(±)-Involucrasin D, a pair of enantiomeric bisflavonoid from the roots of Shuteria involucrata and its anti-inflammatory activity.

An undescribed bisflavonoid, named involucrasin D (1), along with two known flavonoids, 2(S)7,3',5'-trihydroxydihydroflavone (2) and sigmone (3) were isolated from the roots of Shuteria involucrata. A further chiral separation of 1 to yielded a pair of enantiomers (+)-1 and (-)-1. The structures were elucidated based on spectroscopic analyses and electron circular dichroism (ECD) calculations. Among them, bisflavonoid 1 and its enantiomers displayed remarkable anti-inflammatory effects by inhibiting the production of TNF-α and IL-6 in a dose-dependent manner.

Five-Year Follow-Up of POLARIS-01 Phase II Trial: Toripalimab as Salvage Monotherapy in Chinese Patients With Advanced Melanoma.

BACKGROUND: To investigate the efficacy and toxicity after long-term follow-up of anti-PD-1 antibody in advanced melanoma with predominantly acral and mucosal subtypes. METHODS AND PATIENTS: In the POLARIS-01 phase II trial, 128 Chinese patients with advanced melanoma refractory to standard therapy received toripalimab until disease progression or unacceptable toxicity for ≤2 years. For those who progressed after discontinuation due to 2-year treatment completion, rechallenge was allowed. The primary objectives were safety and overall response rate (ORR). RESULTS: As of February 8, 2021, ORR was 17.3% (95% CI: 11.2-25.0) evaluated by the independent radiologic review committee. The median overall survival (OS) for patients with known melanoma subtypes was 16.3 m for acral, 41.5 m for nonacral cutaneous, and 10.3 m for mucosal melanoma. Thereafter, the evaluation was continued by investigators. As of November 4, 2022, 5 years after the last enrollment, median duration of response was 15.6 months (range, 3.7-64.5+), median progression-free survival (PFS) was 3.5 months (95% CI, 2.2-5.3), and 60-month OS rate was 28.5% (95% CI: 20.2-37.2). Thirteen patients completed a 2-year treatment of toripalimab, with the subtypes of acral (2/13), non-acral cutaneous (4/13), mucosal (3/13) and unknown primary (4/13). Five patients were rechallenged. Four of them, all of whom were non-mucosal, completed the rechallenge course of 2 years with PFS ≥ 24 months. CONCLUSIONS: This is the largest prospective anti-PD-1 trial with mature data in advanced melanoma in China. Toripalimab demonstrated a manageable safety profile and durable clinical response in Chinese patients with metastatic melanoma who had failed in standard therapy. Immunotherapy seems less efficacious for long-term responders with mucosal primaries as rechallenge therapy.

Natural history of bone-only metastasis in renal cell carcinoma.

BACKGROUND: Bone metastasis (BM) is considered a poor prognostic factor of renal cell carcinoma (RCC). Confusion exists regarding how to deal with RCC patients with bone-only metastasis. PATIENTS AND METHODS: The clinical data of consecutive RCC patients with bone-only metastasis at Peking University Cancer Hospital between 2006 and 2018 were retrospectively collected and analyzed. RESULTS: Fifty-four eligible patients were screened from an RCC database of 1,878 metastatic patients. After a median follow-up of 43.6 m, 61.1% of the patients were presented with progression of prior BM or new BM. The progression-free survival (PFS) and overall survival (OS) was 16.2 m (95%CI: 11.4-21.0) and 65.2 m, respectively. For the 30 patients with oligo-metastasis (≤3 loci) and 24 ones with multiple-metastasis (>3 loci), the median OS was not reached and 42.0m (95%CI: 12.7-71.2) with statistical difference (P < 0.001). In the oligo-metastasis group, the median PFS of the 15 patients treated with local therapy and of the 13 patients treated with systemic therapy was 14.2 m (95%CI: 5.3-23.3) and 18.0 m (95%CI:15.4-20.6), respectively. In the multiple-metastasis group, the median PFS and OS of the 18 patients treated with systemic therapy was 16.6 m (95%CI: 7.5-25.7) and 63.9 m (95%CI: 21.8-106.0), respectively. Univariate analysis and multivariate analysis showed that the number of metastatic sites (oligo/multiple) and International Metastatic Renal Cell Carcinoma Database Consortium (IMDC) score, RCC pathological subtype were significantly associated with prognosis (P < 0.05). CONCLUSION: RCC patients with bone-only metastases have a favorable prognosis. The number of metastatic sites, IMDC, RCC pathological subtype could serve as survival predictors, which might provide clue of treatment modality.

