In vivo PDX CRISPR/Cas9 screens reveal mutual therapeutic targets to overcome heterogeneous acquired chemo-resistance

Resistance towards cancer treatment represents a major clinical obstacle, preventing cure of cancer patients. To gain mechanistic insights, we developed a model for acquired resistance to chemotherapy by treating mice carrying patient derived xenografts (PDX) of acute lymphoblastic leukemia with widely-used cytotoxic drugs for 18 consecutive weeks. In two distinct PDX samples, tumors initially responded to treatment, until stable disease and eventually tumor re-growth evolved under therapy, at highly similar kinetics between replicate mice. Notably, replicate tumors developed different mutations in TP53 and individual sets of chromosomal alterations, suggesting independent parallel clonal evolution rather than selection, driven by a combination of stochastic and deterministic processes. Transcriptome and proteome showed shared dysregulations between replicate tumors providing putative targets to overcome resistance. In vivo CRISPR/Cas9 dropout screens in PDX revealed broad dependency on BCL2, BRIP1 and COPS2. Accordingly, venetoclax re-sensitized derivative tumors towards chemotherapy, despite genomic heterogeneity, demonstrating direct translatability of the approach. Hence, despite the presence of multiple resistance-associated genomic alterations, effective rescue treatment for polychemotherapy-resistant tumors can be identified using functional testing in preclinical models.

X-linked inhibitor of apoptosis protein represents a promising therapeutic target for relapsed/refractory ALL

Acute lymphoblastic leukemia (ALL) represents the most frequent malignancy in children, and relapse/refractory (r/r) disease is difficult to treat, both in children and adults. In search for novel treatment options against r/r ALL, we studied inhibitor of apoptosis proteins (IAP) and Smac mimetics (SM). SM-sensitized r/r ALL cells towards conventional chemotherapy, even upon resistance against SM alone. The combination of SM and chemotherapy-induced cell death via caspases and PARP, but independent from cIAP-1/2, RIPK1, TNFα or NF-κB. Instead, XIAP was identified to mediate SM effects. Molecular manipulation of XIAP in vivo using microRNA-30 flanked shRNA expression in cell lines and patient-derived xenograft (PDX) models of r/r ALL mimicked SM effects and intermediate XIAP knockdown-sensitized r/r ALL cells towards chemotherapy-induced apoptosis. Interestingly, upon strong XIAP knockdown, PDX r/r ALL cells were outcompeted in vivo, even in the absence of chemotherapy. Our results indicate a yet unknown essential function of XIAP in r/r ALL and reveal XIAP as a promising therapeutic target for r/r ALL.

Tumor Cell Dormancy-Triggered by the Niche

Dormant cancer cells often survive treatment and increase the risk for tumor relapse, associated with dismal prognosis. Two recent papers describe mechanisms used by the bone marrow niche to regulate leukemia dormancy. The findings provide a molecular basis for niche-targeting therapies that may enable elimination of dormant tumor cells.

Ubiquitin Ligases in Cancer Immunotherapy - Balancing Antitumor and Autoimmunity

Considerable progress has been made in understanding the contribution of E3 ubiquitin ligases to health and disease, including the pathogenesis of immunological disorders. Ubiquitin ligases exert exquisite spatial and temporal control over protein stability and function, and are thus crucial for the regulation of both innate and adaptive immunity. Given that immune responses can be both detrimental (autoimmunity) and beneficial (antitumor immunity), it is vital to understand how ubiquitin ligases maintain immunological homeostasis. Such knowledge could reveal novel mechanisms underlying immune regulation and identify new therapeutic approaches to enhance antitumor immunity and safeguard against autoimmunity.

