INNV-33. FUNCTIONAL EX VIVO TESTING PROSPECTIVELY IDENTIFIES NEWLY DIAGNOSED GLIOBLASTOMA PATIENTS SENSITIVE TO TEMOZOLOMIDE TREATMENT IRRESPECTIVE OF MGMT METHYLATION STATUS

Standard of care (SOC) therapy for newly diagnosed (ND) glioblastoma (GBM) patients consist of temozolomide (TMZ) concurrent with radiation therapy. It is well known that patients with an unmethylated MGMT promoter are less likely to respond to TMZ, however, this trend is not universal. We have previously shown that 3D Predict™ glioma can identify patient response to TMZ, often differentially than the methylation status would predict. Here we present expanded clinical data relating to functional ex vivo testing capable of identifying patients responsive to alkylating therapies such as TMZ, regardless of methylation status.

METHODS

Fresh tissue specimens taken from ND GBM patients enrolled into the 3D PREDICT clinical study were examined by 3D Predict glioma to evaluate ex vivo therapeutic response to TMZ. Overall Survival (OS) and Progression Free Survival (PFS) in patients having ≥ 6 months follow-up post-surgery or < 6 months follow up but experiencing progression/death as of September 1, 2022 will be presented. Prospective correlation of clinical response and test-predicted response will be demonstrated in this expanded cohort of ND GBM patients.

IMPACT

This data has the potential to change treatment for ND GBM patients by stratifying according to functional therapeutic response rather than epigenetic factors that are not completely predictive of clinical response. It is feasible that 3D Predict glioma could dramatically impact patient care by determining which unmethylated patients should be treated with TMZ, and methylated patients who would potentially derive greater benefit from clinical trials or other treatment regimens.

CLRM-19 USING FUNCTIONAL PRECISION MEDICINE TO GUIDE CLINICAL TRIAL ENROLLMENT IN GBM

Interventional clinical trials in glioblastoma (GBM) have been consistently disappointing, attributable to various factors such as ineffective therapies, inadequate trial designs including lack of control arms, or enrollment criteria that do not represent real-world practice. Novel paradigms for clinical trial design(s) in GBM are desperately needed to produce clinically useful patient outcomes. KIYATEC has developed a patient- and tumor-specific technology platform to evaluate cellular response(s) to therapeutics using 3D cell culture methods that provide functional, patient-specific response predictions. Employing KIYATEC’s technology to screen compounds against both primary patient-, and PDX-derived specimens, enables clinical prioritization of early-stage assets most likely to have therapeutic response in vivo. In addition, KIYATEC’s 3D Predict™ Glioma test has shown clinical correlation of test-predicted response(s) and clinical outcomes in GBM patients. Incorporating KIYATEC’s 3D ex vivo technology into GBM therapeutic development is positioned to accelerate more successful trial results by 1) identifying early-stage compounds likely to possess clinical effects in vivo, and 2) prospectively identifying patients expected to have a clinical response to therapeutics in development. 3D Predict Glioma provides patient-specific responses within 7-10 days of tissue acquisition, providing an avenue for test integration into adaptive clinical trials, whereby functional characterization could provide gating information relating to trial execution. Specifically, functional response prediction may play a pivotal role in identifying newly diagnosed patients who might derive greater benefit from clinical trials compared to standard of care and by optimizing effective therapeutic selection in the recurrent setting. Therefore, a priori knowledge of an early-stage assets’ potential, combined with therapeutic sensitivity of individual patient tissue, may facilitate a new era for adaptive clinical trial design by assimilating KIYATEC’s analytically and clinically validated test into various steps of clinical trial execution such as randomization, stratification, therapy-switching, or compound addition/discontinuation.

