Current Status of Small-Molecule Tyrosine Kinase Inhibitors Targeting Epidermal Growth Factor Receptor in Colorectal Cancer

Epidermal Growth Factor Receptor Targeting in Colorectal Carcinoma: Antibodies and Patient-Derived Organoids as a Smart Model to Study Therapy Resistance

Colorectal cancer (CRC) is the second leading cause of cancer-related death worldwide. Therefore, the need for new therapeutic strategies is still a challenge. Surgery and chemotherapy represent the first-line interventions; nevertheless, the prognosis for metastatic CRC (mCRC) patients remains unacceptable. An important step towards targeted therapy came from the inhibition of the epidermal growth factor receptor (EGFR) pathway, by the anti-EGFR antibody, Cetuximab, or by specific tyrosine kinase inhibitors (TKI). Cetuximab, a mouse-human chimeric monoclonal antibody (mAb), binds to the extracellular domain of EGFR thus impairing EGFR-mediated signaling and reducing cell proliferation. TKI can affect the EGFR biochemical pathway at different steps along the signaling cascade. Apart from Cetuximab, other anti-EGFR mAbs have been developed, such as Panitumumab. Both antibodies have been approved for the treatment of KRAS-NRAS wild type mCRC, alone or in combination with chemotherapy. These antibodies display strong differences in activating the host immune system against CRC, due to their different immunoglobulin isotypes. Although anti-EGFR antibodies are efficient, drug resistance occurs with high frequency. Resistant tumor cell populations can either already be present before therapy or develop later by biochemical adaptations or new genomic mutations in the EGFR pathway. Numerous efforts have been made to improve the efficacy of the anti-EGFR mAbs or to find new agents that are able to block downstream EGFR signaling cascade molecules. Indeed, we examined the importance of analyzing the anti-EGFR antibody-drug conjugates (ADC) developed to overcome resistance and/or stimulate the tumor host's immunity against CRC growth. Also, patient-derived CRC organoid cultures represent a useful and feasible in vitro model to study tumor behavior and therapy response. Organoids can reflect tumor genetic heterogeneity found in the tissue of origin, representing a unique tool for personalized medicine. Thus, CRC-derived organoid cultures are a smart model for studying the tumor microenvironment and for the preclinical assay of anti-EGFR drugs.

EGFR Blockade Reverts Resistance to KRASG12C Inhibition in Colorectal Cancer

Most patients with KRAS G12C-mutant non-small cell lung cancer (NSCLC) experience clinical benefit from selective KRASG12C inhibition, whereas patients with colorectal cancer bearing the same mutation rarely respond. To investigate the cause of the limited efficacy of KRASG12C inhibitors in colorectal cancer, we examined the effects of AMG510 in KRAS G12C colorectal cancer cell lines. Unlike NSCLC cell lines, KRAS G12C colorectal cancer models have high basal receptor tyrosine kinase (RTK) activation and are responsive to growth factor stimulation. In colorectal cancer lines, KRASG12C inhibition induces higher phospho-ERK rebound than in NSCLC cells. Although upstream activation of several RTKs interferes with KRASG12C blockade, we identify EGFR signaling as the dominant mechanism of colorectal cancer resistance to KRASG12C inhibitors. The combinatorial targeting of EGFR and KRASG12C is highly effective in colorectal cancer cells and patient-derived organoids and xenografts, suggesting a novel therapeutic strategy to treat patients with KRAS G12C colorectal cancer. SIGNIFICANCE: The efficacy of KRASG12C inhibitors in NSCLC and colorectal cancer is lineage-specific. RTK dependency and signaling rebound kinetics are responsible for sensitivity or resistance to KRASG12C inhibition in colorectal cancer. EGFR and KRASG12C should be concomitantly inhibited to overcome resistance to KRASG12C blockade in colorectal tumors.See related commentary by Koleilat and Kwong, p. 1094.This article is highlighted in the In This Issue feature, p. 1079.

