On November 4, 2023 Promontory Therapeutics Inc., a Phase 2 stage biotech company advancing immunogenic small molecule approaches in oncology, reported data demonstrating the molecular mechanism of its lead therapeutic candidate, PT-112, and its ability to induce immunogenic cell death (ICD) in cancer cells (Press release, Promontory Therapeutics, NOV 4, 2023, View Source [SID1234636971]). Data suggest that PT-112-induced ICD is mediated by endoplasmic reticulum (ER) and mitochondrial stresses, which are specific intra-cellular events that comprise part of the larger ICD mechanism. The presentation was made at the Society for Immunotherapy of Cancer (SITC) (Free SITC Whitepaper)’s (SITC) (Free SITC Whitepaper) 38th Annual Meeting, taking place November 1-5, 2023 in San Diego.
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The work was designed in collaboration with the Galluzzi Lab at Weill Cornell Medical College in New York, in order to elucidate the sequence of events – beginning with inhibition of ribosomal biogenesis and culminating in selective ICD – underlying PT-112’s immune effects. Analyzing a panel of mouse cell lines engineered to lack specific genes involved in mitochondrial apoptosis (Bcl2, Bax and Bak1), flow cytometry, immunoblotting, RT-PCR, and immunofluorescence microscopy were used to determine the impact of PT-112 on ER and mitochondrial stress, as well as immunogenic signaling.
"Our continued studies of PT-112 provide mechanistic insights for this promising immunogenic small molecule, which has shown clinical activity in patients with a variety of cancers," said Promontory Therapeutics Senior Vice President of Research and Development Tyler Ames, PhD. "This particular work sheds light on how PT-112 encourages the immunogenic cell death of cancerous cells through ER stress and mitochondrial dysfunction, both of which are known to contribute to immune signaling."
Study findings include:
PT-112 drives ER stress and mitochondrial dysfunction, which promote ICD.
PT-112 effects on mitochondria included increases in mitochondrial mass and reactive oxygen species, changes in membrane polarization, and the release of mitochondrial DNA into the cytosol, a potent immunogenic signal. Some of these effects were impacted by the absence of Bax and Bak1.
PT-112 elicits the phosphorylation of eukaryotic translation initiation factor 2 subunit alpha (EIF2S1, best known as eIF2α), indicating ER stress and the activation of the integrated stress response (ISR).
There is an increase in the levels of Ifnb1 mRNA after PT-112 exposure, indicating PT-112 induces type 1 interferon responses.
PT-112 is the subject of ongoing Phase 2 clinical trials for metastatic castrate-resistant prostate cancer and thymic epithelial tumors, and a completed Phase 2a trial in non-small cell lung cancer. In previous mechanism of action research, data showed that PT-112 causes ribosomal biogenesis inhibition and nucleolar stress, which is the likely driver of PT-112-induced cancer organelle stresses and ICD.
For more information about Promontory Therapeutics and PT-112, visit www.PromontoryTx.com.
About PT-112
PT-112 is a novel inhibitor of ribosomal biogenesis, which leads to selective immunogenic cancer cell death (ICD). PT-112’s mechanism of action governs intracellular events that cause the release of damage associated molecular patterns, known to bind to dendritic cell and natural killer cell receptors, prompting an anti-cancer immune response. PT-112’s potential best-in-class ICD effects may create the conditions for effective and durable responses to treatment. The first in-human study of PT-112 demonstrated an attractive safety profile and evidence of long-lasting responses among heavily pre-treated patients and data were published in eClinicalMedicine, part of The Lancet. The company’s Phase 2 study of PT-112 in late-stage metastatic castration-resistant prostate cancer patients is underway in the United States and France. An active Phase 2 trial is also on-going with the National Cancer Institute utilizing PT-112 in thymic epithelial tumors, a rare disease with no FDA approved drug, for which PT-112 has received FDA Orphan Drug designation. An additional Phase 2a study has been successfully completed for non-small cell lung cancer in combination with PD-L1 inhibition.