Pancreatic cancer gene therapy with heat inducible diphtheria toxin variant CRM197 (DTA197): in vivo preliminary results.

Context Heat shock elements (HSEs) regulate gene transcription of heat shock proteins (HSPs) in response to cellular stress. We ascertained whether an artificial sequence encompassing five tandem HSEs inserted upstream the HSPA6 promoter, controlling the expression of DTA197, is suitable for pancreatic cancer (PC) gene therapy in vivo. Methods Seventeen female nude mice were s.c. inoculated with 3 millions of transfected (eGFP to optimize heat shock or DTA197 for tumor cell killing) or non transfected (control) PC PSN1 cells. To induce transgene expression heat shock was obtained by heating the cutaneous surface employing a device made in house. Results Optimal heat shock (9-fold increase of eGFP mRNA, Q-RT-PCR) was obtained by heating twice the tumor mass, 72 h interval. Heating did not significantly modify the growth pattern of control tumors, which was close to that of untreated PSN1-DTA197. DTA197 mRNA expression was quantified (Q-RT-PCR) in 4 tumor masses, 2 from a control and 2 from experimental mice. With respect to control masses, a 7.13- and 5.60-fold increase was found in the two heated masses. Tumor volume (calliper) of treated PSN1-DTA197 was delayed with respect to that in untreated PSN1-DTA197 masses (repeated measures analysis of variance: F=5.89, P=0.07). In one treated mouse a complete disappearance (10-day follow-up after treatment) of the tumor mass was documented both by calliper and by in vivo bioluminescence imaging. Conclusions DTA197 expression under the control of the heat inducible promoter engineered by us appears to be a promising tool in arresting PC growth in vivo.