Instructor, Radiation Oncology - Radiation Therapy
Honors & Awards
Martin Brown Award for Excellence in Radiation Sciences, Dept. of Radiation Oncology, Stanford University (2018)
AACR Travel Grant, Proteintech-AACR (2017)
Young Researcher Awardee for 64th Lindau Nobel Laureate Meeting, Lindau Nobel Laureate Meetings Foundation, Germany (07/2014)
Fulbright Doctoral Research Fellowship (2013-14), Fulbright, USA (07/2013)
Senior Research Fellowship, Council for Scientific and Industrial Research, Govt. of India (08/2012 to 02/2015)
Young Researcher Award, International Symposium on “Recent Advances in Cancer Research: Therapeutics to Chemoprevention (02/2012)
Junior Research Fellowship, Council for Scientific and Industrial Research, Govt. of India (06/2009 to 06/2011)
Junior Research Fellowship, Department of Biotechnnology, Govt. of India (04/2009)
Galectin-1-driven T cell exclusion in the tumor endothelium promotes immunotherapy resistance.
The Journal of clinical investigation
Immune checkpoint inhibitors (ICIs), although promising, have variable benefit in head and neck cancer (HNC). We noted that tumor galectin-1 (Gal1) levels were inversely correlated with treatment response and survival in patients with HNC who were treated with ICIs. Using multiple HNC mouse models, we show that tumor-secreted Gal1 mediates immune evasion by preventing T cell migration into the tumor. Mechanistically, Gal1 reprograms the tumor endothelium to upregulate cell-surface programmed death ligand 1 (PD-L1) and galectin-9. Using genetic and pharmacological approaches, we show that Gal1 blockade increases intratumoral T cell infiltration, leading to a better response to anti-PD1 therapy with or without radiotherapy. Our study reveals the function of Gal1 in transforming the tumor endothelium into an immune-suppressive barrier and that its inhibition synergizes with ICIs.
View details for DOI 10.1172/JCI129025
View details for PubMedID 31710313
- The Immune Subtypes and Landscape of Squamous Cell Carcinoma CLINICAL CANCER RESEARCH 2019; 25 (12): 3528–37
- Targeting galectin-1 to improve therapeutic efficacy in head and neck cancers AMER ASSOC CANCER RESEARCH. 2017
Hypoxia induces triglycerides accumulation in prostate cancer cells and extracellular vesicles supporting growth and invasiveness following reoxygenation.
2015; 6 (26): 22836-22856
Hypoxia is an independent prognostic indicator of poor outcome in several malignancies. However, precise mechanism through which hypoxia promotes disease aggressiveness is still unclear. Here, we report that under hypoxia (1% O2), human prostate cancer (PCA) cells, and extracellular vesicles (EVs) released by these cells, are significantly enriched in triglycerides due to the activation of lipogenesis-related enzymes and signaling molecules. This is likely a survival response to hypoxic stress as accumulated lipids could support growth following reoxygenation. Consistent with this, significantly higher proliferation was observed in hypoxic PCA cells following reoxygenation associated with rapid use of accumulated lipids. Importantly, lipid utilization inhibition by CPT1 inhibitor etomoxir and shRNA-mediated CPT1-knockdown significantly compromised hypoxic PCA cell proliferation following reoxygenation. Furthermore, COX2 inhibitor celecoxib strongly reduced growth and invasiveness following hypoxic PCA cells reoxygenation, and inhibited invasiveness induced by hypoxic PCA EVs. This establishes a role for COX2 enzymatic products in the enhanced PCA growth and invasiveness. Importantly, concentration and loading of EVs secreted by PCA cells were significantly compromised under delipidized serum condition and by lipogenesis inhibitors (fatostatin and silibinin). Overall, present study highlights the biological significance of lipid accumulation in hypoxic PCA cells and its therapeutic relevance in PCA.
View details for PubMedID 26087400
Silibinin Preferentially Radiosensitizes Prostate Cancer by Inhibiting DNA Repair Signaling.