A rare subgroup of leukemia stem cells harbors relapse-inducing potential in acute lymphoblastic leukemia

After initially successful chemotherapy, relapse frequently jeopardizes the outcome of patients with acute leukemia. Because of their adverse characteristics of self-renewal and dormancy, leukemia stem cells have been hypothesized to play a critical role in resistance to antiproliferative chemotherapy and the development of relapse. The high abundance of stem-like cells in acute lymphoblastic leukemia (ALL), however, suggests that not all leukemia-initiating cells carry these adverse characteristics, complicating the biological characterization of relapse-inducing cells in this malignancy. Here, we review sources of therapy resistance and relapse in acute leukemias, which include tumor cell plasticity and reversible characteristics. We discuss the development of patient-derived mouse models that are genetically engineered to mimic long-term dormancy and minimal residual disease in patients. These models allow the tracking and functional characterization of patient-derived ALL blasts that combine the properties of long-term dormancy, treatment resistance, and stemness. Finally, we discuss possible therapeutic avenues to target the functional plasticity of leukemia-initiating cells in ALL.

Ubiquitin ligases in oncogenic transformation and cancer therapy

The cellular response to external stress signals and DNA damage depends on the activity of ubiquitin ligases (E3s), which regulate numerous cellular processes, including homeostasis, metabolism and cell cycle progression. E3s recognize, interact with and ubiquitylate protein substrates in a temporally and spatially regulated manner. The topology of the ubiquitin chains dictates the fate of the substrates, marking them for recognition and degradation by the proteasome or altering their subcellular localization or assembly into functional complexes. Both genetic and epigenetic alterations account for the deregulation of E3s in cancer. Consequently, the stability and/or activity of E3 substrates are also altered, in some cases leading to downregulation of tumour-suppressor activities and upregulation of oncogenic activities. A better understanding of the mechanisms underlying E3 regulation and function in tumorigenesis is expected to identify novel prognostic markers and to enable the development of the next generation of anticancer therapies. This Review summarizes the oncogenic and tumour-suppressor roles of selected E3s and highlights novel opportunities for therapeutic intervention.

Adaptive Stress Responses During Tumor Metastasis and Dormancy

To survive inhospitable environments, tumor cells are forced to remodel their signaling pathways by altering transcription, translation, and post-translational modifications. This adaptation is regulated in a spatial and temporal manner and gives rise to individual tumor cells with distinct gene expression and metabolic signatures. Such phenotypic heterogeneity is the result of tumor cell plasticity, which-together with the genetic background of the tumor-determines whether cells resist environmental stress, enter dormancy, or metastasize. This review summarizes our understanding of how tumor cells exploit the cellular stress response to balance proliferation, differentiation, and survival signals, and to remodel local and distant environments. We focus in particular on tumor metastasis, which is the greatest impediment to clinical management of cancers today.

Precision Oncology: The Road Ahead

Current efforts in precision oncology largely focus on the benefit of genomics-guided therapy. Yet, advances in sequencing techniques provide an unprecedented view of the complex genetic and nongenetic heterogeneity within individual tumors. Herein, we outline the benefits of integrating genomic and transcriptomic analyses for advanced precision oncology. We summarize relevant computational approaches to detect novel drivers and genetic vulnerabilities, suitable for therapeutic exploration. Clinically relevant platforms to functionally test predicted drugs/drug combinations for individual patients are reviewed. Finally, we highlight the technological advances in single cell analysis of tumor specimens. These may ultimately lead to the development of next-generation cancer drugs, capable of tackling the hurdles imposed by genetic and phenotypic heterogeneity on current anticancer therapies.

Regulators of mitochondrial dynamics in cancer

Mitochondrial dynamics encompasses processes associated with mitochondrial fission and fusion, affecting their number, degree of biogenesis, and the induction of mitophagy. These activities determine the balance between mitochondrial energy production and cell death programs. Processes governing mitochondrial dynamics are tightly controlled in physiological conditions and are often deregulated in cancer. Mitochondrial protein homeostasis, transcriptional regulation, and post-translational modification are among processes that govern the control of mitochondrial dynamics. Cancer cells alter mitochondrial dynamics to resist apoptosis and adjust their bioenergetic and biosynthetic needs to support tumor initiating and transformation properties including proliferation, migration, and therapeutic resistance. This review focuses on key regulators of mitochondrial dynamics and their role in cancer.

