The DNA damage response pathway as a land of therapeutic opportunities for colorectal cancer

BACKGROUND

Colorectal cancer (CRC) represents a major cause of cancer deaths worldwide. Although significant progress has been made by molecular and immune therapeutic approaches, prognosis of advanced stage disease is still dismal. Alterations in the DNA damage response (DDR) pathways are emerging as novel targets for treatment across different cancer types. However, even though preclinical studies have shown the potential exploitation of DDR alterations in CRC, systematic and comprehensive testing is lagging and clinical development is based on analogies with other solid tumors according to a tissue-agnostic paradigm. Recently, functional evidence from patient-derived xenografts and organoids have suggested that maintenance with PARP inhibitors might represent a therapeutic opportunity in CRC patients previously responsive to platinum-based treatment.

DESIGN AND RESULTS

In this review, we highlight the most promising preclinical data and systematically summarize published clinical trials in which DDR inhibitors have been used for CRC and provide evidence that disappointing results have been mainly due to a lack of clinical and molecular selection.

CONCLUSIONS

Future preclinical and translational research will help in better understanding the role of DDR alterations in CRC and pave the way to novel strategies that might have a transformative impact on treatment by identifying new therapeutic options including tailored use of standard chemotherapy.

RET fusions in a small subset of advanced colorectal cancers at risk of being neglected

Background

Recognition of rare molecular subgroups is a challenge for precision oncology and may lead to tissue-agnostic approval of targeted agents. Here we aimed to comprehensively characterize the clinical, pathological and molecular landscape of RET rearranged metastatic colorectal cancer (mCRC).

Patients and methods

In this case series, we compared clinical, pathological and molecular characteristics of 24 RET rearranged mCRC patients with those of a control group of 291 patients with RET negative tumors. RET rearranged and RET negative mCRCs were retrieved by systematic literature review and by taking advantage of three screening sources: (i) Ignyta's phase 1/1b study on RXDX-105 (NCT01877811), (ii) cohorts screened at two Italian and one South Korean Institutions and (iii) Foundation Medicine Inc. database. Next-generation sequencing data were analyzed for RET rearranged cases.

Results

RET fusions were more frequent in older patients (median age of 66 versus 60 years, P = 0.052), with ECOG PS 1-2 (90% versus 50%, P = 0.02), right-sided (55% versus 32%, P = 0.013), previously unresected primary tumors (58% versus 21%, P < 0.001), RAS and BRAF wild-type (100% versus 40%, P < 0.001) and MSI-high (48% versus 7%, P < 0.001). Notably, 11 (26%) out of 43 patients with right-sided, RAS and BRAF wild-type tumors harbored a RET rearrangement. At a median follow-up of 45.8 months, patients with RET fusion-positive tumors showed a significantly worse OS when compared with RET-negative ones (median OS 14.0 versus 38.0 months, HR: 4.59; 95% CI, 3.64-32.66; P < 0.001). In the multivariable model, RET rearrangements were still associated with shorter OS (HR: 2.97; 95% CI, 1.25-7.07; P = 0.014), while primary tumor location, RAS and BRAF mutations and MSI status were not.

Conclusions

Though very rare, RET rearrangements define a new subtype of mCRC that shows poor prognosis with conventional treatments and is therefore worth of a specific management.

How liquid biopsies can change clinical practice in oncology

Cell-free DNA fragments are shed into the bloodstream by tumor cells. The analysis of circulating tumor DNA (ctDNA), commonly known as liquid biopsy, can be exploited for a variety of clinical applications. ctDNA is being used to genotype solid cancers non-invasively, to track tumor dynamics and to detect the emergence of drug resistance. In a few settings, liquid biopsies have already entered clinical practice. For example, ctDNA is used to guide treatment in a subset of lung cancers. In this review, we discuss how recent improvements in the sensitivity and accuracy of ctDNA analyses have led to unprecedented advances in this research field. We further consider what is required for the routine deployment of liquid biopsies in the clinical diagnostic space. We pinpoint technical hurdles that liquid biopsies have yet to overcome, including preanalytical and analytical challenges. We foresee how liquid biopsies will transform clinical practice: by complementing (or replacing) imaging to monitor treatment response and by detecting minimal residual disease after surgery with curative intent.

