Small cell lung cancer (SCLC)

Small cell lung carcinoma (SCLC) remains one of the most lethal human cancers. More than 25,000 patients are diagnosed with SCLC every year in the United States. Unfortunately, most patients usually survive only 6-12 months after diagnosis. Except for the combination of radiation therapy and chemotherapy, there has been no novel therapeutic approach implemented in the past 30 years. Despite a large number of clinical trials, no targeted therapy has been approved for SCLC patients, whose survival rate hovers around 5%. Previous attempts to identify therapeutic targets in SCLC patients have mostly focused on signaling networks within the tumor cells. Here we propose to test a novel immunotherapeutic approach to promote the anti-cancer activity of macrophages. Specifically, we found that SCLC cells express high levels of the CD47 antigen, a marker of self that inhibits the phagocytic activity of macrophages. Based on previous studies from the laboratories of Dr. Weissman and Dr. Garcia at Stanford, we propose to block the interaction between CD47 and SIRPa, an inhibitory receptor expressed on macrophages, to stimulate the engulfment of SCLC cells by macrophages and their eradication. Furthermore, we will identify SCLC-specific antigens and combine CD47-blocking therapies with these antibodies to enhance the recruitment and the activity of macrophages against SCLC cells. Clinical trials testing the CD47-blocking strategies are being initiated in patients with blood cancer and some solid tumors. If successful, our pre-clinical experiments may lead to the rapid implementation of this novel anti-cancer immunotherapy strategy in SCLC patients.

Small cell lung cancer (SCLC) is a common, aggressive, and exceptionally lethal malignancy that is usually metastatic at the time of diagnosis. Newly diagnosed SCLC is remarkably sensitive to chemotherapy, with response rates of over 60% to cisplatin and etoposide even in patients with extensive-stage disease. These chemotherapy responses are often both rapid and deep, but are never curative: extensive-stage disease recurs universally, in most cases within a few months after completion of first-line therapy. Recurrent SCLC is remarkably refractory to treatment. The median overall survival of patients with extensive-stage SCLC is about nine months from the time of initial diagnosis, and the 5-year survival is less than 1%. Defining the basis of acquired chemotherapy resistance in SCLC could have clear and important ramifications for clinical management of this disease. Targeting the key determinants of acquired chemoresistance could be integrated into first-line treatment, and/or could drive rational targeted therapeutic studies for recurrent disease. We now have in hand multiple technical approaches that could comprehensively define the genomic and epigenetic changes that drive acquired resistance in SCLC. In this award application, we propose two parallel approaches to analyzing acquired resistance in SCLC: analysis of primary samples and patient-derived xenografts before and after acquired resistance.

Small cell lung cancer (SCLC) is an aggressive form of lung cancer with dismal survival rates. New strategies are urgently needed to improve clinical outcomes for SCLC patients. Recently, we identified high expression of the DNA-repair protein poly (ADP-ribose) polymerase 1 (PARP-1) in SCLC cell lines and tumors through a large-scale, proteomic profiling project. In vitro data from our group has shown that PARP inhibitors have single-agent activity in SCLC and potentiate the activity of chemotherapies that work by inducing DNA damage. Based on these results, we are conducting an investigator-initiated, Phase II clinical trial of the oral alkylating agent temozolomide (TMZ) with or without the PARP inhibitor ABT-888 for patients with relapsed SCLC. We hypothesize that PARP1’s action as an E2F1 co-activator contributes to the overexpression of multiple E2F1-regulated DNA repair proteins, resulting in resistance to chemotherapy. Thus, targeting PARP1 will decrease expression of E2F1-regulated DNA repair proteins, as well as directly inhibit PARP-mediated DNA repair, resulting in decreased cell viability and improved clinical outcomes in patients treated with TMZ and the PARP inhibitor. In the studies proposed here, we will test in vitro and in vivo sensitivity of SCLC to ABT-888 and TMZ, alone and in combination, and develop predictive biomarkers of response that will be tested in our Phase II clinical trial. The ultimate goal of this laboratory and clinical research is to develop PARP inhibitors as a novel therapy for SCLC.