A mutualistic bacterium rescues a green alga from an antagonist

Photosynthetic protists, known as microalgae, are key contributors to primary production on Earth. Since early in evolution, they coexist with bacteria in nature, and their mode of interaction shapes ecosystems. We have recently shown that the bacterium Pseudomonas protegens acts algicidal on the microalga Chlamydomonas reinhardtii. It secretes a cyclic lipopeptide and a polyyne that deflagellate, blind, and lyse the algae [P. Aiyar et al., Nat. Commun. 8, 1756 (2017) and V. Hotter et al., Proc. Natl. Acad. Sci. U.S.A. 118, e2107695118 (2021)]. Here, we report about the bacterium Mycetocola lacteus, which establishes a mutualistic relationship with C. reinhardtii and acts as a helper. While M. lacteus enhances algal growth, it receives methionine as needed organic sulfur and the vitamins B1, B3, and B5 from the algae. In tripartite cultures with the alga and the antagonistic bacterium P. protegens, M. lacteus aids the algae in surviving the bacterial attack. By combining synthetic natural product chemistry with high-resolution mass spectrometry and an algal Ca2+ reporter line, we found that M. lacteus rescues the alga from the antagonistic bacterium by cleaving the ester bond of the cyclic lipopeptide involved. The resulting linearized seco acid does not trigger a cytosolic Ca2+ homeostasis imbalance that leads to algal deflagellation. Thus, the algae remain motile, can swim away from the antagonistic bacteria and survive the attack. All three involved genera cooccur in nature. Remarkably, related species of Pseudomonas and Mycetocola also act antagonistically against C. reinhardtii or as helper bacteria in tripartite cultures.

Exchange or Eliminate: The Secrets of Algal-Bacterial Relationships

Algae and bacteria have co-occurred and coevolved in common habitats for hundreds of millions of years, fostering specific associations and interactions such as mutualism or antagonism. These interactions are shaped through exchanges of primary and secondary metabolites provided by one of the partners. Metabolites, such as N-sources or vitamins, can be beneficial to the partner and they may be assimilated through chemotaxis towards the partner producing these metabolites. Other metabolites, especially many natural products synthesized by bacteria, can act as toxins and damage or kill the partner. For instance, the green microalga Chlamydomonas reinhardtii establishes a mutualistic partnership with a Methylobacterium, in stark contrast to its antagonistic relationship with the toxin producing Pseudomonas protegens. In other cases, as with a coccolithophore haptophyte alga and a Phaeobacter bacterium, the same alga and bacterium can even be subject to both processes, depending on the secreted bacterial and algal metabolites. Some bacteria also influence algal morphology by producing specific metabolites and micronutrients, as is observed in some macroalgae. This review focuses on algal-bacterial interactions with micro- and macroalgal models from marine, freshwater, and terrestrial environments and summarizes the advances in the field. It also highlights the effects of temperature on these interactions as it is presently known.

The UV-A Receptor CRY-DASH1 Up- and Downregulates Proteins Involved in Different Plastidial Pathways

Algae encode up to five different types of cryptochrome photoreceptors. So far, relatively little is known about the biological functions of the DASH (Drosophila, Arabidopsis, Synechocystis and Homo)-type cryptochromes. The green alga Chlamydomonas reinhardtii encodes two of them. CRY-DASH1 also called DCRY1 has its maximal absorption peak in the UV-A range. It is localized in the chloroplast and plays an important role in balancing the photosynthetic machinery. Here, we performed a comparative analysis of chloroplast proteins from wild type and a knockout mutant of CRY-DASH1 named cry-dash1mut, using label-free quantitative proteomics as well as immunoblotting. Our results show upregulation of enzymes involved in specific pathways in the mutant including key enzymes of chlorophyll and carotenoid biosynthesis consistent with increased levels of photosynthetic pigments in cry-dash1mut. There is also an increase in certain redox as well as photosystem I and II proteins, including D1. Strikingly, CRY-DASH1 is coregulated in a D1 deletion mutant, where its amount is increased. In contrast, key proteins of the central carbon metabolism, including glycolysis/gluconeogenesis, dark fermentation and the oxidative pentose phosphate pathway are downregulated in cry-dash1mut. Similarly, enzymes of histidine biosynthesis are downregulated in cry-dash1mut leading to a reduction in the amount of free histidine. Yet, transcripts encoding for several of these proteins are at a similar level in the wild type and cry-dash1mut or even opposite. We show that CRY-DASH1 can bind to RNA, taking the psbA RNA encoding D1 as target. These data suggest that CRY-DASH1 regulates plastidial metabolic pathways at the posttranscriptional level.

