How genomic heterogeneity associated with acquired resistance to targeted agents affects response to subsequent therapy is unknown. We studied EGFR blockade in colorectal cancer to assess whether ...tissue and liquid biopsies can be integrated with radiologic imaging to monitor the impact of individual oncogenic alterations on lesion-specific responses. Biopsy of a patient's progressing liver metastasis following prolonged response to cetuximab revealed a MEK1(K57T) mutation as a novel mechanism of acquired resistance. This lesion regressed upon treatment with panitumumab and the MEK inhibitor trametinib. In circulating tumor DNA (ctDNA), mutant MEK1 levels declined with treatment, but a previously unrecognized KRAS(Q61H) mutation was also identified that increased despite therapy. This same KRAS mutation was later found in a separate nonresponding metastasis. In summary, parallel analyses of tumor biopsies and serial ctDNA monitoring show that lesion-specific radiographic responses to subsequent targeted therapies can be driven by distinct resistance mechanisms arising within separate tumor lesions in the same patient.
Molecular heterogeneity ensuing from acquired resistance drives lesion-specific responses to subsequent targeted therapies. Analysis of a single-lesion biopsy is inadequate to guide selection of subsequent targeted therapies. ctDNA profiles allow the detection of concomitant resistance mechanisms residing in separate metastases and assessment of the effect of therapies designed to overcome resistance.
Targeted therapies such as kinase inhibitors and monoclonal antibodies have dramatically altered cancer care in recent decades. Although these targeted therapies have improved patient outcomes in ...several cancer types, resistance ultimately develops to these agents. One potential strategy proposed to overcome acquired resistance involves taking repeat tumor biopsies at the time of disease progression, to identify the specific molecular mechanism driving resistance in an individual patient and to select a new agent or combination of agents capable of surmounting that specific resistance mechanism. However, recent studies sampling multiple metastatic lesions upon acquired resistance, or employing "liquid biopsy" analyses of circulating tumor DNA, have revealed that multiple, heterogeneous resistance mechanisms can emerge in distinct tumor subclones in the same patient. This heterogeneity represents a major clinical challenge for devising therapeutic strategies to overcome resistance. In many cancers, multiple drug resistance mechanisms often converge to reactivate the original pathway targeted by the drug. This convergent evolution creates an opportunity to target a common signaling node to overcome resistance. Furthermore, integration of liquid biopsy approaches into clinical practice may allow real-time monitoring of emerging resistance alterations, allowing intervention prior to standard detection of radiographic progression. In this review, we discuss recent advances in understanding tumor heterogeneity and resistance to targeted therapies, focusing on combination kinase inhibitors, and we discuss approaches to address these issues in the clinic.
BRAF mutations occur in approximately 10% of colorectal cancers. Although RAF inhibitor monotherapy is highly effective in BRAF-mutant melanoma, response rates in BRAF-mutant colorectal cancer are ...poor. Recent clinical trials of combined RAF/EGFR or RAF/MEK inhibition have produced improved efficacy, but patients ultimately develop resistance. To identify molecular alterations driving clinical acquired resistance, we performed whole-exome sequencing on paired pretreatment and postprogression tumor biopsies from patients with BRAF-mutant colorectal cancer treated with RAF inhibitor combinations. We identified alterations in MAPK pathway genes in resistant tumors not present in matched pretreatment tumors, including KRAS amplification, BRAF amplification, and a MEK1 mutation. These alterations conferred resistance to RAF/EGFR or RAF/MEK combinations through sustained MAPK pathway activity, but an ERK inhibitor could suppress MAPK activity and overcome resistance. Identification of MAPK pathway reactivating alterations upon clinical acquired resistance underscores the MAPK pathway as a critical target in BRAF-mutant colorectal cancer and suggests therapeutic options to overcome resistance.
RAF inhibitor combinations represent promising approaches in clinical development for BRAF-mutant colorectal cancer. Initial characterization of clinical acquired resistance mechanisms to these regimens identified several MAPK pathway alterations driving resistance by reactivating MAPK signaling, highlighting the critical dependence of BRAF-mutant colorectal cancers on MAPK signaling and offering potential strategies to overcome resistance.
"Liquid biopsy" approaches analyzing cell-free DNA (cfDNA) from the blood of patients with cancer are increasingly utilized in clinical practice. However, it is not yet known whether cfDNA sequencing ...from large cohorts of patients with cancer can detect genomic alterations at frequencies similar to those observed by direct tumor sequencing, and whether this approach can generate novel insights. Here, we report next-generation sequencing data from cfDNA of 1,397 patients with colorectal cancer. Overall, frequencies of genomic alterations detected in cfDNA were comparable to those observed in three independent tissue-based colorectal cancer sequencing compendia. Our analysis also identified a novel cluster of extracellular domain (ECD) mutations in
, mediating resistance by blocking binding of anti-EGFR antibodies. Patients with
ECD mutations displayed striking tumor heterogeneity, with 91% harboring multiple distinct resistance alterations (range, 1-13; median, 4). These results suggest that cfDNA profiling can effectively define the genomic landscape of cancer and yield important biological insights.
