Response to RET-Specific Therapy in RET Fusion-Positive Anaplastic Thyroid Carcinoma

Background: Anaplastic thyroid carcinoma (ATC) remains one of the most challenging malignancies to treat in the modern era. Most patients present with or develop recurrent/metastatic incurable disease with poor response rates to conventional chemotherapy, and life expectancy is short. Next-generation sequencing (NGS) can be leveraged in ATC to identify oncogenic alterations that can be targeted with molecularly specific therapy, offering new effective treatment options to a subset of patients. Patient Findings: A 73-year-old man presenting with locally advanced papillary thyroid carcinoma containing a minor component of ATC was treated with surgery and iodine-131. He developed biopsy-confirmed ATC distant metastases that progressed on cytotoxic chemotherapy. NGS revealed several alterations, including a CCDC6-RET gene fusion. The patient enrolled in LIBRETTO-001, a phase I/II trial of the potent and specific RET inhibitor, LOXO-292. The patient tolerated LOXO-292 well and experienced a deep and durable partial response, ongoing beyond 19 months. Conclusion: This clinically significant response achieved with LOXO-292 in a patient with a CCDC6-RET fusion-positive ATC who had exhausted conventional treatment options highlights the importance of conducting tumor genomic profiling in patients with ATC to identify uncommon but actionable genomic alterations, such as RET gene fusions.

First experience of LOXO-292 in the management of pediatric patients with RET-altered cancers

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Background: Genomic alterations of RET kinase, including chromosomal fusions and activating point mutations, have been identified as oncogenic drivers in pediatric and adult cancers. Multikinase inhibitors have modest activity against RET-altered cancers and are associated with significant toxicity. LOXO-292 is a potent, ATP-competitive, small molecule RET inhibitor with high selectivity for RET, preclinical activity in the brain and excellent pharmacokinetic properties. In an ongoing phase 1/2 study of adult and adolescent patients with advanced RET-altered cancers, LOXO-292 demonstrated marked antitumor activity and was well tolerated. Methods: Pediatric patients with RET-altered cancers who were unable to access LOXO-292 through a phase 1/2 clinical trial were enrolled using FDA-allowed, IRB-approved single patient protocols . Patients received LOXO-292 (capsule/liquid formulation) orally, continuously, at a starting dose of 90 mg/m2 BID. Response was assessed locally by investigators. Results: As of January 31, 2019, 4 female patients aged 13 months–8 years were enrolled from the Republic of Korea (papillary thyroid cancer, n = 1) and the USA (infantile myofibroma/hemangiopericytoma, n = 1; congenital mesoblastic nephroma/infantile fibrosarcoma, n = 1; lipofibromatosis, n = 1). All tumors harbored RET gene fusions (5′ partners: CCDC6, MYH10, SPECC1L, and NCOA4, respectively), detected by next-generation sequencing. Previous therapies included surgery/iodine 131 (n = 1); vandetanib (n = 1); surgery/chemotherapy (n = 1); 1 patient was treatment-naïve. Duration of treatment ranged from 3–120 days and all patients remain on treatment. There were no dose modifications or discontinuations due to adverse events. There were no treatment-related adverse events ≥ grade 3. Two patients who were evaluable for response had partial responses (both ongoing, 1 confirmed, 1 pending confirmation). Conclusions: These preliminary data from a real-world setting suggest that LOXO-292 is effective and safe in pediatric patients whose tumors harbor RET gene fusions.

Vibration from a riveting hammer causes severe nerve damage in the rat tail model

INTRODUCTION

Hand-arm vibration syndrome (HAVS) is an occupational neurodegenerative and vasospastic disorder in workers who use powered hand tools. Frequency weighting (ISO 5349) predicts little risk of injury for frequencies >500 HZ. Potentially damaging high frequencies abound in impact tool-generated shock waves.

METHODS

A rat tail impact vibration model was developed to deliver shock-wave vibration from a riveting hammer to simulate bucking bar exposure. Rat tails were vibrated continuously for 12 min. Tail flick withdrawal times were determined for noxious heat. Nerve trunks and skin were processed for light and electron microscopy.

RESULTS

Immediately after vibration, the tails were hyperalgesic and had disrupted myelinated axons, fragmented nerve endings, and mast-cell degranulation. By 4 days, the tails were hypoalgesic; nerve endings were lost in the skin.

