ABSTRACT:Oral cancer is one of the most painful malignancies, with pain driven primarily by algogenic mediators in the tumor microenvironment, including nerve growth factor (NGF). Although NGF monoclonal antibodies alleviate cancer pain in patients, clinical development was halted because of adverse effects, highlighting the need for safer alternatives. Neuropilin-1 (NRP1), a nonenzymatic NGF coreceptor, mediates NGF and tropomyosin receptor kinase A (TrkA) signaling, yet its role in cancer pain is unknown. We found that NRP1 is robustly coexpressed with TrkA in peptidergic nociceptors of mouse trigeminal ganglia. NRP1 antagonists inhibited NGF-induced sensitization of transient receptor potential vanilloid 1 in isolated trigeminal nociceptors and reduced NGF-induced periorbital mechanical allodynia in mice. Conditioned medium from human tongue squamous carcinoma HSC-3 cells contained NGF and sensitized transient receptor potential vanilloid 1 in trigeminal nociceptors and induced periorbital mechanical allodynia. Immunoneutralization of NGF and NRP1 blockade inhibited these effects. Our results show that NRP1 is a necessary coreceptor for the pronociceptive effects of NGF/TrkA signaling in the trigeminal system and implicate NGF and NRP1 in oral cancer pain. Current oral cancer pain management strategies, including opioids, are inadequate and are burdened by unacceptable side effects. By abrogating the actions of growth factors, including NGF, NRP1-targeted therapies represent an alternative approach to mitigate cancer pain and possibly slow tumor growth.

Protease-activated receptor 2 (PAR2) mediates oral cancer pain. Patients with metastatic (N + ) cancers report greater pain. PAR2 is activated by N-terminal proteolytic cleavage. Here we show that proteases encoded by genes overexpressed in N+ cancers from patients with pain (matrix metallopeptidase 1, MMP1 and serine protease 23, PRSS23) elicit protease-specific receptor redistribution (trafficking) and signaling that differs from that promoted by proteases encoded by genes not differentially expressed (transmembrane serine protease matriptase, ST14 and cathepsin S, CTSS). Mixtures of the proteases prepared to model the oral cancer microenvironment revealed that ST14-mediated PAR2 activation predominated at low protease concentrations. At high concentrations, MMP1 and PRSS23 prevailed over the greater potency of ST14. We propose that PAR2 activation in oral N+ cancers from patients with pain is driven by high levels of MMP1 and PRSS23. Our study informs design of signaling and location-specific antagonists to provide more efficacious analgesia.

Pain is a pervasive and multifaceted condition that imposes a significant medical and economic burden worldwide. This burden is underscored by the urgent need for transformative, non-addictive opioid alternatives. Nanomedicine offers a promising avenue for addressing the many limitations associated with conventional pain treatments, such as off-target effects, poor bioavailability, and rapid clearance, while enabling advanced therapeutic approaches such as precise spatiotemporal control and robust delivery of biologics. In this review, we explore the convergence of nanomedicine and pain management. We examine current literature on pain and chronic pain physiology and provide collated pharmacological data on current therapeutic approaches as a reference for formulation development. Recent advancements in lipid-based, polymeric, and inorganic nanoscale drug delivery systems (NDDS) for pain are surveyed, along with their progress toward clinical translation. Strategies for enhancing the efficacy of NDDS for pain are discussed, including supramolecular depot localization methods, active and passive targeting, controlled release kinetics, and the incorporation of stimuli-responsive elements for triggered release. We identify knowledge and technical gaps limiting progression beyond sustained-release formulations toward designs exploiting pain-specific biology. Overall, this review provides a comprehensive overview of the state-of-the-art in nanomedicine-based approaches for pain management and provides a roadmap for future innovations.