This study provides one of the first examples of how large-scale genomic profiling of cfDNA from patients with colorectal cancer can detect genomic alterations at frequencies comparable to those observed by direct tumor sequencing. Sequencing of cfDNA also generated insights into tumor heterogeneity and therapeutic resistance and identified novel
ectodomain mutations.
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Genetic alterations in the fibroblast growth factor receptor (FGFR) pathway are promising therapeutic targets in many cancers, including intrahepatic cholangiocarcinoma (ICC). The FGFR inhibitor ...BGJ398 displayed encouraging efficacy in patients with FGFR2 fusion-positive ICC in a phase II trial, but the durability of response was limited in some patients. Here, we report the molecular basis for acquired resistance to BGJ398 in three patients via integrative genomic characterization of cell-free circulating tumor DNA (cfDNA), primary tumors, and metastases. Serial analysis of cfDNA demonstrated multiple recurrent point mutations in the
kinase domain at progression. Accordingly, biopsy of post-progression lesions and rapid autopsy revealed marked inter- and intralesional heterogeneity, with different
mutations in individual resistant clones. Molecular modeling and
studies indicated that each mutation led to BGJ398 resistance and was surmountable by structurally distinct FGFR inhibitors. Thus, polyclonal secondary
mutations represent an important clinical resistance mechanism that may guide the development of future therapeutic strategies.
We report the first genetic mechanisms of clinical acquired resistance to FGFR inhibition in patients with FGFR2 fusion-positive ICC. Our findings can inform future strategies for detecting resistance mechanisms and inducing more durable remissions in ICC and in the wide variety of cancers where the FGFR pathway is being explored as a therapeutic target.
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MET inhibition is effective in some patients with MET-amplified esophagogastric cancer (EGC), but understanding acquired and de novo resistance mechanisms will be critical to improving therapy. We ...identified KRAS mutation as a novel cause of acquired resistance in a patient after a 2-year response to a MET inhibitor. We also observed that 40% to 50% of patients with MET-amplified EGC harbor coamplification of HER2 and/or EGFR concurrently in the same tumor cells, which can drive de novo resistance. One patient with concurrent MET and HER2 amplification was refractory to HER2 blockade, but responded to combined MET/HER2 inhibition. We also found striking heterogeneity in MET amplification between distinct metastatic lesions and primary tumors in individual patients with EGC. In these patients, MET inhibition led to mixed responses and disease progression through outgrowth of non-MET-amplified clones, which could be monitored in circulating tumor DNA. Thus, receptor coamplification and molecular heterogeneity may be key drivers of clinical resistance in MET-amplified EGC.
Coamplification of driver oncogenes occurs frequently in EGC and can drive therapeutic resistance, supporting a role for comprehensive molecular analysis prior to targeted therapy. EGCs can also exhibit extensive heterogeneity in gene amplification between distinct tumor lesions within the same patient, suggesting that molecular profiling of a single-lesion biopsy may be insufficient to guide targeted therapy selection.
MEK inhibitors (MEKi) lack monotherapy efficacy in most RAS-mutant cancers. BCL-xL is an anti-apoptotic protein identified by a synthetic lethal shRNA screen as a key suppressor of apoptotic response ...to MEKi.
We conducted a dose escalation study (NCT02079740) of the BCL-xL inhibitor navitoclax and MEKi trametinib in patients with RAS-mutant tumors with expansion cohorts for: pancreatic, gynecologic (GYN), non-small cell lung cancer (NSCLC), and other cancers harboring KRAS/NRAS mutations. Paired pretreatment and day 15 tumor biopsies and serial cell-free (cf)DNA were analyzed.
A total of 91 patients initiated treatment, with 38 in dose escalation. Fifty-eight percent had ≥3 prior therapies. A total of 15 patients (17%) had colorectal cancer, 19 (11%) pancreatic, 15 (17%) NSCLC, and 32 (35%) GYN cancers. The recommended phase II dose (RP2D) was established as trametinib 2 mg daily days 1 to 14 and navitoclax 250 mg daily days 1 to 28 of each cycle. Most common adverse events included diarrhea, thrombocytopenia, increased AST/ALT, and acneiform rash. At RP2D, 8 of 49 (16%) evaluable patients achieved partial response (PR). Disease-specific differences in efficacy were noted. In patients with GYN at the RP2D, 7 of 21 (33%) achieved a PR and median duration of response 8.2 months. No PRs occurred in patients with colorectal cancer, NSCLC, or pancreatic cancer. MAPK pathway inhibition was observed in on-treatment tumor biopsies. Reductions in KRAS/NRAS mutation levels in cfDNA correlated with clinical benefit.
