Tumor-selective activity of RAS-GTP inhibition in pancreatic cancer

Broad-spectrum RAS inhibition holds the potential to benefit roughly a quarter of human cancer patients whose tumors are driven by RAS mutations1,2. RMC-7977 is a highly selective inhibitor of the active GTP-bound forms of KRAS, HRAS, and NRAS, with affinity for both mutant and wild type (WT) variants (RAS(ON) multi-selective)3. As >90% of human pancreatic ductal adenocarcinoma (PDAC) cases are driven by activating mutations in KRAS4, we assessed the therapeutic potential of the RAS(ON) multi-selective inhibitor RMC-7977 in a comprehensive range of PDAC models. We observed broad and pronounced anti-tumor activity across models following direct RAS inhibition at exposures that were well-tolerated in vivo. Pharmacological analyses revealed divergent responses to RMC-7977 in tumor versus normal tissues. Treated tumors exhibited waves of apoptosis along with sustained proliferative arrest whereas normal tissues underwent only transient decreases in proliferation, with no evidence of apoptosis. In the autochthonous KPC model, RMC-7977 treatment resulted in a profound extension of survival followed by on-treatment relapse. Analysis of relapsed tumors identified Myc copy number gain as a prevalent candidate resistance mechanism, which could be overcome by combinatorial TEAD inhibition in vitro. Together, these data establish a strong preclinical rationale for the use of broad-spectrum RAS-GTP inhibition in the setting of PDAC and identify a promising candidate combination therapeutic regimen to overcome monotherapy resistance.

Tumor-selective effects of active RAS inhibition in pancreatic ductal adenocarcinoma

Broad-spectrum RAS inhibition holds the potential to benefit roughly a quarter of human cancer patients whose tumors are driven by RAS mutations. However, the impact of inhibiting RAS functions in normal tissues is not known. RMC-7977 is a highly selective inhibitor of the active (GTP-bound) forms of KRAS, HRAS, and NRAS, with affinity for both mutant and wild type (WT) variants. As >90% of human pancreatic ductal adenocarcinoma (PDAC) cases are driven by activating mutations in KRAS, we assessed the therapeutic potential of RMC-7977 in a comprehensive range of PDAC models, including human and murine cell lines, human patient-derived organoids, human PDAC explants, subcutaneous and orthotopic cell-line or patient derived xenografts, syngeneic allografts, and genetically engineered mouse models. We observed broad and pronounced anti-tumor activity across these models following direct RAS inhibition at doses and concentrations that were well-tolerated in vivo. Pharmacological analyses revealed divergent responses to RMC-7977 in tumor versus normal tissues. Treated tumors exhibited waves of apoptosis along with sustained proliferative arrest whereas normal tissues underwent only transient decreases in proliferation, with no evidence of apoptosis. Together, these data establish a strong preclinical rationale for the use of broad-spectrum RAS inhibition in the setting of PDAC.

Translational regulation of TFH cell differentiation and autoimmune pathogenesis

Little is known regarding T cell translational regulation. We demonstrate that T follicular helper (TFH) cells use a previously unknown mechanism of selective messenger RNA (mRNA) translation for their differentiation, role in B cell maturation, and in autoimmune pathogenesis. We show that TFH cells have much higher levels of translation factor eIF4E than non-TFH CD4⁺ T cells, which is essential for translation of TFH cell fate-specification mRNAs. Genome-wide translation studies indicate that modest down-regulation of eIF4E activity by a small-molecule inhibitor or short hairpin RN impairs TFH cell development and function. In mice, down-regulation of eIF4E activity specifically reduces TFH cells among T helper subtypes, germinal centers, B cell recruitment, and antibody production. In experimental autoimmune encephalomyelitis, eIF4E activity down-regulation blocks TFH cell participation in disease pathogenesis while promoting rapid remission and spinal cord remyelination. TFH cell development and its role in autoimmune pathogenesis involve selective mRNA translation that is highly druggable.

Eukaryotic Translation Initiation Factor 4E (eIF4E) is Required for Development of T Follicular Helper Cells and Pathogenesis of Autoimmune Encephalitis

Multiple sclerosis (MS) is a neuroinflammatory disorder resulting from infiltration of T cells into the central nervous system (CNS) and demyelination of neurons. Since T follicular helper (TFH) cells are associated with MS relapse, their selective inhibition could be an ideal therapeutic. TFH cells require transcription factor BCL6 and active mTORC1/2 for development. When mTORC is active, cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) initiates translation of selective mRNAs. However, the requirement of eIF4E for translation of mRNAs necessary for TFH cell development has not been investigated. Disruption of eIF4E binding to the 5′ mRNA cap with drug 4EGI-1 inhibits TFH and germinal center (GC) B cell development while having no effect on differentiation and effector function of TH1, TH2, TH17, or Tregs. Silencing of eIF4E in only CD4 T cells is sufficient to inhibit their formation of TFH cells. We used polysome profiling to determine which mRNAs are selectively translated by eIF4E and identified salient programs regulated by transcription (BCL6, NFAT) and costimulation (CD28, SLAM). eIF4E is required for translation of BCL6 in human lymph node TFH and GC B cells. Administration of 4EGI-1 during experimental autoimmune encephalitis (EAE) results in significantly decreased infiltration of CD4 T cells in the CNS, demyelination, and clinical score. Further, 4EGI-1 treatment following initiation of symptoms results in rapid improvement of symptoms and partial remission earlier than vehicle-treated animals. Thus, eIF4E is required for differentiation of TFH cells and pathogenesis of autoimmune encephalitis, and 4EGI-1 represents a potential therapeutic.