Estimating motor unit numbers from a CMAP scan: Repeatability study on three muscles at 15 centres

OBJECTIVE

To assess the repeatability and suitability for multicentre studies of MScanFit motor unit number estimation (MUNE), which involves modelling compound muscle action potential (CMAP) scans.

METHODS

Fifteen groups in 9 countries recorded CMAP scans twice, 1-2 weeks apart in healthy subjects from abductor pollicis brevis (APB), abductor digiti minimi (ADM) and tibialis anterior (TA) muscles. The original MScanFit program (MScanFit-1) was compared with a revised version (MScanFit-2), designed to accommodate different muscles and recording conditions by setting the minimal motor unit size as a function of maximum CMAP.

RESULTS

Complete sets of 6 recordings were obtained from 148 subjects. CMAP amplitudes differed significantly between centres for all muscles, and the same was true for MScanFit-1 MUNE. With MScanFit-2, MUNE differed less between centres but remained significantly different for APB. Coefficients of variation between repeats were 18.0% for ADM, 16.8% for APB, and 12.1% for TA.

CONCLUSIONS

It is recommended for multicentre studies to use MScanFit-2 for analysis. TA provided the least variable MUNE values between subjects and the most repeatable within subjects.

SIGNIFICANCE

MScanFit was primarily devised to model the discontinuities in CMAP scans in patients and is less suitable for healthy subjects with smooth scans.

Lasofoxifene as a potential treatment for therapy-resistant ER-positive metastatic breast cancer

Background

Endocrine therapy remains the mainstay of treatment for estrogen receptor-positive (ER+) breast cancer. Constitutively active mutations in the ligand binding domain of ERα render tumors resistant to endocrine agents. Breast cancers with the two most common ERα mutations, Y537S and D538G, have low sensitivity to fulvestrant inhibition, a typical second-line endocrine therapy. Lasofoxifene is a selective estrogen receptor modulator with benefits on bone health and breast cancer prevention potential. This study investigated the anti-tumor activity of lasofoxifene in breast cancer xenografts expressing Y537S and D538G ERα mutants. The combination of lasofoxifene with palbociclib, a CDK4/6 inhibitor, was also evaluated.

Methods

Luciferase-GFP tagged MCF7 cells bearing wild-type, Y537S, or D538G ERα were injected into the mammary ducts of NSG mice (MIND model), which were subsequently treated with lasofoxifene or fulvestrant as single agents or in combination with palbociclib. Tumor growth and metastasis were monitored with in vivo and ex vivo luminescence imaging, terminal tumor weight measurements, and histological analysis.

Results

As a monotherapy, lasofoxifene was more effective than fulvestrant at inhibiting primary tumor growth and reducing metastases. Adding palbociclib improved the effectiveness of both lasofoxifene and fulvestrant for tumor suppression and metastasis prevention at four distal sites (lung, liver, bone, and brain), with the combination of lasofoxifene/palbociclib being generally more potent than that of fulvestrant/palbociclib. X-ray crystallography of the ERα ligand binding domain (LBD) shows that lasofoxifene stabilizes an antagonist conformation of both wild-type and Y537S LBD. The ability of lasofoxifene to promote an antagonist conformation of Y537S, combined with its long half-life and bioavailability, likely contributes to the observed potent inhibition of primary tumor growth and metastasis of MCF7 Y537S cells.

Conclusions

We report for the first time the anti-tumor activity of lasofoxifene in mouse models of endocrine therapy-resistant breast cancer. The results demonstrate the potential of using lasofoxifene as an effective therapy for women with advanced or metastatic ER+ breast cancers expressing the most common constitutively active ERα mutations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01431-w.

Abstract 4370: Lasofoxifene alone or in combination with palbociclib as an effective treatment for therapy-resistant ER-positive metastatic breast cancer

Patients with Estrogen Receptor positive (ER+) metastatic breast cancer (MBC) are currently treated with fulvestrant, a selective estrogen receptor degrader (SERD), or a combination of fulvestrant and palbociclib, a CDK4/6 inhibitor. Approximately 25-40% of patients with MBC have activating mutations in the ERα ligand-binding domain. The two most common mutations are Y537S and D538G, which confer constitutive activity to ERα, resulting in AI/tamoxifen/fulvestrant resistance. Lasofoxifene, a selective estrogen receptor modulator (SERM), was developed for the treatment of vaginal atrophy and osteoporosis. Previous studies from this lab, performed in a mutant ERα MCF-7 xenograph MBC mouse model, showed that lasofoxifene was significantly more effective than fulvestrant at inhibiting tumor growth, as well as metastasis to the lung and liver. In the current dose/response study, we compared the efficacy of lasofoxifene + palbociclib combinations to fulvestrant + palbociclib combinations. Engineered and luciferase-GFP tagged MCF-7 Y537S cells were injected into the mammary ducts of NSG mice (MIND model) and tumor progression was monitored by live luminescence imaging of primary tumors as well as ex vivo imaging of metastatic sites at study endpoint. Our results showed that all dose combinations of lasofoxifene + palbociclib were more effective than fulvestrant + palbociclib at inhibiting primary tumor growth as well as bone, lung, liver and brain metastasis. These data strongly suggest that patients with ERα+ MBC would benefit from orally delivered lasofoxifene + palbociclib therapy and that this combination could be superior to fulvestrant + palbociclib.

