Role of RET protein-tyrosine kinase inhibitors in the treatment RET-driven thyroid and lung cancers.

RET is a transmembrane receptor protein-tyrosine kinase that is required for the development of the nervous system and several other tissues. The mechanism of activation of RET by its glial-cell derived neurotrophic factor (GDNF) ligands differs from that of all other receptor protein-tyrosine kinases owing to the requirement for additional GDNF family receptor-α (GFRα) co-receptors (GFRα1/2/3/4). RET point mutations have been reported in multiple endocrine neoplasia (MEN2A, MEN2B) and medullary thyroid carcinoma. In contrast, RET fusion proteins have been reported in papillary thyroid and non-small cell lung adenocarcinomas. More than a dozen fusion partners of RET have been described in papillary thyroid carcinomas, most frequently CCDC6-RET and NCOA4-RET. RET-fusion proteins, commonly KIF5B-RET, have also been found in non-small cell lung cancer (NSCLC). Several drugs targeting RET have been approved by the FDA for the treatment of cancer: (i) cabozantinib and vandetanib for medullary thyroid carcinomas and (ii) lenvatinib and sorafenib for differentiated thyroid cancers. In addition, alectinib and sunitinib are approved for the treatment of other neoplasms. Each of these drugs is a multikinase inhibitor that has activity against RET. Previous X-ray studies indicated that vandetanib binds within the ATP-binding pocket and forms a hydrogen bond with A807 within the RET hinge and it makes hydrophobic contact with L881 of the catalytic spine which occurs in the floor of the adenine-binding pocket. Our molecular modeling studies indicate that the other antagonists bind in a similar fashion. All of these antagonists bind to the active conformation of RET and are therefore classified as type I inhibitors. The drugs also make variable contacts with other residues of the regulatory and catalytic spines. None of these drugs was designed to bind preferentially to RET and it is hypothesized that RET-specific antagonists might produce even better clinical outcomes. Currently the number of new cases of neoplasms bearing RET mutations or RET-fusion proteins is estimated to be about 10,000 per year in the United States. This is about the same as the incidence of chronic myelogenous leukemia for which imatinib and second and third generation BCR-Abl non-receptor protein-tyrosine kinase antagonists have proven clinically efficacious and which are commercially successful. These findings warrant the continued development of specific antagonists targeting RET-driven neoplasms.

HESX1 mutations in patients with congenital hypopituitarism: variable phenotypes with the same genotype.

INTRODUCTION: Mutations in the transcription factor HESX1 can cause isolated growth hormone deficiency (IGHD) or combined pituitary hormone deficiency (CPHD) with or without septo-optic dysplasia (SOD). So far there is no clear genotype-phenotype correlation. PATIENTS AND RESULTS: We report four different recessive loss-of-function mutations in three unrelated families with CPHD and no midline defects or SOD. A homozygous p.R160C mutation was found by Sanger sequencing in two siblings from a consanguineous family. These patients presented with ACTH, TSH and GH deficiencies, severe anterior pituitary hypoplasia (APH) or pituitary aplasia (PA) and normal posterior pituitary. The p.R160C mutation was previously reported in a case with SOD, CPHD and ectopic posterior pituitary (EPP). Using exome sequencing, a homozygous p.I26T mutation was found in a Brazilian patient born to consanguineous parents. This patient had evolving CPHD, normal ACTH, APH and normal posterior pituitary (NPP). A previously reported patient homozygous for p.I26T had evolving CPHD and EPP. Finally, we identified compound heterozygous mutations in HESX1, p.[R159W];[R160H], in a patient with PA and CPHD. We showed that both of these mutations abrogate the ability of HESX1 to repress PROP1-mediated transcriptional activation. A patient homozygous for p.R160H was previously reported in a patient with CPHD, EPP, APH. CONCLUSION: These three examples demonstrate that HESX1 mutations cause variable clinical features in patients, which suggests an influence of modifier genes or environmental factors on the phenotype.

Central Precocious Puberty as a Complication of Therapy with Adrenocorticotropin (ACTH) and an Aromatase Inhibitor for Refractory Nephrotic Syndrome.

Glucocorticoids are typically prescribed for the treatment of idiopathic nephrotic syndrome of childhood. In selected patients with refractory focal segmental glomuerulosclerosis (FSGS), adrenocorticotropin (ACTH) can be used to induce remission and decrease the progression of the disease. We report a 6 8/12-year-old girl with recurrent proteinuria, resistant to standard immunotherapy. She underwent related renal transplant but again developed proteinuria and was started on ACTH. She subsequently developed peripheral precocious puberty (PPP), presumably from peripheral aromatization of adrenal androgens. She was started on an aromatase inhibitor, and her ACTH dose was slowly decreased. She then developed central precocious puberty (CPP). We hypothesize that treatment of her peripheral precocious puberty with an aromatase inhibitor may have triggered central precocious puberty.

Effect of recombinant growth hormone treatment on children with Crohn's disease and short stature: a pilot study.

BACKGROUND: Growth failure frequently complicates Crohn's disease in childhood. Abnormalities in the growth hormone (GH)/insulin-like growth factor-1 axis may occur. The effects of administered GH on growth have not been studied previously in a randomized trial. METHODS: Seven children (6 boys and 1 girl; age, 11.9-16 yr) with Crohn's disease and growth failure were enrolled. In phase 1, patients were randomized to either GH (0.05 mg/kg per day) or placebo; in phase 2, patients who received placebo during the first year received GH for various time periods. Follow-up was every 3 months for up to 2 years. RESULTS: During placebo treatment (4 patients), mean height-for-age z score (haz) increased 0.23 in the first half year and 0.55 in the second half year. The mean improvement in haz during the first half year of GH treatment (7 patients) was 0.13; during the second half year (5 patients), haz decreased 0.01. Effects of GH varied among patients; 2 patients grew only when nutritional supplementation was added. Observed changes were not statistically significant; however, the number of patients studied was small, and statistical analyses could have been affected by sample size. Serum insulin-like growth factor-1 levels correlated with height velocity. Only 2 patients later reached expected adult height. CONCLUSIONS: In this pilot study, GH treatment at the dose given did not stimulate growth in children with Crohn's disease and short stature. Whether or not GH plus nutritional therapy would be effective in promoting sustained catch-up growth remains to be determined.