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Ahmad Safa, PhD

H.H. Gregg Professor of Cancer Research
Professor of Pharmacology

Research Interest

Targeting multiple signaling pathways in glioblastoma multiforme (GBM) and pancreatic cancer stem cells to eradicate these drug- and radiation-resistant cells; molecular mechanisms of drug-induced apoptosis; mechanisms of acquired resistance to cancer chemotherapeutic agents.

Education

1973

B.S. Biology (Valedictorian) | Esfahan University | Esfahan, Iran

1976

M.S. Biological Sciences | Iowa State University | Ames, Iowa

1977

M.S. Molecular, Cellular, and Developmental Biology | Iowa State University Ames, Iowa

1980

PhD Molecular, Cellular, and Developmental Biology | Iowa State University Ames, Iowa

Editorial Positions

2010-present

Editorial Board Member, Medicinal Chemistry

2010-present

Editorial Board Member, Journal of Drug Metabolism and Toxicology

2009-present

Editorial Board Member, International Journal of Biochemistry and Molecular Biology

2008-present

Editorial Board Member, Journal of Cell Death

2001-present

Editorial Board Member, Molecular Cancer Therapeutics

1996-1998

Editorial Board Member, Investigational New Drugs


Drug Resistance

Our laboratory has been investigating the molecular and biochemical mechanisms of intrinsic and acquired resistance to chemotherapeutic drugs and apoptosis in cancer cells. Drug resistanceis a major problem in cancer treatment, and approximately half of various types of cancers do not respond to chemotherapy either due to intrinsic or acquired drug resistance mechanisms.


A major drug resistance mechanism is overexpression of the ATP-binding cassette (ABC) transporter MDR1 (ABCB1 or P-glycoprotein). We are interested in the regulation of expression of the MDR1 gene in multidrug resistant cells. We have identified a complex of transcription factors and other proteins interacting with the CAAT region of the human MDR1 gene, whose product (P-glycoprotein) causes multidrug resistance in cancer cells. 

We have termed these proteins the multidrug resistance enhancing factor 1 (MEF 1) complex. We purified this complex and found that it consists of 5-7 proteins. We have reported the role of two of these proteins: (1) RNA helicase A (RHA) (Fig. 1) upregulates the MDR1 gene, and (2) another protein in this complex is the catalytic subunit of DNA protein kinase (DNA-PK). We demonstrated that constitutive DNA-protein kinase (DNA-PK) phosphorylates RNA helicase A (RHA) on multiple sites in the MEF 1 complex of the

Fig. 1. DNA-affinity purification of the MEF 1 Transcription Factor Complex and MALDI-TOF-MS identification of RHA

promoter region of the P-gp gene, MDR1, in drug resistant variants, and does not occur in the parental cells. Moreover, an inhibitor of DNA-PKinhibits P-gp expression by preventing DNA-PK-induced RHA phosphorylation. The indispensable role played by DNA-PK in P-gp overexpression in MDR cells identifies targeted DNA-PK inhibition as a rational strategy to reverse drug resistance in cancer. 

Our goals in this project are (1) to identify inhibitors of DNA-PK which inhibit phosphorylation of RHA and P-gp expression, (2) to determine the identity of the other members of the MEF 1 complex and delineate their functional roles in upregulating the MDR1 gene, and (3) to design strategies to prevent expression of the MDR1 product, P-glycoprotein, and circumvent multidrug resistance in cancer cells. 

Proteinase 3 (PR3), also referred to as myeloblastin, belongs to a family of neutrophil serine proteases including leukocyte elastase, cathepsin G, and the catalytically inactive azurocidin. PR3 degrades various extracellular matrix molecules such as type IV collagen, elastin, fibronectin, laminin, and vitronectin, indicating that it might be involved in tissue destruction and neutrophil migration. This serine protease is involved in regulating the growth and differentiation of human leukemia cells. PR3 is found in other cell types including breast cancer cells. We have found that the loss of PR3 causes resistance to chemotherapeutic agents and apoptosis in leukemia and breast cancer cells. PR3 enhances drug-induced apoptosis. Therefore, we are (1) identifying the signaling pathways involved in PR3-mediated drug-induced apoptosis, and (2) exploring the molecular mechanism of loss of PR3, which leads to drug resistance in cancer cells.

Fig. 2. Signaling pathway of TRAIL-induced apoptosis via its receptor DR5. c-FLIP variants [c-FLIP long (c-FLIPL) and c-FLIP short (c-FLIPS)] prevent apoptosis by interacting with pro-caspases-8 and -10.

Apoptosis Signaling Pathways

Death receptor-mediated apoptosis is deficient in many cancer cells resistant to cytokines. Therefore, uncovering strategies to lower the threshold for triggering apoptosis may lead to novel and useful therapeutics to treat various cancers. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) holds enormous promise as a cancer therapeutic due to its selectively inducing apoptosis in neoplastic cells but not in normal cells.  We have shown that TRAIL or a TRAIL recombinant adenovirus preferentially induces robust apoptosis in

P-glycoprotein overexpressing MDR cell lines via selective interaction with the TRAIL receptor DR5. However, many cancer cells express resistance to recombinant soluble TRAIL.Cellular FLICE-like inhibitory protein (c-FLIP) (Fig. 2) is a major TRAIL resistance factor in human malignancies, including ovarian cancer. In addition to its functional role in inhibiting apoptosis by binding to procaspases-8 and -10 and inhibiting the activation of these caspases (Fig. 3), c-FLIP also has other functions including (1) initiating cell proliferation by recruiting and activating downstream signaling proteins including (a) TRAF, RIP, and IKK, and activating NF-κB, or (b) activating RAF and extracellular signal-regulated kinase (ERK), (2) controlling cell survival by activating the Akt, JNK, and Wnt signaling pathways, and (3) participating in carcinogenesis.  

