Publications (44)221.82 Total impact
-
Article: Anti-proliferative effects of continued mitogen activated protein kinase pathway inhibition following acquired resistance to BRAF and/or MEK inhibition in melanoma.
[show abstract] [hide abstract]
ABSTRACT: Inhibitors of the MAPKs, BRAF and MEK, induce tumor regression in the majority of patients with BRAF-mutant metastatic melanoma. The clinical benefit of MAPK inhibitors is restricted by the development of acquired resistance with half of those who benefit having progressed by 6-7 months and long-term responders uncommon. There remains no agreed treatment strategy on disease progression in these patients. Without published evidence, fears of accelerated disease progression on inhibitor withdrawal have led to the continuation of drugs beyond formal disease progression. We now demonstrate that treatment with MAPK inhibitors beyond disease progression can provide significant clinical benefit, and the withdrawal of these inhibitors led to a marked increase in the rate of disease progression in two patients. We also show that MAPK inhibitors retain partial activity in acquired resistant melanoma by examining drug-resistant clones generated to dabrafenib, trametinib or the combination of these drugs. All resistant sublines displayed a markedly slower rate of proliferation when exposed to MAPK inhibitors, and this coincided with a reduction in MAPK signalling, decrease in BrdU incorporation and S-phase inhibition. This cytostatic effect was also associated with diminished levels of cyclin D1 and p-pRb. Two short-term melanoma cultures generated from resistant tumour biopsies also responded to MAPK inhibition with comparable inhibitory changes in proliferation and MAPK signalling. These data provide a rationale for the continuation of BRAF and MEK inhibitors after disease progression and support the development of clinical trials to examine this strategy.Molecular Cancer Therapeutics 05/2013; · 5.23 Impact Factor -
Article: Secondary c-Kit mutations confer acquired resistance to RTK inhibitors in c-Kit mutant melanoma cells.
[show abstract] [hide abstract]
ABSTRACT: Activation of the c-Kit receptor tyrosine kinase is rare in melanoma, but occurs in 20-40% of melanoma arising on mucosal membranes, acral skin, and skin with chronic sun-induced damage. Many activating c-Kit mutations have been shown to be highly sensitive to imatinib mesylate, although the majority of c-kit mutant melanoma patients eventually progress on this inhibitor. We examined acquired resistance to imatinib and the newer generation inhibitor nilotinib in resistant c-kit mutant melanoma sublines. Four imatinib-resistant and six nilotinib-resistant sublines had acquired additional, secondary c-Kit mutations. The secondary A829P c-Kit mutation rendered cells resistant to imatinib, but did not suppress the activity of the tyrosine kinase inhibitors nilotinib and dasatinib. Sublines with an additional T670I c-Kit mutation showed resistance to imatinib, nilotinib and dasatinib, but responded to sunitinib. The concurrent inhibition of the MAPK and PI3K pathways was also effective at promoting apoptosis in the parent and derived resistant sublines. Our data provide a rationale for treating melanoma patients progressing on imatinib or nilotinib with alternative RTK inhibitors or inhibitors targeting the MAPK and PI3K signalling cascades. This article is protected by copyright. All rights reserved.Pigment Cell & Melanoma Research 04/2013; · 5.06 Impact Factor -
Article: Effects of BRAF inhibitors on Human Melanoma Tissue Before Treatment, Early During Treatment and on Progression.
[show abstract] [hide abstract]
ABSTRACT: Selective BRAF inhibitors (BRAFi) are the standard of care for the treatment of BRAF(V600) -mutant metastatic melanoma. We analyzed a unique set of serial triplicate human metastatic melanoma tumor biopsies to identify biomarkers of BRAFi response and resistance. Morphologic features and immunohistochemical biomarkers were analyzed in 37 metastatic melanoma biopsies at pre-treatment (PRE), early during treatment (EDT) and on progression (PROG) from 15 patients treated with a BRAFi and correlated with response and outcome. At EDT proliferative markers decreased regardless of response, whereas markers of cell death increased in responders. High expression of nuclear p27 at baseline was the strongest predictor of a poorer OS, and predicted worse response. The results show that BRAFi are universally anti-proliferative, regardless of clinical response, whereas markers of cell death increased only in responders. The addition of therapies targeting the cell cycle machinery may improve the response and duration of BRAFi, and investigation of the mechanisms of apoptosis may provide additional therapeutic targets. © 2013 John Wiley & Sons A/S.Pigment Cell & Melanoma Research 04/2013; · 5.06 Impact Factor -
Article: Monitoring Oncogenic B-RAF-Induced Senescence in Melanocytes.