Molecular cancer therapeutics
Radiotherapy, a frequent mode of cancer treatment, is often restricted by dose-related toxicity and development of therapeutic resistance. To develop a novel and selective radiosensitizer, we studied the radiosensitizing effects and associated mechanisms of silibinin in prostate cancer. The radiosensitizing effect of silibinin with ionizing radiation (IR) was assessed on radioresistant prostate cancer cell lines by clonogenic, cell cycle, cell death, and DNA repair assays. Tumor xenograft growth, immunohistochemical (IHC) analysis of tumor tissues, and toxicity-related parameters were measured in vivo. Silibinin (25 μmol/L) enhanced IR (2.5-10 Gy)-caused inhibition (up to 96%, P < 0.001) of colony formation selectively in prostate cancer cells, and prolonged and enhanced IR-caused G2-M arrest, apoptosis, and ROS production. Mechanistically, silibinin inhibited IR-induced DNA repair (ATM and Chk1/2) and EGFR signaling and attenuated the levels of antiapoptotic proteins. Specifically, silibinin suppressed IR-induced nuclear translocation of EGFR and DNA-PK, an important mediator of DSB repair, leading to an increased number of γ-H2AX (ser139) foci suggesting lesser DNA repair. In vivo, silibinin strongly radiosensitized DU145 tumor xenograft inhibition (84%, P < 0.01) with higher apoptotic response (10-fold, P < 0.01) and reduced repair of DNA damage, and rescued the mice from IR-induced toxicity and hematopoietic injury. Overall, silibinin enhanced the radiotherapeutic response via suppressing IR-induced prosurvival signaling and DSB repair by inhibiting nuclear translocation of EGFR and DNA-PK. Because silibinin is already in phase II clinical trial for prostate cancer patients, the present finding has translational relevance for radioresistant prostate cancer. Mol Cancer Ther; 14(12); 1-13. ©2015 AACR.
View details for DOI 10.1158/1535-7163.MCT-15-0348
View details for PubMedID 26516160
The role of Glial cell derived neurotrophic factor in head and neck cancer.
2020; 15 (2): e0229311
Glial cell-derived neurotrophic factor (GDNF) is reported to promote the survival of neurons and salivary gland regeneration after radiation damage. This study investigated the effect of GDNF on cell migration, growth, and response to radiation in preclinical models of head and neck squamous cell carcinoma (HNSCC) and correlated GDNF expression to treatment outcomes in HNSCC patients. Our ultimate goal is to determine whether systemic administration of GDNF at high dose is safe for the management of hyposalivation or xerostomia in HNSCC patients. Three HPV-positive and three HPV-negative cell lines were examined for cell migration, growth, and clonogenic survival in vitro and tumor growth assay in vivo. Immunohistochemical staining of GDNF, its receptors GFRalpha1 and its co-receptor RET was performed on two independent HNSCC tissue microarrays (TMA) and correlated to treatment outcomes. Results showed that GDNF only enhanced cell migration in two HPV-positive cells at supra-physiologic doses, but not in HPV-negative cells. GDNF did not increase cell survival in the tested cell lines post-irradiation. Likewise, GDNF treatment affected neither tumor growth in vitro nor response to radiation in xenografts in two HPV-positive and two HPV-negative HNSCC models. High stromal expression of GDNF protein was associated with worse overall survival in HPV-negative HNSCC on multivariate analysis in a combined cohort of patients from Stanford University (n = 82) and Washington University (n = 189); however, the association between GDNF gene expression and worse survival was not confirmed in a separate group of HPV-negative HNSCC patients identified from the Cancer Genome Atlas (TCGA) database. Based on these data, we do not believe that GNDF is a safe systemic treatment to prevent or treat xerostomia in HNSCC and a local delivery approach such as intraglandular injection needs to be explored.
View details for DOI 10.1371/journal.pone.0229311
View details for PubMedID 32084217
Fisetin sensitizes the hypoxia induced chemotherapy resistance in head and neck cancer
AMER CHEMICAL SOC. 2019
View details for Web of Science ID 000525061502269
- Galectin-1 intensifies immunosuppression in head and neck cancer by boosting myeloid-derived suppressive cell (MDSC) expansion AMER ASSOC CANCER RESEARCH. 2018
Aldehyde dehydrogenase 3A1 activation prevents radiation-induced xerostomia by protecting salivary stem cells from toxic aldehydes.
