Lung epithelial proliferation: a biomarker for chemoprevention trials?

Why Great Mitotic Inhibitors Make Poor Cancer Drugs

Chemotherapy is central to oncology, perceived to operate only on prolific cancerous tissue. Yet, many non-neoplastic tissues are more prolific compared with typical tumors. Chemotherapies achieve sufficient therapeutic windows to exert antineoplastic activity because they are prodrugs that are bioactivated in cancer-specific environments. The advent of precision medicine has obscured this concept, favoring the development of high-potency kinase inhibitors. Inhibitors of essential mitotic kinases exemplify this paradigm shift, but intolerable on-target toxicities in more prolific normal tissues have led to repeated failures in the clinic. Proliferation rates alone cannot be used to achieve cancer specificity. Here, we discuss integrating the cancer specificity of prodrugs from classical chemotherapeutics and the potency of mitotic kinase inhibitors to generate a class of high-precision cancer therapeutics.

AMBRA1 links autophagy to cell proliferation and tumorigenesis by promoting c-Myc dephosphorylation and degradation

Inhibition of a main regulator of cell metabolism, the protein kinase mTOR, induces autophagy and inhibits cell proliferation. However, the molecular pathways involved in the cross-talk between these two mTOR-dependent cell processes are largely unknown. Here we show that the scaffold protein AMBRA1, a member of the autophagy signalling network and a downstream target of mTOR, regulates cell proliferation by facilitating the dephosphorylation and degradation of the proto-oncogene C-MYC. We found that AMBRA1 favors the interaction between C-MYC and its phosphatase PP2A and that, when mTOR is inhibited, it enhances PP2A activity on this specific target, thereby reducing the cell division rate. As expected, such a de-regulation of C-MYC correlates with increased tumorigenesis in AMBRA1-defective systems, thus supporting a role for AMBRA1 as a haploinsufficient tumour suppressor gene.

Assessing efficacy in early-phase cancer prevention clinical trials: the case of ki-67 in the lung

This perspective on Kim et al. (beginning on p. 148 in this issue of the journal) examines the value of the Ki-67 proliferation index as a surrogate end point in early-phase clinical lung cancer prevention trials. The clinical trial of Kim et al. shows an effect of the cyclooxygenase-2-selective inhibitor celecoxib at a high dose on Ki-67 expression in the normal bronchial epithelia of current and former smokers. The critical issue of how these data can be used to further drug development is discussed.

Biological activity of celecoxib in the bronchial epithelium of current and former smokers

Non-small cell lung cancer is the primary cause of cancer-related death in Western countries. One important approach taken to address this problem is the development of effective chemoprevention strategies. In this study, we examined whether the cyclooxygenase-2 inhibitor celecoxib, as evidenced by decreased cell proliferation, is biologically active in the bronchial epithelium of current and former smokers. Current or former smokers with at least a 20 pack-year (pack-year = number of packs of cigarettes per day times number of years smoked) smoking history were randomized into one of four treatment arms (3-month intervals of celecoxib then placebo, celecoxib then celecoxib, placebo then celecoxib, or placebo then placebo) and underwent bronchoscopies with biopsies at baseline, 3 months, and 6 months. The 204 patients were primarily (79.4%) current smokers: 81 received either low-dose celecoxib or placebo and 123 received either high-dose celecoxib or placebo. Celecoxib was originally administered orally at 200 mg twice daily and the protocol subsequently increased the dose to 400 mg twice daily. The primary end point was change in Ki-67 labeling (from baseline to 3 months) in bronchial epithelium. No cardiac toxicities were observed in the participants. Although the effect of low-dose treatment was not significant, high-dose celecoxib decreased Ki-67 labeling by 3.85% in former smokers and by 1.10% in current smokers-a significantly greater reduction (P = 0.02) than that seen with placebo after adjusting for metaplasia and smoking status. A 3- to 6-month celecoxib regimen proved safe to administer. Celecoxib (400 mg twice daily) was biologically active in the bronchial epithelium of current and former smokers; additional studies on the efficacy of celecoxib in non-small cell lung cancer chemoprevention may be warranted.

