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CDK12 inhibition reveals melanoma dependence on the RUNX1/CBFβ complex for genomic stability.

Cutaneous melanoma is the deadliest form of skin cancer, frequently driven by hyperactivation of the RAS/mitogen-activated protein kinase (MAPK) pathway. Cyclin-dependent kinase 12 (CDK12), a downstream effector of MAPK signaling, has emerged as a therapeutic target due to its essential role in transcriptional regulation and DNA damage repair. To identify vulnerabilities associated with CDK12 inhibition, we performed a genome-wide CRISPR-Cas9 screen and identified the Runt-related transcription factor RUNX1 and its cofactor CBFβ as synthetic lethal partners of CDK12. RUNX1 inhibition enhanced melanoma sensitivity to CDK12 inhibitors in a p53-independent manner, resulting in DNA damage accumulation and impaired repair capacity. Combined inhibition of CDK12 and RUNX1 suppressed melanoma growth in vivo. These findings identify RUNX1/CBFβ as a compensatory mechanism in CDK12-inhibited melanoma and define a synthetic lethal interaction with translational potential for combinatorial therapy.

Core Binding Factor Alpha 2 Subunit

Inactivation of CDK12 Enhances Mitochondrial Efficiency to Suppress DNA Damage.

Inactivation of cyclin-dependent kinase 12 (CDK12) characterizes a subset of prostate cancers but it is not understood how cells adapt to declining activity of this major transcription elongation kinase. To probe this response, we developed a cell line resistant to an inhibitor targeting CDK12 and its paralog, CDK13. CDK13 can compensate for the loss of CDK12, which is why we used the dual inhibitor THZ531. Targeted drug screening of the parental and resistant cell lines revealed cross-resistance to other transcriptional kinases but no clear acquired point of vulnerability. Using genome-wide mapping of mRNA-stabilization based on metabolic labelling of RNA, we report selective mRNA stabilization of factors promoting oxidative phosphorylation in the resistant cells. We go on to show that loss of CDK12 activity enhances ATP production both in cell line models and in patient tumours. Finally, we show that dual inhibition of CDK12/13 results in excessive phosphorylation of the DNA damage H2AX in prostate cancer cells but not in our CDK12/13 inhibitor-resistant model system. In brief, we propose that inactivation of CDK12 rewires cellular energy metabolism to suppress DNA damage.

Humans

Comprehensive Clinicopathologic, Immunohistochemical, and Genomic Profiling of Sporadic Ampullary Somatostatin-producing D-cell Neuroendocrine Tumors Identifies Recurrent HRAS Hotspot Mutations.

Ampullary somatostatin-producing D-cell neuroendocrine tumors are rare neoplasms that may be associated with type 1 neurofibromatosis. The molecular features of sporadic ampullary somatostatin-producing D-cell neuroendocrine tumors (SAMSOM-NETs) remain poorly characterized. We performed an integrated morphological, immunohistochemical, and genomic analysis of a multicenter series of SAMSOM-NETs. Eleven cases were included (73% male; median age: 63 years). All six patients who underwent lymphadenectomy were staged as pN1, and liver metastases were found in three cases; however, no tumor-related deaths occurred (median follow-up: 104 months). Common histologic features that can pose diagnostic challenges in the differential diagnosis with adenocarcinoma included a tubulo-glandular architecture (100%), periodic Acid-Schiff (PAS)-positive intraluminal mucin (73%), MUC1 expression (100%), and carcinoembryonic antigen (45%) expression. All tumors exhibited dot-like cytoplasmic reactivity for cytokeratins (CK) CAM5.2 or CK AE1/AE3, and 82% were CK7-positive. ISL1 and PDX1 were diffusely expressed in all cases, while CDX2 was positive in 54% and ARX showed only focal expression in four tumors. Genomic profiling revealed microsatellite stability and low tumor mutational burden. Alterations in the RAS pathway, including HRAS mutations (4 cases, 36%), a KRAS mutation (1 case), and NF1 alterations (one case), were identified in 54% of cases and in all tumors with liver metastases. Additional molecular findings included a CDK12 splice-site alteration and an NTRK3::PRDM4 fusion. Potentially actionable alterations affecting kinase-related pathways were detected in 64% of tumors. Our findings support SAMSOM-NET as a peculiar neuroendocrine tumor subtype showing distinctive histologic and molecular characteristics with potential diagnostic and therapeutic implications.

Humans

Genome-wide CRISPR screens map synthetic lethal interactions across recurrent cancer driver alterations.