We are validating c-FLIP as a novel target for developing innovative therapeutic strategies to overcome the dose-limiting toxicity of chemotherapy for cancer. We are interested in defining the roles of c-FLIP variants in TRAIL and Taxol-induced apoptosis, and establishing whether a c-FLIP variant(s) is a rational molecular target for cancer therapy. We are using c-FLIP-specific siRNAs and particular agents capable of downregulating c-FLIP variants, upregulating the expression of the DR5 

Fig. 3. c-FLIP regulates several key signaling pathways involved in preventing apoptosis, increasing cell proliferation and cell survival as well as carcinogenesis.

receptor, and reversing TRAIL resistance in lung, breast, and ovarian cancer cells. These projects may lead to novel modalities of cancer therapy with improved efficacy and less toxicity.

Selected Publications                                            Search for Dr. Safa on PubMed

  • Park SJ, Bijangi-Vishehsaraei K, Safa AR. Selective TRAIL-triggered apoptosis due to overexpression of TRAIL death receptor 5 (DR5) in P-glycoprotein-bearing multidrug resistant CEM/VBL1000 human leukemia cells. Int J Biochem Mol Biol. 2010 Jul;1(1):90-100. PubMed PMID: 20953314; PubMed Central PMCID: PMC2953951.
  • Bijangi-Vishehsaraei K, Saadatzadeh MR, Huang S, Murphy MP, Safa AR. 4-(4-Chloro-2-methylphenoxy)-N-hydroxybutanamide (CMH) targets mRNA of the c-FLIP variants and induces apoptosis in MCF-7 human breast cancer cells. Mol Cell Biochem. 2010 Sep;342(1-2):133-42. Epub 2010 May 6. PubMed PMID: 20446019.
  • Day TW, Sinn AL, Huang S, Pollok KE, Sandusky GE, Safa AR. c-FLIP gene silencing eliminates tumor cells in breast cancer xenografts without affecting stromal cells. Anticancer Res. 2009 Oct;29(10):3883-6. PubMed PMID: 19846923.
  • Day TW, Wu CH, Safa AR. Etoposide induces protein kinase Cdelta- and caspase-3-dependent apoptosis in neuroblastoma cancer cells. Mol Pharmacol. 2009  Sep;76(3):632-40. Epub 2009 Jun 23. PubMed PMID: 19549763; PubMed Central PMCID: PMC2730392.
  • Day TW, Safa AR. RNA interference in cancer: targeting the anti-apoptotic protein c-FLIP for drug discovery. Mini Rev Med Chem. 2009 Jun;9(6):741-8. Review. PubMed PMID: 19519499.
  • Shen F, Bailey BJ, Chu S, Bence AK, Xue X, Erickson P, Safa AR, Beck WT, Erickson LC. Dynamic assessment of mitoxantrone resistance and modulation of multidrug resistance by valspodar (PSC833) in multidrug resistance human cancer cells. J Pharmacol Exp Ther. 2009 Aug;330(2):423-9. Epub 2009 May 7. PubMed PMID: 19423841; PubMed Central PMCID: PMC2713081.
  • Huang S, Day TW, Choi MR, Safa AR. Human beta-galactoside alpha-2,3-sialyltransferase (ST3Gal III) attenuated Taxol-induced apoptosis in ovarian cancer cells by downregulating caspase-8 activity. Mol Cell Biochem. 2009 Nov;331(1-2):81-8. Epub 2009 May 5. PubMed PMID: 19415457.
  • Fischer JL, Kumar MA, Day TW, Hardy TM, Hamilton S, Besch-Williford C, Safa AR, Pollok KE, Smith ML. The Xpc gene markedly affects cell survival in mouse bone marrow. Mutagenesis. 2009 Jul;24(4):309-16. Epub 2009 Apr 16. PubMed PMID: 19372135; PubMed Central PMCID: PMC2701989.
  • Day TW, Huang S, Safa AR. c-FLIP knockdown induces ligand-independent DR5-, FADD-, caspase-8-, and caspase-9-dependent apoptosis in breast cancer cells. Biochem Pharmacol. 2008 Dec 15;76(12):1694-704. Epub 2008 Sep 17. PubMed PMID: 18840411; PubMed Central PMCID: PMC2610355.
  • Wu CH, Kao CH, Safa AR. TRAIL recombinant adenovirus triggers robust apoptosis in multidrug-resistant HL-60/Vinc cells preferentially through death receptor DR5. Hum Gene Ther. 2008 Jul;19(7):731-43. PubMed PMID: 18476767; PubMed Central PMCID: PMC2733364. 

Department of Pharmacology and Toxicology | 635 Barnhill Drive, MS A401 | Indianapolis, IN 46202