The MTT Assay: Utility, Limitations, Pitfalls, and Interpretation in Bulk and Single-Cell Analysis

The MTT assay for cellular metabolic activity is almost ubiquitous to studies of cell toxicity; however, it is commonly applied and interpreted erroneously. We investigated the applicability and limitations of the MTT assay in representing treatment toxicity, cell viability, and metabolic activity. We evaluated the effect of potential confounding variables on the MTT assay measurements on a prostate cancer cell line (PC-3) including cell seeding number, MTT concentration, MTT incubation time, serum starvation, cell culture media composition, released intracellular contents (cell lysate and secretome), and extrusion of formazan to the extracellular space. We also assessed the confounding effect of polyethylene glycol (PEG)-coated gold nanoparticles (Au-NPs) as a tested treatment in PC-3 cells on the assay measurements. We additionally evaluated the applicability of microscopic image cytometry as a tool for measuring intracellular MTT reduction at the single-cell level. Our findings show that the assay measurements are a result of a complicated process dependant on many of the above-mentioned factors, and therefore, optimization of the assay and rational interpretation of the data is necessary to prevent misleading conclusions on variables such as cell viability, treatment toxicity, and/or cell metabolism. We conclude, with recommendations on how to apply the assay and a perspective on where the utility of the assay is a powerful tool, but likewise where it has limitations.

An Outpatient Management for First Cycle of Venetoclax and Hypomethylating Agents Results in Reduced Infection Rate and Hospitalizations in Acute Myeloid Leukemia Patients

Introduction In the setting of clinical trials Venetoclax (VEN) combined with hypomethylating agents (HMAs) has shown fair activity in Relapsed/Refractory (R/R) AML and impressive results in newly diagnosed (ND) elderly AML patients. However, no clear guidelines are available on real-life management, especially in the outpatient setting. This study involving AML patients treated with VEN combined with HMAs aims to amelioratate physicians' knowledge about the administration of these regimens. Methods This is a single-center retrospective study involving AML patients treated with Venetoclax combined with HMAs. Data were collected in accordance with GCP and Helsinky declaration. Adverse events (AEs) were graded according to CTCAE v4.03. Survival is estimated with Kaplan-Meyer method. Results A total of 59 AML patients, 43 R/R and 16 ND, have been treated with VEN plus HMAs from March 2018 to June 2021 and completed at least 1 therapy course (range 1-9, median 2, IQR 1.0 - 4.0). The median age was 70 (range 22-88) years and 15.3 % had a documented ECOG score greater than 1. VEN was combined with azacitidine in 35/59 (59.3 %) patients and with decitabine in 22/59 (37.3 %) patients (Table 1: patient and disease characteristics). The majority of patients (40/59, 67.8 %) (28/43 R/R, 12/16 ND) received the first cycle as out-patients, 19 out of 59 (32.2 %) patients were hospitalized and used as control. No significant differences with regards to disease and patients' characteristics were observed between in- and out-patients. During the ramp-up phase only 2 cases of tumor lysis syndrome (TLS) and 5 AEs were documented. During the first course, a total of 54 AEs were recorded and experienced by 16 over 19 hospitalized patients (84.2 %) and 20 over 40 outpatients (50 %). The 30-day and 60-day mortality were 2.5% (1/40) and 20 % (8/40), respectively, among patients receiving first course as out-patents, comparable to those documented in hospitalized patients. Overall, we reported 118 AEs, of which 74 were grade III-IV and the most common were hematological 23/74 (31.1 %) or infective 41/74 (55.4 %). Regarding infections, at least one bacterial infection was experienced in 10/40 (25%) and 12/19 (63.1%) patients of the outpatient and hospitalized cohorts, respectively (p = 0.009, IC 1.37 - 19.74, OR 4.98). Pneumonia and sepsis (13 and 18 cases) were the most frequent infections. Sepsis incidence was higher among hospitalized patients (13/19, 68.4 %, vs 5/40, 12.5 %, p = 0.000029). No significant difference in infective risk was documented between R/R and ND patients (65.1 vs 50 %). Thirty-two out of 59 (54.2 %) patients experienced at least one VEN withdrawal due to treatment toxicity. Twenty out of 43 AEs requiring VEN suspensions occurred during the first cycle. Patients treated in-patient showed the tendency for a higher probability to suspend therapy due to treatment toxicity (10/19 IN vs 10/40 OUT, p = 0.04). While twenty-three out of 59 (38.9 %) patients were hospitalized for treatment complications at least once, the average number of days spent in hospital was significantly different between patients receiving the first course as outpatients as compared to those who were hospitalized (5.9 vs 39.7, respectively, p < 0.0001). With a median follow-up of 117 days (IQR 92 - 173.75) in ND patients the Overall Response Rate (ORR), defined as CR + CRi + HI, was 62.5 % (10/16), with a CR/CRi rate of 50 % (8/16) and a median OS of 247 days (95% C.I. 177.71- 316.58)(Fig 1a). In the R/R setting the ORR rate was 41.8 % (18/43), with a CR/CRi rate of 25.6 % (11/43) and a median OS of 219 days (95% C.I. 91.8 - 346.2) (Fig 2a). No differences in OS were documented between patients who underwent VEN plus HMAs outpatient and patients who underwent the first cycle hospitalized (p = 0,38) (Fig. 1b-2b). Conclusions With the limitations of a single-center retrospective study, our real-life data indicate that VEN plus HMAs is feasible in an outpatient management, with minimal TLS rate and no limiting toxicities. Of note, infections rate was acceptable, bacterial infections and sepsis risk were lower in outpatients than in hospitalized patients. There was no significant impact of the outpatient management on treatment effectiveness, with data in line with published AML cohorts. Further studies evaluating the clinical, social and economic impact of outpatient VEN-based treatments are highly warranted. Figure 1 Figure 1. Disclosures Papayannidis: Pfizer, Amgen, Novartis: Honoraria. Cavo: Adaptive Biotechnologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Accommodations, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Speakers Bureau; Novartis: Honoraria; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol-Myers Squib: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Curti: Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees.

