Preclinical data on CBO-212, a CD73-targeting drug-Fc conjugate (DFC) candidate being developed by Cidara Therapeutics, were presented at the ESMO Targeted Anticancer Therapies Congress (ESMO TAT) in Paris, March 6-8, 2023.[1]

The investigational agent consist of a multi-valent conjugate of a novel small molecule CD73 inhibitor to a proprietary immune-silent hIgG1 Fc. It combines the strengths of small molecule inhibitors and antibodies targeting CD73 and is based on the Cidara’s Cloudbreak® technology platform.

Targeting CD73
CD73 contributes to immune evasion in solid tumors by producing immune-suppressive adenosine in the tumor microenvironment. CD73’s main function is to convert extracellular ATP to immunosuppressive adenosine in concert with CD39 in normal tissues to limit excessive immune response. However, tumors are able to take advantage of the CD73-mediated adenosinergic mechanism to protect them from immune attack. [2]

CBO-212 was evaluated in cell-free and cell-based assays. Functional activity was measured in a PBMC rescue assay in the presence of AMP and binding to cancer cells was measured in the presence and absence of AMP by flow cytometry.

CD73 internalization was determined using MDA-MB-231 cells. Pharmacokinetic (PK) studies were conducted in Balb/c mice. Plasma concentrations were measured using an anti-hIgG in combination with CD73 capture ELISA.

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Efficacy of CBO-212 was evaluated in syngeneic mouse models with established CT26.WT tumors.

“The preclinical data for CBO-212, a potent, AMP-competitive CD73 inhibitor, presented at ESMO TAT represent important progress for us in oncology, as these nonclinical results are the first supporting the anti-tumor potential of a Cloudbreak product candidate,” noted Jeffrey Stein, Ph.D. president and chief executive officer of Cidara.

CBO-212 is a first-in-class CD73 targeting drug-Fc conjugate, which comprises a multi-valent conjugate of a novel small molecule CD73 inhibitor to a proprietary immune-silent hIgG1 Fc.  The investigational drug is based on the company’s proprietary Cloudbreak® technology platform which is designed to couple targeted small molecule and peptide drugs to a human antibody fragment (Fc).

These highly potent, long-acting drug-Fc conjugates are designed to inhibit specific disease targets while simultaneously engaging the immune system.*

CBO-212 combines the strengths of small molecule inhibitors and monoclonal antibodies targeting CD73.

Preclinical development
Researchers at Cidara investigated CBO-212. In both cell-free and cell-based CD73 inhibition assays, CBO-212 IC50 was observed in single digit nM, making the investigational agent superior to small molecule inhibitors and anti-CD73 antibodies in clinical development. In contrast to most anti-CD73 antibodies, CBO-212 demonstrated complete enzyme inhibition. CBO-212 also demonstrated an EC50 in a human PBMC rescue assay of 6 nM, which was equivalent to small molecule inhibitor controls and approximately 100-fold more potent than anti-CD73 antibody controls.

Summary
The presented preclinical studies evaluated the functional activity, internalization and inhibition of CD73 by CBO-212 in both cell-free and cell-based assays. There

  • CBO-212 inhibited cell-anchored and soluble forms of CD73, both of which can contribute to immune-suppressive adenosine production in the tumor microenvironment, whereas positive control CD73 inhibitor antibodies currently in clinical development acted primarily on cell-anchored CD73.
  • CBO-212 restored activation of human peripheral blood mononuclear cells suppressed with adenosine monophosphate to a greater extent than the antibodies comparators, and similar to the small molecule inhibitors tested.
  • CBO-212 triggered CD73 internalization, similar to some anti-CD73 antibodies. In animal studies wye mice, CBO-212 demonstrated long half-life and stability, while in a syngeneic mouse colon cancer model, a single 20 mg/kg dose of CBO-212 resulted in 37.9% relatiive tumor growth inhibition (TGI; P=0.0152).

Unlike tested small molecule inhibitors currently in development, the multivalent presentation of CD73 inhibitors on CBO-212 induced receptor internalization and subsequent reduction of CD73 receptors expressed on a human breast cancer cell line.
These attributes, coupled with the long half-life mediated by the CD73-targeting drug-Fc conjugate domain, led to significant tumor reduction in a mouse syngeneic tumor model after a single dose of CBO-212.

“We are initially focused on CD73 due to its documented contribution to immune evasion through the production of immune-suppressive adenosine in the tumor microenvironment.” Stein added.

“We believe that a CD73-targeted DFC, which combines positive attributes of small molecule and monoclonal antibody inhibitors, has the potential to ultimately provide a meaningful solution for patients.”

Cidara is currently advancing CD421, which is an enhanced version of CBO-212 that confers reduced immunogenic properties.

Note: * In addition to multiple oncology programs, Cidara Therapeutics is advancing its antiviral DFC CD388 through Phase 1 and Phase 2a clinical trials in partnership with Janssen for the universal prevention and treatment of influenza. Cidara is also advancing DFC programs to target other life-threatening viruses, such as SARS-CoV-2.

Reference
[1] Levin J, Döhrmann S, Dedeic N, Almaguer A, Zuill D, Abelovski E, Grewal R, Fortier J, Zhao, et al. 45P – Discovery of CBO-212, a first-in-class drug Fc-conjugate (DFC), targeting CD73 in cancer. Presented during the ESMO Targeted Anticancer Therapies (TAT ) Conference, held March 6 – 8, 2023, Paris France.
[2] Roh M, Wainwright DA, Wu JD, Wan Y, Zhang B. Targeting CD73 to augment cancer immunotherapy. Curr Opin Pharmacol. 2020 Aug;53:66-76. doi: 10.1016/j.coph.2020.07.001. Epub 2020 Aug 7. PMID: 32777746; PMCID: PMC7669683.

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