An overview of farnesyltransferase inhibitors and their role in lung cancer therapy

First-line Chemotherapy Responsiveness and Patterns of Metastatic Spread Identify Clinical Syndromes Present Within Advanced KRAS Mutant Non-Small-cell Lung Cancer With Different Prognostic Significance

BACKGROUND

Unsuccessful KRAS-specific treatment approaches in non-small-cell lung cancer (NSCLC) might reflect underlying disease heterogeneity. We sought to define clinical "syndromes" within advanced KRAS mutant NSCLC to improve future clinical trials and create a clinical framework for future molecular development.

PATIENTS AND METHODS

To test a series of a priori hypotheses regarding KRAS-mutant NSCLC clinical syndromes, we conducted a multi-institutional retrospective medical record review. Survival probabilities were estimated using the Kaplan-Meier model. Between-group differences were assessed using the log-rank test. Multivariate Cox regression analyses and Wilcoxon rank sum testing were used to assess progression-free survival and overall survival (OS) differences.

RESULTS

Among 218 patients with advanced KRAS-mutant NSCLC, OS and progression-free survival with first-line chemotherapy did not differ by intrathoracic versus extrathoracic spread, smoking intensity, or the specific KRAS mutation. Metastatic disease at diagnosis resulted in significantly worse OS than recurrent, unresectable disease (median OS, 14.6 vs. 40.9 months; P = .001). Among the patients with metastatic disease at diagnosis, nonscalp, soft tissue metastases (syndrome X; 6% of cases; 95% confidence interval [CI], 2.5%-10.1%) signified a poor prognosis (median OS, 7.5 vs. 15.9 months for the controls; P = .021). The response to first-line chemotherapy (syndrome Y; 41% of cases; 95% CI, 32.3%-50.6%) signified a good prognosis (median OS, 26.7 vs. 11.9 months; P = .002). The overlap between these 2 syndromes was minimal (2 of 111). Multivariate analysis confirmed these observations. The hazard ratio for death for syndromes X and Y was 2.64 (95% CI, 1.13-6.14) and 0.45 (95% CI, 0.28-0.76), respectively.

CONCLUSION

Chemotherapy-responsive disease and nonscalp, soft tissue spread might represent distinct clinical syndromes within KRAS-mutant NSCLC. The molecular biology underlying this heterogeneity warrants future studies.

Farnesyl diphosphate analogues with aryl moieties are efficient alternate substrates for protein farnesyltransferase

Farnesylation is an important post-translational modification essential for the proper localization and function of many proteins. Transfer of the farnesyl group from farnesyl diphosphate (FPP) to proteins is catalyzed by protein farnesyltransferase (FTase). We employed a library of FPP analogues with a range of aryl groups substituting for individual isoprene moieties to examine some of the structural and electronic properties of the transfer of an analogue to the peptide catalyzed by FTase. Analysis of steady-state kinetics for modification of peptide substrates revealed that the multiple-turnover activity depends on the analogue structure. Analogues in which the first isoprene is replaced with a benzyl group and an analogue in which each isoprene is replaced with an aryl group are good substrates. In sharp contrast with the steady-state reaction, the single-turnover rate constant for dansyl-GCVLS alkylation was found to be the same for all analogues, despite the increased chemical reactivity of the benzyl analogues and the increased steric bulk of other analogues. However, the single-turnover rate constant for alkylation does depend on the Ca(1)a(2)X peptide sequence. These results suggest that the isoprenoid transition-state conformation is preferred over the inactive E·FPP·Ca(1)a(2)X ternary complex conformation. Furthermore, these data suggest that the farnesyl binding site in the exit groove may be significantly more selective for the farnesyl diphosphate substrate than the active site binding pocket and therefore might be a useful site for the design of novel inhibitors.

Farnesyl transferase expression determines clinical response to the docetaxel-lonafarnib combination in patients with advanced malignancies

BACKGROUND

Lonafarnib (LNF) is a protein farnesyl transferase (FTase) inhibitor that has shown synergistic activity with taxanes in preclinical models and early stage clinical trials. Preclinical findings suggested tubulin acetylation and FTase expression levels may be important determinants of drug sensitivity that would help identify patient populations more likely to benefit from this regimen. This pilot study evaluated the biological effects of LNF and docetaxel (DTX) combination therapy in refractory solid tumors by comparing pretreatment and post-treatment tumor biopsies.

METHODS

Patients with histologically confirmed locally advanced or metastatic solid malignancies refractory to standard therapies or with no effective therapies available were eligible. Patients were randomized to 1 of 4 dosing cohorts: 1) 30 mg/m², 100 mg; 2) 36 mg/m², 100 mg; 3) 30 mg/m², 150 mg; or 4) 36 mg/m², 150 mg of DTX intravenously weekly, LNF orally twice daily, respectively.

