Targeting nucleolin overcomes MCL-1-mediated venetoclax resistance in acute myeloid leukemia

BCL-2 inhibitors, such as venetoclax, have become a standard treatment for acute myeloid leukemia (AML), particularly for patients ineligible for intensive chemotherapy. However, a significant number of patients are refractory or acquire resistance, which remains a major clinical challenge. MCL-1, an anti-apoptotic Bcl-2 family protein, is well recognized to play critical roles in resistance to venetoclax treatment and there is a significant unmet need for the development of effective therapies that inhibit MCL-1 to overcome venetoclax resistance. Nucleolin (NCL) is a multifunctional protein frequently overexpressed on the surface of AML cells and is implicated in promoting cancer cell survival and drug resistance by regulating various oncogenic transcripts. This study provides the first evidence that NCL acts as an upstream regulator of MCL-1 and that inhibition of NCL can effectively overcome venetoclax resistance in AML by downregulating MCL-1. As a result, we found that the expression levels of NCL and MCL-1 were significantly elevated in venetoclax-resistant AML cell lines, and that siRNA-mediated genetic knockdown of NCL led to a significant reduction of MCL-1 expression levels along with a corresponding induction of cleaved caspase-3, confirming the activation of apoptosis. APTA-16 is a first-in-class therapeutic for AML that specifically targets NCL developed using aptamer-drug conjugation (APTA-DC) technology. To confirm the role of NCL in MCL-1-mediated venetoclax resistance, we treated venetoclax-resistant AML cell lines with Apta-16, and Apta-16 significantly reduced in both NCL and MCL-1 expression levels and activated caspase-3. Furthermore, in a C1498 syngeneic mouse model of venetoclax-resistance in vivo, Apta-16 monotherapy significantly improved the survival rate, whereas venetoclax showed no therapeutic benefit. In addition, we also confirmed that in vivo Apta-16 treatment markedly decreased intratumoral levels of NCL and MCL-1 expression.In conclusion, our findings demonstrate that the NCL-MCL-1 axis plays a critical role in mediating venetoclax resistance in AML and inhibition of NCL can be a promising strategy to disrupt this axis and overcome venetoclax resistance. Therefore, the results suggest that Apta-16 has strong potential as an effective therapy approach to overcome venetoclax resistance in in patients with relapsed or refractory AML. GLP safety/toxicity studies of APTA-16 have been completed, and orphan drug designation (ODD) was granted by FDA.