Differential protein stability and clinical responses of EML4-ALK fusion variants to various ALK inhibitors in advanced ALK-rearranged non-small cell lung cancer

Background

Anaplastic lymphoma kinase (ALK) inhibition using crizotinib has become the standard of care in advanced ALK-rearranged non-small cell lung cancer (NSCLC), but the treatment outcomes and duration of response vary widely. Echinoderm microtubule-associated protein-like 4 (EML4)-ALK is the most common translocation, and the fusion variants show different sensitivity to crizotinib in vitro. However, there are only limited data on the specific EML4-ALK variants and clinical responses of patients to various ALK inhibitors.

Patients and methods

By multiplex reverse-transcriptase PCR, which detects 12 variants of known EML4-ALK rearrangements, we retrospectively determined ALK fusion variants in 54 advanced ALK rearrangement-positive NSCLCs. We subdivided the patients into two groups (variants 1/2/others and variants 3a/b) by protein stability and evaluated correlations of the variant status with clinical responses to crizotinib, alectinib, or ceritinib. Moreover, we established the EML4-ALK variant-expressing system and analyzed patterns of sensitivity of the variants to ALK inhibitors.

Results

Of the 54 tumors analyzed, EML4-ALK variants 3a/b (44.4%) was the most common type, followed by variants 1 (33.3%) and 2 (11.1%). The 2-year progression-free survival (PFS) rate was 76.0% [95% confidence interval (CI) 56.8-100] in group EML4-ALK variants 1/2/others versus 26.4% (95% CI 10.5-66.6) in group variants 3a/b (P = 0.034) among crizotinib-treated patients. Meanwhile, the 2-year PFS rate was 69.0% (95% CI 49.9-95.4) in group variants 1/2/others versus 32.7% (95% CI 15.6-68.4) in group variants 3a/b (P = 0.108) among all crizotinib-, alectinib-, and ceritinib-treated patients. Variant 3a- or 5a-harboring cells were resistant to ALK inhibitors with >10-fold higher half maximal inhibitory concentration in vitro.

Conclusion

Our findings show that group EML4-ALK variants 3a/b may be a major source of ALK inhibitor resistance in the clinic. The variant-specific genotype of the EML4-ALK fusion allows for more precise stratification of patients with advanced NSCLC.

Functional analysis of the hydrophobic patch on nuclear transport factor 2 involved in interactions with the nuclear pore in vivo

Nuclear transport factor 2 (NTF2) is a small homodimeric protein that interacts simultaneously with both RanGDP and FxFG nucleoporins. The interaction between NTF2 and Ran is essential for the import of Ran into the nucleus. Here we use mutational analysis to dissect the in vivo role of the interaction between NTF2 and nucleoporins. We identify a series of surface residues that form a hydrophobic patch on NTF2, which when mutated disrupt the NTF2-nucleoporin interaction. Analysis of these mutants in vivo demonstrates that the strength of this interaction can be significantly reduced without affecting cell viability. However, cells cease to be viable if the interaction between NTF2 and nucleoporins is abolished completely, indicating that this interaction is essential for the function of NTF2 in vivo. In addition, we have isolated a dominant negative mutant of NTF2, N77Y, which has increased affinity for nucleoporins. Overexpression of the N77Y protein blocks nuclear protein import and concentrates Ran at the nuclear rim. These data support a mechanism in which NTF2 interacts transiently with FxFG nucleoporins to translocate through the pore and import RanGDP into the nucleus.

Molecular mechanism of translocation through nuclear pore complexes during nuclear protein import

The trafficking of macromolecules between cytoplasm and nucleus through nuclear pore complexes is mediated by specific carrier molecules such as members of the importin-beta family. Nuclear pore proteins (nucleoporins) frequently contain sequence repeats based on FG cores and carriers appear to move their cargo through the pores by hopping between successive FG cores. A major question is why some macromolecules are transported while others are not. This selectivity may be generated by the ability to bind FG repeats, a local concentration of carrier-cargo complexes near the entrance to the pore channel, and steric hindrance produced by high concentrations of nucleoporins in the channel.

