The Role of Coronary Artery Calcium Score to Assess Risk of Cardiovascular Disease in Irradiated Esophageal Cancer Patients

PURPOSE/OBJECTIVE(S)

Coronary artery calcium (CAC) score is an important predictive imaging marker of cardiovascular disease (CVD). While studies have found positive association between CAC score and cardiac toxicity in irradiated lung and breast cancer patients, there are no studies assessing CAC scores in esophageal cancer (EC). While a cardiac-gated CT is required for standard Agatston CAC score, visual assessment of CAC via ordinal scoring on non-gated CT has shown good concordance with Agatston score. In this study, we sought to examine whether visual assessment of CAC, measured on standard of care, non-contrast chest CT, predicts the development of adverse cardiovascular events (ACVE) in irradiated EC patients.

MATERIALS/METHODS

This is a single institution retrospective study of EC patients treated with RT from 2010-2021. We included patients with available PET/CT at diagnosis or chest CT simulation scan without contrast, and excluded those with history of percutaneous coronary intervention, coronary bypass surgery, or prior thoracic RT. Pre-treatment characteristics, clinical factors, and grade ≥ 3 (G3+) adverse cardiovascular events (ACVE) (CTCAEv5.0) were evaluated. Visual assessment of CAC was performed using ordinal method (CAC scored from 0 to 12), by a thoracic radiologist. Fine and Gray regression was used to compute hazard ratios for time to first ACVE. Univariate analyses using Cox proportional hazards were used for overall survival (OS). ACVEs were recorded from start of oncologic treatment and OS calculated after completion of RT.

RESULTS

A total of 118 patients were analyzed with a median follow-up of 16 months. Median age was 67 years, 65% male, 43% white, 59% with EC of distal esophagus, and 59% had squamous cell carcinoma. Median mean heart dose was 21.93 Gy (range 0.15-36.94). 24% developed G3+ ACVEs: atrial fibrillation 9%, stroke 6%, heart failure 4%, pulmonary embolism 4%, pericardial effusion 3%, myocardial infarction 2%, heart block 2%, and cardiac death 1%. On univariate analyses, CAC >1 vs. CAC ≤ 1 trended towards increased risk of ACVE (HR = 1.95, 95% CI = 0.89-4.26; p = 0.094), however it is not predictive of OS (HR = 1.31, 95% CI = 0.75-2.30; p = 0.343). Proportion of patients with ACVEs was greater in CAC>1 group (Table). When compared to patients with CAC ≤ 1, those with CAC >1 were older (median age 62 vs 72 years, p = 0.0015), less likely to be never smokers (38% vs 30%, p = 0.0437), and more likely to have hypertension (43% vs 64%, p = 0.0197), and hyperlipidemia (30% vs 47%, p = 0.0557).

CONCLUSION

This is the first study to investigate the relationship between CAC score and ACVEs in EC. While the study was underpowered (likely due to low rates of recorded ACVEs), to detect a significant association between CAC score and ACVEs, there was a trend towards increased risk of ACVEs in patients with a CAC score >1 by visual ordinal scoring. Further prospective evaluation with a larger cohort is warranted.

Is 80 the New 70? Octogenarians with Oropharyngeal Squamous Cell Carcinoma

PURPOSE/OBJECTIVE(S)

As the human papilloma virus (HPV) pandemic evolves and life expectancy increases, the number of older adults with oropharyngeal squamous cell carcinoma (OPSCC) continues to increase. However, there is a paucity of data regarding the fastest growing subset of this population: octogenarians (OGs). We sought to understand differences in treatment tolerability and clinical outcomes between septuagenarians (SGs) and OGs with OPSCC.

MATERIALS/METHODS

We identified SGs (age 70-79) and OGs (age 80-89) with OPSCC from a cohort of older adults with nonrecurrent, nonmetastatic head and neck squamous cell carcinoma (HNSCC) treated curatively from 2007-2020. We compared demographics, treatment characteristics and toxicities using Fischer's exact test. Time-to-event outcomes, overall survival (OS), locoregional control (LRC), and disease-specific survival (DSS), were evaluated using the Kaplan-Meier method.