Chemoradiotherapy versus radiotherapy in patients with advanced nasopharyngeal cancer: phase III randomized Intergroup study 0099

PURPOSE

The Southwest Oncology Group (SWOG) coordinated an Intergroup study with the participation of Radiation Therapy Oncology Group (RTOG), and Eastern Cooperative Oncology Group (ECOG). This randomized phase III trial compared chemoradiotherapy versus radiotherapy alone in patients with nasopharyngeal cancers.

MATERIALS AND METHODS

Radiotherapy was administered in both arms: 1.8- to 2.0-Gy/d fractions Monday to Friday for 35 to 39 fractions for a total dose of 70 Gy. The investigational arm received chemotherapy with cisplatin 100 mg/m2 on days 1, 22, and 43 during radiotherapy; postradiotherapy, chemotherapy with cisplatin 80 mg/m2 on day 1 and fluorouracil 1,000 mg/m2/d on days 1 to 4 was administered every 4 weeks for three courses. Patients were stratified by tumor stage, nodal stage, performance status, and histology.

RESULTS

Of 193 patients registered, 147 (69 radiotherapy and 78 chemoradiotherapy) were eligible for primary analysis for survival and toxicity. The median progression-free survival (PFS) time was 15 months for eligible patients on the radiotherapy arm and was not reached for the chemo-radiotherapy group. The 3-year PFS rate was 24% versus 69%, respectively (P < .001). The median survival time was 34 months for the radiotherapy group and not reached for the chemo-radiotherapy group, and the 3-year survival rate was 47% versus 78%, respectively (P = .005). One hundred eighty-five patients were included in a secondary analysis for survival. The 3-year survival rate for patients randomized to radiotherapy was 46%, and for the chemoradiotherapy group was 76% (P < .001).

CONCLUSION

We conclude that chemoradiotherapy is superior to radiotherapy alone for patients with advanced nasopharyngeal cancers with respect to PFS and overall survival.

Clinical applications of high dose rate endorectal brachytherapy for patients with rectal cancer

With the establishment of total mesorectal excision for the treatment of rectal cancer, local recurrence rates have significantly decreased. The addition of preoperative external beam irradiation further reduces this risk to less than 6%. As the local treatment becomes successful and more widely used, the associated treatment-related toxicity is becoming clinically important. If 4 to 6% of the patients are to benefit from neo-adjuvant therapy before total mesorectal excision, the acute and the long-term toxicity burden must be reasonable. With the introduction of better-quality imaging for tumour visualization and treatment planning, a new-targeted radiation treatment was introduced with high dose rate endorectal brachytherapy. The treatment concept was tested in phase I and II studies first in the preoperative setting, then as a boost after external beam radiation therapy as a dose escalation study to achieve higher tumour local control in a radical treatment setting with no surgery. High dose rate endorectal brachytherapy is safe and effective in achieving high tumour regression rate and was well tolerated. It is presently explored in a phase III dose escalation study in the non-operative management of patients with operable rectal cancer.

A141 IS SURGERY STILL THE ONLY TREATMENT OPTION FOR CURABLE RECTAL CANCER?

Background

Rectal cancer is curable by standard surgery with Total Mesorectal Excision (TME). However, there are well known associated long-term bowel and sexual dysfunctions. Non-operative management (NOM) is an emerging treatment for patients with operable rectal cancer. There is evidence supporting dose response for tumor control in rectal adenocarcinoma.

Aims

In the era of modern technologies, Image-guided adaptive endorectal brachytherapy is a means to deliver local radiotherapy boost treatments. We explored its role in a randomized phase II/III trial (NCT03051464) for patients aiming to achieve cure without surgery. Total Mesorectal Excision (TME) free survival at 2 years was the primary endpoint. We now present the interim analysis upon accrual of the first 40 patients.

