Structural basis of acquired resistance to selpercatinib and pralsetinib mediated by non-gatekeeper RET mutations

BACKGROUND

Selpercatinib (LOXO-292) and pralsetinib (BLU-667) are highly potent RET-selective protein tyrosine kinase inhibitors (TKIs) for treating advanced RET-altered thyroid cancers and non-small-cell lung cancer (NSCLC). It is critical to analyze RET mutants resistant to these drugs and unravel the molecular basis to improve patient outcomes.

PATIENTS AND METHODS

Cell-free DNAs (cfDNAs) were analyzed in a RET-mutant medullary thyroid cancer (MTC) patient and a CCDC6-RET fusion NSCLC patient who had dramatic response to selpercatinib and later developed resistance. Selpercatinib-resistant RET mutants were identified and cross-profiled with pralsetinib in cell cultures. Crystal structures of RET-selpercatinib and RET-pralsetinib complexes were determined based on high-resolution diffraction data collected with synchrotron radiation.

RESULTS

RETG810C/S mutations at the solvent front and RETY806C/N mutation at the hinge region were found in cfDNAs of an MTC patient with RETM918T/V804M/L, who initially responded to selpercatinib and developed resistance. RETG810C mutant was detected in cfDNAs of a CCDC6-RET-fusion NSCLC patient who developed acquired resistance to selpercatinib. Five RET kinase domain mutations at three non-gatekeeper residues were identified from 39 selpercatinib-resistant cell lines. All five selpercatinib-resistant RET mutants were cross-resistant to pralsetinib. X-ray crystal structures of the RET-selpercatinib and RET-pralsetinib complexes reveal that, unlike other TKIs, these two RET TKIs anchor one end in the front cleft and wrap around the gate wall to access the back cleft.

CONCLUSIONS

RET mutations at the solvent front and the hinge are resistant to both drugs. Selpercatinib and pralsetinib use an unconventional mode to bind RET that avoids the interference from gatekeeper mutations but is vulnerable to non-gatekeeper mutations.

P0525ROLE OF NADPH OXIDASE 4 IN ACUTE KIDNEY INJURY ASSOCIATED TO MASSIVE INTRAVASCULAR HEMOLYSIS

Background and Aims

Massive intravascular hemolysis is a common condition of several pathologies. It is associated with acute kidney injury (AKI) and progressive impairment of renal function. In this context, free hemoglobin (Hb) can exert harmful effects by accumulating in the kidney, where induces oxidative stress and it becomes cytotoxic. NADPH oxidase 4 (Nox4) is the principal source of reactive oxygen species (ROS) in the kidney. Nox4 is mostly expressed in proximal tubular cells with lower levels in glomerulus. The role of Nox4 in renal damage is not clear, with studies reporting beneficial or deleterious actions depending of the environmental conditions. For that reason we aimed to investigate the role of Nox4 in massive intravascular hemolysis-associated AKI.

Method

To study the role of Nox4 in AKI caused by massive intravascular hemolysis, we performed an experimental model of intravascular hemolysis by intraperitoneal injection of phenylhydrazine (200 mg/kg) in wild type (Nox4+/+) and Nox4 knockout mice (Nox4-/-). Mice were sacrificed 24 and 72 hours after intravascular hemolysis induction. We collected serum, urine and tissues sample. We analyzed renal function, oxidative stress, cell death and inflammation in these samples. In other experiments, wild type mice were treated with GKT137831 (10mg/kg/day), a potent Nox4 and Nox1 inhibitor, and mice were sacrificed 72h after induction of hemolysis. We also performed in vitro experiments in murine tubular epithelial cells (MCT) and murine podocytes cells to investigate the regulation of Nox4 in Hb-stimulated cells treated or not with GKT137831.

