Citations

AbstractBackgroundHidradenitis suppurativa (HS) is a chronic inflammatory skin condition that causes substantial physical, emotional and psychological burdens. Guselkumab, a monoclonal antibody that binds to the p19 subunit of interleukin‐23, has demonstrated high levels of efficacy in the treatment of inflammatory diseases, including psoriasis and psoriatic arthritis.ObjectiveTo evaluate the effect of guselkumab on the treatment of HS, a phase 2, multicentre, randomized, placebo‐controlled, double‐blind, proof‐of‐concept study was conducted.MethodsPatients ≥18 years of age with moderate‐to‐severe HS for ≥1 year were randomized to (1) guselkumab 200 mg by subcutaneous (SC) injection every 4 weeks (q4w) through Week 36 (guselkumab SC); (2) guselkumab 1200 mg intravenously (IV) q4w for 12 weeks, then switched to guselkumab 200 mg SC q4w from Weeks 12 through 36 (guselkumab IV); or (3) placebo for 12 weeks, with re‐randomization to guselkumab 200 mg SC q4w at Weeks 16 through 36 (placebo → guselkumab 200 mg) or guselkumab 100 mg SC at Weeks 16, 20, 28 and 36 and placebo at Weeks 24 and 32 (placebo → guselkumab 100 mg). End points included HS clinical response (HiSCR) and patient‐reported outcomes.ResultsAlthough guselkumab SC or guselkumab IV resulted in numerically higher HiSCR versus placebo at Week 16 (50.8%, 45.0%, 38.7%, respectively), statistical significance was not achieved. Numerically greater improvements in patient‐reported outcomes were also observed for guselkumab SC and guselkumab IV versus placebo at Week 16. Through Week 40, no clear differences to suggest a dose response were observed for HiSCR and patient‐reported outcomes.ConclusionsDespite modest improvements, the primary end point was not met and the overall findings do not support the efficacy of guselkumab in the treatment of HS. Clinicaltrials.gov: NCT 03628924.

Abstract Metastatic pancreatic cancer patients who previously progressed on nab-paclitaxel/gemcitabine (average of 3 previous lines if treatment) were treated with elraglusib in combination with a rechallenge of this combination. The majority of patients demonstrated a prolonged progression free survival. While this early clinical evidence is highly encouraging, the biological determinants of elraglusib response are unknown. In vitro screens of elraglusib on pancreatic PDX cell lines showed that some tumor cells possess modest intrinsic resistance to elraglusib as measured by LD50 which ranged from 316.9 nM to 1080 nM in a screen of 10 cell lines. To explore this phenomena further, we induced resistance in three cell line models by growing cells in the presence of increasing concentrations of elraglusib. We then sequenced the transcriptome of the parental and resistant lines to identify potential mechanisms of elraglusib resistance. Comparison of RNA sequencing profiles identified upregulation of the Aldo-keto reductase (AKR) family of genes. This upregulation was confirmed by qRT-PCR and by immunoblot demonstrating that AKRs were upregulated at both the transcriptomic and protein level. We further quantified the AKR levels in the remainder of the 10 cell lines and found that many of the more resistant lines had high expression of AKR1C2. However, not all of the resistant lines had high expression which could be because they have a separate mechanism of resistance to elraglusib. A large body of literature has found that AKR genes provide resistance to many other small molecule inhibitors either by direct metabolism or by indirectly relieving oxidative stress. Given these results, we identify aldo-keto reductases as potentially associated with elraglusib resistance, but further investigation is warranted to establish a causal link between AKR and the resistant phenotype. Citation Format: Taylor Weiskittel, Ding Li, Lingling Han, Joseph McDermott, Benedito Caneiro, Hu Li, Daniel Billadeau, Andrew Mazar. Exploring mechanisms of resistance to elraglusib in pancreatic cancer PDX models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3857.

