Drug combinations identified by high-throughput screening promote cell cycle transition and upregulate Smad pathways in myeloma

Drug resistance and disease progression are common in multiple myeloma (MM) patients, underscoring the need for new therapeutic combinations. A high-throughput drug screen in 47 MM cell lines and in silico Huber robust regression analysis of drug responses revealed 43 potentially synergistic combinations. We hypothesized that effective combinations would reduce MYC expression and enhance p16 activity. Six combinations cooperatively reduced MYC protein, frequently over-expressed in MM and also cooperatively increased p16 expression, frequently downregulated in MM. Synergistic reductions in viability were observed with top combinations in proteasome inhibitor-resistant and sensitive MM cell lines, while sparing fibroblasts. Three combinations significantly prolonged survival in a transplantable Ras-driven allograft model of advanced MM closely recapitulating high-risk/refractory myeloma in humans and reduced viability of ex vivo treated patient cells. Common genetic pathways similarly downregulated by these combinations promoted cell cycle transition, whereas pathways most upregulated were involved in TGFβ/SMAD signaling. These preclinical data identify potentially useful drug combinations for evaluation in drug-resistant MM and reveal potential mechanisms of combined drug sensitivity.

Fatty acid oxidation is required for embryonic stem cell survival during metabolic stress

Metabolic regulation is critical for the maintenance of pluripotency and the survival of embryonic stem cells (ESCs). The transcription factor Tfcp2l1 has emerged as a key factor for the naïve pluripotency of ESCs. Here, we report an unexpected role of Tfcp2l1 in metabolic regulation in ESCs-promoting the survival of ESCs through regulating fatty acid oxidation (FAO) under metabolic stress. Tfcp2l1 directly activates many metabolic genes in ESCs. Deletion of Tfcp2l1 leads to an FAO defect associated with upregulation of glucose uptake, the TCA cycle, and glutamine catabolism. Mechanistically, Tfcp2l1 activates FAO by inducing Cpt1a, a rate-limiting enzyme transporting free fatty acids into the mitochondria. ESCs with defective FAO are sensitive to cell death induced by glycolysis inhibition and glutamine deprivation. Moreover, the Tfcp2l1-Cpt1a-FAO axis promotes the survival of quiescent ESCs and diapause-like blastocysts induced by mTOR inhibition. Thus, our results reveal how ESCs orchestrate pluripotent and metabolic programs to ensure their survival in response to metabolic stress.

Efficacy, Tolerability, and Pharmacokinetics of Combined Targeted MEK and Dual mTORC1/2 Inhibition in a Preclinical Model of Mucosal Melanoma

Melanomas arising in the mucous membranes are a rare and aggressive subtype. New treatment approaches are needed, yet accumulating sufficient evidence to improve patient outcomes is difficult. Clinical and pathological correlates between human and canine mucosal melanomas are substantial, and the relatively greater incidence of spontaneous naturally occurring mucosal melanoma in dogs represents a promising opportunity for predictive modeling. The genomic landscapes of human and canine mucosal melanoma appear highly diverse and generally lack recurring hotspot mutations associated with cutaneous melanomas. Although much remains to be determined, evidence indicates that Ras/MAPK and/or PI3K/AKT/mTOR signaling pathway activations are common in both species and may represent targets for therapeutic intervention. Sapanisertib, an mTORC1/2 inhibitor, was selected from a PI3K/mTOR inhibitor library to collaborate with MEK inhibition; the latter preclinical efficacy was demonstrated previously for canine mucosal melanoma. Combined inhibition of MEK and mTORC1/2, using trametinib and sapanisertib, produced apoptosis and cell-cycle alteration, synergistically reducing cell survival in canine mucosal melanoma cell lines with varying basal signaling activation levels. Compared with individual inhibitors, a staggered sapanisertib dose, coupled with daily trametinib, was optimal for limiting primary mucosal melanoma xenograft growth in mice, and tumor dissemination in a metastasis model, while minimizing hematologic and renal side effects. Inhibitors downmodulated respective signaling targets and the combination additionally suppressed pathway reciprocal crosstalk. The combination did not significantly change plasma sapanisertib pharmacokinetics; however, trametinib area under the curve was increased in the presence of sapanisertib. Targeting Ras/MAPK and PI3K/AKT/mTOR signal transduction pathways appear rational therapies for canine and human mucosal melanoma.

Mouse tumor susceptibility genes identify drug combinations for multiple myeloma

Long-term genetic studies utilizing backcross and congenic strain analyses coupled with positional cloning strategies and functional studies identified Cdkn2a, Mtor, and Mndal as mouse plasmacytoma susceptibility/resistance genes. Tumor incidence data in congenic strains carrying the resistance alleles of Cdkn2a and Mtor led us to hypothesize that drug combinations affecting these pathways are likely to have an additive, if not synergistic effect in inhibiting tumor cell growth. Traditional and novel systems-level genomic approaches were used to assess combination activity, disease specificity, and clinical potential of a drug combination involving rapamycin/everolimus, an Mtor inhibitor, with entinostat, an histone deacetylase inhibitor. The combination synergistically repressed oncogenic MYC and activated the Cdkn2a tumor suppressor. The identification of MYC as a primary upstream regulator led to the identification of small molecule binders of the G-quadruplex structure that forms in the NHEIII region of the MYC promoter. These studies highlight the importance of identifying drug combinations which simultaneously upregulate tumor suppressors and downregulate oncogenes.

