Functional screening reveals HORMAD1-driven gene dependencies associated with translesion synthesis and replication stress tolerance.

HORMAD1 expression is usually restricted to germline cells, but it becomes mis-expressed in epithelial cells in ~60% of triple-negative breast cancers (TNBCs), where it is associated with elevated genomic instability (1). HORMAD1 expression in TNBC is bimodal with HORMAD1-positive TNBC representing a biologically distinct disease group. Identification of HORMAD1-driven genetic dependencies may uncover novel therapies for this disease group. To study HORMAD1-driven genetic dependencies, we generated a SUM159 cell line model with doxycycline-inducible HORMAD1 that replicated genomic instability phenotypes seen in HORMAD1-positive TNBC (1). Using small interfering RNA screens, we identified candidate genes whose depletion selectively inhibited the cellular growth of HORMAD1-expressing cells. We validated five genes (ATR, BRIP1, POLH, TDP1 and XRCC1), depletion of which led to reduced cellular growth or clonogenic survival in cells expressing HORMAD1. In addition to the translesion synthesis (TLS) polymerase POLH, we identified a HORMAD1-driven dependency upon additional TLS polymerases, namely POLK, REV1, REV3L and REV7. Our data confirms that out-of-context somatic expression of HORMAD1 can lead to genomic instability and reveals that HORMAD1 expression induces dependencies upon replication stress tolerance pathways, such as translesion synthesis. Our data also suggest that HORMAD1 expression could be a patient selection biomarker for agents targeting replication stress.

High KIFC1 expression is associated with poor prognosis in prostate cancer.

Kinesins play important roles in the progression and development of cancer. Kinesin family member C1 (KIFC1), a minus end-directed motor protein, is a novel Kinesin involved in the clustering of excess centrosomes found in cancer cells. Recently KIFC1 has shown to play a role in the progression of many different cancers, however, the involvement of KIFC1 in the progression of prostate cancer (PCa) is still not well understood. This study investigated the expression and clinical significance of KIFC1 in PCa by utilizing multiple publicly available datasets to analyze KIFC1 expression in patient samples. High KIFC1 expression was found to be associated with high Gleason score, high tumor stage, metastatic lesions, high ploidy levels, and lower recurrence-free survival. These results reveal that high KIFC1 levels are associated with a poor prognosis for PCa patients and could act as a prognostic indicator for PCa patients as well.

BRAF/MEK inhibitors for BRAF V600E-mutant cancers in non-approved setting: a case series.

The management of cancer has been traditionally dependent on the primary tumour type and specific histologic subtypes. Recently, the introduction of molecular profiling tools and its increasing use in clinical practice has facilitated the emergence of novel genomically driven treatment options within the standard of care landscape as well as in the clinical trial setting. One such aberration is mutation in v-Raf murine sarcoma viral oncogene homolog B (BRAF), which results in hyperactivation of RAS-RAF-MEK-ERK signaling in the Mitogen-activated protein kinases (MAPK) pathway. BRAF and Mitogen-activated protein kinase, extracellular signal-regulated kinase kinase (MEK) inhibitors, although being currently approved for melanoma, non-small cell lung cancer (NSCLC) and colon cancer, have reported activity across other various cancers harbouring BRAF aberrations. It has been proposed that combined MEK and BRAF inhibition could overcome the acquired resistance commonly developed among patients receiving BRAF or MEK inhibitors as monotherapy. We report five cases of BRAF V600E (substitution of glutamic acid for valine in codon 600) aberrant refractory metastatic cancers treated with dual BRAF/MEK combination inhibitor therapy leading to an excellent clinical and radiological response and protracted duration of disease control.

Recent Progress in the Systemic Treatment of Advanced/Metastatic Cholangiocarcinoma.