An approach using Caenorhabditis elegans screening novel targets to suppress tumour cell proliferation

OBJECTIVES

Tumour cell proliferation requires high metabolism to meet the bioenergetics and biosynthetic needs. Dauer in Caenorhabditis elegans is characterized by lower metabolism, and we established an approach with C elegans to find potential tumour therapy targets.

MATERIALS AND METHODS

RNAi screening was used to find dauer-related genes, and these genes were further analysed in glp-1(-) mutants for tumour-suppressing testing. The identified tumour-related genes were verified in clinical tumour tissues.

RESULTS

The lifespan of glp-1(-) mutants was found to be extended by classical dauer formation signalling. Then, 61 of 287 kinase-coding genes in Caenorhabditis elegans were identified as dauer-related genes, of which 27 were found to be homologous to human oncogenes. Furthermore, 12 dauer-related genes were randomly selected for tumour-suppressing test, and six genes significantly extended the lifespan of glp-1(-) mutants. Of these six genes, F47D12.9, W02B12.12 and gcy-21 were newly linked to dauer formation. These three new dauer-related genes significantly suppressed tumour cell proliferation and thus extended the lifespan of glp-1(-) mutants in a longevity- or dauer-independent manner. The mRNA expression profiles indicated that these dauer-related genes trigged similar low metabolism pattern in glp-1(-) mutants. Notably, the expression of homolog gene DCAF4L2/F47D12.9, TSSK6/W02B12.12 and NPR1/gcy-21 was found to be higher in glioma compared with adjacent normal tissue. In addition, the high expression of TSSK6/W02B12.12 and NPR1/gcy-21 correlated with a worse survival in glioma patients.

CONCLUSIONS

Dauer gene screening in combination with tumour-suppressing test in glp-1(-) mutants provided a useful approach to find potential targets for tumour therapy via suppressing tumour cell proliferation and rewiring tumour cell metabolism.

Antitumor Activity of HM781-36B, alone or in Combination with Chemotherapeutic Agents, in Colorectal Cancer Cells

Purpose

HM781-36B is a novel and irreversible pan-human epidermal growth factor receptor (HER) inhibitor with TEC cytoplasmic kinase inhibition. The aim of this study is to evaluate the antitumor activity and mechanism of action for HM781-36B in CRC cell lines.

Materials and Methods

The CRC cell lines were exposed to HM781-36B and/or oxaliplatin (L-OHP), 5-fluorouracil (5-FU), SN-38. The cell viability was examined by Cell Titer-Glo luminescent cell viability assay kit. Change in the cell cycle and protein expression was determined by flow cytometry and immunoblot analysis, respectively. Synergism between 2 drugs was evaluated by the combination index.

Results

The addition of HM781-36B induced potent growth inhibition in both DiFi cells with EGFR overexpression and SNU-175 cells (IC₅₀ = 0.003 and 0.005 μM, respectively). Furthermore, HM781-36B induced G1 arrest of the cell cycle and apoptosis, and reduced the levels of HER family and downstream signaling molecules, pERK and pAKT, as well as nonreceptor/cytoplasmic tyrosine kinase, BMX. The combination of HM781-36B with 5-FU, L-OHP, or SN-38 showed an additive or synergistic effect in most CRC cells.

Conclusion

These findings suggest the potential roles of HM781-36B as the treatment for EGFR-overexpressing colon cancer, singly or in combination with chemotherapeutic agents. The role of BMX expression as a marker of response to HM781-36B should be further explored.

Epidermal growth factor receptor serum (sEGFR) level may predict response in patients with EGFR-positive advanced colorectal cancer treated with gefitinib?

PURPOSE

Epidermal growth factor receptor-overexpression reported in colorectal cancer, justifies therapeutic use of EGFR-inhibitors. We have recently conducted a phase II study in 57 patients with EGFR-positive advanced colorectal cancer (ACC) who received gefitinib-FOLFOX6 followed by gefitinib-single agent as maintenance. Main biological objective was to assess sEGFR as surrogate marker of tyrosine kinase inhibition and as predictor of response.