Abstract Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer. Tyrosine kinase inhibitors (TKIs) are approved as a first-line treatment for unresectable HCC. Lenvatinib and cabozantinib are two of the most used TKIs, but the therapeutic duration is limited due to the development of drug resistance. Therefore, understanding the mechanisms of resistance and combining TKIs with other drugs antagonizing resistance should lead to antitumor synergy, eliminating drug resistance. It turns out that the simultaneous use of TKIs together with an inhibitor of stearoyl-CoA desaturase 1 (SCD1) prevents the development of drug resistance, leading to a durable response. SCD1 is the enzyme responsible for de novo fatty acid (FAs) synthesis, converting saturated fatty acids (SFAs) into monounsaturated fatty acids (MUFAs). MUFAs are an alternative energy source to glucose, integral to cellular membranes, and prevent endoplasmic reticulum (ER) stress and other signaling pathways. In our laboratory, we developed a novel, highly specific SCD1 inhibitor - SSI-4. We have tested the biological activity of SSI-4 against different HCC cell lines and patient-derived xenografts (PDX) mouse models. Of the twelve tested HCC cell lines, four were highly sensitive to SSI-4 (IC50 1-50 nM). Other cell lines showed moderate or no sensitivity to SSI-4. We tested the concomitant use of SSI-4 with lenvatinib and cabozantinib, tyrosine kinase inhibitors (TKIs) FDA-approved for HCC, in HCC cell lines in vitro and using HCC PDX in vivo mouse models. Our studies showed that the combination of the SCD1 inhibitor with both lenvatinib and cabozantinib showed a highly synergistic effect and no development of drug resistance i.e. durable response versus single TKI therapy. Ongoing mechanistic studies are examining whether known molecular targets of tested TKI’s such as VEGFR1, 2, and 3, PDGFRα, FGFR, KIT, and RET dominate in HCC drug resistance to lenvatinib and cabozantinib, and how the use of SSI-4 overcomes the phenomenon of resistance. Citation Format: Justyna J. Gleba, Aylin Alasonyalilar-Demirer, Matthew L. Pawlush, Ahmet Bilgili, Peyton G. Hickman, Kabir Mody, Lewis R. Roberts, Steven R. Alberts, Mark J. Truty, Tushar C. Patel, Han W. Tun, John A. Copland. Synergistic activity of SCD1 blockade in combination with tyrosine kinase inhibitors lenvatinib and cabozantinib in hepatocellular carcinoma (HCC). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5489.

9569 Background: Immune-checkpoint inhibitor (ICI) immunotherapy increases survival in patients with melanoma. Yet only half of the patients respond, and 10-40% of patients experience immune-related adverse events (irAEs). Previous studies have found a correlation between the development of an irAE and treatment response. Modifying the gut microbiome could positively affect response to ICIs and reduce toxicities. We sought to determine if the microbiome at the onset of treatment, during an irAE, and at 12 weeks, can predict the response or toxicity during ICI treatment for metastatic melanoma. Methods: Melanoma patients (pts) > 18 yo treated with ICI enrolled in a prospective observational cohort study at The Ohio State University Comprehensive Cancer Center Skin Cancer Clinic. Excluded were patients on corticosteroids at the start of ICI cycle 1, except for adrenal physiologic replacement. Stools were collected at baseline, within 2 days of an adverse event assessed by physician chart review using CTCAE (Common Terminology Criteria for Adverse Events) v5.0, and at 12 weeks. Response (ORR) to ICIs was assessed by Response Evaluation Criteria in Solid Tumors (RECIST v1.1) q12 weeks and progression-free survival recorded. Metagenomic whole-genome shotgun sequencing was performed on an Illumina NovaSeq 6000 and classified using HUMAnN3. The effect of microbe relative abundances on irAEs was modeled by logistic regression with the R package glmm. Results: Of the 88 patients enrolled, 48 had metastatic disease with 32 assessable for response. ORR at 12 weeks was 28% (1 CR, 8 PR, 17 SD, and 6 PD) and 24 patients showed PFS at 12 months. Grade > 2 irAEs were observed in 11/48 pts. Abundance of Bacteroides dorei (False Discovery Rate Corrected p-value = 9.5E-07) and Blautia species CAG:257 (padj = 0.001) were enriched in responders, Prevotella Stercorea (padj = 1.1E-07) and a phage with a predicted target of Salmonella (padj = 8.3E-09) in non-responders. Responders with an irAE had enrichment of Bacteroides plebeius (padj = 4.2E-13) and Bacteroides coprophilus (padj = 0.0002) whereas responders without irAE had enrichment of Eubacterium siraeum (padj = 7.2E-05). Conclusions: Longitudinal and event-driven biospecimen collection in patients treated with ICIs showed several bacteria and viruses but no fungi associated with response, with and without the development of an irAE. The abundance of the two high-taxonomic rank microbe groups is significantly associated with irAEs. The association with the Bacteroides Genus is consistent with previous studies and is associated with response to ICIs. A microbiome abundant in Bacteroides and lacking Prevotella is associated with response to ICI. An abundance of Bacteroides could be a biomarker for irAEs, and an abundance of Eubacterium, a biomarker for response without irAEs. Future analyses are necessary to assign causal roles for microbe biomarkers with specific irAEs. Clinical trial information: NCT05102773 .

