CDK12 Loss Promotes Prostate Cancer Development While Exposing Vulnerabilities to Paralog-Based Synthetic Lethality.

Biallelic loss of cyclin-dependent kinase 12 (CDK12) defines a unique molecular subtype of metastatic castration-resistant prostate cancer (mCRPC). It remains unclear, however, whether CDK12 loss per se is sufficient to drive prostate cancer development-either alone, or in the context of other genetic alterations-and whether CDK12-mutant tumors exhibit sensitivity to specific pharmacotherapies. Here, we demonstrate that tissue-specific Cdk12 ablation is sufficient to induce preneoplastic lesions and robust T cell infiltration in the mouse prostate. Allograft-based CRISPR screening demonstrated that Cdk12 loss is positively associated with Trp53 inactivation but negatively associated with Pten inactivation-akin to what is observed in human mCRPC. Consistent with this, ablation of Cdk12 in prostate organoids with concurrent Trp53 loss promotes their proliferation and ability to form tumors in mice, while Cdk12 knockout in the Pten-null prostate cancer mouse model abrogates tumor growth. Bigenic Cdk12 and Trp53 loss allografts represent a new syngeneic model for the study of androgen receptor (AR)-positive, luminal prostate cancer. Notably, Cdk12/Trp53 loss prostate tumors are sensitive to immune checkpoint blockade. Cdk12-null organoids (either with or without Trp53 co-ablation) and patient-derived xenografts from tumors with CDK12 inactivation are highly sensitive to inhibition or degradation of its paralog kinase, CDK13. Together, these data identify CDK12 as a bona fide tumor suppressor gene with impact on tumor progression and lends support to paralog-based synthetic lethality as a promising strategy for treating CDK12-mutant mCRPC.

Pigment cell progenitor heterogeneity and reiteration of developmental signaling underlie melanocyte regeneration in zebrafish.

Tissue-resident stem and progenitor cells are present in many adult organs, where they are important for organ homeostasis and repair in response to injury. However, the signals that activate these cells and the mechanisms governing how these cells renew or differentiate are highly context-dependent and incompletely understood, particularly in non-hematopoietic tissues. In the skin, melanocyte stem and progenitor cells are responsible for replenishing mature pigmented melanocytes. In mammals, these cells reside in the hair follicle bulge and bulb niches where they are activated during homeostatic hair follicle turnover and following melanocyte destruction, as occurs in vitiligo and other skin hypopigmentation disorders. Recently, we identified melanocyte progenitors in adult zebrafish skin. To elucidate mechanisms governing melanocyte progenitor renewal and differentiation we analyzed individual transcriptomes from thousands of melanocyte lineage cells during the regeneration process. We identified transcriptional signatures for progenitors, deciphered transcriptional changes and intermediate cell states during regeneration, and analyzed cell-cell signaling changes to discover mechanisms governing melanocyte regeneration. We identified KIT signaling via the RAS/MAPK pathway as a regulator of melanocyte progenitor direct differentiation and asymmetric division. Our findings show how activation of different subpopulations of mitfa-positive cells underlies cellular transitions required to properly reconstitute the melanocyte pigmentary system following injury.

KIT Suppresses BRAFV600E-Mutant Melanoma by Attenuating Oncogenic RAS/MAPK Signaling.

The receptor tyrosine kinase KIT promotes survival and migration of melanocytes during development, and excessive KIT activity hyperactivates the RAS/MAPK pathway and can drive formation of melanomas, most notably of rare melanomas that occur on volar and mucosal surfaces of the skin. The much larger fraction of melanomas that occur on sun-exposed skin is driven primarily by BRAF- or NRAS-activating mutations, but these melanomas exhibit a surprising loss of KIT expression, which raises the question of whether loss of KIT in these tumors facilitates tumorigenesis. To address this question, we introduced a kit(lf) mutation into a strain of Tg(mitfa:BRAFV600E); p53(lf) melanoma-prone zebrafish. Melanoma onset was accelerated in kit(lf); Tg(mitfa:BRAFV600E); p53(lf) fish. Tumors from kit(lf) animals were more invasive and had higher RAS/MAPK pathway activation. KIT knockdown also increased RAS/MAPK pathway activation in a BRAFV600E-mutant human melanoma cell line. We found that pathway stimulation upstream of BRAFV600E could paradoxically reduce signaling downstream of BRAFV600E, and wild-type BRAF was necessary for this effect, suggesting that its activation can dampen oncogenic BRAFV600E signaling. In vivo, expression of wild-type BRAF delayed melanoma onset, but only in a kit-dependent manner. Together, these results suggest that KIT can activate signaling through wild-type RAF proteins, thus interfering with oncogenic BRAFV600E-driven melanoma formation. Cancer Res; 77(21); 5820-30. ©2017 AACR.

