Murine Pten T-ALL requires non-redundant PI3K/mTOR and DLL4/Notch1 signals for maintenance and γc/TCR signals for thymic exit

T cell acute lymphoblastic leukemias (T-ALLs) commonly display constitutively active PI3K/mTOR and Notch signaling. However, controversy surrounds whether these pathways have independent functions and whether Pten loss is sufficient to generate resistance to Notch inhibition. Here we report that Pten^−/− T-ALL is sensitive to either PI3K/mTOR or Notch inhibition alone, each pathway controlling distinct downstream signaling events that cannot be rescued by activation of the other pathway, consistent with independent, non-redundant functions. Although many human T-ALLs display constitutively activating Notch1 mutations, primary Pten^−/− T-ALLs expressed wild-type Notch1 and depended on the Notch ligand DLL4 in vivo. Pten^−/− T-ALLs with or without γc/TCR signaling responded similarly to PI3K/mTOR and Notch inhibition, although extended culture in vitro occasionally induced Notch-independent growth. However, unlike the T-ALLs lacking only Pten, eight of 23 Pten^−/− T-ALLs that also lacked γc/TCR signaling accumulated Notch1 mutations, suggesting crosstalk between γc/TCR and Notch signaling. Importantly, we concluded that loss of γc/TCR signaling also inhibited thymic exit of Pten^−/− T-ALLs. Our results may be clinically relevant in revealing that Pten loss is not sufficient to engender resistance to Notch inhibition, uncovering a role in T-ALL for ligand-dependent induction of wild-type Notch1, and suggesting that γc/TCR signaling could be targeted for preventing metastasis.     

Is α/β for breast cancer really low?

Purpose

Low α/β ratio for breast cancer has drawn a growing interest for exploring hypofractionation for breast irradiation. This work is to confirm the low α/β ratio based on large randomized clinical trials of breast irradiation.

Methods and materials

A model based on the generalized linear-quadratic (LQ) model and Poisson statistical model was developed to calculate disease-free survival with consideration of clonogen proliferation during the course of radiation treatment and exponential behavior of survival rate with follow-up time. Outcome data from a series of randomized clinical trials of early-stage breast radiotherapy were fitted to estimate the model parameters. Other clinical outcomes, including treatments with surgery alone or radiotherapy alone were used to validate the model and the estimated parameters. Hypofractionation regimens were proposed based on the newly estimated LQ parameters.

Results

Plausible population averaged radiobiologic parameters for breast cancer (95% confidence level) are α/β = 2.88 (0.75–5.01) Gy; α = 0.08 ± 0.02 Gy⁻¹; potential doubling time T_d = 14.4 ± 7.8 day. The analysis of the radiation-alone data suggested an α/β ratio of 3.89 ± 6.25 Gy, verifying the low α/β ratio based on the post-lumpectomy irradiation data. The hypofractionation regimens that are equivalent to the conventional regimen of 2.0 Gy × 25 in 5 weeks include 2.26 Gy × 20, 3.34 Gy × 10, 4.93 Gy × 5 or 3.39 Gy × 10 (BID).

Conclusions

The analysis of the available clinical data from multiple institutions support that breast cancer has a low ratio of α/β, encouraging hypofractionated radiotherapy regimens for breast cancer.     

Resected non-small-cell lung cancer stage I/II: indication for adjuvant/neoadjuvant therapy?

Complete surgical resection remains the current standard of care for operable patients with stage-I or stage-II non-small-cell lung cancer. However, there is a strong rationale that supports the concept of the addition of systemic therapy to surgery either preoperatively or postoperatively even in patients with early-stage disease, as distant relapse continues to be the dominant form of relapse after surgical resection of NSCLC. Earlier trials of adjuvant therapy have yielded mixed results and the survival gains demonstrated have been modest at best. However, recently presented data of randomised phase-III trials showed an absolute survival benefit of 12-15% for patients with completely resected stage-IB and stage-II NSCLC receiving adjuvant platinum-based chemotherapy compared with observation alone. These trials provide resounding approval for adjuvant chemotherapy being the new standard of care for patients with early-stage non-small-cell lung cancer who have undergone complete resection of the tumour.     

How low is the alpha/beta ratio for prostate cancer?