METHODS

sEGFR, evaluated by quantitative ELISA, was investigated as predictive factor both taking into account the basal value only, and its whole pattern over time. sEGFR was collected at baseline and at every 2-months assessment in 42 cases. Thirty-three patients reported CR/PR as best objective response (BOR), while nine showed SD/PD.

RESULTS

Retrospectively, on average, the sEGFR values reported by both responders (CR/PR) and not responders (SD/PD) were already different at baseline (49.4 +/- 6.2 and 42.4 +/- 8.4 ng/ml respectively). This difference was statistically significant (p = 0.042). Although sEGFR trend over time confirmed the basal difference (p = 0.032), this result should be taken with caution, due to the small number of patients reporting EGFR values besides the basal one.

CONCLUSIONS

Higher sEGFR at baseline was associated to BOR and may be considered a significant predictor of outcome in patients with ACC.

Targeting the epidermal growth factor receptor in metastatic colorectal cancer

Although significant advances have been made in the treatment of metastatic colorectal cancer (CRC), prognosis remains poor, with a 5-year survival of less than 10%. Monoclonal antibodies that target the epidermal growth factor receptor (EGFR) have shown clinical benefit as single agents and in combination with standard chemotherapy in the refractory setting, with tolerable toxicity. This article will discuss the role of the EGFR pathway in the pathogenesis of CRC, the data supporting the current use of cetuximab and panitumumab in the treatment of CRC, and clinical trials of EGFR tyrosine kinase inhibitors in CRC. Novel strategies of targeting the EGFR pathway to improve efficacy, as well as ongoing research in identifying molecular predictors of response to anti-EGFR agents, will also be reviewed.

First clinical experience of orally active epidermal growth factor receptor inhibitor combined with simplified FOLFOX6 as first-line treatment for metastatic colorectal cancer

BACKGROUND

Gefitinib, an orally active inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, combined with chemotherapy, has shown efficacy as second-line treatment for advanced colorectal cancer (CRC). Gefitinib combined with FOLFOX6 (oxaliplatin plus folinic acid and 5-fluorouracil) was tested as a first-line therapy.

METHODS

Patients with metastatic EGFR-positive CRC received gefitinib at a dose of 250 mg/day combined with simplified FOLFOX6. Gefitinib was continued as maintenance treatment in nonprogressing patients. Responses were assessed by Response Evaluation Criteria in Solid Tumors (RECIST) criteria and adverse events were assessed with the National Cancer Institute Common Toxicity Criteria (NCI-CTC) scale.

RESULTS

A total of 56 patients were recruited. There were 26 men and 30 women, with a median age of 57.5 years. The Eastern Cooperative Oncology Group (ECOG) performance status was as follows: 0 in 39 patients, 1 in 12 patients, and 2 in 5 patients. Thirty-nine patients (69.6%) had stage IV disease at diagnosis, 92.9% had liver involvement, and 46.4% had > or =2 metastatic sites. All patients were evaluated for safety, and 53 were evaluated for response: 40 patients (71.4%; 95% confidence interval [95% CI], 57.8%-82.6%) had complete or partial responses, and 11 patients (19.6%) had stable disease. Median time to progression was 7 months (range, 2.1-33.0 months; 95% CI, 6.2-9.0 months). Radical surgery or thermoablation of metastatic sites was performed in 14 patients (25%). NCI-CTC grade 3-4 events occurred in 36 patients (64.3%): diarrhea in 9 patients (16.1%), and hematologic toxicity in 13 patients (23.2%). Four patients (7.1%) were withdrawn for drug-related adverse events.

CONCLUSIONS

The regimen has shown promising efficacy with manageable toxicity as a first-line treatment for patients with advanced CRC.

