[Background on medical need in hematology]Even though significant progress has been made in a number of hematological malignancies in recent years, an unmet medical need still remains in indications such as multiple myeloma (MM), chronic lymphocytic leukemia (CLL) or acute myeloid leukemia (AML) due to refractory disease, severe adverse events or the failure to achieve sustained minimal residual disease. As a consequence, novel therapies are required to prevent relapse, be safer in administration and to target residual disease. We present here for the first time a novel and innovative therapeutic approach with the potential to treat patients suffering from hard-to-treat hematological malignancies based on the tumor´s pathophysiology and reactive oxygen species (ROS) phenotype.

[Background on Ag5]TMC are created by combining the atoms of certain transition metals under specific conditions to form novel molecules with entirely distinct properties from "traditional" metal. For example, silver can be used to create clusters of different and defined sizes, based on the number of atoms making up the final drug candidate. More specifically, Ag5 contains five silver atoms arranged in a specific conformation, is the first TMC derived from this novel platform and has entirely different physiological properties than the three silver atom containing Ag3.

Ag5 is a water-soluble and heat stable molecule, it is orally bioavailable and a freely diffusible pan-tumor therapeutic. It selectively kills those cells with high ROS concentrations by oxidizing their antioxidant systems and subsequently drives these cells to programmed cell death. In consequence, Ag5 will preferentially kill cancer cells which typically have higher ROS levels, but will spare normal cells which display lower ROS due to their functional REDOX homeostasis.

More specifically, Ag5 efficiently catalyzes the oxidation of thiol groups of thioredoxins and peroxiredoxins and thereby drives sensitive cells above a threshold to irreversible protein misfolding, protein degradation and programmed cell death.

[Background on Ag5 experiments]We characterized Ag5 efficacy using a wide range ofin vitroassays and found potent Ag5 efficacy against a number of MM, CLL and AML cell lines with an IC50 in the low nM range. Ag5 sensitivity of all cell lines was correlated with ROS levels, more specifically superoxide, as measured by dihydroethidium (DHE) or MitoSOX. Furthermore, we were able to demonstrate that Ag5 treatment resulted in a concentration dependent cell cycle arrest in G1 phase, mitochondrial swelling and induction of apoptosis. Treatment of primary CLL tumor samples resulted in low nM efficacy. Finally, we could demonstrate that Ag5 was not only safely administered without any side effects in mouse and rat studies, but was equally effective as the stand-of-care bortezomib in a multiple myelomain vivomodel.

[Conclusion and clinical significance]In summary, Ag5 is a novel and innovative therapeutic candidate that was shown to be safe and effective in preclinical studies, and has the promise to address the unmet medical need in hard-to-treat hematological malignancies.

Keywords: Ag5, Therapeutic molecular cluster (TMC), Redox, ROS, catalysis, Ag3, AML, MM, CLL


Porto González:Arjuna:Research Funding.Carneiro:Arjuna:Research Funding.Lopez-Quintela:Arjuna:Current equity holder in private company.Treder:Arjuna:Current Employment.Dominguez:Arjuna:Current equity holder in private company.

Author notes


Asterisk with author names denotes non-ASH members.

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