Community Academic Profiles - Faculty & Researchers - Stanford Medicine

Bio

Honors & Awards

Sanjiv Sam Gambhir?Philips Fellow, Stanford Medicine - PHIND (2021)
The Alavi-Mandell Award - 2020, Society of Nuclear Medicine and Molecular Imaging (SNMMI) (2020)
Scholarship for Training Course on Experimental Modeling of Human Cancer, The Jackson Laboratory (2019)
Student Travel Award, Radiological Society of North America (RSNA) (2018)
Scholar-in-Training Award, American Association for Cancer Research (AACR) (2018)
Graduate School Research Grant Competition Award, University of Wisconsin-Madison Graduate School (2018)

Professional Education

Doctor of Philosophy (Ph.D.), University of Wisconsin-Madison, Clinical Investigation (2020)
Master of Science (MS), University of Wisconsin-Madison, Biotechnology (2014)
Bachelor of Technology (B.Tech), Uttar Pradesh Technical University, Biotechnology (2010)

Stanford Advisors

Tanya Stoyanova, Postdoctoral Faculty Sponsor

Publications

All Publications

Measuring Glucose Uptake in Primary Invasive Breast Cancer Using Simultaneous Time-of-Flight Breast PET/MRI: A Method Comparison Study with Prone PET/CT. Radiology. Imaging cancer Fowler, A. M., Kumar, M. n., Bancroft, L. H., Salem, K. n., Johnson, J. M., Karow, J. n., Perlman, S. B., Bradshaw, T. J., Hurley, S. A., McMillan, A. B., Strigel, R. M. 2021; 3 (1): e200091
Abstract

To compare the measurement of glucose uptake in primary invasive breast cancer using simultaneous, time-of-flight breast PET/MRI with prone time-of-flight PET/CT.In this prospective study, women with biopsy-proven invasive breast cancer undergoing preoperative breast MRI from 2016 to 2018 were eligible. Participants who had fasted underwent prone PET/CT of the breasts approximately 60 minutes after injection of 370 MBq (10 mCi) fluorine 18 fluorodeoxyglucose (18F-FDG) followed by prone PET/MRI using standard clinical breast MRI sequences performed simultaneously with PET acquisition. Volumes of interest were drawn for tumors and contralateral normal breast fibroglandular tissue to calculate standardized uptake values (SUVs). Spearman correlation, Wilcoxon signed ranked test, Mann-Whitney test, and Bland-Altman analyses were performed.Twenty-three women (mean age, 50 years; range, 33-70 years) were included. Correlation between tumor uptake values measured with PET/MRI and PET/CT was strong (r s = 0.95-0.98). No difference existed between modalities for tumor maximum SUV (SUVmax) normalized to normal breast tissue SUVmean (normSUVmax) (P = .58). The least amount of measurement bias was observed with normSUVmax, +3.86% (95% limits of agreement: -28.92, +36.64).These results demonstrate measurement agreement between PET/CT, the current reference standard for tumor glucose uptake quantification, and simultaneous time-of-flight breast 18F-FDG PET/MRI.Keywords: Breast, Comparative Studies, PET/CT, PET/MR Supplemental material is available for this article. � RSNA, 2021See also the commentary by Mankoff and Surti in this issue.

View details for DOI 10.1148/rycan.2021200091

View details for PubMedID 33575660

View details for PubMedCentralID PMC7850238
Recent Advances in Imaging Steroid Hormone Receptors in Breast Cancer JOURNAL OF NUCLEAR MEDICINE Kumar, M., Salem, K., Tevaarwerk, A. J., Strigel, R. M., Fowler, A. M. 2020; 61 (2): 172?76
Abstract

Estrogen receptor (ER) and progesterone receptor (PR) are important prognostic and predictive biomarkers in breast cancer. PET using ER- and PR-specific radioligands enables a whole-body, noninvasive assessment of receptor expression. Recent investigations of ER imaging with 18F-fluoroestradiol have focused on diagnosing ER-positive metastatic disease, optimizing ER-targeted drug dosage, and predicting endocrine therapy benefit. Studies of PR imaging with 18F-fluorofuranyl norprogesterone have investigated how imaging changes in PR expression as a downstream target of ER activation may reflect an early response to ER-targeted therapy. This focused review highlights recent achievements in preclinical and clinical imaging of ER and PR in breast cancer.

