Therapeutics Award

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.

Advanced (stage IV) lung adenocarcinoma is an incurable disease. Treatment mostly consists of chemotherapy, which provides a consistent but small survival benefit. Standard therapy includes a platinum-doublet (pemetrexed or paclitaxel) often in combination with bevacizumab, followed by maintenance bevacizumab or pemetrexed. Programmed death 1 (PD-1) is a T-cell surface receptor that when activated, delivers a negative signal to T cells. This feedback mechanism dampens immune responses when no longer needed, preventing damaging autoimmune reactions. Tumors can co-opt this T-cell control mechanism to escape surveillance and/or rejection by the immune system. Thus, reversing this tumor action can result in antitumor activity worthy of clinical evaluation. Recently it has been demonstrated that inhibition of the PD-1 receptor with an anti-PD-1 monoclonal antibody (nivolumab) has significant clinical activity in lung cancer with an ORR of 26%. As remarkable as this may be, given the heavily pretreated population of lung cancer patients studied, this also indicates that 74% of patients did not respond and remained resistant to this approach. Therefore, going forward it is important to develop combination therapies to improve the efficacy of this approach, and to discover resistance mechanisms that may allow for better patient (and tumor) selection. One potential class of agents to be used in combination with anti-PD-1 is the adenosine A2AR antagonists. Given that A2AR on T cells within the tumor microenvironment contributes to immune escape and therapeutic resistance, the addition of PBF-509 is expected to improve the efficacy of nivolumab.

Cancer therapy needs to be better personalized to individual patients, each of whom carries a unique spectrum of mutations, inherited and/or acquired. One of the best cases for this is lung cancer, where molecular subgrouping patients and targeting their mutations has shown promise. While many groups have searched fervently for additional tumor-acquired mutations that are associated with drug sensitivity and resistance, few have emerged since the discovery of the initial mutations, such as EGFR. In contrast, we have applied our expertise in microRNAs (miRNAs), their biologic function and interaction with oncogenes, and as a result have discovered a new class of inherited, germ-line mutations that appear to have strong potential as companion diagnostics. These mutations are in a relatively unexplored region of the genome, the 3’ untranslated regions (UTRs), once thought to be junk DNA. The first such discovered biomarker, the “KRAS-variant,” is an inherited 3’UTR mutation in KRAS, which affects microRNA (miRNA) binding and KRAS pathway expression, as well as tumor biology. The KRAS-variant was first shown to be a genetic marker for an increased risk of developing non-small cell lung cancer (NSCLC). In addition, our data indicate that this variant represents an inherited form of an activated KRAS allele, one of the most important human oncogenes. Several groups have found that the KRAS-variant acts as a biomarker of poor outcomes across multiple cancers, including head and neck cancer, ovarian cancer, and colon cancer. We as well as others have shown that this biomarker is predictive of response to specific cancer treatments, and is not just prognostic of aggressive tumor biology. For example, the KRAS-variant predicts resistance to cisplatin in ovarian and head and neck cancer, resistance to cetuximab in combination with irinotecan chemotherapy, but sensitivity to cetuximab when delivered alone. Furthermore, our preliminary data in this proposal indicate that the KRAS-variant is a powerful companion diagnostic predicting poor response to specific agents, and excellent response to others. These findings, combined with evidence that this allele of KRAS can be targeted using siRNA and miRNA strategies that we have pioneered, leads us to believe that this KRAS-3’UTR mutation is a powerful companion diagnostic in lung cancer, and ultimately may be a critical new target for cancer therapy.

The genotype-directed use of EGFR TKIs in EGFR-mutant lung cancer patients has fundamentally changed the face of the disease with improved response to therapy, preserved quality of life, and prolonged progression-free survival. However, tumors that initially respond become resistant after ~ 1 year (i.e., acquired resistance, AR). The biology of AR is incompletely understood and is largely inferred from pre-clinical models. Our group at Mass General implemented a wide-scale program to perform repeat biopsies on EGFR-mutant patients with AR to first-generation EGFR inhibitors (gefitinib, erlotinib). This translational research paradigm has been instrumental in gaining insight into AR and has led to novel observations such as PIK3CA and BRAF mutations as mechanisms of AR and the abundant frequency of phenotypic changes at the time of AR like small cell lung cancer and epithelial-to-mesenchymal transitions. The repeat biopsy results have directly helped our patients as well, by informing choices about the most relevant clinical trials or alternative treatments. Currently, a new cohort of EGFR TKIs is entering the clinic: 2^nd-generation irreversible pan-HER inhibitors and 3^rd-generation T790M-specific inhibitors. Little is known about how AR develops to these newer therapies or how the biology of EGFR-mutant cancers evolves over time after exposure to sequential EGFR blockers.

Our proposal aims to discover the mechanisms of AR to next-generation EGFR TKIs and to understand the evolution of EGFR-mutant cancers as they face the selective pressure of sequential types of EGFR-directed therapies. To accomplish this we will collaborate across institutions to amass a large number of pre-treatment and post-treatment paired patient biopsies which we will interrogate via allele-specific genotyping as well as whole genome sequencing to define mechanisms of AR. In addition we will utilize an innovative technique of taking tumor tissue directly from a biopsy and deriving patient-specific in vitro and in vivo models in the laboratory. Expansion of these models will yield a larger supply of AR cancer material to aid descriptive and functional research about the biology of AR. In addition, establishment of pre-treatment patient-specific models will allow us to verify whether the mechanism of AR derived in the lab through ex-vivo therapy mirrors the eventual clinical mode of AR.

Platinum-based concurrent chemoradiation (CRT) remains the standard treatment for patients with locally advanced, stage III non-small cell lung cancer (NSCLC). Outcomes for this large subgroup remain dismal, and no progress has been made in this area in the last three decades. Novel treatment options and predictive biomarkers to improve upon the outcome and reduce the toxicity of our current treatment paradigms are sorely needed. Our overall hypothesis is that the identification of acquired resistance pathways and synergistic targets for platinum-radiation therapy will lead to improved treatments and patient selection. We will pursue in vitro and in vivo xenograft studies to assess the synergistic role of PARP inhibition and ERCC1 modulation in the setting of CRT and will correlate these findings with a biomarker study using human tumor specimens. We will further validate YAP as a promising actionable target and will assess the interactions of concurrent chemoradiation with YAP blockade based on our preliminary data of synergy. Then, we will pursue an unbiased, functional shRNA genetic screen to identify further essential treatment resistance pathways, and carefully selected targets will be validated through a series of biochemical and functional assessment steps. The predictive value of biomarkers will be tested in retrospective cohorts of patients treated with cisplatin-radiation for locally advanced non-small cell lung cancer enrolled in our lung cancer database. Last, our unique tissue bank of pre- and post-neoadjuvant treatment specimens will be used for the identification of novel resistance markers based on modulation of expression upon neoadjuvant therapy, and functional validation of resistance biomarkers and novel treatment candidates will be pursued. These studies should provide the foundation for biomarker-driven translational and clinical studies in this area of major unmet clinical need.