Proceedings of the National Academy of Sciences of the United States of America
Xerostomia (dry mouth) is the most common side effect of radiation therapy in patients with head and neck cancer and causes difficulty speaking and swallowing. Since aldehyde dehydrogenase 3A1 (ALDH3A1) is highly expressed in mouse salivary stem/progenitor cells (SSPCs), we sought to determine the role of ALDH3A1 in SSPCs using genetic loss-of-function and pharmacologic gain-of-function studies. Using DarkZone dye to measure intracellular aldehydes, we observed higher aldehyde accumulation in irradiated Aldh3a1-/- adult murine salisphere cells and in situ in whole murine embryonic salivary glands enriched in SSPCs compared with wild-type glands. To identify a safe ALDH3A1 activator for potential clinical testing, we screened a traditional Chinese medicine library and isolated d-limonene, commonly used as a food-flavoring agent, as a single constituent activator. ALDH3A1 activation by d-limonene significantly reduced aldehyde accumulation in SSPCs and whole embryonic glands, increased sphere-forming ability, decreased apoptosis, and improved submandibular gland structure and function in vivo after radiation. A phase 0 study in patients with salivary gland tumors showed effective delivery of d-limonene into human salivary glands following daily oral dosing. Given its safety and bioavailability, d-limonene may be a good clinical candidate for mitigating xerostomia in patients with head and neck cancer receiving radiation therapy.
View details for PubMedID 29794221
Chemical Space Mimicry for Drug Discovery
JOURNAL OF CHEMICAL INFORMATION AND MODELING
2017; 57 (4): 875-882
We describe a new library generation method, Machine-based Identification of Molecules Inside Characterized Space (MIMICS), that generates sets of molecules inspired by a text-based input. MIMICS-generated libraries were found to preserve distributions of properties while simultaneously increasing structural diversity. Newly identified MIMICS-generated compounds were found to be bioactive as inhibitors of specific components of the unfolded protein response (UPR) and the VEGFR2 pathway in cell-based assays, thus confirming the applicability of this methodology toward drug design applications. Wider application of MIMICS could facilitate the efficient utilization of chemical space.
View details for DOI 10.1021/acs.jcim.6b00754
View details for Web of Science ID 000400204900023
View details for PubMedID 28257191
Silibinin attenuates ionizing radiation-induced pro-angiogenic response and EMT in prostate cancer cells
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
2015; 456 (1): 262-268
Radiotherapy of is well established and frequently utilized in prostate cancer (PCa) patients. However, recurrence following therapy and distant metastases are commonly encountered problems. Previous studies underline that, in addition to its therapeutic effects, ionizing radiation (IR) increases the vascularity and invasiveness of surviving radioresistant cancer cells. This invasive phenotype of radioresistant cells is an upshot of IR-induced pro-survival and mitogenic signaling in cancer as well as endothelial cells. Here, we demonstrate that a plant flavonoid, silibinin can radiosensitize endothelial cells by inhibiting expression of pro-angiogenic factors. Combining silibinin with IR not only strongly down-regulated endothelial cell proliferation, clonogenicity and tube formation ability rather it strongly (p<0.001) reduced migratory and invasive properties of PCa cells which were otherwise marginally affected by IR treatment alone. Most of the pro-angiogenic (VEGF, iNOS), migratory (MMP-2) and EMT promoting proteins (uPA, vimentin, N-cadherin) were up-regulated by IR in PCa cells. Interestingly, all of these invasive and EMT promoting actions of IR were markedly decreased by silibinin. Further, we found that potentiated effect was an end result of attenuation of IR-activated mitogenic and pro-survival signaling, including Akt, Erk1/2 and STAT-3, by silibinin.