Synthetic lethality (SL) provides a treatment paradigm for targeting cancer with alterations in driver genes that are not conventionally druggable, including tumor suppressor genes. We execute a series of genome-wide CRISPR screens using functionally validated isogenic cell lines and conduct a large-scale SL analysis using data from the cancer dependency map (DepMap). We chart SL interactions across 15 driver alterations: FBXW7, CCNE1, CDK12, ARID1A, KMT2D, DNMT3A, TET2, KEAP1, STK11, IDH1, SF3B1, SRSF2, U2AF1, chromosome 18q loss, and chromosome 13q loss. We show validation of several SL interactions, including ARID1A and the hexosamine biosynthetic pathway aminotransferase GFPT1, STK11 with CAMK protein kinase MARK2, FBXW7 and the CDK1 regulatory kinase PKMYT1, and CCNE1 amplification and the anaphase-promoting complex or cyclosome (APC/C). In summary, this study offers a rich resource of genetic interactions across cancer drivers enabling the discovery of biological insights and drug targets for future therapeutic development.

CP: cancer

Expression patterns of potential targets for antibody-directed therapy in metastatic castration-resistant prostate cancer patients.

INTRODUCTION: Survival in metastatic castration-resistant prostate cancer (mCRPC) patients remains limited and treatment is complicated by tumor heterogeneity. As antibody-based therapeutics emerge, identifying actionable antigen targets and patient subgroups most likely to benefit is essential. MATERIALS & METHODS: Gene expression of 62 antibody-targetable proteins was analyzed in 296 mCRPC biopsies. These genes encode proteins targeted by approved or investigational antibody-based cancer therapeutics. Associations between target expression with genomic classifications and transcriptomic subtypes were evaluated. Target expression was also assessed in tumors with low expression of established mCRPC targets. Subgroup-specific targets were validated in an independent cohort and single-cell transcriptomics. RESULTS: Established targets KLK2, FOLH1 (PSMA) and STEAP1 showed the highest median expression across the cohort. Target expression did not correlate with genomic classifications, including homologous recombination deficiency, microsatellite instability, CDK12, TP53, PTEN or AR alterations Target expression did associate with transcriptomic subtypes: CRPC-AR (driven by androgen receptor-signaling) and CRPC-SCL (stem cell-like features, AP-1/YAP/TAZ-driven), displayed the highest expression of multiple targets, including KLK2, FOLH1, and SLC44A4. CRPC-NE (neuroendocrine phenotype) showed heterogeneous expression, with high CD46 expression, whereas CRPC-WNT (Wnt-signaling driven) generally showed low target expression. Notably, CD46 was highly expressed in tumors with low KLK2, FOLH1, and STEAP1 expression, a subgroup associated with poor prognosis. CONCLUSIONS: Although several antibody targets showed broad expression in mCRPC-tumors, expression varied by transcriptomic subtype. Subgroups such as CRPC-WNT expressed fewer targets, suggesting the need for alternative therapeutic strategies. CD46 emerged as a promising target, with wide expression across multiple subtypes, including clinically challenging CRPC-NE and mCRPC tumors lacking expression of established targets.

Humans

Prevalence of homologous recombination repair genes alterations in metastatic castration-resistant prostate cancer, a multicentric study.

INTRODUCTION: Homologous Recombination Repair (HRR) genes alterations are a resistance mechanism to therapies by taxanes or Androgen Receptor Signalling inhibitors in Metastatic Castration Resistant Prostate Cancer (mCRPC). BRCA-mutated mCRPC patients are eligible to poly adenosine diphosphateribose polymerase inhibitors (PARPi). Therefore, assessing the population-specific prevalence of HRR-related genes alterations is of public healthcare importance. METHODS: This retrospective, non-interventional, multicentric study was conducted across 6 reference French centers in a "real-life" setting. 788 paraffin-embedded mCRPC patient-samples were included and submitted to testing for BRCA1/2 in six different centers; additionally, non-BRCA HRR-related genes were investigated in two different centers. RESULTS: Among the samples, n=602 (76.4%) were contributive for molecular testing. In multivariate analysis by logistic regression and sensitivity analysis, only sample age (P<0.01), sample surface area (P=0.02) and institution (P=0.018) remained statistically significant. BRCA alterations were detected in n=39/602 (6.5%) of contributive samples, with n=35 and n=4 alterations of BRCA2 and BRCA1 respectively. Non-BRCA HRR-related genes alterations were detected in n=12/157 (7.6%) of contributive samples, with alterations of mainly ATM (n=6, 3.8%), CDK12 (n=4, 2.5%) and CHEK2 (n=2, 1.3%). DISCUSSION: In this study, testing contributivity was similar or higher that of other studies in the literature, and observed mutations prevalences were similar to that of other screenings of western populations. Harmonising per-centres protocols and enhancing molecular testing contributivity with the screening of circulating DNA samples and expanding its range by including non-BRCA HRR-related genes in all reference centres will enable more patients to be accurately treated by targeted therapies. LEVEL OF EVIDENCE: 3 (grade C).

