Molecular Testing for Bethesda III Thyroid Nodules: Trends in Implementation, Cytopathology Call Rates, Surgery Rates, and Malignancy Yield at a Single Institution

Background: Molecular testing (MT) has become standard practice to more accurately rule out malignancy in indeterminate Bethesda III (BIII) thyroid lesions. We sought to assess the adoption of this technology and its impact on cytology reporting, malignancy yield, and rates of surgery across community and academic sites affiliated with a tertiary medical center. Methods: We performed a retrospective cross-sectional study including all fine-needle aspirations (FNAs) analyzed at our institution from 2017 to 2021. We analyzed trends in MT utilization by platform and by community or academic site. We compared BIII call rates, MT utilization rates, rates of subsequent surgery, and malignancy yield on final pathology before and after MT became readily available using chi-square analysis and linear regression. Results: A total of 8960 FNAs were analyzed at our institution from 2017 to 2021. There was broad adoption of MT across both community and academic sites. There was a significant increase in both the BIII rate and the utilization of MT between the pre- and post-MT periods (p < 0.001 and p < 0.001). There was no significant change in the the malignancy yield on final pathology (57.1% vs. 50.0%, p = 0.347), while the positive predictive value of MT decreased from 85% to 50% (p = 0.008 [confidence interval 9.5-52.5% decrease]). Conclusions: The use of MT increased across the institution over the study period, with the largest increase seen after a dedicated pass for MT was routinely collected. This increased availability of MT may have led to an unintended increase in the rates of BIII lesions, MT utilization, and surgery for benign nodules. Physicians who use MT should be aware of potential consequences of its adoption to appropriately counsel patients.

The impact of social determinants of health on thyroid cancer mortality and time to treatment

BACKGROUND

Whereas racial disparities in thyroid cancer care are well established, the role of social determinants of health is less clear. We aimed to assess the individual and cumulative impact of social determinants of health on mortality and time to treatment among patients with thyroid cancer.

METHODS

We collected social determinants of health data from thyroid cancer patients registered in the National Cancer Database from 2004 to 2017. We created a count variable for patients in the lowest quartile of each social determinant of health (ie, low income, low education, and no insurance). We assessed the association of social determinants of health with mortality and time to treatment and the association between cumulative social determinants of health count and time to treatment using Cox regression.

RESULTS

Of the 142,024 patients we identified, patients with longer time to treatment had greater mortality compared to patients treated within 90 days (90-180 days, adjusted hazard ratio 1.21 (95% confidence interval 1.13-1.29, P < .001); >180 days, adjusted hazard ratio 1.57 (95% confidence interval 1.41-1.76, (P < .001). Compared to patients with no adverse social determinants of health, patients with 1, 2, or 3 adverse social determinants of health had a 10%, 12%, and 34%, respectively, higher likelihood of longer time to treatment (1 social determinant of health, hazard ratio 0.90, 95% confidence interval 0.89-0.92, P < .001; 2 social determinants of health, hazard ratio 0.88, 95% confidence interval 0.87-0.90, P < .001; 3 social determinants of health, hazard ratio 0.66, 95% confidence interval 0.62-0.71, P < .001 for all). On subgroup analysis by race, each adverse social determinant of health was associated with an increased likelihood of a longer time to treatment for Black and Hispanic patients (P < .05).

CONCLUSION

A greater number of adverse social determinants of health leads to a higher likelihood of a longer time to treatment for patients with thyroid cancer, which, in turn, is associated with an increased risk for mortality.

Limited disease progression in endocrine surgery patients with treatment delays due to COVID-19

BACKGROUND

The COVID-19 pandemic profoundly impacted the delivery of care and timing of elective surgical procedures. Most endocrine-related operations were considered elective and safe to postpone, providing a unique opportunity to assess clinical outcomes under protracted treatment plans.

METHODS

American Association of Endocrine Surgeon members were surveyed for participation. A Research Electronic Data Capture survey was developed and distributed to 27 institutions to assess the impact of COVID-19-related delays. The information collected included patient demographics, primary diagnosis, resumption of care, and assessment of disease progression by the surgeon.