e19548 Background: Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare lymphoma accounting for less than 1% of mature T-cell lymphomas. Its natural history is not understood due to lack of large studies with long-term followup and an optimal therapeutic approach is not well-defined. Methods: The National Cancer Database was queried for patients aged 18 years and older diagnosed with SPTCL between 2004 and 2018. We excluded patients who lost to follow-up. Kaplan-Meier and multivariate Cox regression were used in the analyses. Results: 353 patients with SPTCL were included. 63% were females, 62% Caucasian, and 26% African American, 50% had early stage (I and II) and 32% had advanced stage (III and IV). 58.4% received chemotherapy, 38.2% did not receive chemotherapy and 3.4% had unknown chemotherapy status. The median age at diagnosis was 49 years (range 18-90). The median overall survival (mOS) for the whole cohort was not reached In early-stage (N = 178), 49.5% had chemotherapy with 39% receiving single-agent chemotherapy and 60% receiving multi-agent chemotherapy. 18.5% received radiation. In advanced-stage (N = 112), 75.9% received chemotherapy with 19% receiving single-agent chemotherapy and 81% receiving multi-agent chemotherapy. 9.8% received radiation There was no significant difference in the mOS between advanced-stage and early-stage (161.5 months vs not reached, P = 0.051) In early stage, there was no significant difference in the OS between chemotherapy and no chemotherapy (mOS was not reached in both groups, P = 0.324). The same trend was seen in the advanced stage (mOS was not reached in both groups, P = 0.851) Compared to Caucasian, African American patients were younger (median age 47 vs 54 years), but there was no significant difference in disease stage, receiving chemotherapy or radiation or other disease related characteristics (IPI score, B-symptoms, and HIV infection). African American patients had better OS (mOS was not reached, P = 0.003). This significant difference was seen in early stage (mOS was not reached, P = 0.003), but not in advanced stage (mOS 162 vs 122 months, P = 0.113) On multivariate analysis, age and Charlson-Deyo score ≥3 were associated with worse OS (HR 1.028 95% CI 1.005-1.052; P = 0.018 and HR 14.711 95% CI 2.316-93.449; P = 0.004, respectively), whereas disease stage and chemotherapy status did not affect the OS (HR 0.938 95% CI 0.545-1.617; P = 0.819, HR 1.271 95% CI 0.175-9.255; P = 0.813, and HR 0.922 95% CI 0.489-1.738; P = 0.802, respectively). Conclusions: Our study indicates that SPTCL is predominantly an indolent lymphoma associated with long-term survival irrespective of stage and chemotherapy. A conservative therapeutic approach appears to be more appropriate than intensive therapeutic approach in most patients. A risk stratification algorithm is needed to determine the therapeutic intensity.