Cholangiocarcinomas (CCAs) comprise of a heterogeneous group of cancers arising in the biliary tract (intrahepatic or iCCA, perihilar or pCCA and distal or dCCA; the latter are known under the collective term of eCCA), each subtype having its own particularities in carcinogenesis, management and prognosis. The increasing incidence in recent decades, limited treatment options and high mortality rates, even in the early stages, have led to an imperious need for more in-depth understanding and development of tailored treatments for this type of aggressive tumour. The wide use of molecular profiling has increased the understanding of biology and identified key molecular drivers, for example, IDH1 mutations or FGFR2 fusions for iCCA, or BRAF mutations in eCCA. Most recently, the FDA approved pemigatinib, an FGFR inhibitor and ivosidenib, an IDH1 inhibitor, but even though progress has been made to better understand the mechanisms of tumorigenesis, genetic make-up, and tumour resistance to standard chemotherapy and targeted therapies, cholangiocarcinomas still represent an important challenge in the daily clinical practice of oncology. The purpose of this review is to highlight the recent progress in the systemic treatment of advanced/metastatic CCAs with a focus on targeted drugs and their biomarkers currently evaluated in early-phase clinical trials.

An in vitro tumor swamp model of heterogeneous cellular and chemotherapeutic landscapes.

The heterogenous, highly metabolic stressed, poorly irrigated, solid tumor microenvironment - the tumor swamp - is widely recognized to play an important role in cancer progression as well as the development of therapeutic resistance. It is thus important to create realistic in vitro models within the therapeutic pipeline that can recapitulate the fundamental stress features of the tumor swamp. Here we describe a microfluidic system which generates a chemical gradient within connected microenvironments achieved through a static diffusion mechanism rather than active pumping. We show that the gradient can be stably maintained for over a week. Due to the accessibility and simplicity of the experimental platform, the system allows for not only well-controlled continuous studies of the interactions among various cell types at single-cell resolution, but also parallel experimentation for time-resolved downstream cellular assays on the time scale of weeks. This approach enables simple, compact implementation and is compatible with existing 6-well imaging technology for simultaneous experiments. As a proof-of-concept, we report the co-culture of a human bone marrow stromal cell line and a bone-metastatic prostate cancer cell line using the presented device, revealing on the same chip a transition in cancer cell survival as a function of drug concentration on the population level while exhibiting an enrichment of poly-aneuploid cancer cells (PACCs) as an evolutionary consequence of high stress. The device allows for the quantitative study of cancer cell dynamics on a stress landscape by real-time monitoring of various cell types with considerable experimental throughput.

Generation of Heterogeneous Drug Gradients Across Cancer Populations on a Microfluidic Evolution Accelerator for Real-Time Observation.

Conventional cell culture remains the most frequently used preclinical model, despite its proven limited ability to predict clinical results in cancer. Microfluidic cancer-on-chip models have been proposed to bridge the gap between the oversimplified conventional 2D cultures and more complicated animal models, which have limited ability to produce reliable and reproducible quantitative results. Here, we present a microfluidic cancer-on-chip model that reproduces key components of a complex tumor microenvironment in a comprehensive manner, yet is simple enough to provide robust quantitative descriptions of cancer dynamics. This microfluidic cancer-on-chip model, the "Evolution Accelerator," breaks down a large population of cancer cells into an interconnected array of tumor microenvironments while generating a heterogeneous chemotherapeutic stress landscape. The progression and the evolutionary dynamics of cancer in response to drug gradient can be monitored for weeks in real time, and numerous downstream experiments can be performed complementary to the time-lapse images taken through the course of the experiments.

Polyploid giant cancer cells: Unrecognized actuators of tumorigenesis, metastasis, and resistance.

Cancer led to the deaths of more than 9 million people worldwide in 2018, and most of these deaths were due to metastatic tumor burden. While in most cases, we still do not know why cancer is lethal, we know that a total tumor burden of 1 kg-equivalent to one trillion cells-is not compatible with life. While localized disease is curable through surgical removal or radiation, once cancer has spread, it is largely incurable. The inability to cure metastatic cancer lies, at least in part, to the fact that cancer is resistant to all known compounds and anticancer drugs. The source of this resistance remains undefined. In fact, the vast majority of metastatic cancers are resistant to all currently available anticancer therapies, including chemotherapy, hormone therapy, immunotherapy, and systemic radiation. Thus, despite decades-even centuries-of research, metastatic cancer remains lethal and incurable. We present historical and contemporary evidence that the key actuators of this process-of tumorigenesis, metastasis, and therapy resistance-are polyploid giant cancer cells.