Citation Format: Muriel Laine, Justyna D. Kurleto, Marianne E. Greene, Linda Phung, Barry S. Komm, Geoffrey L. Greene. Lasofoxifene alone or in combination with palbociclib as an effective treatment for therapy-resistant ER-positive metastatic breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4370.

The Lineage Determining Factor GRHL2 Collaborates with FOXA1 to Establish a Targetable Pathway in Endocrine Therapy-Resistant Breast Cancer

Notwithstanding the positive clinical impact of endocrine therapies in estrogen receptor-alpha (ERα)-positive breast cancer, de novo and acquired resistance limits the therapeutic lifespan of existing drugs. Taking the position that resistance is nearly inevitable, we undertook a study to identify and exploit targetable vulnerabilities that were manifest in endocrine therapy-resistant disease. Using cellular and mouse models of endocrine therapy-sensitive and endocrine therapy-resistant breast cancer, together with contemporary discovery platforms, we identified a targetable pathway that is composed of the transcription factors FOXA1 and GRHL2, a coregulated target gene, the membrane receptor LYPD3, and the LYPD3 ligand, AGR2. Inhibition of the activity of this pathway using blocking antibodies directed against LYPD3 or AGR2 inhibits the growth of endocrine therapy-resistant tumors in mice, providing the rationale for near-term clinical development of humanized antibodies directed against these proteins.

Lasofoxifene as a potential treatment for ER+ metastatic breast cancer

1056

Background: Estrogen receptor positive (ER+) metastatic breast cancers (MBC) that express constitutively active somatic ESR1 mutations at Y537S and D538G allow tumors to progress in the presence of approved endocrine therapies. For patients with ER+ MBC, fulvestrant is the first line of treatment. Palbociclib or other CDK4/6 inhibitors are now being included. Preliminary studies show that lasofoxifene, a selective ERα modulator (SERM), was effective in reducing tumor growth in an endocrine resistant xenograph model expressing ERα mutations Y537S or D538G. Additionally, lasofoxifene more effectively inhibited the development of liver and lung metastases than fulvestrant. Lasofoxifene is currently under evaluation in a phase 2 study. Because certain combinations of a hormonal agents like fulvestrant improved efficacy, we investigated the combination of palbociclib and lasofoxifene as a potential therapeutic for mutant ESR1 MBC. We hypothesized that this combination should improve outcome and compared it to a combination with fulvestrant. Methods: We first determined the optimal dose of lasofoxifene in an intraductal (MIND) xenograph model of MCF-7 cells that express active ERα Y537S and D538G. Subsequently, we performed combination studies with lasofoxifene (10mg/kg 5/week SQ) +/- palbociclib (100mg/kg gavage, 5/week) or fulvestrant (5mg/mouse/week, SQ) +/- palbociclib. Results: Lasofoxifene alone was significantly more effective than fulvestrant at inhibiting the metastasis of both MCF7 Y537S and D538G tumors to the lungs and liver. Lasofoxifene + palbociclib was more effective than fulvestrant + palbociclib at reducing primary tumor growth; both combinations demonstrated an increased response. Lasofoxifene + palbociclib was more effective at inhibiting liver metastasis than either drug alone and was more effective than fulvestrant + palbociclib at reducing metastasis to the liver and lung. Structural studies showed that lasofoxifene effectively disrupts the active conformation of the ERα Y537S ligand-binding domain. Conclusions: These results demonstrate that lasofoxifene, in combination with CDK4/6 inhibitors like palbociclib, has promise for treating endocrine therapy resistant ER+ MBC patients whose tumors express activating ESR1 mutations, more effectively than either drug alone.