Methods

In randomized trial, patients with operable cT2-3ab N0 M0 rectal cancer received 45 Gy in 25 fractions of pelvic external beam radiotherapy (EBRT) with concurrent 5-FU/ Capecitabine. They were randomized to receive either an EBRT boost of 9 Gy in 5 fractions (Arm A), or three weekly adaptive brachytherapy boosts for a total of 30 Gy in 3 fractions (Arm B).

Results

Forty patients were included (20 per arm). The median age was 66 years; baseline characteristics were well balanced in terms of age, tumor location, T stage and tumor size (Table 1). The acute treatment related toxicities are similar as shown in table 2 but in arm B, there were two deaths: one patient died during his chemotherapy and external beam treatment from congestive heart failure and one patient from a heart attack after treatment prior to salvage TME surgery. The proportion of complete clinical response was 50% (n=10/20) in Arm A and 90% in Arm B (n=18/20). With a median follow-up of 2.2 years, local regrowth at 2 years occurred in 4/10 patients (40%) in Arm A and 4/18 patients (22%) in Arm B. TME-free survival rate at 2 years was 45.9% in Arm A and 85.1% in Arm B (p=0.0036) (Figure 1).

Conclusions

The interim analysis of this trial suggests that these two strategies of radiation dose escalation are feasible and lead to high chances of organ preservation in patients with operable rectal cancer. The Independent Monitoring Comittee (IDMC) approved the continuation of patient recruitment in the phase III study as planned.

Funding Agencies

Elekta

A121 QUANTIFYING INTER-OBSERVER VARIABILITY IN THE SEGMENTATION OF RECTAL TUMORS IN ENDOSCOPY IMAGES AND ITS EFFECTS ON DEEP LEARNING

Background

Tumor delineation in endoscopy images is a crucial part of clinical diagnoses and treatment planning for rectal cancer patients. However, it is challenging to detect and adequately determine the size of tumors in these images, especially for inexperienced clinicians. This motivates the need for a standardized, automated segmentation method. While deep learning has proven to be a powerful tool for medical image segmentation, it requires a large quantity of high-quality annotated training data. Since the annotation of endoscopy images is prone to high inter-observer variability, creating a robust unbiased deep learning model for this task is challenging.

Aims

To quantify the inter-observer variability in the manual segmentation of tumors in endoscopy images of rectal cancer patients and investigate an automated approach using deep learning.

Methods

Three gastrointestinal physicians and radiation oncologists (G1, G2, and G3) segmented 2833 endoscopy images into tumor and non-tumor regions. The whole image classifications and the pixelwise classifications into tumor and non-tumor were compared to quantify the inter-observer variability. Each manual annotator is from a different institution.

Three different deep learning architectures (FCN32, U-Net, and SegNet) were trained on the binary contours created by G2. This naive approach investigates the effectiveness of neglecting any information about the uncertainty associated with the task of tumor delineation.

Finally, segmentations from G2 and the deep learning models’ predictions were compared against ground truth labels from G1 and G3, and accuracy, sensitivity, specificity, precision, and F1 scores were computed for images where both segmentations contained tumors.

Results

The deep-learning segmentation took less than 1 second, while manual segmentation took approximately 10 seconds per image. There was significant inter-observer variability for the whole-image classifications made by the manual annotators (Figure 1A). The segmentation scores achieved by the deep learning models (SegNet F1:0.80±0.08) were comparable to the inter-observer variability for the pixel-wise image classification (Figure 1B).

Conclusions

The large inter-observer variability observed in this study indicates a need for an automated segmentation tool for tumors in endoscopy images of rectal cancer patients. While deep learning models trained on a single observer’s labels can segment tumors with an accuracy similar to the inter-observer variability, these models do not accurately reflect the intrinsic uncertainty associated with tumor delineation. In our ongoing studies, we investigate training a model with all observers’ contours to reflect the uncertainty associated with the tumor segmentations.

Funding Agencies

CIHRNSERC

A comparison of structural features and vulnerability between government and nongovernment alcohol and other drug (AOD) treatment providers

OBJECTIVE

Both public (government-run), and not-for-profit (nongovernment) service providers provide alcohol and other drug (AOD) treatment services. Research has rarely studied the structural features of these providers, such as workforce characteristics, procurement arrangements, and funding security. The study reported here sought to document and analyze the differences between these two AOD treatment provider types in Australia.