INNV-16. CLINICAL APPLICABILITY OF INDIVIDUALIZED DRUG RESPONSE PROFILING UTILIZING EX-VIVO TISSUE-DERIVED 3D CELL CULTURE ASSAYS IN HIGH-GRADE GLIOMA: A SINGLE INSTITUTION CASE SERIES USING 3D-PREDICT RESULTS

Recurrent high-grade glioma is a challenging disease process, without consensus on effective second-line therapy options. Individualized, patient-specific, biologically-based data is desirable in driving therapeutic decision-making. Patients with recurrent high-grade glioma and planned surgical re-resection at our institution were prospectively enrolled into the 3D-PREDICT study. Tissue was collected at the time of surgery for ex vivo 3D cell culture assays comprising a panel of agents commonly used for high-grade glioma, including chemotherapies and targeted therapies used in other solid cancers. In all cases, therapeutic agent selection was guided by the neuro-oncologist’s clinical judgement, factoring the patient’s age, performance status, comorbidities, toxicities/side effect profile of potential agents, and drug accessibility, plus ex-vivo drug response RESULTS: We present 3 cases in which the selection of agents was influenced by the tissue-derived 3D cell culture results; treatment led to clinical response observed in terms of progression free survival, quality of life, and pharmacologic tolerability. In Case 1, a patient with recurrent anaplastic astrocytoma was treated with a BRAF inhibitor for 12 months with excellent tolerability and no radiographic progression. Case 2 demonstrates the use of combination bevacizumab and irinotecan after disease progression subsequent to standard treatment. This patient had local radiographic control for 7 months, tolerating the regimen well. In Case 3, an individual with recurrent glioblastoma was treated with combination carboplatin and etoposide based on assay response prediction to both agents; treatment has been tolerated well with radiographic stability at 6 months while maintaining good performance status. This case series represents our institutional experience of utilizing patient-specific, ex-vivo tissue-derived cell drug response profiling to guide choice of therapy for recurrent high-grade glioma patients. Using individualized, tumor-specific drug sensitivity data to guide these decisions is representative of the ongoing paradigm shift into the realm of individualized medicine to improve outcomes in cancer patients.

A Highly Sensitive and Quantitative Test Platform for Detection of NSCLC EGFR Mutations in Urine and Plasma

INTRODUCTION

In approximately 60% of patients with NSCLC who are receiving EGFR tyrosine kinase inhibitors, resistance develops through the acquisition of EGFR T790M mutation. We aimed to demonstrate that a highly sensitive and quantitative next-generation sequencing analysis of EGFR mutations from urine and plasma specimens is feasible.

METHODS

Short footprint mutation enrichment next-generation sequencing assays were used to interrogate EGFR activating mutations and the T790M resistance mutation in urine or plasma specimens from patients enrolled in TIGER-X (NCT01526928), a phase 1/2 clinical study of rociletinib in previously treated patients with EGFR mutant-positive advanced NSCLC.

RESULTS

Of 63 patients, 60 had evaluable tissue specimens. When the tissue result was used as a reference, the sensitivity of EGFR mutation detection in urine was 72% (34 of 47 specimens) for T790M, 75% (12 of 16) for L858R, and 67% (28 of 42) for exon 19 deletions. With specimens that met a recommended volume of 90 to 100 mL, the sensitivity was 93% (13 of 14 specimens) for T790M, 80% (four of five) for L858R, and 83% (10 of 12) for exon 19 deletions. A comparable sensitivity of EGFR mutation detection was observed in plasma: 93% (38 of 41 specimens) for T790M, 100% (17 of 17) for L858R, and 87% (34 of 39) for exon 19 deletions. Together, urine and plasma testing identified 12 additional T790M-positive cases that were either undetectable or inadequate by tissue test. In nine patients monitored while receiving treatment with rociletinib, a rapid decrease in urine T790M levels was observed by day 21.

CONCLUSIONS

DNA derived from NSCLC tumors can be detected with high sensitivity in urine and plasma, enabling diagnostic detection and monitoring of therapeutic response from these noninvasive "liquid biopsy" samples.

Abstract 30: Quantitative monitoring of EGFR mutations in urinary circulating tumor DNA enables non-invasive pharmacodynamic assessment of anti-EGFR drug response

Background: Acquisition of the EGFR T790M resistance mutation is a hallmark of disease progression in patients with metastatic EGFR mutant lung adenocarcinoma treated with first generation anti-EGFR inhibitors. Utilizing a single copy sensitivity mutation detection platform and implementing daily collection of urine samples, we sought to demonstrate the feasibility of detecting EGFR mutations in urinary ctDNA and understand mechanisms of resistance to targeted therapies in patients with EGFR-mutated lung adenocarcinoma.