Background: Inflammatory bowel disease (IBD) involves relapsing inflammation of the gastrointestinal tract and is frequently associated with abdominal pain, yet effective treatments remain limited. Proteolytic activity is elevated in IBD patients, and proteases can activate visceral pain pathways via protease-activated receptors (PARs). Notably, protease activity from the gut bacterium, Bacteroides vulgatus, has recently been correlated with IBD severity, suggesting a potential microbial contribution to IBD-related pain. We hypothesize that proteases produced by B. vulgatus activate colonic afferent nerves involved in nociception. Methods: B. vulgatus cell-free supernatant (ATCC 8482 strain) or brain heart infusion (BHI) media on nociceptive neuronal activity were examined using ex vivo single-unit colonic afferent recordings from C57Bl/6 mice. Cellular mechanisms were probed by Ca 2 + imaging of dissociated DRG neurons exposed to supernatant superfusion. To specifically assess sensitization, we examined whether exposure of DRG neurons to B. vulgatus supernatant enhanced TRPV1-mediated Ca 2 + influx to capsaicin. A protease inhibitor cocktail (PIC) evaluated protease involvement, and Nav1.8-PAR2 knockout mice determined PAR2 dependence. In vivo visceromotor responses (VMR) to colorectal distension (CRD) were assessed after intracolonic administration of supernatant. Colonic permeability was measured ex vivo via FITC-dextran flux in Ussing chambers. PAR2 N-terminal cleavage by B. vulgatus supernatant was assessed using a fluorescent enzymatic assay. Results: Superfusion of DRG neurons with B. vulgatus supernatant, but not BHI, significantly increased Ca 2+ influx in response to the pro-nociceptive mediator, capsaicin (100 nM; p< 0.0001) by 49%. Ex vivo luminal perfusion of B. vulgatus supernatant, but not BHI, significantly increased spontaneous activity by 50% (p< 0.001) and mechanosensitivity of colonic afferent axons by 48% (p< 0.05). Pre-incubation of B. vulgatus supernatant with a PIC blocked the excitatory effect observed in both bioassays. Additionally, this excitation was suppressed using DRG neurons and colons from Nav1.8 PAR2 knockout mice, whereas it was maintained in the Cre controls. In vivo enema administration of B. vulgatus supernatant significantly increased VMR to CRD by 183% (p< 0.05), whereas consecutive BHI enemas had no effect. Exposure to B. vulgatus supernatant significantly increased colonic mucosal permeability, as indicated by elevated FITC-dextran flux across the colonic epithelium compared with BHI application, an effect blocked using the PIC (p = 0.05). Lastly, PAR2 cleavage was detected in the B. vulgatus supernatant, which was blocked using serine and metalloprotease inhibitors. Conclusion: Proteases secreted by B. vulgatus disrupt permeability and sensitize nociceptive visceral afferent nerves and may be a novel target for pain management in IBD. This work highlights the potential for microbiome-derived proteases to contribute directly to abdominal pain and mucosal injury in IBD patients. Funded by CIHR. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

BACKGROUND:Proteases and histamine, co-secreted by mast cells and bacteria, sensitise colonic nociceptors and contribute to irritable bowel syndrome (IBS) pain. OBJECTIVE:To determine whether irreversible proteolytic cleavage of protease-activated receptor-2 (PAR2) and its continued activity in endosomes amplify and sustain otherwise transient pronociceptive actions of histamine receptors to cause recurrent pain, the defining symptom of IBS. DESIGN:We investigated PAR2 and H1R coexpression in nociceptors using RNAscope and assessed the consequences of coactivation using electrophysiological assays of nociceptor sensitisation and biophysical measurements of receptor and effector activity. RESULTS:PAR2 and H1R were co-expressed by human and mouse dorsal root ganglion nociceptors. Intracolonic infusion of faecal supernatants from patients with IBS with elevated histamine and proteolytic activity enhanced mechanosensitivity of colonic nociceptors in mice. Antagonists of PAR2 or H1R abolished this response. Combined administration of subthreshold concentrations of trypsin and histamine replicated the effects of faecal supernatant and caused hyperexcitability of isolated nociceptors. Pre-activation with trypsin sensitised histamine-induced hyperexcitability in nociceptors from wild-type but not Par2 -/- mice. Endocytosis inhibitors prevented this hypersensitivity, consistent with sustained endosomal signalling of PAR2 and persistent nociceptor hyperexcitability. Trypsin amplified histamine-induced activation of H1R and β-arrestin2 and Gαq effectors at the plasmalemma and in endosomes. Conversely, histamine did not sensitise trypsin-induced hyperexcitability of neurons, in line with the inability of histamine to induce sustained nociceptor hypersensitivity. CONCLUSIONS:By amplifying and maintaining the otherwise transient actions of H1R and possibly other pain receptors, persistent PAR2 endosomal signalling makes a dominant contribution to IBS-related colonic pain.