View details for DOI 10.2967/jnumed.119.228858

View details for Web of Science ID 000512119600008

View details for PubMedID 31732674
Progesterone Receptor Gene Variants in Metastatic Estrogen Receptor Positive Breast Cancer HORMONES & CANCER Fowler, A. M., Salem, K., DeGrave, M., Ong, I. M., Rassman, S., Powers, G. L., Kumar, M., Michel, C. J., Mahajan, A. M. 2020; 11 (2): 63?75
Abstract

Tumor mutations in the gene encoding estrogen receptor alpha (ESR1) have been identified in metastatic breast cancer patients with endocrine therapy resistance. However, relatively little is known about the occurrence of mutations in the progesterone receptor (PGR) gene in this population. The study objective was to determine the frequency and prognostic significance of tumor PGR mutations for patients with estrogen receptor (ER)-positive metastatic breast cancer. Thirty-five women with metastatic or locally recurrent ER+ breast cancer were included in this IRB-approved, retrospective study. Targeted next-generation sequencing of the PGR gene was performed on isolated tumor DNA. Associations between mutation status and clinicopathologic factors were analyzed as well as overall survival (OS) from time of metastatic diagnosis. The effect of the PGR variant Y890C (c.2669A>G) identified in this cohort on PR transactivation function was tested using ER-PR- (MDA-MB-231), ER+PR+ (T47D), and ER+PR- (T47D PR KO) breast cancer cell lines. There were 71 occurrences of protein-coding PGR variants in 67% (24/36; 95% CI 49-81%) of lesions. Of the 49 unique variants, 14 are single nucleotide polymorphisms (SNPs). Excluding SNPs, the median OS of patients with PGR variants was 32�months compared to 79�months with wild-type PGR (p?=?0.42). The most frequently occurring (4/36 lesions) non-SNP variant was Y890C. Cells expressing Y890C had reduced progestin-stimulated PR transactivation compared to cells expressing wild-type PR. PGR variants occur frequently in ER+ metastatic breast cancer. Although some variants are SNPs, others are predicted to be functionally deleterious as demonstrated with Y890C PR.

View details for DOI 10.1007/s12672-020-00377-3

View details for Web of Science ID 000507348600001

View details for PubMedID 31942683

View details for PubMedCentralID PMC7152560
Longitudinal molecular imaging of progesterone receptor reveals early differential response to endocrine therapy in breast cancer with an activating ESR1 mutation. Journal of nuclear medicine : official publication, Society of Nuclear Medicine Kumar, M. n., Salem, K. n., Jeffery, J. J., Yan, Y. n., Mahajan, A. M., Fowler, A. M. 2020
Abstract

Activating mutations in the estrogen receptor (ER) alpha gene (ESR1) result in constitutive transcriptional activity in the absence of estrogen and is associated with endocrine resistance in metastatic ER+ breast cancer. It is not known how activating ESR1 mutations may alter the predictive values of molecular imaging agents for endocrine therapy response. This study investigated the effect of an activating ESR1 mutation on pre-treatment 18F-fluoroestradiol (18F-FES) uptake and early assessment of endocrine therapy response using 18F-FDG and 18F-fluorofuranylnorprogesterone (18F-FFNP) PET/CT imaging of tumor glucose metabolism and progesterone receptor (PR) expression, respectively. Methods: ER+PR+ T47D breast cancer cells expressing wild-type (WT)-ER or an activating ESR1 mutation, Y537S-ER, were used to generate tumor xenografts in ovariectomized female immunodeficient mice supplemented with 17?-estradiol. Tumor growth curves were determined in the presence or absence of estrogen and for ethanol vehicle control or fulvestrant treatment, a selective ER degrader. Pre-treatment 18F-FES uptake was compared between Y537S-ER and WT-ER tumors. Longitudinal PET/CT imaging with 18F-FFNP and 18F-FDG was performed before and 7 to 9 days after starting endocrine therapy with fulvestrant. Radiopharmaceutical uptake in Y537S-ER and WT-ER tumors were compared between baseline and follow-up scans. Statistical significance was determined using paired t-tests for longitudinal imaging and two-way ANOVA for 18F-FFNP tissue biodistribution assay. Results: Y537S-ER xenografts showed estrogen-independent growth, while WT-ER tumors grew only with estrogen. Fulvestrant treatment for 28 days significantly reduced tumor volumes for WT-ER, but only stabilized volumes for Y537S-ER. Baseline 18F-FES uptake was not significantly different between WT-ER and Y537S-ER tumors. Fulvestrant treatment induced a similar early metabolic response for both WT-ER and Y537S-ER tumors. 18F-FFNP uptake in WT-ER tumors was significantly reduced after 7 days of fulvestrant treatment; however, this reduction did not occur in Y537S-ER tumors which showed no significant change between baseline and follow-up PET/CT. Conclusion: Molecular imaging of PR expression dynamics could be a non-invasive approach for early identification of reduced effectiveness of endocrine therapy resulting from activating ESR1 mutations.