Methods: In a biomarker study of 100 patients with EGFR-mutant metastatic lung adenocarcinoma (34 patients enrolled), urine was collected at either daily or monthly time points up to 4 months prior to radiologic detection of progression on erlotinib, and at multiple time points post-progression on next line therapy. Urinary ctDNA was extracted by a method that preferentially isolates short, fragmented ctDNA. Quantitative analysis of EGFR activating mutations and T790M resistance mutation was performed using blocker technology and PCR enrichment coupled with NGS detection (MiSeq). Urine was collected daily after the initiation of second line anti-EGFR therapy in 10 patients. Early pharmacodynamic events that occur within the first hours to days of anti-EGFR therapy were further studied by quantitating ctDNA for EGFR exon 19deletions, L858R, and T790M.

Results: Interim analysis was conducted on 34 patients receiving first line anti-EGFR therapy with erlotinib; twenty-two of 34 patients demonstrated radiographic progression. Analysis of longitudinal samples revealed that the EGFR T790M mutation was detected in the urine specimens of 15 out of 22 (68%) patients on erlotinib. All 10 patients who were positive for T790M mutation by tissue were also positive by urine. Urine testing identified five additional T790M-positive patients who had a high clinical suspicion of T790M progressive disease. Three of these patients were tissue negative but both plasma and urine positive for T790M. EGFR T790M was detected up to 15 weeks prior to radiolographic detection of progression on first line erlotinib. Early peaks in ctDNA on days 1-4 correlated with tumor lysis. An observed sustained decrease in mutational levels after week 1 of therapy confirms the cytostatic effect of the tyrosine kinase inhibitor (TKI). The size of the initial peaks in ctDNA for EGFR exon 19deletions, L858R, and T790M correlated with CT radiographic response after two cycles of therapy.

Conclusion: We demonstrate that the T790M mutation can be successfully detected in urinary ctDNA months before progression on anti-EGFR TKIs. Urinary ctDNA testing identifies additional patients who potentially are eligible for anti-T790M treatment. Initial results from 10 patients demonstrated that kinetic changes in EGFR ctDNA mutational load after drug adminstration can be used with pharmacokinetic data to better understand dyanmic changes in tumor biology, drug bioavailability, and assist in early drug development. The clinical utility of daily kinetic monitoring of ctDNA in urine after drug adminstration is being further validated in a larger study.

Citation Format: Hatim Husain, Karena Kosco, Saege Hancock, Errin Samuelsz, Shiloh Guerrero, Brian Woodward, Cecile Rose Vibat, Vlada Melnikova, Mark Erlander, Scott Lippman, Razelle Kurzrock. Quantitative monitoring of EGFR mutations in urinary circulating tumor DNA enables non-invasive pharmacodynamic assessment of anti-EGFR drug response. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr 30.

Quantitation of Na+-K+-2Cl- cotransport splice variants in human tissues using kinetic polymerase chain reaction

A kinetic reverse transcription-polymerase chain reaction (RT-PCR)-based assay is described that can discriminate and quantitate differentially spliced mRNAs. This assay should be generally applicable for high-throughput quantitation of differentially spliced transcripts. The utility of this method was assessed for spliced transcripts encoded by the human Na+-K+-2Cl- cotransporter gene hNKCC1. Evidence is presented that the NKCC1 isoform of the human Na+-K+-2Cl- cotransporter is differentially spliced analogous to that recently described for the mouse Na+-K+-2Cl- cotransporter gene BSC2. The nucleotide sequences of the two human splice variants predict Na+-K+-2Cl- cotransporter proteins differing only in length. Stable transfectants expressing these human splice variants, designated NKCC1a or NKCC1b, were constructed. Both splice variants produce functional Na+-K+-2Cl- cotransporters in vivo. The abundance of NKCC1 mRNA and patterns of differential splicing in 10 different tissue types and three cell lines were quantitated using the kRT-PCR assay. The results showed that the total amount of NKCC1 mRNA varied by more than 30-fold in the human tissues and cell lines examined. The ratio of NKCC1a/NKCC1b varied nearly 70-fold among these same tissues and cell lines suggesting that differential splicing of the NKCC1 transcript may play a regulatory role in human tissues.