RESULTS

Of 293 patients (age 70-89) with HNSCC, 39% (n = 114) had OPSCC: 93 SGs (median age: 73; interquartile range [IQR]: 71-76), and 21 OGs (median age: 81, IQR: 80-84). The median follow-up for included patients was 2.4 years; 82% were male, 64% white, 48% > 20 pack year smoking history, 37% ECOG 1. Patients had AJCC 8th edition Stage: I (27%); II (33%); III (18%); IV (22%) OPSCC. Treatment consisted of adjuvant radiation (RT) (19%), adjuvant chemoradiation (CRT) (8%), surgery alone (6%), induction/concurrent CRT (27%), concurrent CRT (28%), or RT (12%), with no significant differences in stage or treatment modalities noted between SGs and OGs. Of note, 69% of SGs and 76% of OGs were HPV+. Among 107 patients who received any RT, 24% experienced a treatment interruption (19% of SGs vs. 48% of OGs, p = 0.001) and 2 patients (both HPV- SGs) died on treatment due to unrelated health conditions. Percutaneous endoscopic gastrostomy (PEG) tubes were placed prior to or during treatment in 43% of SGs and 62% of OGs, with OGs more likely to have a PEG placed during treatment (p = 0.025). There was no difference in the prevalence of late (> 6 months) CTCAE grade 2+ dysphagia (36%) or xerostomia (31%) between SGs and OGs. Estimated 3-year LRC, DSS, and OS were not significantly different between SGs (LRC:85%; DSS:87%; OS:76%) and OGs (LRC: 81%; DSS:94%; OS: 55%, p-values: 0.98, 0.42, 0.052, respectively). However, HPV+ disease significantly increased estimated 3-year OS for both SGs (HPV+: 84%; HPV-: 56%, p = 0.0006) and OGs (HPV+: 68%; HPV-: 20%, p = 0.008).

CONCLUSION

In our cohort, OGs had a higher proportion of HPV+ OPSCC, which was associated with improved OS. This finding may provide insight into the latency of the virus. While there were similar amounts of toxicities among SGs and OGs, OGs more frequently underwent PEG tube placement and experienced more treatment interruptions. Given high rates of HPV+ OPSCC in OGs, our findings suggest that de-escalation strategies should be further investigated to improve tolerability and maximize outcomes for this neglected population.

Pupil plane differential detection microscopy

Differential interference contrast (DIC) microscopy is a powerful technique for imaging phase objects in transparent samples but does not work with scattering samples. This Letter, to the best of our knowledge, describes a new technique for obtaining DIC-like phase-gradient images in scattering media based on differential detection of forward-scattered light, using detectors arranged in a ring configuration around the microscope objective pupil or its conjugate pupil plane. This method, called pupil plane differential detection (P2D2) microscopy, does not need polarization optics or a confocal pinhole, yet produces images that are free of speckles and interference noises. We compared the P2D2 imaging technique with reflectance confocal microscopy and demonstrated P2D2 as a simple add-on to conventional laser scanning microscopes.

Diffuse fluorescence fiber probe for in vivo detection of circulating cells

There has been significant recent interest in the development of technologies for enumeration of rare circulating cells directly in the bloodstream in many areas of research, for example, in small animal models of circulating tumor cell dissemination during cancer metastasis. We describe a fiber-based optical probe that allows fluorescence detection of labeled circulating cells in vivo in a diffuse reflectance configuration. We validated this probe in a tissue-mimicking flow phantom model in vitro and in nude mice injected with fluorescently labeled multiple myeloma cells in vivo. Compared to our previous work, this design yields an improvement in detection signal-to-noise ratio of 10 dB, virtually eliminates problematic motion artifacts due to mouse breathing, and potentially allows operation in larger animals and limbs.

Tomographic sensing and localization of fluorescently labeled circulating cells in mice in vivo

Sensing and enumeration of specific types of circulating cells in small animals is an important problem in many areas of biomedical research. Microscopy-based fluorescence in vivo flow cytometry methods have been developed previously, but these are typically limited to sampling of very small blood volumes, so that very rare circulating cells may escape detection. Recently, we described the development of a 'diffuse fluorescence flow cytometer' (DFFC) that allows sampling of much larger blood vessels and therefore circulating blood volumes in the hindlimb, forelimb or tail of a mouse. In this work, we extend this concept by developing and validating a method to tomographically localize circulating fluorescently labeled cells in the cross section of a tissue simulating optical flow phantom and mouse limb. This was achieved using two modulated light sources and an array of six fiber-coupled detectors that allowed rapid, high-sensitivity acquisition of full tomographic data sets at 10 Hz. These were reconstructed into two-dimensional cross-sectional images using Monte Carlo models of light propagation and the randomized algebraic reconstruction technique. We were able to obtain continuous images of moving cells in the sample cross section with 0.5 mm accuracy or better. We first demonstrated this concept in limb-mimicking optical flow photons with up to four flow channels, and then in the tails of mice with fluorescently labeled multiple myeloma cells. This approach increases the overall diagnostic utility of our DFFC instrument.

