Janus soars in early (Phase 1a) prostate cancer data that could challenge Novartis’ Pluvicto3 Dec 2024 12:35
The newest interim data from Janux Therapeutics’ Phase 1a prostate cancer trial have driven the company’s shares $JANX up 66% premarket Tuesday as investors mull the increasing probability of a buyout.
JANX007 is a tumor-activated T cell engager, or TRACTr, targeting both prostate-specific membrane antigen (PSMA) and CD3. The Phase 1a trial is testing once-weekly doses of 2 mg to 9 mg in patients with advanced or metastatic castration-resistant prostate cancer (mCRPC). The trial subjects had received a median of four prior lines of therapy, but had not yet been treated with Novartis’ radiopharmaceutical Pluvicto.
As of the Nov. 15 data cutoff, the Monday presentation shows that 16 patients had seen deep declines in prostate-specific antigen (PSA) levels; all achieved PSA50; 63% of patients achieved PSA90; and 31% hit PSA99. Three-quarters of the patients maintained PSA50 declines after at least three months, and 50% of patients maintained PSA90 declines at the same time point.
Janux said that these deep and durable PSA responses came irrespective of resistance driver mutation status or prior treatment with a taxane or androgen receptor pathway inhibitors. In RECIST-evaluable patients, confirmed and unconfirmed partial responses were seen in four of eight patients for an ORR of 50%. The disease control rate was 63%.
The safety of JANX007 also appears impressive. Cytokine release syndrome and related adverse events were “primarily limited to cycle 1 and grades 1 and 2,” according to Janux, as were treatment-related adverse events. The maximum tolerated dose was not reached.
Janux still has some way to go, though: Investors will need to judge how Monday’s data might translate into progression-free survival, the approval endpoint used in second- and third-line mCRPC Phase 3 trials, where control arms generally produce six to eight months and Pluvicto yielded 12 months.
Still, analysts from Leerink Partners suggested ahead of the readout that JANX007 could “effectively compete” with radioligand therapy, including Pluvicto, as well as antibody-drug conjugates. They suggest risk-adjusted peak sales of JANX007 could hit $1.5 billion in 2035.
That will require further trials in earlier settings, and Janux says the new data have allowed it to pin down two once-weekly step dose regimens for Phase 1b studies in second- and third-line mCRPC patients. These will be 0.3/1.5/6 mg and 0.3/2/9 mg.
Another question for investors is whether Janux will be the company to conduct such a study. The biotech was already being talked about as a takeover target, and potential buyers will find little in Monday’s data to put them off, even as the purchase price has climbed.
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