Use of a Dual mobility cup to prevent hip early arthroplasty dislocation in patients at high falls risk

INTRODUCTION

Hip fracture is a common serious injury that occurs mainly in elderly. Dual-mobility hip arthroplasty or bipolar emiarthroplasty for its treatment remains a controversial decision. Co-morbidities and risk of fall represent additional aspects to be considered. The aim of our study was to determine the rate of mechanical complications for these two types of implants related to fall risk status of patients.

PATIENTS AND METHODS

Our study is a retrospective clinical trial of patients operated with a biarticular hemiarthroplasty or a dual-mobility total hip arthroplasty. Primary outcome was dislocation rate and need for any revision procedure. Patients were treated in a single center from January 2013 to March 2017. In all cases Morse Fall Scale (MSF) was calculated at patient admission to evaluate the risk of postoperative fall. Inclusion criteria to the study were: subcapital or femoral neck fracture of non-pathologic nature, patients with neuromuscular disorders or cognitive dysfunction, age > 75 years with MFS ≥ 45. The patients were reviewed postoperatively at 8 weeks, 6 months, 12 months, and then annually. Patients had clinical (Harris hip score) and radiological assessment.

RESULTS

The mean duration of the follow-up was 283 months. There were five dislocations in Group A (5,6%) and no dislocations in Group B (0%). All dislocations occurred within the first 6 months after surgery. The mean Harris Hip score was 81,7 in Group A patients and 79, 8 in Group B patients.

DISCUSSION

Treatment of hip fractures on non-cooperative patients still represents a dilemma. Falls and runaway motions represent high risk factors of dislocation. Use of dual-mobility cup has been found to be associated with a not statistically proved decrease of dislocation compared to traditional cups.

CONCLUSION

Dual-mobility cups might be considered a valuable option to prevent postoperative dislocation but further study is needed before extending the indications for dual-mobility following a fracture of the femoral neck, to assess the potential cost and complications of a longer procedure. So far, despite a lower dislocation risk, the authors actually cannot recommend widely use of a dual-motility cup instead of emiarthroplasty in high falls risk patients.

Review: Peering through a keyhole: liquid biopsy in primary and metastatic central nervous system tumours

Tumour molecular profiling by liquid biopsy is being investigated for a wide range of research and clinical purposes. The possibility of repeatedly interrogating the tumour profile using minimally invasive procedures is helping to understand spatial and temporal tumour heterogeneity, and to shed a light on mechanisms of resistance to targeted therapies. Moreover, this approach has been already implemented in clinical practice to address specific decisions regarding patients’ follow‐up and therapeutic management. For central nervous system (CNS) tumours, molecular profiling is particularly relevant for the proper characterization of primary neoplasms, while CNS metastases can significantly diverge from primary disease or extra‐CNS metastases, thus compelling a dedicated assessment. Based on these considerations, effective liquid biopsy tools for CNS tumours are highly warranted and a significant amount of data have been accrued over the last few years. These results have shown that liquid biopsy can provide clinically meaningful information about both primary and metastatic CNS tumours, but specific considerations must be taken into account, for example, when choosing the source of liquid biopsy. Nevertheless, this approach is especially attractive for CNS tumours, as repeated tumour sampling is not feasible. The aim of our review was to thoroughly report the state‐of‐the‐art regarding the opportunities and challenges posed by liquid biopsy in both primary and secondary CNS tumours.

Dynamic molecular analysis and clinical correlates of tumor evolution within a phase II trial of panitumumab-based therapy in metastatic colorectal cancer

Background

Mutations in rat sarcoma (RAS) genes may be a mechanism of secondary resistance in epidermal growth factor receptor inhibitor-treated patients. Tumor-tissue biopsy testing has been the standard for evaluating mutational status; however, plasma testing of cell-free DNA has been shown to be a more sensitive method for detecting clonal evolution.

