Patients with multiple myeloma (MM) carrying high-risk cytogenetic abnormalities (CA) have inferior outcome despite achieving similar complete response (CR) rates when compared to cases with standard-risk CA. This questions the legitimacy of CR as treatment endpoint for high-risk MM, and represents a biological conundrum regarding the nature of tumor reservoirs persisting after therapy in patients with standard- and high-risk CA. Here, we used next-generation flow (NGF) to evaluate measurable residual disease (MRD) in MM patients with standard- (N=300) vs high-risk CA (N=90) enrolled in the PETHEMA/GEM2012MENOS65 trial (NCT01916252), and to identify mechanisms determining MRD resistance in both patient subgroups (N=40). The 36-month progression-free and overall survival rates were higher than 90% in patients with undetectable MRD, with no significant differences (P≥0.202) between cases having standard- vs high-risk CA. Persistent MRD resulted in median progression-free survival of approximately three and two years in patients with standard- and high-risk CA, respectively (P<0.001). Further use of NGF to isolate MRD followed by whole-exome sequencing of paired diagnostic and MRD tumor cells, revealed greater clonal selection in patients with standard-risk CA, higher genomic instability with acquisition of new mutations in high-risk MM, and no unifying lost or acquired genetic abnormalities driving MRD resistance. Conversely, RNA sequencing of diagnostic and MRD tumor cells uncovered the selection of MRD clones with singular transcriptional programs and ROS-mediated MRD resistance in high-risk MM. Our study supports undetectable MRD as treatment endpoint for MM patients with high-risk CA and proposes characterizing MRD clones to understand and overcome MRD resistance.

Refractory or relapsed diffuse large B-cell lymphoma (DLBCL) often associates with the activated B-cell-like (ABC) subtype and genetic alterations that drive constitutive NF-κB activation and impair B-cell terminal differentiation. Here, we show that DNA damage response by p53 is a central mechanism suppressing the pathogenic cooperation of IKK2ca-enforced canonical NF-κB and impaired differentiation resulting from Blimp1 loss in ABC-DLBCL lymphomagenesis. We provide evidences that the interplay between these genetic alterations and the tumor microenvironment select for additional molecular addictions that promote lymphoma progression, including aberrant coexpression of FOXP1 and the B-cell mutagenic enzyme activation-induced deaminase, and immune evasion through major histocompatibility complex class II downregulation, PD-L1 upregulation, and T-cell exhaustion. Consistently, PD-1 blockade cooperated with anti-CD20-mediated B-cell cytotoxicity, promoting extended T-cell reactivation and antitumor specificity that improved long-term overall survival in mice. Our data support a pathogenic cooperation among NF-κB-driven prosurvival, genetic instability, and immune evasion mechanisms in DLBCL and provide preclinical proof of concept for including PD-1/PD-L1 blockade in combinatorial immunotherapy for ABC-DLBCL.

For millions of years, endogenous retroelements have remained transcriptionally silent within mammalian genomes by epigenetic mechanisms. Modern anticancer therapies targeting the epigenetic machinery awaken retroelement expression, inducing antiviral responses that eliminate tumors through mechanisms not completely understood. Here, we find that massive binding of epigenetically activated retroelements by RIG-I and MDA5 viral sensors promotes ATP hydrolysis and depletes intracellular energy, driving tumor killing independently of immune signaling. Energy depletion boosts compensatory ATP production by switching glycolysis to mitochondrial oxidative phosphorylation, thereby reversing the Warburg effect. However, hyperfunctional succinate dehydrogenase in mitochondrial electron transport chain generates excessive oxidative stress that unleashes RIP1-mediated necroptosis. To maintain ATP generation, hyperactive mitochondrial membrane blocks intrinsic apoptosis by increasing BCL2 dependency. Accordingly, drugs targeting BCL2 family proteins and epigenetic inhibitors yield synergistic responses in multiple cancer types. Thus, epigenetic therapy kills cancer cells by rewiring mitochondrial metabolism upon retroelement activation, which primes mitochondria to apoptosis by BH3-mimetics. Significance: The state of viral mimicry induced by epigenetic therapies in cancer cells remodels mitochondrial metabolism and drives caspase-independent tumor cell death, which sensitizes to BCL2 inhibitor drugs. This novel mechanism underlies clinical efficacy of hypomethylating agents and venetoclax in acute myeloid leukemia, suggesting similar combination therapies for other incurable cancers. This article is highlighted in the In This Issue feature, p. 995

Normal cell counterparts of solid and myeloid tumors accumulate mutations years before disease onset; whether this occurs in B lymphocytes before lymphoma remains uncertain. We sequenced multiple stages of the B lineage in elderly individuals and patients with lymphoplasmacytic lymphoma, a singular disease for studying lymphomagenesis because of the high prevalence of mutated MYD88 . We observed similar accumulation of random mutations in B lineages from both cohorts and unexpectedly found MYD88 L265P in normal precursor and mature B lymphocytes from patients with lymphoma. We uncovered genetic and transcriptional pathways driving malignant transformation and leveraged these to model lymphoplasmacytic lymphoma in mice, based on mutated MYD88 in B cell precursors and BCL2 overexpression. Thus, MYD88 L265P is a preneoplastic event, which challenges the current understanding of lymphomagenesis and may have implications for early detection of B cell lymphomas.

To determine the effect of retinoic acid (RA) in neuroblastoma we treated RA sensitive neuroblastoma cell lines with 9-cis RA or ATRA for 9 days, or for 5 days followed by absence of RA for another 4 days. Both isomers induced apoptosis and reduced cell density as a result of cell differentiation and/or apoptosis. Flow cytometry revealed that 9-cis RA induced apoptosis more effectively than ATRA. The expression profile of apoptosis and survival pathways was cell line specific and depended on the isomer used.

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Hydroxysteroid (17-beta) dehydrogenase (HSD17B) are the enzymes responsible for the reversible interconversion of 17-hydroxy and 17-keto steroids. The human and mouse type 8 17b-HSD (HSD17B8) selectively catalyze the conversion of estradiol (E2) to estrone (E1). We previously described that HSD17B8 is transcriptionally regulated by C/EBPb, and that C/EBPb is bound to CCAAT boxes located at K5 and K46 of the transcription start site in basal conditions in HepG2 cells. Furthermore, ectopic expression of C/EBPb transactivated the HSD17B8 promoter activity. Here, we show that HSD17B8 expression is up-regulated in response to E2 in the estrogen receptor a (ERa) positive MCF-7 cells. Results showed that this induction is mediated by ERa because i) E2 did not induce HSD17B8 expression in ERa negative HepG2 cells, ii) ectopic expression of ERa restored E2-induced HSD17B8 expression, and iii) this induction was blocked by the anti-ER ICI 182 780. Additional experiments showed that no estrogen response element was necessary for this regulation. However, the CCAAT boxes located at the HSD17B8 proximal promoter were required for E2-induced transcription. Furthermore, co-immunoprecipitation studies revealed tethering of ERato C/EBPb in response to E2 in cells expressing ERa. Additionally, chromatin immunoprecipitation assays demonstrated that, in response to E2, ERa is recruited to the CCAAT boxes in which C/EBPb is already bound. Taken together, our results reveal that ERa is involved in the transcriptional regulation of HSD17B8 gene in response to E2 through its interaction with C/EBPb.