Cutaneous melanocytic tumor with CRTC1::TRIM11 fusion: a case report.

BACKGROUND: Cutaneous Melanocytic Tumor with CRTC1::TRIM11 Fusion (CMTCT) represents a novel and rare entity in the realm of dermatological oncology, characterized by distinct melanocytic differentiation. This particular tumor type has yet to be officially recognized by the World Health Organization (WHO). CMTCT is generally perceived as a tumor with a relatively indolent nature; however, it is not devoid of metastatic potential. Therefore, ensuring complete surgical excision of the tumor, coupled with rigorous long-term follow-up, is paramount for patient management. In this context, we report the case of an 18-year-old female patient who presented with a dull red nodule on her left leg. Initial surgical intervention led to a pathological diagnosis of CMTCT, but it was determined that the tumor had not been fully excised. Consequently, a second surgical procedure was undertaken to achieve complete removal of the tumor. During a follow-up period of six months post-surgery, the patient showed no signs of local recurrence or metastasis, indicating a successful outcome. CASE PRESENTATION: An 18-year-old female patient noticed a dull red nodule on her left leg three years ago, which exhibited slow growth over time. She underwent a subcutaneous tumor resection. Histological examination under high-power magnification revealed that the neoplasm consisted of epithelioid cells arranged in nests, fascicles, bundles, or sheets. The tumor cells had round or ovoid nuclei with prominent nucleoli and visible mitotic figures. Notably, areas resembling nevus cell clusters were observed. Immunohistochemical analysis confirmed melanocytic differentiation. Next-generation sequencing (NGS) identified a CRTC1::TRIM11 fusion, and fluorescence in situ hybridization (FISH) for CRTC1 confirmed rearrangement. Consequently, a diagnosis of cutaneous melanocytic tumor with CRTC1::TRIM11 fusion was established. CONCLUSIONS: CMTCT is a rare tumor characterized by melanocytic differentiation. In this case, the tumor predominantly comprised epithelioid cells with localized nevus cell clusters. The expression of melanocyte markers could easily lead to a misdiagnosis as cutaneous melanoma. However, several distinguishing features were noted: the tumor was not connected to the epidermis, exhibited low cellular heterogeneity and proliferation index, and showed minimal cellular atypia. Additionally, tests for EWSR1 rearrangement (FISH) and BRAF V600E mutation (PCR-ARMS) were negative.This case underscores the importance of a comprehensive diagnostic approach when clinical, microscopic, immunohistochemical, and molecular findings do not align. The presence of nevus cell clusters morphology in the tumor cells enhances our understanding of this disease's histological spectrum and aids in avoiding misdiagnosis or missed diagnosis.

Anlotinib plus camrelizumab achieved long-term survival in a patient with metastatic esophageal neuroendocrine carcinoma.

BACKGROUND: Esophageal neuroendocrine carcinoma (NEC) is a rare cancer with an extremely poor prognosis. The average overall survival of patients with metastatic disease is only 1 year. The efficacy of anti-angiogenic agents combined with immune checkpoint inhibitors remains unknown. CASE PRESENTATION: A 64-year-old man, initially diagnosed with esophageal NEC, underwent neoadjuvant chemotherapy and esophagectomy. Although the patient remained disease-free for 11 months, eventually the tumor progressed and did not respond to three lines of combined therapy (etoposide plus carboplatin with local radiotherapy, albumin-bound paclitaxel plus durvalumab, and irinotecan plus nedaplatin). The patient then received anlotinib plus camrelizumab, and a dramatic regression was observed (confirmed by positron emission tomography-computed tomography). The patient has been disease-free for over 29 months and has survived for over 4 years since diagnosis. CONCLUSION: Combined therapy with anti-angiogenic agents and immune checkpoint inhibitors may be a promising strategy for esophageal NEC, although more evidence is warranted to validate its efficacy.

Camrelizumab Plus Apatinib and Temozolomide as First-Line Treatment in Patients With Advanced Acral Melanoma: The CAP 03 Phase 2 Nonrandomized Clinical Trial.