Navitoclax in combination with trametinib was tolerable. Durable clinical responses were observed in patients with RAS-mutant GYN cancers, warranting further evaluation in this population.
Hepatocellular carcinoma is a highly deadly malignancy, accounting for approximately 800,000 deaths worldwide every year. Mutation of the p53 tumor suppressor gene is a common genetic change in HCC, ...present in 30% of cases. p53R175H (corresponding to p53R172H in mice) is a hotspot for mutation that demonstrates "prometastatic" gain-of-function in other cancer models. Since the frequency of p53 mutation increases with tumor grade in HCC, we hypothesized that p53R172H is a gain-of-function mutation in HCC that contributes to a decrease in tumor-free survival and an increase in metastasis. In an HCC mouse model, we found that p53R172H/flox mice do not have decreased survival, increased tumor incidence, or increased metastasis, relative to p53flox/flox littermates. Analysis of cell lines derived from both genotypes indicated that there are no differences in anchorage-independent growth and cell migration. However, shRNA-mediated knockdown of mutant p53 in p53R172H-expressing HCC cell lines resulted in decreased cell migration and anchorage-independent growth. Thus, although p53 mutant-expressing cells and tumors do not have enhanced properties relative to their p53 null counterparts, p53R172H-expressing HCC cells depend on this mutant for their transformation. p53 mutants have been previously shown to bind and inhibit the p53 family proteins p63 and p73. Interestingly, we find that the levels of p63 and p73 target genes are similar in p53 mutant and p53 null HCC cells. These data suggest that pathways regulated by these p53 family members are similarly impacted by p53R172H in mutant expressing cells, and by alternate mechanisms in p53 null cells, resulting in equivalent phenotypes. Consistent with this, we find that p53 null HCC cell lines display lower levels of the TA isoforms of p63 and p73 and higher levels of ΔNp63. Taken together these data point to the importance of p63 and p73 in constraining HCC progression.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The X-linked gene Rnf12 encodes the ubiquitin ligase really interesting new gene (RING) finger LIM domain-interacting protein (RLIM)/RING finger protein 12 (Rnf12), which serves as a major ...sex-specific epigenetic regulator of female mouse nurturing tissues. Early during embryogenesis, RLIM/Rnf12 expressed from the maternal allele is crucial for the development of extraembryonic trophoblast cells. In contrast, in mammary glands of pregnant and lactating adult females RLIM/Rnf12 expressed from the paternal allele functions as a critical survival factor for milk-producing alveolar cells. Although RLIM/Rnf12 is detected mostly in the nucleus, little is known about how and in which cellular compartment(s) RLIM/Rnf12 mediates its biological functions. Here we demonstrate that RLIM/Rnf12 protein shuttles between nucleus and cytoplasm and this is regulated by phosphorylation of serine S214 located within its nuclear localization sequence. We show that shuttling is important for RLIM to exert its biological functions, as alveolar cell survival activity is inhibited in cells expressing shuttling-deficient nuclear or cytoplasmic RLIM/Rnf12. Thus regulated nucleocytoplasmic shuttling of RLIM/Rnf12 coordinates cellular compartments during mammary alveolar cell survival.
For successful infection, avian sarcoma leukosis virus subgroup A (ASLV-A) requires its receptor, tumor virus A (TVA), to be present on the surface of target cells. This is the basis of the RCAS-TVA ...gene delivery system: Mammalian cells lack the gene encoding TVA and are normally resistant to infection by ASLV; however, transgenic targeting of TVA to specific cell types or tissues in the mouse renders these cells uniquely susceptible to infection by ASLV-A-based RCAS viruses. The RCAS-TVA system is a powerful tool for effectively modeling human tumors, including pancreatic, ovarian, and breast cancers, gliomas, and melanomas. RCAS viruses can deliver cDNAs (≤2.8 kb), as well as short hairpin RNAs (shRNAs), microRNAs (miRNAs), and other noncoding RNAs. Compared with traditional transgenic and knockout mice, the RCAS-TVA system has several strengths. First, virus delivery is generally performed postnatally and results in a relatively low infection rate of target cells; the sporadic postnatal expression of the gene of interest mimics the situation in developing human tumors. Second, a single transgenic mouse line can be used to compare the consequences of specific genes on tumor development, with viruses encoding oncogenes or shRNAs targeting specific tumor suppressor genes. TVA mouse strains can also be easily combined with transgenic, knock-in, and knockout mouse models to study cooperating genetic events.
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