Instrument for fluorescence sensing of circulating cells with diffuse light in mice in vivo

Accurate quantification of circulating cell populations in mice is important in many areas of preclinical biomedical research. Normally, this is done either by extraction and analysis of small blood samples or, more recently, by using microscopy-based in vivo fluorescence flow cytometry. We describe a new technological approach to this problem using detection of diffuse fluorescent light from relatively large blood vessels in vivo. The diffuse fluorescence flow cytometer (DFFC) uses a laser to illuminate a mouse limb and an array of optical fibers coupled to a high-sensitivity photomultiplier tube array operating in photon counting mode to detect weak fluorescence signals from cells. We first demonstrate that the DFFC instrument is capable of detecting fluorescent microspheres and Vybrant-DiD-labeled cells in a custom-made optical flow phantom with similar size, optical properties, linear flow rates, and autofluorescence as a mouse limb. We also present preliminary data demonstrating that the DFFC is capable of detecting circulating cells in nude mice in vivo. In principle, this device would allow interrogation of the whole blood volume of a mouse in minutes, with sensitivity improvement by several orders of magnitude compared to current approaches.

Validation of a device for fluorescence sensing of rare circulating cells with diffusive light in an optical flow phantom model

Detection and quantification of rare circulating cells in biological tissues is an important problem and has many applications in biomedical research. Current methods normally involve extraction of blood samples and counting of cells ex vivo, or the use of microscopy-based fluorescence in vivo flow cytometry. The goal of this work is to develop an instrument for non-invasively enumerating very rare circulating cells in small animals with diffuse light with several orders of magnitude sensitivity improvement versus current approaches. In this work, we describe the design of our system and show that single, fluorescent microspheres can be detected in limb-mimicking optical flow phantoms with varying optical properties chosen to simulate in vivo conditions. Further, we demonstrate single cell counting capabilities using fluorescently (Vybrant-DiD) labeled Jurkat and Multiple Myeloma cells. Ongoing work includes in vivo testing and characterization of our system in mice.

Dual targeting of the PI3K/Akt/mTOR pathway as an antitumor strategy in Waldenstrom macroglobulinemia

We have previously shown clinical activity of a mammalian target of rapamycin (mTOR) complex 1 inhibitor in Waldenstrom macroglobulinemia (WM). However, 50% of patients did not respond to therapy. We therefore examined mechanisms of activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR in WM, and mechanisms of overcoming resistance to therapy. We first demonstrated that primary WM cells show constitutive activation of the PI3K/Akt pathway, supported by decreased expression of phosphate and tensin homolog tumor suppressor gene (PTEN) at the gene and protein levels, together with constitutive activation of Akt and mTOR. We illustrated that dual targeting of the PI3K/mTOR pathway by the novel inhibitor NVP-BEZ235 showed higher cytotoxicity on WM cells compared with inhibition of the PI3K or mTOR pathways alone. In addition, NVP-BEZ235 inhibited both rictor and raptor, thus abrogating the rictor-induced Akt phosphorylation. NVP-BEZ235 also induced significant cytotoxicity in WM cells in a caspase-dependent and -independent manner, through targeting the Forkhead box transcription factors. In addition, NVP-BEZ235 targeted WM cells in the context of bone marrow microenvironment, leading to significant inhibition of migration, adhesion in vitro, and homing in vivo. These studies therefore show that dual targeting of the PI3K/mTOR pathway is a better modality of targeted therapy for tumors that harbor activation of the PI3K/mTOR signaling cascade, such as WM.

Src tyrosine kinase regulates adhesion and chemotaxis in Waldenstrom macroglobulinemia

PURPOSE

Waldenstrom macroglobulinemia is a lymphoplasmacytic lymphoma characterized by widespread involvement of the bone marrow. Despite different options of therapy, Waldenstrom macroglobulinemia is still incurable. Src tyrosine kinase has been shown to play a central role in the regulation of a variety of biological processes, such as cell proliferation, migration, adhesion, and survival in solid tumors. We sought to determine whether the protein tyrosine kinase Src regulates adhesion, migration, and survival in Waldenstrom macroglobulinemia.