A randomized phase II chemoprevention trial of 13-CIS retinoic acid with or without alpha tocopherol or observation in subjects at high risk for lung cancer

No chemoprevention strategies have been proven effective for lung cancer. We evaluated the effect of 13-cis retinoic acid (13-cis RA), with or without alpha tocopherol, as a lung cancer chemoprevention agent in a phase II randomized controlled clinical trial of adult subjects at high risk for lung cancer as defined by the presence of sputum atypia, history of smoking, and airflow obstruction, or a prior surgically cured nonsmall cell lung cancer (disease free, >3 years). Subjects were randomly assigned to receive either 13-cis RA, 13-cis RA plus alpha tocopherol (13-cis RA/alpha toco) or observation for 12 months. Outcome measures are derived from histologic evaluation of bronchial biopsy specimens obtained by bronchoscopy at baseline and follow-up. The primary outcome measure is treatment "failure" defined as histologic progression (any increase in the maximum histologic score) or failure to return for follow-up bronchoscopy. Seventy-five subjects were randomized (27/22/26 to observations/13-cis RA/13-cis RA/alpha toco); 59 completed the trial; 55 had both baseline and follow-up bronchoscopy. The risk of treatment failure was 55.6% (15 of 27) and 50% (24 of 48) in the observation and combined (13 cis RA plus 13 cis RA/alpha toco) treatment arms, respectively (odds ratio adjusted for baseline histology, 0.97; 95% confidence interval, 0.36-2.66; P = 0.95). Among subjects with complete histology data, maximum histology score in the observation arm increased by 0.37 units and by 0.03 units in the treated arms (difference adjusted for baseline, -0.18; 95% confidence interval, -1.16 to 0.81; P = 0.72). Similar (nonsignificant) results were observed for treatment effects on endobronchial proliferation as assessed by Ki-67 immunolabeling. Twelve-month treatment with 13-cis RA produced nonsignificant changes in bronchial histology, consistent with results in other trials. Agents advancing to phase III randomized trials should produce greater histologic changes. The addition of alpha tocopherol did not affect toxicity.

Bronchial epithelial Ki-67 index is related to histology, smoking, and gender, but not lung cancer or chronic obstructive pulmonary disease

PURPOSE

To determine whether increased bronchial epithelial proliferation is associated with histology, smoking status, gender, age, chronic obstructive pulmonary disease (COPD), or lung cancer.

EXPERIMENTAL DESIGN

Cross-sectional study of 113 subjects undergoing white light and autofluorescence bronchoscopy: 27 never smokers; 27 current or ex-smokers with normal spirometry; 31 current or ex-smokers with COPD; and 28 current, ex-, or never smokers with lung cancer. Ki-67 expression was determined by immunohistochemistry on all evaluable biopsy sites without carcinoma. Relationships between Ki-67 index (percentage of epithelial cells expressing Ki-67), demographic variables, smoking, histology, and the presence of COPD and/or lung cancer were determined.

RESULTS

Results for both maximal and mean Ki-67 index are similar, so only the former are reported. Average maximal Ki-67 index was higher in current smokers than either ex-smokers or never smokers (48.0% versus 30.6% versus 22.6%; P<0.001). Males had higher Ki-67 index than females (39.9% versus 23.6%; P<0.001). Compared with subjects without disease (Ki-67 index=30.0%), maximal Ki-67 index was not significantly elevated (P=0.44) in subjects with either lung cancer (Ki-67=39.1%) or COPD (Ki-67=38.9%).

CONCLUSIONS

Smoking status, bronchial histology, and gender were significantly associated with Ki-67 index. No increase in Ki-67 index was found in the nonmalignant epithelium of patients with lung cancer or COPD. Although Ki-67 index may provide insight into the short-term effects of chemoprevention agents on cell proliferation, its lack of association with lung cancer or COPD raises question regarding its utility as a lung cancer risk biomarker.

Proliferative changes in the bronchial epithelium of former smokers treated with retinoids

BACKGROUND

Retinoids have shown antiproliferative and chemopreventive activity. We analyzed data from a randomized, placebo-controlled chemoprevention trial to determine whether a 3-month treatment with either 9-cis-retinoic acid (RA) or 13-cis-RA and alpha-tocopherol reduced Ki-67, a proliferation biomarker, in the bronchial epithelium.

