Anaptysbio (ANAB) Says Imsidolimab POPLAR Phase 2 Clinical Trial in Moderate-to-Severe Palmoplantar Pustulosis Did Not Meet Primary Endpoint

AnaptysBio, Inc. (Nasdaq: ANAB), a clinical-stage biotechnology company developing first-in-class antibody product candidates focused on emerging immune control mechanisms applicable to inflammation and immuno-oncology indications, today announced that top-line data from its Phase 2 clinical trial of imsidolimab for the treatment of moderate-to-severe palmoplantar pustulosis (PPP), also known as the POPLAR trial, failed to meet its primary endpoint.

While further clinical development in PPP is not currently anticipated, AnaptysBio will continue development of imsidolimab in five other immuno-dermatological indications, including GPP, EGFRi-mediated skin toxicity, ichthyosis, hidradenitis suppurativa and acne. Initiation of a Phase 3 clinical trial in GPP is anticipated during mid-2021 following completion of protocol alignment with the FDA.

“While the top-line results are disappointing, I would like to sincerely thank everyone involved in the POPLAR trial, including the patients, the investigators, their staff and our employees,” said Hamza Suria, president and chief executive officer of AnaptysBio. “Imsidolimab is currently being advanced in 5 other immuno-dermatology indications and we look forward to multiple additional clinical readouts during 2021 and 2022.”

POPLAR Trial Data
Top-line data from the POPLAR trial are as follows:

• Mean baseline Palmoplantar Pustular Psoriasis Area Severity Index (PPPASI) scores were 16 for the 30 patients enrolled in the imsidolimab arm and 19 for the 29 patients enrolled in the placebo arm, with an overall average of 18. Mean baseline Palmoplantar Pustulosis Investigator Global Assessment (PPPIGA) was 3.1 for each arm. Patients were on average 50 years of age and 78% were female.
• The primary endpoint of least-squares mean difference (LSMD) PPPASI improvement at week 16 (Day 113) was 6.1 for imsidolimab-treated patients and 6.3 for placebo-treated patients relative to their respective baselines, which has a p-value of 0.93 for the difference between the groups. Twenty-four patients completed the week 16 primary endpoint analysis in each arm of the trial.

• Imsidolimab-treated patients had a mean PPPASI change from baseline of 5.78 or 38% improvement, while placebo-treated patients improved by 6.78 or 33% improvement, each relative to baseline. Percent PPPASI improvement versus baseline was numerically greater for imsidolimab-treated patients relative to placebo-treated patients at each study timepoint (Days 3, 8, 15, 22, 29, 43, 57, 71, 85 and 113), ranging from approximately 3% to 19%.
• Nine (38%) patients achieved fifty percent PPPASI improvement (PPPASI50) and 4 (17%) patients achieved seventy five percent PPPASI improvement (PPPASI75) in the imsidolimab arm at week 16, while 12 (50%) and 3 (13%) achieved these responder thresholds in the placebo arm, respectively.
• Five (21%) imsidolimab-treated patients achieved a PPPIGA score of zero (clear) or 1 (almost clear) at week 16 relative to 3 (13%) placebo-dosed patients.

• Imsidolimab was generally well-tolerated with a similar frequency of adverse events between treatment groups, and no severe or serious adverse events were observed in the imsidolimab arm. One severe and one serious adverse event was reported in the placebo-treated arm. The most common adverse events observed in the imsidolimab and placebo arms were three and four cases of mild nasopharyngitis, respectively, that were each deemed treatment unrelated.

POPLAR Phase 2 Trial Design
Fifty-nine PPP patients were enrolled in this trial at 36 sites located within North America and Europe. Patients were washed out of prior PPP therapy and no concomitant therapy was permitted during the trial. Key inclusion criteria included age between 18 and 75 years, clinically confirmed ongoing moderate-to-severe PPP disease with minimum PPPIGA score of at least 3 (moderate), disease history of at least 3 months, and active pustules on palms and/or soles upon enrollment. Patients were treated with a 200mg subcutaneous induction dose of imsidolimab at Day 1, followed by monthly 100mg subcutaneous doses on Days 29, 57 and 85. The primary endpoint of this trial was mean change in PPPASI at week 16 relative to baseline and the estimator for between-group comparison was LSMD. Baseline clinical assessments were conducted for each patient on Day 1 prior to imsidolimab dosing. Missing data was modeled using mixed model for repeated measures (MMRM) methodology.

About Imsidolimab
Imsidolimab, previously known as ANB019, is an antibody that inhibits the function of the interleukin-36-receptor, or IL-36R, which AnaptysBio plans to initially develop as a potential first-in-class therapy for patients suffering from generalized pustular psoriasis, or GPP, EGFR-mediated skin toxicity, ichthyosis, hidradenitis suppurativa and acne.

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