Robert N. Eisenman

MYC is one of the most frequently dysregulated oncogenic drivers across many cancers, yet direct therapeutic targeting has remained difficult because its function is mediated by disordered regions and transient protein-protein interactions. Here we design proteins that bind epitopes within regions of MYC whose sequence is conserved between human and mouse, including intrinsically disordered motifs required for oncogenic activity. In vitro, the designs bind MYC with nanomolar affinity and in cells they engage MYC, disrupt interactions with MAX, and remodel MYC-associated protein complexes. Expression of the binders decreases cell proliferation across diverse MYC-dependent hematopoietic, liver, pancreatic, and patient-derived tumor models, and in an orthotopic pancreatic cancer model, binder-expressing tumor cells were selectively depleted. This work establishes de novo protein design as a generalizable strategy to therapeutically target intrinsically disordered transcription factors. One-sentence summary: We developed a panel of de novo designed intracellular protein binders that target conserved functional regions of MYC with nanomolar affinity, remodel MYC complexes and interaction networks in cells, suppress proliferation across MYC-dependent cancer models, and are depleted from orthotopic pancreatic tumors in vivo.

MYC amplification contributes to poor survival and outcome in pancreatic ductal adenocarcinoma (PDAC). Here we show that in PDAC cell lines with amplified MYC, MondoA is required for viability, facilitating proliferation while suppressing apoptosis in vitro and in vivo. Transcriptional and genomic profiling demonstrates that loss of MondoA leads to altered expression of direct MondoA targets as well as MYC target genes and is accompanied by shifts in genomic occupancy of MYC, MNT, and the MondoA paralog ChREBP. This altered genomic binding by MYC network members is associated with transcriptional perturbation of multiple metabolic and stress pathways, as well as global changes in N6-methyladenosine modification (m ⁶ A) of messenger RNA (mRNA). MondoA inhibition disrupts coordination between MYC network members and the Integrated Stress Response (ISR), resulting in decreased translation of ATF4 mRNA, discordant gene regulation of shared targets of MYC and ATF4 and, ultimately, apoptosis. Reestablishing ATF4 protein expression rescues the diminished viability due to loss of MondoA expression or activity, providing direct evidence of a link between deregulated MYC and the transcriptional machinery of the ISR. Last, we find that small-molecule inhibition of MondoA is lethal in a subset of PDAC cell lines, including patient-derived organoids, suggesting that the ability to target MYC via chemical inhibition of MondoA transcriptional activity may have broad efficacy.

MYC amplification contributes to poor survival and outcome in pancreatic ductal adenocarcinoma (PDAC). Here we show that in PDAC cell lines with amplified MYC, MondoA is required for viability, facilitating proliferation while suppressing apoptosis in vitro and in vivo . Transcriptional and genomic profiling demonstrates that loss of MondoA leads to altered expression of direct MondoA targets as well as MYC target genes and is accompanied by shifts in genomic occupancy of MYC, MNT, and the MondoA paralog ChREBP. This altered genomic binding by MYC network members is associated with transcriptional perturbation of multiple metabolic and stress pathways, as well as global changes in N6-methyladenosine modification (m ⁶ A) of mRNA. MondoA inhibition disrupts coordination between MYC network members and the Integrated Stress Response (ISR), resulting in decreased translation of ATF4 mRNA, discordant gene regulation of shared targets of MYC and ATF4 and, ultimately, apoptosis. Re-establishing ATF4 protein expression rescues the diminished viability due to loss of MondoA expression or activity, providing direct evidence of a link between deregulated MYC and the transcriptional machinery of the ISR. Lastly, we find that small-molecule inhibition of MondoA is lethal in a subset of PDAC cell lines, including patient-derived organoids, suggesting that the ability to target MYC via chemical inhibition of MondoA transcriptional activity may have broad efficacy. Significance Statement: This report investigates mechanisms underlying the dependence of MYC-amplified pancreatic cancer cells on the MYC network member MondoA which, as a heterodimer with MLX, is a nutrient-sensing transcription factor. We show this dependency is linked to genomic crosstalk between MYC, components of the proximal MYC network, and the master regulator of the integrated stress response, ATF4. Moreover, we find that small molecule inhibitors of MondoA-MLX transcriptional activity abrogate survival of MYC-amplified PDAC lines and patient derived organoids. The significance of this work relates to its focus on a unique vulnerability intrinsic to MYC, an oncogenic driver associated with a wide range of cancers, which is considered to be “undruggable”.