Intracellular Cl regulates Na-K-Cl cotransport activity in human trabecular meshwork cells

The trabecular meshwork (TM) of the eye plays a central role in modulating intraocular pressure by regulating aqueous humor outflow, although the mechanisms are largely unknown. We and others have shown previously that aqueous humor outflow facility is modulated by conditions that alter TM cell volume. We have also shown that the Na-K-Cl cotransport system is a primary regulator of TM cell volume and that its activity appears to be coordinated with net efflux pathways to maintain steady-state volume. However, the cellular mechanisms that regulate cotransport activity and cell volume in TM cells have yet to be elucidated. The present study was conducted to investigate the hypothesis that intracellular Cl concentration ([Cl]i) acts to regulate TM cell Na-K-Cl cotransport activity, as has been shown previously for some other cell types. We demonstrate here that the human TM cell Na-K-Cl cotransporter is highly sensitive to changes in [Cl]i. Our findings reveal a marked stimulation of Na-K-Cl cotransport activity, assessed as ouabain-insensitive, bumetanide-sensitive K influx, in TM cells following preincubation of cells with Cl-free medium as a means of reducing [Cl]i. In contrast, preincubation of cells with media containing elevated K concentrations as a means of increasing [Cl]i results in inhibition of Na-K-Cl cotransport activity. The effects of reducing [Cl]i, as well as elevating [Cl]i, on Na-K-Cl cotransport activity are concentration dependent. Furthermore, the stimulatory effect of reduced [Cl]i is additive with cell-shrinkage-induced stimulation of the cotransporter. Our studies also show that TM cell Na-K-Cl cotransport activity is altered by a variety of Cl channel modulators, presumably through changes in [Cl]i. These findings support the hypothesis that regulation of Na-K-Cl cotransport activity, and thus cell volume, by [Cl]i may participate in modulating outflow facility across the TM.

Localization of histidine residues responsible for heme axial ligation in cytochrome b556 of complex II (succinate:ubiquinone oxidoreductase) in Escherichia coli

Complex II (succinate:ubiquinone oxidoreductase) from Escherichia coli contains four different subunits. Two of the subunits (SDHC and SDHD) are hydrophobic and anchor the two more hydrophilic (flavin and iron-sulfur) subunits (SDHA and SDHB) to the cytoplasmic membrane. Previous studies have shown that the complex of SDHC/SDHD is required to maintain the heme B component of the enzyme and that the heme B is ligated to the protein by two histidine ligands. In the current work, the histidines within SDHC and SDHD have been systematically mutated. SDHC-His91 and SDHD-His14 were eliminated as potential ligands by these studies. SDHC-His84 and SDHD-His71 have been identified as the most likely heme axial ligands in the E. coli enzyme, suggesting that the heme bridges these two subunits in the membrane. Furthermore, the results show that the four-subunit Complex II assembles and retains function despite the absence of the heme B prosthetic group in the membrane. The results do not rule out completely SDHC-His30 as a candidate for heme ligation, but do show that mutation at this position prevents assembly of Complex II in the membrane.

Molecular characterization of the Na-K-Cl cotransporter of bovine aortic endothelial cells

The Na-K-Cl cotransporter is an important regulator of endothelial cell volume and may also contribute to flux of Na and Cl across the endothelium of the blood-brain barrier. To date, two Na-K-Cl cotransport isoforms have been identified, the cotransporter in secretory epithelia, NKCC1, and that in absorptive renal epithelia, NKCC2. Our previous studies showed that a monoclonal antibody to the cotransporter of human colonic T84 epithelial cells, an NKCC1 isoform, recognizes a 170-kDa glycoprotein from endothelial cells. The molecular identity of the Na-K-Cl cotransporter present in endothelial cells, however, has been unknown. In addition, although evidence has been provided that phosphorylation of the endothelial cotransporter plays a role in regulating its activity, little is known about potential sites for protein kinase interaction with the cotransporter. The present study was conducted to determine the molecular structure of the endothelial Na-K-Cl cotransporter. Using a 1.0-kilobase (kb) cDNA fragment from a conserved region of the T84 cell cotransporter, we screened a bovine aortic endothelial cell cDNA library and subsequently identified and sequenced two overlapping clones that together spanned the entire coding region. The endothelial cotransporter is a 1,201-amino acid protein with 12 putative transmembrane segments and large amino and carboxy termini, each containing several consensus sites for phosphorylation by protein kinases. Comparison of the endothelial cotransporter amino acid sequence with known NKCC1 and NKCC2 sequences revealed a 96% identity with NKCC1. Northern blot analysis using a cDNA probe from the endothelial cotransporter revealed high expression of approximately 7.5-kb transcripts in a number of bovine tissues. Finally, a prominent expression of Na-K-Cl cotransporter was found by Western blot analysis in both cultured and freshly isolated endothelial cells of bovine aorta and cerebral microvessels.