Crystallization and initial X-ray diffraction characterization of complexes of FxFG nucleoporin repeats with nuclear transport factors

NTF2 and importin-beta are transport factors that mediate nuclear protein import and which interact with nuclear pore proteins (nucleoporins) during translocation from the cytoplasm to the nucleus through nuclear pore complexes. We employed a native gel electrophoresis method to assess the interaction of nucleoporin constructs that contain FxFG sequence repeats with NTF2 and truncation mutants of importin-beta to determine suitable fragments for crystallization. Based on these data, we obtained crystals of complexes between yeast NTF2 and a construct containing five FxFG nucleoporin repeats from the yeast nucleoporin Nsp1p and between a construct containing residues 1-442 of human importin-beta and the same nucleoporin construct. The yeast NTF2-nucleoporin crystals have trigonal symmetry and diffract past 2.8 A resolution using synchrotron radiation, whereas the importin-beta-nucleoporin complex crystals have P2(1)2(1)2 orthorhombic symmetry and diffract past 3.2 A resolution.

Structural basis for the interaction between FxFG nucleoporin repeats and importin-beta in nuclear trafficking

We describe the crystal structure of a complex between importin-beta residues 1-442 (Ib442) and five FxFG nucleoporin repeats from Nsp1p. Nucleoporin FxFG cores bind on the convex face of Ib442 to a primary site between the A helices of HEAT repeats 5 and 6, and to a secondary site between HEAT repeats 6 and 7. Mutations at importin-beta Ile178 in the primary FxFG binding site reduce both binding and nuclear protein import, providing direct evidence for the functional significance of the importin-beta-FxFG interaction. The FxFG binding sites on importin-beta do not overlap with the RanGTP binding site. Instead, RanGTP may release importin-beta from FxFG nucleoporins by generating a conformational change that alters the structure of the FxFG binding site.

The molecular mechanism of transport of macromolecules through nuclear pore complexes

Trafficking of macromolecules between nuclear and cytoplasmic compartments takes place through the nuclear pore complexes (NPCs) of the nuclear envelope. Nuclear trafficking involves a complex series of interactions between cargo, soluble transport factors (carriers) and nuclear pore proteins (nucleoporins) that are orchestrated by the Ras-family GTPase Ran. The primary role of Ran is probably to establish directionality and to sort molecules to be transported by controlling the interaction between carriers and cargoes, so that they bind in one compartment but dissociate in the other. Translocation of carriers and cargo-carrier complexes through NPCs requires interactions between the carriers and nucleoporins that contain distinctive tandem sequence repeats based on cores rich in glycine and phenylalanine residues that are separated by hydrophilic linkers. Much recent work has focused on these interactions and, in particular, their specificity, regulation and function. Evidence is accumulating that carriers move through the NPC by distinct but overlapping routes using specific subsets of nucleoporins.

Interaction between NTF2 and xFxFG-containing nucleoporins is required to mediate nuclear import of RanGDP

Nuclear transport factor 2 (NTF2) is a small, homodimeric protein that binds to both RanGDP and xFxFG repeat-containing nucleoporins, such as yeast Nsp1p and vertebrate p62. NTF2 is required for efficient nuclear protein import and has been shown to mediate the nuclear import of RanGDP. We have used the crystal structures of rat NTF2 and its complex with RanGDP to design a mutant, W7A-NTF2, in which the affinity for xFxFG-repeat nucleoporins is reduced while wild-type binding to RanGDP is retained. The 2.5 A resolution crystal structure of W7A-NTF2 is virtually superimposable upon the wild-type protein structure, indicating that the mutation had not introduced a more general conformational change. Therefore, our data suggest that the exposed side-chain of residue 7 is crucial to the interaction between NTF2 and xFxFG repeat-containing nucleoporins. Consistent with its reduced affinity for xFxFG nucleoporins, fluorescently labelled W7A-NTF2 binds less strongly to the nuclear envelope of permeabilized cultured cells than wild-type NTF2 and, when microinjected into Xenopus oocytes, colloidal gold coated with W7A-NTF2 binds less strongly to the central channel of nuclear pore complexes than wild-type NTF2-coated gold. Significantly, W7A-NTF2 only weakly stimulated the nuclear import of fluorescein-labelled RanGDP, providing direct evidence that an interaction between NTF2 and xFxFG repeat-containing nucleoporins is required to mediate the nuclear import of RanGDP.