Materials and methods

Archival pre- and post-treatment tumor biopsy samples from a phase II study of panitumumab in combination with irinotecan in patients with metastatic colorectal cancer (mCRC) that also collected plasma samples before, during, and after treatment were analyzed for emergence of mutations during/post-treatment by next-generation sequencing and BEAMing.

Results

The rate of emergence of tumor tissue RAS mutations was 9.5% by next-generation sequencing (n = 21) and 6.3% by BEAMing (n = 16). Plasma testing of cell-free DNA by BEAMing revealed a mutant RAS emergence rate of 36.7% (n = 39). Exploratory outcomes analysis of plasma samples indicated that patients who had emergent RAS mutations at progression had similar median progression-free survival to those patients who remained wild-type at progression. Serial analysis of plasma samples showed that the first detected emergence of RAS mutations preceded progression by a median of 3.6 months (range, −0.3 to 7.5 months) and that there did not appear to be a mutant RAS allele frequency threshold that could predict near-term outcomes.

Conclusions

This first prospective analysis in mCRC showed that serial plasma biopsies are more inclusive than tissue biopsies for evaluating global tumor heterogeneity; however, the clinical utility of plasma testing in mCRC remains to be further explored.

ClinicalTrials.gov Identifier

NCT00891930

Cerebrospinal fluid cell-free tumour DNA as a liquid biopsy for primary brain tumours and central nervous system metastases

Challenges in obtaining tissue specimens from patients with brain tumours limit the diagnosis and molecular characterisation and impair the development of better therapeutic approaches. The analysis of cell-free tumour DNA in plasma (considered a liquid biopsy) has facilitated the characterisation of extra-cranial tumours. However, cell-free tumour DNA in plasma is limited in quantity and may not reliably capture the landscape of genomic alterations of brain tumours. Here, we review recent work assessing the relevance of cell-free tumour DNA from cerebrospinal fluid in the characterisation of brain cancer. We focus on the advances in the use of the cerebrospinal fluid as a source of cell-free tumour DNA to facilitate diagnosis, reveal actionable genomic alterations, monitor responses to therapy, and capture tumour heterogeneity in patients with primary brain tumours and brain and leptomeningeal metastases. Profiling cerebrospinal fluid cell-free tumour DNA provides the opportunity to precisely acquire and monitor genomic information in real time and guide precision therapies.

Targeting the human epidermal growth factor receptor 2 (HER2) oncogene in colorectal cancer

Human epidermal growth factor receptor 2 (HER2) is an oncogenic driver, and a well-established therapeutic target in breast and gastric cancers. Using functional and genomic analyses of patient-derived xenografts, we previously showed that a subset (approximately 5%) of metastatic colorectal cancer (CRC) tumors is driven by amplification or mutation of HER2. This paper reviews the role of HER2 amplification as an oncogenic driver, a prognostic and predictive biomarker, and a clinically actionable target in CRC, considering the specifics of HER2 testing in this tumor type. While the role of HER2 as a biomarker for prognosis in CRC remains uncertain, its relevance as a therapeutic target has been established. Indeed, independent studies documented substantial clinical benefit in patients treated with biomarker-driven HER2-targeted therapies, with an impact on response rates and duration of response that compared favorably with immunotherapy and other examples of precision oncology. HER2-targeted therapeutic strategies have the potential to change the treatment paradigm for a clinically relevant subgroup of metastatic CRC patients.

