Inclusion Criteria:

• Signed Informed Consent Form.
• In the opinion of the Principle Investigator, participation in the study is in the best interest of the patient.
• Ability to comply with the requirements of the study protocol, according to the investigator’s best judgment.
• Taken part in a previous study of PRM-151, as follows:
  • Participated in Study PRM-151-202 (completed the 28-week placebo-controlled period and entered the OLE), and tolerated the study drug in the opinion of the investigator (Cohort A); OR
  • Completed study treatment in Study WA42293 (Cohort B); OR
  • Participated in Study WA42293 but have discontinued from study treatment (Cohort C; patients who completed treatment in Study WA42293, but no longer wish to take PRM-151 may also join
  • Cohort C).
• For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraception, as defined below:
  • Women must remain abstinent or use contraceptive methods with a failure rate of 1% per year during the treatment period and for 8 weeks after the final dose of PRM-151;
  • A woman is considered to be of childbearing potential if she is postmenarchal, has not reached a postmenopausal state (≥ 12 continuous months of amenorrhea with no identified cause other than menopause), and is not permanently infertile due to surgery (i.e., removal of ovaries, fallopian tubes, and/or uterus) or another cause as determined by the investigator (e.g., Müllerian agenesis). The definition of childbearing potential may be adapted for alignment with local guidelines or regulations;
  • Examples of contraceptive methods with a failure rate of < 1% per year include bilateral tubal ligation, male sterilization, hormonal contraceptives that inhibit ovulation, hormone-releasing intrauterine devices, and copper intrauterine device;
  • Hormonal contraceptive methods must be supplemented by a barrier method;
  • The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or postovulation methods) and withdrawal are not adequate methods of contraception. If required per local guidelines or regulations, locally recognized adequate methods of contraception and information about the reliability of abstinence will be described in the local Informed Consent Form.
• For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use a condom, and agreement to refrain from donating sperm, as defined below: 
  • With a female partner of childbearing potential or pregnant female partner, men must remain abstinent or use a condom during the treatment period and for 8 weeks after the final dose of PRM-151 to avoid exposing the embryo. Men must refrain from donating sperm during this same period. 
  • The reliability of sexual  abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or postovulation methods) and withdrawal are not adequate methods of preventing drug exposure. If required per local guidelines or regulations, information about the reliability of abstinence will be described in the local Informed Consent Form.

Exclusion Criteria:

• Received any experimental treatment other than PRM-151 within 4 weeks or five half-lives of the experimental drug, whichever is longer, prior to the first dose in the OLE study.
• Receiving strong inhibitor or inducer of CYP1A2 in patients taking pirfenidone.
• Receiving potent inhibitor or inducer of P-gp in patients taking nintedanib.
• Acute respiratory or systemic bacterial, viral, or fungal infection at the first visit of the OLE, or within 2 weeks of the first visit for patients joining Cohort A (from Study PRM-151-202).
• History of smoking (including cigarette, cannabis, cigar, pipe, and vaping) within 3 months prior to the first visit in the OLE.
• History of alcohol or substance use disorder within 2 years prior to the first visit of the OLE or known or suspected active alcohol or substance-use disorder.
• History of severe allergic reaction or anaphylactic reaction to PRM-151. 
• Clinically significant abnormality on ECG or laboratory tests (hematology, serum chemistry, and urinalysis) that, in the opinion of the investigator, may pose an additional risk in administering study drug to the patient.
• Any of the following laboratory abnormalities known at the time of the first visit:
  • ALT and/or AST ≥  2.5 xupper limit of normal (ULN);
  • Total bilirubin ≥ 2 x ULN;
• Pregnant or breastfeeding, or intending to become pregnant during the study.