Inhibition of Ras/Raf interaction by anti-oncogenic mutants of neurofibromin, the neurofibromatosis type 1 (NF1) gene product, in cell-free systems

The USP10/13 inhibitor, spautin-1, attenuates the progression of glioblastoma by independently regulating RAF-ERK mediated glycolysis and SKP2

Glioblastoma is a malignant brain tumor with poor prognosis. Though several dysregulated pathways were found to mediate the tumor progression, hyperactivation of RAS-RAF-ERK pathway, enhanced glycolysis and SKP2 are associated with several glioblastomas. Recent findings on the role of USP10 in the transition from pro-neural to mesenchymal subtype of glioblastoma and, USP13 in the stabilization of RAF1 in mouse embryonic stem cells prompted us to examine their role in the mechanisms mediating the progression of glioblastoma. In the present study, we have examined the role of spautin-1, a pharmacological inhibitor of USP10 and USP13 in the mechanisms mediating glioblastoma. Our results indicate that spautin-1 as well as knockdown of its downstream targets, USP10 and USP13, reduced the proliferation and migration of glioblastoma cells. Also, spautin-1 mediated inhibition of RAF-ERK pathway or inhibition of RAF1 and MEK1 per se reduced the glycolytic function via PKM2/Glut-1 and inhibited the progression of glioblastoma. Further, the protooncogene, SKP2, which was shown to be a direct target of USP10 /USP13 was also reduced by spautin-1. While inhibition of SKP2 enhanced its downstream target p21, no apparent changes in the RAF-ERK levels or glycolytic function were evident. Also, inhibition of MEK1 did not affect SKP2 levels, indicating that these two pathways act independent of each other. Overall, our findings indicate that spautin-1 by virtue of its inhibitory effects on USP10/13 counteracts RAS-RAF-ERK mediated glycolysis and SKP2 that are critical in the progression of glioblastoma. Hence, further preclinical validation is warranted for taking the present observations forward.

Treatment-related adverse effects with pazopanib, sorafenib and sunitinib in patients with advanced soft tissue sarcoma: a pooled analysis

Objective

Research efforts have investigated therapies targeting tyrosine kinase signaling pathways. We performed a pooled analysis to determine the frequency of severe adverse effects in patients with soft tissue sarcoma treated with pazopanib, sorafenib and sunitinib.

Materials and methods

We performed a comprehensive search of PubMed, Web of Science, Ovid, the Cochrane Library and Embase databases from the drugs’ inception to May 2017 to identify clinical trials. All-grade and severe adverse events (AEs; grade≥3) were analyzed.

Results

A total of 10 trials published between 2009 and 2016, including 843 patients, were eligible for analysis. We included 424 patients (three studies) who received pazopanib 800 mg daily, 353 patients (five studies) who received sorafenib 400 mg twice daily and 66 patients (two studies) who received sunitinib 37.5 mg daily. The incidence of AEs is different among the three VEGFR-tyrosine kinase inhibitors (TKIs). Pazopanib showed higher incidence of all-grade nausea, diarrhea and hypertension compared with sorafenib and sunitinib. However, patients in the sorafenib group experienced a significantly higher frequency of all-grade rash (26.1%), hand–foot syndrome (33.4%) and mucositis (38.5%). The difference was highly significant for sorafenib vs. pazopanib in the incidence of all-grade rash (odds ratio [OR] 1.649, 95% CI 1.086–2.505, P=0.023), hand–foot syndrome (OR 3.096, 95% CI 1.271–7.544, P=0.009) and mucositis (OR 4.562, 95% CI 2.132–9.609, P<0.001). Moreover, the frequency of grade ≥3 mucositis was significantly higher in the sunitinib group compared with the pazopanib or sorafenib group (7.6% vs. 1.3%, OR 6.448, 95% CI 1.499–27.731, P=0.013).