Gefitinib and irinotecan in patients with fluoropyrimidine-refractory, irinotecan-naive advanced colorectal cancer: a phase I-II study

BACKGROUND

To establish the recommended dose level (RDL) and to evaluate the efficacy and safety of gefitinib plus irinotecan in patients with advanced fluoropyrimidine-refractory colorectal cancer (CRC).

PATIENTS AND METHODS

Patients with advanced CRC progressing on or within 12 weeks of fluoropyrimidine-based chemotherapy, irinotecan naive and performance status of two or less were recruited. During dose-finding phase, dose-limiting toxicity (DLT) was encountered at dose level 1, therefore subsequent dose de-escalation and pharmacokinetic (PK) studies were carried out. The RDL was then expanded in a multicentre setting to further evaluate safety and efficacy.

RESULTS

From June 2002 to February 2005, 39 patients were treated in total with 27 at the RDL. The RDL was established at irinotecan 225 mg/m(2) every 3 weeks and gefitinib 250 mg daily. The DLTs were neutropenia and diarrhoea. For the patients treated at RDL, the objective tumour response rate was 11.1% (95% confidence interval 2.4% to 29.2%) and median survival was 9.3 months. PK studies indicated that the addition of irinotecan to gefitinib resulted in an average of 50% increase in exposure to gefitinib (P < 0.05), but gefitinib did not alter the PK profiles of irinotecan or SN-38. Grade 3-4 toxic effects in all patients included diarrhoea (35.9%), lethargy (15.4%), neutropenia (15.4%), febrile neutropenia (10.3%) and skin rash (7.7%).

CONCLUSIONS

Irinotecan and gefitinib at this dose schedule was tolerable, but gefitinib did not appear to add substantial efficacy to irinotecan.

Recurrent genomic alterations with impact on survival in colorectal cancer identified by genome-wide array comparative genomic hybridization

BACKGROUND & AIMS

Although genetic aspects of tumorigenesis in colorectal cancer (CRC) have been well studied, reliable biomarkers predicting prognosis are scarce. We aimed to identify recurrently altered genomic regions (RAR) in CRC with high resolution, to investigate their implications on survival and to explore novel cancer-related genes in prognosis-associated RARs.

METHODS

A 1-Mb resolution microarray-based comparative genomic hybridization (array CGH) was applied to 59 CRCs. RARs, defined as genomic alterations, detected in more than 10 cases were identified and analyzed for their association with survival. Expression levels of genes in prognosis-associated RARs were examined by real-time quantitative polymerase chain reaction.

RESULTS

Twenty-seven RARs were identified. Eleven high-level amplifications and 2 homozygous deletions also were detected, but they were not as common as RARs. Multivariate analysis revealed RAR-L1 (loss on 1p36; hazard ratio = 8.15, P = .002) and RAR-L20 (loss on 21q22; hazard ratio = 3.53, P = .034) are independent indicators of poor prognosis. Expression of CAMTA1, located in RAR-L1, was reduced frequently in CRCs, and low CAMTA1 expression was associated significantly with poor prognosis, which indicates that CAMTA1 may play a role as a tumor suppressor in CRC. Five pairs of RARs were correlated significantly to each other and 3 pairs share genes involved in the same biological functions, suggesting possible collaborative roles in tumorigenesis.

CONCLUSIONS

We identified recurrent genomic changes in 59 CRCs. RARs could be more important in sporadic tumors where the effect of genomic changes on tumorigenesis is relatively smaller than in familial cancer. Our results and analysis strategy will be helpful to elucidate pathogenesis of CRCs or to develop biomarkers for predicting prognosis.

Comparing antibody and small-molecule therapies for cancer

The 'magic bullet' concept of specifically targeting cancer cells at the same time as sparing normal tissues is now proven, as several monoclonal antibodies and targeted small-molecule compounds have been approved for cancer treatment. Both antibodies and small-molecule compounds are therefore promising tools for target-protein-based cancer therapy. We discuss and compare the distinctive properties of these two therapeutic strategies so as to provide a better view for the development of new drugs and the future direction of cancer therapy.