Palbociclib in combination with sunitinib exerts a synergistic anti-cancer effect in patient-derived xenograft models of various human cancers types.

The efficacy/safety of combining palbociclib (a CDK4/6 inhibitor) and sunitinib (a multi-targeted receptor tyrosine kinase inhibitor) was evaluated, using patient-derived xenograft (PDX) models. Twenty-three PDX mice models were developed from patients with various solid tumors. The mice were randomized to 4 groups (5-6 mice in each): control/palbociclib (100 mg/kg)/sunitinib (50 mg/kg)/combination. Drugs were administered orally, 5 days/week. In 17/23 PDX models (74%), the combination demonstrated a synergistic inhibitory effect vs the monotherapies ("responder" models) with no unexpected toxicities. In 13/17 responder models, where standard-of-care (SOC) was an additional comparator, the combination was more effective than SOC in 7 models, as effective in 4, and less effective in 2. The mean ± SEM experiment duration in 15/17 responder models (2/17 were excluded due to technical issues) was 86 ± 12 and 31 ± 5 days for the combination and control groups, respectively (p = 0.0002). The effect of the combination was dose-dependent. Cell-viability experiments in A549/MDA-MB-231/HT-29 cell lines and experiments using tumor-derived primary cell spheroids supported the PDX findings. In conclusion, combination of palbociclib and sunitinib exerts a synergistic anti-tumor effect without adding unexpected toxicity. A clinical trial assessing this combination is underway.

Establishing 3-Dimensional Spheroids from Patient-Derived Tumor Samples and Evaluating their Sensitivity to Drugs.

Despite remarkable advances in understanding tumor biology, the vast majority of oncology drug candidates entering clinical trials fail, often due to a lack of clinical efficacy. This high failure rate illuminates the inability of the current preclinical models to predict clinical efficacy, mainly due to their inadequacy in reflecting tumor heterogeneity and the tumor microenvironment. These limitations can be addressed with 3-dimensional (3D) culture models (spheroids) established from human tumor samples derived from individual patients. These 3D cultures represent real-world biology better than established cell lines that do not reflect tumor heterogeneity. Furthermore, 3D cultures are better than 2-dimensional (2D) culture models (monolayer structures) since they replicate elements of the tumor environment, such as hypoxia, necrosis, and cell adhesion, and preserve the natural cell shape and growth. In the present study, a method was developed for preparing primary cultures of cancer cells from individual patients that are 3D and grow in multicellular spheroids. The cells can be derived directly from patient tumors or patient-derived xenografts. The method is widely applicable to solid tumors (e.g., colon, breast, and lung) and is also cost-effective, as it can be performed in its entirety in a typical cancer research/cell biology lab without relying on specialized equipment. Herein, a protocol is presented for generating 3D tumor culture models (multicellular spheroids) from primary cancer cells and evaluating their sensitivity to drugs using two complementary approaches: a cell-viability assay (MTT) and microscopic examinations. These multicellular spheroids can be used to assess potential drug candidates, identify potential biomarkers or therapeutic targets, and investigate the mechanisms of response and resistance.