Male

Intramuscular patient-derived xenografts achieve high engraftment rates in gastric cancer: implications for pharmacodynamic testing and genomic biomarker discovery.

BACKGROUND: Gastric cancer (GC) exhibits marked inter-patient heterogeneity, limiting empirical chemotherapy efficacy. Patient-derived xenograft (PDX) models preserve the molecular features of parental tumors and can serve as pharmacodynamic surrogates, but conventional subcutaneous PDX suffers from low engraftment rates. This study evaluated an optimized intramuscular PDX platform for individualized drug testing in GC and applied whole exome sequencing (WES) for biomarker identification (Clinical trial registry: ChiCTR-OOC-17012731). MATERIALS AND METHODS: Ninety-eight treatment-naive GC patients were enrolled between April 2018 and December 2020. Fresh tumor tissues were engrafted into NCG mice by intramuscular transplantation. Drug efficacy was evaluated using tumor cell necrosis rate and Ki-67 expression. WES was performed on 32 engrafted tumorgrafts to characterize driver mutations in fast- and slow-growing subgroups. RESULTS: An engraftment rate of 71.7% (43/60) was achieved, substantially exceeding rates reported in prior studies. Clinical characteristics were independent of engraftment success and outgrowth time (all p&#x2009;>&#x2009;0.05). Fast- and slow-growing tumorgrafts diverged in frequently altered genes: KMT2C, APOB, CDK12 and MSH2 predominated in fast-growing grafts, whereas TP53, CHD3 and TET2 were enriched in slow-growing grafts. Slow-growing tumorgrafts correlated with longer progression-free survival (p&#x2009;=&#x2009;0.02). PDX-guided treatment was associated with improved prognosis. CONCLUSIONS: Intramuscular transplantation into NCG mice yields high engraftment rates for GC PDX. PDX-guided chemotherapy selection is associated with favorable outcomes. Driver mutation divergence between fast- and slow-growing tumorgrafts provides candidate prognostic biomarkers.

Animals

Targeting the Disease Response With NlpD and LytM for Effective Nonantibiotic Treatment of Urinary Tract Infections.

BACKGROUND: Finding new ways of treating bacterial infections is essential. The NlpD protein, which inhibits RNA polymerase II (Pol II), has shown therapeutic efficacy against urinary tract infection. This study investigated the mechanism of Pol II inhibition and protection by NlpD and its LytM peptide. METHODS: Recombinant NlpD and LytM were screened for interactions with constituents of the Pol II complex, using AlphaFold predictions and protein interaction technology. Treatment effects were quantified in infected tissues and regulated host response pathways identified by genome-wide transcriptomics analysis in models of acute pyelonephritis and acute cystitis in Irf3-/- and Asc-/- mice, respectively. RESULTS: LytM was shown to interact with constituents of the Pol II multiprotein complex, inhibiting the CDK12 kinase from phosphorylating the Pol II subunit RPB1 and disrupting Pol II complex formation by interfering with the interaction between PAF1C and RPB1. The protection by LytM against acute pyelonephritis was accompanied by a reduction in gene expression in infected kidneys from >1900 significantly regulated genes (fold change >6) in the placebo group to about 150 in LytM-treated mice. The inhibition of gene expression in infected kidneys particularly targeted the excessive innate immune response. A similar effect was observed in acute cystitis. Bacterial clearance was accelerated in both model by LytM treatment, with effects against antibiotic-sensitive and resistant Escherichia coli strains. CONCLUSIONS: The results suggest that inhibiting the disease response of the host, using NlpD or LytM, may offer an efficient alternative to antibiotics in these models.

Animals

Disruption of Microhomology-mediated End-joining in Ewing Sarcoma.

Ewing sarcoma (EwS) is a group of bone and soft tissue cancers in children and young adults. Since EwS cells have pronounced sensitivity to radiation and chemotherapy-induced DNA damage, the role of the oncoprotein, EWS-FLI1, in DNA repair is likely. Here, we demonstrate that EWS-FLI1 causes a defect in microhomology-mediated end-joining (MMEJ) repair. EWSR1 is a splicing factor that promotes the faithful splicing of the POLQ pre-mRNA, required for the expression of POL&#x398;, a critical protein in the MMEJ pathway. Expression of EWS-FLI1, or loss of EWSR1, causes exon 25 skipping of the POLQ transcript, decreased POL&#x398; expression, impaired MMEJ, and cellular sensitivity to inhibitors of the Fanconi Anemia (FA), NHEJ, or HR pathways, through the mechanism of synthetic lethality. Knockdown of EWS-FLI1 expression restores POL&#x398; mitotic foci and increases MMEJ activity. Inhibitors of the FA, NHEJ, or HR therefore may provide a targeted therapy for patients with EwS.

Alternative end-joining