METHODS

The study administered an online survey instrument targeted at managers of AOD treatment sites. The survey comprised three sections: (1) the service (e.g., treatment types); (2) workforce (e.g., total number of staff); and (3) funding and procurement arrangements (e.g., contract length). The study completed a total of 207 site surveys. The studied compared government and nongovernment services on structural features that may create a more or less sustainable or vulnerable service (funding arrangements, payment mechanisms, and contract length).

RESULTS

Government providers were more likely to provide medically oriented treatment types such as withdrawal management and pharmacotherapy, whereas nongovernment organization (NGO) providers were more likely to offer rehabilitation. Consistent with this, government services were more likely to employ medical professionals and nurses, indicative of a more medically oriented workforce, while NGO services were more likely to employ AOD workers, youth workers, peer workers, and counselors. Our data illustrate that NGO services were more likely to be subject to competitive tendering and to have shorter contract lengths, compared with government services, and overall to be more structurally vulnerable.

CONCLUSION

Despite the reliance on NGOs to provide the majority of specialist care (71% of all treatment episodes in Australia), these services are more vulnerable than their government counterparts. To ensure that a comprehensive suite of treatment services is available, procurement arrangements that support stability and security in nongovernment service providers and government service providers are essential.

Migraine therapeutics differentially modulate the CGRP pathway

Background

The clinical efficacy of migraine therapeutic agents directed towards the calcitonin-gene related peptide (CGRP) pathway has confirmed the key role of this axis in migraine pathogenesis. Three antibodies against CGRP – fremanezumab, galcanezumab and eptinezumab – and one antibody against the CGRP receptor, erenumab, are clinically approved therapeutics for the prevention of migraine. In addition, two small molecule CGRP receptor antagonists, ubrogepant and rimegepant, are approved for acute migraine treatment. Targeting either the CGRP ligand or receptor is efficacious for migraine treatment; however, a comparison of the mechanism of action of these therapeutic agents is lacking in the literature.

Methods

To gain insights into the potential differences between these CGRP pathway therapeutics, we compared the effect of a CGRP ligand antibody (fremanezumab), a CGRP receptor antibody (erenumab) and a CGRP receptor small molecule antagonist (telcagepant) using a combination of binding, functional and imaging assays.

Results

Erenumab and telcagepant antagonized CGRP, adrenomedullin and intermedin cAMP signaling at the canonical human CGRP receptor. In contrast, fremanezumab only antagonized CGRP-induced cAMP signaling at the human CGRP receptor. In addition, erenumab, but not fremanezumab, bound and internalized at the canonical human CGRP receptor. Interestingly, erenumab also bound and internalized at the human AMY₁ receptor, a CGRP receptor family member. Both erenumab and telcagepant antagonized amylin-induced cAMP signaling at the AMY₁ receptor while fremanezumab did not affect amylin responses.

Conclusion

The therapeutic effect of agents targeting the CGRP ligand versus receptor for migraine prevention (antibodies) or acute treatment (gepants) may involve distinct mechanisms of action. These findings suggest that differing mechanisms could affect efficacy, safety, and/or tolerability in migraine patients.

Session 3: Boosting primary and recurrent rectal cancer: how far can we push the radiotherapy envelope?

Neoadjuvant pelvic radiotherapy is widely used for patients with advanced rectal cancer. The trade-off between dose and response is well-established, yet little consensus remains on the precise methods of delivery and doses given in different scenarios. Professor Vuong reviews the evidence base and trial evidence on the escalation of radiotherapy dose and the methods of achieving this.

Eastern Canadian Colorectal Cancer Consensus Conference 2013: Emerging Therapies in the Treatment of Pancreatic, Rectal, and Colorectal Cancers

The annual Eastern Canadian Colorectal Cancer Consensus Conference held in Montreal, Quebec, 17–19 October 2013, marked the 10-year anniversary of this meeting that is attended by leaders in medical, radiation, and surgical oncology. The goal of the attendees is to improve the care of patients affected by gastrointestinal malignancies. Topics discussed during the conference included pancreatic cancer, rectal cancer, and metastatic colorectal cancer.

