Highlights d Multiple SCLC molecular subtypes arise from a neuroendocrine cell of origin d MYC drives the NEUROD1 + and YAP1 + subtypes of SCLC in a temporal evolution d MYC directly activates NOTCH signaling to reprogram neuroendocrine fate d Multiple SCLC molecular subtypes are present within individual human tumors

Models that recapitulate the complexity of human tumors are urgently needed to develop more effective cancer therapies. We report a bank of human patient-derived xenografts (PDXs) and matched organoid cultures from tumors that represent the greatest unmet need: endocrine-resistant, treatment-refractory and metastatic breast cancers. We leverage matched PDXs and PDX-derived organoids (PDxO) for drug screening that is feasible and cost-effective with in vivo validation. Moreover, we demonstrate the feasibility of using these models for precision oncology in real time with clinical care in a case of triple-negative breast cancer (TNBC) with early metastatic recurrence. Our results uncovered a Food and Drug Administration (FDA)-approved drug with high efficacy against the models. Treatment with this therapy resulted in a complete response for the individual and a progression-free survival (PFS) period more than three times longer than their previous therapies. This work provides valuable methods and resources for functional precision medicine and drug development for human breast cancer.

Purpose miR-29b directly or indirectly targets genes involved in acute myeloid leukemia (AML) i.e., DNMTs, CDK6, SP1, KIT and FLT3. Higher miR-29b pretreatment expression is associated with improved response to decitabine and better outcome in AML. Thus designing a strategy to increase miR-29b levels in AML blasts may be of therapeutic value. However, free synthetic miRs are easily degraded in bio-fluids and have limited cellular uptake. To overcome these limitations, we developed a novel transferrin-conjugated nanoparticle delivery system for synthetic miR-29b (Tf-NP-miR-29b). Experiment Design Delivery efficiency was investigated by flow-cytometry, confocal microscopy and quantitative-PCR. The expression of miR-29b targets was measured by immunoblotting. The anti-leukemic activity of Tf-NP-miR-29b was evaluated by measuring cell proliferation and colony formation ability and in a leukemia mouse model. Results Tf-NP-miR-29b treatment resulted in >200-fold increase of mature miR-29b compared to free miR-29b and was about twice as efficient as treatment with non-Tf-conjugated NP-miR-29b. Tf-NP-miR-29b treatment significantly downregulated DNMTs, CDK6, SP1, KIT and FLT3 and decreased AML cell growth by 30–50% and impaired colony formation by approximately 50%. Mice engrafted with AML cells and then treated with Tf-NP-miR-29b had significantly longer survival compared to Tf-NP-scramble (P=0.015) or free miR-29b (P=0.003). Furthermore, priming AML cell with Tf-NP-miR-29b before decitabine resulted in strong cell viability decrease in vitro and showed improved anti-leukemic activity compared with decitabine alone (P=0.001) in vivo. Conclusion Tf-NP effectively delivered functional miR-29b, resulting in target downregulation and anti-leukemic activity, and warrants further investigation as a novel therapeutic approach in AML.

Changes in the enzymatic activity of protein arginine methyltransferase (PRMT) 5 have been associated with cancer; however, the protein's role in acute myeloid leukemia (AML) has not been fully evaluated. Here, we show that increased PRMT5 activity enhanced AML growth in vitro and in vivo while PRMT5 downregulation reduced it. In AML cells, PRMT5 interacted with Sp1 in a transcription repressor complex and silenced miR-29b preferentially via dimethylation of histone 4 arginine residue H4R3. As Sp1 is also a bona fide target of miR-29b, the miR silencing resulted in increased Sp1. This event in turn led to transcription activation of FLT3, a gene that encodes a receptor tyrosine kinase. Inhibition of PRMT5 via sh/siRNA or a first-in-class small-molecule inhibitor (HLCL-61) resulted in significantly increased expression of miR-29b and consequent suppression of Sp1 and FLT3 in AML cells. As a result, significant antileukemic activity was achieved. Collectively, our data support a novel leukemogenic mechanism in AML where PRMT5 mediates both silencing and transcription of genes that participate in a 'yin-yang' functional network supporting leukemia growth. As FLT3 is often mutated in AML and pharmacologic inhibition of PRMT5 appears feasible, the PRMT5-miR-29b-FLT3 network should be further explored as a novel therapeutic target for AML.

Current treatments for acute myeloid leukemia (AML) are designed to target rapidly dividing blast populations with limited success in eradicating the functionally distinct leukemia stem cell (LSC) population, which is postulated to be responsible for disease resistance and relapse. We have previously reported high miR-126 expression levels to be associated with a LSC-gene expression profile. Therefore, we hypothesized that miR-126 contributes to “stemness” and is a viable target for eliminating the LSC in AML. Here we first validate the clinical relevance of miR-126 expression in AML by showing that higher expression of this microRNA (miR) is associated with worse outcome in a large cohort of older (≥60 years) cytogenetically normal AML patients treated with conventional chemotherapy. We then show that miR-126 overexpression characterizes AML LSC-enriched cell subpopulations and contributes to LSC long-term maintenance and self-renewal. Finally, we demonstrate the feasibility of therapeutic targeting of miR-126 in LSCs with novel targeting nanoparticles (NP) containing antagomiR-126 resulting in in vivo reduction of LSCs likely by depletion of the quiescent cell subpopulation. Our findings suggest that by targeting a single miR, i.e., miR-126, it is possible to interfere with LSC activity, thereby opening potentially novel therapeutic approaches to treat AML patients.