Conclusion

Statistically significant differences in certain common adverse effects, such as all-grade and severe AEs, were detected among pazopanib, sorafenib and sunitinib in the current study. Early and prompt management is critically needed to avoid unnecessary dose reductions and treatment-related discontinuations.

Dermatofibrosarcoma protuberans (DFSP) successfully treated with sorafenib: case report

DFSP is a locally invasive, slow-growing tumor of the subcutaneous tissue that rarely metastasizes but recurs frequently after surgical excision. We report herein a case of highly recurrent, locally invasive DFSP that failed both postoperative radiation therapy and complete trial of Imatinib, but was successfully treated with Sorafenib, which showed unprecedented response.

Phase II study of sorafenib in patients with metastatic or recurrent sarcomas

PURPOSE Since activity of sorafenib was observed in sarcoma patients in a phase I study, we performed a multicenter phase II study of daily oral sorafenib in patients with recurrent or metastatic sarcoma. PATIENTS AND METHODS We employed a multiarm study design, each representing a sarcoma subtype with its own Simon optimal two-stage design. In each arm, 12 patients who received 0 to 1 prior lines of therapy were treated (0 to 3 for angiosarcoma and malignant peripheral-nerve sheath tumor). If at least one Response Evaluation Criteria in Solid Tumors (RECIST) was observed, 25 further patients with that sarcoma subtype were accrued. Results Between October 2005 and November 2007, 145 patients were treated; 144 were eligible for toxicity and 122 for response. Median age was 55 years; female-male ratio was 1.8:1. The median number of cycles was 3. Five of 37 patients with angiosarcoma had a partial response (response rate, 14%). This was the only arm to meet the RECIST response rate primary end point. Median progression-free survival was 3.2 months; median overall survival was 14.3 months. Adverse events (typically dermatological) necessitated dose reduction for 61% of patients. Statistical modeling in this limited patient cohort indicated sorafenib toxicity was correlated inversely to patient height. There was no correlation between phosphorylated extracellular signal regulated kinase expression and response in six patients with angiosarcoma with paired pre- and post-therapy biopsies. CONCLUSION As a single agent, sorafenib has activity against angiosarcoma and minimal activity against other sarcomas. Further evaluation of sorafenib in these and possibly other sarcoma subtypes appears warranted, presumably in combination with cytotoxic or kinase-specific agents.

A systems perspective of ras signaling in cancer

The development of cancer reflects the complex interactions and properties of many proteins functioning as part of large biochemical networks within the cancer cell. Although traditional experimental models have provided us with wonderful insights on the behavior of individual proteins within a cancer cell, they have been deficient in simultaneously keeping track of many proteins and their interactions in large networks. Computational models have emerged as a powerful tool for investigating biochemical networks due to their ability to meaningfully assimilate numerous network properties. Using the well-studied Ras oncogene as an example, we discuss the use of models to investigate pathologic Ras signaling and describe how these models could play a role in the development of new cancer drugs and the design of individualized treatment regimens.

Point mutants of c-raf-1 RBD with elevated binding to v-Ha-Ras

A mutational analysis of the Ras-binding domain (RBD) of c-Raf-1 identified three amino acid positions (Asn(64), Ala(85), and Val(88)) where amino acid substitution with basic residues increases the binding of RBD to recombinant v-Ha-Ras. The greatest increase in binding (6-9-fold) was observed with the A85K-RBD mutant. The elevated binding for the A85K-RBD and V88R-RBD mutants was also detected with Ras expressed in cultured mammalian cells, namely NIH-3T3 and BAF cells. None of the wild type residues in RBD positions Asn(64), Ala(85), and Val(88) have been previously implicated in the interaction with Ras (Block, C., Janknecht, R., Herrmann, C., Nassar, N., and Wittinghofer, A. (1996) Nat. Struct. Biol. 3, 244-251; Nassar, N., Horn, G., Herrmann, C., Scherer, A., McCormick, F., and Wittinghofer, A. (1995) Nature 375, 554-560). The discovery of elevated binding among the mutants in these positions implies that additional RBD residues can be used to generate the Ras. RBD complex. These findings are of particular significance in the design of Ras antagonists based on the RBD prototype. The A85K-RBD mutant can be used to develop an assay for measuring the level of activated Ras in cultured cells; Sepharose-linked A85K-RBD.GST fusion protein served as an activation-specific probe to precipitate Ras.GTP but not Ras.GDP from epidermal growth factor-stimulated cells. A85K-RBD precipitates up to 5-fold more Ras.GTP from mammalian cells than wild type RBD.