[show abstract] [hide abstract]
ABSTRACT: The B-RAF kinase is a downstream effector of the RAS family of proto-oncogenes and is constitutively activated in the majority of human melanomas. The common oncogenic B-RAF(V600E) mutant cooperates with additional genetic lesions to transform immortal murine and human cells. In primary cells, however, B-RAF(V600E) triggers a rapid cell cycle arrest that is phenotypically indistinguishable from cellular senescence. Here we describe the analyses of B-RAF-induced senescence in primary human melanocytes using recombinant lentiviruses.Methods in molecular biology (Clifton, N.J.) 01/2013; 965:313-26. -
Article: p16(INK) (4a) deficiency promotes DNA hyper-replication and genetic instability in melanocytes.
[show abstract] [hide abstract]
ABSTRACT: Activated oncogenes restrict cell proliferation and transformation by triggering a DNA damage-dependent senescence checkpoint in response to DNA hyper-replication. Here we show that loss of the p16(INK) (4a) cyclin dependent kinase inhibitor and melanoma tumour suppressor facilitates a DNA damage response after a hyper-replicative phase in human melanocytes. Unlike cells expressing activated oncogenes however, melanocytes depleted for p16(INK) (4a) display enhanced proliferation and an extended replicative lifespan in the presence of replication-associated DNA damage. Analysis of human benign naevi confirmed that DNA damage and loss of p16(INK) (4a) expression co-segregate closely. Thus, we propose that loss of p16(INK) (4a) facilitates tumourigenesis by promoting the proliferation of genetically unstable cells. © 2012 John Wiley & Sons A/S.Pigment Cell & Melanoma Research 12/2012; · 5.06 Impact Factor -
Article: Oncogenic B-RAF(V600E) Signaling Induces the T-Box3 Transcriptional Repressor to Repress E-Cadherin and Enhance Melanoma Cell Invasion.
[show abstract] [hide abstract]
ABSTRACT: Approximately 50% of melanomas require oncogenic B-RAF(V600E) signaling for proliferation, survival, and metastasis, and the use of highly selective B-RAF inhibitors has yielded remarkable, although short-term, clinical responses. Reactivation of signaling downstream of B-RAF is frequently associated with acquired resistance to B-RAF inhibitors, and the identification of B-RAF targets may therefore provide new strategies for managing melanoma. In this report, we applied whole-genome expression analyses to reveal that oncogenic B-RAF(V600E) regulates genes associated with epithelial-mesenchymal transition in normal cutaneous human melanocytes. Most prominent was the B-RAF-mediated transcriptional repression of E-cadherin, a keratinocyte-melanoma adhesion molecule whose loss is intimately associated with melanoma invasion and metastasis. Here we identify a link between oncogenic B-RAF, the transcriptional repressor Tbx3, and E-cadherin. We show that B-RAF(V600E) induces the expression of Tbx3, which potently represses E-cadherin expression in melanocytes and melanoma cells. Tbx3 expression is normally restricted to developmental embryonic tissues and promoting cell motility, but it is also aberrantly increased in various cancers and has been linked to tumor cell invasion and metastasis. We propose that this B-RAF/Tbx3/E-cadherin pathway has a critical role in promoting the metastasis of B-RAF-mutant melanomas.Journal of Investigative Dermatology advance online publication, 29 November 2012; doi:10.1038/jid.2012.421.Journal of Investigative Dermatology 11/2012; · 6.31 Impact Factor -
Article: A parallel genome-wide mrna and microrna profiling of the frontal cortex of HIV patients with and without HIV-associated dementia shows the role of axon guidance and downstream pathways in HIV-mediated neurodegeneration.
