Virtual Library

Start Your Search

Vibha Raghavan



Author of

  • +

    MA27 - Novel Drugs and PDX Models (ID 931)

    • Event: WCLC 2018
    • Type: Mini Oral Abstract Session
    • Track: Targeted Therapy
    • Presentations: 2
    • Moderators:
    • Coordinates: 9/26/2018, 13:30 - 15:00, Room 206 BD
    • +

      MA27.03 - Multi-Omic Characterization of TKI-Treated Drug-Tolerant Cell Population in an EGFR-Mutated NSCLC Primary-Derived Xenograft (ID 13370)

      13:40 - 13:45  |  Author(s): Vibha Raghavan

      • Abstract
      • Presentation
      • Slides

      Background

      Sixty to eighty percent of advanced stage lung adenocarcinoma patients with epidermal growth factor receptor (EGFR) mutated tumors respond to first generation EGFR tyrosine kinase inhibitors (TKIs). However, cure is not yet achievable with any EGFR TKI monotherapy, as patients eventually progress due to acquired resistance. In vitro evidence suggests that minor populations of epigenetically modified drug tolerant cells (DTCs) may be important for tumor cells surviving TKI. We hypothesize that molecularly characterizing DTCs in vivo and comparing them to the untreated tumor in a patient-derived xenograft (PDX) model may delineate mechanisms of tolerance that closely mimic those occurring in patients.

      a9ded1e5ce5d75814730bb4caaf49419 Method

      DTCs were produced via chronic exposure to erlotinib in a lung adenocarcinoma PDX harbouring an exon 19 deletion. Histological, genomic, transcriptomic (including single-cell RNA-seq), and epigenetic characterizations were performed on DTCs and compared to untreated baseline (BL) tumors.

      4c3880bb027f159e801041b1021e88e8 Result

      Compared to BL, DTCs exhibit decreased levels of proliferation (Ki67 by immunohistochemistry (IHC) and increased expression of senescence/quiescence (p21) and anti-apoptosis (BCL-XL) immunohistochemistry (IHC) markers, while maintaining EGFR pathway signaling (pEGFR, pAKT, pERK, pS6 IHC). Whole exome-sequencing provides evidence that DTCs likely do not represent mutationally distinct subclones from the bulk tumor. Instead, DTCs exhibit a number of differentially expressed genes compared to BL tumors that are involved in cell cycle arrest, senescence/quiescence, differentiation, vesicles, and inflammation. Genes with epigenetic differences (chromatin openness and/or promoter methylation) are involved in similar cellular processes. A minor (<2%) subpopulation of transcriptomically-defined DTC-like cells in the BL tumors are very similar to the DTCs, supporting the hypothesis that DTCs may exist prior to treatment. A number of transcription regulators are found to have differential gene expression and epigenetic regulation as well as DNA-binding motifs found in regions of chromatin uniquely open in DTCs or baseline tumors. These transcription regulators are involved in cell maintenance, proliferation, and differentiation, and may play key roles in promoting DTC phenotype.

      8eea62084ca7e541d918e823422bd82e Conclusion

      In this specific EGFR mutant PDX model sensitive to first generation TKIs, DTC-like cells are found in the BL untreated tumors, and its resultant phenotype after exposure to TKI appears to be involved in cell cycle, differentiation, senescence/quiescence, proliferation and maintenance. PDX models may provide insights into therapeutic strategies to target DTCs, and further improve the survival of EGFR-mutated NSCLC patients.

      6f8b794f3246b0c1e1780bb4d4d5dc53

      Only Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login, select "Add to Cart" and proceed to checkout. If you would like to become a member of IASLC, please click here.

      Only Active Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login or select "Add to Cart" and proceed to checkout.

