Herpes simplex virus vector-mediated gene delivery for the treatment of lower urinary tract pain

Abstract

Interstitial cystitis (IC)/painful bladder syndrome (PBS) is a painful debilitating chronic visceral pain disorder of unknown etiology that affects an estimated 1 million people in the United States alone. It is characterized by inflammation of the bladder that results in chronic pelvic pain associated with bladder symptoms of urinary frequency and urgency. Regardless of the etiology, IC/PBS involves either increased and/or abnormal activity in afferent nociceptive sensory neurons. Pain-related symptoms in patients with IC/PBS are often very difficult to treat. Both medical and surgical therapies have had limited clinical utility in this debilitating disease and numerous drug treatments, such as heparin, dimethylsulfoxide and amitriptyline, have proven to be palliative at best, and in some IC/PBS patients provide no relief whatsoever. Although opiate narcotics have been employed to help alleviate IC/PBS pain, this strategy is fraught with problems as systemic narcotic administration causes multiple unwanted side effects including mental status change and constipation. Moreover, chronic systemic narcotic use leads to dependency and need for dose escalation due to tolerance; therefore, new therapies are desperately needed to treat refractory IC/PBS. This has led our group to develop a gene therapy strategy that could potentially alleviate chronic pelvic pain using the herpes simplex virus-directed delivery of analgesic proteins to the bladder.

Figure 1

The proposed pathogonesis of IC/PBS and standard therapies for IC/PBS. An initial insult to the bladder results in the damage of the bladder epithelial layer that, for example, allows potassium to leak in and to prompt a cascade of events, each contributing to tissue inflammation and sensory fiber activation thereby inducing pain sensation in the lower urinary tract (LUT). Various standard drug treatments that have been employed for IC/PBS are depicted showing the level(s) at which these factors are involved in blocking the inflammatory or neurogenic processes that lead to IC/PBS pain. IC/PBS, interstitial cystitis/painful bladder syndrome.

Figure 2

Schematic diagram of gene therapy strategies for IC/PBS. Gold particles coated with POMC or PPE DNA were used to bombard the bladder wall. These plasmid DNAs encode the peptides (POMC and PPE) that can only locally block pain by suppressing further neuropeptide release. HSV vectors expressing either the PPE gene (HSV-PPE) or the lacZ control (HSV-lacZ) are injected into bladder wall where viral genomes can encode enkephalins locally and virus can be transported to bladder afferent pathways. In contrast to using gold particles with the gene gun technology, HSV-PPE vector genomes present within L6-S1 DRG bladder afferents synthesize and release enkephalins within the dorsal horn of spinal cord, and binding of met- and leu-enk to opioid receptors present on postsynaptic second-order spinal tract neurons and presynaptic bladder afferents may allow better suppression of synaptic transmission of the bladder pain responses. DRG, dorsal root ganglia; HSV, herpes simplex virus; IC/PBS, interstitial cystitis/painful bladder syndrome; POMC, pro-opiomelanocortin; PPE, preproenkephalin.

Figure 3

Effects of non-viral and viral vector-mediated opioid gene expression on bladder hyperactivity induced by nociceptive stimuli in rats. Gene gun-mediated delivery of gold particles linked either to the (a) POMC or (b) PPE gene expression cassettes was used to deliver three particles to three different sites within the bladder wall of rats with a lower midline incision to expose the bladder. In similar studies, (c) HSV-PPE or HSV-lacZ control vector were injected into the rat bladder wall Intercontraction intervals (ICIs) during cystometry were decreased by intravesical application of acetic acid (AA) or capsaicin (Cap). However, gene gun (GOLD-PPE or GOLD-POMC) or HSV-PPE-treated animals exhibited a smaller reduction in ICI compared with controls, which was reversed by naloxon (Nal). HSV, herpes simplex virus; POMC, pro-opiomelanocortin; PPE, preproenkephalin.