A novel human RasGAP-like gene that maps within the prostate cancer susceptibility locus at chromosome 1q25

We report the molecular cloning of a human cDNA that encodes a molecule having striking homology with Ras-specific GTPase-activating proteins (RasGAPs). Among previously described RasGAPs, the cDNA product is most closely related to Caenorhabditis elegans GAP-2, including a predicted coiled-coil structure near the carboxyl terminus. Expression of the cDNA in Saccharomyces cerevisiae defective in one of two RasGAPs, Ira2, complemented loss of the Ira2 function, indicating that the cDNA product functions as a RasGAP. The RasGAP-like gene is located on the human chromosome 1q25, the locus that appears to contain a hereditary prostate cancer susceptible gene, HPC1.

Structural analysis of the GAP-related domain from neurofibromin and its implications

Neurofibromin is the product of the NF1 gene, whose alteration is responsible for the pathogenesis of neurofibromatosis type 1 (NF1), one of the most frequent genetic disorders in man. It acts as a GTPase activating protein (GAP) on Ras; based on homology to p120GAP, a segment spanning 250-400 aa and termed GAP-related domain (NF1GRD; 25-40 kDa) has been shown to be responsible for GAP activity and represents the only functionally defined segment of neurofibromin. Missense mutations found in NF1 patients map to NF1GRD, underscoring its importance for pathogenesis. X-ray crystallographic analysis of a proteolytically treated catalytic fragment of NF1GRD comprising residues 1198-1530 (NF1-333) of human neurofibromin reveals NF1GRD as a helical protein that resembles the corresponding fragment derived from p120GAP (GAP-334). A central domain (NF1c) containing all residues conserved among RasGAPs is coupled to an extra domain (NF1ex), which despite very limited sequence homology is surprisingly similar to the corresponding part of GAP-334. Numerous point mutations found in NF1 patients or derived from genetic screening protocols can be analysed on the basis of the three-dimensional structural model, which also allows identification of the site where structural changes in a differentially spliced isoform are to be expected. Based on the structure of the complex between Ras and GAP-334 described earlier, a model of the NF1GRD-Ras complex is proposed which is used to discuss the strikingly different properties of the Ras-p120GAP and Ras-neurofibromin interactions.

Crystal structure of the GTPase-activating domain of human p120GAP and implications for the interaction with Ras

Ras-related GTP-binding proteins function as molecular switches which cycle between GTP-bound 'on'- and GDP-bound 'off'-states. GTP hydrolysis is the common timing mechanism that mediates the return from the 'on' to the 'off'-state. It is usually slow but can be accelerated by orders of magnitude upon interaction with GTPase-activating proteins (GAPs). In the case of Ras, a major regulator of cellular growth, point mutations are found in approximately 30% of human tumours which render the protein unable to hydrolyse GTP, even in the presence of Ras-GAPs. The first structure determination of a GTPase-activating protein reveals the catalytically active fragment of the Ras-specific p120GAP (ref. 2), GAP-334, as an elongated, exclusively helical protein which appears to represent a novel protein fold. The molecule consists of two domains, one of which contains all the residues conserved among different GAPs for Ras. From the location of conserved residues around a shallow groove in the central domain we can identify the site of interaction with Ras x GTP. This leads to a model for the interaction between Ras and GAP that satisfies numerous biochemical and genetic data on this important regulatory process.