Protease-activated receptor 2 (PAR2) is a central regulator of intestinal barrier function, inflammation, and pain. Upregulated intestinal proteolysis and PAR2 signaling are implicated in inflammatory bowel diseases (IBDs) and irritable bowel syndrome (IBS), conditions often associated with gut microbiome alterations. To identify potential bacterial regulators of PAR2 activity, we developed a functional assay for PAR2 processing to screen a library of diverse gut microbes. We identify multiple bacteria that secrete proteases capable of cleaving host PAR2. Using chemoproteomic profiling with a covalent irreversible inhibitor, we uncovered a previously uncharacterized Bacteroides fragilis serine protease 1 (Bfp1) and show that it cleaves and activates PAR2 in multicellular and murine models. PAR2 cleavage by Bfp1 disrupts the intestinal barrier, sensitizes nociceptors, and triggers colonic inflammation and abdominal pain. Collectively, our findings uncover Bfp1-mediated PAR2 processing as an axis of host-commensal interaction in the gut that has the potential to be targeted for therapeutic intervention in IBD or IBS.

Protease-activated receptor 2 (PAR2) is a central regulator of intestinal barrier function, inflammation and pain. Upregulated intestinal proteolysis and PAR2-signaling are implicated in inflammatory bowel diseases (IBDs) and irritable bowel syndrome (IBS). To identify potential bacterial regulators of PAR2 activity, we developed a functional assay for PAR2 processing and used it to screen conditioned media from a library of diverse gut commensal microbes. We found that multiple bacteria secrete proteases that cleave host PAR2. Using chemoproteomic profiling with a covalent irreversible inhibitor, we identified a previously uncharacterized Bacteroides fragilis serine protease Bfp1, and showed that it cleaves and activates PAR2 in multicellular and murine models. PAR2 cleavage by Bfp1 disrupts the intestinal barrier, sensitizes nociceptors, and triggers colonic inflammation and abdominal pain. Collectively, our findings uncover Bfp1-mediated PAR2-processing as a new axis of host-commensal-interaction in the gut that has the potential to be targeted for therapeutic intervention in IBD or IBS.

Objective Oral mucositis (OM) after radiation therapy (RT) for head and neck cancer (HNC) usually resolves within 1 to 2 months. A few cases of chronic OM have been reported, defined as persistent or recurrent beyond 3 months after end of therapy. The objective of this analysis is to examine the incidence of chronic OM after RT for HNC. Methods OraRad is a prospective observational multicenter cohort study of patients receiving RT for HNC. OM scoring using the World Health Organization scale was conducted by trained examiners before RT and at 6, 12, 18, and 24 months after RT. For this analysis, OM scores of 2 or greater (indicating presence of ulceration) at the 6-month visit or later were examined across all study sites. In addition, a review of research and clinical records was performed at one study site. Results Of 521 participants at the 6-month visit, 23 (4.4%) had an OM score of 2 or greater (18 with score 2, 3 with score 3, 2 with score 4). Of 448 participants at the 12-month visit, 10 (2.2%) had an OM score of 2 or greater (7 with score 2, 3 with score 3, none with score 4). Of 445 participants at the 18-month visit, 7 (1.6%) had an OM score of 2 or higher (5 with score 2, 2 with score 3, none with score 4). Of 437 participants at the 24-month visit, 4 (0.9%) had an OM score of 2 or higher (2 with score 2, one with score 3, one with score 4). Record reviews of the 2 UConn participants with an OM score of 2 at the 6-month visit revealed initial contribution of cheek-biting to a nonhealing ulcer of the buccal mucosa in one participant who received 6600 cGy. The other participant received 7000 cGy and had diabetes mellitus. Conclusions In the OraRad cohort, a World Health Organization OM score of 2 or greater was infrequently recorded at the 6-month or later visits. Detailed record reviews are planned to rule out alternative explanations for the recorded OM scores.

