Abstract P082: Distinct and significant anti-cancer efficacy of plinabulin in patient derived small cell lung cancer (SCLC) 3D soft agar clonogenic assays
Authors: Lloyd George K. , Tonra James , Goettlich Claudia , Deigner Tobias , Mohanlal Ramon , Huang Lan 
Published: December 2021

Abstract
Plinabulin (Plin) is a new chemical entity and a selective immunomodulating microtubule-targeting agent (SIMBA), which exerts immune-enhancing effects through increasing dendritic cell (DC) maturation and DC-dependent antigen presentation to CD4+ and CD8+ T-Cells. Here we evaluated whether Plin also exerts direct anti-cancer effects against approximately 80 patient derived (PDX) models. Plin was characterized for its ability to inhibit anchorage independent growth and ex vivo colony formation of PDX tumor cells in semi-solid medium. The compound was investigated in PDX models of various cancer types, using a 3D clonogenic assay in a 96-well format. Briefly, tumor cell suspensions were prepared from subcutaneous xenografts in NMRI nu/nu mice and seeded into 96 well ultra-low attachment plates within a layer of semi-solid medium. Plin was added to the assay plate at either day 2 or day 7 and tested at 9 concentrations in half-log increments up to a concentration of 3 µM. Supernatant was exchanged 24 h after dosing and cells were further incubated at 37°C and 7.5 % CO2 up to a total assay time of 8 or 13 days. Colony counts based on image analysis were utilized to evaluate efficacy. Plin inhibited tumor colony formation in a concentration-dependent manner. With Plin treatment beginning 2 days after PDX cell seeding, the most sensitive cancer types were small cell lung cancer (mean absolute IC70 = 0.035 μM; n = 7), bladder cancer (mean absolute IC70 = 0.038 μM; n = 9), and soft tissue sarcoma (mean absolute IC70 = 0.057 μM; n = 10). Melanoma models were observed to be the least sensitive to Plin monotherapy, with a mean absolute IC70 of 1.105 μM (n = 19). With Plin treatment beginning 7 days after PDX cell seeding, based on absolute IC70 values, 9 out of 68 tumor models were sensitive towards plinabulin. The most sensitive histotypes were gastric cancer (Asian, mean abs. IC70 = 0.319 µM, n = 3), small cell lung cancer (mean abs. IC70 = 0.385 µM, n = 7; 3 below 50 nM), osteosarcoma (mean abs. IC70 = 0.624 µM, n = 3), and central nervous system cancer (mean abs. IC70 = 1.521 µM, n = 6). Overall, the most responsive models based on IC70 were the small cell lung cancer models 2156 (abs. IC70 = 0.015 µM), 1129 (abs. IC70 = 0.032 µM) and 650 (abs. IC70 = 0.032 µM), and the osteosarcoma model 1186 (abs. IC70 = 0.027 µM). Soft tissue sarcoma models (n = 8), Her2-enriched breast cancer models (n = 6), melanoma models (n = 9), bladder cancer models (n = 6), and gastric cancer models (Caucasian, n = 3) were observed to be the least sensitive cancer types with a mean IC70 value &gt; 3 µM. In conclusion, using patient-derived tumor models in a 3D clonogenic assay, SCLC tumor types were the most sensitive to Plin. These results provide mechanistic support for the preliminary positive results recently reported with Plin in combination with Nivolumab and Ipilimumab in SCLC patients (Malhotra ASCO 2021).
Citation Format: George K. Lloyd, James Tonra, Claudia Goettlich, Tobias Deigner, Ramon Mohanlal, Lan Huang. Distinct and significant anti-cancer efficacy of plinabulin in patient derived small cell lung cancer (SCLC) 3D soft agar clonogenic assays [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P082.