PURPOSE: Recently, low alpha/beta values of 1.2 and 1.5 Gy for prostate tumors have been derived from clinical results of external beam radiotherapy and of permanent implants of (125)I and (103)Pd. In the analyses the contributions of tumor repopulation, and edema as a result of inserting radioactive seeds in the prostate, have been ignored. In this paper we reanalyzed the clinical data and introduced the contribution of repopulation and edema. METHODS AND MATERIALS: The linear quadratic-biologically effective dose model was used for reanalysis. In this model, the influence of repopulation and edema has been taken into account. The biologically effective dose was calculated as a function of alpha/beta for 2 brachytherapy regimens with (125)I and (103)Pd and 2 fractionated treatments, and for different half-times for repair of sublethal damage for the brachytherapy regimens. RESULTS: We have found a plausible alpha/beta value of 3.1 to 3.9 Gy, an alpha value of 0.1 to 0.15 Gy(-1), and a half-time of repair of about 0.5 h. CONCLUSIONS: It seems now that the alpha/beta value is low, 3.1-3.9 Gy, but not as low as the 1.2 and 1.5 Gy reported earlier.     

How low is the alpha/beta ratio for prostate cancer?

PURPOSE: It has been suggested recently that the alpha/beta ratio for human prostate cancer is low (around 1.5 Gy), and much debate on the evidence for such a low value is ongoing. Analyses reported so far ignored the contribution of tumor repopulation. Extremely low alpha values and unrealistic cell numbers of tumor clonogens are found in these studies. In this paper, we present a comprehensive analysis of the updated clinical data to derive a self-consistent set of parameters for the linear-quadratic (LQ) model. METHODS AND MATERIALS: The generalized LQ model, considering the effects of dose rate, sublethal damage repair, and clonogenic proliferation, was used to analyze the recently reported clinical data for prostate cancer using either external-beam radiotherapy or brachytherapy. Three LQ parameters, alpha, alpha/beta, and the repair time, were determined based on the clinical finding that the external-beam radiotherapy and the 125I and (103)Pd permanent implants are biologically equivalent. The tumor control probability model was used also to analyze the clinical data to obtain an independent relationship of alpha/beta vs. alpha and to estimate clonogenic cell numbers for patients in different risk groups. RESULTS: Based on the analysis of clinical data and a consideration of repopulation effect, we have derived a self-consistent set of LQ parameters for prostate cancer: alpha = 0.15 +/- 0.04 Gy(-1), alpha/beta = 3.1 +/- 0.5 Gy. Our analysis indicates the half-time of sublethal damage repair to be in the range from 0 to 90 min with a best estimate of 16 min. The best estimate of clonogenic cell numbers in prostate tumors is found to range from 10(6) to 10(7) according to the patient risk level. These values are more realistic than those derived previously (only 10-100). CONCLUSION: The effect of tumor repopulation is not negligible in determining the LQ parameters for prostate cancer, especially for the low-dose-rate permanent implants. Analysis of clinical data for prostate cancer with corrections for damage repair and repopulation effects results in a low alpha/beta ratio of 3.1 Gy. Unrealistic clonogenic cell numbers and extremely small values of alpha reported in the literature can be resolved by correcting for repopulation effect. The LQ parameters derived presently from the clinical data are consistent with reports of intrinsic radiosensitivity in vitro.     

Calretinin is essential for mesothelioma cell growth/survival in vitro: A potential new target for malignant mesothelioma therapy?

Malignant mesothelioma (MM) are highly aggressive asbestos‐related neoplasms, which show strong chemotherapy resistance, and there is no effective cure for MM so far. Calretinin (CR) is widely used as a diagnostic marker for epithelioid and mixed (biphasic) mesothelioma; however, little is known about CR's putative functions in tumorigenesis. CR protects against asbestos‐induced acute cytotoxicity mediated by the AKT/PI3K pathway, and furthermore, SV40 early region genes are able to upregulate CR in mesothelial cells. However, the precise role of CR in mesothelioma is still unknown. Downregulation of CR via lentiviral‐mediated short‐hairpin RNA significantly decreased the viability and proliferation of mesothelioma cells in vitro. The effect was strong in epithelioid‐dominated cell lines (ZL55 and MSTO‐211H). A weaker and delayed effect was observed in mesothelioma cells with prevalent sarcomatoid morphology (SPC111, SPC212 and ZL34). The specificity of the effect was confirmed by stable enhanced green fluorescent protein‐CR expression in mesothelioma cell lines and subsequent downregulation. Depletion of CR led these cancer cell lines to enter apoptosis within 72 hr postinfection via strong activation of the intrinsic caspase 9‐dependent pathway. Downregulation of CR in immortalized mesothelial cells LP9/TERT‐1 strongly blocked proliferation and caused a G₁ block without decreasing viability or activating apoptosis pathways. These results demonstrate that downregulation of CR had a strong effect on the viability of MM cells and that CR is essential for cells derived from MM. The authors anticipate these findings to reveal CR as a highly interesting new putative therapeutic target for mesothelioma treatment of especially the epithelioid, as well as of the mixed and sarcomatoid type.     

