Targeting the Fanconi Anemia/BRCA Pathway Circumvents Drug Resistance in Multiple Myeloma

Abstract

The Fanconi Anemia (FA)/BRCA DNA damage repair pathway plays a pivotal role in the cellular response to replicative stress induced by DNA alkylating agents and greatly influences drug response in cancer treatment. We recently reported that FA/BRCA genes are overexpressed and causative for drug resistance in human melphalan-resistant multiple myeloma (MM) cell lines. However, the transcriptional regulation of the FA/BRCA pathway is not understood. In this report, we describe for the first time a novel function of the NF-κB subunits, RelB/p50, as transcriptional activators of the FA/BRCA pathway. Specifically, our findings point to constitutive phosphorylation of IκB Kinase IKKα and subsequent alterations in FANCD2 expression and function as underlying events leading to melphalan resistance in repeatedly exposed MM cells. Inhibiting NF-κB by siRNA, blocking the IKK complex with BMS-345541, or using the proteasome inhibitor bortezomib drastically reduced FA/BRCA gene expression and FANCD2 protein expression in myeloma cells, resulting in diminished DNA damage repair and enhanced melphalan sensitivity. Importantly, we also found that bortezomib decreases FA/BRCA gene expression in multiple myeloma patients. These results show for the first time that NF-κB transcriptionally regulates the FA/BRCA pathway, and provide evidence for targeting FA-mediated DNA repair to enhance chemotherapeutic response and circumvent drug resistance in myeloma patients.

Monitoring a Nuclear Factor-κB Signature of Drug Resistance in Multiple Myeloma

“…Although MM patients initially respond to chemotherapy, treatment failure is inevitable because of the emergence of drug resistance. Because of the importance of detecting acquired drug resistance (ADR) for patient assessment and treatment, numerous mechanisms of ADR have been elucidated for MM in vitro, utilizing cell line models developed by chronic exposure to chemotherapy (2)(3)(4)(5)(6)(7). These models were designed to identify potential drug targets to reverse ADR as well as to discover prognostic or chemopredictive biomarkers that could be translated to assessment of MM patients.…”

“…The biology of one such model of ADR, the 8226/LR5 cell line, selected by chronic exposure of RPMI-8226 MM cells to the DNA-damaging agent, melphalan, has been extensively characterized, leading to the identification of causative mech-anisms of drug resistance in MM, including activation of NFB signaling networks, modulated expression of Bcl-2 family members, and enhanced DNA damage repair capacity (2,(5)(6)(7). The relationships between these different protein networks have been defined using traditional cancer biology techniques (Fig.…”

“…NFB transactivation has also been shown to inhibit apoptosis and to contribute to drug resistance in cancer cells, including MM (9,10). Moreover, in the melphalan-selected 8226/LR5 myeloma cell line, constitutive activation of NFB (RelB/p50) signaling regulates expression of apoptotic proteins (particularly Bcl-x L ) and DNA damage repair via the Fanconi Anemia (FA) pathway, and confers drug resistance (7). As a result, the inhibition of NFB is a viable strategy to reverse ADR in MM.…”

“…Experimental evidence indicates that NFB subunits may be important prognostic or predictive biomarkers in MM. Therefore, expression measurements of NFB proteins may be useful in directing and optimizing therapeutic regimens for advancing personalized medicine (7,11,12).…”

“…The repair of the interstrand crosslinks contributes to drug resistance in MM and other malignancies (31,32). Furthermore, enhanced DNA-repair capacity correlates with the development of drug resistance in cell lines (5,7) as well as with poor patient outcomes (33,34). Therefore, evaluation of DNA repair pathways could be a viable approach for predicting response and detecting resistance to DNA-damaging agents, including melphalan.…”