Importance: Acral melanoma, known for low tumor mutation burden, responds poorly to immunotherapy. A standard therapy is still lacking. Objective: To investigate the activity and safety of camrelizumab (an anti-programmed cell death-1 antibody) plus apatinib (a vascular endothelial growth factor receptor 2 inhibitor) and temozolomide as first-line treatment in patients with advanced acral melanoma. Design, Setting, and Participants: In this single-arm, single-center, phase 2 nonrandomized clinical trial, patients with treatment-naive unresectable stage III or IV acral melanoma were enrolled at Peking University Cancer Hospital and Institute between June 4, 2020, and August 24, 2021. The data cutoff date was April 10, 2022. Interventions: Patients received 4-week cycles of intravenous camrelizumab, 200 mg, every 2 weeks; oral apatinib 250 mg, once daily; and intravenous temozolomide, 200 mg/m2, once daily on days 1 to 5 until disease progression or unacceptable toxic effects. Main Outcomes and Measures: The primary end point was objective response rate as assessed by investigators according to the Response Evaluation Criteria In Solid Tumors (version 1.1). Secondary end points included progression-free survival, time to response, duration of response, disease control rate, overall survival, and safety. Results: A total of 50 patients (32 men [64%]; median age, 57 years [IQR, 52-62 years]) were enrolled and received treatment. The median follow-up duration was 13.4 months (IQR, 9.6-16.2 months). The objective response rate was 64.0% (32 of 50; 95% CI, 49.2%-77.1%). The median time to response and duration of response were 2.7 months (IQR, 0.9-2.9 months) and 17.5 months (95% CI, 12.0 to not reached), respectively. The disease control rate was 88.0% (44 of 50; 95% CI, 75.7%-95.5%). The estimated median progression-free survival was 18.4 months (95% CI, 10.6 to not reached). The median overall survival was not reached. The most common grade 3 or 4 treatment-related adverse events were increased gamma-glutamyltransferase levels (15 [30%]), decreased neutrophil count (11 [22%]), increased conjugated bilirubin levels (10 [20%]), and increased aspartate aminotransferase levels (10 [20%]). No treatment-related deaths occurred. Conclusions and Relevance: The findings of this nonrandomized clinical trial suggest that camrelizumab plus apatinib and temozolomide may be a potential first-line treatment option for patients with advanced acral melanoma, which warrants further validation in a randomized clinical trial. Trial Registration: ClinicalTrials.gov Identifier: NCT04397770.

Study on the dynamic variation of the secondary metabolites in Viscum coloratum using targeted metabolomics.

Viscum coloratum (Kom.) Nakai is a well-known medicinal plant. However, the optimal harvest time for V. coloratum is unknown. Few studies were performed to analyze compound variation during storage and to improve post-harvest quality control. Our study aimed to comprehensively evaluate the quality of V. coloratum in different growth stages, and determine the dynamic variation of metabolites. Ultra-performance liquid chromatography tandem mass spectrometry was used to quantify 29 compounds in V. coloratum harvested in six growth periods, and the associated biosynthetic pathways were explored. The accumulation of different types of compounds were analyzed based on their synthesis pathways. Grey relational analysis was used to evaluate the quality of V. coloratum across different months. The compound variation during storage was analyzed by a high-temperature high-humidity accelerated test. The results showed that the quality of V. coloratum was the hightest in March, followed by November, and became the lowest in July. During storage, compounds in downstream steps of the biosynthesis pathway were first degraded to produce the upstream compounds and some low-molecular-weight organic acids, leading to an increase followed by a decrease in the content of some compounds, and resulted in a large gap during the degradation time course among different compounds. Due to the rapid rate and large degree of degradation, five compounds were tentatively designated as "early warning components" for quality control. This report provides reference for better understanding the biosynthesis and degradation of metabolites in V. coloratum and lays a theoretical foundation for rational application of V. coloratum and better quality control of V. coloratum during storage.

Analysis of a Yp11.2 region deletion in a Chinese female with Turner syndrome: A case report.