Surgical technique. Intravenous access: obtaining large-bore access in the shocked patient

Images

Mortality in elderly patients admitted for respite care

OBJECTIVE

To determine whether admitting elderly patients to hospital to give temporary relief to their carers is associated with increased mortality.

DESIGN

Prospective multicentre study comparing the mortality of patients admitted on a one off or rotational basis with that experienced while they were awaiting admission.

SETTING

A wide range of urban and rural district general, geriatric or long stay, and general practitioner hospitals.

PATIENTS

474 Patients aged 70 or over who had 601 admissions.

MAIN OUTCOME MEASURE

Death.

RESULTS

16 (3.4%) Of the 474 patients (2.7% of all 601 admissions) died while in hospital during an average stay of 15.7 days whereas 23 (4.9%) patients died while awaiting admission (average waiting time was 34.2 days). The 16 deaths in hospital and the 23 deaths during the longer waiting period correspond to death rates of 19.9 and 12.5 per 10,000 person days respectively. The difference between these of 7.4 is not statistically significant (95% confidence interval -3.6 to 18.3). The estimated relative risk of dying in hospital is 1.59 but the 95% confidence interval is wide (0.84 to 3.01).

CONCLUSION

Although the death rates are slightly higher in those admitted to hospital for relief care than in those awaiting admission, the difference was not significant, and the death rate in both groups was reassuringly small.

The bowel, the genitourinary tract, and infective endocarditis

Of 582 episodes of infective endocarditis 75 were attributable to organisms normally resident in the bowel and 12 others were associated with alimentary tract operations, investigations, or disease. The mean age of the 87 patients in this particular group was higher (59.7 years) than that of all the patients with infective endocarditis (51.4 years). As far as could be ascertained 41% had no pre-existing cardiac abnormality, and in a little under a half no predisposing event to initiate the illness was apparent. Where the portal of entry of the organism to the blood stream was evident it was slightly more often in the genitourinary than the alimentary tract. Bowel organisms are no less important than those associated with the teeth in causing infective endocarditis. It is suggested that in all those patients with known cardiac abnormalities and possibly in those over the age of 60 with normal hearts antibiotic cover should be considered when they undergo genitourinary or alimentary tract surgery or instrumentation.

The microbiology and pathogenesis of infective endocarditis

Some details of 544 episodes of infective endocarditis occurring in 541 patients during 1981 and 1982 are reported. The mean age of patients was 51.6 years and there was a greater proportion of males (2:1). Of the 544 episodes 347 (63%) were due to streptococci, 19% to staphylococci, and 14% to bowel organisms. A wide variety of other organisms were responsible for a few cases, and 10% were culture negative. In 60% the portal of entry of the infection could not be ascertained: 19% were probably of dental origin: 16% arose from the alimentary, genitourinary, or respiratory tracts or from the skin or in association with drug addiction, fractures, or pregnancy; the remaining 5% were related to cardiac or other vascular surgery, cardiac catheterisation, haemodialysis, or other procedures involving the blood stream. Seventy-four (14%) of the 541 patients (mean age 59.0 years) died; the mortality was 30% in staphylococcal cases, 14% in infections due to bowel organisms, and 6% in other streptococcal infections. One hundred and seventy-one (32%) of the patients appeared to have had normal hearts before the onset of illness and another 59 (11%) had cardiac lesions not previously recognised. The aortic valve was the most common site of infection. Ninety (17%) of the patients had prosthetic valves or had undergone other cardiac surgery while 34 (6%) had had a previous episode of infective endocarditis. Nine (1.6%) episodes were not diagnosed until necropsy or operation and 34 (6.3%) required urgent valve replacement.