ESMO consensus guidelines for the management of patients with metastatic colorectal cancer

Colorectal cancer (CRC) is one of the most common malignancies in Western countries. Over the last 20 years, and the last decade in particular, the clinical outcome for patients with metastatic CRC (mCRC) has improved greatly due not only to an increase in the number of patients being referred for and undergoing surgical resection of their localised metastatic disease but also to a more strategic approach to the delivery of systemic therapy and an expansion in the use of ablative techniques. This reflects the increase in the number of patients that are being managed within a multidisciplinary team environment and specialist cancer centres, and the emergence over the same time period not only of improved imaging techniques but also prognostic and predictive molecular markers. Treatment decisions for patients with mCRC must be evidence-based. Thus, these ESMO consensus guidelines have been developed based on the current available evidence to provide a series of evidence-based recommendations to assist in the treatment and management of patients with mCRC in this rapidly evolving treatment setting.

Consensus on precision medicine for metastatic cancers: a report from the MAP conference

Recent advances in biotechnologies have led to the development of multiplex genomic and proteomic analyses for clinical use. Nevertheless, guidelines are currently lacking to determine which molecular assays should be implemented in metastatic cancers. The first MAP conference was dedicated to exploring the use of genomics to better select therapies in the treatment of metastatic cancers. Sixteen consensus items were covered. There was a consensus that new technologies like next-generation sequencing of tumors and ddPCR on circulating free DNA have convincing analytical validity. Further work needs to be undertaken to establish the clinical utility of liquid biopsies and the added clinical value of expanding from individual gene tests into large gene panels. Experts agreed that standardized bioinformatics methods for biological interpretation of genomic data are needed and that precision medicine trials should be stratified based on the level of evidence available for the genomic alterations identified.

Tumor MGMT promoter hypermethylation changes over time limit temozolomide efficacy in a phase II trial for metastatic colorectal cancer

BACKGROUND

Objective response to dacarbazine, the intravenous form of temozolomide (TMZ), in metastatic colorectal cancer (mCRC) is confined to tumors harboring O(6)-methylguanine-DNA-methyltransferase (MGMT) promoter hypermethylation. We conducted a phase II study of TMZ enriched by MGMT hypermethylation in archival tumor (AT), exploring dynamic of this biomarker in baseline tumor (BT) biopsy and plasma (liquid biopsy).

PATIENTS AND METHODS

We screened 150 mCRC patients for MGMT hypermethylation with methylation-specific PCR on AT from FFPE specimens. Eligible patients (n = 29) underwent BT biopsy and then received TMZ 200 mg/m(2) days 1-5 q28 until progression. A Fleming single-stage design was used to determine whether progression-free survival (PFS) rate at 12 weeks would be ≥35% [H0 ≤ 15%, type I error = 0.059 (one-sided), power = 0.849]. Exploratory analyses included comparison between MGMT hypermethylation in AT and BT, and MGMT methylation testing by MethylBEAMing in solid (AT, BT) and LB with regard to tumor response.

RESULTS

The PFS rate at 12 weeks was 10.3% [90% confidence interval (CI) 2.9-24.6]. Objective response rate was 3.4% (90% CI 0.2-15.3), disease control rate 48.3% (90% CI 32.0-64.8), median OS 6.2 months (95% CI 3.8-7.6), and median PFS 2.6 months (95% CI 1.4-2.7). We observed the absence of MGMT hypermethylation in BT in 62.7% of tumors.

CONCLUSION

Treatment of mCRC with TMZ driven by MGMT promoter hypermethylation in AT samples did not provide meaningful PFS rate at 12 weeks. This biomarker changed from AT to BT, indicating that testing BT biopsy or plasma is needed for refined target selection.

Digital PCR quantification of MGMT methylation refines prediction of clinical benefit from alkylating agents in glioblastoma and metastatic colorectal cancer

BACKGROUND

O(6)-methyl-guanine-methyl-transferase (MGMT) silencing by promoter methylation may identify cancer patients responding to the alkylating agents dacarbazine or temozolomide.

PATIENTS AND METHODS

We evaluated the prognostic and predictive value of MGMT methylation testing both in tumor and cell-free circulating DNA (cfDNA) from plasma samples using an ultra-sensitive two-step digital PCR technique (methyl-BEAMing). Results were compared with two established techniques, methylation-specific PCR (MSP) and Bs-pyrosequencing.