SUN-006 Lasofoxifene Achieves Potent Anti-Tumor Activity in Hormone-Resistant Breast Tumors by Maintaining High Affinity Binding for Y537S ERα

Activating somatic mutations to the ligand binding domain (LBD) of ESR1 (the gene for estrogen receptor alpha) may arise after prolonged hormone treatments. Y537S and D538G are the most prevalent mutations, accounting for 16% and 32% of cases respectively. Both mutations resist tamoxifen by favoring the receptor’s active state in the absence of hormone to reduce the selective estrogen receptor modulator’s binding affinity. Fulvestrant, a selective estrogen receptor degrader, is the only clinically approved molecule that can fully ablate Y537S estrogen receptor alpha (ERα) transcriptional activity, but does so at decreased potency due to a reduced ligand binding affinity. Interestingly, lasofoxifene, a selective estrogen receptor modulator, possesses significant anti-tumor activity in preclinical models of luminal breast cancers harboring WT, Y537S, and D538G ERα. Comprehensive structural and biochemical studies were undertaken to determine the molecular basis for lasofoxifene potency towards Y537S ERα. X-ray crystal structures of lasofoxifene in complex with WT and Y537S ERα LBD show that the molecule adopts an identical conformation within the hormone binding pocket. While, a competitive ligand binding assay shows that lasofoxifene possesses the same affinity towards WT and Y537S ERα LBD in vitro, compared to 5-10 fold decrease compared to other SERMs and SERDs. Collectively, these data suggest that lasofoxifene achieves improved anti-tumor activity by retaining its high affinity binding for the Y537S ERα somatic mutant.

Human stem cell factor promoter deoxyribonucleic acid sequence and regulation by cyclic 3',5'-adenosine monophosphate in a Sertoli cell line

Stem cell factor (SCF) gene expression is regulated by FSH in testicular Sertoli cells. Many functions of FSH are mediated through the second messenger cAMP. We show that cAMP activates transcription of the human SCF promoter in a Sertoli cell line. The human SCF promoter was cloned in cosmid vector pWE15, and its DNA sequence was determined for the promoter region extending 2.3 kilobase pairs upstream from the translation start site at +184 bp. The in vivo messenger RNA (mRNA) start site, by primer-extension studies, was located in exon 1 at +109 bp in human testis mRNA, and at +99 bp in mouse SF7 Sertoli cell line or GC1 germ cell line mRNA. To test which regions of the SCF promoter are necessary for regulation by cAMP, a series of 5'-end deletions of this region were cloned onto the luciferase reporter gene in plasmid pXP1. The SCF promoter region was fused to luciferase downstream (at +120) from its +109 mRNA start site, extending upstream a variable distance to BstXI (-162), BamHI (-313), Bgl2 (-853), or XbaI (-2185). The shortest of these fragments extending only to -162 bp, contains possible SP1 and AP-2 elements. When mouse Sertoli SF7 or human JEG.3 cell lines were transfected with these plasmids, all of the mutants were regulated by 8Br-cAMP or forskolin, as expected for the SCF gene, whereas FSH and TPA had no effect. In the shortest promoter deletion -162, luciferase expression from SF7 cells in serum-free media was at a moderate basal level, but it was induced in six h about 2-fold by 8Br-cAMP, and over 7-fold by forskolin (an adenylate cyclase activator) to high levels, similar to the SV40 positive control promoter. In SCF-luc plasmids extending to -853 or -2185, luciferase expression was still inducible by 8Br-cAMP and forskolin to high levels, but basal promoter activity was repressed to levels over 15-fold lower, in both the absence or presence of testosterone in the media for SF7 cells. The distal portion of the human SCF promoter (between -313 and -853, and also -853 and -2185) inhibits the basal level of transcription, while the proximal region (5' of -162) can mediate activation by cAMP.

Replacement of the Escherichia coli trp operon attenuation control codons alters operon expression

To test features of the current model of transcription attenuation in amino acid biosynthetic operons, alterations were introduced into the trp operon leader region and expression of the mutated operons was examined in miaA and miaA+ Escherichia coli strains that lacked the trp repressor. The miaA mutation prevents modification of the adenosine residue immediately 3' of the anticodon of tRNAs that interact with codons beginning with uridine. The undermodified tRNA(Trp) in miaA strains is thought to increase readthrough at the trp attenuator by slowing ribosome movement over two tandem Trp codons in the 14-codon leader peptide coding region. The rate of translation of these two "control codons" is thought to be the key step in determining the extent of transcription attenuation in the trp leader region. Sequential deletion of trpL DNA specifying the leader peptide initiation region, RNA segment 1, RNA segment 2 and RNA segment 3 alternately decreased and increased trp operon expression, a result consistent with previous findings in another bacterium and the generally accepted model for transcription attenuation. Replacement of the tandem Trp control codons by AGG-UGC (Arg-Cys) codons eliminated the miaA-dependent increase in transcription readthrough. Replacement of the Trp control codons by AGG-UGA (Arg-stop) codons caused complete readthrough at the trp attenuator as well as abolishing the miaA effect. Presumably, the ribosome terminating translation at the new UGA codon mimics the effect of a stalled ribosome at the Trp control codons. This finding suggests that ribosome dissociation at some stop codons is slow relative to the time required for transcription of the trp leader region. Thus, most ribosomes translating the trp leader peptide coding region may remain attached to the natural UGA stop codon until after the attenuation decision is made. The interpretation supports models for trp operon attenuation in which the elevated basal level readthrough is determined by occasional ribosome release prior to synthesis of the 3:4 terminator hairpin.

