Therapeutic efficacy of ABT-737, a selective inhibitor of BCL-2, in small cell lung cancer

Bcl-2 is a central regulator of cell survival that is overexpressed in the majority of small cell lung cancers (SCLC) and contributes to both malignant transformation and therapeutic resistance. We compared primary SCLC xenografts prepared from de novo human tumors with standard cell line-based xenografts in the evaluation of a novel and highly potent small molecule inhibitor of Bcl-2, ABT-737. ABT-737 induced dramatic regressions in tumors derived from some SCLC cell lines. In contrast, only one of three primary xenograft SCLC tumors showed significant growth inhibition with ABT-737. Explanations for this apparent dichotomy may include relatively low expression of Bcl-2 in the primary xenografts or inherent differences in the model systems. The addition of etoposide to ABT-737 in the primary xenografts resulted in significant decreases in tumor growth, underscoring the clinical potential of ABT-737 in combination therapy. To identify factors that may contribute to resistance to ABT-737 and related inhibitors, we isolated resistant derivatives of an initially sensitive cell line-based xenograft. Acquired resistance in this model was associated with decreases in the expression of the primary target Bcl-2, of proapoptotic partners of Bcl-2 (Bax and Bim), and of Bcl-2:Bim heterodimers. Expression profiling reveals 85 candidate genes demonstrating consistent changes in gene expression with acquired resistance. Taken together, these data have specific implications for the clinical development of Bcl-2 inhibitors for SCLC and broader implications for the testing of novel anticancer strategies in relevant preclinical models.

Current status of second-line treatment and novel therapies for small cell lung cancer

Despite high response rates to first-line standard treatment, the great majority of patients with small cell lung cancer (SCLC) will relapse and succumb to their disease rather quickly. In the context of salvage therapy, symptom palliation and quality-of-life improvements, besides survival prolongation, are primary treatment endpoints. A variety of single-agent and multi-agent chemotherapy regimens have been tested with limited success in patients with recurrent SCLC. A number of combination regimens have demonstrated high response rates in second-line settings, but these can be considered only for patients with good performance status. Treatment outcome depends on many factors, including type of response to first-line therapy, treatment-free interval, and performance status. Currently, topotecan represents an effective, tolerable therapeutic option and is the only agent approved for this indication. The management of patients with recurrent disease remains an area of active research. This review provides an update of clinical research on second-line chemotherapy of SCLC and of recent results obtained with novel molecular targeted approaches in both first- and second-line therapy.

Antisense therapy in malignant diseases: status quo and quo vadis?

Preclinical and clinical studies indicate a role for AS ODNs (antisense oligonucleotides) as therapeutics for malignant diseases. The principle of antisense technology is the sequence-specific binding of an AS ODN to the target mRNA, resulting in a translational arrest. The specificity of hybridization makes antisense strategy attractive to selectively modulate the expression of genes involved in the pathogenesis of malignant diseases. One antisense drug has been approved for local therapy of CMV (cytomegalovirus) retinitis, and a number of AS ODNs are currently being tested in clinical trials, including AS ODN targeting Bcl-2, XIAP (X-linked inhibitor of apoptosis protein) and TGF-beta-2 (transforming growth factor beta-2). AS ODNs are well tolerated and may have therapeutic activity. In particular, an AS ODN to Bcl-2 has been tested in phase III clinical trials in chronic lymphocytic leukaemia, multiple myeloma and malignant melanoma. In this review, therapeutic concepts, clinical studies and new promising molecular targets to treat malignancies with AS ODNs are summarized.