View details for DOI 10.2967/jnumed.120.249508

View details for PubMedID 32859700
F-18-Fluoroestradiol PET Imaging of Activating Estrogen Receptor-alpha Mutations in Breast Cancer JOURNAL OF NUCLEAR MEDICINE Kumar, M., Salem, K., Michel, C., Jeffery, J. J., Yan, Y., Fowler, A. M. 2019; 60 (9): 1247?52
Abstract

The purpose of this study was to determine the effect of estrogen receptor-? gene (ESR1) mutations at the tyrosine (Y) 537 amino acid residue within the ligand binding domain on 18F-fluoroestradiol (18F-FES) binding and in vivo tumor uptake compared with wild-type (WT)-estrogen receptor ? (ER). Methods: ER-negative MDA-MB-231 breast cancer cells were used to generate stable cell lines that express WT-ER, Y537S, or Y537C mutant ER. Receptor expression and localization were confirmed by Western blot and immunofluorescence, respectively. ER transcriptional function was measured using an estrogen response element-luciferase reporter gene assay and quantitative polymerase chain reaction analysis of ER-regulated endogenous target genes. Saturation binding and competition assays were performed to determine equilibrium dissociation constant (Kd) and half maximal inhibitory concentration (IC50) values. 18F-FES uptake was measured in tumor xenografts grown in female athymic nude mice by small-animal PET/CT imaging and tissue biodistribution using 5.55 MBq (150 ?Ci) of 18F-FES. A 10-fold-lower injected dose of 0.555 MBq (15 ?Ci) of 18F-FES was also used for tissue biodistribution. Statistical significance was determined using ANOVA. Results: Y537S and Y537C mutations resulted in increased ER transcriptional activity in the absence of estrogen compared with WT-ER (11.48 � 2.42 fold; P = 0.0002, and 5.89 � 0.94 fold; P = 0.04, respectively). Constitutive ER activation of two target genes (PGR and TFF1) in the absence of estrogen was also observed in Y537S- and Y537C-ER cells compared with WT-ER. Kd values for 18F-FES were 0.98 � 0.54 nM for Y537S-ER (P = 0.27) and 0.24 � 0.03 nM for Y537C-ER (P = 0.95) compared with 0.07 � 0.03 nM for WT-ER. IC50 values were 0.22 � 0.09 nM for Y537S-ER (P = 0.97), 0.18 � 0.09 nM for Y537C-ER (P = 0.99), and 0.19 � 0.11 nM for WT-ER. Tumor xenografts expressing Y537S-ER (mean percentage injected dose per gram, 1.45 � 0.06; P = 0.77) and Y537C-ER (2.09 � 0.20; P = 0.21) had similar 18F-FES uptake compared with WT-ER (1.68 � 0.12). Comparable 18F-FES uptake between Y537S-, Y537C-, and WT-ER xenografts was also observed using a 10-fold-lower injected dose with the tissue biodistribution assay. Conclusion: Since tumoral uptake of 18F-FES is not significantly impacted by Y537S-ER or Y537C-ER mutations, the potential diagnostic utility of 18F-FES PET imaging is expected to be equally valid for patients with or without these activating ESR1 mutations.