Transcription pausing by Escherichia coli RNA polymerase is modulated by downstream DNA sequences

Escherichia coli RNA polymerase pauses immediately after transcription of certain sequences that can form stable secondary structures in the nascent RNA transcript; pausing appears to be essential for several types of bacterial transcription attenuation mechanisms. Because base changes that weaken the RNA secondary structures reduce the half-life of pausing by RNA polymerase, nascent transcript RNA hairpins are thought to cause pausing at these sites. We show here that, for the well characterized trpL pause site, the determinants of transcription pausing are not limited to the RNA hairpin, but include the not-yet-transcribed sequence of DNA immediately downstream from the pause site. We show that this effect extends to bases up to fourteen nucleotides downstream from the pause site, that placement of a oligo(dT) tract in the nontranscribed strand in this region does not convert the pause site to a termination site, and that shifting the position of pausing by one nucleotide downstream almost eliminates pausing. From an analysis of many variants of this downstream sequence, we argue that the effect of downstream sequence is not related simply to its GC content. We suggest that these effects are mediated by altered interactions between RNA polymerase and the DNA template downstream from the enzyme's active site.

[Acute attacks of hepatic porphyria. Treatment with hematin. 5 cases]

The effectiveness of 2 hematins administered by intravenous infusion was compared in acute intermittent porphyria. Judging from subjective symptoms (abdominal pain), clinical improvement was complete and constant. There was a rapid decrease in urinary excretion of porphyrins precursors, with a clearer response of delta-aminolevulinic acid than of porphobilinogen. Urine levels of uroporphyrin often returned to normal after two infusions. The drugs were very well tolerated. Provided it is administered early, before neurological complications develop, treatment with hematin completely relieves abdominal symptoms and suppresses most of the biochemical changes associated with hepatic porphyria.

Recurrence risk estimation of acute intermittent porphyria based on analysis of porphobilinogen deaminase activity: a Bayesian approach

Red cell porphobilinogen deaminase is known to be an indicator of the carrier state for acute intermittent porphyria (AIP). This enzyme was assayed in three groups of individuals at least 15 years old: 105 affected individuals or obligate carriers, 234 unaffected first-degree relatives of patients, and 217 unrelated control persons. Analysis of the distribution of the control enzyme activities suggested presence of three commingled distributions. Also, the overlap between carrier-group and control-group values must be taken into account for genetic counseling of relatives whose enzyme activity lies within the overlap. A Bayesian approach is proposed to derive risks for these individuals, using the observed carrier and control distributions. The method is illustrated by deriving risks for a family from our sample.

Harderoporphyria: a variant hereditary coproporphyria

Three siblings with intense jaundice and hemolytic anemia at birth were found to excrete a high level of coproporphyrin in their urine and feces; the pattern of fecal porphyrin excretion was atypical for hereditary coproporphyria because the major porphyrin was harderoporphyrin (greater than 60%; normal value is less than 20%). The lymphocyte coproporphyrinogen III oxidase activity of each patient was 10% of control values, which suggests a homozygous state. Both parents showed only mild abnormalities in porphyrin excretion and lymphocyte coproporphyrinogen III oxidase activity decreased to 50% of normal values, as is expected in heterozygous cases of hereditary coproporphyria. Kinetic parameters of coproporphyrinogen III oxidase from these patients were clearly modified, with a Michaelis constant 15-20-fold higher than normal values when using coproporphyrinogen or harderoporphyrinogen as substrates. Maximal velocity was half the normal value, and we also observed a marked sensitivity to thermal denaturation. The possibility that a mutation affecting the enzyme on the active center which is specifically involved in the second decarboxylation (from harderoporphyrinogen to protoporphyrinogen) was eliminated by experiments on rat liver that showed that coproporphyrinogen and harderoporphyrinogen were metabolized at the same active center. The pattern of porphyrin excretion and the coproporphyrinogen oxidase from the three patients exhibited abnormalities that were different from the abnormalities found in another recently described homozygous case of hereditary coproporphyria. We suggest naming this variant of coproporphyrinogen oxidase defect "harderoporphyria."