RESULTS

Thresholds for MGMT methylated status for each technique were established in a training set of 98 glioblastoma (GBM) patients. The prognostic and the predictive value of MGMT methylated status was validated in a second cohort of 66 GBM patients treated with temozolomide in which methyl-BEAMing displayed a better specificity than the other techniques. Cutoff values of MGMT methylation specific for metastatic colorectal cancer (mCRC) tissue samples were established in a cohort of 60 patients treated with dacarbazine. In mCRC, both quantitative assays methyl-BEAMing and Bs-pyrosequencing outperformed MSP, providing better prediction of treatment response and improvement in progression-free survival (PFS) (P < 0.001). Ability of methyl-BEAMing to identify responding patients was validated in a cohort of 23 mCRC patients treated with temozolomide and preselected for MGMT methylated status according to MSP. In mCRC patients treated with dacarbazine, exploratory analysis of cfDNA by methyl-BEAMing showed that MGMT methylation was associated with better response and improved median PFS (P = 0.008).

CONCLUSIONS

Methyl-BEAMing showed high reproducibility, specificity and sensitivity and was applicable to formalin-fixed paraffin-embedded tissues and cfDNA. This study supports the quantitative assessment of MGMT methylation for clinical purposes since it could refine prediction of response to alkylating agents.

Therapeutic implications of resistance to molecular therapies in metastatic colorectal cancer

Metastatic colorectal cancer (mCRC) patients carrying KRAS mutated tumors do not benefit from epidermal growth factor receptor (EGFR)-targeted cetuximab- or panitumumab-based therapies. Indeed, the mutational status of KRAS is currently a validated predictive biomarker employed to select mCRC patients for EGFR targeted drugs. When patients fail standard 5-fluorouracil-, oxaliplatin-, irinotecan- and bevacizumab-based therapies, EGFR-targeted salvage therapy can be prescribed only for those individuals with KRAS wild-type cancer. Thus, clinicians are now facing the urgent issue of better understanding the biology of KRAS mutant disease, in order to devise novel effective therapies in such defined genetic setting. In addition to KRAS, recent data point out that BRAF and PIK3CA exon 20 mutations hamper response to EGFR-targeted treatment in mCRC, potentially excluding from treatment also patients with these molecular alterations in their tumor. This review will focus on current knowledge regarding the molecular landscape of mCRC including and beyond KRAS, and will summarize novel rationally-developed combinatorial regimens that are being evaluated in early clinical trials.

KRAS and BRAF mutational status as response biomarkers to cetuximab combination therapy in advanced gastric cancer patients

e15503

Background: The prognosis of advanced gastric cancer (GC) patients (pt) is still poor despite the introduction of new chemotherapy regimens. In colorectal cancer (CRC) it has been demonstrated that KRAS or BRAF mutations are associated with resistance to treatment with the anti-EGFR mAbs. We have assessed whether, and to what extent, the mutational profile of KRAS and BRAF genes affects the response to cetuximab combination therapy in GC. Methods: We have collected 44 tumor samples from pts affected by locally advanced or metastatic GC undergoing cetuximab combination therapy as first-line treatment in two consecutive phase II studies. Thirteen pts received cetuximab plus FOLFIRI (FOLCETUX Study) and 31 pts cetuximab plus cisplatin and docetaxel (DOCETUX Study). Genomic DNA was extracted from paraffin-embedded tumor specimens from all cases. The mutational status of KRAS (exon 2) and BRAF (exon 15) was ascertained by PCR amplification followed by direct sequencing. The objective response was evaluated every 6 weeks by CT according to RECIST criteria. Results: KRAS and BRAF mutations were detected in 5 (11.4%) and 1 (2.3%), respectively, of the 44 tumors analyzed. These frequencies are consistent with those previously reported in GC. In the case of KRAS, 3 cases displayed amino acid substitutions of codon 12 and 1 of codon 13. One case had the A11V variant that had been reported in hematopoietic and lymphoid tissue of the stomach. The only BRAF mutation found in 1 sample was the classic V600E substitution. As a whole, 13.6 % of the analyzed tumors carried a mutation in either KRAS or BRAF genes. K-RAS and BRAF mutations were, as expected, mutually exclusive. In this pt cohort oncogenic activation of KRAS/BRAF-signaling pathways was not significantly associated to objective response (p= 0.757). Also, we found no correlation between KRAS/BRAF mutations and clinical outcome measured as overall survival. Conclusions: In advanced GC the frequency of mutations in KRAS and BRAF is lower as compared with CRC cancer. In our cases, the mutational status of KRAS and BRAF genes does not correlate with the response to cetuximab-based therapy in advanced gastric cancer patients.