View details for DOI 10.1016/j.bbrc.2014.11.069
View details for Web of Science ID 000348483600040
View details for PubMedID 25446081
Silibinin inhibits aberrant lipid metabolism, proliferation and emergence of androgen-independence in prostate cancer cells via primarily targeting the sterol response element binding protein 1
2014; 5 (20): 10017-10033
Prostate cancer (PCA) kills thousands of men every year, demanding additional approaches to better understand and target this malignancy. Recently, critical role of aberrant lipogenesis is highlighted in prostate carcinogenesis, offering a unique opportunity to target it to reduce PCA. Here, we evaluated efficacy and associated mechanisms of silibinin in inhibiting lipid metabolism in PCA cells. At physiologically achievable levels in human, silibinin strongly reduced lipid and cholesterol accumulation specifically in human PCA cells but not in non-neoplastic prostate epithelial PWR-1E cells. Silibinin also decreased nuclear protein levels of sterol regulatory element binding protein 1 and 2 (SREBP1/2) and their target genes only in PCA cells. Mechanistically, silibinin activated AMPK, thereby increasing SREBP1 phosphorylation and inhibiting its nuclear translocation; AMPK inhibition reversed silibinin-mediated decrease in nuclear SREBP1 and lipid accumulation. Additionally, specific SREBP inhibitor fatostatin and stable overexpression of SREBP1 further confirmed the central role of SREBP1 in silibinin-mediated inhibition of PCA cell proliferation and lipid accumulation and cell cycle arrest. Importantly, silibinin also inhibited synthetic androgen R1881-induced lipid accumulation and completely abrogated the development of androgen-independent LNCaP cell clones via targeting SREBP1/2. Together, these mechanistic studies suggest that silibinin would be effective against PCA by targeting critical aberrant lipogenesis.
View details for Web of Science ID 000348036500039
View details for PubMedID 25294820
Acacetin Inhibits In Vitro and In Vivo Angiogenesis and Downregulates Stat Signaling and VEGF Expression
CANCER PREVENTION RESEARCH
2013; 6 (10): 1128-1139
Angiogenesis is an effective target in cancer control. The antiangiogenic efficacy and associated mechanisms of acacetin, a plant flavone, are poorly known. In the present study, acacetin inhibited growth and survival (up to 92%; P < 0.001), and capillary-like tube formation on Matrigel (up to 98%; P < 0.001) by human umbilical vein endothelial cells (HUVEC) in regular condition, as well as VEGF-induced and tumor cells conditioned medium-stimulated growth conditions. It caused retraction and disintegration of preformed capillary networks (up to 91%; P < 0.001). HUVEC migration and invasion were suppressed by 68% to 100% (P < 0.001). Acacetin inhibited Stat-1 (Tyr701) and Stat-3 (Tyr705) phosphorylation, and downregulated proangiogenic factors including VEGF, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2), and basic fibroblast growth factor (bFGF) in HUVEC. It also suppressed nuclear localization of pStat-3 (Tyr705). Acacetin strongly inhibited capillary sprouting and networking from rat aortic rings and fertilized chicken egg chorioallantoic membrane (CAM; ∼71%; P < 0.001). Furthermore, it suppressed angiogenesis in Matrigel plugs implanted in Swiss albino mice. Acacetin also inhibited tyrosine phosphorylation of Stat-1 and -3, and expression of VEGF in cancer cells. Overall, acacetin inhibits Stat signaling and suppresses angiogenesis in vitro, ex vivo, and in vivo, and therefore, it could be a potential agent to inhibit tumor angiogenesis and growth.
View details for DOI 10.1158/1940-6207.CAPR-13-0209
View details for Web of Science ID 000325272400015
View details for PubMedID 23943785
View details for PubMedCentralID PMC3808880
In vitro and in vivo anticancer efficacy of silibinin against human pancreatic cancer BxPC-3 and PANC-1 cells
2013; 334 (1): 109-117
Silibinin suppresses the growth of many cancers; however, its efficacy against pancreatic cancer has not been evaluated in established preclinical models. Here, we investigated in vitro and in vivo effects of silibinin against lower and advanced stages of human pancreatic carcinoma cells. Silibinin (25-100μM) treatment for 24-72h caused a dose- and time-dependent cell growth inhibition of 27-77% (P<0.05-0.001) in BxPC-3 cells, and 22-45% (P<0.01-0.001) in PANC-1 cells. Silibinin showed a strong dose-dependent G1 arrest in BxPC-3 cells (upto 72% versus 45% in control; P<0.001), but a moderate response in advanced PANC-1 cells. Cell death observed in cell growth assay, was accompanied by up to 3-fold increase (P<0.001) in apoptosis in BxPC-3 cells, and showed only slight effect on PANC-1 cells. Dietary feeding of silibinin (0.5%, w/w in AIN-93M diet for 7weeks) inhibited BxPC-3 and PANC-1 tumor xenografts growth in nude mice without any apparent change in body weight gain and diet consumption. Tumor volume and weight were decreased by 47% and 34% (P⩽0.001) in BxPC-3 xenograft, respectively. PANC-1 xenograft showed slower growth kinetics and silibinin decreased tumor volume by 34% (P<0.001) by 7weeks. Another 4weeks of silibinin treatment to PANC-1 xenograft showed 28% and 33% decrease in tumor volume and weight, respectively. Silibinin-fed group of BxPC-3 tumors showed decreased cell proliferation and angiogenesis and an increased apoptosis, however, considerable inhibitory effect was observed only for angiogenesis in PANC-1 tumors. Overall, these findings show both in vitro as well as in vivo anticancer efficacy of silibinin against pancreatic cancer that could involve inhibition of cell proliferation, cell cycle arrest, apoptosis induction and/or decrease in tumor angiogenesis.