RESULTS

Twelve out of 27 institutions completed the survey (44.4%). Of 850 patients, 74.8% (636) were female; median age was 56 (interquartile range, 44-66) years. Forty percent (34) of patients had not been seen since their original surgical appointment was delayed; 86.2% (733) of patients had a delay in care with women more likely to have a delay (87.6% vs 82.2% of men, χ² = 3.84, P = .05). Median duration of delay was 70 (interquartile range, 42-118) days. Among patients with a delay in care, primary disease site included thyroid (54.2%), parathyroid (37.2%), adrenal (6.5%), and pancreatic/gastrointestinal neuroendocrine tumors (1.3%). In addition, 4.0% (26) of patients experienced disease progression and 4.1% (24) had a change from the initial operative plan. The duration of delay was not associated with disease progression (P = .96) or a change in operative plan (P = .66).

CONCLUSION

Although some patients experienced disease progression during COVID-19 delays to endocrine disease-related care, most patients with follow-up did not. Our analysis indicated that temporary delay may be an acceptable course of action in extreme circumstances for most endocrine-related surgical disease.

Optimal surgeon-volume threshold for neck dissections in the setting of primary thyroid malignancies

BACKGROUND

Although the surgeon-volume relationship is well documented for thyroidectomy, less is known about central neck and lateral neck dissections. The aim of this study was to evaluate and determine the surgeon-volume threshold for central neck and lateral neck dissections for thyroid cancer.

METHODS

A retrospective analysis of patients with thyroid malignancies who received a central or lateral neck dissection in the New York Statewide Planning and Research Cooperative System was performed (2007-2017). Demographic variables included age, sex, race, and a Charlson Comorbidity Score. Thirty-day complications were identified using International Classification of Diseases (ICD) codes for central neck, lateral neck, and other surgical complications. Optimal surgeon-volume threshold was estimated using a change-point logistic regression. Using the identified threshold, surgeons were then classified to low versus high volume surgeons. Logistic regression analysis was conducted to examine the effect of high-volume status on outcomes.

RESULTS

In total, 3,808 patients who underwent neck dissections (3,485 central neck dissections and 977 lateral neck dissections) were analyzed. Surgeon-volume threshold to distinguish high volume surgeons for central neck dissections and lateral neck dissections was 7.0 (95% bootstrap confidence interval 1.3-7.5) and 3.3 (1.2-4.8) neck dissections/year, respectively. For central neck dissection, high volume surgeons were associated with a lower rate of vocal cord paralysis (odds ratio 0.45 [0.24-0.82]), hypocalcemia (0.31 [0.14-0.65]), and all-cause complications (0.42 [0.29-0.59]). For lateral neck dissection, high volume surgeons were associated with a lower odds all-cause complications (0.42 [0.23-0.74]) but not lateral neck specific complications (0.18 [0.01-1.07]).

CONCLUSION

A threshold of 7.0 central neck dissections and 3.3 lateral neck dissections for thyroid cancer per year improves outcomes. Guidelines for training and centralization of care can be guided by these results to reduce complications.

Open repair of a plantar artery pseudoaneurysm after Morton's neurectomy

A 65-year-old woman presented to our institution with 4 months of severe pain on the plantar aspect of her foot. She had chronic foot pain secondary to Morton's neuroma and had recently undergone neurectomy. She was found to have a large pseudoaneurysm on the plantar aspect of her foot. She was taken to the operating room for an open repair from a plantar approach. We obtained the patient's consent to publish this case.

Evaluation of Encephaloduroarteriosynangiosis Efficacy Using Probabilistic Independent Component Analysis Applied to Dynamic Susceptibility Contrast Perfusion MRI

BACKGROUND AND PURPOSE

Indirect cerebral revascularization has been successfully used for treatment in Moyamoya disease and symptomatic intracranial atherosclerosis. While angiographic neovascularization has been demonstrated after surgery, measurements of local tissue perfusion are scarce and may not reflect the reported successful clinical outcomes. We investigated probabilistic independent component analysis and conventional perfusion parameters from DSC-MR imaging to measure postsurgical changes in tissue perfusion.

MATERIALS AND METHODS

In this prospective study, 13 patients underwent unilateral indirect cerebral revascularization and DSC-MR imaging before and after surgery. Conventional perfusion parameters (relative cerebral blood volume, relative cerebral blood flow, and TTP) and probabilistic independent components that reflect the relative contributions of DSC signals consistent with arterial, capillary, and venous hemodynamics were calculated and examined for significant changes after surgery. Results were compared with postsurgical DSA studies to determine whether changes in tissue perfusion were due to postsurgical neovascularization.