In recent years, an increasing number of abnormal DNA genotypes caused by chromosomal abnormalities have been revealed in cases of individual identification and sex-typing analysis, especially analyses of the amelogenin and short tandem repeat (STR) loci on the sex chromosomes. Here, we report a 17-year-old female with Turner syndrome typed as male due to the presence of the amelogenin Y allele. The Y-STR haplotype showed allele dropout of three Y-STR loci (DYS549, DYS392 and DYS448). Further examination showed that the proband's karyotype was 45,X/46,X,del(Y) (q11.23), and the deletion of the Yp11.2 region was confirmed to encompass the observed microdeletion of the azoospermia factor (AZF)b + c region. One challenge in forensics is inaccurate sex typing of individuals at the molecular level, particularly for individuals with chromosomal abnormalities. This case suggests that various medical evaluations, including the examination of sex-related manifestations, karyotypes, and clinical phenotypes of individuals, along with the detection of sex-typing gene markers will be beneficial to overcome the issues caused by cytogenetic disorders of the sex chromosomes.

Reply to "Comment on: 'Isolating Vibrational Polariton 2D-IR Transmission Spectra'".

In a Comment on our recent Letter, the authors take issue with our method of refining 2D-IR transmission spectra to remove a background contribution that arises from nonpolaritonic molecules in the cavity. In our response to their Comment, we describe how our approach was motivated by the previous work of the authors, and we present a spatially dependent molecule-cavity Tavis-Cummings model that can account for the significant response from localized molecules with nonzero oscillator strengths. The telltale signature of the localized molecule response is the spectral diffusion dynamics of the bare W(CO)6 molecules in the polar butyl acetate solvent. Inhomogeneous broadening is absent from polaritonic states due to the extreme degree of exchange narrowing in coupling very large numbers of molecules to a cavity mode.

TGFß1+CCR5+ neutrophil subset increases in bone marrow and causes age-related osteoporosis in male mice.

TGFß1 induces age-related bone loss by promoting degradation of TNF receptor-associated factor 3 (TRAF3), levels of which decrease in murine and human bone during aging. We report that a subset of neutrophils (TGFß1+CCR5+) is the major source of TGFß1 in murine bone. Their numbers are increased in bone marrow (BM) of aged wild-type mice and adult mice with TRAF3 conditionally deleted in mesenchymal progenitor cells (MPCs), associated with increased expression in BM of the chemokine, CCL5, suggesting that TRAF3 in MPCs limits TGFß1+CCR5+ neutrophil numbers in BM of young mice. During aging, TGFß1-induced TRAF3 degradation in MPCs promotes NF-κB-mediated expression of CCL5 by MPCs, associated with higher TGFß1+CCR5+ neutrophil numbers in BM where they induce bone loss. TGFß1+CCR5+ neutrophils decreased bone mass in male mice. The FDA-approved CCR5 antagonist, maraviroc, reduced TGFß1+CCR5+ neutrophil numbers in BM and increased bone mass in aged mice. 15-mon-old mice with TGFßRII specifically deleted in MPCs had lower numbers of TGFß1+CCR5+ neutrophils in BM and higher bone volume than wild-type littermates. We propose that pharmacologic reduction of TGFß1+CCR5+ neutrophil numbers in BM could treat or prevent age-related osteoporosis.

Lipopolysaccharide sensitizes the therapeutic response of breast cancer to IAP antagonist.

Inhibitor of apoptosis protein (IAP) is a class of E3 ubiquitin ligases functioning to support cancer survival and growth. Many small-molecule IAP antagonists have been developed, aiming to degrade IAP proteins to kill cancer. We have evaluated the effect of lipopolysaccharide (LPS), a component of the bacterial outer membrane, on IAP antagonists in treating breast cancer in a mouse model to guide future clinical trials. We show that LPS promotes IAP antagonist-induced regression of triple-negative breast cancer (TNBC) from MDA-MB-231 cells in immunodeficient mice. IAP antagonists such as SM-164, AT-406, and BV6, do not kill MDA-MB-231 cells alone, but allow LPS to induce cancer cell apoptosis rapidly. The apoptosis caused by LPS plus SM-164 is blocked by toll-like receptor 4 (TLR4) or MyD88 inhibitor, which inhibits LPS-induced TNFα production by the cancer cells. Consistent with this, MDA-MB-231 cell apoptosis induced by LPS plus SM-164 is also blocked by the TNF inhibitor. LPS alone does not kill MDA-MB-231 cells because it markedly increases the protein level of cIAP1/2, which is directly associated with and stabilized by MyD88, an adaptor protein of TLR4. ER+ MCF7 breast cancer cells expressing low levels of cIAP1/2 undergo apoptosis in response to SM-164 combined with TNFα but not with LPS. Furthermore, TNFα but not LPS alone inhibits MCF7 cell growth in vitro. Consistent with these, LPS combined with SM-164, but not either of them alone, causes regression of ER+ breast cancer from MCF7 cells in immunodeficient mice. In summary, LPS sensitizes the therapeutic response of both triple-negative and ER+ breast cancer to IAP antagonist therapy by inducing rapid apoptosis of the cancer cells through TLR4- and MyD88-mediated production of TNFα. We conclude that antibiotics that can reduce microbiota-derived LPS should not be used together with an IAP antagonist for cancer therapy.