View details for DOI 10.1016/j.canlet.2012.09.004
View details for Web of Science ID 000320413500017
View details for PubMedID 23022268
Advances in Prostate Cancer Chemoprevention: A Translational Perspective
NUTRITION AND CANCER-AN INTERNATIONAL JOURNAL
2013; 65: 12-25
Chemopreventive interventions are steadily emerging as an important aspect of cancer management and control. Herein, we have discussed the major epidemiological and clinical studies advocating the role of androgen inhibitors, flavonoids and antioxidants in preventing prostate cancer (PCa). Androgen inhibitors have lately been discussed not only in treatment of PCa, but also as preventive agents especially after trials with Finasteride and Dutasteride. Flavonoids such as silibinin, green tea polyphenols, genistein, curcumin have shown great promise, but avenues to improve their bioavailability are requisite. Agents with antioxidant potentials like lycopene, selenium, and vitamin E have also been explored. Antioxidant trials have yielded mixed results or benefitted only a subgroup of population, although further studies are needed to establish them as preventive agent. Although a majority of the trials resulted in positive outcomes supporting their role as preventive agents; one should be cautious of neutral or negative results as well. For clinical applicability of these agents, we need to identify the ideal target population, time of intervention, appropriate dosage, and extent of intervention required. Incoherency of data with these agents urges for a stringent study design and thorough interpretation to accurately judge the necessity and feasibility of the preventive measures.
View details for DOI 10.1080/01635581.2013.785006
View details for Web of Science ID 000319511100003
View details for PubMedID 23682779
Usnic Acid Inhibits Growth and Induces Cell Cycle Arrest and Apoptosis in Human Lung Carcinoma A549 Cells
NUTRITION AND CANCER-AN INTERNATIONAL JOURNAL
2013; 65: 36-43
Usnic acid (UA) is a secondary metabolite abundantly found in lichens. Some studies have shown the anticancer potential of UA; however, its efficacy and associated mechanisms are yet to be fully explored. Herein, we assessed the anticancer potency and associated molecular alterations by UA in human lung carcinoma A549 cells. UA treatment (25-100 μM) for 24 and 48 h decreased total cell number by 39-67% (P < 0.01) and 68-89% (P < 0.001), respectively, and enhanced cell death by up to twofold and eightfold (P < 0.001), respectively. UA (1-10 μM) also significantly (P < 0.001) suppressed colony formation of A549 cells. The cell growth inhibition was associated with cell cycle arrest at G0/ G1 phase. UA decreased the expression of cyclin-dependent kinase (CDK)4, CDK6, and cyclin D1 and increased the expression of CDK inhibitor (CDKI) p21/cip1 protein. While examining the cell death associated molecular changes, we observed that UA induces mitochondrial membrane depolarization and led to more than twofold increase (P < 0.01) in apoptotic cells. The apoptotic effect of UA was accompanied by enhanced poly(ADP-ribose) polymerase cleavage. This study shows that UA inhibits cell growth involving G0/G1 phase cell cycle arrest and induces cell death via mitochondrial membrane depolarization and induction of apoptosis in human lung carcinoma cells.
