AAV6-hSyn-mCherry

There is increasing evidence that intractable pain can reduce the quality of life and survival of cancer patients. Here, the researchers used two different chronic pain models in mice, neuropathic pain and persistent postoperative pain, with Lewis lung carcinoma (LLC) as the tumor cell. In these pain models, tumor growth was significantly promoted. As well as these pain models, tumor growth of LLC, severe osteosarcoma (AXT) and B16 melanoma cells was significantly promoted by concomitant activation of sensory neurons in AAV6-hM3Dq-injected mice treated with the designer drug clozapine-N-oxide (CNO). Significant increases in mRNA levels of tachykinin precursor 1 (Tac1), vascular endothelial growth factor-A (Vegfa), and calcitonin-related polypeptide alpha (Calca) in the ipsilateral side of dorsal root ganglion of AAV6-hM3Dq-injected mice were observed by concomitant activation of sensory neurons due to CNO administration. Furthermore, in a bone cancer pain model in which AXT cells were implanted into the right femoral medullary cavity of mice, inhibition of sensory neurons in AAV6-hM4Di-injected mice by repeated administration of CNO significantly prolonged survival. These findings suggest that persistent pain signals may promote tumor growth by increasing the expression of sensory localizing peptides and growth factors, and that controlling cancer pain may prolong cancer survival.

AAV6-hSyn-hM3Dq-mCherry or AAV6-hSyn-mCherry control vector was injected into the sciatic nerve of mice. Within 2 weeks after AAV injection, hM3Dq-mCherry was expressed in the lumbar spine and DRG as projections of sensory nerves (Figure 1A). In addition, in the DRG of AAV-injected mice, hM3Dq-mCherry expression was highly co-localized with markers for peptidergic C fiber neurons, calcitonin gene-related peptide (CGRP) and substance P (SP), and a marker for small unmyelinated C fiber and thinly myelinated Aδ fiber neurons, peripherin (Figure 1B). Under these conditions, the researchers found that Gq-DREADD-mediated activation of CNO sensory nerves resulted in thermal hyperalgesia on the ipsilateral side but not on the contralateral side from 30 minutes to 10 hours after CNO injection more than 2 weeks after AAV injection (Figure 1C). On the other hand, these mice showed no spontaneous pain-like behaviors.

Figure 1. A Qualitative observation of hM3Dq-mCherry fluorescence in tissue sections. B Lumbar DRG sections stained with CGRP, SP, or peripherin-specific antibodies (all shown in green). C Changes in pain threshold induced by CNO administration to activate sensory neurons in hM3Dq-expressing mice were measured by plantar test. (Tanaka K, et al., 2023)