The role of heterogeneous environment and docetaxel gradient in the emergence of polyploid, mesenchymal and resistant prostate cancer cells.

The ability of a population of PC3 prostate epithelial cancer cells to become resistant to docetaxel therapy and progress to a mesenchymal state remains a fundamental problem. The progression towards resistance is difficult to directly study in heterogeneous ecological environments such as tumors. In this work, we use a micro-fabricated "evolution accelerator" environment to create a complex heterogeneous yet controllable in-vitro environment with a spatially-varying drug concentration. With such a structure we observe the rapid emergence of a surprisingly large number of polyploid giant cancer cells (PGCCs) in regions of very high drug concentration, which does not occur in conventional cell culture of uniform concentration. This emergence of PGCCs in a high drug environment is due to migration of diploid epithelial cells from regions of low drug concentration, where they proliferate, to regions of high drug concentration, where they rapidly convert to PGCCs. Such a mechanism can only occur in spatially-varying rather than homogeneous environments. Further, PGCCs exhibit increased expression of the mesenchymal marker ZEB1 in the same high-drug regions where they are formed, suggesting the possible induction of an epithelial to mesenchymal transition (EMT) in these cells. This is consistent with prior work suggesting the PGCC cells are mediators of resistance in response to chemotherapeutic stress. Taken together, this work shows the key role of spatial heterogeneity and the migration of proliferative diploid cells to form PGCCs as a survival strategy for the cancer population, with implications for new therapies.

Uptake of prostate-specific membrane antigen-targeted 18F-DCFPyL in avascular necrosis of the femoral head.

In recent years, the emergence of prostate-specific membrane antigen (PSMA)-targeted positron-emission tomography (PET) imaging has brought about a paradigm shift in the way that prostate cancer (PCa) is imaged in many parts of the world. Although PSMA-targeted PET imaging has been demonstrated to be a highly sensitive and specific imaging modality for the identification of sites of PCa, its clinical utility hinges on the ability of imaging specialists and their clinical colleagues to recognize potential false-positive sources of uptake and to tailor therapy based on that recognition. In this manuscript, we report the case of a 74-year-old male with a history of recurrent PCa who was referred for a restaging PSMA-targeted 18F-DCFPyL PET/computed tomography (PET/CT). PET images demonstrated low level but focal and definitive uptake in the left femoral head. This uptake corresponded to sclerotic changes on CT whose morphology was most compatible with avascular necrosis without femoral head collapse. In the presented case, the integrated assessment of the CT imaging together with the PET findings was fundamental to avoid misinterpretation of the left femur finding as metastatic disease, which would have ultimately altered the clinical management of the patient.

AXL Is a Putative Tumor Suppressor and Dormancy Regulator in Prostate Cancer.

Prostate cancer bone metastasis remains lethal and incurable, and often arises years after elimination of the primary tumor. It is unclear what underlies the decades-long clinical latency before recurrence, but evidence points to the existence of dormant residual tumor cells that disseminated before the primary tumor was eliminated. To design therapies to prevent progression of disseminated tumor cells (DTC) into lethal metastases, it is crucial to understand the mechanism(s) underlying this dormancy. The current study functionally validated our previous observation that implicated the GAS6/AXL axis in mediating DTC dormancy in the bone marrow. AXL-null and AXL-overexpressing prostate cancer cell lines were generated to determine if AXL was necessary and/or sufficient for dormancy. Characterization of these cells in vitro and using in vivo mouse models of DTC growth demonstrated that AXL was indeed sufficient to induce dormancy, but was unable to maintain it long-term and was not absolutely required for a dormancy period. Clinically, AXL expression correlated with longer survival in prostate cancer patients, and AXL was not expressed by cancer cells in primary or metastatic tissue. These data point to a tumor-suppressive role for AXL in prostate cancer, and future work is required to determine if AXL is expressed on human bone marrow DTCs. IMPLICATIONS: The ability of AXL to initiate but not maintain dormancy, coupled with its dispensability, suggests that targeting AXL alone will not prevent lethal metastatic outgrowth, and likely a cooperative network of factors exists to mediate long-term cellular dormancy.

