Rainer Wiewrodt

Targeting BCL‐2 family proteins to overcome drug resistance in non‐small cell lung cancer

Cytotoxic chemotherapies are standard of care for patients suffering from advanced non‐small cell lung cancer (NSCLC). However, objective responses are only achieved in 20% of cases and long‐term survival is rarely observed. Clinically applied anticancer drugs exert at least some of their activities by inducing apoptosis. A critical step in apoptotic signal transduction is the permeabilization of the mitochondrial outer membrane (MOM), which is regulated by the BCL‐2 family of proteins. Hence, therapeutic targeting of BCL‐2 proteins is a promising approach to increase the drug‐sensitivity of cancers. To this end we have assessed the impact of conditional expression of the proapoptotic multidomain (BH1‐2‐3) protein BAK, which directly permeabilizes the MOM, and the BH3‐mimetic ABT‐737, which acts indirectly by derepressing BH1‐2‐3 proteins, on apoptosis and drug sensitivity of NSCLC cells. Conditionally expressed BAK sensitized resistant NSCLC cells to drug‐induced apoptosis. In contrast, ABT‐737 was ineffective in those NSCLC cells expressing high levels of the anti‐apoptotic MCL‐1 protein. Tissue microarray analysis of tumor samples from 84 chemotherapy‐naïve NSCLC patients revealed MCL‐1 expression in 56% of cases, thus supporting the relevance of this resistance factor in a clinical setting. Enforced expression of the BH3‐only protein NOXA, which targets MCL‐1, overcame resistance to ABT‐737. Moreover, combining conditionally expressed BAK with ABT‐737 enhanced apoptosis in NSCLC cells independently of their MCL‐1 status. In conclusion, the heterogeneity of apoptosis defects observed in drug‐resistant NSCLC demands individually tailored molecular therapies. Targeting the MOM permeabilizer BAK appears to have a broader apoptogenic activity than the BH3‐only mimetic ABT‐737.

Treatment of malignant pleural effusion with the trifunctional antibody catumaxomab (Removab) (anti-EpCAM x Anti-CD3): results of a phase 1/2 study.

Catumaxomab is a trifunctional monoclonal antibody consisting of a mouse immunoglobulin G2a part and a rat immunoglobulin G2b part with 2 different antigen binding sites binding the epithelial cell adhesion molecule antigen on tumor cells and CD3 on T lymphocytes. The intact Fc region provides a third functional binding site, binding and activating selectively Fcγ receptor I, IIa, and III-positive accessory cells. These binding properties lead to specific tumor cell killing. As catumaxomab demonstrated efficacy in patients with malignant ascites, we performed this phase 1/2 trial in patients with malignant pleural effusion (MPE). We investigated a series of 3 escalating doses of 5 to 200 μg catumaxomab administered intrapleurally to patients with MPE containing epithelial cell adhesion molecule -positive cells. Primary objectives were determination of dose-limiting toxicity, safety, and tolerability. Secondary objectives were efficacy and pharmacodynamics. Twenty-four patients were treated with catumaxomab. Most frequent adverse events were pyrexia, elevated liver enzymes, nausea, and decreased lymphocytes. Dose-limiting toxicities were observed in 2 patients: One had pleural empyema and fatal sepsis and 1 had grade 3 erythema and hepatobiliary disorder. Five patients with breast cancer out of 7 evaluable patients had a response to treatment. Intrapleural administration of catumaxomab is feasible although the substantial number of drop-outs and deaths in short proximity to study treatment raise questions whether MPE is the right indication for catumaxomab or whether the patient population should be defined different. Safety profile was as expected reflecting catumaxomabs mode of action. Preliminary efficacy showed a suggestion of improvement in some patients.

c-kit Expression in Adenocarcinomas of the Lung

The tyrosine-kinase receptor c-kit (CD117) and its ligand stem cell factor are considered to be co-expressed in various solid tumors, including adenocarcinomas of the lung. The frequency of c-kit expression and its association with clinical parameters has not yet been evaluated in a larger population of lung adenocarcinomas. Therefore, tumor tissue of 95 consecutive patients with adenocarcinoma of the lung was stained using a polyclonal c-kit antibody. c-kit expression was correlated with relevant clinical parameters obtained by chart review. Positive c-kit expression in tumor tissue was observed in 61 of 95 patients (64%). Univariate analysis showed a significant effect of T (p = 0.003), N (p = 0.001) and M stage (p < 0.001) as well as of performance status (p = 0.001), surgical resection (p < 0.001), and LDH serum levels (p = 0.016) on survival. In contrast, c-kit protein expression was non- significant (p = 0.913). However, multivariate Cox regression with the influential parameters revealed a significant effect of c-kit expression on survival. Forward stepwise selection showed a 1.77-fold increased risk to die (hazard ratio, HR; 95% confidence interval, CI: 1.00–3.14, p = 0.047) for patients with c-kit-positive tumors. Similar data for c-kit expression were obtained by backward stepwise selection (HR: 1.78; 95% CI: 1.00–3.16; p = 0.044). In conclusion, the receptor tyrosine kinase c-kit is frequently expressed in adenocarcinomas of the lung and has a relevant effect on patient survival. The results of this study support clinical trials targeting the c-kit receptor with specific c-kit inhibitors (e.g. imatinib).