Hypomorphic mTOR Downregulates CDK6 and Delays Thymic Pre-T LBL Tumorigenesis

PI3K/AKT/mTOR pathway hyperactivation is frequent in T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/LBL). To model inhibition of mTOR, pre-T-cell lymphoblastic leukemia/lymphoma (pre-T LBL) tumor development was monitored in mice with T lymphocyte-specific, constitutively active AKT (Lck-MyrAkt2) that were either crossed to mTOR knockdown (KD) mice or treated with the mTOR inhibitor everolimus. Lck-MyrAkt2;mTOR KD mice lived significantly longer than Lck-MyrAkt2;mTOR wild-type (WT) mice, although both groups ultimately developed thymic pre-T LBL. An increase in survival was also observed when Lck-MyrAkt2;mTOR WT mice were treated for 8 weeks with everolimus. The transcriptional profiles of WT and KD thymic lymphomas were compared, and Ingenuity Pathway Upstream Regulator Analysis of differentially expressed genes in tumors from mTOR WT versus KD mice identified let-7 and miR-21 as potential regulatory genes. mTOR KD mice had higher levels of let-7a and miR-21 than mTOR WT mice, and rapamycin induced their expression in mTOR WT cells. CDK6 was one of the most downregulated targets of both let-7 and miR21 in mTOR KD tumors. CDK6 overexpression and decreased expression of let-7 in mTOR KD cells rescued a G₁ arrest phenotype. Combined mTOR (rapamycin) and CDK4/6 (palbociclib) inhibition decreased tumor size and proliferation in tumor flank transplants, increased survival in an intravenous transplant model of disseminated leukemia compared with single agent treatment, and cooperatively decreased cell viability in human T-ALL/LBL cell lines. Thus, mTOR KD mice provide a model to explore drug combinations synergizing with mTOR inhibitors and can be used to identify downstream targets of inhibition.

The transcription factor CBFB suppresses breast cancer through orchestrating translation and transcription

Translation and transcription are frequently dysregulated in cancer. These two processes are generally regulated by distinct sets of factors. The CBFB gene, which encodes a transcription factor, has recently emerged as a highly mutated driver in a variety of human cancers including breast cancer. Here we report a noncanonical role of CBFB in translation regulation. RNA immunoprecipitation followed by deep sequencing (RIP-seq) reveals that cytoplasmic CBFB binds to hundreds of transcripts and regulates their translation. CBFB binds to mRNAs via hnRNPK and enhances translation through eIF4B, a general translation initiation factor. Interestingly, the RUNX1 mRNA, which encodes the transcriptional partner of CBFB, is bound and translationally regulated by CBFB. Furthermore, nuclear CBFB/RUNX1 complex transcriptionally represses the oncogenic NOTCH signaling pathway in breast cancer. Thus, our data reveal an unexpected function of CBFB in translation regulation and propose that breast cancer cells evade translation and transcription surveillance simultaneously through downregulating CBFB.

CBFB is highly mutated in breast cancers and is known to interact with RUNX proteins to regulate transcription. Here, the authors describe a non-canonical role of CBFB in translation regulation in which it binds to mRNAs through hnRNPK, facilitating translation by eIF4B.

Pax8, Napsin A, and CD10 as Immunohistochemical Markers of Canine Renal Cell Carcinoma

Pax8, napsin A, and CD10 are useful immunohistochemical markers of human renal cell carcinoma (RCC); however, their diagnostic utility in canine RCC is unclear. Forty formalin-fixed paraffin-embedded renal cell carcinomas from dogs (15 papillary, 12 solid, and 13 tubular) and 10 metastases were evaluated for expression of Pax8, napsin A, and CD10. Thirty-nine (98%), 24 (60%), and 19 (50%) tumors expressed Pax8 (nuclear labeling), napsin A (cytoplasmic labeling), and CD10 (cytoplasmic and membranous labeling), respectively. Pax8 was expressed in 92% of solid, 100% of papillary, and 100% of tubular tumors. Napsin A was expressed in 58% of solid, 60% of papillary, and 62% of tubular RCC. CD10 was expressed in 33% of solid, 47% of papillary, and 62% of tubular RCC. Pax8 was expressed in 80% of the metastatic tumors, napsin A in 60%, and CD10 in 50%. Additionally, Pax8 immunoreactivity was stronger overall than that of napsin A or CD10. In summary, Pax8 is a more sensitive marker than napsin A or CD10 for primary and metastatic canine RCC; its nuclear and more intense reactivity also makes it easier to interpret. Tubular and papillary RCCs were more likely than solid RCC to express all 3 markers. These findings highlight the utility of Pax8 as an immunohistochemical marker in diagnosing all major subtypes of canine primary and metastatic renal cell carcinoma.

Dose-related induction of hepatic preneoplastic lesions by diethylnitrosamine in C57BL/6 mice

The C57BL/6 mouse strain (or derivation of this strain) is used as a background for many transgenic mouse models. This strain has a relatively low susceptibility to chemically induced hepatocarcinogenesis compared with other commonly used experimental mouse strains. In the present study, the authors treated C57BL/6 mice with 25, 50, and 75 mg/kg of diethylnitrosamine (DEN) for 4 or 8 weeks by intraperitoneal injection to investigate the dose-response pattern of preneoplastic and neoplastic lesion formation in the liver. DEN induced preneoplastic lesions and cytokeratin 8/18-positive foci in a dose-dependent manner. In the 75 mg/kg for 8 weeks treatment group, hepatocellular adenoma, cholangioma and hemangioma, and cytokeratin 19-positive foci were also induced, but a significant decrease in body weight was observed. The suitable DEN treatment range for this strain was concluded to be from 75 mg/kg for 4 weeks (total amount = 300 mg/kg) to 50 mg/kg for 8 weeks (total amount = 400 mg/kg). These results should prove useful for future studies investigating hepatocarcinogenesis in both the background C57BL/6 strain and other transgenic mouse models derived from it.