RESULTS

Before surgery, tissue within the affected hemisphere demonstrated a high probability for hemodynamics consistent with venous flow and a low probability for hemodynamics consistent with arterial flow, whereas the contralateral control hemisphere demonstrated the reverse. Consistent with symptomatic improvement, the probability for venous hemodynamics within the affected hemisphere decreased with time after surgery (P = .002). No other perfusion parameters demonstrated this association. Postsurgical DSA revealed an association between an increased preoperative venous probability in the symptomatic hemisphere and neovascularization after surgery.

CONCLUSIONS

Probabilistic independent component analysis yielded sensitive measurements of changes in local tissue perfusion that may be associated with newly formed vasculature after indirect cerebral revascularization surgery.

Angiographic Structural Differentiation between Native Arteriogenesis and Therapeutic Synangiosis in Intracranial Arterial Steno-Occlusive Disease

BACKGROUND AND PURPOSE

Encephaloduroarteriosynangiosis has been shown to generate collateral vessels from the extracranial-to-intracranial circulation in patients with Moyamoya disease and intracranial arterial steno-occlusive disease. The mechanisms involved are not well-understood. We hypothesized that angiogenesis is the leading mechanism forming collaterals after encephaloduroarteriosynangiosis because there are no pre-existing connections. Angiogenesis-generated collaterals should exhibit higher architectural complexity compared with innate collaterals.

MATERIALS AND METHODS

Pre- and postoperative digital subtraction angiograms were analyzed in patients enrolled in a prospective trial of encephaloduroarteriosynangiosis surgery. Branching angioscore, tortuosity index, and local connected fractal dimension were compared between innate and postoperative collaterals.

RESULTS

One hundred one angiograms (50 preoperative, 51 postoperative) were analyzed from 44 patients (22 with intracranial atherosclerosis and 22 with Moyamoya disease). There was a significantly higher median branching angioscore (13 versus 4, P < .001) and a lower median tortuosity index (1.08 versus 1.76, P < .001) in the encephaloduroarteriosynangiosis collaterals compared with innate collaterals. Higher mean local fractal dimension peaks (1.28 ± 0.1 versus 1.16 ± 0.11, P < .001) were observed in the encephaloduroarteriosynangiosis collaterals compared with innate collaterals for both intracranial atherosclerosis (P < .001) and Moyamoya disease (P < .001) groups. The observed increase in high connectivity was greater in the intracranial atherosclerosis group compared with patients with Moyamoya disease (P = .01).

CONCLUSIONS

The higher median branching angioscore and local connected fractal dimension, along with the lower median tortuosity index of encephaloduroarteriosynangiosis collaterals, are consistent with the greater complexity observed in the process of sprouting and splitting associated with angiogenesis.

Transient Surface CCR5 Expression by Naive CD8+ T Cells within Inflamed Lymph Nodes Is Dependent on High Endothelial Venule Interaction and Augments Th Cell-Dependent Memory Response

In inflamed lymph nodes, Ag-specific CD4(+) and CD8(+) T cells encounter Ag-bearing dendritic cells and, together, this complex enhances the release of CCL3 and CCL4, which facilitate additional interaction with naive CD8(+) T cells. Although blocking CCL3 and CCL4 has no effect on primary CD8(+) T cell responses, it dramatically impairs the development of memory CD8(+) T cells upon Ag rechallenge. Despite the absence of detectable surface CCR5 expression on circulating native CD8(+) T cells, these data imply that naive CD8(+) T cells are capable of expressing surface CCR5 prior to cognate Ag-induced TCR signaling in inflamed lymph nodes; however, the molecular mechanisms have not been characterized to date. In this study, we show that CCR5, the receptor for CCL3 and CCL4, can be transiently upregulated on a subset of naive CD8(+) T cells and that this upregulation is dependent on direct contact with the high endothelial venule in inflamed lymph node. Binding of CD62L and CD11a on T cells to their ligands CD34 and CD54 on the high endothelial venule can be enhanced during inflammation. This enhanced binding and subsequent signaling promote the translocation of CCR5 molecules from intracellular vesicles to the surface of the CD8(+) T cell. The upregulation of CCR5 on the surface of the CD8(+) T cells increases the number of contacts with Ag-bearing dendritic cells, which ultimately results in increased CD8(+) T cell response to Ag rechallenge.

