Precision Targeting of Ion Channel Blocker for the Treatment of AML

The survival rate of patients with acute myeloid leukemia (AML) remains modest and thus, there is a clear need for advanced treatments. Here we describe two drug leads for AML that inhibit cellular sodium release without requiring drug internalization. EDC1 and EDC8 are two very potent extracellular antibody drug conjugates that selectively inhibit the all-important Na,K-ATPase, an ion pump required by cells to export excess sodium and to maintain ion gradients needed to import and export many important nutrients and waste products. We first demonstrate that dysadherin (a known metastatic cancer marker), is expressed on the surface many types of AML cell lines and can be used to direct Na,K-ATPase inhibitors using EDC1. We next demonstrate that ATRA inducible AML cells types are selectively destroyed with Na,K-ATPase inhibitors targeted to CD38 using EDC8 and ATRA.

Since dysadherin expression is a known to be correlated to metastasis and stemness but yet to be studied in AML, we first analyzed a number of leukemia cell lines and AML patient samples for dysadherin expression by analyzing their surface expression and/or their sensitivity to EDC1. We observed that many cultured AML cells express dysadherin and are sensitive to EDC1 with EC50 values ranged from 0.02 to 1.0 nanoMolar and cell viability after 72 hours of exposure ranging from zero to 10%. For the three primary AML patient specimens analyzed, dysadherin expression was seen. Interestingly, in two of these three samples, the majority of intense staining was found in the CD123+ CD34+ population.

Since CD38 expression and inducible expression can now be diagnosed in patients with AML, we analyzed if ATRA was required to sensitize AML to EDC8. Using multiple leukemic cell lines (HL60, U937, MV411, KG1, K562, and OCI/AML3) known to express CD38 with or without requiring ATRA, we analyzed EDC8 sensitivity before and after ATRA addition. We found that CD38 expression was required for EDC8 sensitivity and once expressed, EDC8 displayed potent activity with few viable cells detectable.

Further studies analyzing dysadherin and CD38 expression in patient samples are needed to better understand the AML cell populations that may be affected by these EDCs but these results show the potential of this new type of antibody drug conjugate technology for the treatment of AML. EDCs that inhibit a required membrane bound ion pump with the precision of antibodies without requiring internalization may provide a new tool for doctors in their fight against AML.