(T1530-04-20) Anti-inflammatory and Analgesic Effects of Lapatinib in Rats

Purpose: Cyclooxygenase (COX) enzymes COX-1 and COX-2 convert arachidonic acid to prostaglandin H2 (PGH2). Microsomal prostaglandin E2 synthase 1 (mPGES-1) is an inducible enzyme that preferentially uses COX-2-derived PGH2 to produce prostaglandin E2 (PGE2).¹ At basal levels, PGE2 regulates normal physiological functions. However, overproduction of PGE2 causes pathologic inflammation and pain. Traditional anti-inflammatory drugs, known as nonsteroidal anti-inflammatory drugs (NSAIDs), target COX enzymes to inhibit the synthesis of PGE2. However, these drugs indiscriminately inhibit all prostaglandins, which leads to life-threatening adverse effects (i.e., cardiovascular, cerebrovascular, and gastrointestinal effects). Since mPGES-1 is an inducible enzyme that acts downstream of COX-1 and COX-2, its inhibition will only block the overproduction of PGE2 without affecting the synthesis of other physiologically beneficial prostaglandins. In our previous work, analysis of clinical trial data revealed that lapatinib therapy significantly alleviated various types of pain,² and structural-based virtual screening of all FDA-approved drugs identified lapatinib as a potent mPGES-1 inhibitor (IC₅₀ of 0.8µM and 12µM for human and mouse mPGES-1, respectively).³ Further analysis of clinical pharmacokinetic (PK) data revealed that the maximum drug concentration (Cmax) of lapatinib is 8.598 µM (under the FDA-approved oral dose of 1500 mg/day),² which is ten times higher than the IC₅₀ of human mPGES-1, suggesting that lapatinib might have significant anti-inflammatory and analgesic effects even with an oral dose a few times lower than 1500 mg.² In the present study, we evaluated the analgesic effects of lapatinib in animal models of acute pain.

Methods: In this study, the analgesic effects of lapatinib were evaluated in male Sprague-Dawley rats using two models. In model #1, 100 μL of 1% λ-carrageenan were subcutaneously injected into the plantar surface of the hind paw to induce edema and hyperalgesia. Lapatinib or vehicle was injected (IP) 2 hours before carrageenan injection. Paw withdrawal latency (PWL) and paw volume were measured to quantify hyperalgesia and edema, respectively. Additionally, to determine PGE2 levels in paw tissue, the rats were sacrificed at 26 hours post carrageenan injection. The skin, muscle, and connective tissue on the plantar and dorsal surface of the hind paw were excised and used to assess PGE2 levels with an ELISA kit (catalog #514531). In model #2, intra-articular injection of complete Freund’s adjuvant (CFA) induced mono-arthritis in the hind knee joint. Lapatinib or vehicle was injected (IP) on days 3, 4, 5, and 6 post-CFA injection, and PWL was measured 2 hours later. The arthritis score was recorded daily for 12 days by observing the rats in their home cages and scoring limb posture using a subjective pain score with 0-normal; 1-curling of toes; 2-eversion of the paw; 3-partial weight bearing; 4-non-weight bearing and guarding; and 5-avoidance of any contact with the hindlimb.⁴ The Ugo Basile Thermal Plantar Instrument (Stoelting, Wood Dale, IL) measured PWL, and a digital water displacement plethysmometer (Harvard Apparatus, Cambridge, MA) measured paw volume. To calculate significant differences between treatment groups, we used GraphPad Prism 9.4.1. For arthritis score data, we used the Mann-Whitney test, and a two-way ANOVA followed by multiple comparisons with Turkey correction was used to analyze PWL data.

Results: In carrageenan-injected rats (i.e., model #1), lapatinib significantly alleviated edema and hyperalgesia and suppressed carrageenan-induced PGE2 overproduction in the paw tissue. The average PGE2 level was 4.78 ± 2.33 pg/mg in the sham group, 8.49 ± 3.17 pg/mg in the vehicle group (p = 0.0217 vs. sham group), and 2.52 ± 1.21 pg/mg in the lapatinib group (p = 0.0004 vs. vehicle group). There was no significant difference between the sham and lapatinib groups. In CFA-induced knee-joint arthritis (i.e., model #2), the median arthritis score for all groups of rats gradually increased from 0 to 4 from day 0 to day 3, respectively. Compared to the vehicle group, treatment with lapatinib gradually decreased the arthritis score, with days 5 and 6 showing a significant improvement with 100 mg/kg lapatinib treatment. For example, on day 6, the median arthritis score was 3 for the vehicle group, 3 for the 50 mg/kg lapatinib group (p = 0.035 vs. vehicle group), and 0 for the 100 mg/kg lapatinib group (p = 0.0025 vs. vehicle group). Treatment with lapatinib also dose-dependently increased the PWL, with significant differences between all three groups on day 6, where the average PWL was 6.42 s for the vehicle group, 10.56 s for the 50 mg/kg lapatinib group (p = 0.0170 vs. vehicle), and 12.43 s for the 100 mg/kg lapatinib group (p = 0.0001 vs. vehicle).

Conclusion: Our animal data strongly support lapatinib's potential as a robust and sustained analgesic for acute pain. These findings offer promising prospects for repurposing lapatinib in pain therapeutics, with the potential to mitigate the adverse effects associated with current analgesics.

References: 1. Smith WL, DeWitt DL, Garavito RM. Cyclooxygenases: structural, cellular, and molecular biology. Annual review of biochemistry. 2000;69(1):145-82.
2. Zhou S, Zheng F, Zhan CG. Clinical data mining reveals analgesic effects of lapatinib in cancer patients. Sci Rep. 2021;11(1):3528. Epub 20210211. doi: 10.1038/s41598-021-82318-w. PubMed PMID: 33574423; PMCID: PMC7878815.
3. Zhou S, Zhou Z, Ding K, Yuan Y, Loftin C, Zheng F, Zhan CG. DREAM-in-CDM Approach and Identification of a New Generation of Anti-inflammatory Drugs Targeting mPGES-1. Sci Rep. 2020;10(1):10187. Epub 20200623. doi: 10.1038/s41598-020-67283-0. PubMed PMID: 32576928; PMCID: PMC7311425.
4. Hammell DC, Zhang LP, Ma F, Abshire SM, McIlwrath SL, Stinchcomb AL, Westlund KN. Transdermal cannabidiol reduces inflammation and pain-related behaviours in a rat model of arthritis. Eur J Pain. 2016;20(6):936-48. Epub 20151030. doi: 10.1002/ejp.818. PubMed PMID: 26517407; PMCID: PMC4851925.

Acknowledgements: This work was supported in part by the U.S. Department of Defense (DOD) Chronic Pain Management Research Program (CPMRP) Investigator-Initiated Research Award W81XWH2211000.


Fig.1: Showing PGE2 levels for paw tissues collected from carrageenan-injected rats. Treatment with lapatinib significantly reduced PGE2 levels in these rats (p=0.0004 vs. vehicle; one-way ANOVA followed by posthoc test).


Fig.2: Showing median pain scores on days 0, 3, and 6 post-CFA. Arthritis pain scores were maximal on day 3 post-CFA and were significantly reduced by lapatinib (100mg/kg ) on day 6 (p=0.0025 vs. vehicle; Mann-Whitney test).


Fig.3: Lapatinib (100 mg/kg) reduced hind paw hyperalgesia with significant differences in PWL on days 5 (p=0.0018 vs. vehicle), 6 (p=0.0001 vs. vehicle), and 7 (p=0.0039 vs. vehicle) post-CFA; two-way ANOVA)