New perspectives in lung cancer. 2. Growth factors and lung cancer

Role of epidermal growth factor receptor in lung cancer and targeted therapies

Lung cancer is the foremost cause of cancer-related deaths world-wide. Both, the major forms of lung cancer, Non-small cell lung cancer (NSCLC) and Small cell lung cancers (SCLC), have responded effectively to chemo-, radiation and adjuvant-therapies. Tumor removal through surgery also appeared as a good therapeutic strategy. However, these therapies demonstrated unfavourable side-effects, and hence novel drugs targeting lung cancer emerged essential. Activation of epidermal growth factor receptor (EGFR)-tyrosine kinases is a key reason for lung cancer progression. Two important strategies that have attenuated lung cancers were through treatments with EGFR-tyrosine kinase-inhibitors, erlotinib and gefitinib, or EGFR-neutralizing antibodies, cetuximab and bevacizumab. A major advantage with erlotinib and gefitinib was their role in second and third-line treatments following chemotherapies. Phase II/III clinical trials showed that combinatorial treatment of tyrosine kinase (TK)-inhibitors with chemotherapeutics, such as docetaxel and pemetrexed, caused significant improvements in progression-free survival and overall survival.Phase I and II clinical studies also revealed that combination of tyrosine kinase-inhibitors with the EGFR-targeted antibodies was an effective approach for treating lung cancer. However, patients having T790M-mutations within EGFR gene were resistant to erlotinib and gefitinib. Alternatively, another second-generation EGFR-tyrosine kinase-inhibitor, afatinib, that could circumvent the problem of drug resistance has been developed as lung cancer therapy. The current review focuses on the role of EGFR in lung cancer progression and apprises about the EGFR-targeted therapies. The review also informs on the adverse side-effects of these therapies and enlightens the need for safer therapeutic regimens to eradicate this dreaded disease.

Transferrin receptor expression in nonsmall cell lung cancer. Histopathologic and clinical correlates

BACKGROUND

In the search for tumor-related antigens with survival-predictive value, previous studies have yielded varied conclusions regarding the expression of one such antigen, the transferrin receptor in lung cancer. The goal of this study was to define the frequency of expression of transferrin receptor in lung cancer specimens and gather preliminary data regarding the prognostic value of this tumor-related antigen.

METHODS

Tissue immunoreactivity was studied with a murine monoclonal antibody to transferrin receptor in patients with nonsmall cell lung cancer who underwent surgical resection at the Medical Center Hospital of Vermont during the period from January, 1988, to May, 1991.

RESULTS

The study group consisted of 32 patients (21 males and 11 females) with an average follow-up length of 27 months (standard deviation of 16 months). There were 17 patients with adenocarcinoma, 14 with squamous cell carcinoma, and 1 with large cell carcinoma. At the end of data accumulation, a total of 16 deaths had been recorded (8 with squamous cell, 8 with adenocarcinoma). Normal lung tissue did not stain for transferrin receptor; however, 13 of 17 (76%) adenocarcinomas, 13 of 14 (93%) squamous cell carcinomas, and the 1 large cell carcinoma stained positively for transferrin receptor. Staining for transferrin receptor was graded according to pattern and intensity and categorized as absent-weak or strong. Survival analysis was performed to evaluate patient outcome based on a variety of clinical and experimentally determined characteristics. Groups based on N-status (N0 vs. N1 + N2, P = 0.08), stage (Stage 1 vs. Stage 2 + 3 P = 0.13), age (younger than 60 vs. 60 years or older, P = 0.09), and transferrin receptor staining (absent-weak vs. strong, P = 0.14) achieved nearly significant differences in survival. Further analysis of the differences in survival for groupings based on transferrin receptor staining found that these differences in survival reached significance for patients with larger tumors (T2 or T3, P = 0.02).

CONCLUSIONS

Transferrin receptor is expressed in the majority of lung cancers and the presence of transferrin receptor in nonsmall cell lung cancers may be an indicator of poorer prognosis in certain groups of patients.

Characterization of somatostatin receptors and growth inhibition by the somatostatin analogue BIM23014 in small cell lung carcinoma xenograft: SCLC-6

Human small cell lung cancer (SCLC) is a neuroendocrine tumour with a very poor prognostic. Receptors for somatostatin-14 and its synthetic analogue BIM23014 (Lanreotide) were characterized in 3 human SCLC xenografts (SCLC-6, SCLC-10 and SCLC-75) transplanted in nude mice. The binding activity of both iodinated ligands was tested by cross-linking assay. One major complex of 57kDa was identified by both ligands in all 3 tumours. Two other minor complexes were only detected by the natural ligand: 90kDa in all 3 tumours and 70kDa in 2 out of the 3 tumours (SCLC-6 and SCLC-75). Analysed by Northern hybridization, the expression of the gene encoding for the receptor subtype I was detected in all 3 tumours whereas the expression of the receptor subtype II was only detected in 2 out of the 3 tumours (SCLC-6 and SCLC-75). No receptor subtype III transcript was observed. The relative quantification of the detected messengers and of the cross-linked complexes determined by densitometry suggested that SCLC-6 contained a large amount of somatostatin receptors. SCLC-6 growing in nude mice was used to evaluate the antiproliferative effect of BIM23014. BIM23014 (250 micrograms, b.i.d. for 5 days) significantly inhibited tumor growth and had an additive effect with cis-platinum (1.5 mg/kg/day for 2 days) when given concomitantly. Values of the relative tumour volume as compared to control were: BIM23014 alone 57%, cis-platinum alone 57% and BIM23014 + cis-platinum: 78%. These experimental data suggest that BIM23014 given alone or in combination with cis-platinum could have a therapeutic potential in the treatment of somatostatin receptor positive SCLCs.

Production of multiple growth factors by a human non-small cell lung carcinoma cell line

The 1PT cell line, derived from an undifferentiated bronchial carcinoma, produced, in conditioned medium, immunoreactive basic fibroblast growth factor (bFGF), insulin-like growth factors I and II (IGF-I and IGF-II), epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), and transforming growth factor beta-2 (TGF beta 2) in its latent form, but not platelet-derived growth factor (PDGF), tumour necrosis factor alpha (TNF alpha), or transforming growth factor beta-1 (TGF beta 1). Comparative studies of growth stimulation of human umbilical vein (HUV) endothelial cells indicated that the growth factors detected in 1PT-conditioned medium do not solely account for its proliferative effects on these cells. These results support previous characterization studies [1,2] that suggest the production of a potentially novel tumour-derived endothelial cell growth factor by the 1PT cell line.

Therapeutic use and perspectives of synthetic peptides in oncology

Several native peptides can regulate tumour cell proliferation. After binding to specific membrane receptors they have the ability to stimulate or inhibit directly cell growth. Peptides can also control the regulation of endocrine or paracrine growth factor secretion. Agonist and antagonist molecules have been synthesized for therapeutic purposes. Hypothalamic neuropeptides are used in oncology. GnRH agonists lead to biochemical castration which is useful in treatment of hormone-dependent tumours (breast and prostate). Somatostatin analogues are beneficial in the treatment of gut neuroendocrine tumours and have demonstrated an antitumoural effect in experimental studies. Cytostatic agents, such as Gastrin Releasing Peptide antagonists, may be of interest as an adjuvant to chemotherapy or surgery in small cell lung cancer and other malignancies. The role of peptides in antigenic presentation, cell proliferation control and the metastatic process suggests a new therapeutic potential for these compounds. Progress in biotechnology could provide specific tools to screen new molecules and increase the understanding of mechanisms of action. Improvement in drug delivery techniques will allow for more convenient routes of administration.