METHODS

Former smokers (n = 225) were randomly assigned to receive 3 months of daily oral 9-cis-RA (100 mg), 13-cis-RA (1 mg/kg) and alpha-tocopherol (1200 IU), or placebo. Bronchoscopic biopsy specimens obtained before and after treatment were immunohistochemically assessed for changes in the Ki-67 proliferative index (i.e., percentage of cells with Ki-67-positive nuclear staining) in the basal and parabasal layers of the bronchial epithelium. Per-subject and per-biopsy site analyses were conducted. Multicovariable analyses, including a mixed-effects model and a generalized estimating equations model, were used to investigate the treatment effect (Ki-67 labeling index and percentage of bronchial epithelial biopsy sites with a Ki-67 index > or = 5%) with adjustment for multiple covariates, such as smoking history and metaplasia. Coefficient estimates and 95% confidence intervals (CIs) were obtained from the models. All statistical tests were two-sided.

RESULTS

In per-subject analyses, Ki-67 labeling in the basal layer was not changed by any treatment; the percentage of subjects with a high Ki-67 labeling in the parabasal layer dropped statistically significantly after treatment with 13-cis-RA and alpha-tocopherol treatment (P = .04) compared with placebo, but the drop was not statistically significant after 9-cis-RA treatment (P = .17). A similar effect was observed in the parabasal layer in a per-site analysis; the percentage of sites with high Ki-67 labeling dropped statistically significantly after 9-cis-RA treatment (coefficient estimate = -0.72, 95% CI = -1.24 to -0.20; P = .007) compared with placebo, and after 13-cis-RA and alpha-tocopherol treatment (coefficient estimate = -0.66, 95% CI = -1.15 to -0.17; P = .008).

CONCLUSIONS

In per-subject analyses, treatment with 13-cis-RA and alpha-tocopherol, compared with placebo, was statistically significantly associated with reduced bronchial epithelial cell proliferation; treatment with 9-cis-RA was not. In per-site analyses, statistically significant associations were obtained with both treatments.

Celecoxib decreases Ki-67 proliferative index in active smokers

PURPOSE

This study evaluated the feasibility of cyclooxygenase-2 (COX-2) inhibition for lung cancer chemoprevention. We hypothesized that treatment with oral Celecoxib, a selective COX-2 inhibitor, would favorably alter the biomarkers of lung cancer risk as measured by the Ki-67 proliferative labeling index (Ki-67 LI).

EXPERIMENTAL DESIGN

Twenty active heavy smokers were enrolled into a pilot study and treated with Celecoxib for 6 months. Bronchoscopies with bronchial biopsies were done before and after 6 months of Celecoxib treatment. H&E stain for histologic grading and immunohistochemical examination for Ki-67 LI, COX-2, and survivin were carried out on serially matched biopsy samples to determine responses to treatment.

RESULTS

Treatment with Celecoxib significantly reduced Ki-67 LI in smokers by 35% (P = 0.016), and increased the expression of nuclear survivin by 23% (P = 0.036) without significantly changing that of cytoplasmic survivin.

CONCLUSIONS

Our findings suggest that oral Celecoxib may be capable of modulating the proliferation indices and apoptotic balance in bronchial tissue of active smokers.

Development of tobacco smoke-induced lung tumors in mice fed Bowman-Birk protease inhibitor concentrate (BBIC)

Male strain A/J mice were exposed, 6h a day, 5 days a week for 5 months to a mixture of 89% cigarette sidestream and 11% cigarette mainstream smoke and then allowed to recover for another 4 months in air. The animals were fed Bowman-Birk protease inhibitor concentrate (BBIC) at a concentration of 1% in AIN-93G diet either during smoke exposure, following smoke exposure or during the entire 9 months. At the end of the experiment, the incidence and multiplicity of lung tumors were determined. In a positive control experiment, strain A/J mice were injected with 3-methylcholanthrene (MCA) and fed a diet containing 1% BBIC; these animals were killed 5 months later. It was found that in the animals treated with MCA, BBIC decreased lung tumor multiplicities, whereas in the smoke exposed mice, BBIC did not modulate lung tumor development.