No significant financial relationships to disclose.

Correlation of PIK3CA mutation-associated gene expression signature (PIK3CA-GS) with deactivation of the PI3K pathway and with prognosis within the luminal-B ER+ breast cancers

533

Background: The phosphathidylinositol-3-kinase (PI3K) signaling pathway is frequently deregulated in tumor biology and is an attractive target for cancer therapy. Our aim was to characterize the molecular and clinical outcome effects of PIK3CA mutations in breast cancer (BC). Methods: We analyzed 173 BC samples for PIK3CA mutations. Corresponding gene expression profiles were used to understand its effects on the PI3K pathway. We validated a PIK3CA-GS in 2 independent BC cohorts (n = 183) with known PIK3CA mutation status and evaluated its correlation with clinical outcome in 1748 BC samples stratified by treatment and subtype. Results: 26% of BCs had a PIK3CA mutation. Tumors with PIK3CA mutation demonstrated a distinct gene expression signature (p = 0.03 after 1000 perm). In 2 datasets it could discriminate PIK3CA mutation carriers from wild-type (ROC 0.68, 0.71, p = 0.001for both). However, the PIK3CA-GS was correlated with deactivation of the PI3K pathway probably through a negative feedback loop. This observation was supported by: 1) the PIK3CA-GS was significantly correlated with gene expression changes induced by PI3K inhibitors (Connectivity Map, Gene set enrichment analyses) and 2) the PIK3CA-GS was anti-correlated with a GS of PTEN loss (R = -0.3; Saal et al, 2007). Higher levels of the PIK3CA signature were observed in HER-2+ and estrogen receptor positive (ER+), luminal BC subtypes. Whilst there was no association with mutation status alone and prognosis, increasing expression of the PIK3CA-GS (suggesting deactivation) was significantly associated with better clinical outcome in both untreated (p = 0.04) and particularly ER+, luminal-B, tamoxifen only-treated (p = 0.004) BC. Multivariate analysis (HR: 0.4; 95%CI: 0.3–0.7; p = 0.002) confirmed that the PI3KCA-GS provided independent prognostic information. Conclusions: Paradoxically, the PIK3CA-GS correlates with inhibition of the PI3K pathway in ER+ BC and identifies a subgroup of luminal B BCs with a favorable outcome. The PIK3CA-GS may be a better indicator of PI3K pathway dysfunction than mutation status, potentially indicating patients who may benefit from combined endocrine therapy and PI3K inhibition.

No significant financial relationships to disclose.

