MET Exon 14 Splice-Site Mutations Preferentially Activate KRAS Signaling to Drive Tumourigenesis

Simple Summary

MET exon 14 splice-site mutations occur in ~3–4% of lung adenocarcinoma cases, defining a cohort of patients which might benefit from anti-MET targeted therapy. Such therapies have yielded mixed results, however, pointing to the need for better treatment design. Our study sought to aid this by characterizing key changes in mutant MET signaling behaviour. We first compared the transcriptional profiles of lung tumours with either METΔex14 or wild-type MET-amplification. METΔex14-mutant tumours exhibited increased activation of the Ras-MAPK pathway, consistent with our observations in an isogenic model system. Furthermore, sustained activity of this pathway is necessary for proliferation and maintenance of METΔex14 tumours, while forced reactivation of this pathway is sufficient to restore growth in the absence of MET activity. Our findings suggest that the MAPK pathway represents a main effector of METΔex14-driven cancer, lending credence to the possibility of combined MET-MAPK inhibition to improve therapeutic outcomes.

Abstract

Targeted therapies for MET exon 14-skipping (METΔex14)-driven lung cancers have generated some promising results but response rates remain below that seen for other kinase-driven cancers. One strategy for improving treatment outcomes is to employ rational combination therapies to enhance the suppression of tumour growth and delay or prevent the emergence of resistance. To this end, we profiled the transcriptomes of MET-addicted lung tumours and cell lines and identified the RAS-mitogen-activated protein kinase (MAPK) pathway as a critical effector required for METΔex14-dependent growth. Ectopic expression of MET in an isogenic cell line model showed that overexpression of the mutant MET receptor led to higher levels of MAPK phosphorylation and nuclear import, resulting in increased expression and phosphorylation of nuclear MAPK targets. In comparison, other known MET effectors were unaffected. Inhibition of this pathway by KRAS knockdown in MET-addicted cells in vitro led to decreased viability in only the METΔex14-mutant cells. Conversely, decoupling RAS-MAPK axis, but not other effector pathways, from MET activity via the introduction of constitutively active mutants conferred resistance to MET inhibitors in vitro. Our results suggest that aberrant hyperactivity of the MET receptor caused by the exon 14-skipping mutation does not uniformly upregulate all known downstream effectors, rather gaining a predilection for aberrantly activating and subsequently relying on the RAS-MAPK pathway. These findings provide a rationale for the co-targeting of the RAS-MAPK pathway alongside MET to prolong therapeutic response and circumvent resistance to improve patient survival.

Drug Sensitivity and Allele Specificity of First-Line Osimertinib Resistance EGFR Mutations

Osimertinib, a mutant-specific third-generation EGFR tyrosine kinase inhibitor, is emerging as the preferred first-line therapy for EGFR-mutant lung cancer, yet resistance inevitably develops in patients. We modeled acquired resistance to osimertinib in transgenic mouse models of EGFR^L858R -induced lung adenocarcinoma and found that it is mediated largely through secondary mutations in EGFR-either C797S or L718V/Q. Analysis of circulating free DNA data from patients revealed that L718Q/V mutations almost always occur in the context of an L858R driver mutation. Therapeutic testing in mice revealed that both erlotinib and afatinib caused regression of osimertinib-resistant C797S-containing tumors, whereas only afatinib was effective on L718Q mutant tumors. Combination first-line osimertinib plus erlotinib treatment prevented the emergence of secondary mutations in EGFR. These findings highlight how knowledge of the specific characteristics of resistance mutations is important for determining potential subsequent treatment approaches and suggest strategies to overcome or prevent osimertinib resistance in vivo. SIGNIFICANCE: This study provides insight into the biological and molecular properties of osimertinib resistance EGFR mutations and evaluates therapeutic strategies to overcome resistance. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/10/2017/F1.large.jpg.

Impact on lipoprotein profile after long-term testosterone replacement in hypogonadal men

Testosterone serum levels may influence the lipoprotein metabolism and possibly atherogenic risk. Our aim was to investigate the effects of long-term testosterone supplementation in hypogonadal men on multiple lipoprotein markers. 18 Hypogonadal men were studied before and after 3, 6, and 18 (n = 7) months of treatment with testosterone enanthate. During treatment, serum testosterone and estradiol increased, reaching normal levels (p < 0.0001 and 0.003, respectively). This was associated with a decrease in HDL cholesterol (from 1.40 +/- 0.10 mmol/l to 1.22 +/- 0.08 mmol/l, p < 0.001) after six months at the expense of HDL2 cholesterol (p < 0.01), as well as apoprotein A1 (from 139 +/- 3.4 mg/dl to 126 +/- 3.0 mg/dl, p < 0.005). Hepatic lipase activity increased (p < 0.05) and correlated positively with testosterone (r = 0.56, p < 0.02) and negatively with HDL cholesterol (r = - 0.58, p < 0.02). Total and LDL cholesterol, triglycerides, and apoprotein B did not increase. Among the seven patients who completed 18 months of treatment, triglycerides, total cholesterol, LDL and HDL cholesterol, as well as total cholesterol/HDL cholesterol ratio values did not differ from baseline while apoprotein A1 (p < 0.03) and HDL cholesterol (p < 0.015) remained decreased and hepatic lipase unchanged. Restoration of testosterone levels in hypogonadal men in this study did not reveal unfavorable changes based on total cholesterol/HDL cholesterol and LDL cholesterol/apoprotein B ratios, which are both atherogenic risk markers. Whether the changes in light of lipoprotein metabolism will adversely influence cardiovascular risk over time remains to be determined.

Sildenafil improves nocturnal penile erections in organic impotence

We studied the effects of sildenafil on nocturnal penile erections. We prospectively evaluated 36 patients with organic or psychogenic impotence and 5 normal, potent men. All patients completed 3 sessions of consecutive nights using the RigiScan Plus device. The first two nights the patients were asked to take placebo before the session and to take 50 mg of sildenafil before the third session. In the organic impotence group the use of sildenafil induced a significant improvement in time of rigidity 60-100%, rigidity and tumescence activity unit values and rigidity and tumescence activity unit values per hour in the tip and base. In the psychogenic impotence group it caused significant improvement only in rigidity activity unit per hour in the tip. In the potent men, changes were statistically insignificant. Sildenafil improves nocturnal penile erectile activity in organic impotence. Our study shows that phosphodiesterase inhibitors can improve penile erections not induced by sexual stimulation.