EXPERIMENTAL DESIGN

We tested the expression of Src tyrosine kinase in Waldenstrom macroglobulinemia and normal cells, and the effect of the specific Src inhibitor AZD0530 on the adhesion, migration, cell cycle, and survival of a Waldenstrom macroglobulinemia cell line and patient samples. Moreover, we tested the effect of AZD0530 on cytoskeletal and cell cycle signaling in Waldenstrom macroglobulinemia.

RESULTS

We show that Src is overexpressed in Waldenstrom macroglobulinemia cells compared with control B cells, and that the use of the Src inhibitor AZD0530 led to significant inhibition of adhesion, migration, and cytoskeletal signaling induced by SDF1. Moreover, inhibition of Src activity induced G(1) cell cycle arrest; however, it had minimal effect on survival of Waldenstrom macroglobulinemia cells, and no significant effect on survival of normal cells.

CONCLUSIONS

Taken together, these results delineate the role of Src kinase activity in Waldenstrom macroglobulinemia and provide the framework for future clinical trials using Src inhibitors in combination with other drugs to improve the outcome of patients with Waldenstrom macroglobulinemia.

Novel therapeutic agents in Waldenström's macroglobulinemia

Within the past few years, major advances in the preclinical and clinical testing of novel therapeutic agents have occurred in Waldenström's macroglobulinemia (WM). These include agents that target the PI3K/Akt/mTOR pathway, PKC pathways, NF-kB signaling pathway, as well as tyrosine kinases and histone deacetylase inhibitors. In this review, we summarize the current understanding of the clinical development of these agents in WM.

Role of selectins in the pathogenesis of multiple myeloma

11103

Background: Multiple myeloma (MM) is characterized by the disseminated involvement of the bone-marrow (BM), and its progression involves a continuous circulation of the MM cells (MMCs) in the peripheral blood and homing back to the BM. Selectins are adhesion molecules involved in the primary interaction of lymphocytes with the endothelial cells (ECs) of blood vessels. In this study we studied the role selectins in the pathogenesis of MM. Methods: We have characterized the expression of E, L and P-selectins and their ligands on MM cell lines, patient sample and plasma cells from normal subjects (NPCs). We have tested the effect of blockade of each of the selectins and selectin-ligands on the interaction of MMCs with ECs. Moreover, we tested the effect of a pan selectin inhibitor on MMCs adhesion to ECs, and trans-well (through filter) and trans-endothelial SDF1-induced migration in vitro, and characterized its effect on cytoskeletal signaling induced by the interaction of MMCs and ECs. Moreover, we have tested the effect of the inhibitor on homing of MMCs to the BM in mice using in vivo flow cytometry to detect the number of circulating cells, and in vivo confocal microscopy to directly visualize the homing. Results: All MM cell lines and patient samples had low expression of all selectins and high expression of L and P, but not E, selectin ligands. While NPCs showed low expression of all selectins and ligands. Blockade of L and P-selectin ligands reduced the interaction of MMCs with ECs in vitro, while blockade of E-selectin ligand or any of selectins did not show any effect. The pan-selectin inhibitor reduced the interaction of MMCs with ECs in vitro, did not alter their SDF1-induced migration through filter, but reduced significantly the migration through ECs. The inhibitor inhibited the activation of FAK and ERK induced by interaction of MMCs and ECs. Moreover, the selectin inhibitor extending the circulation time of MM cells in mice, and reduced the homing of MMCs. Conclusions: We found that L and P selectin ligands are highly expressed in MMCs compared to NPCs, and that those play a major role in homing of MMCs to the BM. Moreover, the pan-selectin inhibitor prevented the homing of MMCs to the BM. This provides a basis for testing the effect of the inhibitor on MM tumor progression and initiation.

No significant financial relationships to disclose.