RESULTS

Of the 38 patients enrolled, 36 were treated, and 29 were evaluable for toxicity and response assessment. The combination of LNF and DTX was tolerated in all cohorts with the exception of a 28% incidence of grade 3/4 diarrhea, which was manageable with aggressive antidiarrheal regimens. Seven patients derived clinically meaningful benefit from this combination treatment; these patients had significantly lower basal FTase-beta mRNA expression levels than the mean study population level (P < .05). Correlation of clinical benefit with tubulin acetylation content as well as basal acetyl-tubulin content were evaluated. However, no significant correlation was found.

CONCLUSIONS

Despite the small number of patients, these findings support our preclinical mechanistic studies and warrant further clinical investigations using FTase-beta mRNA expression as a potential predictive biomarker to select for an enriched patient population to study the effects of taxane and FTase inhibitor combination therapies.

Computer-aided drug design and ADMET predictions for identification and evaluation of novel potential farnesyltransferase inhibitors in cancer therapy

We have used various computational methodologies including molecular dynamics, density functional theory, virtual screening, ADMET predictions and molecular interaction field studies to design and analyze four novel potential inhibitors of farnesyltransferase (FTase). Evaluation of two proposals regarding their drug potential as well as lead compounds have indicated them as novel promising FTase inhibitors, with theoretically interesting pharmacotherapeutic profiles, when compared to the very active and most cited FTase inhibitors that have activity data reported, which are launched drugs or compounds in clinical tests. One of our two proposals appears to be a more promising drug candidate and FTase inhibitor, but both derivative molecules indicate potentially very good pharmacotherapeutic profiles in comparison with Tipifarnib and Lonafarnib, two reference pharmaceuticals. Two other proposals have been selected with virtual screening approaches and investigated by us, which suggest novel and alternatives scaffolds to design future potential FTase inhibitors. Such compounds can be explored as promising molecules to initiate a research protocol in order to discover novel anticancer drug candidates targeting farnesyltransferase, in the fight against cancer.

The protein farnesyltransferase regulates HDAC6 activity in a microtubule-dependent manner

The cytoplasmic deacetylase HDAC6 is an important regulator of cellular pathways that include response to stress, protein folding, microtubule stability, and cell migration, thus representing an attractive target for cancer chemotherapy. However, little is known about its upstream regulation. Our previous work has implicated HDAC6 as a new protein target for the farnesyltransferase inhibitors (FTIs), although HDAC6 lacks a farnesylation motif. Here we show that the protein farnesyltransferase (FTase) and HDAC6 are present in a protein complex together with microtubules in vivo and in vitro. FTase binds microtubules directly via its alpha subunit, and this association requires the C terminus of tubulin. Treatment with an FTI removed FTase, but not HDAC6, from the protein complex, suggesting that the active form of FTase is bound to microtubules. Importantly, the removal of FTase from microtubules abrogated HDAC6 activity, as did a stable knockdown of the alpha subunit of FTase (FTalphaKD). Interestingly, the FTalphaKD cells showed increased sensitivity to the antiproliferative effects of Taxol and the FTI lonafarnib when used either as single agents or in combination as compared with parental cells. Altogether, these data suggest that FTase, via its tubulin-association, is a critical upstream regulator of HDAC6 activity and that FTase expression could help stratify cancer patients that would most benefit from this treatment.

Farnesyltransferase inhibitors reverse taxane resistance

The combination of farnesyltransferase inhibitors (FTIs) and taxanes has been shown to result in potent antiproliferative and antimitotic synergy. Recent phase I and II clinical trials have shown that this combination shows clinical activity in taxane-refractory or taxane-resistant cancer patients. To understand the mechanism behind these clinical observations, we used a cancer cell model of paclitaxel resistance and showed that the FTI/taxane combination retains potent antiproliferative, antimitotic, and proapoptotic activity against the paclitaxel-resistant cells, at doses where each drug alone has little or no activity. To probe the mechanistic basis of these observations, paclitaxel activity was monitored in living cells using the fluorescently conjugated paclitaxel, Flutax-2. We observed that all FTIs tested increase the amount of microtubule-bound Flutax-2 and the number of microtubules labeled with Flutax-2 in both paclitaxel-resistant and paclitaxel-sensitive cells. Importantly, we observed a consequential increase in microtubule stability and tubulin acetylation with the combination of the two drugs, even in paclitaxel-resistant cells, confirming that the enhanced taxane binding in the presence of FTI affects microtubule function. Furthermore, this mechanism is dependent on the function of the tubulin deacetylase, HDAC6, because in cells overexpressing a catalytically inactive HDAC6, FTIs are incapable of enhancing Flutax-2-microtubule binding. Similar results were obtained by using an FTI devoid of farnesyltransferase inhibitory activity, indicating that functional inhibition of farnesyltransferase is also required. Overall, these studies provide a new insight into the functional relationship between HDAC6, farnesyltransferase, and microtubules, and support clinical data showing that the FTI/taxane combination is effective in taxane-refractory patients.