The MYC transcription factor requires MAX for DNA binding and widespread activation of gene expression in both normal and neoplastic cells. Inactivating mutations in MAX are associated with a subset of neuroendocrine cancers including pheochromocytoma, pituitary adenoma, and small cell lung cancer. Neither the extent nor the mechanisms of MAX tumor suppression are well understood. Deleting Max across multiple mouse neuroendocrine tissues, we find that Max inactivation alone produces pituitary adenomas, while Max inactivation cooperates with Rb1 / Trp53 loss to accelerate medullary thyroid C cell and pituitary adenoma development. In the thyroid tumor cell lines, MAX loss triggers a marked shift in genomic occupancy by other members of the MYC network (MNT, MLX, MondoA) supporting metabolism, survival, and proliferation of neoplastic neuroendocrine cells. Our work reveals MAX as a broad suppressor of neuroendocrine tumorigenesis through its ability to maintain a balance of genomic occupancies among the diverse transcription factors in the MYC network.

The MYC transcription factor requires MAX for DNA binding and widespread activation of gene expression in both normal and neoplastic cells. Surprisingly, inactivating mutations in MAX are associated with a subset of neuroendocrine cancers including pheochromocytoma, pituitary adenoma and small cell lung cancer. Neither the extent nor the mechanisms of MAX tumor suppression are well understood. Deleting Max across multiple mouse neuroendocrine tissues, we find Max inactivation alone produces pituitary adenomas while Max loss cooperates with Rb1 / Trp53 loss to accelerate medullary thyroid C-cell and pituitary adenoma development. In the thyroid tumor cell lines, MAX loss triggers a striking shift in genomic occupancy by other members of the MYC network (MNT, MLX, MondoA) supporting metabolism, survival and proliferation of neoplastic neuroendocrine cells. Our work reveals MAX as a broad suppressor of neuroendocrine tumorigenesis through its ability to maintain a balance of genomic occupancies among the diverse transcription factors in the MYC network. Teaser: MAX inactivation deregulates multiple transcription factors to induce neuroendocrine cancers

Oncogenic activation of MYC in cancers predominantly involves increased transcription rather than coding region mutations. However, MYC-dependent lymphomas frequently acquire point mutations in the MYC phosphodegron, including at threonine 58 (T58), where phosphorylation permits binding via the FBW7 ubiquitin ligase triggering MYC degradation. To understand how T58 phosphorylation functions in normal cell physiology, we introduced an alanine mutation at T58 (T58A) into the endogenous c-Myc locus in the mouse germline. While MYC-T58A mice develop normally, lymphomas and myeloid leukemias emerge in ∼60% of adult homozygous T58A mice. We found that primitive hematopoietic progenitor cells from MYC-T58A mice exhibit aberrant self-renewal normally associated with hematopoietic stem cells (HSCs) and up-regulate a subset of MYC target genes important in maintaining stem/progenitor cell balance. In lymphocytes, genomic occupancy by MYC-T58A was increased at all promoters compared with WT MYC, while genes differentially expressed in a T58A-dependent manner were significantly more proximal to MYC-bound enhancers. MYC-T58A lymphocyte progenitors exhibited metabolic alterations and decreased activation of inflammatory and apoptotic pathways. Our data demonstrate that a single point mutation stabilizing MYC is sufficient to skew target gene expression, producing a profound gain of function in multipotential hematopoietic progenitors associated with self-renewal and initiation of lymphomas and leukemias.

Oncogenic activation of MYC in cancers predominantly involves increased transcription rather than coding region mutations. However, MYC-dependent lymphomas frequently contain point mutations in the MYC phospho-degron, including at threonine-58 (T58), where phosphorylation permits binding by the FBW7 ubiquitin ligase triggering MYC degradation. To understand how T58 phosphorylation functions in normal cell physiology, we introduced an alanine mutation at T58 (T58A) into the endogenous c-Myc locus in the mouse germline. While MYC-T58A mice develop normally, lymphomas and myeloid leukemias emerge in ∼60% of adult homozygous T58A mice. We find that primitive hematopoietic progenitor cells from MYC-T58A mice exhibit aberrant self-renewal normally associated with hematopoietic stem cells (HSCs) and upregulate a subset of Myc target genes important in maintaining stem/progenitor cell balance. Genomic occupancy by MYC-T58A was increased at all promoters, compared to WT MYC, while genes differentially expressed in a T58A-dependent manner were significantly more proximal to MYC-bound enhancers. MYC-T58A lymphocyte progenitors exhibited metabolic alterations and decreased activation of inflammatory and apoptotic pathways. Our data demonstrate that a single point mutation in Myc is sufficient to produce a profound gain of function in multipotential hematopoietic progenitors associated with self-renewal and initiation of lymphomas and leukemias.

