Prospective Study of Tirapazamine Targeting in Cervical Cancer
Patients with locally advanced cervical cancer can have a poor clinical outcome with
standard cisplatin and pelvic radiation therapy. It is well established that pre-treatment
tumor hypoxia is a significant prognostic factor in tumors and may be one of the most
important and modifiable mechanisms of radiation resistance in this group of tumours.
Significant levels of hypoxia are not present in all locally advanced cervical tumors. Hence
measurement of the pretreatment tumour oxygenation status is imperative, and can be assessed
using various means. Immunohistochemical staining of various intrinsic hypoxia markers to
include Ca9, Glut1, HIF-1 alpha on the pre-treatment tumours can be performed.
Tirapazamine, a bio-reductively activated hypoxic cell selective anti-tumour agent, has been
found to act synergistically with cisplatinum, resulting in a significantly higher cell kill
than expected based on additive action. We proposed to measure the cell killing effect of
tirapazamine with the following tests:
- Comet assay: Tirapazamine causes DNA damage that can predict for cell killing by
measuring DNA damage in cells from tumor biopsies using the alkaline comet assay.
- Measurement of phosphorylation of histone gamma H2AX: It has been explored as a measure
of radiosensitivity in response to clinically relevant doses of radiation. The histone
gamma H2AX phosphorylation can be used to detect tirapazamine induced DNA double-strand
breaks and collapsed replication forks.
There is some evidence that the drug delivery may be impaired and in fact the drug may not
actually be reaching all of the hypoxic tumour cells. A recent study has shown that, in an
experimental setting, tirapazamine causes a decrease in vascular perfusion which can be
measured with contrast enhanced MRI. We propose to assess if this mechanism is operative in
Clinical studies have demonstrated that tumour vascular can increase during the course of
radiation therapy, consistent with re-oxygenation and that this is suggestive of a better
outcome. Tumours that become less hypoxic during the course of therapy have an increased
likelihood of response to the given treatment. However, response to tirapazamine may be
reduced. In order to assess both the vascular change that may occur directly because of
tirapazamine infusion, as well as any increase in tumour vascularity and perhaps increase in
tumour oxygenation during the course of therapy, we plan to assess these tumours during the
course of therapy. Assessment of tumour perfusion and vessel permeability after 10 radiation
treatments (on day 12) of chemo-radiation therapy will be performed via T1 weighted dynamic
contrast enhanced MRI (DCMRI).
We hypothesize that:
1. Tirapazamine (a hypoxic cell cytotoxin and radiosensitizer) will result in increased
DNA damage and a better clinical outcome if:
1. the pre-treatment tumor demonstrates significant hypoxia
2. tirapazamine treatment results in increased DNA damage
2. tirapazamine acts, in part, by changing vascular perfusion in the tumour and that these
changes can be measured with dynamic contrast enhanced MRI.
Observational Model: Cohort, Time Perspective: Prospective
Christina Aquino-Parsons, MD
British Columbia Cancer Agency
Canada: Health Canada
TPZ Targeting Cervix Study