Carbonic anhydrase IX promotes tumor growth and necrosis in vivo and inhibition enhances anti-VEGF therapy.

in Clinical cancer research : an official journal of the American Association for Cancer Research by Alan McIntyre, Shalini Patiar, Simon Wigfield, Ji-Liang Li, Ioanna Ledaki, Helen Turley, Russell Leek, Cameron Snell, Kevin Gatter, William S Sly, Richard D Vaughan-Jones, Pawel Swietach, Adrian L Harris

TLDR

  • This study investigated the effect of combining CAIX inhibition with bevacizumab treatment for cancer. CAIX expression was associated with increased growth rate and poor prognosis, but surprisingly, also with increased necrosis and apoptosis.
  • Knocking down CAIX expression enhanced the effect of bevacizumab treatment, reducing tumor growth rate and improving treatment outcomes.
  • This research provides evidence for the potential value of CAIX inhibition in combination with bevacizumab treatment for cancer therapy.

Abstract

Bevacizumab, an anti-VEGFA antibody, inhibits the developing vasculature of tumors, but resistance is common. Antiangiogenic therapy induces hypoxia and we observed increased expression of hypoxia-regulated genes, including carbonic anhydrase IX (CAIX), in response to bevacizumab treatment in xenografts. CAIX expression correlates with poor prognosis in most tumor types and with worse outcome in bevacizumab-treated patients with metastatic colorectal cancer, malignant astrocytoma, and recurrent malignant glioma. We knocked down CAIX expression by short hairpin RNA in a colon cancer (HT29) and a glioblastoma (U87) cell line which have high hypoxic induction of CAIX and overexpressed CAIX in HCT116 cells which has low CAIX. We investigated the effect on growth rate in three-dimensional (3D) culture and in vivo, and examined the effect of CAIX knockdown in combination with bevacizumab. CAIX expression was associated with increased growth rate in spheroids and in vivo. Surprisingly, CAIX expression was associated with increased necrosis and apoptosis in vivo and in vitro. We found that acidity inhibits CAIX activity over the pH range found in tumors (pK = 6.84), and this may be the mechanism whereby excess acid self-limits the build-up of extracellular acid. Expression of another hypoxia inducible CA isoform, CAXII, was upregulated in 3D but not two-dimensional culture in response to CAIX knockdown. CAIX knockdown enhanced the effect of bevacizumab treatment, reducing tumor growth rate in vivo. This work provides evidence that inhibition of the hypoxic adaptation to antiangiogenic therapy enhances bevacizumab treatment and highlights the value of developing small molecules or antibodies which inhibit CAIX for combination therapy.

Overview

  • The study investigated the effect of bevacizumab, an anti-VEGFA antibody, on the developing vasculature of tumors and explored the potential of combining it with CAIX inhibition.
  • The study used xenografts, cell lines, and 3D culture to investigate the effects of CAIX expression on tumor growth rate, hypoxia, and bevacizumab treatment.
  • The primary objective was to understand the relationship between CAIX expression, hypoxia, and bevacizumab treatment, with the goal of improving treatment outcomes by targeting CAIX.

Comparative Analysis & Findings

  • CAIX expression was associated with increased growth rate in spheroids and in vivo, but surprisingly, it was also associated with increased necrosis and apoptosis in vivo and in vitro.
  • CAIX knockdown enhanced the effect of bevacizumab treatment, reducing tumor growth rate in vivo, and increased the effect of combination therapy.
  • Expression of CAIX was upregulated in 3D culture but not 2D culture in response to knockdown, and CAIX expression correlated with poor prognosis in most tumor types.

Implications and Future Directions

  • The study highlights the potential value of developing small molecules or antibodies that inhibit CAIX for combination therapy with bevacizumab.
  • Further research is needed to investigate the mechanism of CAIX inhibition and to explore its potential use in combination with other treatments.
  • The study provides evidence that inhibition of the hypoxic adaptation to antiangiogenic therapy enhances bevacizumab treatment, which may lead to improved treatment outcomes.
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