Nerve growth factor (NGF) monoclonal antibodies inhibit chronic pain, yet failed to gain approval due to worsened joint damage in osteoarthritis patients. We report that neuropilin-1 (NRP1) is a coreceptor for NGF and tropomyosin-related kinase A (TrkA) pain signaling. NRP1 was coexpressed with TrkA in human and mouse nociceptors. NRP1 inhibitors suppressed NGF-stimulated excitation of human and mouse nociceptors and NGF-evoked nociception in mice. NRP1 knockdown inhibited NGF/TrkA signaling, whereas NRP1 overexpression enhanced signaling. NGF bound NRP1 with high affinity and interacted with and chaperoned TrkA from the biosynthetic pathway to the plasma membrane and endosomes, enhancing TrkA signaling. Molecular modeling suggested that the C-terminal R/KXXR/K NGF motif interacts with the extracellular "b" NRP1 domain within a plasma membrane NGF/TrkA/NRP1 of 2:2:2 stoichiometry. G α interacting protein C-terminus 1 (GIPC1), which scaffolds NRP1 and TrkA to myosin VI, colocalized in nociceptors with NRP1/TrkA. GIPC1 knockdown abrogated NGF-evoked excitation of nociceptors and pain-like behavior. Thus, NRP1 is a nociceptor-enriched coreceptor that facilitates NGF/TrkA pain signaling. NRP binds NGF and chaperones TrkA to the plasma membrane and signaling endosomes via the GIPC1 adaptor. NRP1 and GIPC1 antagonism in nociceptors offers a long-awaited nonopioid alternative to systemic antibody NGF sequestration for the treatment of chronic pain.

Objectives To determine the relationships between the number and class of xerogenic medications on whole stimulated salivary flow rates and oral health-related quality of life (OH-QOL) measures in patients who received high-dose external beam radiation therapy (RT) for head and neck cancer (HNC). Study Design Complete medication lists were generated using patient electronic health records from every attended study visit for 146 HNC patients. Whole stimulated salivary flow was measured before RT, and 6 and 18-months after RT. Ten single-item questions and two composite scales of swallowing problems and senses problems (taste and smell) were assessed at baseline and at 6-month intervals up to 24 months after RT. Linear mixed-effects models examined associations between the total number and class of medications and stimulated salivary flow and OH-QOL. Results There was no detected association between the total number of medications and stimulated salivary flow (p-value = .18). Only antidepressant usage was significantly associated with stimulated salivary flow (P = .006). Number of medications, narcotic analgesic, and antidepressant usage were significantly associated with a clinically meaningful decrease in OH-QOL. Conclusion Antidepressants were associated with reduced stimulated salivary flow, but no cumulative negative effect on whole stimulated salivary flow was identified. Polypharmacy was associated with worse OH-QOL.

By improving the delivery and tumor retention of chemotherapeutics, nanomedicines hold potential for cancer treatment. The usefulness of nanoparticle (NP)-encapsulated analgesics for the cancer pain treatment is comparatively unexplored. We investigated whether NPs encapsulating olcegepant (OCP), an antagonist of the calcitonin receptor-like receptor (CLR) for the calcitonin gene-related peptide (CGRP), effectively relieved oral cancer pain in mice. Because persistent endosomal CLR signaling in Schwann cells mediates craniofacial pain, we reasoned that the predisposition of NPs to accumulate in endosomes could be leveraged to effectively relieve oral cancer pain. By expressing biosensors for activated CLR, Gα proteins and β-arrestins in HEK293T and Schwann cells, we found that CGRP activates CLR signaling first at the plasma membrane and then in early, late and recycling endosomes and the cis- and trans-Golgi apparatus. We synthesized biocompatible NPs encapsulating OCP and fluorophores by integrating hydrophobic ion pairing nanoformulation with Flash NanoPrecipitation. NPs slowly released OCP and accumulated in early endosomes, leading to sustained inhibition of endosomal CLR signaling in HEK293T and Schwann cells. Oral cancers were established in mice, which led to heightened pain-like responses. After intra-tumoral injection, NPs were retained in tumors for at least one week. OCP-loaded NPs almost completely reversed allodynia and hyperalgesia for a prolonged period, whereas unencapsulated OCP had small and transient effects. The NP accumulation in endosomal sites of pain signaling, the sustained release of antagonist, and the retention of NPs in tumors explain their beneficial actions. Thus, NP-encapsulation holds promise for the relief of painful cancers that are inadequately treated by opioids.