HOXB13 interaction with MEIS1 modifies proliferation and gene expression in prostate cancer.

BACKGROUND: The recurrent p.Gly84Glu germline mutation (G84E) in HOXB13 is consistently associated with prostate cancer (PCa), although the mechanisms underlying such linkage remain elusive. The majority of the PCa-associated HOXB13 mutations identified are localized to two conserved domains in HOXB13 that have been shown to mediate the interaction with MEIS cofactors belonging to the TALE family of homeodomain transcription factors. In this study, we sought to interrogate the biochemical and functional interactions between HOXB13 and MEIS in prostatic cells with a goal of defining how the HOXB13-MEIS complex impacts PCa pathobiology and define the extent to which the oncogenic activity of G84E is related to its effect on HOXB13-MEIS interaction/function. METHODS: HOXB13 and MEIS paralog expression in prostate epithelial cells and PCa cell lines was characterized by qPCR and immunoblot analyses. HOXB13 and MEIS1 co-expression in human prostate tissue was confirmed by IHC, followed by co-IP mapping of HOXB13-MEIS1 interactions. Proliferation of the PCa cell line LAPC4 following shRNA-mediated knockdown of each gene or both genes was assessed using DNA- and metabolic-based assays. Transcriptional targets of HOXB13 and MEIS1 were identified by gene expression profiling and qPCR. Finally, protein stability of HOXB13 in the context of MEIS1 was determined using pulse-chase assays. RESULTS: HOXB13 and MEIS1 are co-expressed and interact in prostate cells. Both of the putative MEIS interacting domains (MID) within HOXB13 were shown to be capable of mediating the interaction between HOXB13 and MEIS1 independently and such interactions were not influenced by the G84E mutation. The inhibitory effect of either HOXB13 or MEIS1 knockdown on cellular proliferation was augmented by knockdown of both genes, and MEIS1 knockdown abolished HOXB13-driven regulation of BCHE and TNFSF10 mRNA expression. Notably, we demonstrated that MEIS1 stabilized the HOXB13 protein in LAPC4 cells. CONCLUSIONS: Our study provides evidence for functional HOXB13-MEIS1 interactions in PCa. MEIS1 may contribute to the cancer-promoting actions of HOXB13 in cellular proliferation and gene regulation by prolonging HOXB13 half-life. Our data demonstrates that G84E is not a loss-of-function mutation that interferes with HOXB13 stability or ability to interact with MEIS1.

Cancer dormancy and criticality from a game theory perspective.

BACKGROUND: The physics of cancer dormancy, the time between initial cancer treatment and re-emergence after a protracted period, is a puzzle. Cancer cells interact with host cells via complex, non-linear population dynamics, which can lead to very non-intuitive but perhaps deterministic and understandable progression dynamics of cancer and dormancy. RESULTS: We explore here the dynamics of host-cancer cell populations in the presence of (1) payoffs gradients and (2) perturbations due to cell migration. CONCLUSIONS: We determine to what extent the time-dependence of the populations can be quantitively understood in spite of the underlying complexity of the individual agents and model the phenomena of dormancy.

Epithelial and mesenchymal prostate cancer cell population dynamics on a complex drug landscape.

We have improved our microfluidic cell culture device that generates an in vitro landscape of stress heterogeneity. We now can do continuous observations of different cancer cell lines and carry out downstream analysis of cell phenotype as a function of position on the stress landscape. We use this technology to probe adaption and evolution dynamics in prostate cancer cell metapopulations under a stress landscape of a chemotherapeutic drug (docetaxel). The utility of this approach is highlighted by analysis of heterogenous prostate cancer cell motility changes as a function of position in the stress landscape. Because the technology presented here is easily adapted to a standard epifluorescence microscope it has the potential for broad application in preclinical drug development and assays of likely drug efficacy.