View details for DOI 10.2967/jnumed.118.224667

View details for Web of Science ID 000484372100017

View details for PubMedID 30850489

View details for PubMedCentralID PMC6735277
Sensitivity and Isoform Specificity of F-18-Fluorofuranylnorprogesterone for Measuring Progesterone Receptor Protein Response to Estradiol Challenge in Breast Cancer JOURNAL OF NUCLEAR MEDICINE Salem, K., Kumar, M., Yan, Y., Jeffery, J. J., Kloepping, K. C., Michel, C. J., Powers, G. L., Mahajan, A. M., Fowler, A. M. 2019; 60 (2): 220?26
Abstract

The purpose of this study was to evaluate the ability of 21-18F-fluoro-16?,17?-[(R)-(1'-?-furylmethylidene)dioxy]-19-norpregn-4-ene-3,20-dione (18F-FFNP) to measure alterations in progesterone receptor (PR) protein level and isoform expression in response to estradiol challenge. Methods: T47D human breast cancer cells and female mice-bearing T47D tumor xenografts were treated with 17?-estradiol (E2) to increase PR expression. 18F-FFNP uptake was measured using cell uptake and tissue biodistribution assays. MDA-MB-231 breast cancer clonal cell lines were generated that express the A or B isoforms of human PR. PR protein levels, transcriptional function, and subcellular localization were determined. In vitro 18F-FFNP binding was measured via saturation and competitive binding curves. In vivo 18F-FFNP uptake was measured using tumor xenografts and positron emission tomography. Statistical significance was determined using analysis of variance and t-tests. Results: After 48 and 72 h of E2, 18F-FFNP uptake in T47D cells was maximally increased compared to both vehicle and 24 h E2 treatment (p<0.0001 vs ethanol; P = 0.02 and P = 0.0002 vs 24 h for 48 and 72 h, respectively). T47D tumor xenografts in mice treated with 72 h E2 had maximal 18F-FFNP uptake compared to ethanol-treated mice (11.3�1.4 vs 5.2�0.81 %ID/g; P = 0.002). Corresponding tumor-to-muscle uptake ratios were 4.1�0.6, 3.9�0.5, and 2.3�0.4 for 48 h E2, 72 h E2, and ethanol-treated mice, respectively. There was no significant preferential 18F-FFNP binding or uptake by PR-A versus PR-B in the PR isoform-specific cell lines and tumor xenografts. Conclusion:18F-FFNP is capable of measuring estrogen-induced shifts in total PR expression in human breast cancer cells and tumor xenografts with equivalent isoform binding.

View details for DOI 10.2967/jnumed.118.211516

View details for Web of Science ID 000457479800020

View details for PubMedID 30030339
F-18-16 alpha-17 beta-Fluoroestradiol Binding Specificity in Estrogen Receptor-Positive Breast Cancer RADIOLOGY Salem, K., Kumar, M., Powers, G. L., Jeffery, J. J., Yan, Y., Mahajan, A. M., Fowler, A. M. 2018; 286 (3): 868?76
Abstract

Purpose To determine the binding specificity of 18F-16?-17?-fluoroestradiol (FES) in estrogen receptor (ER) ?-positive breast cancer cells and tumor xenografts. Materials and Methods Protocols were approved by the office of biologic safety and institutional animal care and use committee. By using ER-negative MDA-MB-231 breast cancer cells, clonal lines were created that expressed either wild-type (WT; 231 WT ER) or G521R mutant ER? (231 G521R ER), which is defective in estradiol binding. ER? protein levels, subcellular localization, and transcriptional function were confirmed. FES binding was measured by using an in vitro cell uptake assay. In vivo FES uptake was measured in tumor xenografts by using small-animal positron emission tomographic/computed tomographic imaging of 24 mice (17 WT ER tumors, nine mutant G521R ER tumors, eight MDA-MB-231 tumors, and four MCF-7 ER-positive tumors). Statistical significance was determined by using Mann-Whitney (Wilcoxon rank sum) test. Results ER? transcriptional function was abolished in the mutated 231 G521R ER cells despite appropriate receptor protein expression and nuclear localization. In vitro FES binding in the 231 G521R ER cells was reduced to that observed in the parental cells. Similarly, there was no significant FES uptake in the 231 G521R ER xenografts (percent injected dose [ID] per gram, 0.49 � 0.042), which was similar to the negative control MDA-MB-231 xenografts (percent ID per gram, 0.42 � 0.051; P = .20) and nonspecific muscle uptake (percent ID per gram, 0.41 � 0.0095; P = .06). Conclusion This study showed that FES retention in ER-positive breast cancer is strictly dependent on an intact receptor ligand-binding pocket and that FES binds to ER? with high specificity. These results support the utility of FES imaging for assessing tumor heterogeneity by localizing immunohistochemically ER-positive metastases that lack receptor-binding functionality. � RSNA, 2017 Online supplemental material is available for this article.