Effects of dna-dependent protein kinase inhibition by NU7026 on dna repair and cell survival in irradiated gastric cancer cell line N87

Repair of radiation-induced dna double-strand breaks is a key mechanism in cancer cell radio-resistance. The synthesized compound NU7026 specifically inhibits dna-dependent protein kinase (dna-pk) within the non-homologous end-joining repair mechanism. Earlier studies demonstrated increased radiosensitivity in dna-pk deficient cells compared with wild-type cells. In chronic leukemia cells, NU7026 appears to enhance the cytotoxic effect of chlorambucil. The radio-modifying effects of NU7026 on cell survival, cell cycle, apoptosis, and dna double-strand break repair have yet to be studied in gastric cancer cells.

METHODS

The gastric cancer cell line N87 was treated with 0 Gy or 4 Gy in the presence of NU7026 at a dose range of 0-20 μmol/L. Clonogenic assays were used to assess cell survival after treatment. Cell-cycle distribution was analyzed using propidium iodide with fluorescence-activated cell sorting. Apoptosis was detected using annexin-V and propidium iodide with fluorescence-activated cell sorting. The γH2AX assay was used to measure dna double-strand breaks.

RESULTS

Statistically significant increases in G2/M arrest were observed in N87 cells treated with radiation and NU7026 compared with those treated with radiation alone (p = 0.0004). Combined treatment also led to an increase in apoptosis (p = 0.01). At 24 hours, the γH2AX analysis revealed more dna double-strand breaks in N87 cells treated with radiation and NU7026 than in those treated with radiation alone (p = 0.04). Clonogenic assays demonstrated declining cell survival as both the radiation and the NU7026 dose increased. The dose enhancement factor at 0.1 survival fraction was 1.28 when N87 cells were treated with 4 Gy radiation and 5 μmol/L NU7026.

CONCLUSIONS

In gastric cancer cells, NU7026 appears to enhance the cytotoxic effect of irradiation as assessed by clonogenic assays. This increased cytotoxicity might be the result of an increase in dna double-strand breaks resulting in G2/M cell arrest and possibly higher levels of apoptosis.

The experience of pain and anxiety in rectal cancer patients during high-dose-rate brachytherapy

BACKGROUND

Pain and anxiety have been reported as primary concerns for patients with head-and-neck, gynecologic, and prostate cancers undergoing high dose rate (hdr) brachytherapy. However, almost no research has been published on the degree to which these symptoms are experienced by rectal cancer patients undergoing hdr brachytherapy. We conducted a pilot study examining the experiences of rectal cancer patients during hdr brachytherapy, specifically the intensity and trajectory of their anxiety and pain.

METHODS

Rectal cancer patients (n = 25) who received hdr brachytherapy treatment at a hospital in Montreal, Quebec, completed verbal analog scales for pain and anxiety at 4 time points over 4 treatment days.

RESULTS

On all 4 days, a subset of patients reported moderate-to-severe anxiety before applicator insertion. Pain increased significantly from the time patients were lying on the table to immediately after insertion of the applicator (p < 0.001). Insertion of the applicator appears to be the most painful part of the procedure, and although anxiety declined to below baseline after applicator removal, pain remained somewhat elevated. Some patients required conscious sedation; however, reports of moderate-to-severe pain were more frequent from patients who received pain medications than from patients who did not receive such medication (p < 0.05).

CONCLUSIONS

Most patients with rectal cancer tolerated hdr rectal brachytherapy well, although the procedure is stressful and painful for some. Insertion of the applicator was found to be the point of maximal pain, and medication was not always completely successful at alleviating the pain, suggesting that additional psychosocial interventions might be needed, with particular emphasis on the time of applicator insertion.

Short-term outcome after neoadjuvant high-dose-rate endorectal brachytherapy or short-course external beam radiotherapy in resectable rectal cancer

AIM

Total mesorectal excision with preoperative radiotherapy reduces local recurrence in rectal cancer, but radiotherapy increases the risk of complications. This study compared the immediate postoperative outcome after external beam radiotherapy with outome after high-dose-rate endorectal brachytherapy (HDREBT).

