I have an extensive track record in cancer molecular and cell biology and therapeutics. Research areas include cell signaling, identification of new targets, molecular mechanisms of Hedgehog signaling, oncogene driven survival signaling, regulation of GLI by oncogenic KRAS, regulation of cell death, death receptors of the TNF receptor superfamily, cancer molecular genetics in experimental models and human tumors, developmental therapeutics, mechanism of drug action, drug resistance, histone modification and drug response, DNA damage signaling, transcription factors, cDNA microarray gene profiling for novel target identification, human solid tumors, colon carcinoma, disease-specific phenotypes.
Current Research Focus:
In normal cellular processes the canonical Hedgehog (HH) signaling pathway is pivotal in embryonic development, tissue patterning, and differentiation. The GLI genes (GLI1, GLI2) encode transcription factors that regulate target genes at the distal end of the HH pathway (SHH->PTCH->SMO->GLI). HH-GLI signaling is dysregulated in many types of human cancers with constitutive activation of GLI, advancing during progression and in metastatic disease. Oncogenic signaling pathways, including KRAS/BRAF in colon cancer, circumvent the HH-GLI axis to converge on and further activate GLI, which serves as a nodal channel for oncogenic signals. GLI is constitutively activated early during colonic epithelial cell transformation, requiring interaction between mutant APC, KRAS and p53 signaling pathways. The small molecule GLI inhibitor GANT61, which inhibits GLI-dependent transcription, induces extensive cell death in all human colon carcinoma cell line models examined in contrast to normal cells due to targeting constitutively activated GLI. GANT61 binds specifically to GLI and not to DNA or to other transcription factors, demonstrating selectivity and specificity for the GLI target, with no known off-target effects. Mechanistically GANT61 inhibits the binding of GLI to the promoters of target genes with redistribution of key regulators of the transcriptional machinery (Pol II, DSIF, NELF, PTEFb) on chromatin. RNA:DNA hybrids within R-loop regions accumulate during transcriptional inhibition and gH2AX foci are formed. gH2AX foci are formed in S-phase and non-S-phase cells following transcriptional inhibition, accumulating at the G1/S boundary where DNA damage is recognized at the initiation of DNA replication. Cells accumulate in early S, are unable to progress through S-phase, and undergo cell death. Critical regulators of the G1/S boundary, that are GLI targets, are downregulated following GANT61 treatment, including FOXM1 and CDC6. FOXM1 is a transcription factor that plays a key role in the G1/S transition, is transcriptionally regulated by GLI1, and is an effector of KRAS/BRAF signaling. CDC6 is involved in assembly of the PreReplication Complex (PRC), initiation of DNA replication, early S-phase progression, and activation of the intra-S-phase checkpoint. Inhibition of the GLI-regulated FOXM1/CDC6 pathway and the G1/S transition by GANT61 may prevent progression from early S-phase. Alternatively, DNA replication forks can stall when transcription is inhibited and the accumulating RNA:DNA hybrids are in conflict with the DNA replication machinery. These events inhibit initiation of DNA replication from unfired origins at early replicons and inhibit progression through S-phase. Thus, conflicts between transcription (R-loops) and the DNA replication machinery are anticipated to occur at the initiation of DNA replication.
Current projects include: 1) The mechanism of inhibition of GLI-dependent transcription by GANT61; 2) the role of accumulation of RNA:DNA hybrids and R-loops in the mechanism of DNA damage and early S-phase arrest; 3) the role of the FOXM1/CDC6 pathway in inhibition of the G1/S transition following GANT61; 4) mechanism of transmission of GANT61-induced DNA damage to a cell death response; 5) drug discovery initiatives for inhibitors of GLI; 6) mechanism(s) of induction of constitutive GLI activation during colonic epithelial cell transformation.
Selected from 145 peer-reviewed publications
1. Agyeman A, Jha B, Mazumdar T, Houghton JA. Mode and specificity of binding of the small molecule GANT61 to GLI determines inhibition of GLI-DNA binding. Oncotarget 5: 4492-4503, 2014 ((PMID 24962990). http://www.impactjournals.com/oncotarget/index.php?journal=oncotarget&page=issue&op=view&path=69 (front cover feature article, June 30, 2014)
2. Mazumdar T, Sandhu R, Qadan M, DeVecchio J, Magloire V, Agyeman, A, Li B, Houghton JA. Hedgehog signaling regulates Telomerase Reverse Transcriptase in human cancer cells. PLoS ONE Sep25;8(9): e75253. doi:10.1371/journal.pone.0075253, 2013 (PMID 24086482).