Somatic mutations of EGFR signal transducers and expression of tumor suppressor PTEN in biliary tract carcinoma

4582

Background: Biliary tract carcinomas express EGFR and are potential candidates to EGFR target therapies. We recently described somatic mutations of EGFR that can enhance MAPK or Akt activation (Clin Cancer Res, 2006). Some of them are identical to those previously reported to confer sensitivity to some tyrosine kinase inhibitors (TKIs) like erlotinib or gefitinib in lung cancer. Here we report a molecular analysis of EGFR transducers potentially involved in TKI response. Methods: In 49 samples of biliary tract carcinoma we performed mutational analysis of exons from 18 to 21 of EGFR, exons 9 and 20 of phosphatidylinositol 3’-kinase (PI3K), exon 2 of K-Ras, exon 15 of B-Raf and exons from 5 to 8 of PTEN. Nuclear PTEN expression was analyzed by immunohistochemistry and the expression in cancer cells was compared to that of normal cholangiocites. Results: Mutations of EGFR have been detected in 7 out of 49 samples (14.3%). One of them was a new stop-codon mutation. Five hotspot mutations of PI3K (codon 545, 546, 1048 and 1059) were found in 4 cases (8.2%); 3 cases (6.1%) had single mutations in K-Ras and 4 (8.2%) had the V599E mutation in B-Raf. In some samples, mutations of multiple trasducers were present simultaneously. PI3K mutations were significantly more frequent in EGFR mutated samples compared to wild type (28% vs. 4.7% respectively, p<0.05). A single F271L mutation of PTEN was observed (2%). We did not find loss of nuclear PTEN in biliary tract carcinoma cells; rather, a stronger labelling intensity (score 2+ or 3+) was present in biliary tract carcinoma compared to normal cholangiocites (score 1+). Moreover, the median percentage of PTEN labeled nuclei in tumor cells was 31.8%, but in samples with activating EGFR mutation was 60%, suggesting that a compensatory change in the level of the phosphatase might counteract the EGFR activition. Conclusions: These results corroborate our previous finding of EGFR pathway activation in EGFR mutated biliary tract carcinoma and suggest that an accurate analysis of the entire series of EGFR transducers may be done before planning treatments with TKIs.

No significant financial relationships to disclose.

Genetic analysis of the kinome and phosphatome in cancer

Protein phosphorylation is a well-characterized biochemical process for reversible regulation of protein activity. Protein kinases and protein phosphatases are the key complementary players in this process, and through their coordinated activity cell homeostasis is tightly controlled. If these enzymes display aberrant activity, cells may undergo unrestrained growth, thus giving rise to complex diseases such as cancer. The technological platform gathered during the Human Genome Project recently allowed the systematic identification of the genetic alterations present in the kinase (the kinome) and the phosphatase (the phosphatome) gene families. These studies suggest that most if not all human tumors carry genetic alterations in at least one phosphatase or kinase gene. Here we integrate the biochemical knowledge on the properties of these molecules with the information collected through their systematic genetic analysis in cancer. We also analyze why the molecular profiling of the kinome and phosphatome in individual cancers is revolutionizing basic and clinical oncology.

A phosphatase associated with metastasis of colorectal cancer

To gain insights into the molecular basis for metastasis, we compared the global gene expression profile of metastatic colorectal cancer with that of primary cancers, benign colorectal tumors, and normal colorectal epithelium. Among the genes identified, the PRL-3 protein tyrosine phosphatase gene was of particular interest. It was expressed at high levels in each of 18 cancer metastases studied but at lower levels in nonmetastatic tumors and normal colorectal epithelium. In 3 of 12 metastases examined, multiple copies of the PRL-3 gene were found within a small amplicon located at chromosome 8q24.3. These data suggest that the PRL-3 gene is important for colorectal cancer metastasis and provide a new therapeutic target for these intractable lesions.

Carcinogen-specific induction of genetic instability

It has been proposed recently that the type of genetic instability in cancer cells reflects the selection pressures exerted by specific carcinogens. We have tested this hypothesis by treating immortal, genetically stable human cells with representative carcinogens. We found that cells resistant to the bulky-adduct-forming agent 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) exhibited a chromosomal instability (CIN), whereas cells resistant to the methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) exhibited a microsatellite instability (MIN) associated with mismatch repair defects. Conversely, we found that cells purposely made into CIN cells are resistant to PhIP, whereas MIN cells are resistant to MNNG. These data demonstrate that exposure to specific carcinogens can indeed select for tumor cells with distinct forms of genetic instability and vice versa.