LFA-1 and CD62L dependent transient surface CCR5 expression in naïve CD8+ T cells enhances T cell immune memory (CCR3P.214)

The initiation of an effective adaptive immune response requires choreographed interaction among rare antigen-bearing dendritic cells (DCs) with antigen-specific CD4+ and CD8+ T cells in the lymph node (LN). This interaction is especially critical for the magnitude of memory T cell generation. We and others have previously demonstrated that CCL3/CCL4 secretion from productive interaction between antigen-specific T cell and antigen-bearing DCs promote local recruitment of naïve CD8+ T cells in the inflamed LNs, implying that naïve CD8+ T cells can express CCR5 in the inflamed LN microenvironment. Here, we examined the kinetics of CCR5 expression on naïve T cells upon entering an inflamed LN. Maximum surface CCR5 expression occurs in 10-30% of newly arrived naive T cells within the first 6 hours via mobilization of pre-existing CCR5 protein found in intracellular vesicles, and this transient up-regulation of surface CCR5 expression in CD8+ T cells was dependent on direct physical contact with LFA and CD62L, as ligation of CD8+ T cells with anti-CD11a and/or anti-CD62L antibodies enhances surface CCR5 expression within 1 hour in the absence of TCR stimulation. More importantly, CCR5+ fraction of naïve CD8+ T cells exhibit enhanced ability to become memory T cells. Our study implicates an important functional role for CCR5 expression by naïve lymphocytes prior to cognate antigen recognition for enhanced memory T cell development.

Administration of reconstituted polyphenol oil bodies efficiently suppresses dendritic cell inflammatory pathways and acute intestinal inflammation

Polyphenols are natural compounds capable of interfering with the inflammatory pathways of several in vitro model systems. In this study, we developed a stable and effective strategy to administer polyphenols to treat in vivo models of acute intestinal inflammation. The in vitro suppressive properties of several polyphenols were first tested and compared for dendritic cells (DCs) production of inflammatory cytokines. A combination of the polyphenols, quercetin and piperine, were then encapsulated into reconstituted oil bodies (OBs) in order to increase their stability. Our results showed that administration of low dose reconstituted polyphenol OBs inhibited LPS-mediated inflammatory cytokine secretion, including IL-6, IL-23, and IL-12, while increasing IL-10 and IL-1Rα production. Mice treated with the polyphenol-containing reconstituted OBs (ROBs) were partially protected from dextran sodium sulfate (DSS)-induced colitis and associated weight loss, while mortality and inflammatory scores revealed an overall anti-inflammatory effect that was likely mediated by impaired DC immune responses. Our study indicates that the administration of reconstituted quercetin and piperine-containing OBs may represent an effective and potent anti-inflammatory strategy to treat acute intestinal inflammation.

The effect of intravenous administration of a chimeric anti-IgE antibody on serum IgE levels in atopic subjects: efficacy, safety, and pharmacokinetics

CGP 51901 is a non-anaphylactogenic mouse/human chimeric anti-human IgE antibody that binds to free IgE and surface IgE of IgE-expressing B cells but not to IgE bound to high affinity IgE receptors (Fc epsilonR1) on mast cells and basophils or low affinity IgE receptors (Fc epsilonR2) on other cells. A phase 1 double-blind, placebo-controlled, single dose study with doses of 3, 10, 30, and 100 mg of CGP 51901 was conducted in 33 pollen-sensitive subjects who had raised levels of serum IgE and received either intravenous CGP 51901 or placebo. The administration of CGP 51901 was well tolerated and resulted in a decrease of serum free IgE levels in a dose-dependent manner, with suppression after 100 mg of CGP 51901 reaching > 96%. Time of recovery to 50% of baseline IgE correlated with the dose of administered antibody and ranged from a mean of 1.3 d for the 3 mg to 39 d for the 100 mg dose. Total IgE, comprised of free and complexed IgE, increased as stored and newly synthesized IgE bound to CGP 51901. Complexed IgE was eliminated at a rate comparable with the terminal half-life of free CGP 51901 (11-13 d at all doses). Only one subject showed a weak antibody response against CGP 51901. We conclude that the use of anti-human IgE antibody is safe and effective in reducing serum IgE levels in atopic individuals and provides a potential therapeutic approach to the treatment of atopic diseases.

