraceptive method.

Exclusion Criteria

• Participant has other disease(s) that might confound the evaluations of benefit of NDI-034858 therapy, including but not limited to rheumatoid arthritis (RA), axial spondyloarthritis (this does not include a primary diagnosis of PsA with spondylitis), systemic lupus erythematosus, Lyme disease, or fibromyalgia.
• Participant has a history of lack of response to any therapeutic agent targeting IL-12, IL17, and/or IL23 at approved doses after at least 12 weeks of therapy, and/or received one of these therapies within 6 months prior to baseline (Day 1).
• Participant has a history of lack of response to > 1 therapeutic agent targeting tumor necrosis factor.
• Participant has received infliximab, golimumab, adalimumab, or certolizumab pegol, or any biosimilar of these agents, within 8 weeks prior to baseline (Day 1).
• Participant has received etanercept, or any biosimilar of etanercept, within 4 weeks prior to baseline (Day 1).
• Participant has received rituximab or any immune-cell-depleting therapy within 6 months prior to baseline (Day 1).
• Participant has received any marketed or investigational biological agent, other than those specified in other inclusion/exclusion criteria, within 12 weeks or 5 half-lives prior to baseline (Day 1).
• Participant is currently receiving a non-biological investigational product or device or has received one within 4 weeks prior to baseline (Day 1).
• Participant has received apremilast or other non-biologic systemic treatment for PsA within 4 weeks prior to baseline (Day 1), other than methotrexate (MTX), sulfasalazine, corticosteroids, NSAIDs, or paracetamol/acetaminophen, which are allowed at stable doses as described in Inclusion Criterion 7. For participants not receiving MTX and sulfasalazine at screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1). Participant has received leflunomide within 8 weeks of baseline (Day 1) if no elimination procedure was followed or adhere to an elimination procedure. For participants not receiving MTX and sulfasalazine at Screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1).
• Participant has received intraarticular injection (including corticosteroids), intramuscular steroids, intralesional steroids, or intravenous steroids within 4 weeks prior to baseline (Day 1). For participants not receiving MTX and sulfasalazine at screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1). For participants not receiving MTX and sulfasalazine at screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1).
• Participant has received high potency opioid analgesics (eg, methadone, hydromorphone, or morphine) within 2 weeks prior to baseline (Day 1).
• Participant has used any topical medication that could affect PsA or psoriasis (including corticosteroids, ret