Tryptophan substitutions at the lipid-exposed transmembrane segment M4 of Torpedo californica acetylcholine receptor govern channel gating

Our previous amino acid substitutions at the postulated lipid-exposed transmembrane segment M4 of the Torpedo californica acetylcholine receptor (AChR) focused on the alpha C418 position. A tryptophan substitution on the alpha C418 produced a 3-fold increase in normalized macroscopic response to acetylcholine in voltage-clamped Xenopus laevis oocytes (Lee et al., 1994). This result was explained by a 23-fold decrease in the closing rate constant measured from single-channel analysis (Ortiz-Miranda et al., 1996). In this study, we introduce more tryptophan substitutions at different positions of this postulated lipid-exposed segment M4 in order to examine functional consequences at the single-channel level. From a series of amino acid substitutions at alpha G421, only phenylalanine and tryptophan produced a substantial increase in the open time constant. The lack of response from a tyrosine substitution at the alpha G421 suggests that the side chain volume is not the main structural element responsible for the effect of tryptophan on the stabilization of the open state of the channel. Three multiple mutants, alpha C418W/G421A, alpha C418W/G421W, and alpha C418W/beta C447W, were constructed in order to establish the correlation between the number of lipid-exposed tryptophans and the channel open time constant. The alpha C418W/G421A double mutant demonstrated that when both previous mutations are combined the open time constant was increased 1.5-fold relative to the alpha C418W. When the two mutants (alpha C418W and alpha G421W) were combined in a single mutation, a functional receptor was expressed and the open time constant of the new double mutant increased to 33.4 ms, an 80-fold increase relative to wild type. Estimations of free energy changes calculated from the rate constant for the opening transition suggest that each tryptophan contributes to the stabilization of the open state of the channel by about 0.8 kcal/mol, and the effect of tryptophan substitutions on the free energy is additive. This result suggests that in the channel gating mechanism of the AChR, each subunit contributes independently to the energy barrier between the open and closed state. At selected positions within the postulated lipid surface of the AChR, tryptophan substitutions could establish hydrophobic and perhaps dipole interactions that may play a dramatic role in the channel gating mechanism.

Two hydrophobic subunits are essential for the heme b ligation and functional assembly of complex II (succinate-ubiquinone oxidoreductase) from Escherichia coli

Complex II (succinate-ubiquinone oxidoreductase) from Escherichia coli is composed of four nonidentical subunits encoded by the sdhCDAB operon. Gene products of sdhC and sdhD are small hydrophobic subunits that anchor the hydrophilic catalytic subunits (flavoprotein and iron-sulfur protein) to the cytoplasmic membrane and are believed to be the components of cytochrome b556 in E. coli complex II. In the present study, to elucidate the role of two hydrophobic subunits in the heme b ligation and functional assembly of complex II, plasmids carrying portions of the sdh gene were constructed and introduced into E. coli MK3, which lacks succinate dehydrogenase and fumarate reductase activities. The expression of polypeptides with molecular masses of about 19 and 17 kDa was observed when sdhC and sdhD were introduced into MK3, respectively, indicating that sdhC encodes the large subunit (cybL) and sdhD the small subunit (cybS) of cytochrome b556. An increase in cytochrome b content was found in the membrane when sdhD was introduced, while the cytochrome b content did not change when sdhC was introduced. However, the cytochrome b expressed by the plasmid carrying sdhD differed from cytochrome b556 in its CO reactivity and red shift of the alpha absorption peak to 557.5 nm at 77 K. Neither hydrophobic subunit was able to bind the catalytic portion to the membrane, and only succinate dehydrogenase activity, not succinate-ubiquinone oxidoreductase activity, was found in the cytoplasmic fractions of the cells. In contrast, significantly higher amounts of cytochrome b556 were expressed in the membrane when sdhC and sdhD genes were both present, and the catalytic portion was found to be localized in the membrane with succinate-ubiquitnone oxidoreductase and succinate oxidase activities. These results strongly suggest that both hydrophobic subunits are required for heme insertion into cytochrome b556 and are essential for the functional assembly of E. coli complex II in the membrane. Accumulation of the catalytic portion in the cytoplasm was found when sdhCDAB was introduced into a heme synthesis mutant, suggesting the importance of heme in the assembly of E. coli complex II.

