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MINI 27 - Biology and Other Issues in SCLC (ID 152)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Small Cell Lung Cancer
- Presentations: 1
MINI27.09 - A DLL3-Targeted ADC Effectively Targets Pulmonary Neuroendocrine Tumor-Initiating Cells to Result in Sustained Tumor Regressions (ID 2533)
16:45 - 18:15 | Author(s): L.R. Saunders
Pulmonary neuroendocrine tumors such as small cell lung cancer (SCLC) and large cell neuroendocrine cancer (LCNEC) remain among the most deadly malignancies and are increasing in incidence. Patient-derived xenograft (PDX) tumors provide excellent models to study tumor biology and discover tumor-initiating cell (TIC) populations. Novel therapies that target and eradicate TIC represent a promising strategy to improve survival. An effectively targeted antibody-drug conjugate (ADC) carrying a cell-cycle independent toxin should result in significant anti-tumor activity and eliminate TIC.
Whole transcriptome sequencing was performed using TIC isolated by fluorescence-activated cell sorting from SCLC and LCNEC PDX tumors. Quantitative RT-PCR, microarray analysis of PDX tumors and cell lines, and mining of publically available transcriptome and proteome datasets were executed to validate that prospective targets, such as Delta-like protein 3 (DLL3), were highly expressed in neuroendocrine tumors, but limited in their expression in normal tissues. DLL3-specific monoclonal antibodies were generated and used to determine protein expression by immunohistochemistry, flow cytometry and ELISA. Select DLL3-specific antibodies were conjugated to a cell-cycle independent pyrrolobenzodiazepine (PBD) dimer toxin and evaluated for their ability to internalize and mediate cell killing. Finally, established SCLC and LCNEC PDX tumors were treated in vivo with a lead anti-DLL3 ADC (i.e. SC16LD6.5). Limiting dilution assay (LDA) serial transplantation experiments were executed to assess the impact of SC16LD6.5 on TIC.
Elevated expression of DLL3 mRNA was discovered in TIC of SCLC and LCNEC PDX tumors and confirmed in additional distinct primary SCLC and LCNEC tumor samples and PDX tumors. In contrast, little to no mRNA expression was detected in vital organs and other normal tissues outside of the brain. DLL3-specific antibodies confirmed protein expression on the cell surface in both primary SCLC and LCNEC tumors and in PDX tumors initiated from patients with these diseases, whereas protein was scarce in normal tissues. SC16LD6.5 rapidly internalizes and localizes to late endosomes, and treatment of 10 SCLC and 2 LCNEC PDX tumor models resulted in significant and durable tumor regression with a median time to progression benefit of 75 days versus 16 days with standard-of-care (SOC: SCLC, cisplatin/etoposide; LCNEC, cisplatin). During the course of these in vivo studies, many mice were cured as tumors often did not recur despite being followed for 120+ days post-randomization and treatment. LDA experiments executed using tumors actively responding to SC16LD6.5 provided further functional evidence that the common lack of tumor recurrence following treatment resulted from effective targeting of DLL3-expressing TIC. In vivo efficacy strongly correlated with DLL3 protein expression, and responses were observed in PDX tumor models initiated from patients with both limited and extensive stage disease and independent of their sensitivity to SOC.
The DLL3-targeted ADC, SC16LD6.5, effectively targets and eradicates TIC in SCLC and LCNEC PDX tumors. SC16LD6.5 (i.e. rovalpituzumab teserine) is currently concluding Phase 1b trials and is a promising first-in-class therapeutic for the treatment of high grade pulmonary neuroendocrine tumors.
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