The use of granulocyte colony stimulating factor to enhance oocyte release in women with the luteinized unruptured follicle syndrome

PURPOSE

To determine if an injection of granulocyte colony stimulating factor (G-CSF) prevoulatory can enable oocyte release from the follicle in women who have failed to release in natural cycles despite an endogenous luteinizing hormone (LH) surge, and also despite treatment with human chorionic gonadotropin (hCG) or a gonadotropin releasing hormone agonist (GnRHa).

MATERIALS AND METHODS

A single injection of 100 mg G-CSF was given in the late follicular phase followed by hCG 10,000 units at peak follicular maturation in women with at least three consecutive cycles of luteinization without oocyte release.

RESULTS

Six women had ten cycles with G-CSF and hCG. Definite release occurred in four, inconclusive in four, and definitely the luteinized unruptured follicle in two. Biochemical pregnancies occurred in two of the cycles where oocyte release occurred and a live delivered pregnancy in another cycle of release.

CONCLUSIONS

Without controls one cannot state with certainty that G-CSF enabled oocyte release when hCG and leuprolide failed. Nevertheless, the data do support a trial with G-CSF before proceeding to IVF-ET.

Immunogenic, cellular, and angiogenic drivers of tumor dormancy--a melanoma view

In tumor cells, the ability to maintain viability over long time periods without proliferation is referred to as a state of dormancy. Maintenance of dormancy is controlled by numerous cellular and environmental factors, from immune surveillance and tumor-stroma interaction to intracellular signaling. Interference of dormancy (to an 'awaken' state) is associated with reduced response to therapy, resulting in relapse or in metastatic burst. Thus, maintaining a dormant state should prolong therapeutic responses and delay metastasis. Technical obstacles in studying tumor dormancy have limited our understanding of underlying mechanisms and hampered our ability to target dormant cells. In this review, we summarize the progress of research in the field of immunogenic, angiogenic, and cellular dormancy in diverse malignancies with particular attention to our current understanding in melanoma.

In non-transformed cells Bak activates upon loss of anti-apoptotic Bcl-XL and Mcl-1 but in the absence of active BH3-only proteins

Mitochondrial apoptosis is controlled by proteins of the B-cell lymphoma 2 (Bcl-2) family. Pro-apoptotic members of this family, known as BH3-only proteins, initiate activation of the effectors Bcl-2-associated X protein (Bax) and Bcl-2 homologous antagonist/killer (Bak), which is counteracted by anti-apoptotic family members. How the interactions of Bcl-2 proteins regulate cell death is still not entirely clear. Here, we show that in the absence of extrinsic apoptotic stimuli Bak activates without detectable contribution from BH3-only proteins, and cell survival depends on anti-apoptotic Bcl-2 molecules. All anti-apoptotic Bcl-2 proteins were targeted via RNA interference alone or in combinations of two in primary human fibroblasts. Simultaneous targeting of B-cell lymphoma-extra large and myeloid cell leukemia sequence 1 led to apoptosis in several cell types. Apoptosis depended on Bak whereas Bax was dispensable. Activator BH3-only proteins were not required for apoptosis induction as apoptosis was unaltered in the absence of all BH3-only proteins known to activate Bax or Bak directly, Bcl-2-interacting mediator of cell death, BH3-interacting domain death agonist and p53-upregulated modulator of apoptosis. These findings argue for auto-activation of Bak in the absence of anti-apoptotic Bcl-2 proteins and provide evidence of profound differences in the activation of Bax and Bak.

UPR, autophagy, and mitochondria crosstalk underlies the ER stress response

Cellular stress, induced by external or internal cues, activates several well-orchestrated processes aimed at either restoring cellular homeostasis or committing to cell death. Those processes include the unfolded protein response (UPR), autophagy, hypoxia, and mitochondrial function, which are part of the global endoplasmic reticulum (ER) stress (ERS) response. When one of the ERS elements is impaired, as often occurs under pathological conditions, overall cellular homeostasis may be perturbed. Further, activation of the UPR could trigger changes in mitochondrial function or autophagy, which could modulate the UPR, exemplifying crosstalk processes. Among the numerous factors that control the magnitude or duration of these processes are ubiquitin ligases, which govern overall cellular stress outcomes. Here we summarize crosstalk among the fundamental processes governing ERS responses.