A Bayesian population PK–PD model for ispinesib/docetaxel combination-induced myelosuppression

Purpose  Ispinesib, a kinesin spindle protein inhibitor, blocks assembly of a functional mitotic spindle, leading to G2/M arrest. Docetaxel promotes tubulin assembly into microtubules while inhibiting microtubule de-polymerization leading to mitotic arrest. Prolonged (≥5 days) Gr 4 neutropenia and/or febrile neutropenia were the observed dose-limiting toxicities with both agents. Both agents are substrates and inhibitors of CYP3A4; thus, the potential for a drug–drug interaction exists. The goal was to fit a Bayesian population PK/PD model to characterize the relationship between the ispinesib/docetaxel combination and absolute neutrophil counts (ANC). Methods  Escalating doses of docetaxel (60–75 mg/m²) were administered over 1 h followed by a 1-h infusion of escalating doses of ispinesib (8–12 mg/m²) on a 21-day schedule. At least 3 pts were treated at each dose level. Limited PK samples were obtained. ANC were measured weekly on days 1, 8, 15, and 22. More ANC samples were taken from some subjects. The PK properties of ispinesib and docetaxel, and the relationship of PK with ANC were investigated using nonlinear mixed-effects models and Bayesian methods. With a limited dataset, informative prior distributions for the model parameters were needed. These prior distributions were formed using information from a previous study for ispinesib, and from the literature for docetaxel. Results  Twenty-four pts were treated in this study. The PK of ispinesib and docetaxel were well characterized by a two-compartment model and a three-compartment model, respectively. There is no obvious PK interaction between ispinesib and docetaxel. The model for ANC consisted of a proliferating compartment, three transit compartments that represented maturation, and a compartment of circulating blood cells. This ANC model has been used previously for ispinesib given as monotherapy, and for other chemotherapeutic drugs in the literature. Using Bayesian methods, the model was successfully fit for the PK of both compounds and the PD simultaneously. Conclusions  The PK/PD model developed for ispinesib/docetaxel, may be used to examine different schedules, doses, and infusion times of both agents. Bayesian methods allow for the use of prior information available for the model parameters.     

An identity crisis for fps/fes: oncogene or tumor suppressor?

Fps/Fes proteins were among the first members of the protein tyrosine kinase family to be characterized as dominant-acting oncoproteins. Addition of retroviral GAG sequences or other experimentally induced mutations activated the latent transforming potential of Fps/Fes. However, activating mutations in fps/fes had not been found in human tumors until recently, when mutational analysis of a panel of colorectal cancers identified four somatic mutations in sequences encoding the Fps/Fes kinase domain. Here, we report biochemical and theoretical structural analysis demonstrating that three of these mutations result in inactivation, not activation, of Fps/Fes, whereas the fourth mutation compromised in vivo activity. These results did not concur with a classic dominant-acting oncogenic role for fps/fes involving activating somatic mutations but instead raised the possibility that inactivating fps/fes mutations might promote tumor progression in vivo. Consistent with this, we observed that tumor onset in a mouse model of breast epithelial cancer occurred earlier in mice targeted with either null or kinase-inactivating fps/fes mutations. Furthermore, a fps/fes transgene restored normal tumor onset kinetics in targeted fps/fes null mice. These data suggest a novel and unexpected tumor suppressor role for Fps/Fes in epithelial cells.     

Is mda-7/IL-24 a "magic bullet" for cancer?

The "holy grail" of cancer therapy is to identify and exploit genetic elements and signal transduction pathways capable of selectively destroying tumor cells without eliciting harmful effects in normal cells or tissues. To achieve this objective, subtraction hybridization was combined with a "differentiation therapy" model of cancer in which human melanoma cells were induced to revert to a more "normal" state, growth arrest irreversibly, and terminally differentiate by treatment with fibroblast IFN and mezerein. This strategy permitted the cloning of a variety of genes involved in regulating important physiologic processes, including cell cycle, response to cytokines and viruses, tumorigenesis and metastasis, cancer growth control, apoptosis, and senescence. A specific gene, melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24), displaying cancer-specific apoptosis-inducing properties isolated using this scheme has now come into the limelight as a new gene therapy for divergent cancers. Although the mechanism of cancer cell selectivity of mda-7/IL-24 remains to be delineated, numerous attributes enable this gene as an effective therapy for cancer, including an ability to discriminate between normal and cancer cells, induce apoptosis in diverse tumor cells, promote "bystander" antitumor effects, inhibit tumor growth and angiogenesis in animal models, synergize with radiation, and modulate immune responses. These unique features combined with successful transition into the clinic instill confidence that mda-7/IL-24, as a single or more likely as part of a combinatorial approach, may provide profound therapeutic benefit for cancer patients.     