3. AgyemanA, Mazumdar T, Houghton JA. Regulation of DNA damage following termination of Hedgehog (HH) survival signaling at the level of the GLI genes in human colon cancer. Oncotarget 8:854-868, 2012 (PMID 22922219).
4. Mazumdar T, DeVecchio J, Agyeman A, Shi T, Houghton JA. The GLI genes as the molecular switch in disrupting Hedgehog signaling in colon cancer. Oncotarget 2:638-645, 2011 (PMID 21860067).
5. Mazumdar T, DeVecchio J, Agyeman A, Shi T, Houghton JA. Blocking Hedgehog survival signaling at the level of the GLI genes induces DNA damage and extensive cell death in human colon carcinoma cells. Cancer Res 71:5904-5914, 2011 (PMID 21747117).
6. Dabir S, Kluge A, Aziz MA, Houghton JA, Dowlati A. Identification of STAT3-independent regulatory effects for protein inhibitor of activated STAT3 by binding to novel transcription factors. Cancer Biol Ther 12: 122-134, 2011 (PMID 21532337).
7. Mazumdar T, DeVecchio J, Shi T, Jones J, Agyeman A, Houghton JA. Hedgehog (HH) signaling drives cellular survival in human colon carcinoma cells. Cancer Res 71: 1092-1102, 2011 (PMID 21135115).
8. Shi T, Mazumdar T, DeVecchio J, Duan Z-H, Agyeman A, Aziz M, Houghton JA. cDNA microarray gene expression profiling of Hedgehog signaling pathway inhibition in human colon cancer cells. PLoS ONE 5: 1-23, 2010 (pii: e13054; (PMID 20957031).
9. Jani TS, Devecchio J, Mazumdar T, Agyeman A, Houghton JA. Inhibition of NF-kB signaling by quinacrine is cytotoxic to human colon carcinoma cell lines (cc) and is synergistic in combination with TRAIL or oxaliplatin. J.Biol Chem 285:19162-19172, 2010 (PMID: 23097684).
10. Nawrocki ST, Carew JS, Douglas L, Cleveland JL, Humphreys R, Houghton JA. Histone deacetylase inhibitors enhance lexatumumab-induced apoptosis via a p21Cip1-dependent decrease in survivin levels. Cancer Res 67:6987-6994, 2007.
11. Martin S, Phillips DC, Szekely-Szucs K, Elghazi L, Desmots F, Houghton JA. Cyclooxygenase-2 inhibition sensitizes human colon carcinoma cells to TRAIL-Induced apoptosis through clustering of DR5 and concentrating death-inducing signaling complex components into ceramide-enriched caveolae. Cancer Res 65:11447-11458, 2005.
12. Izeradjene K, Douglas L, Delaney A, Martin S, Houghton JA. Casein Kinase II (CK2) regulates FADD and caspase-8 recruitment to the death-inducing signaling complex (DISC) in TRAIL-induced apoptosis in human colon carcinoma cell lines. Oncogene 24:2050-2058, 2005.
13. GellerJI, Szekely-SzucsK, PetakI, DoyleB, HoughtonJA. P21Cip1 is a critical mediator of the cytotoxicaction of thymidylate synthase (TS) inhibitors in colorectal carcinoma cells. Cancer Res 64:6296-6303, 2004.
14. Turner PK, Houghton JA, Petak I, Tillman DM, Douglas L, Schwartzberg L, Billups C, Tan M, Panetta J, Stewart CF. Pharmacokinetics and pharmacodynamics of subcutaneous interferon gamma in patients receiving 5-fluorouracil and leucovorin. Cancer Chemother Pharmacol 53:253-260, 2004.
15. Geller J, Petak I, Szekely Szucs K, Nagy K, Tillman DM, Houghton JA. Interferon-g-induced sensitization of colon carcinomas to ZD9331 targets caspases, downstream of Fas, independent of mitochondrial signaling and the IAP survivin. Clin Cancer Res 9:6504-6515, 2003.
16. Petak I, Danam RP, Tillman DM, Vernes R, Howell SR, Brent TP, Houghton JA. Hypermethylation of the gene promoter and enhancer region can regulate Fas expression and sensitivity in colon carcinoma Cell Death Diff 10:211-217, 2003.
17. Schwartzberg L, Petak I, Stewart C, Turner PK, Ashley J, Tillman DM, Douglas L, Mihalik R, Weir A, Tauer K, Shope S, Houghton JA. Modulation of the Fas signaling pathway by interferon-g in therapy of colon cancer: Phase I trial and correlative studies of interferon-g, 5-fluorouracil and leucovorin. Clin Cancer Res 8:2488-2498, 2002.