Acquired mutations are pervasive across normal tissues. However, understanding of the processes that drive transformation of certain clones to cancer is limited. Here we study this phenomenon in the ...context of clonal hematopoiesis (CH) and the development of therapy-related myeloid neoplasms (tMNs). We find that mutations are selected differentially based on exposures. Mutations in ASXL1 are enriched in current or former smokers, whereas cancer therapy with radiation, platinum and topoisomerase II inhibitors preferentially selects for mutations in DNA damage response genes (TP53, PPM1D, CHEK2). Sequential sampling provides definitive evidence that DNA damage response clones outcompete other clones when exposed to certain therapies. Among cases in which CH was previously detected, the CH mutation was present at tMN diagnosis. We identify the molecular characteristics of CH that increase risk of tMN. The increasing implementation of clinical sequencing at diagnosis provides an opportunity to identify patients at risk of tMN for prevention strategies.
We present a powerful experimental-computational technology for inferring network models that predict the response of cells to perturbations, and that may be useful in the design of combinatorial ...therapy against cancer. The experiments are systematic series of perturbations of cancer cell lines by targeted drugs, singly or in combination. The response to perturbation is quantified in terms of relative changes in the measured levels of proteins, phospho-proteins and cellular phenotypes such as viability. Computational network models are derived de novo, i.e., without prior knowledge of signaling pathways, and are based on simple non-linear differential equations. The prohibitively large solution space of all possible network models is explored efficiently using a probabilistic algorithm, Belief Propagation (BP), which is three orders of magnitude faster than standard Monte Carlo methods. Explicit executable models are derived for a set of perturbation experiments in SKMEL-133 melanoma cell lines, which are resistant to the therapeutically important inhibitor of RAF kinase. The resulting network models reproduce and extend known pathway biology. They empower potential discoveries of new molecular interactions and predict efficacious novel drug perturbations, such as the inhibition of PLK1, which is verified experimentally. This technology is suitable for application to larger systems in diverse areas of molecular biology.
Aberrant activation of the ERK pathway is common in human tumors. This pathway consists of a three-tiered kinase module comprising the kinases RAF, mitogen-activated protein kinase (MAPK) kinase ...(MEK), and extracellular signal-regulated kinase (ERK) that functions as a negative feedback amplifier to confer robustness and stabilization of pathway output. Because this pathway is frequently dysregulated in human cancers, intense efforts are under way to develop selective inhibitors of the ERK pathway as anticancer drugs. Although promising results have been reported in early trials for inhibitors of RAF or MEK, resistance invariably occurs. Amplification of the upstream oncogenic driver of ERK signaling has been identified as a mechanism for MEK inhibitor resistance in cells with mutant BRAF or KRAS. Increased abundance of the oncogenic driver (either KRAS or BRAF in the appropriate cellular context) in response to prolonged drug treatment results in increased flux through the ERK pathway and restoration of ERK activity above the threshold required for cell growth. For patients with BRAF mutant tumors, the results suggest that the addition of a RAF inhibitor to a MEK inhibitor may delay or overcome drug resistance. The data thus provide a mechanistic basis for ongoing trials testing concurrent treatment with RAF and MEK inhibitors.
Tumors with mutant BRAF and some with mutant RAS are dependent upon ERK signaling for proliferation, and their growth is suppressed by MAPK/ERK kinase (MEK) inhibitors. In contrast, tumor cells with ...human EGF receptor (HER) kinase activation proliferate in a MEK-independent manner. These findings have led to the development of RAF and MEK inhibitors as anticancer agents. Like MEK inhibitors, the RAF inhibitor PLX4032 inhibits the proliferation of BRAF V600E tumor cells but not that of HER kinase-dependent tumors. However, tumors with RAS mutation that are sensitive to MEK inhibition are insensitive to PLX4032. MEK inhibitors inhibit ERK phosphorylation in all normal and tumor cells, whereas PLX4032 inhibits ERK signaling only in tumor cells expressing BRAF V600E . In contrast, the drug activates MEK and ERK phosphorylation in cells with wild-type BRAF. In BRAF V600E tumor cells, MEK and RAF inhibitors affect the expression of a common set of genes. PLX4032 inhibits ERK signaling output in mutant BRAF cells, whereas it transiently activates the expression of these genes in tumor cells with wild-type RAF. Thus, PLX4032 inhibits ERK signaling output in a mutant BRAF-selective manner. These data explain why the drug selectively inhibits the growth of mutant BRAF tumors and suggest that it will not cause toxicity resulting from the inhibition of ERK signaling in normal cells. This selectivity may lead to a broader therapeutic index and help explain the greater antitumor activity observed with this drug than with MEK inhibitors.
Ploidy abnormalities are a hallmark of cancer, but their impact on the evolution and outcomes of cancers is unknown. Here, we identified whole-genome doubling (WGD) in the tumors of nearly 30% of ...9,692 prospectively sequenced advanced cancer patients. WGD varied by tumor lineage and molecular subtype, and arose early in carcinogenesis after an antecedent transforming driver mutation. While associated with TP53 mutations, 46% of all WGD arose in TP53-wild-type tumors and in such cases was associated with an E2F-mediated G1 arrest defect, although neither aberration was obligate in WGD tumors. The variability of WGD across cancer types can be explained in part by cancer cell proliferation rates. WGD predicted for increased morbidity across cancer types, including KRAS-mutant colorectal cancers and estrogen receptor-positive breast cancers, independently of established clinical prognostic factors. We conclude that WGD is highly common in cancer and is a macro-evolutionary event associated with poor prognosis across cancer types.