[show abstract] [hide abstract]
ABSTRACT: BACKGROUND: HIV-associated dementia (HAD) is the most common dementia type in young adults less than 40 years of age. Although the neurotoxins, oxidative/metabolic stress and impaired activity of neurotrophic factors are believed to be underlying reasons for the development of HAD, the genomic basis, which ultimately defines the virus-host interaction and leads to neurologic manifestation of HIV disease is lacking. Therefore, identifying HIV fingerprints on the host gene machinery and its regulation by microRNA holds a great promise and potential for improving our understanding of HAD pathogenesis, its diagnosis and therapy. RESULTS: A parallel profiling of mRNA and miRNA of the frontal cortex autopsies from HIV positive patients with and without dementia was performed using Illumina Human-6 BeadChip and Affymetrix version 1.0 miRNA array, respectively. The gene ontology and pathway analysis of the two data sets showed high concordance between miRNA and mRNAs, revealing significant interference with the host axon guidance and its downstream signalling pathways in HAD brains. Moreover, the differentially expressed (DE) miRNAs identified in this study, in particular miR-137, 153 and 218, based on which most correlations were built cumulatively targeted neurodegeneration related pathways, implying their future potential in diagnosis, prognosis and possible therapies for HIV-mediated and possibly other neurodegenerative diseases. Furthermore, this relationship between DE miRNAs and DE mRNAs was also reflected in correlation analysis using Bayesian networks by splitting-averaging strategy (SA-BNs), which revealed 195 statistically significant correlated miRNA-mRNA pairs according to Pearson's correlation test (P<0.05). CONCLUSIONS: Our study provides the first evidence on unambiguous support for intrinsic functional relationship between mRNA and miRNA in the context of HIV-mediated neurodegeneration, which shows that neurologic manifestation in HIV patients possibly occurs through the interference with the host axon guidance and its downstream signalling pathways. These data provide an excellent avenue for the development of new generation of diagnostic/prognostic biomarkers and therapeutic intervention strategies for HIV-associated neurodegeneration.BMC Genomics 11/2012; 13(1):677. · 4.07 Impact Factor -
Dataset: medic et al., 2011 suppl
-
Dataset: medic et al., 2011 suppl
-
Article: Intratumoral molecular heterogeneity in a BRAF-mutant, BRAF inhibitor-resistant melanoma: a case illustrating the challenges for personalized medicine.
[show abstract] [hide abstract]
ABSTRACT: Targeted therapies are increasingly being used to treat a variety of cancers. Their efficacy depends upon the accurate detection and targeting of a specific mutation or aberration in the tumour. All cancers such as melanoma are molecularly heterogeneous, with drug resistant subclones present prior to treatment or emerging as a result of targeted therapies. Here we show intra-lesional molecular heterogeneity in a progressing V600E BRAF-mutant melanoma metastasis from a patient treated for 7 months with the BRAF inhibitor vemurafenib. In the single metastasis, two distinct subclones were observed, both V600E BRAF-mutant, and only one with an additional G13R NRAS-mutation. Molecular heterogeneity even at the intra-lesional level demonstrates that personalising or adjusting therapies based on genotyping of a portion of a single lesion, might not accurately depict the molecular profile or drivers of oncogenesis across the entire patient's melanoma.Molecular Cancer Therapeutics 09/2012; · 5.23 Impact Factor -
Article: Absence of distinguishing senescence traits in human melanocytic nevi.
[show abstract] [hide abstract]
ABSTRACT: Cellular senescence permanently restricts the replicative capacity of cells in response to various stress signals, including aberrant activation of oncogenes. The presence of predictive senescence markers in human premalignant lesions suggests that senescence may function as a genuine tumor suppressor. These markers are not exclusive to the senescence program, however, and it is possible that their expression in vivo does not discriminate irreversible from reversible forms of proliferative arrest. In this study, we aimed to clarify whether human nevus cells can be distinguished from primary and transformed melanocytes by examining the expression of eight senescence markers, including those previously purported to define nevi as senescent tumors. Specifically, we analyzed effectors of senescence, including p16(INK4a), p53, and DNA damage (γ-H2AX), as well as predictive markers of senescence including Ki67, PML, senescence-associated β-galactosidase, heterochromatic foci (H3K9Me, 4'-6-diamidino-2-phenylindole), and nuclear size. We found that these commonly accepted senescence markers do not in fact distinguish nevi from precursor/normal and transformed/malignant melanocytes. We conclude that on the basis of current evidence it cannot be reasonably inferred that nevi are permanently growth arrested via senescence.Journal of Investigative Dermatology 04/2012; 132(9):2226-34. · 6.31 Impact Factor -
Article: Acquired resistance to BRAF inhibition can confer cross-resistance to combined BRAF/MEK inhibition.