View details for DOI 10.1148/radiol.2017162956

View details for Web of Science ID 000425583200015

View details for PubMedID 28956736

View details for PubMedCentralID PMC5882239
Determination of binding affinity of molecular imaging agents for steroid hormone receptors in breast cancer. American journal of nuclear medicine and molecular imaging Salem, K. n., Kumar, M. n., Kloepping, K. C., Michel, C. J., Yan, Y. n., Fowler, A. M. 2018; 8 (2): 119?26
Abstract

16?-[18F]Fluoro-17?-estradiol ([18F]FES) and 21-[18F]-Fluoro-16?,17?-[(R)-(1'-?-furylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione ([18F]FFNP) are being investigated as imaging biomarkers for breast cancer patients. Quantitative positron emission tomography (PET) reflects both total receptor content and binding affinity. To study factors that may alter radiopharmaceutical binding and impact PET accuracy, assays that can separate receptor amount from binding affinity are needed. The study purpose was to quantify the binding parameters of [18F]FES and [18F]FFNP in breast cancer. Estrogen receptor-alpha (ER) and progesterone receptor (PR) positive breast cancer cell lines (MCF-7 and T47D) were used to measure [18F]FES and [18F]FFNP binding parameters via saturation and competitive binding curves. The equilibrium dissociation constant (Kd) and total receptor density (Bmax) were determined using nonlinear regression of the saturation binding curves. Half-maximal inhibitory concentration (IC50) was determined using nonlinear regression of the competitive binding curves. Linear correlation between increasing cell number and tracer uptake was observed for both [18F]FES and [18F]FFNP (R2=0.99 and 0.91, respectively). Using [18F]FES, the Kd for ER in MCF-7 cells was 0.13�0.02 nM with a Bmax of 1901�89.3 fmol/mg protein and IC50 of 0.085 nM (95% CI: 0.069-0.104 nM). Using [18F]FFNP, the Kd for PR in T47D cells was 0.41�0.05 nM with a Bmax of 1984�75.6 fmol/mg protein and IC50 of 2.6 nM (95% CI: 2.0-3.4 nM). The ligand binding function of ER and PR can be quantified using [18F]FES and [18F]FFNP and are comparable to previous studies using tritiated radioligands. [18F]FES and [18F]FFNP can be used in cell-based assays to quantify receptor-radioligand binding affinity, which cannot be obtained from a single PET examination.

View details for PubMedID 29755845

View details for PubMedCentralID PMC5944827
Dendrimer-stabilized smart-nanoparticle (DSSN) platform for targeted delivery of hydrophobic antitumor therapeutics PHARMACEUTICAL RESEARCH Tekade, R. K., Tekade, M., Kumar, M., Chauhan, A. S. 2015; 32 (3): 910?28
Abstract

To formulate dendrimer-stabilized smart-nanoparticle (DSSN; pD-ANP-f) for the targeted delivery of the highly hydrophobic anticancer drug, Paclitaxel (PTXL).The developed nanoformulations were evaluated for particle size, surface-charge, loading efficiency, particle density, in-vitro drug release, SEM/TEM, cytotoxicity assay, fluorescence uptake, HPLC quantitative cell uptake assay, flow cytometry, tubulin polymerization, and stability assessments.The developed pD-ANP-f nanoformulation (135.17 � 7.39 nm; -2.05 � 0.37 mV and 80.11 � 4.39% entrapment) exhibited a pH-dependent drug release; remained stable in physiological pH, while rapid releasing PTXL under tumorous environment (pH 5.5). The cytotoxicity assay performed in cervical, breast, blood, and liver cancer cell lines showed pD-ANP-f to be strongly suppressing the growth of cancer cells. We investigated the fluorescence based intracellular trafficking and HPLC based cellular uptake of nanoformulated drug and the result indicates higher cellular uptake of pD-ANP-f compared to other formulations. pD-ANP-f prominently induced apoptosis (73.11 � 3.84%) and higher polymerization of tubulins (59.73 � 6.22%). DSSN nanoformulation was found to be extremely biocompatible (<1% hemolytic) compared to naked PTXL (19.22 � 1.01%) as well as PTXL-dendrimer nanocomplex (8.29 � 0.71%).DSSN strategy is a novel and promising platform for biomedical applications that can be effectively engaged for the delivery of drug/gene/siRNA targeting.

View details for DOI 10.1007/s11095-014-1506-0

View details for Web of Science ID 000349357300014

View details for PubMedID 25205461

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