7575 Background: Extranodal natural killer/T-cell lymphoma (ENKTL), nasal type, is a rare and aggressive Epstein-Barr virus driven lymphoma, which is most prevalent in East Asia and Latin America. There have been very few large studies outside of Asia. Therapeutic and survival outcomes have not been well characterized in the US. Methods: The National Cancer Database was queried for patients who were diagnosed at aged ≥18 years between 2004 and 2019. Patients who were lost to follow-up were excluded. Kaplan-Meier and multivariate Cox regression analyses were performed. Results: The cohort consists of 2,036 evaluable patients with 68% males, 74% Caucasian, 22% Hispanic Caucasian and 9% African American. The median age at diagnosis was 54 (18-90) years. The median follow up was 71 months (95% CI 66.8-75.7). Early-stage disease (I and II) was reported in 64% while advanced stage disease (III and IV) constituted 36%. Treatment groups include chemotherapy alone (29%), radiation alone (10%), combined modality therapy (CMT-chemoradiation) (42%). The median overall survival (OS) for the whole cohort was 27 months (95% CI 20.6-33.7). Median OS was better in patients with early stage compared to advanced stage disease (90 vs. 6 months, P < 0.001). Among therapeutic groups in early-stage disease, CMT (N = 616) had significantly better median OS than radiation alone (N = 152) or chemotherapy alone (N = 168) (194 vs. 34 vs. 14 months, P < 0.001). No significant difference was seen between radiation alone and chemotherapy alone (P = 0.617). Among patients treated with CMT, chemotherapy-first CMT (N = 134) had better OS than radiation-first CMT (N = 347) (median OS not reached vs. 194 months, P = 0.017). In the advanced stage disease, chemotherapy-treated patients (N = 418) had better median OS compared to patients who did not receive chemotherapy (N = 103) (7.6 vs 1.3 months, P < 0.001). Among patients who received chemotherapy, patients consolidated with SCT (N = 59) had better median OS compared to the patients who received chemotherapy only (N = 353) (63 vs 6 months, P < 0.001) In multivariate analysis, factors associated with worse OS were age (HR 1.021 95% CI 1.015-1.026; P < 0.001) and B-symptoms (HR 1.463 95% CI 1.276-1.678; P < 0.001). Whereas factors associated with better OS were early stage (HR 0.450 95% CI 0.387-0.524, P < 0.001), radiation therapy (HR 0.526 95% CI 0.458-0.603, P < 0.001) and chemotherapy (HR 0.546 95% CI 0.473-0.630, P < 0.001). Conclusions: The study represents one of the largest studies on ENKTL in the US. Early-stage disease is highly curable with CMT with chemotherapy-first sequencing being superior to radiation-first sequencing. Advanced stage disease is associated with extremely poor prognosis overall but is associated with a significant improvement in OS with consolidative SCT with possible role of consolidative RT in advanced stage.

6539 Background: HER2-enriched breast cancer (estrogen and progesterone receptors negative and HER2-positive) has no worse prognosis than other breast cancers if it is treated with HER2-targeted therapy. Medicaid expansion under the Affordable Care Act (ACA) has been shown to be associated with improved access to care and outcomes for many cancers, but its impact on care for HER2-enriched breast cancer is unknown. To fill this gap, we examined the association of Medicaid expansion with receipt of guideline-concordant treatment, time to treatment, and survival among newly diagnosed nonelderly women with HER2-enriched breast cancer. Methods: Women aged 18-62 years newly diagnosed with HER2-enriched breast cancer between 2010 and 2018 were identified from the National Cancer Database. Our primary outcomes included receipt of stage-based guideline-concordant treatment, initiation of treatment <60 days, and stage-specific 2-year overall survival. A difference-in-differences (DD) approach compared outcome changes following the expansion in Medicaid expansion vs. non-expansion states. A linear probability model estimated treatment outcome, and a flexible parametric survival model evaluated survival. All models were clustered at the state level and adjusted for age group, race/ethnicity, rurality of residence, zip code-level income, comorbidity, and diagnosis year. Results: A total of 31,354 patients with HER2-enriched breast cancer were included, including 19,255 in expansion states and 12,099 in non-expansion states. Compared to patients in expansion states, patients in non-expansion states were more likely to be racial/ethnic minorities, uninsured, and diagnosed at late-stage. Medicaid expansion was not significantly associated with changes in receipt of surgery for stage I-III disease but was associated with an increase of 4.42 percentage points (ppt, 95% CI: 0.09, 8.74) in receipt of chemotherapy/targeted therapy for stage IV disease, with an increase from 90.4% pre-expansion to 92.8% post-expansion in expansion states and a decrease from 93.7% to 91.9% in non-expansion states. Medicaid expansion was also significantly associated with a 2.41 ppt increase in initiating guideline-concordant treatment within 60 days (95% CI: 0.66, 4.17; 83.5% to 82.5% in expansion states vs. 86.6% to 83.7% in non-expansion states), and a 1.18 ppt increase in two-year survival rate (95% CI: 0.03, 2.33; 94.0% to 94.9% in expansion states vs. 94.3% to 94.1% in non-expansion states). The increase in two-year survival associated with Medicaid expansion was most prominent for stage III patients (DD=3.63 ppt; 95% CI: 0.64, 6.62). Conclusions: Medicaid expansion was associated with increased receipt of timely treatment and improved 2-year survival among nonelderly women newly diagnosed with HER2-enriched breast cancer.