Results

Induction of intravascular hemolysis in Nox4+/+ mice increased creatinine and BUN levels and enhanced the expression of tubular injury markers, such as NGAL. These pathological effects were reduced in Nox4 knockout mice. Then, we analyzed oxidative stress in our experimental model thought determination of HO-1, ferritin, GSH and lipid peroxidation levels. All of these oxidative markers were reduced in Nox4-/- mice with intravascular hemolysis as compared with Nox4+/+ mice. We also observed that inflammatory markers such as IL-6, cell death and podocytes injury markers were reduced in Nox4-/- mice than in wild type mice, specially 72 hours after phenylhydrazine injection. In line with these results, GKT137831 administration ameliorated intravascular hemolysis-associated renal function impairment. Moreover, oxidative stress, tubular injury markers and podocyte injury were reduced in hemolytic mice treated with GKT137831. GKT137831 also reduced Hb- and heme-mediated oxidative stress in MCT and podocytes.

Conclusion

Our results show the important role of Nox4 in renal injury associated to massive intravascular hemolysis. Moreover, the inhibition of Nox4 may be a potential therapeutic target to prevent renal damage associated to Hb accumulation. These findings provide new insights into novel aspects of Hb-toxicity and may have important pathogenic and therapeutic implications for intravascular hemolysis related diseases

Lamotrigine induced subacute cutaneous lupus erythematous

A 48-year-old woman developed drug-induced subacute lupus erythematosus while taking lamotrigine. The eruption resolved after discontinuance of lamotrigine, suggesting this drug as the cause.

Clinical diagnosis of toenail onychomycosis is possible in some patients: cross-sectional diagnostic study and development of a diagnostic rule

BACKGROUND

Suspected toenail onychomycosis is a frequent problem. Clinical diagnosis has been considered inadequate.

OBJECTIVES

To assess the diagnostic accuracy of clinical findings for detecting fungi in toenails, and to develop and validate a clinical diagnostic rule aimed at improving dermatologists' diagnosis of onychomycosis.

METHODS

A cross-sectional diagnostic study was performed including a total of 277 patients seen by 12 dermatologists. The gold standard was the presence of dermatophytes on culture or a positive nail plate biopsy. For each sign we described prevalence, sensitivity, specificity, positive and negative predictive values, and likelihood ratios for positive and negative results. We developed a diagnostic clinical rule and validated it in a subsample.

RESULTS

Helpful findings to predict the presence of fungi are: previous diagnosis of fungal disease; abnormal plantar desquamation (affecting > 25% of the sole); onychomycosis considered the most probable diagnosis by a dermatologist; and presence of interdigital tinea. When dermatologists considered onychomycosis the most probable diagnosis and plantar desquamation was present (13% of patients), the positive predictive value for presence of fungi was 81%. When both signs were absent (34% of patients), the positive predictive value for absence of fungi was 71%. In other situations, clinical diagnosis might not give enough information to decide on therapy.

CONCLUSIONS

In 13% of the patients (a large number in absolute terms), when dermatologists consider onychomycosis the most probable diagnosis and plantar desquamation is present, therapy should be started without any further test, as clinical diagnosis is at least as accurate as laboratory tests. In other situations, an optimal management strategy should be defined.

[Prevalence of birthmarks and transient skin lesions in 1,000 Spanish newborns]

BACKGROUND AND OBJECTIVES

Almost all newborn children have some sort of birthmark or transient benign skin lesion. Few studies, however, have analyzed their frequency, particularly in Spain. The aims of this study were to determine their prevalence in 1000 newborn children in the health care area of Ferrol in northwest Spain and to compare the results with those of 9 other studies with similar characteristics.

PATIENTS AND METHODS

We undertook a descriptive study of 1000 newborn infants seen in the first 3 days of life at the neonatal clinic in the Department of Pediatrics, Hospital Arquitecto Marcide, Ferrol, Spain. Each infant was examined for the presence of 19 different transient benign skin lesions and 11 birthmarks.

