Janux impresses Wall Street with new prostate cancer drug results

Shares of Janux Therapeutics surged to record highs following the release of study results for a drug that, if ultimately successful in testing, would represent a new type of therapy for prostate cancer. 

The findings come from an early-stage study testing the biotechnology company’s therapy, dubbed JANX007, in 16 people with a form of advanced prostate cancer. Data Janux first disclosed earlier this year vaulted the company’s market value past $2 billion. While early and from a small clinical trial, the new results announced Monday afternoon pushed Janux’s shares nearly 75% higher, changing hands Tuesday morning at more than $70 apiece.

The company is “exceeding investor expectations and raising the bar” in so-called metastatic, castration-resistant prostate cancer, wrote William Blair analyst Matt Phipps, in a Tuesday note to investors. He and multiple other Wall Street analysts raised their share price targets for Janux.

Janux’s drug is what’s known as a T cell engager, a type of dual-acting antibody that draws immune cells to cancerous ones. Several T cell engagers are currently available to treat blood malignancies, but solid tumors have proven more elusive targets. T cell engagers are also associated with side effects, like a kind of overactive immune response known as cytokine release syndrome, that can require drugmakers to lower dosing. 

Janux’s answer is a method of “masking” its T cell engagers so they don’t interfere with healthy tissue but still target malignant cells. The approach is designed to widen the range of effective and safe doses, sidestepping some of the problems other T cell engagers have had with solid tumors. The new results “further demonstrated the therapeutic window-widening value proposition,” wrote Leerink Partners analyst Jeffrey La Rosa on Tuesday. 

Janux is testing JANX007 in metastatic, castration-resistant prostate cancer, a target of several large companies and a market that analysts at the investment bank Stifel believe could surpass $10 billion annually in the U.S. alone by next decade. Novartis’ closely watched radiopharmaceutical drug Pluvicto, for instance, has already surpassed $1 billion in sales this year. The Swiss company has said yearly sales could reach $5 billion. 

In its Phase 1a study, Janux enrolled patients who’d received a median of four prior treatments. As of a Nov. 15 cutoff, 16 who hadn’t yet received Pluvicto achieved at least a 50% reduction in prostate-specific antigens, a marker indicative of a treatment benefit in prostate cancer.

The durability of those responses “looks promising,” wrote Phipps, of William Blair, with three quarters of the patients with at least a 50% decline in PSA levels maintaining those results after at least three months. Half of the study volunteers who had 90% PSA declines saw their responses hold for at least three months as well. Four of the eight who could be evaluated for tumor responses had a partial response to treatment, Janux said. 

Notably, instances of CRS, as well as overall treatment-related side effects, were largely mild to moderate in severity. Janux said it hasn’t yet found the maximal tolerated dose for JANX007, indicating it could test higher doses.  

Uncertainties remain, given the small patient numbers, “still-early durability” and “relatively modest” efficacy signal so far, wrote Leerink’s La Rosa. Nonetheless, the company demonstrated “best-in-disease” effects on PSA and a “best-in-class, differentiated safety profile,” he added. 

Janux has selected doses for Phase 1b expansion trials in patients who are earlier in their disease course and haven’t yet received Pluvicto. Updated results are expected next year. 

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