Molecular mechanisms targeting drug-resistance and metastasis in colorectal cancer: Updates and beyond

Colorectal cancer (CRC) is the third most diagnosed malignancy and a major leading cause of cancer-related deaths worldwide. Despite advances in therapeutic regimens, the number of patients presenting with metastatic CRC (mCRC) is increasing due to resistance to therapy, conferred by a small population of cancer cells, known as cancer stem cells. Targeted therapies have been highly successful in prolonging the overall survival of patients with mCRC. Agents are being developed to target key molecules involved in drug-resistance and metastasis of CRC, and these include vascular endothelial growth factor, epidermal growth factor receptor, human epidermal growth factor receptor-2, mitogen-activated extracellular signal-regulated kinase, in addition to immune checkpoints. Currently, there are several ongoing clinical trials of newly developed targeted agents, which have shown considerable clinical efficacy and have improved the prognosis of patients who do not benefit from conventional chemotherapy. In this review, we highlight recent developments in the use of existing and novel targeted agents against drug-resistant CRC and mCRC. Furthermore, we discuss limitations and challenges associated with targeted therapy and strategies to combat intrinsic and acquired resistance to these therapies, in addition to the importance of implementing better preclinical models and the application of personalized therapy based on predictive biomarkers for treatment selection.

YAP/TAZ Signaling and Resistance to Cancer Therapy

Drug resistance is a major challenge in cancer treatment. Emerging evidence indicates that deregulation of YAP/TAZ signaling may be a major mechanism of intrinsic and acquired resistance to various targeted and chemotherapies. Moreover, YAP/TAZ-mediated expression of PD-L1 and multiple cytokines is pivotal for tumor immune evasion. While direct inhibitors of YAP/TAZ are still under development, FDA-approved drugs that indirectly block YAP/TAZ activation or critical downstream targets of YAP/TAZ have shown promise in the clinic in reducing therapy resistance. Finally, BET inhibitors, which reportedly block YAP/TAZ-mediated transcription, present another potential venue to overcome YAP/TAZ-induced drug resistance.

Isolated lung perfusion as an adjuvant treatment of colorectal cancer lung metastases: a preclinical study in a pig model

BACKGROUND

The lung is a frequent site of colorectal cancer (CRC) metastases. After surgical resection, lung metastases recurrences have been related to the presence of micrometastases, potentially accessible to a high dose chemotherapy administered via adjuvant isolated lung perfusion (ILP). We sought to determine in vitro the most efficient drug when administered to CRC cell lines during a short exposure and in vivo its immediate and delayed tolerance when administered via ILP.

METHODS

First, efficacy of various cytotoxic molecules against a panel of human CRC cell lines was tested in vitro using cytotoxic assay after a 30-minute exposure. Then, early (operative) and delayed (1 month) tolerance of two concentrations of the molecule administered via ILP was tested on 19 adult pigs using hemodynamic, biological and histological criteria.

RESULTS

In vitro, gemcitabine (GEM) was the most efficient drug against selected CRC cell lines. In vivo, GEM was administered via ILP at regular (20 µg/ml) or high (100 µg/ml) concentrations. GEM administration was associated with transient and dose-dependant pulmonary vasoconstriction, leading to a voluntary decrease in pump inflow in order to maintain a stable pulmonary artery pressure. After this modulation, ILP using GEM was not associated with any systemic leak, systemic damage, and acute or delayed histological pulmonary toxicity. Pharmacokinetics studies revealed dose-dependant uptake associated with heterogenous distribution of the molecule into the lung parenchyma, and persistent cytotoxicity of venous effluent.

CONCLUSIONS

GEM is effective against CRC cells even after a short exposure. ILP with GEM is a safe and reproducible technique.

Bevacizumab combined with chemotherapy in the second-line treatment of metastatic colorectal cancer: results from the phase II BEVACOLOR study

BACKGROUND

This prospective phase II study assessed the efficacy and safety of bevacizumab plus chemotherapy regimens commonly used in the second-line treatment of metastatic colorectal cancer (mCRC).

METHODS

Patients with mCRC who progressed or relapsed after first-line oxaliplatin-based or irinotecan-based treatment received bevacizumab 2.5 mg/kg/week plus chemotherapy until disease progression. The primary endpoint was disease-control rate (DCR). Secondary endpoints included progression-free survival (PFS), overall survival (OS), objective response rate (ORR), and safety.

RESULTS

Fifty-three patients (66% men; median age, 62 years old) received second-line bevacizumab plus folinic acid, fluorouracil, and irinotecan (FOLFIRI; 57%), folinic acid, fluorouracil, oxaliplatin (FOLFOX; 26%), irinotecan (15%), or capecitabine plus irinotecan (XELIRI; 2%). The DCR was 87% (95% CI, 77%-97%); ORR was 32% (95% CI, 19%-46%). Median PFS was 6.5 months (95% CI, 5.8-7.8 months) and median OS 19.3 months, (95% CI, 14.2-25.1 months).The most frequent grade 3/4 adverse events included neutropenia (21%), diarrhea (15%), asthenia, and vomiting (9% each). Five patients (9%) had grade 3/4 targeted toxicities: grade 3 hypertension (n = 2), grade 3 venous thromboembolism (n = 2), and grade 4 arterial thromboembolism (n = 1). None of these events led to death during the study.

CONCLUSION

Bevacizumab plus standard second-line chemotherapy is highly active in patients with mCRC and has an acceptable safety profile.

Is there a palliative benefit of gemcitabine plus fluoropyrimidines in patients with refractory colorectal cancer? A review of the literature previously presented: poster at the 2008 Gastrointestinal Cancer Symposium (Abstract No. 512)

INTRODUCTION

Fluoropyrimidines with oxaliplatin or irinotecan plus bevacizumab is the standard chemotherapy combination in patients with advanced colorectal cancer (CRC). Gemcitabine acts synergistically with fluoropyrimidines to enhance the binding of thymidylate synthase and increase inhibition of DNA synthesis. The objective of this review is to evaluate the literature for evidence of efficacy and safety of fluoropyrimidine plus gemcitabine (FG) in patients with advanced CRC.

METHODS

Relevant studies were identified in PubMed, Ovid, Cochrane database and the American Society of Clinical Oncology abstracts using the following search terms: gemcitabine, fluorouracil, capecitabine and colorectal cancer. Only studies using the FG combination were selected.

RESULTS

Forty-two advanced CRC patients were evaluated in two Phase I studies and the maximum tolerated dose of gemcitabine was 900 - 1,000 mg/m(2) weekly with either bolus 5-fluorouracil (5-FU) or capecitabine. A total of 216 advanced CRC patients were evaluated in six Phase II studies. Gemcitabine (750 - 1,250 mg/m2) with either 5-FU (continuous infusion or bolus) or capecitabine was administered as first-line therapy in two studies and as third-line therapy in three studies. The range reported for overall response rate was 30 - 38.3%, median time to progression was 4 - 8.3+ months and median survival was 9.8 - 18+ months. The most commonly reported grade 3 - 4 toxicities were neutropenia, thrombocytopenia and mucositis.

CONCLUSIONS

Fluoropyrimidine plus gemcitabine is clinically active in patients with refractory CRC demonstrating prolonged median time to progression and acceptable toxicity only when bolus 5-FU was not used. Studies are underway to evaluate the combinations of FG with other chemotherapy or targeted agents. Meanwhile, FG may be considered for patients with advanced CRC who are refractory to primary treatment without other options or who are not eligible for clinical studies.