To identify molecular factors that determine duration of response to EGFR tyrosine kinase inhibitors and to identify novel mechanisms of drug resistance, we molecularly profiled
-mutant tumors prior ...to treatment and after progression on EGFR TKI using targeted next-generation sequencing.
Targeted next-generation sequencing was performed on 374 consecutive patients with metastatic
-mutant lung cancer. Clinical data were collected and correlated with somatic mutation data. Erlotinib resistance due to acquired MTOR mutation was functionally evaluated by
and
studies.
In 200
-mutant pretreatment samples, the most frequent concurrent alterations were mutations in
, and
and focal amplifications in
, and
Shorter time to progression on EGFR TKI was associated with amplification of
(HR = 2.4,
= 0.015) or
(HR = 3.7,
= 0.019), or mutation in
(HR = 1.7,
= 0.006). In the 136 posttreatment samples, we identified known mechanisms of acquired resistance: EGFR T790M (51%),
(7%), and
amplifications (5%). In the 38 paired samples, novel acquired alterations representing putative resistance mechanisms included
fusion,
fusion,
amplification,
loss, and an MTOR E2419K mutation. Functional studies confirmed the contribution of the latter to reduced sensitivity to EGFR TKI
and
-mutant lung cancers harbor a spectrum of concurrent alterations that have prognostic and predictive significance. By utilizing paired samples, we identified several novel acquired alterations that may be relevant in mediating resistance, including an activating mutation in MTOR further validated functionally.
.
Approximately 200 BRAF mutant alleles have been identified in human tumours. Activating BRAF mutants cause feedback inhibition of GTP-bound RAS, are RAS-independent and signal either as active ...monomers (class 1) or constitutively active dimers (class 2). Here we characterize a third class of BRAF mutants-those that have impaired kinase activity or are kinase-dead. These mutants are sensitive to ERK-mediated feedback and their activation of signalling is RAS-dependent. The mutants bind more tightly than wild-type BRAF to RAS-GTP, and their binding to and activation of wild-type CRAF is enhanced, leading to increased ERK signalling. The model suggests that dysregulation of signalling by these mutants in tumours requires coexistent mechanisms for maintaining RAS activation despite ERK-dependent feedback. Consistent with this hypothesis, melanomas with these class 3 BRAF mutations also harbour RAS mutations or NF1 deletions. By contrast, in lung and colorectal cancers with class 3 BRAF mutants, RAS is typically activated by receptor tyrosine kinase signalling. These tumours are sensitive to the inhibition of RAS activation by inhibitors of receptor tyrosine kinases. We have thus defined three distinct functional classes of BRAF mutants in human tumours. The mutants activate ERK signalling by different mechanisms that dictate their sensitivity to therapeutic inhibitors of the pathway.
Abstract Background Despite a similar histologic appearance, upper tract urothelial carcinoma (UTUC) and urothelial carcinoma of the bladder (UCB) tumors have distinct epidemiologic and ...clinicopathologic differences. Objective To investigate whether the differences between UTUC and UCB result from intrinsic biological diversity. Design, setting, and participants Tumor and germline DNA from patients with UTUC ( n = 83) and UCB ( n = 102) were analyzed using a custom next-generation sequencing assay to identify somatic mutations and copy number alterations in 300 cancer-associated genes. Outcome measurements and statistical analysis We described co-mutation patterns and copy number alterations in UTUC. We also compared mutation frequencies in high-grade UTUC ( n = 59) and high-grade UCB ( n = 102). Results and limitations Comparison of high-grade UTUC and UCB revealed significant differences in the prevalence of somatic alterations. Genes altered more commonly in high-grade UTUC included FGFR3 (35.6% vs 21.6%; p = 0.065), HRAS (13.6% vs 1.0%; p = 0.001), and CDKN2B (15.3% vs 3.9%; p = 0.016). Genes less frequently mutated in high-grade UTUC included TP53 (25.4% vs 57.8%; p < 0.001), RB1 (0.0% vs 18.6%; p < 0.001), and ARID1A (13.6% vs 27.5%; p = 0.050). Because our assay was restricted to genomic alterations in a targeted panel, rare mutations and epigenetic changes were not analyzed. Conclusions High-grade UTUC tumors display a spectrum of genetic alterations similar to high-grade UCB. However, there were significant differences in the prevalence of several recurrently mutated genes including HRAS , TP53 , and RB1 . As relevant targeted inhibitors are being developed and tested, these results may have important implications for the site-specific management of patients with urothelial carcinoma. Patient summary Comparison of next-generation sequencing of upper tract urothelial carcinoma (UTUC) with urothelial bladder cancer identified that similar mutations were present in both cancer types but at different frequencies, indicating a potential need for unique management strategies. UTUC tumors were found to have a high rate of mutations that could be targeted with novel therapies.
Vemurafenib, a selective RAF inhibitor, extends survival among patients with BRAF V600E-mutant melanoma. Vemurafenib inhibits ERK signaling in BRAF V600E-mutant cells but activates ERK signaling in ...BRAF wild-type cells. This paradoxical activation of ERK signaling is the mechanistic basis for the development of RAS-mutant squamous-cell skin cancers in patients treated with RAF inhibitors. We report the accelerated growth of a previously unsuspected RAS-mutant leukemia in a patient with melanoma who was receiving vemurafenib. Exposure to vemurafenib induced hyperactivation of ERK signaling and proliferation of the leukemic cell population, an effect that was reversed on drug withdrawal.
PDF