[show abstract] [hide abstract]
ABSTRACT: Aberrant activation of the BRAF kinase occurs in ∼60% of melanomas, and although BRAF inhibitors have shown significant early clinical success, acquired resistance occurs in most patients. Resistance to chronic BRAF inhibition often involves reactivation of mitogen-activated protein kinase (MAPK) signaling, and the combined targeting of BRAF and its downstream target MAPK/ERK kinase (MEK) may delay or overcome resistance. To investigate the efficacy of combination BRAF and MEK inhibition, we generated melanoma cell clones resistant to the BRAF inhibitor GSK2118436. These BRAF inhibitor-resistant sublines acquired resistance through several distinct mechanisms, including the acquisition of activating N-RAS mutations and increased accumulation of COT1. These alterations uniformly promoted MAPK reactivation and most conferred resistance to MEK inhibition and to the concurrent inhibition of BRAF and MEK. These data indicate that melanoma tumors are likely to develop heterogeneous mechanisms of resistance, many of which will confer resistance to multiple MAPK inhibitory therapies.Journal of Investigative Dermatology 03/2012; 132(7):1850-9. · 6.31 Impact Factor -
Article: Differential PAX3 functions in normal skin melanocytes and melanoma cells.
[show abstract] [hide abstract]
ABSTRACT: The PAX3 transcription factor is the key regulator of melanocyte development during embryogenesis and is also frequently found in melanoma cells. While PAX3 is known to regulate melanocyte differentiation, survival, proliferation and migration during development, it is not clear if its function is maintained in adult melanocytes and melanoma cells. To clarify this we have assessed which genes are targeted by PAX3 in these cells. We show here that similar to its roles in development, PAX3 regulates complex differentiation networks in both melanoma cells and melanocytes, in order to maintain cells as "stem" cell-like (via NES and SOX9). We show also that mediators of migration (MCAM and CSPG4) are common to both cell types but more so in melanoma cells. By contrast, PAX3-mediated regulation of melanoma cell proliferation (through TPD52) and survival (via BCL2L1 and PTEN) differs from that in melanocytes. These results suggest that by controlling cell proliferation, survival and migration as well as maintaining a less differentiated "stem" cell like phenotype, PAX3 may contribute to melanoma development and progression.Biochemical and Biophysical Research Communications 08/2011; 411(4):832-7. · 2.48 Impact Factor -
Article: Selective loss of wild-type p16(INK4a) expression in human nevi.
Journal of Investigative Dermatology 07/2011; 131(11):2329-32. · 6.31 Impact Factor -
Article: Selective Loss of Wild-Type p16INK4a Expression in Human Nevi
Journal of Investigative Dermatology 07/2011; 131(11):2329-2332. · 6.31 Impact Factor -
Article: P53 in human melanoma fails to regulate target genes associated with apoptosis and the cell cycle and may contribute to proliferation.
[show abstract] [hide abstract]
ABSTRACT: Metastatic melanoma represents a major clinical problem. Its incidence continues to rise in western countries and there are currently no curative treatments. While mutation of the P53 tumour suppressor gene is a common feature of many types of cancer, mutational inactivation of P53 in melanoma is uncommon; however, its function often appears abnormal. In this study whole genome bead arrays were used to examine the transcript expression of P53 target genes in extracts from 82 melanoma metastases and 6 melanoma cell lines, to provide a global assessment of aberrant P53 function. The expression of these genes was also examined in extracts derived from diploid human melanocytes and fibroblasts. The results indicated that P53 target transcripts involved in apoptosis were under-expressed in melanoma metastases and melanoma cell lines, while those involved in the cell cycle were over-expressed in melanoma cell lines. There was little difference in the transcript expression of P53 target genes between cell lines with null/mutant P53 compared to those with wild-type P53, suggesting that altered expression in melanoma was not related to P53 status. Similarly, down-regulation of P53 by short-hairpin RNA (shRNA) had limited effect on P53 target gene expression in melanoma cells, whereas there were a large number of P53 target genes whose mRNA expression was significantly altered by P53 inhibition in melanocytes. Analysis of whole genome gene expression profiles indicated that the ability of P53 to regulate genes involved in the cell cycle was significantly reduced in melanoma cells. Moreover, inhibition of P53 in melanocytes induced changes in gene expression profiles that were characteristic of melanoma cells and resulted in increased proliferation. Conversely, knockdown of P53 in melanoma cells resulted in decreased proliferation. These results indicate that P53 target genes involved in apoptosis and cell cycle regulation are aberrantly expressed in melanoma and that this aberrant functional activity of P53 may contribute to the proliferation of melanoma.BMC Cancer 01/2011; 11:203. · 3.01 Impact Factor -
Article: Oncogene-induced senescence pathways in melanocytes.