View details for DOI 10.1080/01635581.2013.785007
View details for Web of Science ID 000319511100005
View details for PubMedID 23682781
Fisetin inhibits various attributes of angiogenesis in vitro and in vivo-implications for angioprevention
2012; 33 (2): 385-393
Studies have shown that fisetin, a small phytochemical molecule, has antitumor activity; however, its antiangiogenic activity has not yet been examined. Accordingly, herein, we investigated the antiangiogenic efficacy and associated mechanisms of fisetin in human umbilical vein endothelial cells (HUVECs). Fisetin (10-50 μM) strongly inhibited the regular serum plus growth supplement- and vascular endothelial growth factor (VEGF)-induced growth (up to 92%, P < 0.001) and survival (up to 16%, P < 0.001) of HUVEC in a dose- and time-dependent manner. Fisetin also caused cell cycle arrest at G(1) (strong) and G(2)/M (moderate) phases together with a decrease in cyclin D1 and an increase in p53 levels. Fisetin-caused cell death was accompanied by decreased expression of survivin and an increase in cleaved levels of caspases-3 and -7 and poly-(ADP-ribose) polymerase along with an increased ratio of Bax to Bcl-2. Furthermore, fisetin inhibited capillary-like tube formation on Matrigel (up to 85%, P < 0.001) as well as migration (up to 66%, P < 0.001), which were associated with decreased expression of endothelial nitric oxide synthase (eNOS) and VEGF in HUVEC. It also decreased the expression of eNOS, VEGF, inducible nitric oxide synthase, matrix metalloproteinase-2 and -9 in A549 and DU145 human cancer cells. In vivo matrigel plug assay in mice showed significant decrease in size (up to 43%, P < 0.001), vascularization and hemoglobin content (up to 94%, P < 0.001) in the plugs from fisetin-treated, compared with control mice. Overall, these results suggest that fisetin inhibits various attributes of angiogenesis, which might contribute to its reported antitumor effects, and therefore, fisetin warrants further investigation for its angiopreventive potential toward cancer control.
View details for DOI 10.1093/carcin/bgr282
View details for Web of Science ID 000300039800020
View details for PubMedID 22139440
Effects of phytochemicals on ionization radiation-mediated carcinogenesis and cancer therapy
MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH
2011; 728 (3): 139-157
Ionizing radiation (IR)-induced cellular damage is implicated in carcinogenesis as well as therapy of cancer. Advances in radiation therapy have led to the decrease in dosage and localizing the effects to the tumor; however, the development of radioresistance in cancer cells and radiation toxicity to normal tissues are still the major concerns. The development of radioresistance involves several mechanisms, including the activation of mitogenic and survival signaling, induction of DNA repair, and changes in redox signaling and epigenetic regulation. The current strategy of combining radiation with standard cytotoxic chemotherapeutic agents can potentially lead to unwanted side effects due to both agents. Thus agents are needed that could improve the efficacy of radiation killing of cancer cells and prevent the damage to normal cells and tissues caused by the direct and bystander effects of radiation, without have its own systemic toxicity. Chemopreventive phytochemicals, usually non-toxic agents with both cancer preventive and therapeutic activities, could rightly fit in this approach. In this regard, naturally occurring compounds, including curcumin, parthenolide, genistein, gossypol, ellagic acid, withaferin, plumbagin and resveratrol, have shown considerable potential. These agents suppress the radiation-induced activation of receptor tyrosine kinases and nuclear factor-κB signaling, can modify cell survival and DNA repair efficacy, and may potentiate ceramide signaling. These radiosensitizing and counter radioresistance mechanisms of phytochemicals in cancer cells are also associated with changes in epigenetic gene regulation. Because radioresistance involves multiple mechanisms, more studies are needed to discover novel phytochemicals having multiple mechanisms of radiosensitization and to overcome radioresistance of cancer cells. Pre-clinical studies are needed to address the appropriate dosage, timing, and duration of the application of phytochemicals with radiation to justify clinical trials. Nonetheless, some phytochemicals in combination with IR may play a significant role in enhancing the therapeutic index of cancer treatment.
View details for DOI 10.1016/j.mrrev.2011.07.005
View details for Web of Science ID 000296933400006
View details for PubMedID 22030216