Alternative CD44 splicing identifies epithelial prostate cancer cells from the mesenchymal counterparts.

An epithelial to mesenchymal transition (EMT) has been shown to be a necessary precursor to prostate cancer metastasis. Additionally, the differential expression and splicing of mRNAs has been identified as a key means to distinguish epithelial from mesenchymal cells by qPCR, western blotting and immunohistochemistry. However, few markers exist to differentiate between these cells by flow cytometry. We previously developed two cell lines, PC3-Epi (epithelial) and PC3-EMT (mesenchymal). RNAseq was used to determine the differential expression of membrane proteins on PC3-Epi/EMT. We used western blotting, qPCR and flow cytometry to validate the RNAseq results. CD44 was one of six membrane proteins found to be differentially spliced between epithelial and mesenchymal PC3 cells. Although total CD44 was positive in all PC3-Epi/EMT cells, PC3-Epi cells had a higher level of CD44v6 (CD44 variant exon 6). CD44v6 was able to differentiate epithelial from mesenchymal prostate cancer cells using either flow cytometry, western blotting or qPCR.

Glycolysis is the primary bioenergetic pathway for cell motility and cytoskeletal remodeling in human prostate and breast cancer cells.

The ability of a cancer cell to detach from the primary tumor and move to distant sites is fundamental to a lethal cancer phenotype. Metabolic transformations are associated with highly motile aggressive cellular phenotypes in tumor progression. Here, we report that cancer cell motility requires increased utilization of the glycolytic pathway. Mesenchymal cancer cells exhibited higher aerobic glycolysis compared to epithelial cancer cells while no significant change was observed in mitochondrial ATP production rate. Higher glycolysis was associated with increased rates of cytoskeletal remodeling, greater cell traction forces and faster cell migration, all of which were blocked by inhibition of glycolysis, but not by inhibition of mitochondrial ATP synthesis. Thus, our results demonstrate that cancer cell motility and cytoskeleton rearrangement is energetically dependent on aerobic glycolysis and not oxidative phosphorylation. Mitochondrial derived ATP is insufficient to compensate for inhibition of the glycolytic pathway with regard to cellular motility and CSK rearrangement, implying that localization of ATP derived from glycolytic enzymes near sites of active CSK rearrangement is more important for cell motility than total cellular ATP production rate. These results extend our understanding of cancer cell metabolism, potentially providing a target metabolic pathway associated with aggressive disease.

The presence of androgen receptor elements regulates ZEB1 expression in the absence of androgen receptor.

Zinc finger E-box binding homeobox 1 (ZEB1) is a transcription factor that plays a central role in the epithelial to mesenchymal transition (EMT) of cancer cell lines. Studies on its regulation have mostly focused on the negative 3'UTR binding of miR200c. Interestingly, it has been previously reported that androgen receptor (AR) regulates ZEB1 expression in breast and prostate cancers. In order to validate this, various ZEB1 promoter deletions were cloned into a luciferase reporter system to elucidate the contribution of two putative androgen response elements (AREs). The in vivo contribution of AR was also assessed in cell lines after R1881 treatment using qPCR with prostate specific antigen (PSA) as the positive control. We discovered that AR upregulates the levels of expression of ZEB1 10-fold on a luciferase promoter that only contains the distal ARE. However, when the proximal ARE is included, no additional activation is apparent with AR or its hormone independent variant, AR-V7. Furthermore, we demonstrate here that a promoter construct containing both AREs activates transcription of ZEB1 even in the AR-null cell lines DU145 and PC3. Incubation of the AR-positive cell line, LNCaP with R1881, failed to substantially increase the expression levels of ZEB1. Despite the presence of AREs in the promoter region, it appears that ZEB1 expression can be induced even without AR. In addition, the region around the distal ARE is a potent repressor in AR-null cell lines.