5077 Background: In the phase 3 PRESTO study, intensified androgen deprivation therapy (ADT) with apalutamide (Apa) with or without abiraterone acetate plus prednisone (AAP), administered for a finite treatment period of 52 weeks, prolonged prostate-specific antigen progression-free survival (PSA PFS) in pts with high-risk biochemically relapsed prostate cancer (BRPC). We evaluated the association between PSA nadir within 3 months of treatment initiation with subsequent PSA PFS in this study. Methods: PRESTO is a randomized phase 3, open-label trial in pts with BRPC following radical prostatectomy (RP) and PSA doubling time (PSADT) ≤ 9 months, without distant metastases on conventional imaging (NCT03009981). Pts were randomized 1:1:1 to receive a finite 52-week treatment course with ADT, ADT + Apa, or ADT + Apa + AAP, stratified by PSADT (< 3 vs 3–9 months), with post-treatment follow-up. The association between PSA nadir within the first three months on treatment with subsequent PSA PFS was analyzed in a post hoc fashion. Results: 504 pts were randomized to ADT alone (N = 167), ADT + Apa (N = 168) or ADT + Apa + AAP (N = 169). 463 pts were evaluable for PSA nadir at 3 months. Across the three treatment arms, a PSA nadir of less than 0.1, between 0.1 – 0.2, and ≥ 0.2 ng/mL within the first three months of treatment was observed in 86.3%, 4.4%, and 9.3% of patients, respectively. A PSA nadir of < 0.2 ng/mL was reached within 3 months of treatment initiation in 79.8%, 96.9%, and 95.0% of pts randomized to the ADT, ADT + Apa, and ADT + Apa + AAP arms, respectively. The association between time to PSA nadir and subsequent PSA PFS was -0.30 (standard error = 0.03, Kendall’s tau modified for bivariate censoring), and median time to PSA nadir was 2.0 months (interquartile range 1.12 – 4.76 months). Failure to reach a PSA nadir < 0.2 ng/mL within the first three months of treatment was associated with a significantly shorter PSA PFS compared to pts with a PSA nadir ≤ 0.1 ng/mL (median PSA PFS of 13.9 vs. 22.8 months from 3 months post-treatment initiation; hazard ratio = 5.60, 95% CI: 3.58 – 8.75, p < 0.0001). There was also a significant difference in PSA PFS in those with a three-month PSA nadir between 0.1 – 0.2 vs ≤ 0.1 ng/mL (median PSA PFS 17.4 vs 22.8 months, HR = 2.63, 95:CI: 1.49 – 4.63, p = 0.0008). Conclusions: Using a landmark analysis at 3 months, a failure to reach PSA nadir less than 0.1 ng/mL within three months following initiation of ADT in BRPC is associated with shorter time to subsequent progression following treatment discontinuation. Follow-up is ongoing to integrate genomic profiling of primary prostate cancer tissues and whole blood RNA in pts with suboptimal PSA nadir to identify potential markers of relative androgen pathway inhibitor resistance. Clinical trial information: NCT03009981 .

