Pyxis Oncology is shelving a clinical-stage monoclonal antibody to focus on its lead antibody-drug conjugate (ADC) after sharing preliminary results for the ADC last month.
The Boston biotech is suspending clinical investments for PYX-106, a candidate Pyxis in-licensed from China-based Biosion in 2022 for $10 million upfront, according to a release shared after market close Dec. 19. Biosion retained rights in China to the anti-Siglec-15 antibody.
Pyxis evaluated PYX-106 as a monotherapy in a phase 1 trial that enrolled 45 patients with advanced solid tumors. The study, which was still listed as recruiting on ClinicalTrials.gov as of Nov. 25, found the candidate to be generally safe and well tolerated across all tested doses, which range from 0.5 mg/kg to 22.5 mg/kg. A maximum tolerated dose wasn’t established.
Pyxis didn't mention an objective response from the study, an omission William Blair analysts interpret as "PYX-106 not providing any meaningful clinical benefit," according to a Dec. 19 note. Given that interpretation, the analyst agrees with the company's decision to discontinue the program.
“Deprioritizing the PYX-106 clinical program as a monoclonal antibody represents a strategic and judicious use of our resources, allowing us to focus on advancing PYX-201,” Pyxis CEO and President Lara Sullivan, M.D., said in the release.
Almost exactly one month ago, the biotech shared "encouraging" phase 1 dose-escalation results on PYX-201—which was originally in-licensed from Pfizer—in a range of solid tumors, including in tough-to-treat head and neck cancer.
However, even after the data drop, PYX-201 is still “difficult to differentiate among emerging investigational drugs” in that indication, William Blair analysts wrote in a Nov. 21 note to clients. That challenge is likely what sent the biotech’s stock tumbling 40% that week—and more than 60% over the last month.
In the Dec. 19 note, William Blair's Andy Hsieh, Ph.D., doubled down on the sentiment, writing that "PYX-201’s clinical activity might not be sufficient to impact the treatment paradigm."
Hsieh also noted that expectations from the Street were “low” because of the “historical development challenges” with these types of antibodies, and, “accordingly, we do not ascribe any value to the program.”
Unsurprisingly, then, they “agree with management’s decision to discontinue further investments into the program,” adding that: “We continue to believe that while active, PYX-201’s clinical activity might not be sufficient to impact the treatment paradigm in head and neck cancer.”
Despite the poor reception from investors, Pyxis is forging ahead with plans to launch both monotherapy and combination therapy expansion trials for PYX-201 early next year. The trials include a front-line head and neck squamous cell carcinoma study assessing the ADC in combination with Keytruda, plus another Keytruda combo among patients with HR+/HER2- and triple-negative breast cancer.
The biotech’s current cash runway is expected to fund the planned trials and stretch into the second half of 2026, according to the release.
Since emerging in 2019, Pyxis’ pipeline grew with a $152 million series B and an in-licensing deal with Pfizer for ADCs PYX-201 and PYX-203 in March 2021. The biotech also touted a third ADC, PYX-202, that was licensed from LegoChem Biosciences in 2020.
The biotech then went public and has endured the brunt of biotech’s bearish market for the last few years now.
Last November, in efforts to save cash, Pyxis cut down its workforce by 40% following an all-stock acquisition of Apexigen, a deal valued at around $10.7 million. Pyxis has since out-licensed three of Apexigen’s programs, with PYX-201 now the only clinical candidate remaining in the company’s internal pipeline.