Value of circulating cell-free DNA analysis as a diagnostic tool for breast cancer: a meta-analysis.

OBJECTIVES: The aim of this study was to systematically evaluate the diagnostic value of cell free DNA (cfDNA) for breast cancer. RESULTS: Among 308 candidate articles, 25 with relevant diagnostic screening qualified for final analysis. The mean sensitivity, specificity and area under the curve (AUC) of SROC plots for 24 studies that distinguished breast cancer patients from healthy controls were 0.70, 0.87, and 0.9314, yielding a DOR of 32.31. When analyzed in subgroups, the 14 quantitative studies produced sensitivity, specificity, AUC, and a DOR of 0.78, 0.83, 0.9116, and 24.40. The 10 qualitative studies produced 0.50, 0.98, 0.9919, and 68.45. For 8 studies that distinguished malignant breast cancer from benign diseases, the specificity, sensitivity, AUC and DOR were 0.75, 0.79, 0.8213, and 9.49. No covariate factors had a significant correlation with relative DOR. Deek's funnel plots indicated an absence of publication bias. MATERIALS AND METHODS: Databases were searched for studies involving the use of cfDNA to diagnose breast cancer. The studies were analyzed to determine sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio (DOR), and the summary receiver operating characteristic (SROC). Covariates were evaluated for effect on relative DOR. Deek's Funnel plots were generated to measure publication bias. CONCLUSIONS: Our analysis suggests a promising diagnostic potential of using cfDNA for breast cancer screening, but this diagnostic method is not yet independently sufficient. Further work refining qualitative cfDNA assays will improve the correct diagnosis of breast cancers.

Intracranial AAV-IFN-ß gene therapy eliminates invasive xenograft glioblastoma and improves survival in orthotopic syngeneic murine model.

The highly invasive property of glioblastoma (GBM) cells and genetic heterogeneity are largely responsible for tumor recurrence after the current standard-of-care treatment and thus a direct cause of death. Previously, we have shown that intracranial interferon-beta (IFN-ß) gene therapy by locally administered adeno-associated viral vectors (AAV) successfully treats noninvasive orthotopic glioblastoma models. Here, we extend these findings by testing this approach in invasive human GBM xenograft and syngeneic mouse models. First, we show that a single intracranial injection of AAV encoding human IFN-ß eliminates invasive human GBM8 tumors and promotes long-term survival. Next, we screened five AAV-IFN-ß vectors with different promoters to drive safe expression of mouse IFN-ß in the brain in the context of syngeneic GL261 tumors. Two AAV-IFN-ß vectors were excluded due to safety concerns, but therapeutic studies with the other three vectors showed extensive tumor cell death, activation of microglia surrounding the tumors, and a 56% increase in median survival of the animals treated with AAV/P2-Int-mIFN-ß vector. We also assessed the therapeutic effect of combining AAV-IFN-ß therapy with temozolomide (TMZ). As TMZ affects DNA replication, an event that is crucial for second-strand DNA synthesis of single-stranded AAV vectors before active transcription, we tested two TMZ treatment regimens. Treatment with TMZ prior to AAV-IFN-ß abrogated any benefit from the latter, while the reverse order of treatment doubled the median survival compared to controls. These studies demonstrate the therapeutic potential of intracranial AAV-IFN-ß therapy in a highly migratory GBM model as well as in a syngeneic mouse model and that combination with TMZ is likely to enhance its antitumor potency.

Loss of 5-hydroxymethylcytosine is an epigenetic hallmark of melanoma.

DNA methylation at the 5 position of cytosine (5-mC) is a key epigenetic mark that is critical for various biological and pathological processes. 5-mC can be converted to 5-hydroxymethylcytosine (5-hmC) by the ten-eleven translocation (TET) family of DNA hydroxylases. Here, we report that "loss of 5-hmC" is an epigenetic hallmark of melanoma, with diagnostic and prognostic implications. Genome-wide mapping of 5-hmC reveals loss of the 5-hmC landscape in the melanoma epigenome. We show that downregulation of isocitrate dehydrogenase 2 (IDH2) and TET family enzymes is likely one of the mechanisms underlying 5-hmC loss in melanoma. Rebuilding the 5-hmC landscape in melanoma cells by reintroducing active TET2 or IDH2 suppresses melanoma growth and increases tumor-free survival in animal models. Thus, our study reveals a critical function of 5-hmC in melanoma development and directly links the IDH and TET activity-dependent epigenetic pathway to 5-hmC-mediated suppression of melanoma progression, suggesting a new strategy for epigenetic cancer therapy.