Lovastatin versus bezafibrate: efficacy, tolerability, and effect on urinary mevalonate

Lovastatin and benzafibrate have proved effective in lowering low-density-lipoprotein (LDL) cholesterol and elevating high-density-lipoprotein (HDL) cholesterol. We compared their tolerability, safety, and effects on lipoproteins and urinary mevalonate excretion in a short-term study. Forty patients with primary hypercholesterolemia were enrolled in a single-blind randomized study with a diet/placebo period of 8 weeks and a treatment period of 12 weeks. Twenty patients received lovastatin (final average dose 70.5 mg/day), and 20 patients received bezafibrate 400 mg/day. LDL cholesterol was lowered by 35% (from 323 to 208 mg/dl) with lovastatin and by 8% (from 289 to 264 mg/dl) with benzafibrate. HDL cholesterol increased by 21 and 20% with lovastatin and benzafibrate, respectively. Twenty-four-hour urinary mevalonic acid output decreased by 37% during treatment with lovastatin and by 2% during treatment with bezafibrate. Thus, the lowering of cholesterol by lovastatin, but not by bezafibrate, can be attributed to inhibition of HMG CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase. Both lovastatin and bezafibrate are well tolerated.

Synthesis and antiherpetic activity of (+/-)-9-[[(Z)-2-(hydroxymethyl)cyclopropyl]methyl]guanine and related compounds

A series of analogues of acyclovir and ganciclovir were prepared in which conformational constraints were imposed by incorporation of a cyclopropane ring or unsaturation into the side chain. In addition, several related base-modified compounds were synthesized. These acyclonucleosides were evaluated for enzymatic phosphorylation and DNA polymerase inhibition in a staggered assay and for inhibitory activity against herpes simplex virus types 1 and 2 in vitro. Certain of the guanine or 8-azaguanine derivatives were good substrates for the viral thymidine kinase and were further converted to triphosphate, but none was a potent inhibitor of the viral DNA polymerase. Nevertheless, one member of this group, (+/-)-9-[[(Z)-2-(hydroxymethyl)cyclopropyl]methyl]guanine (3a), displayed significant antiherpetic activity in vitro, superior to that of the corresponding cis olefin 4a. Another group, typified by (+/-)-9-[[(E)-2-(hydroxymethyl)cyclopropyl]methyl]adenine (17b), possessed modest antiviral activity despite an apparent inability to be enzymatically phosphorylated. The relationship of side-chain conformation and flexibility to biological activity in this series is discussed.

Stereochemical considerations in the enzymatic phosphorylation and antiviral activity of acyclonucleosides. I. Phosphorylation of 2'-nor-2'-deoxyguanosine

The antiviral compound 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (2'-nor-2'-deoxyguanosine, 2'-NDG) is phosphorylated by the HSV-1-induced thymidine kinase to the monophosphate (2'-NDG-MP) and this is further phosphorylated by cellular kinases to the triphosphate (2'-NDG-TP) which is a potent inhibitor of DNA polymerases. Since phosphorylation of 2'-NDG creates a chiral center in the molecule, it was of interest to examine whether both monophosphate enantiomers were produced by the viral thymidine kinase, whether they both could be further phosphorylated by cellular kinases and, if so, whether the respective triphosphates were equally inhibitory to the DNA polymerases. The time course of the phosphorylation by GMP kinase of a chemically synthesized, racemic 2'-NDG-MP was compared to that of a 2'-NDG-MP preparation obtained by enzymatic phosphorylation of 2'-NDG with HSV-1 thymidine kinase. The results indicated that the two enantiomeric monophosphates were phosphorylated by GMP kinase with different rates and that phosphorylation of 2'-NDG by HSV-1 thymidine kinase gave only one of the isomers, whose structure was determined to be S. Both enantiomeric diphosphates were further phosphorylated to the respective triphosphates and it was shown that, in contrast to the triphosphate obtained from the 2'-NDG-MP prepared by viral thymidine kinase which was a potent inhibitor of HSV-1 DNA polymerase, the triphosphate obtained from the slow-reacting R isomer had little or no inhibitory activity against this enzyme.