RACK1 Function in Cell Motility and Protein Synthesis

The receptor for activated C kinase 1 (RACK1) serves as an adaptor for a number of proteins along the MAPK, protein kinase C, and Src signaling pathways. The abundance and near ubiquitous expression of RACK1 reflect its role in coordinating signaling molecules for many critical biological processes, from mRNA translation to cell motility to cell survival and death. Complete deficiency of Rack1 is embryonic lethal, but the recent development of genetic Rack1 hypomorphic mice has highlighted the central role that RACK1 plays in cell movement and protein synthesis. This review focuses on the importance of RACK1 in these processes and places the recent work in the larger context of understanding RACK1 function.

The neural crest transcription factor Brn3a is expressed in melanoma and required for cell cycle progression and survival

Pigment cells and neuronal cells both are derived from the neural crest. Here, we describe the Pit-Oct-Unc (POU) domain transcription factor Brn3a, normally involved in neuronal development, to be frequently expressed in melanoma, but not in melanocytes and nevi. RNAi-mediated silencing of Brn3a strongly reduced the viability of melanoma cell lines and decreased tumour growth in vivo. In melanoma cell lines, inhibition of Brn3a caused DNA double-strand breaks as evidenced by Mre11/Rad50-containing nuclear foci. Activated DNA damage signalling caused stabilization of the tumour suppressor p53, which resulted in cell cycle arrest and apoptosis. When Brn3a was ectopically expressed in primary melanocytes and fibroblasts, anchorage-independent growth was increased. In tumourigenic melanocytes and fibroblasts, Brn3a accelerated tumour growth in vivo. Furthermore, Brn3a cooperated with proliferation pathways such as oncogenic BRAF, by reducing oncogene-induced senescence in non-malignant melanocytes. Together, these results identify Brn3a as a new factor in melanoma that is essential for melanoma cell survival and that promotes melanocytic transformation and tumourigenesis.

Selective induction of cell death in melanoma cell lines through targeting of Mcl-1 and A1

Melanoma is an often fatal form of skin cancer which is remarkably resistant against radio- and chemotherapy. Even new strategies that target RAS/RAF signaling and display unprecedented efficacy are characterized by resistance mechanisms. The targeting of survival pathways would be an attractive alternative strategy, if tumor-specific cell death can be achieved. Bcl-2 proteins play a central role in regulating survival of tumor cells. In this study, we systematically investigated the relevance of antiapoptotic Bcl-2 proteins, i.e., Bcl-2, Bcl-xL, Bcl-w, Mcl-1, and A1, in melanoma cell lines and non-malignant cells using RNAi. We found that melanoma cells required the presence of specific antiapoptotic Bcl-2 proteins: Inhibition of Mcl-1 and A1 strongly induced cell death in some melanoma cell lines, whereas non-malignant cells, i.e., primary human fibroblasts or keratinocytes were not affected. This specific sensitivity of melanoma cells was further enhanced by the combined inhibition of Mcl-1 and A1 and resulted in 60% to 80% cell death in all melanoma cell lines tested. This treatment was successfully combined with chemotherapy, which killed a substantial proportion of cells that survived Mcl-1 and A1 inhibition. Together, these results identify antiapoptotic proteins on which specifically melanoma cells rely on and, thus, provide a basis for the development of new Bcl-2 protein-targeting therapies.

