Molecular therapy for residual squamous cancer
A major problem in head and neck cancer management is the high rate of loco-regional
recurrence following surgery and post-operative radiotherapy. Tumour cells that remain
in the surgical margins are the likely source for this recurrence. Gene-mediated
approaches, that take advantage of the genetic profile of these tumours, have the
potential to eliminate these remaining cells. The high frequency of p53 mutation in
head and neck cancers makes this gene a good candidate for therapy. The majority of
residual cancer models used for treatment investigations are established subcutaneously
in immunodeficient hosts. However, residual cancer models in muscle of
immunocompetent hosts would more closely mimic the clinical scenario.
In vitro studies established the suitability of the p53 mutated PDVC57 cell line for
adenoviral-p53-mediated tumour destruction. PDVC57 cells showed 70% transduction
efficiency. Polymerase chain reaction, Western blotting and immunocytochemistry
confirmed the expression of the p53 transgene. Western blot analysis demonstrated
increases in p21 WAFl, MDM2 and BAX proteins following Ad5CMV-p53 transduction.
A significant reduction in PDVC57 number was observed following transduction of 625
vp/cell Ad5CMV-p53. The TUNEL assay and acridine orange/ethidium bromide
incorporation suggested apoptotic death in 50010 and 70% of PDVC57 cells 48 hours
after transduction with 2500 vp/cell Ad5CMV-p53 respectively.
A new model of residual cancer was established by implanting 1 x 105 PDVC57 cells
into the muscle of syngeneic immunocompetent hosts, and its reproducibility
demonstrated. The reduction in tumour area following cisplatin treatment demonstrated
the potential of this model for examining treatment efficacy. However, infection with 5
x 1010 vp Ad5CMV-p53 failed to destroy tumour in the muscle, likely due to the
insufficient expression of the transgene. In comparison, Ad5CMV-p53 infection of a
PDVC57 derived subcutaneous model of residual cancer, eliminated tumour in 4/6
cases. These studies highlight the requirement for improved gene delivery strategies for
tumour in muscle.