Comparison of the modes of antiviral action of 2'-nor-deoxyguanosine and its cyclic phosphate, 2'-nor-cyclic GMP

The metabolisms of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (2'NDG) and its cyclic phosphate, 9-[(2-hydroxy-1,3,2-dioxophosphorinan-5-yl) oxymethyl]guanine P-oxide (2'-nor-cGMP), were compared in cultures of primary rabbit kidney cells infected with herpes simplex virus type 1 (HSV-1). 2'-Nor-cGMP was taken up by the cells essentially intact, after which it was opened to the acyclic monophosphate and phosphorylated further, ultimately to the triphosphate. Formation of the triphosphate was independent of HSV thymidine kinase expression, unlike what is observed with 2'NDG. In addition, there was a direct correlation between the antiviral activity of 2'NDG and the level of triphosphate formed in HSV-1-infected cells, whereas such a correlation was absent with 2'-nor-cGMP. In vivo experiments indicated that only a small percentage of free 2'NDG was formed in the bloodstream of mice after oral administration of 2'-nor-cGMP. Incubation of 2'-nor-cGMP with crude extracts of HSV-1-infected or uninfected HeLa cells resulted in the direct production of 2'NDG triphosphate. The possibility that the triphosphate of 2'NDG produced from 2'-nor-cGMP was the enantiomer of the triphosphate made from 2'NDG by viral and cellular kinases was investigated and disproved. Taken together, these data indicate that (i) 2'-nor-cGMP does not act simply as a prodrug of 2'NDG, (ii) 2'-nor-cGMP does not require viral thymidine kinase for its activity, and (iii) 2'-nor-cGMP may have an additional, triphosphate-independent mode of action.

Enzymatic phosphorylation of the antiherpetic agent 9-[(2,3-dihydroxy-1-propoxy)methyl]guanine

The antiherpetic agent 9-[(2,3-dihydroxy-1-propoxy)methyl]guanine (iNDG) is phosphorylated by HSV1 thymidine kinase, and its phosphorylated products inhibit DNA polymerase activity. iNDG exists in two enantiomeric forms, each with a primary and a secondary hydroxyl; thus, a number of possibilities for preferential phosphorylation exist, which were explored in this study. HSV1 thymidine kinase phosphorylates the primary hydroxyl of both the R and the S isomers of iNDG. This was established by comparison with analogues in which either the primary or the secondary hydroxyl was replaced by fluorine or hydrogen and also by a study of the NMR spectrum of the monophosphate. GMP kinase phosphorylates the R and the S monophosphates to the respective diphosphates. Further phosphorylation, however, is much more efficient with the S than with the R isomer. Furthermore, (S)-iNDG triphosphate is a more potent inhibitor of HSV1 DNA polymerase than (R)-iNDG triphosphate. These differences in the biochemical specificities of the two isomers account for the observed higher antiviral potency of (S)-iNDG as compared to that of (R)-iNDG.

Synthesis and antiherpetic activity of (S)-, (R)-, and (+/-)-9-[(2,3-dihydroxy-1-propoxy)methyl]guanine, linear isomers of 2'-nor-2'-deoxyguanosine

Racemic 9-[(2,3-dihydroxy-1-propoxy)methyl]guanine [(+/-)-iNDG], a new analogue of acyclovir (ACV) and a structural analogue of 2'-nor-2'-deoxyguanosine (2'NDG), was synthesized and found to inhibit the replication of herpes simplex virus types 1 (HSV-1) and 2 (HSV-2). Subsequently, its optical isomers, (R)- and (S)-iNDG, were prepared from chiral intermediates. The chloromethyl ethers of 1,2-di-O-benzyl-D- and -L-glycerol were made and reacted with tris(trimethylsilyl)guanine to give the 9-alkylated guanines, which were deprotected by catalytic hydrogenolysis. Against HSV-1 and HSV-2 in cell culture, (S)-iNDG was approximately 10- to 25-fold more active than the R enantiomer and had an ED50 comparable to those for ACV and 2'NDG. The inferior activity of (R)-iNDG paralleled the poor inhibition of viral DNA polymerase by its phosphorylation products. In mice infected intraperitoneally or orofacially with HSV-1 or intravaginally with HSV-2, (S)-9-[(2,3-dihydroxy-1-propoxy)methyl]guanine [(S)-iNDG] was less efficacious than 2'NDG but comparable to or more active than ACV.