Proapoptotic signaling induced by RIG-I and MDA-5 results in type I interferon-independent apoptosis in human melanoma cells

The retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated antigen 5 (MDA-5) helicases sense viral RNA in infected cells and initiate antiviral responses such as the production of type I IFNs. Here we have shown that RIG-I and MDA-5 also initiate a proapoptotic signaling pathway that is independent of type I IFNs. In human melanoma cells, this signaling pathway required the mitochondrial adapter Cardif (also known as IPS-1) and induced the proapoptotic BH3-only proteins Puma and Noxa. RIG-I- and MDA-5-initiated apoptosis required Noxa but was independent of the tumor suppressor p53. Triggering this pathway led to efficient activation of mitochondrial apoptosis, requiring caspase-9 and Apaf-1. Surprisingly, this proapoptotic signaling pathway was also active in nonmalignant cells, but these cells were much less sensitive to apoptosis than melanoma cells. Endogenous Bcl-xL rescued nonmalignant, but not melanoma, cells from RIG-I- and MDA-5-mediated apoptosis. In addition, we confirmed the results of the in vitro studies, demonstrating that RIG-I and MDA-5 ligands both reduced human tumor lung metastasis in immunodeficient NOD/SCID mice. These results identify an IFN-independent antiviral signaling pathway initiated by RIG-I and MDA-5 that activates proapoptotic signaling and, unless blocked by Bcl-xL, results in apoptosis. Due to their immunostimulatory and proapoptotic activity, RIG-I and MDA-5 ligands have therapeutic potential due to their ability to overcome the characteristic resistance of melanoma cells to apoptosis.

Effect of periosteal stripping on cortical bone perfusion: a laser doppler study in sheep

The goals of internal fixation are an accurate reduction and stable fixation in the presence of adequate bony vascularity. This can be achieved by a variety of means including plate fixation. A certain amount of periosteal stripping is necessary for proper open reduction of a fracture and for proper plate application. With displaced diaphyseal fractures, cortical bone perfusion (CBP) is already compromised. Further damage, in terms of periosteal stripping for plate fixation, may not be acceptable. Little information is available as to what extent the periosteum contributes to cortical bone perfusion. The purpose of this study was to determine the acute effects of periosteal stripping on cortical bone perfusion in a sheep tibia model. Twenty-three sheep were operated on and had the medial aspect of their right tibia exposed. Cortical bone perfusion measurements were obtained using laser Doppler flowmetry prior to periosteal stripping and after periosteal stripping. The results of this study show that the cortical bone perfusion significantly decreased by 20% after periosteal stripping over the entire length of the tibia. We therefore conclude that the periosteum contributes to diaphyseal bone perfusion and that it is important to preserve this source with fractures where blood supply is already significantly compromised.

Cortical bone perfusion in plated fractured sheep tibiae

The limited contact dynamic compression plate and partial contact plate were designed to decrease contact with cortical bone in an attempt to decrease cortical ischemia, remodeling, and eventual porosis under the plate after use of standard dynamic compression plates. This study quantified cortical bone blood flow beneath the plate with these three different designs in a sheep tibia fracture model. In 18 skeletally immature sheep, the right tibia was fractured and then was internally fixed with an interfragmentary screw and a dynamic compression plate, limited contact dynamic compression plate, or partial contact plate. At 12 weeks, cortical bone perfusion was assessed with laser Doppler flowmetry in nine areas beneath the plate. The baseline (before fracture) cortical bone cell flux averaged 100 +/- 60 mV. After fracture, this decreased to 60 +/- 48 mV (p < 0.0003); immediately after plating, the perfusion averaged 29 +/- 25 mV (p < 0.01). Cortical bone perfusion then increased to 106 +/- 52, 165 +/- 71, and 163 +/- 71 mV at 2, 6, and 12 weeks after fracture (p < 0.001 for all when compared with values after plating). No significant differences in cortical perfusion were seen between the types of plate. Cortical porosity under the plate was assessed with digital density analysis of microradiographs of this region. No significant difference was seen between the types of plate in this analysis or in biomechanical and disulphine blue perfusion analysis. Thus, no significant advantage was seen for the new plate designs used in this model. This lack of advantage may be a result of the immature animals used in the study, the protocol for blood flow measurement, the invasive periosteal stripping employed to create the fracture, or all three. However, as advantages with the new plate designs have been seen in other studies, this area warrants further investigation.