IntroductionPatients with oral cancer often experience intense functional pain due to mechanical stimulation at the cancer site. The role of mechanosensitive ion channels in oral cancer pain, such as TRPV4, is not fully understood.ObjectivesOur objective was to investigate the role of Schwann cell TRPV4 in oral cancer pain.MethodsWe examined the impact of TRPV4 inhibition on oral cancer pain in NU/J and C57BL/6J mice injected with human tongue cancer cell line (HSC-3) and mouse oral cancer cell line (MOC2) in the hind paw or tongue. Mechanical and heat sensitivity were assessed using the von Frey and Hargreaves tests, respectively. TRPV4 expression and functional activity in Schwann cells were analyzed using immunohistochemistry, qRT-PCR, Ca2+ imaging, and patch-clamp electrophysiology. The effect of TRPV4 activation on Schwann cell responses to mechanical stimulation was evaluated using a piezo stimulator. Conditioned media (CM) from TRPV4-activated Schwann cells were injected into the mouse paw to evaluate the contribution of TRPV4 in Schwann cells to mechanical hypersensitivity.ResultsTRPV4 inhibition reduced paw cancer mechanical nociception in mice dose-dependently without affecting heat sensitivity. TRPV4 inhibition also decreased facial nociception in tongue cancer mice. TRPV4 was expressed mainly on the plasma membrane of mouse Schwann cells and activation of TRPV4 induced Ca2+ responses and whole-cell membrane currents in human Schwann cells. Mechanoactivated currents in human Schwann cells were inhibited by the TRPV4 antagonist HC-067047. Schwann cell CM induced mechanical hypersensitivity in mice, which was blocked by pre-treatment with HC-067047.ConclusionTRPV4 activation plays a role in mediating mechanically induced pain of oral cancer.

Oral cancer is notoriously painful. Activation of protease-activated receptor 2 (PAR2, encoded by F2RL1) by proteases in the cancer microenvironment is implicated in oral cancer pain. PAR2 is a G protein-coupled receptor (GPCR) expressed on neurons and cells in the cancer microenvironment. Sustained signaling of PAR2 from endosomes of neurons mediates sensitization and nociception. We focused on the differential contribution of PAR2 on oral cancer cells and neurons to oral cancer pain and whether encapsulation of a PAR2 inhibitor, AZ3451 in nanoparticles (NP) more effectively reverses PAR2 activation. We report that F2RL1 was overexpressed in human oral cancers and cancer cell lines. Deletion of F2RL1 on cancer cells reduced cancer-associated mechanical allodynia. A third-generation polyamidoamine dendrimer, functionalized with cholesterol was self-assembled into NPs encapsulating AZ3451. NP encapsulated AZ3451 (PAMAM-Chol-AZ NPs) more effectively reversed activation of PAR2 at the plasma membrane and early endosomes than free drug. The PAMAM-Chol-AZ NPs showed greater efficacy in reversing nociception than free drug, with respect to both level and duration, in three preclinical mouse models of oral cancer pain. The antinociceptive efficacy was confirmed with an operant orofacial assay. Genetic deletion of F2RL1 on cancer cells or F2rl1 on neurons each partially reversed mechanical cancer allodynia. The remaining nociception could be effectively reversed by PAMAM-Chol-AZ NPs. These findings suggest that PAR2 on oral cancer cells and neurons contribute to oral cancer nociception and NPs loaded with a PAR2 antagonist provide increased antinociception and improved oral function compared to free drug.

Analgesia by non-steroidal anti-inflammatory drugs (NSAIDs) is ascribed to inhibition of prostaglandin (PG) biosynthesis and ensuing inflammation. However, NSAIDs have life-threatening side effects, and inhibition of inflammation delays pain resolution. Decoupling the mechanisms underlying PG-evoked pain vs. protective inflammation would facilitate pain treatment. Herein, we reveal that selective silencing of the PGE2 receptor 2 (EP2) in Schwann cells via adeno-associated viral vectors abrogates the indomethacin-sensitive component of pain-like responses in mice elicited by inflammatory stimuli without affecting inflammation. In human Schwann cells and in mice, EP2 activation and optogenetic stimulation of adenylyl cyclase evokes a plasma membrane-compartmentalized cyclic adenosine monophosphate (cAMP) signal that, via A-kinase anchor protein-associated protein kinase A, sustains inflammatory pain-like responses, but does not delay their resolution. Thus, an unforeseen and druggable EP2 receptor in Schwann cells, via specific cAMP nanodomains, encodes PGE2-mediated persistent inflammatory pain but not PG-dependent protective inflammation.