Where Do the New Drugs Fit in for Relapsed/Refractory Hodgkin Lymphoma?

The standard approach for relapsed or refractory (rel/ref) Hodgkin lymphoma (HL) following frontline treatment failure is salvage therapy followed by consolidation with high-dose therapy and autologous stem cell transplant (HDT/ASCT). While this overall treatment paradigm has been in place for several decades, recent studies have aimed to improve the efficacy and tolerability of salvage therapies by incorporating newer drugs, such as brentuximab vedotin (BV) and checkpoint inhibitors. Following HDT/ASCT, survival is improved due to the availability of BV and the checkpoint inhibitors, nivolumab and pembrolizumab; however, for patients responding to checkpoint inhibition, the appropriate length of treatment and the role of allogeneic stem cell transplant are unclear. In this review, we discuss our management of rel/ref HL, with particular focus on how BV, nivolumab, and pembrolizumab are currently incorporated into the treatment paradigms for rel/ref HL.     

EORTC consensus recommendations for the treatment of mycosis fungoides/Sézary syndrome

Several reviews and guidelines on the management of mycosis fungoides and Sézary syndrome (MF/SS) have been published; however, treatment strategies for patients with MF/SS vary from institution to institution and no European consensus has yet been established. There are few phase III trials to support treatment decisions for MF/SS and treatment is often determined by institutional experience. In order to summarise the available evidence and review 'best practices' from each national group, the European Organisation for Research and Treatment of Cancer (EORTC) Cutaneous Lymphoma Task Force met in September 2004 to establish European guidelines for the treatment of MF/SS. This article reviews the treatment regimens selected for inclusion in the guidelines and summarises the clinical data for treatments appropriate for each stage of MF/SS. Guideline recommendations are presented according to the quality of supporting data, as defined by the Oxford Centre for Evidence-Based Medicine. Skin-directed therapies are the most appropriate option for early-stage MF/SS and most patients can look forward to a normal life expectancy. Patients with advanced disease should be encouraged to participate in clinical trials and maintenance of quality of life should be paramount.     

Novel role for CRK adaptor proteins as essential components of SRC/FAK signaling for epithelial–mesenchymal transition and colorectal cancer aggressiveness

Epithelial–mesenchymal transition (EMT) is a cell plasticity process required for metastasis and chemoresistance of carcinoma cells. We report a crucial role of the signal adaptor proteins CRK and CRKL in promoting EMT and tumor aggressiveness, as well as resistance against chemotherapy in colorectal and pancreatic carcinoma. Genetic loss of either CRKL or CRK partially counteracted EMT in three independent cancer cell lines. Strikingly, complete loss of the CRK family shifted cells strongly toward the epithelial phenotype. Cells exhibited greatly increased E-cadherin and grew as large, densely packed clusters, completely lacked invasiveness and the ability to undergo EMT induced by cytokines or genetic activation of SRC. Furthermore, CRK family-deficiency significantly reduced cell survival, proliferation and chemoresistance, as well as ERK1/2 phosphorylation and c-MYC protein levels. In accordance, MYC-target gene expression was identified as novel hallmark process positively regulated by CRK family proteins. Mechanistically, CRK proteins were identified as pivotal amplifiers of SRC/FAK signaling at focal adhesions, mediated through a novel positive feedback loop depending on RAP1. Expression of the CRK family and the EMT regulator ZEB1 was significantly correlated in samples from colorectal cancer patients, especially in invasive regions. Further, high expression of CRK family genes was significantly associated with reduced survival in locally advanced colorectal cancer, as well as in pan-cancer datasets from the TCGA project. Thus, CRK family adaptor proteins are promising therapeutic targets to counteract EMT, chemoresistance, metastasis formation and minimal residual disease. As proof of concept, CRK family-mediated oncogenic signaling was successfully inhibited by a peptide-based inhibitor.