Hypothesis / aims of study
EG110A is a novel non-replicative herpes simplex virus 1 (HSV1)-derived vector carrying the sequence of the light chain of the botulinum toxin F (BoNT-F/LC) under the control of a human calcitonin gene related peptide (hCGRP) promoter. When administered locally, EG110A infects sensory fibers and is retrogradely transported to the cell bodies of sensory neurons in the dorsal root ganglia (DRG). The hCGRP promoter allows selective expression of the BoNT-F/LC transgene which inhibits neurotransmission in a subpopulation of sensory neurons: the type C neurons or C fibers.
EG110A is being developed as a potential new treatment for neurogenic detrusor overactivity (NDO). Intradetrusor injection of EG110A vectors is expected to lead to a long-term sustained inhibition of signaling via the sensory C fibers and to decrease the involuntary detrusor contractions. The selective transgene expression in sensory type C neurons is expected to preserve the ability of the bladder muscle to contract and to not cause urinary retention.
We previously demonstrated the efficacy of EG110A following intradetrusor injection in an acute non-clinical intravesical capsaicin model for NDO. Here we show efficacy of EG110A in a dose dependent manner. We also show long term expression of the transgene in DRGs following intradetrusor injection of EG110A.
Study design, materials and methods
Pharmacological studies were performed in the rat intravesical acute capsaicin model of NDO. Four different doses of EG110A (6,56E+06, 3,28E+07, 1,64E+08 and 3,28E+08 plaque forming unit, PFU) or vehicle were injected in the detrusor. After 5 weeks, animals were anesthetized, and a catheter connected to a pressure transducer was inserted in the bladder through the dome. The bladder was continuously perfused with saline during a stabilization period of 90 min followed by perfusion with 30 µM of capsaicin for 60 min. Intravesical pressure was recorded via cystometry throughout the experiment and parameters of reflex-evoked bladder contractions were measured. Data were computed over 15 min intervals during the capsaicin irritation period. At the end of the cystometry, the post void residual urine volume (urine volume left in the bladder after the last micturition) was measured. Long term transgene expression in DRGs was measured in a separate study. DRGs were collected at 1, 5, 12 and 24 weeks after intradetrusor injection of EG110A. Expression of BONTF-LC was measured by ddPCR (digital droplet Polymerase Chain Reaction) following reverse transcription. Expression of the transgene was also measured in bladders.
Results
EG110A, at any dose, did not produce any adverse effects or mortality during the 5 weeks
of duration of the study. In addition, there were no biologically relevant changes in body weight observed during the study. During the capsaicin treatment, EG110A decreased the frequency of bladder voiding contractions and improved bladder capacity, decreased intravesical pressure and improved bladder compliance. A clear dose-dependent effect was observed. Importantly, the post void residual urine volume at the end of the cystometry was unchanged between EG110A at any dose and vehicle controls (Figure 1). Measurement by ddPCR in DRGs following intradetrusor injection of EG110A showed long term expression of the transgene for at least 6 months (Figure 2). No expression of the transgene was detected in bladder tissues.
Interpretation of results
The main finding of this study is that EG110A consistently counteracted in a dose-dependent manner the capsaicin-mediated activation of bladder sensory C fibers, as evidenced by a significant decrease in the frequency of micturition. EG110A did not cause any increase in post-void residual urine volume. This indicates that EG110A preserves the ability of the bladder muscle to contract and has no effect on the efferent parasympathetic pathway. Measurement by ddPCR in DRGs shows that EG110A, when injected in the detrusor, is retrogradely transported to sensory neuron cell bodies, and achieves long term transgene expression. Importantly, no transgene expression was found at the site of administration in the bladder, showing that EG110A functional effect is exclusively mediated by transgene expression in sensory neurons.