A comparison of the antiviral agents 2'-nor-2'-deoxyguanosine and acyclovir: uptake and phosphorylation in tissue culture and kinetics of in vitro inhibition of viral and cellular DNA polymerases by their respective triphosphates

A comparative study was conducted between the antiherpetic agents 2'-nor-2'-deoxyguanosine (2'NDG) and acyclovir (ACV) with respect to 1) the relative rates of uptake and phosphorylation to the "active" triphosphate species in tissue culture and 2) the in vitro inhibition of viral and cellular DNA polymerases by their respective triphosphates. The results indicated that a) six hours after HSV1 infection of primary rabbit kidney cells there was seven times more 2'NDG-triphosphate in the cells than ACV triphosphate; b) the relative rate of triphosphate formation in HSV1-infected versus uninfected cells was 4.5 times higher for 2'NDG than for ACV and c) the triphosphate of 2'NDG (2'NDG-TP) was a more selective inhibitor of the viral compared to the cellular DNA alpha-polymerase than the triphosphate of ACV (ACV-TP). The Km/Ki ratios for 2'NDG-TP and ACV-TP (in the competitive inhibition of dGTP) were 3.10 and 1.37, respectively, for the highly purified HSV1 polymerase; and 0.05 and 1.11, respectively, for the partially-purified HeLa alpha-polymerase. Neither triphosphate inhibited the HeLa DNA beta-polymerase to any significant extent. These results are in line with the findings [Ashton et al. (1982), Biochem. Biophys. Res. Commun. 108, 1716-1721] that 2'NDG has superior in vivo antiherpetic activity compared to ACV without apparent toxicity.

9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine: a selective inhibitor of herpes group virus replication

9-([2-Hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine (2'-nor-2'-deoxyguanosine; 2'NDG) selectively inhibits the replication of herpes group viruses. In cell culture studies 2'NDG was at least 10-fold more potent than acyclovir (ACV) in inhibition of human cytomegalovirus replication and Epstein-Barr virus-induced lymphocyte transformation and was about as effective as ACV in inhibition of herpes simplex viruses 1 and 2 and varicella zoster virus. Orally administered 2'NDG was 6- to 50-fold more efficacious than ACV in treating systemic or local HSV-1 infection or HSV-2 intravaginal infection in mice. The mode of action of 2'NDG appears to involve phosphorylation by herpes simplex virus thymidine kinase and subsequent phosphorylations by cellular kinases to produce 2'NDG triphosphate, which is a potent inhibitor of herpes virus DNA polymerase. Compared to ACV, 2'NDG was a more efficient substrate for HSV-1 thymidine kinase (Vmax/Km for 2'NDG 30-fold higher than that of ACV), whereas 2'NDG monophosphate is a more efficient substrate for GMP kinase (Vmax/Km for 2'NDG monophosphate 492-fold higher than that for ACV monophosphate). The combined effect is more rapid production of the inhibitory triphosphate from 2'NDG than from ACV.

Position of transfer ribonucleic acid on Escherichia coli ribosomes. Distance from the 3' end of 16S ribonucleic acid to three points on phenylalanine-accepting transfer ribonucleic acid in the donor site of 70S ribosomes

Escherichia coli 16S RNA from 30S ribosomal subunits was isolated, oxidized at the 3' end, and labeled with the thiosemicarbazide derivatives of fluorescein or eosin. Labeled 16S RNA was reconstituted into 30S subunits. They were almost fully active compared to 30S subunits reconstituted from unlabeled 16S RNA by using a poly(uridylic acid)-directed polyphenylalanine synthesis assay. Fluorophores were placed at three different positions of tRNAPhe. E. coli and yeast tRNAPhe were oxidized at the 3' end and labeled with the thiosemicarbazide derivative of fluorescein or with the hydrazide of N-methylanthranilic acid. The Y base in the anticodon loop of yeast tRNAPhe was replaced by proflavin or 1-aminoanthracene. Also, E. coli tRNAPhe was photochemically cross-linked between 4-thiouridine at position 8 and cytidine at position 13. After reduction, this site was used as a fluorescent probe. The labeled tRNAs were bound into the peptidyl site of 70S ribosomes, and then the distances from the fluorophore in the modified tRNA to the fluorophore at the 3' end of 16S RNA were measured by nonradiative energy transfer. Calculations were based on measurements of fluorescence lifetimes. The distances to the 3' end of 16S RNA were found to be as follows: 3' end of tRNA, 67-74 A; cross-linked t RNA, 53-60 A; anticodon loop of tRNA, greater than 61 A.