RESULTS

Birthmarks or benign skin lesions were present in 994 neonates (99.4%). Transient skin lesions were present in 99.2% and birthmarks in 72%. The 5 most prevalent lesions were sebaceous hyperplasia (75%), salmon patch (64.2%), hypertrichosis (59%), sucking calluses (54%), and palatine cysts (53.7%).

CONCLUSIONS

The results of this study show that most neonates have benign skin lesions. The findings of studies to assess their frequency are influenced not only by geographic location (affecting variables such as climate, social and health care conditions, and ethnic group) but also by the timing of examination, the inclusion criteria applied, and the terminology used.

[Salmon patch: a descriptive study]

BACKGROUND AND OBJECTIVES

salmon patch is a congenital venous malformation that usually affects the midline. Although it is very common, few studies have analyzed its prevalence or predisposing factors. The aim of this study was to determine the prevalence and clinical characteristics of salmon patch in a group of newborn infants from a health care area in northwest Spain and to assess its association with neonatal and maternal variables.

PATIENTS AND METHODS

a descriptive study was undertaken of live newborn children seen in the neonatal unit of the Department of Pediatrics at Hospital Arquitecto Marcide, Ferrol, Spain between May 1, 2008 and January 31, 2009. The study protocol included collection of data on neonatal variables (including gestational age, sex, ethnic origin, weight, and presence and anatomical site of salmon patch) and maternal variables (including age and number of previous pregnancies).

RESULTS

of the 600 newborn infants included in the study, 59% had salmon patches. The most commonly affected sites were the nape of the neck (226 infants, 37.6%) and eyelids (211 infants, 35.1%). In a number of cases, more than one part of the body was affected. There was a higher prevalence of salmon patch in full-term or post-term births, in girls, white children, heavier children, and infants born to mothers aged between 30 and 34 years or who had not been pregnant previously.

CONCLUSIONS

salmon patch occurred most frequently on the nape of the neck, the eyelids, and the glabella. Its prevalence was associated with certain neonatal and maternal factors.

[Usefulness of meal replacement: analysis of the principal meal replacement products commercialised in Spain]

INTRODUCTION

Obesity has become a serious health problem. It is nowadays considered a pandemia and it is therefore a priority to develop different strategies on its prevention and treatment: lifestyle changes, community interventions as well as pharmacological and non-pharmacological activities. In this way, meal replacement products (energy reduced products designed to replace one or two regular meals providing a supously nutritionally balanced low fat meal) can be an alternative to traditional reduced calorie diet.

OBJECTIVE

Our aim was to revise the literature on meal replacement and compare the nutritional composition and the different forms of presentation of the main meal replacement products commercialised in Spain.

METHODOLOGY

We made a research in pharmacies, weight loss centers and big supermarkets of food products specially designed to replace a meal. We compared the nutritional composition regarding macronutrients and micronutrients of the thirty-two different products founded, including their different form of presentation (bars, powder, drink-shakes and crackers). In order to judge their nutritional composition, we compared one meal replaced with these products with the Recommended Dietary Allowances (RDA).

RESULTS

The most common form of meal replacement products were bars (23 of 32 analyzed products), followed by powder for making shakes (6 products), bricks (2 products) and crackers (1 product). When we analysed a single meal replaced with these products, we founded that the global distribution of macronutrients was: 45% as carbohydrates, 29% as fats, 26% as proteins, and 4.45 grams of fiber. Their average energy was 266 Kcal per meal. Regarding micronutrients (vitamins and minerals), there was a great variability among the different products, but in average their composition was above the 33% of the RDA per meal specially in iron and vitamins B1, B6 and D. Calcium, magnesium, folic acid and vitamin B12 were the micronutrients less plentiful.

CONCLUSION

Partial meal replacement can be an alternative or a complementary therapeutic option to conventional hipocaloric diets in obesity since they appear to have an easier understanding and follow up. It is therefore important to consider them in weight management programs and more studies are required to establish strict criteria on their nutritional composition by a legal normative.