Receptor tyrosine kinases as therapeutic targets: the model of the MET oncogene

Control of cell growth and differentiation occurs via extracellular signals known as growth factors. Growth factors are high affinity ligands for transmembrane receptors belonging to the family of receptor tyrosine kinases (RTKs). A number of genetic evidences have implicated RTKs in human diseases including developmental disorders and cancer. For instance, germline missense mutations involving the Ret receptor are found in patients affected by multiple endocrine neoplasia types 2A and 2B (MEN2A and MEN2B) or familial medullary thyroid carcinomas. Somatic mutations in the Kit receptor are found in mastocytomas and in gastrointestinal tumors. Germline and sporadic mutations of the Met receptor have been described in kidney and hepatocellular carcinomas. Overexpression of the HER-2/neu receptor in breast cancer has been associated with tumor progression. The enzymatic activity of RTKs is strictly regulated and is usually inhibited under basal conditions. Receptor activation triggers a biochemical signalling cascade inside the cytoplasm, named signal transduction, which is subverted during the malignant transformation of cells. Signal transduction by RTKs is a multistep process which includes: (i) Ligand binding and receptor dimerization, (ii) receptor phosphorylation on tyrosine residues; (iii) recruitment to the receptor and activation of cytoplasmic signaling molecules that transmit signals to the nucleus. Each of the steps involved in this process can potentially be targeted to block the aberrant properties of tyrosine kinase receptors. By using the MET oncogene as a model this review focuses on the strategies that can be applied to therapeutically target RTKs.

Different point mutations in the met oncogene elicit distinct biological properties

The MET proto-oncogene, encoding the tyrosine kinase receptor for HGF, controls genetic programs leading to cell growth, invasiveness, and protection from apoptosis. Recently, MET mutations have been identified in hereditary and sporadic forms of papillary renal carcinoma (PRC). Introduction of different naturally occurring mutations into the MET cDNA results in the acquisition of distinct biochemical and biological properties of transfected cells. Some mutations result in a high increase in tyrosine kinase activity and confer transforming ability in focus forming assays. These mutants hyperactivate the Ras signaling pathway. Other mutations are devoid of transforming potential but are effective in inducing protection from apoptosis and sustaining anchorage-independent growth. These Met(PRC) receptors interact more efficiently with the intracellular transducer Pi3Kinase. The reported results show that MET(PRC) mutations can be responsible for malignant transformation through different mechanisms, either by increasing the growth ability of cells or by protecting cells from apoptosis and allowing accumulation of other genetic lesions.-Giordano, S., Maffe, A., Williams, T. A., Artigiani, S., Gual, P., Bardelli, A., Basilico, C., Michieli, P., Comoglio, P. M. Different point mutations in the met oncogene elicit distinct biological properties.

MET(PRC) mutations in the Ron receptor result in upregulation of tyrosine kinase activity and acquisition of oncogenic potential

Ron and Met are structurally related receptor tyrosine kinases that elicit a complex biological response leading to invasive growth. Naturally occurring point mutations activate the Met kinase in papillary renal carcinomas (MET(PRC) mutations). By site-directed mutagenesis, we generated homologous amino acid substitutions in the Ron kinase domain and analyzed the biochemical and biological properties of the mutant receptors. Among the mutations studied, D(1232)H and M(1254)T displayed transforming activity in NIH3T3 cells, inducing focus formation and anchorage-independent growth. The D(1232)H and M(1254)T substitutions resulted in increased Ron autophosphorylation both in vivo and in vitro and constitutive binding to intracellular signal transducers. Both mutations yielded a dramatic increase in catalytic efficiency, indicating a direct correlation between kinase activity and oncogenic potential. Molecular modeling of the Ron D(1232)H mutation suggests that this single amino acid substitution favors the transition of the kinase from the inactive to the active state. These data demonstrate that point mutations can confer transforming activity to the Ron receptor and show that RON is a potential oncogene.