Differential desensitization properties of rat neuronal nicotinic acetylcholine receptor subunit combinations expressed in Xenopus laevis oocytes

1. Chronic administration of nicotine up-regulates mammalian neuronal nicotinic acetylcholine receptors (nAChRs). A key hypothesis that explains up-regulation assumes that nicotine induces desensitization of receptor function. This is correlated with behaviorally expressed tolerance to the drug. 2. The present experiments were conducted to: (a) obtain information on the nicotine-induced desensitization of neuronal nAChR function, a less understood phenomenon as compared to that of the muscle and electric fish receptor counterparts; (b) test the hypothesis that different receptor subunit combinations exhibit distinct desensitization patterns. 3. Xenopus laevis oocytes were injected with mRNAs encoding rat receptor subunits alpha 2, alpha 3, or alpha 4 in pairwise combination with the beta 2 subunit. The responses to various concentrations of acetylcholine (ACh) or nicotine were analyzed by the two electrode voltage clamp technique. 4. Concentration-effect curves showed that nicotine was more potent than ACh for all the receptor subunit combinations tested. Only the alpha 4 beta 2 combination exhibited a depression of the maximum effect at concentrations higher than 20 microM nicotine. 5. After a single nicotine pulse, receptor desensitization (calculated as a single exponential decay) was significantly slower for alpha 4 beta 2 than for either alpha 3 beta 2 or alpha 2 beta 2. 6. Concentrations of nicotine that attained a near maximum effect were applied, washed, and re-applied in four minute cycles. The responses were calculated as percentages of the current evoked by the initial application. Following 16 minutes of this protocol, the alpha 4 beta 2 combination showed a greater reduction of the original response as compared to the alpha 2 beta 2 and alpha 3 beta 2 subunit combinations. Taking points 5 and 6 together, these experiments suggest that the alpha 4 beta 2 receptor subtype desensitizes at a slower rate and remains longer in the desensitized state. 7. Because alpha 4 beta 2 is the main receptor subunit combination within the brain and is up-regulated by nicotine, our data may be important for understanding the molecular basis of tolerance to this drug.

Genomic replacement in Escherichia coli K-12 using covalently closed circular plasmid DNA

A number of gene replacements at different loci were constructed using covalently closed circular (ccc) plasmid DNA in the recB21 recC22 sbcB15 sbcC201 mutant of Escherichia coli (JC7623). Selected constructs representing deletions and insertion mutations formed from double-crossover events involving the ccc plasmid molecules and the genome were confirmed by Southern blots, and the frequency of double-crossover events was evaluated. It is reported that such mutants may be constructed without linearizing plasmid DNA, as described previously.

One-step purification from Escherichia coli of complex II (succinate: ubiquinone oxidoreductase) associated with succinate-reducible cytochrome b556

Complex II (succinate:ubiquinone oxidoreductase) is an important component of both the tricarboxylic acid cycle and of the aerobic respiratory chains of eukaryotic and prokaryotic organisms. The enzyme has been purified from numerous sources and appears to be highly conserved from considerations of both the amino acid sequences of the catalytic subunits and from the prosthetic groups associated with the enzyme. The sdh operon has been cloned and sequenced from Escherichia coli, but the enzyme from this source has, so far, resisted attempts at biochemical purification. In this work, a one-step purification of the enzyme is described which yields a stable four-subunit enzyme which has a high specific activity. This purification takes advantage of a strain which overproduces the enzyme by 10-fold due to the presence of a multicopy plasmid containing the cloned sdh operon. The purified complex II has one FAD, eight non-heme irons, seven acid-labile sulfides, and one protoheme IX per molecule. The enzyme has been reconstituted in phospholipid vesicles and demonstrated to reduce ubiquinone-8, the natural electron acceptor, at a high rate.