MicroRNAs 15a and 16–1 regulates tumor proliferation in multiple myeloma

e14640

Background: MicroRNAs (miRNAs) are non-coding RNAs that act as negative regulators of gene expression. They have been described to play roles in solid tumors and hematologic malignancies. However the role of miRNAs in multiple myeloma (MM) has not been yet fully described. Methods: We performed miRNA-profiling of primary bone marrow-derived CD138+ MM cells, compared to their normal cellular counterparts and validated data by qRT-PCR. In vitro and in vivo functional studies were performed on miRNA-15a- and -16–1-precursors-transfected MM cells. Effect of miRNA-15a and -16–1 on signaling cascades have been evaluated by western blot and immunofluorescence. NF-kB activity has been studied using the Active Motif TransAM kit. In vivo MM cell growth has been evaluated by either using an in vivo imaging model or bioluminescence. Angiogenesis has been studied both in vitro and in vivo using the chorioallantoic membrane model. Results: We identified a MM-specific miRNA signature characterized by down-expression of miRNA-15a, -16–1 and over-expression of miRNA-222/-221/-382/-181a/-181b (P<0.01). Data were confirmed by qRT-PCR on matched samples. Predicted targets for the decreased miRNAs in MM patients included pro-angiogenic cytokines, oncogenes, cell cycle regulators, NFkB activators. Conversely, predicted targets for the increased miRNAs included cell cycle inhibitors, suppressors of cytokine signaling, and pro-apoptotic factors. We demonstrated that miRNA-15a and - 16–1 regulate proliferation and growth of MM cells. Indeed, transfected cells showed decreased DNA synthesis; decreased cyclinD1/cyclinD3/CDC25a/pRb protein expression; phase G1 cell cycle arrest. Moreover, transfected cells showed inhibition of NFkB pathway as shown by reduced p65-/p50-/p52-NFkB activities; downregulation of p-p65/p50/p52 nuclear protein level; upregulation of cttosolic phospho-IkB; and inhibited translocation of p-p65 from the cytolplasm to the nucleus. Similarly, inhibition of MM cell growth was confirmed in vivo; and anti-angiogenic properties of miRNA-15a and -16–1 were demonstrated both in vitro and in vivo. Conclusions: These data indicate that miRNAs play a pivotal role in the biology of MM; providing the basis for the development of new miRNA-based targeted therapies in this disease.

No significant financial relationships to disclose.

microRNA expression in the biology, prognosis, and therapy of Waldenström macroglobulinemia

Multilevel genetic characterization of Waldenström macroglobulinemia (WM) is required to improve our understanding of the underlying molecular changes that lead to the initiation and progression of this disease. We performed microRNA-expression profiling of bone marrow-derived CD19(+) WM cells, compared with their normal cellular counterparts and validated data by quantitative reverse-transcription-polymerase chain reaction (qRT-PCR). We identified a WM-specific microRNA signature characterized by increased expression of microRNA-363*/-206/-494/-155/-184/-542-3p, and decreased expression of microRNA-9* (ANOVA; P < .01). We found that microRNA-155 regulates proliferation and growth of WM cells in vitro and in vivo, by inhibiting MAPK/ERK, PI3/AKT, and NF-kappaB pathways. Potential microRNA-155 target genes were identified using gene-expression profiling and included genes involved in cell-cycle progression, adhesion, and migration. Importantly, increased expression of the 6 miRNAs significantly correlated with a poorer outcome predicted by the International Prognostic Staging System for WM. We further demonstrated that therapeutic agents commonly used in WM alter the levels of the major miRNAs identified, by inducing downmodulation of 5 increased miRNAs and up-modulation of patient-downexpressed miRNA-9*. These data indicate that microRNAs play a pivotal role in the biology of WM; represent important prognostic marker; and provide the basis for the development of new microRNA-based targeted therapies in WM.

Targeting Akt and heat shock protein 90 produces synergistic multiple myeloma cell cytotoxicity in the bone marrow microenvironment

PURPOSE

We hypothesized that targeting both Akt and heat shock protein (HSP) 90 would induce cytotoxic activity against multiple myeloma (MM) cells and target the bone marrow (BM) microenvironment to inhibit angiogenesis, osteoclast formation, as well as migration and adhesion of MM cells.

EXPERIMENTAL DESIGN

MM cell lines were incubated with perifosine (5 and 10 micromol/L) and 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG; 50 and 100 nmol/L) alone and in combination.

RESULTS

The combination of Akt inhibitor perifosine and HSP90 inhibitor 17-DMAG was synergistic in inducing MM cell cytotoxicity, evidenced by inhibition of DNA synthesis and induction of apoptosis. In addition, perifosine and 17-DMAG almost completely inhibited osteoclast formation: perifosine interfered with both early and late stages of osteoclast progenitor development, whereas 17-DMAG targeted only early stages. We next showed that combined therapy overcomes tumor growth and resistance induced by BM stromal cells and endothelial cells as well as the proliferative effect of exogenous interleukin-6, insulin-like growth factor-I, and vascular endothelial growth factor. Moreover, the combination also induced apoptosis and growth inhibition in endothelial cells and inhibited angiogenesis. Finally, we showed that the two agents prevented migration of MM cells toward stromal-derived factor-1 and vascular endothelial growth factor, which are present in the BM milieu, and also prevented adhesion of MM cells to fibronectin.