1509 Background: Medicaid expansion under the Affordable Care Act has been shown to increase insurance coverage and early-stage cancer diagnoses for young adults (YAs), the age group with the highest uninsured rate. We examined whether Medicaid expansion was associated with increased receipt of timely, guideline-concordant treatment and survival among YA women newly diagnosed with breast cancer, the most common YA cancer diagnosis. Methods: Using the National Cancer Database, we identified 51,675 women aged 18-39 years who were diagnosed with breast cancer in 2011-2018. We applied the difference-in-differences (DD) method to estimate outcome changes pre vs. post Medicaid expansion, in expansion- vs. non-expansion states. Linear probability models estimated associations of Medicaid expansion with receipt of guideline-concordant treatment – including any endocrine therapy among women with ER-positive or PR-positive breast cancer, and any chemotherapy or targeted therapy among women with ER-negative and PR-negative breast cancer – and initiation of guideline-concordant treatment (surgery, chemotherapy, or targeted therapy for stage I-III diagnoses, and systemic therapy for stage IV diagnoses) <60 days after diagnosis. Flexible parametric survival models were used to estimate 2-year overall survival. DD models also adjusted for age, race/ethnicity, rurality, zip code-level income, comorbidity, and diagnosis year, with standard errors clustered at the state level. Analyses were stratified by stage at diagnosis (stage I-III vs. IV). Results: Of the subset of women with stage I-III ER-positive or PR-positive breast cancer, the percentage receiving endocrine therapy increased in expansion states (85.20% pre-expansion to 86.46% post-expansion), but decreased in non-expansion states (84.32% to 82.79%), resulting in a net increase of 2.42 percentage points (ppt; 95% CI = 0.56 to 4.28) associated with Medicaid expansion in the adjusted DD model. Among all women with stage I-III breast cancer, the percentage with treatment initiation <60 days after diagnosis decreased less in expansion states (84.10% pre-expansion to 82.36% post-expansion) than in non-expansion states (86.95% to 83.98%), resulting in a net reduction of 1.61 ppt (95% CI = 0.05 to 3.18) in treatment delays associated with Medicaid expansion. Notably, the 2-year overall survival increased in expansion states (96.84% pre-expansion to 96.99% post-expansion), but decreased in non-expansion states (97.24% to 96.30%), resulting in a net survival increase of 1.00 ppt (95% CI = 0.21 to 1.79) associated with Medicaid expansion. Conclusions: Among YA women with stage I-III breast cancer, Medicaid expansion was associated with increased receipt of guideline-concordant treatment, reduced delays in treatment initiation, and improved 2-year survival.

Succinate dehydrogenase (SDH) is a key enzyme in the tricarboxylic acid (TCA) cycle, as well as Complex II of the electron transport chain (ETC). In the SDH reaction, succinate is oxidized to fumarate in the TCA cycle, producing FADH2 contributing to the proton gradient that drives the reduction of ubiquinone to ubiquinol in the ETC. Thus, measurement of the maximum velocity of the SDH reaction (SDHmax) provides insight into both TCA cycle and ETC contributions to the maximum respiratory capacity of mitochondria. The goal of the present study was to use a quantitative histochemical technique, which we previously developed in skeletal muscle fibers, to quantify the SDHmax in permeabilized (45 μg/mL saponin) cardiomyocytes isolated from male Sprague-Dawley rats. In the SDH reaction, the oxidation of succinate (80 mM succinate; determined to be the maximum substrate concentration) to fumarate is coupled to the reduction of nitroblue tetrazolium (NBT; 1.5 mM) to its diformazan (NBTdfz) using 1-methoxyphenazine methosulphate (mPMS; 1 mM) as an exogenous electron carrier and azide (0.75 mM) to inhibit Complex IV. The progressive accumulation of NBTdfz as the reaction proceeds is measured by repeated densitometric (at 570 nm, the peak absorbance wavelength for NBTdfz) measurements. The optical density (OD) measurements are converted to mM fumarate using the Beer-Lambert-Bouger equation based on pathlength for light absorbance and the molar extinction coefficient for NBTdfz. Importantly, the pathlength for light absorbance must be controlled. In cross-sections of skeletal muscle fibers, pathlength was controlled by cryosectioning at 6 μm. In the present study, pathlength was controlled by optical sectioning using a confocal microscope. The isolated cardiomyocytes were imaged in 3D using a Nikon Eclipse A1 laser scanning confocal system with a ×40x/1.3 NA oil-immersion lens with an optical slice set at 0.5 μm. Changes in OD within a series of 10 optical slices were measured every 15 s over a 5 min period and expressed as mM fumarate/min using the Beer-Lambert-Bouger equation. We found that the SDH reaction was linear across 5 min, and that the change in OD was consistent throughout all 10 optical slices within a cardiomyocyte, suggesting that NBTdfz accumulates in the cytoplasm. Our results confirm that this assay of SDHmax is reproducible in cardiomyocytes and offers a single cell alternative to high-resolution respirometry. The ability to measure SDHmax in single cells is in contrast to respirometry, which only measures the average O2 consumption of aggregates of cells (isolated or in tissue). Thus, a direct measurement of SDHmax can provide valuable physiological insight into variation in mitochondrial function across a population of cardiomyocytes, e.g., as might occur with ischemic injury. Supported by the Mayo Clinic This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.