The teeth and infective endocarditis

During 1981 and 1982 544 cases of infective endocarditis were investigated retrospectively by means of a questionnaire. Only 13.7% had undergone any dental procedure within three months of the onset of the illness, and in 42.5% there was no known cardiac abnormality before the onset of the disease. Furthermore, the number of cases occurring annually was about the same as or more than it was before the introduction of penicillin. The mouth and nasopharynx were the most likely sources of the commonest organism, Streptococcus viridans, and it is suggested that it is not dental extractions themselves which are of importance but good dental hygiene. In most patients with infective endocarditis the portal of entry of the organism whatever its nature cannot be identified. If this is so antibiotics are being given to only a small proportion of those at risk, and this would explain why the number of cases is much the same as it was before the introduction of penicillin. Furthermore, the large proportion of patients with no known previous cardiac abnormality adds to the difficulty of providing effective prophylaxis. The evidence suggests that antibiotic prophylaxis should still be given before dental procedures, and a schedule is appended. Much more importance should be given, however, to encouraging people to seek better routine dental care. We also believe that doctors and dentists should appreciate that the pattern of the disease has changed considerably in the past 50 years and that the information given here warrants a revised approach to the problem.

Giant ovarian dermoid masked by obesity

A 37-year-old female, weighing 194.1 kg, is described. Her gross obesity was in part due to a massive ovarian dermoid cyst weighing at least 42 kg, which had been overlooked in the past. A dermoid tumour of this size has not previously been reported. The possible presence of cystic ovarian tumours should be considered in patients presenting with severe generalized obesity.

The effect of weight gain on gonadotrophins and prolactin in anorexia nervosa

Serum levels of gonadotrophins and prolactin and their response to luteinizing hormone/follicle stimulating hormone--releasing hormone (LRH) and thyrotrophin releasing hormone (TRH) were measured in 14 females with anorexia nervosa when at low body weight and again in 6 cases during, and 12 cases after weight gain. Mean serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were low initially and whereas FSH increased significantly with weight gain, LH levels remained subnormal in most patients. LH responses to LRH were grossly impaired or absent in patients whose weight was below 75% of the ideal, but increased dramatically above this weight over-shadowing the more modest increase in FSH response. In three patients, however, impaired LH responses persisted as ideal weight was approached. Basal prolactin levels were well within the normal range in all patients. During weight gain there was no change in basal levels but the prolactin level 20 min after TRH was significantly increased.

Hashimoto's thyroiditis presenting as T3 toxicosis

Images

Hypothalamo-pituitary-thyroid function in anorexia nervosa: influence of weight gain

The functional state of the hypothalamo-pituitary-thyroid axis was assessed in 14 women and girls with anorexia nervosa when at low body weight and again in 12 cases after they had gained weight. Mean serum thyroxine concentrations were low before and after weight gain. Mean serum triiodothyronine (T3) concentrations were substantially reduced at low weight and doubled after weight gain, the absolute values being linearly correlated with body weight expressed as a percentage of the ideal. Concentrations of reverse T3 were greatly increased in some patients initially and fell with weight gain. Basal concentrations of thyroid-stimulating hormone (TSH) were unchanged after weight gain but the TSH response to thyrotrophin-releasing hormone was significantly augmented; delayed patterns of response were found in seven out of 12 patients tested before and three out of 12 patients tested after weight gain. Changes in the hypothalamo-pituitary-thyroid axis are common in anorexia nervosa and probably represent both peripheral and central adaptations to the altered nutritional state.