Cell cycle (Georgetown, Tex.) 12/2010; 9(24):4778-9. · 5.36 Impact Factor -
Article: IGFBP7 is not required for B-RAF-induced melanocyte senescence.
[show abstract] [hide abstract]
ABSTRACT: Induction of senescence permanently restricts cellular proliferation after oncogenic stimulation thereby acting as a potent barrier to tumor development. The relevant effector proteins may therefore be fundamental to cancer development. A recent study identified IGFBP7 as a secreted factor mediating melanocyte senescence induced by oncogenic B-RAF, which is found commonly in cutaneous nevi. In contrast to the previous report, we demonstrate that B-RAF signaling does not induce IGFBP7 expression, nor the expression of the IGFBP7 targets, BNIP3L, SMARCB1, or PEA15, in human melanocytes or fibroblasts. We also found no correlation between B-RAF mutational status and IGFBP7 protein expression levels in 22 melanoma cell lines, 90 melanomas, and 46 benign nevi. Furthermore, using a lentiviral silencing strategy we show that B-RAF induces senescence in melanocytes and fibroblasts, irrespective of the presence of IGFBP7. Therefore, we conclude that the secreted protein IGFBP7 is dispensable for B-RAF(V600E)-induced senescence in human melanocytes.Cell 05/2010; 141(4):717-27. · 32.40 Impact Factor -
Article: Oncogenic B-RAF(V600E) promotes anchorage-independent survival of human melanocytes.
Journal of Investigative Dermatology 05/2010; 130(8):2144-7. · 6.31 Impact Factor -
Article: Predicting functional significance of cancer‐associated p16INK4a mutations in CDKN2A
[show abstract] [hide abstract]
ABSTRACT: Inherited mutations affecting the INK4a/ARF locus (CDKN2A) are associated with melanoma susceptibility in 40% of multiple case melanoma families. Over 60 different germline INK4a/ARF mutations have been detected in more than 190 families worldwide. The majority of these alterations are missense mutations affecting p16INK4a, and only 25% of these have been functionally assessed. There is therefore a need for an accurate and rapid assay to determine the functional significance of p16INK4a mutations. We reviewed the performance of several in vivo functional assays that measure critical aspects of p16INK4a function, including subcellular location, CDK binding and cell cycle inhibition. In this report the function of 28 p16INK4a variants, many associated with melanoma susceptibility were compared. We show that assessment of CDK4 binding and subcellular localization can accurately and rapidly determine the functional significance of melanoma-associated p16INK4a mutations. p16INK4a-CDK6 binding affinity was unhelpful, as no disease-associated mutation showed reduced CDK6 affinity while maintaining the ability to bind CDK4. Likewise, in silico analyses did not contribute substantially, with only 12 of 25 melanoma-associated missense variants consistently predicted as deleterious. The ability to determine variant functional activity accurately would identify disease-associated mutations and facilitate effective genetic counselling of individuals at high risk of melanoma. Hum Mutat 31:1–10, 2010. © 2010 Wiley-Liss, Inc.Human Mutation 03/2010; 31(6):692 - 701. · 5.69 Impact Factor
Top co-authors
Top Journals
Institutions
-
2009–2013
-
Melanoma Institute Australia
Sydney, New South Wales, Australia -
University of Sydney
- Westmead Institute for Cancer Research (WICR)
Sydney, New South Wales, Australia
-
-
2003–2013
-
Westmead Hospital
Sydney, New South Wales, Australia
-
-
2005
-
Westmead Millennium Institute
Paramatta, New South Wales, Australia
-
