Biomarkers for NSCLC radiosensitization by proteasome inhibition

2013

David E. Kozono, MD, PhD

Dana-Farber Cancer Institute

Boston

Dr. Kozono is studying which genetic types of lung cancer are the most resistant to radiation, and which of these may be best treated with a combination of radiation and bortezomib, a drug already FDA-approved for another type of cancer.

Research Summary

Lung cancer is frequently diagnosed after it has spread beyond the original tumor but not outside the chest. Patients with these “locally advanced” cancers can be treated with radiation therapy, chemotherapy and/or surgery, but unfortunately only 25% of the 60,000 patients diagnosed each year in the US are cured. The poor outcomes are largely due to an inability to give sufficient radiation to destroy the tumor without damaging surrounding vital organs. Efforts have therefore focused on increasing the ability of radiation to kill cancer cells selectively by combining radiation with specialized drugs. Unfortunately, for most patients, the available drugs increase cure rates by only about 5%. We examined the effect of deactivating each of nearly 18,000 genes on the survival of cultured lung cancer cells. The gene whose suppression resulted in the most reproducible effect was PSMA1. PSMA1 is a core component of the proteasome, the cellular machinery responsible for the recycling of proteins. Bortezomib, a drug that suppresses the proteasome, is already FDA-approved for multiple myeloma. It has been tested in lung cancer patients, but not extensively with radiation. In preparation for further clinical studies, we propose studies to determine which genetic types of lung cancer are the most resistant to radiation, and which of these may be best treated with bortezomib. Specifically, we propose to test treatment in mice that develop tumors of various genetic types commonly found in patients, and to study gene patterns in these and patient samples that may predict need for better therapies.

Technical Abstract

Whole genome pooled retroviral shRNA screens were performed in NSCLC cell lines A549 and NCI-H460. Out of nearly 18,000 genes, the top hit whose knockdown most reproducibly showed cytoxicity was PSMA1, a core subunit of the 20S proteasome. The combination of radiotherapy and PSMA1 knockdown significantly enhanced tumor control in a mouse xenograft model. We observed that proteasome inhibition results in increases in nuclear 1κBa, which in turn decreases NF-κB binding to the promoters of Fanconi Anemia/Homologous Recombination (HR) genes including FANCD2 and BRCA1. This reduces the expression and subsequent availability of these DNA repair proteins for recruitment to double strand breaks (DSBs) induced by radiation. These mechanistic studies provided the basis for the proposed hypothesis-driven translational research.

The central hypothesis is that high levels of HR-mediated repair of radiation-induced DNA DSBs are associated with poor tumor control, which may be improved with proteasome inhibitors. First, CT-guided fractionated radiotherapy ± bortezomib will be tested in diverse genetically engineered mouse models of NSCLC to identify mutations and other biomarkers associated with responses to radiation and/or proteasome inhibitors. Immunofluorescence and immunohistochemistry against proteins, identified in prior mechanistic studies, as well as gene expression profiling (GEP), will be performed. Then, the biomarkers will be examined in archived specimens from patients treated with radiotherapy, to assess associations with outcomes. DASL will be used to perform GEP studies using formalin-fixed, paraffin-embedded specimens. The goal will be to identify pathway-based expression signatures that predict poor outcomes with radiotherapy and improved outcomes with addition of proteasome inhibitors.

Key words

Adenocarcinoma

Biomarker or biomarker testing

Chemotherapy

Large cell carcinoma

NFκB

Non-small cell lung cancer (NSCLC)

Radiotherapy

Squamous cell lung cancer

Biomarkers for NSCLC radiosensitization by proteasome inhibition

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