    • +

      MA27.07 - Lung Adenocarcinoma Harboring BRAF G469V Mutation is Uniquely Sensitive to EGFR Tyrosine Kinase Inhibitors (ID 12771)

      14:10 - 14:15  |  Author(s): Vibha Raghavan

      • Abstract
      • Presentation
      • Slides

      Background

      BRAF mutations occur in 2-5% of non-small cell lung cancers with ~50% being non-V600E. Previous studies reported that two BRAF G469 mutations, G469V and G469A increase kinase activity and MAPK activation, thus are likely oncogenic. Patients with non-V600E mutations are mostly not sensitive to approved BRAF inhibitors vemurafenib or dabrafenib. We established a lung adenocarcinoma (LUAD) patient derived xenograft (PDX) that is epidermal growth factor receptor (EGFR) wild type and non-amplified, but harbors BRAF G469V mutation, yet is sensitive to gefitinib. We performed functional studies to characterize the oncogenicity and sensitivity of BRAF G469 mutations to EGFR tyrosine kinase inhibitors (TKIs).

      a9ded1e5ce5d75814730bb4caaf49419 Method

      PDX12 was established in NOD-SCID mice from a resected stage IIIA LUAD. The XDC12 cell line was established from PDX12. NCI-H1395 and -H1755 LUAD cell lines with BRAF G469A mutation were obtained from ATCC. BRAF mutant driver activity was characterized by shRNA knockdown of BRAF in LUAD cell lines and the ability of the mutants to promote IL3-independent growth when expressed in Ba/F3 cells. PDX12 responsiveness to TKIs was evaluated by tumor volume shrinkage while cell line sensitivity was quantified using the MTS assay. Drug effects on signaling were assessed by phospho-immunoblotting. Computational modeling was used to predict how the mutations promote BRAF activation and sensitivity to EGFR-TKIs, while purified BRAF proteins were used to validate predictions.

      4c3880bb027f159e801041b1021e88e8 Result

      Knockdown of BRAF by shRNA inhibited growth of all BRAF mutant cell lines, while ectopic BRAF G469V and G469A expression in Ba/F3 cells promoted IL3-independent MAPK activation and growth, supporting both mutations being oncogenic drivers. The XDC12 cell line was sensitive to EGFR-TKIs (gefitinib, erlotinib, afatinib, and osimertinib), but resistant to the BRAF inhibitor dabrafenib, which correlated with inhibition of MAPK phosphorylation. By contrast, H1395 and H1755 cell lines with BRAF G469A mutations were resistant to both the EGFR-TKIs and the BRAF inhibitor. Similarly, only Ba/F3 cells expressing BRAF G469V, but not G469A, were sensitive to EGFR-TKIs. Consistent with the in vitro data and our initial PDX findings with gefitinib, multiple EGFR-TKIs induced tumor shrinkage in PDX12 in vivo.

      8eea62084ca7e541d918e823422bd82e Conclusion

      BRAF G469V/A mutations are oncogenic drivers but are insensitive to BRAF inhibitors. However, only BRAF G469V, but not G469A mutation, is sensitive to EGFR-TKIs. Thus, two different driver alterations affecting the same BRAF codon can lead to distinct drug sensitivities.

      6f8b794f3246b0c1e1780bb4d4d5dc53

      Only Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login, select "Add to Cart" and proceed to checkout. If you would like to become a member of IASLC, please click here.

      Only Active Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login or select "Add to Cart" and proceed to checkout.

  • +

    MTE01 - Preclinical Models of Lung Cancer (Ticketed Session) (ID 811)

    • Event: WCLC 2018
    • Type: Meet the Expert Session
    • Track: Biology
    • Presentations: 1
    • Moderators:
    • Coordinates: 9/24/2018, 07:00 - 08:00, Room 206 F
    • +

      MTE01.02 - Lung Patient Derived Xenograft and Organoid (ID 11547)

      07:30 - 08:00  |  Author(s): Vibha Raghavan

      • Abstract
      • Presentation
      • Slides

      Abstract not provided

      Only Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login, select "Add to Cart" and proceed to checkout. If you would like to become a member of IASLC, please click here.

      Only Active Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login or select "Add to Cart" and proceed to checkout.