Male germ cell (GC) production is a metabolically driven and apoptosis-prone process. Here, we show that the glucose-sensing transcription factor (TF) MAX-Like protein X (MLX) and its binding partner MondoA are both required for male fertility in the mouse, as well as survival of human tumor cells derived from the male germ line. Loss ofMlxresults in altered metabolism as well as activation of multiple stress pathways and GC apoptosis in the testes. This is concomitant with dysregulation of the expression of male-specific GC transcripts and proteins. Our genomic and functional analyses identify loci directly bound by MLX involved in these processes, including metabolic targets, obligate components of male-specific GC development, and apoptotic effectors. These in vivo and in vitro studies implicate MLX and other members of the proximal MYC network, such as MNT, in regulation of metabolism and differentiation, as well as in suppression of intrinsic and extrinsic death signaling pathways in both spermatogenesis and male germ cell tumors (MGCTs).

Background & Aims: The c-Myc (Myc) bHLH-ZIP transcription factor is deregulated in most cancers. In association with Max, Myc controls target genes that supervise metabolism, ribosome biogenesis, translation and proliferation. This “Myc Network” cross-talks with the “Mlx Network”, which consists of the Myc-like proteins MondoA and ChREBP and Max-like Mlx. Together, this “Extended Myc Network” regulates both common and distinct genes targets. Here we studied the consequence of Myc and/or Mlx ablation in the liver, particularly those pertaining to hepatocyte proliferation, metabolism and spontaneous tumorigenesis. Methods: We examined the ability of hepatocytes lacking Mlx ( Mlx KO) or Myc+Mlx (double KO or DKO) to repopulate the liver over an extended period of time in a murine model of Type I tyrosinemia. We also compared this and other relevant behaviors, phenotypes and transcriptomes of the livers to those from previously characterized Myc KO, Chrebp KO and Myc KO x Chrebp KO mice. Results: Hepatocyte regenerative potential deteriorated as the Extended Myc Network was progressively dismantled. Genes and pathways dysregulated in Mlx KO and DKO hepatocytes included those pertaining to translation, mitochondrial function and non-alcoholic fatty liver disease (NAFLD). The Myc and Mlx Networks were shown to cross-talk, with the latter playing a disproportionate role in target gene regulation. All cohorts also developed NAFLD and molecular evidence of early steatohepatitis. Finally, Mlx KO and DKO mice displayed extensive hepatic adenomatosis. Conclusions: In addition to demonstrating cooperation between the Myc and Mlx Networks, this study revealed the latter to be more important in maintaining proliferative, metabolic and translational homeostasis, while concurrently serving as a suppressor of benign tumorigenesis. Synopsis: The Myc and Mlx Networks exhibit extensive cross-talk and regulate distinct but overlapping sets of transcriptional targets. The current work demonstrates the cooperation between these two Networks in supporting the regenerative capabilities of normal hepatocytes while also revealing that the Mlx Network serves as a suppressor of spontaneous hepatic adenomatosis

MGA, a transcription factor and member of the MYC network, is mutated or deleted in a broad spectrum of malignancies. As a critical test of a tumor suppressive role, we inactivated Mga in two mouse models of non-small cell lung cancer using a CRISPR-based approach. MGA loss significantly accelerated tumor growth in both models and led to de-repression of non-canonical Polycomb ncPRC1.6 targets, including genes involved in metastasis and meiosis. Moreover, MGA deletion in human lung adenocarcinoma lines augmented invasive capabilities. We further show that MGA-MAX, E2F6, and L3MBTL2 co-occupy thousands of promoters and that MGA stabilizes these ncPRC1.6 subunits. Lastly, we report that MGA loss also induces a pro-growth effect in human colon organoids. Our studies establish MGA as a bona fide tumor suppressor in vivo and suggest a tumor suppressive mechanism in adenocarcinomas resulting from widespread transcriptional attenuation of MYC and E2F target genes mediated by MGA-MAX associated with a non-canonical Polycomb complex.