CONCLUSIONS

Shock-wave vibration causes severe nerve damage. Frequency weighting seriously underestimates the risk of nerve injury with impact tools.

Aqueous solution of [bmim][PF6]: ion and solvent effects on structure and dynamics

A dilute aqueous solution of the salt 1-n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) has been studied using molecular dynamics simulations to investigate the effect of ions on water and vice versa. The anion is found to diffuse faster than the cation in the solution, in contrast to observations in the pure ionic liquid. Distributions of pair energies have been employed to identify ion association, and around 13% of the ions were found to exist as pairs. The mean potential energy of water molecules present in the coordination shell of an anion is less than that of water molecules coordinated to a cation. The former kind also exhibit two distinct orientational preferences with respect to the anion. The larger diffusion coefficient of the anion is related to the faster dynamics of water molecules in its hydration layer, as evidenced from the relaxation of their residence time correlation function.

Intermolecular correlations in an ionic liquid under shear

The behavior of a model room temperature ionic liquid under shear is explored using non-equilibrium molecular dynamics simulations. The external field reduces intermolecular structure in the liquid. However, orientational ordering of the molecules in the form of a nematic phase is observed under shear.

Changes in gene expression during senescence of adrenocortical cells in culture

Bovine adrenocortical cells undergo a process in which expression of steroid hydroxylases is lost progressively as a function of population doubling level (PDL) in culture. Each cytochrome P450 shows a characteristic rate of loss of expression as a function of PDL (in order of rates of loss: CYP11B >CYP21 >CYP17 >CYP11A). CYP11B and CYP21 require insulin-like growth factor I as well as cyclic AMP; these are the only factors required for induction in the primary culture. Middle- and later passage cells do not express CYP11B and CYP21 under the same conditions, but will do so when cells are grown in extracellular matrix Matrigel. In late-passage cells neither CYP17, CYP21, nor CYP11B are expressed, even in the presence of Matrigel; only CYP11A is expressed in late-passage cultures. When the different environmental factors required for induction of CYP11B and CYP21 are taken into account, induction of these genes disappears with the same kinetics as previously shown for CYP17 as a function of PDL. The primary cause of the loss of expression of these genes is likely to be a phenotypic switching event similar to that previously demonstrated for CYP17 by in situ hybridization. The mechanism of phenotypic switching is unknown. However, one HpaII site at -2.3 kb of CYP17 was methylated in the bovine adrenal cortex in vivo but showed rapid and complete demethylation when adrenocortical cells were placed in culture. This indicates a unique, reproducible, environmentally determined change in methylation, with as yet undetermined consequences. However, data from reporter constructs suggest that phenotypic switching does not result from a simple loss of regulatory factors that act within 2.5 kb of the promoter. Previous data suggested that SV40 T antigen may affect phenotypic switching, and thus that SV40 may be useful for the derivation of functional adrenocortical cell lines. Adaptation of methods previously used for bovine cells to human adrenocortical cells to produce SV40 T antigen-transfected clones yielded data indicating preservation of essential aspects of the human adrenocortical cell differentiated phenotype.

Ultrastructural, immunochemical, and cytochemical study of myeloperoxidase in myeloid leukemia HL-60 cells following treatment with succinylacetone, an inhibitor of heme biosynthesis

Myeloperoxidase (MPO) is a heme-containing glycoprotein found in the primary granules (or azurophilic granules) of human polymorphonuclear leukocytes. In the present study, cultured myeloid leukemia HL-60 cells were exposed for 0-72 h to 250 microM 4,6-dioxoheptanoic acid (succinylacetone, SA), a specific inhibitor of heme biosynthesis, and the effects were evaluated using ultrastructural, immunochemical, and cytochemical methods. En bloc peroxidase staining of glutaraldehyde-fixed cells was accomplished with a 30-min exposure to 3,3'-diaminobenzidine (DAB) tetrahydrochloride. Ultrastructural examination revealed that peroxidase reactivity in the endoplasmic reticulum (ER) was relatively unchanged for 8 h and decreased between 12 and 24 h; however, ER lacked DAB-reactive peroxidase at 48-72 h. Peroxidase reactivity in the ER reappeared within 4 h after removal of SA. Seventy-two hours after exposure to SA the number of condensed cytoplasmic granules stained with DAB was significantly decreased, and many of the granules had a "target" appearance with a central DAB-reactive dense core. Staining of mitochondria was observed with overnight exposure to DAB and persisted in HL-60 cells treated 72 h with SA. Mitochondrial and nuclear morphology appeared unaltered. Immunostaining of MPO in thin sections of paraformaldehyde/glutaraldehyde-fixed unosmicated HL-60 cells, embedded in Lowicryl K4M, was accomplished with sequential exposure to an affinity-purified monospecific rabbit antibody to HL-60-MPO and protein A conjugated to 5- or 10-nm colloidal gold. Compared to untreated control HL-60 cells, cells exposed to SA for 48 h exhibited comparable to increased immunoreactive MPO in the ER, despite the absence of heme-dependent peroxidase reactivity. The data indicate that SA inhibits formation of enzymatically active MPO and that in the presence of SA, the ER contains a form(s) of MPO that lacks enzymatic reactivity.

