On October 31, 2017 Siamab Therapeutics, Inc., a biopharmaceutical company developing novel cancer immunotherapies, reported the presentation of new preclinical data demonstrating the safety of its novel anti-Sialyl-Tn (STn) antibody drug conjugates (ADCs) in multiple animal models, including non-human primates (NHPs) (Press release, Siamab Therapeutics, OCT 31, 2017, View Source [SID1234521355]). These results add to the company’s efficacy data findings showing that its anti-STn antibody therapeutics inhibit tumor progression in cell-line-derived and patient-derived xenograft (PDX) ovarian cancer and pancreatic cancer mouse models, with complete regression observed in some treatment arms. The preclinical efficacy and safety data were presented in a poster presentation at the 2017 AACR (Free AACR Whitepaper)-NCI-EORTC AACR-NCI-EORTC (Free AACR-NCI-EORTC Whitepaper) International Conference on Molecular Targets and Cancer Therapeutics (EORTC-NCI-AACR) (Free ASGCT Whitepaper) (Free EORTC-NCI-AACR Whitepaper), held October 26-30, 2017, in Philadelphia.
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Siamab’s platform enables the development of highly specific monoclonal antibody (mAb) therapeutics that target cancer cell surface glycans called tumor-associated carbohydrate antigens (TACAs), a novel class of cancer-specific antigens. TACAs are implicated in immune suppression, chemoresistance, and a cancer stem cell (CSC) phenotype.
“Our lead ST1 program shows compelling efficacy and safety across a range of PDX and xenograft studies, underscoring the promise of our anti-STn antibody approach to treat chemoresistant solid tumors,” said Jeff Behrens, president and chief executive officer of Siamab. “The new data from a pilot pharmacokinetic/toxicity study in primates demonstrate the favorable safety and tolerability of ST1 in large animals. The NHP results are extremely encouraging and provide an important step to de-risk IND-enabling GLP toxicity studies, which we plan to initiate in 2018.”
The poster presentation, titled “Humanized anti-Sialyl-Tn monoclonal antibody-drug conjugates (ADCs) inhibit tumor growth in vitro and in vivo,” was presented during the Therapeutic Agents: Biological poster session. In the poster, Siamab scientists and collaborators reported data demonstrating anti-tumor effect in vitro utilizing humanized anti-STn ADCs as well as inhibition of tumor progression in vivo in both cell line and PDX ovarian cancer models with complete regressions observed in some treatment groups. No significant weight loss was observed for any of the treatment groups in these models indicating the therapy was well tolerated by all the groups. In addition, the poster featured new safety data demonstrating Siamab’s anti-STn ADC has an excellent safety profile through the completion of a non-GLP pilot pharmacokinetic/toxicity study in non-human primates. Two doses were administered at days 1 and 22. Dose levels were 1mg/kg, 3mg/kg, and 6mg/kg. No weight loss or deaths occurred in the study and no gross pathology changes were observed in all organs examined. All clinical chemistry results (liver, kidney function, etc.) were normal throughout the study.
ST1, Siamab’s lead antibody program targeting STn, is in late stage preclinical development for the treatment of solid tumors. The elevated presence of STn—a key TACA observed in a number of solid tumors, including ovarian, prostate, pancreatic, gastric, and colon—is associated with metastatic disease, poor prognosis, and reduced overall survival. Elevation of STn expression is linked to chemotherapy resistance and enables tumors to evade the host immune system. Siamab has also identified the presence of STn on myeloid-derived suppressor cells (MDSCs), which are major regulators of immune response in cancer and influence the tumor microenvironment by suppressing T cells. STn is a major reported constituent of two established CSC biomarkers, CD44 and MUC1, which reside on both CSCs and mature malignant cells in some cancer types.
Siamab is utilizing STn-selective antibodies to develop both tissue- and serum-based biomarker assays with the potential to become companion diagnostics for both the stratification of patients as well as tools for assessing the pharmacodynamic action of the anti-STn therapeutic in the clinic.
Siamab recently announced it has entered into a strategic discovery collaboration with Boehringer Ingelheim with the goal of developing anti-cancer therapeutics targeting TACAs. Siamab will apply its proprietary technology platform to generate TACA-specific antibodies for use in multiple solid tumor applications. Financial terms of the agreement were not disclosed.