Chemotherapy‐induced peripheral neuropathy (CIPN) is a major clinical challenge, particularly for patients treated with paclitaxel (PTX), a highly effective yet neurotoxic chemotherapeutic agent. PTX often causes debilitating neuropathic pain, including mechanical and cold allodynia, driven by neuroinflammation and altered peripheral neuron excitability. This study investigates PTX‐loaded cationic PAMAM‐Chol nanoparticles (PTX NPs) as a novel strategy to mitigate CIPN. PTX NPs exhibit high drug loading efficiency (99%), sustained release, and reduced neurotoxicity in neuronal cell models. In a murine CIPN model, PTX NPs produce an 85% overall reduction in cold allodynia with a peak inhibition of 90% at day 8 and accelerate the recovery of mechanical allodynia, restoring withdrawal thresholds to baseline levels by day 14, compared to persistent nociception with unencapsulated PTX. PTX NPs also suppress dorsal root ganglia inflammation, reducing the expression of proinflammatory cytokines TNFα and IL‐1β. Furthermore, as indicated by phosphorylated ERK, neuronal activation is prevented in PTX NP‐treated mice, suggesting a reduction in central sensitization. Importantly, PTX NPs demonstrate no observable toxicity in liver or kidney function. These findings establish a proof of concept that nanomedicine‐mediated delivery can alleviate CIPN effectively, offering a promising approach to refine PTX‐based chemotherapy regimens.

Although many internalized G protein-coupled receptors (GPCRs) continue to signal, the mechanisms and outcomes of intracellular GPCR signaling are uncertain due to the challenges of measuring organelle-specific signals and of selectively antagonizing receptors in intracellular compartments. Herein, genetically encoded biosensors targeted to the plasma membrane and early endosomes were used to analyze compartmentalized signaling of protease-activated receptor 2 (PAR 2 ); the propensity of nanoparticles (NPs) to accumulate in endosomes was leveraged to preferentially antagonize intracellular PAR 2 signaling of pain. PAR 2 agonists evoked sustained activation of PAR 2 , Gαq, and β-arrestin-1 in early endosomes and activated extracellular signal regulated kinase (ERK) in the cytosol and nucleus, measured with targeted biosensors. Fluorescent dendrimer and core-shell polymeric NPs accumulated in endosomes of HEK293T cells, colonic epithelial cells, and nociceptors, detected by confocal microscopy. NPs efficiently encapsulated and slowly released AZ3451, a negative allosteric PAR 2 modulator. NP-encapsulated AZ3451, but not unencapsulated AZ3451, rapidly and completely reversed PAR 2 , Gαq, and β-arrestin-1 activation in early endosomes and ERK activation in the cytosol and nucleus. When administered into the mouse colon lumen, fluorescent dendrimer NPs accumulated in endosomes of colonocytes and polymeric NPs accumulated in neurons, sites of PAR 2 expression. Both NP formulations of AZ3451, but not unencapsulated AZ3451, caused long-lasting analgesia and normalized aberrant behavior in preclinical models of inflammatory bowel disease. These results provide evidence that PAR 2 endosomal signaling mediates pain and that nanomedicines that antagonize PAR 2 in endosomes effectively relieve pain. NP-mediated delivery may improve the efficacy of other GPCR antagonists for treatment of diverse diseases.

OBJECTIVE:To compare salivary flow rates between females and males, before and after radiation therapy (RT) for head and neck cancer (HNC). METHODS:Prospective observational multicenter cohort study (OraRad). Stimulated whole salivary flow was measured before RT and at 6 and 18 months after RT. RESULTS:Mean (95% confidence interval) salivary flow in g/min before RT was 0.81 (0.71, 0.90) in females (n = 107) and 1.20 (1.15, 1.25) in males (n = 391) (p < 0.001); at 6 months was 0.34 (0.24, 0.44) in females and 0.50 (0.44, 0.55) in males (p = 0.01); at 18 months was 0.49 (0.38, 0.59) in females and 0.70 (0.64, 0.75) in males (p < 0.001). Median nadir salivary flow after RT was 0.22 in females and 0.35 in males (p < 0.001). A lower nadir salivary flow in females, but not males, was associated with an increased risk for tooth failure (p = 0.02). CONCLUSIONS:Females with HNC have lower stimulated whole salivary flow than males, before and after RT. Low salivary flow after RT may be a risk factor for tooth failure among females. The lower pre-RT salivary flow rates in females, combined with prior literature in other populations, indicates that, in general, females have lower stimulated salivary flow than males.