Novel targeted therapies for non-small cell lung cancer

Targeted therapies will advance the treatment of NSCLC as we improve our understanding of the underlying biology of NSCLC and enhance our ability to clinically target the optimal therapy to an individual's cancer. Ongoing translational research including tissue arrays, genomic, and proteomic studies will help to identify clinically useful biomarkers that will allow further classification of NSCLC and may allow accurate prediction of response to specific chemotherapeutic regimens. Advances in targeted therapy in NSCLC are already yielding exciting results, and promises to become an increasingly important adjunct to surgical management of NSCLC.

Targeted therapy for non-small cell lung cancer

The overall survival for the treatment of lung cancer patients is less than 15%, despite advances in chemotherapy, radiation therapy, and surgery, due to the inability to control metastatic disease. Over the past three decades, the genetics of lung cancer has been progressively delineated. Small molecule drugs or monoclonal antibodies have been developed that target and inactivate specific cancer-related proteins, such as growth factor receptors or their kinases. This article will review the therapeutic implications of molecular changes associated with non-small cell lung cancer and the status of targeted therapies in its treatment.

Novel Strategies for the Early Detection and Prevention of Lung Cancer

Lung cancer is the leading cause of cancer death in the United States. Despite evidence of molecular abnormalities in biological specimens, progress in this disease is hampered by the lack of diagnostic markers useful for clinical practice. The majority of patients with lung cancer are still diagnosed at an advanced stage, when prognosis is poor. This article reviews new strategies being studied for the early detection of lung cancer. These strategies involve new methods of imaging (including low-dose computed tomography [CT] scanning), DNA analysis, and proteomic-based techniques. These strategies have not only improved our understanding of lung cancer but show promise in offering better survival to patients with this deadly disease. Of paramount importance in the search for methods of early detection is the need for the identification of the ideal population to screen, a multidisciplinary approach, and validation of promising techniques.

Current Management of Advanced Non-Small Cell Lung Cancer: Targeted Therapy

Lung cancer is one of the most frequent causes of cancer-related death in the United States. For patients with advanced non-small cell lung cancer (NSCLC), chemotherapy, alone or in combination with radiation therapy, is considered the standard treatment. Although this treatment may result in a modest improvement in patient survival, overall prognosis of these patients remains dismal, and the treatment is nonspecific, nonselective, and toxic. Therefore, new therapeutic strategies are needed. During the past decade, several molecules that contribute to lung cancer progression and metastasis have been identified. Growth factors and proangiogenic factors have been the focus of intense research in cancer since therapeutic approaches for their inhibition do exist. The role of these factors was studied in different organs and tumors and was found to be phenotypically distinct. Several molecular targeted therapies have shown efficacy and had been approved for treatment of specific cancers. Most advanced in clinical research for lung cancer are targeted therapies that inhibit the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor (VEGF) signaling pathways. Others are signaling pathway inhibitors. The first targeted therapy for lung cancer is gefitinib, an EGFR inhibitor, which was approved in several countries in 2003. Goals of molecular targeted therapy studies include the following: better understanding of the exact role of particular growth factors in specific tumors; establishment of new clinical study designs for biological agents; and tailoring appropriate combinations of conventional chemotherapy and/or radiotherapy with biological therapy for specific patients. Achievement of these goals will hopefully lead to incorporation of biological therapy into the current anticancer arsenal, for the benefit of lung cancer patients.

Mechanisms of and potential treatment strategies for metastatic disease in non-small cell lung cancer

Lung cancer consumes over one million lives in the world every year, with surgical resection playing a dominant role in the curative treatment of lung cancer with nonsmall cell histology. Mortality usually is the result of systemic spread of the disease, with little impact on survival when chemotherapy is applied in the adjuvant or palliative setting. Conventional cytotoxic chemotherapy has reached a plateau in efficacy. The future of treatment lies in the elucidation of the biology of lung cancer and the application of targeted therapies either alone or in combination with chemotherapy. The impact of the first generation of targeted therapies on lung cancer has been modest, with studies suggesting improvement in response rates, but no evidence of improved survival. As we expand our understanding of the mechanisms governing lung cancer progression and metastasis, we will be able to apply the growing armamentarium against this disease with a goal toward prolonging survival and increasing the chance for cure.