Cortical bone blood flow in reamed and unreamed locked intramedullary nailing: a fractured tibia model in sheep

We compared the effects of reamed versus unreamed locked intramedullary nailing on cortical bone blood flow in a fractured sheep tibia model. A standardized spiral fracture was created by three-point bending with torsion, and each tibia was stabilized by insertion of a locked intramedullary nail. Eleven animals were randomized into two groups: one that had reaming before nail insertion and one that did not. Blood flow was measured in real time using laser Doppler flowmetry. Cortical bone perfusion measurements were made at three locations (proximal diaphysis, fracture site, distal diaphysis) and at eight time intervals (prefracture, postfracture, postreaming, postnail insertion, postlocking, and at 2-, 6-, and 12-week follow-up). All animals were killed at 12 weeks postoperatively. After reamed nail insertion, cortical bone perfusion was significantly decreased (p < 0.0009). After unreamed nail insertion, perfusion was decreased less (p < 0.003). Insertion of locking screws did not affect blood flow. Cortical bone perfusion was greater in the unreamed group at completion of the procedure (p < 0.011), at 2-week follow-up (p < 0.006) and at 6-week follow-up (p < 0.027). The findings suggest that cortical revascularization had occurred by 6 weeks in the unreamed group but not until 12 weeks in the reamed group. The study demonstrates that cortical circulation is spared to a greater degree by unreamed nailing. This may be advantageous in severe open tibial fractures where blood supply is already significantly compromised.

Geometric changes in the cervical spinal canal during impact

SUMMARY OF BACKGROUND DATA

Although the extent of injury after cervical spine fracture can be visualized by imaging, the deformations that occur in the spinal canal during injury are unknown.

STUDY DESIGN

This study compared spinal canal occlusion and axial length changes occurring during a simulated compressive burst fracture with the residual deformations after the injury.

METHODS

Canal occlusion was measured from changes in pressure in a flexible tube with fluid flowing through it, placed in the canal space after removal of the cord in cadaver specimens. To measure canal axial length, cables were fixed in C1 and led through the foramen transversarium from C2-T1, then out through the base, where they were connected to the core rods of linearly variable differential transformers (LVDT). Axial compressive burst fractures were created in each of ten cadaveric cervical spine specimens using a drop-weight, while force, distraction, and occlusion were monitored throughout the injury event. Pre- and post-injury radiographs and computed tomography scans compared transient and post-injury spinal canal geometry changes.

RESULTS

In all cases, severe compressive injuries were produced. Three had an extension component in addition to compression of the vertebra and retropulsion of bone into the canal. The mean post-injury axial height loss measured from radiographs was only 35% of that measured transiently (3.1 mm post-injury, compared with 8.9 mm measured transiently), indicating significant recovery of axial height after impact. Post-injury and transient height loss were not significantly correlated (r2 = 0.230, P = 0.16) demonstrating that it is not a good measure of the extent of injury. Similarly, mean post injury canal area was 139% of the minimum area measured during impact, indicating recovery of canal space, and post-injury and transient values were not significantly correlated (r2 = 0.272, P = 0.12). Mean post-injury midsagittal diameter was 269% of the minimum transient diameter and showed a weak but significant correlation (r2 = 0.481, P = 0.03).

CONCLUSIONS

Two potential spinal cord injury-causing mechanisms in axial bursting injuries of the cervical spine are occlusion and shortening of the canal. Post-injury radiographic measurements significantly underestimate the actual transient injury that occurs during impact.

Cortical bone microperfusion: response to ischemia and changes in major arterial blood flow

In order to investigate the effects of short-term ischemia on cortical bone microperfusion, an isolated porcine tibia diaphyseal preparation based on intact nutrient vessels was developed. Laser Doppler flowmetry (LDF) was utilized to assess continuously the cortical microcirculation and the response to short-term ischemia. The femoral artery was isolated and clamped to develop the condition of bone ischemia. On release of the clamp, reactive hyperemia was documented in all animals. Using a roller pump connected to a segment of femoral artery, the same preparation was utilized to investigate the effect of a changing femoral artery flow on the cortical microcirculation. A positive correlation between LDF output and change in arterial inflow (r = 0.64) was defined. This model has the potential for studying the effect of ischemia on bone cell viability.