Covalent cross-linking of transfer ribonucleic acid to the ribosomal P site. Mechanism and site of reaction in transfer ribonucleic acid

The covalent cross-linking of unmodified Escherichia coli N-acetylvalyl-tRNA to the 16S RNA of Escherichia coli ribosomes upon near-UV irradiation previously reported by us [Schwartz, I., & Ofengand, J. (1978) Biochemistry 17, 2524--2530] has been studied further. Up to 70% of the unmodified tRNA, nonenzymatically bound to tight-couple ribosomes at 7 mM Mg2+, could be cross-linked by 310--335-nm light. Covalent attachment was solely to the 16S RNA. It was dependent upon both irradiation and the presence of mRNA but was unaffected by the presence or absence of 4-thiouridine in the tRNA. The kinetics of cross-linking showed single-hit behavior. Twofold more cross-linking was obtained w-th tight-couple ribosomes than with salt-washed particles. Puromycin treatment after irradiation released the bound N-acetyl[3H]valine, demonstrating that the tRNA was covalently bound at the P site and that irradiation and covalent linking did not affect the peptidyl transferase reaction. Cross-linking was unaffected by the presence of O2, argon, ascorbate (1 mM), or mercaptoethanol (10 mM). Prephotolysis of a mixture of tRNA and ribosomes in the absence of puly(U2,G) did not block subsequent cross-linking in its presence nor did it generate any long-lived chemically reactive species. There was a strong tRNA specificity. E. coli tRNA1Val and tRNA1Ser and Bacillus subtilis tRNAVal and tRNAThr could be cross-linked, but E. coli tRNA2Val, 5-fluorouracil-substituted tRNA1Val, tRNAPhe, or tRNAFMet could not. By sequence comparison of the reactive and nonreactive tRNAs, the site of attachment in the tRNA was deduced to be the 5'-anticodon base, cmo5U, or ,o5U in all of the reactive tRNAs. The attachment site in 16S RNA is described in the accompanying paper [Zimmerman, R. A., Gates, S. M., Schwartz, I., & Ofengand, J. (1979) Biochemistry (following paper in this issue)]. The link between tRNA and 16S RNA is either direct or involves mRNA bases at most two nucleotides apart since use of the trinucleotide GpUpU in place of poly(U2,G) to direct the binding and cross-linking of N-acetylvalyl-tRNA to the P site did not affect either the rate or yield of cross-linking. Both B. subtilis tRNAVal (mo5U) and E. coli tRNA1Val (cmo5U) gave the same rate and yield of cross-linking when directed by the trinucleotide GpUpU. Therefore, the presence of the charged carboxyl group in the cmo5U-containing tRNA apparently does not markedly perturb the orientation of this base with respect to its reaction partner in the 16S RNA. The cross-linking of AcVal-tRNA only takes place from the P site. At 75 mM KCl and 75 mM NH4Cl, less than 0.4% cross-linking was found at the A site, while 55.5% was obtained at the P site. However, when the salt concentration was lowered to 50 mM NH4Cl, 5% cross-linking to the A site was detected, compared to 49% at the P site. Thus, a simple change in the ionic strength of the incubation mixture was able to alter the affinity labeling pattern of the ribosome.

Ability of modified forms of phenylalanine tRNA to stimulate guanosine pentaphosphate synthesis by the stringent factor-ribosome complex of E. coli

tRNA(Phe) of E. coli, modified at its 4-thiouridine ((4)Srd) and 3-(3-amino-3-carboxypropyl)uridine (nbt(3)Urd) residues, was tested for its ability to induce (p)ppGpp synthesis. The (4)Srd residue was derivatized with the p-azido-phenacyl group, cross-linked to Cyd(13), and the borohydride reduction product of the cross-link was prepared. The nbt(3)Urd residue was derivatized with the N-(4-azido-2-nitrophenyl)glycyl group. None of these derivatives had more than a minor effect on the affinity of the tRNA for the stringent factor-ribosome complex, and no effect at all on the maximum velocity of (p)ppGpp synthesis, either at 2 or 82 mM NH(4)Cl. These two regions of the tRNA which are on opposite faces of the tRNA molecule do not appear to be structurally important for recognition by the stringent factor-ribosome complex. They may provide useful sites, therefore, for the introduction of photoaffinity or fluorescent probes with which to study tRNA-stringent factor recognition.