Microbiome Dynamics During Chemoradiotherapy for Anal Cancer

IMPORTANCE: Patients with localized squamous cell carcinoma of the anus (SCCA) who experience treatment toxicity or recurrences have few therapeutic options. Investigation into the microbiome's influence on treatment toxicity or its potential use as a predictive biomarker in this rare disease could improve these patients' outcomes. OBJECTIVE: To longitudinally characterize the SCCA tumor microbiome and assess its association with treatment-related toxicities. DESIGN: Prospective cohort study. SETTING: Single tertiary cancer center. PARTICIPANTS: Twenty-two patients with biopsy-confirmed non-metastatic SCCA receiving standard-of-care chemoradiotherapy as part of an Institutional Review Board-approved study from April 2017 to July 2019. MAIN OUTCOMES AND MEASURES: Diversity and taxonomic characterization of the SCCA microbiome throughout chemoradiotherapy using swab-based anorectal microbial specimen collection and 16S rRNA gene sequencing. RESULTS: Twenty-two SCCA patients were included in this study with a median (range) age of 58.5 (39-77), and 18 (82%) were women. Alpha diversity remained relatively stable throughout chemoradiotherapy, except for decreases in the Chao1 (P=0.03) and Observed Features (P=0.03) indices at week 5 relative to baseline. Tumor microbial compositions measured using weighted UniFrac changed significantly by the end of treatment (P=0.03). Linear discriminant analysis effect sizes revealed differential enrichment of bacteria at specific time points, including the enrichment of Clostridia at both baseline and follow-up and the enrichment of Corynebacterium at week 5. Patients experiencing high toxicity at week 5 had higher relative abundances of Clostridia, Actinobacteria, and Clostridiales at baseline (P=0.03 for all). CONCLUSIONS AND RELEVANCE: Our study presents the first longitudinal characterization of the SCCA microbiome throughout chemoradiation. The tumor microbiome undergoes significant changes during and after chemoradiotherapy, and patient-reported toxicity levels are associated with patients' microbial profiles. Further studies into these microbial characterizations and associations are needed to elucidate the tumor microbiome's role in predicting treatment-related outcomes for SCCA patients.