CONCLUSIONS

This study provides the preclinical framework for treatment protocols targeting both the Akt and HSP pathways in MM.

The Akt pathway regulates survival and homing in Waldenstrom macroglobulinemia

Waldenstrom macroglobulinemia (WM) is an incurable low-grade lymphoplasmacytic lymphoma. We demonstrate up-regulated Akt activity in WM, and that Akt down-regulation by Akt knockdown and the inhibitor perifosine leads to significant inhibition of proliferation and induction of apoptosis in WM cells in vitro, but not in normal donor peripheral blood and hematopoietic progenitors. Importantly, down-regulation of Akt induced cytotoxicity of WM cells in the bone marrow microenvironment (BMM) context. Perifosine induced significant reduction in WM tumor growth in vivo in a subcutaneous xenograft model through inhibition of Akt phosphorylation and downstream targets. We also demonstrated that Akt pathway down-regulation inhibited migration and adhesion in vitro and homing of WM tumor cells to the BMM in vivo. Proteomic analysis identified other signaling pathways modulated by perifosine, such as activation of ERK MAPK pathway, which induces survival of tumor cells. Interestingly, MEK inhibitor significantly enhanced perifosine-induced cytotoxicity in WM cells. Using Akt knockdown experiments and specific Akt and PI3K inhibitors, we demonstrated that ERK activation is through a direct effect, rather than feedback activation, of perifosine upstream ERK pathway. These results provide understanding of biological effects of Akt pathway in WM and provide the framework for clinical evaluation of perifosine in WM patients.

Mechanisms of regulation of CXCR4/SDF-1 (CXCL12)-dependent migration and homing in multiple myeloma

The mechanisms by which multiple myeloma (MM) cells migrate and home to the bone marrow are not well understood. In this study, we sought to determine the effect of the chemokine SDF-1 (CXCL12) and its receptor CXCR4 on the migration and homing of MM cells. We demonstrated that CXCR4 is differentially expressed at high levels in the peripheral blood and is down-regulated in the bone marrow in response to high levels of SDF-1. SDF-1 induced motility, internalization, and cytoskeletal rearrangement in MM cells evidenced by confocal microscopy. The specific CXCR4 inhibitor AMD3100 and the anti-CXCR4 antibody MAB171 inhibited the migration of MM cells in vitro. CXCR4 knockdown experiments demonstrated that SDF-1-dependent migration was regulated by the P13K and ERK/ MAPK pathways but not by p38 MAPK. In addition, we demonstrated that AMD3100 inhibited the homing of MM cells to the bone marrow niches using in vivo flow cytometry, in vivo confocal microscopy, and whole body bioluminescence imaging. This study, therefore, demonstrates that SDF-1/CXCR4 is a critical regulator of MM homing and that it provides the framework for inhibitors of this pathway to be used in future clinical trials to abrogate MM trafficking.

Moloney leukemia virus immortalizes B lymphocytes in vitro

An in vitro culture system in which Moloney murine leukemia virus induces immortalization of mature B lymphocytes has been developed. The cell lines derived in this way are nontumorigenic, and virus production is not required to sustain them. This system provides a new in vitro model with which to study the stepwise process of transformation by retroviruses lacking oncogenes.

Isolation of a bacterial host selective for bacteriophage T4 containing cytosine in its DNA

An Escherichia coli B strain, B834 galU56, has been isolated which supports growth of bacteriophage T4 with cytosine in its DNA while restricting growth of T4 with hydroxymethylcytosine. This host is partially deficient in uridine diphosphoglucose as determined by the ability of DNA isolated from T4 grown on it to accept glucose in an in vitro assay. In this mutant an intact rgl restriction system recognizes unglucosylated hydroxymethylcytosine residues in phage DNA, while the absence of a functional rB restriction function prevents degradation of unmodified DNA containing cytosine.

A model for the packing of cells

A model is presented for the statistical and geometrical aspects of the packing of cells. The model is closely related to lattice polymer models and the Ising model of ferromagnetism. Fundamental questions of existence and analyticity in the infinite volume limit are discussed, and the results of some initial numerical studies are given.