Demethylation of specific sites in the 5'-flanking region of the CYP17 genes when bovine adrenocortical cells are placed in culture

DNA methylation of CYP17 (steroid 17 alpha-hydroxylase) was studied in bovine adrenocortical cells, which lose the capacity to express this tissue-specific gene in culture by phenotypic switching. Restriction enzyme digestions, and sequencing of a lambda clone of a second CYP17 gene (CYP17A2), showed that there are at least three CYP17 genes in the bovine genome. Southern blotting of DNA digested with Msp I or Hpa II together with Eco RI was used to investigate the methylation status of Hpa II sites at -1.0 kb (H1), -1.8 kb (H2), and -2.3 kb (H4) in CYP17A1 and CYP17A2 and at -0.7 kb (H0) in CYP17A3. In cells and tissues other than white blood cells, H0 was nonmethylated whereas H1 was always methylated; H2 and H4 showed variation in methylation status among different cells and tissues. In particular, whereas H4 was methylated in the bovine adrenal cortex in vivo, there was a rapid and complete demethylation at H4 when adrenocortical cells were placed in culture. Sites downstream from H4 did not change methylation over the first six passages in culture; additionally, the coding region of CYP17 remained fully methylated under all conditions. In contrast to adrenocortical cells, DNA from fibroblasts was nonmethylated at H2, whereas all downstream sites were fully methylated. Digestion with another methylation-sensitive enzyme, Bsa HI, which has a site between H2 and H4, showed that this region is methylated in intact adrenal cortex but nonmethylated both in cultured adrenocortical cells and in fibroblasts. The specific changes in methylation at this site and at H4 in adrenocortical cells indicate a reproducible, environmentally determined change in methylation in adrenocortical cells when they are placed in culture.

Changes in gene expression and DNA methylation in adrenocortical cells senescing in culture

Recent experiments in cultured bovine adrenocortical cells show that the previously observed phenotypic switching of CYP17 (steroid 17 alpha-hydroxylase) expression is preceded at a much earlier time by changes in methylation in the CYP17 5' flanking region. Two CpG sites that are methylated in the adrenal cortex in vivo were observed to undergo rapid demethylation when adrenocortical cells were placed in culture. Two adjacent CpG sites that are also methylated in vivo did not demethylate; these two sites are completely nonmethylated in fibroblasts. All CpG sites downstream, in the promoter or coding region, are always methylated in all tissues and in bovine adrenocortical cells even after many population doublings in culture. In contrast to the specific and rapid demethylation of sites in CYP17, satellite I shows a slower and apparently random loss of methylation that extends over the entire replicative life span. These changes in methylation provide examples of genetic instability in cells that undergo senescence in culture. Future experiments will focus on the relationship of these events to the phenotypic switching process.

Purification and properties of 4-hydroxyphenylacetic acid 3-hydroxylase from Pseudomonas putida

4-Hydroxyphenylacetic acid 3-hydroxylase is a key enzyme in the pathway for the microbial degradation of phenylalanine, tyrosine and many aromatic amines. This enzyme was purified to homogeneity from Pseudomonas putida by affinity chromatography. The protein had a molecular weight of 91,000 and was a dimer of identical subunits. It was a typical external flavoprotein monooxygenase and showed an absolute requirement of NADH for activity. The enzyme had a pH optimum of 7.5 and the Km values for 4-hydroxyphenylacetic acid and NADH were 2 x 10(-4) M and 5.9 x 10(-5) M respectively. It was strongly inhibited by heavy metal ions and thiol reagents, suggesting the possible involvement of -SH group(s) in enzyme reaction.