FibroGen Unveils Early Data From Prostate Cancer Candidate, Analyst Advocates Further Exploration In The Landscape

FibroGen Inc FGEN announced topline data from the Fortis Therapeutics-sponsored Phase 1 study of FG-3246 (also known as FOR46), a potential first-in-class anti-CD46 antibody drug conjugate (ADC) with an MMAE-containing payload.

In a dose-escalation and dose-expansion trial, the study enrolled patients with metastatic castration-resistant prostate cancer whose tumors have progressed on at least one androgen receptor-signaling inhibitor.

In the efficacy analysis, prostate-specific antigens (PSA) reductions of over 50% were observed in 36% of PSA evaluable patients. 

20% met the criteria of a partial response, or tumor reduction in size of over 30%, with a median duration of response of 7.5 months. The median radiographic progression-free survival (rPFS) in this heavily pretreated patient population was 8.7 months.

The most frequent adverse events were consistent with other MMAE-based ADCs and included infusion-related reactions, fatigue, weight loss, neutropenia, and peripheral neuropathy.

William Blair writes that initial FG-3246 results appear to offer numerically improved efficacy metrics relative to alternate novel hormone therapy. 

Although the FDA advises against drawing definitive conclusions solely from the point estimate of progression-free survival in single-arm studies, suggesting it be interpreted alongside hazard ratios, William Blair advocates for additional exploration of FG-3246 in prostate cancer due to the study’s heavily pretreated participants and inclusion of an unselected population.

William Blair writes that the company plans to enhance the therapeutic effectiveness of FG-3246 in two key ways:

• Firstly, it will utilize a dosing scheme based on adjusted body weight, inspired by AbbVie Inc’s ABBV approach with Elahere in ovarian cancer treatment. 
• Secondly, it will utilize an imaging agent called 89Zr-based CD46 PET to select patients most likely to benefit from FG-3246 in the Phase 2 study. 

FibroGen management intends to consult with the FDA about the development pathway and commence the Phase 2 study in the latter half of the year.

Price Action: FGEN shares are down 18.30% at $1.77 on the last check Wednesday.