METHOD

Patients (n = 318) treated with preoperative HDREBT (6.5 Gy, daily, over 4 days) followed by surgery 4-8 weeks later were matched with 318 patients from the Swedish Rectal Cancer Register treated with short-course radiotherapy (SCRT; 5 Gy, daily, over 5 days) and surgery in the subsequent week and with 318 patients who had surgery only (i.e. no preoperative radiotherapy; RT-) All 954 patients were followed for 30 days after surgery. Complications were divided into surgical, cardiovascular and infectious.

RESULTS

The SCRT group had fewer cardiovascular complications (3.1%) than did HDREBT (9.4%, P = 0.002) and RT- (7.2%, P = 0.03) groups. There was less perioperative bleeding in HDREBT patients (379.3 ml) than in SCRT (947.2 ml; P < 0.0001) or RT- (918.9 ml) patients, and the re-intervention rate was lower in HDREBT (4.1%) patients than in SCRT (14.2%; P = 0.005) and RT- (12.3%; P < 0.005) patients. The HDREBT group had fewer R2 resections than did the SCRT and RT- groups, but had a higher proportion of R0 resections compared with the RT- group (P = 0.03).

CONCLUSION

No major differences in postoperative complications were found. HDREBT patients had a higher rate of cardiovascular complications, but less perioperative bleeding and fewer re-interventions. A longer interval between radiotherapy and surgery may be beneficial for tumour regression and this could be reflected in the number of radical resections.

EGFR and K-ras gene mutation status in squamous cell anal carcinoma: a role for concurrent radiation and EGFR inhibitors?

BACKGROUND

There is a growing appreciation for radio-sensitiser use in multi-modal cancer treatment models. Squamous cell anal carcinoma (SCAC) is a rare gastrointestinal tumour traditionally treated with concurrent chemotherapy and radiation. Cetuximab, an epidermal growth factor receptor (EGFR) inhibitor, has demonstrated significant efficacy when combined with radiation in squamous cell carcinoma of the head and neck (SccH&N). We wanted to assess EGFR and Kirsten-ras (K-ras) status in SCAC to see whether it compares with SccH&N.

METHODS

Over 90 SCAC paraffin-embedded biopsies were mounted onto a tissue microarray and were assessed for EGFR expression by immunohistochemistry. These samples were also assessed for the most frequently mutated K-ras and EGFR exons by high-resolution melting analysis.

RESULTS

The EGFR was present in over 90% of samples tested. The K-ras and EGFR mutations were absent in all samples tested, although a synonymous single-nucleotide polymorphism was found in 3 out of 89 samples tested for EGFR exon 19.

CONCLUSION

The low rate of K-ras and EGFR mutations, coupled with the high surface expression of EGFR, suggests similarity in the EGFR signalling pathway between SCAC and SccH&N, and thus a potential role for EGFR inhibitors in SCAC. To our knowledge this is the largest cohort of invasive SCAC samples investigated for EGFR and K-ras mutations reported to date.

Characterization of the Arabidopsis augmin complex uncovers its critical function in the assembly of the acentrosomal spindle and phragmoplast microtubule arrays

Plant cells assemble the bipolar spindle and phragmoplast microtubule (MT) arrays in the absence of the centrosome structure. Our recent findings in Arabidopsis thaliana indicated that AUGMIN subunit3 (AUG3), a homolog of animal dim γ-tubulin 3, plays a critical role in γ-tubulin-dependent MT nucleation and amplification during mitosis. Here, we report the isolation of the entire plant augmin complex that contains eight subunits. Among them, AUG1 to AUG6 share low sequence similarity with their animal counterparts, but AUG7 and AUG8 share homology only with proteins of plant origin. Genetic analyses indicate that the AUG1, AUG2, AUG4, and AUG5 genes are essential, as stable mutations in these genes could only be transmitted to heterozygous plants. The sterile aug7-1 homozygous mutant in which AUG7 expression is significantly reduced exhibited pleiotropic phenotypes of seriously retarded vegetative and reproductive growth. The aug7-1 mutation caused delocalization of γ-tubulin in the mitotic spindle and phragmoplast. Consequently, spindles were abnormally elongated, and their poles failed to converge, as MTs were splayed to discrete positions rendering deformed arrays. In addition, the mutant phragmoplasts often had disorganized MT bundles with uneven edges. We conclude that assembly of MT arrays during plant mitosis depends on the augmin complex, which includes two plant-specific subunits.