Safety and Tolerability of Anti-Angiogenic Protein Kinase Inhibitors and Vascular-Disrupting Agents in Cancer: Focus on Gastrointestinal Malignancies

Angiogenesis is an essential process for tumor growth and metastasis. Inhibition of angiogenesis as an anticancer strategy has shown significant results in a plethora of tumors. Anti-angiogenic agents are currently part of many standard-of-care options for several metastatic gastrointestinal cancers. Bevacizumab, aflibercept, ramucirumab, and regorafenib have significantly improved both progression-free and overall survival in different lines of treatment in metastatic colorectal cancer. Second-line ramucirumab and third-line apatinib are effective anti-angiogenic treatments for patients with metastatic gastric cancer. Unfortunately, the anti-angiogenic strategy has major practical limitations: resistance inevitably develops through redundancy of signaling pathways and selection for subclonal populations adapted for hypoxic conditions. Anti-angiogenic agents may be more effective in combination therapies, with not only cytotoxics but also other emerging compounds in the anti-angiogenic class or in the separate class of the so-called vascular-disrupting agents. This review aims to provide an overview of the approved and "under development" anti-angiogenic compounds as well as the vascular-disrupting agents in the treatment of gastrointestinal cancers, focusing on the actual body of knowledge available on therapy challenges, pharmacodynamic and pharmacokinetic mechanisms, safety profiles, promising predictive biomarkers, and future perspectives.

The role of tumor angiogenesis as a therapeutic target in colorectal cancer

INTRODUCTION

Angiogenesis is a complex process regulated by several pro- and anti-angiogenic factors, thus the loss of its fine equilibrium plays a key role in colorectal cancer (CRC) development and progression. Therapeutic agents targeting VEGF/VEGFR signaling, the main regulator of this process, proved to be effective across different treatment lines in metastatic CRC (mCRC) and contributed greatly to improve patients' survival in recent years. Areas covered: This review aimed to summarize the actual body of knowledge available on the VEGF pathway in CRC, including currently available anti-angiogenic drugs and treatment challenges, mechanisms of resistance, promising predictive biomarkers and future perspectives. Expert commentary: Angiogenesis inhibition in subsequent lines of treatment is a valid strategy in the continuum of care of mCRC patients. In this scenario, the availability of multiple agents warrants to tailor therapy to an individualized approach. However, the validation of predictive biomarkers to aid therapeutic decisions remains an issue. Intrinsic and adaptive resistance to anti-angiogenic agents comprises distinct and intertwined processes, eventually leading to treatment failure and disease progression. The expanding knowledge on the mechanisms underlying the angiogenesis pathway, different potential treatment targets and mechanisms of tumor resistance, may lead to promising new perspectives in this field.

Regorafenib

Regorafenib (BAY 73-4506, Stivarga^®) is an oral diphenylurea multi-kinase inhibitor that targets angiogenic (VEGFR1-3, TIE2), stromal (PDGFR-β, FGFR), and oncogenic receptor tyrosine kinases (KIT, RET, and RAF). Regorafenib is the first small-molecule multi-kinase inhibitor to achieve survival benefits in metastatic colorectal cancer that has progressed after all standard therapies. Consequently, Regorafenib was FDA approved for this indication in 2012. In addition, Regorafenib treatment resulted in a significant improvement in progression-free survival (PFS) compared to placebo in patients with metastatic gastrointestinal stromal tumors (GIST) after progression on standard treatments and is also FDA-approved in this indication since 2013. In 2017, Regorafenib has been FDA approved for the treatment of patients with advanced hepatocellular carcinoma (HCC) previously treated with Sorafenib. In this situation, Regorafenib significantly improved PFS and overall survival (OS) compared to placebo. Regorafenib has also been examined in several clinical trials (mostly phase II) in different tumor entities, including renal cell carcinoma (RCC), soft-tissue sarcoma (STS), and additional phase II trials ongoing (e.g., second- and third-line treatment for medullary thyroid cancer, NCT02657551).

Recent Developments in Regorafenib Treatment for Gastrointestinal Cancers: Presentations at the Meeting of the European Society for Medical Oncology (ESMO) Congress 2016

The European Society for Medical Oncology (ESMO) Congress was held in Copenhagen, Denmark from 7th–11th October 2016. The use of the promiscuous multikinase inhibitor regorafenib (Stivarga®, BAY 73-4506) in the treatment of cancers of the gastrointestinal (GI) tract was strongly featured at this meeting. Regorafenib targets multiple kinases involved in oncogenesis and angiogenesis, and is US Food and Drug Administration (FDA)-approved for the treatment of advanced metastatic colorectal cancer and GI stromal tumours, following progression on standard therapies. In this review, we summarise the results of completed clinical trials on the use of regorafenib alone or in combination with other therapies for the treatment of GI cancers. We highlight the results of the Phase III RESORCE study which demonstrated the efficacy of regorafenib as a second-line therapy in patients with advanced hepatocellular carcinoma who have progressed on sorafenib. We review some promising preliminary data on the use of regorafenib in other GI cancers, such as gastric cancer, oesophageal cancer, pancreatic cancer, and soft tissue carcinomas, and provide a brief overview of ongoing and planned trials. Finally, we discuss the incidence and management of regorafenib-related toxicities and summarise attempts to identify predictive biomarkers of regorafenib sensitivity.