The effect of compatibility of Aconiti Radix and honey on the pharmacokinetics of five Aconitum alkaloids in rat plasma.

Aconiti Radix [Chuanwu (CW)] is widely used to treat chronic and intractable diseases due to its remarkable curative effect. CW has been combined with honey for thousands of years to reduce toxicity and enhance efficacy. This study first determined the compatibility mechanism of CW with honey using a comparative pharmacokinetic concept. We developed and validated a simple, sensitive, specific, and accurate UHPLC-MS/MS method to simultaneously determine five Aconitum alkaloids in rat plasma after the oral administration of CW decoction and CW-honey concentrated solution. Pharmacokinetic parameters were significantly different between the two groups (P < 0.01 and P < 0.05). Compared with the CW group, Cmax and AUC0 → t decreased in the CW-honey group for three diester-diterpenoid alkaloids (hypaconitine, mesaconitine, and aconitine); Tmax and T1/2 were prolonged. However, Cmax and AUC0 → t increased in the CW-honey group for two monoester-diterpenoid alkaloids (benzoylaconine and benzoylmesaconine); Tmax was shortened, and T1/2 was prolonged. These findings suggest that honey affected the pharmacokinetic behaviors of five Aconitum alkaloids. We speculate that the detoxification and synergism of honey might result from reducing the toxicity of diester-diterpenoid alkaloids and promoting the biological activity of monoester-diterpenoid alkaloids in vivo. This study provides a theoretical basis for the clinical use of CW combined with honey.

Elevated serum CEA is associated with liver metastasis and distinctive circulating tumor DNA alterations in patients with castration-resistant prostate cancer.

BACKGROUND: Elevated serum carcinoembryonic antigen (CEA) is used to identify "treatment emergent" forms of castration-resistant prostate cancer (CRPC) such as aggressive variant prostate cancer (AVPC). However, its individual utility as a prognostic marker and the genetic alterations associated with its expression have not been extensively studied in CRPC. METHODS: This study retrospectively analyzed clinical outcomes and circulating tumor DNA profiles in 163 patients with CRPC and elevated or normal serum CEA. These same patients were then classified as AVPC or non-AVPC and compared to determine the uniqueness of CEA-associated gene alterations. RESULTS: Patients with elevated CEA demonstrated higher rates of liver metastasis (37.5% vs. 19.1%, p = 0.02) and decreased median overall survival from CRPC diagnosis (28.7 vs. 73.2 mo, p < 0.0001). In addition, patients with elevated CEA were more likely to harbor copy number amplifications (CNAs) in AR, PIK3CA, MYC, BRAF, CDK6, MET, CCNE1, KIT, RAF1, and KRAS. Based on variant allele frequency we also defined "clonal" single-nucleotide variants (SNVs) thought to be driving disease progression in each patient and found that CEA expression was negatively correlated with clonal AR SNVs and positively correlated with clonal TP53 SNVs. Of these genetic associations, only the increases in clonal TP53 SNVs and KRAS amplifications were recapitulated among patients with AVPC when compared to patients without AVPC. CONCLUSIONS: Together these findings suggest that CEA expression in CRPC is associated with aggressive clinical behavior and gene alterations distinct from those in AVPC.

Plumbagin is a NF-κB-inducing kinase inhibitor with dual anabolic and antiresorptive effects that prevents menopausal-related osteoporosis in mice.

Osteoporosis is caused by enhanced bone resorption and relatively reduced bone formation. There is an unmet need to develop new agents with both antiresorptive and anabolic effects to treat osteoporosis, although drugs with either effect alone are available. A small molecular compound, plumbagin, was reported to inhibit receptor activator of nuclear factor kappa-B ligand-induced osteoclast (OC) differentiation by inhibiting IκBα phosphorylation-mediated canonical NF-κB activation. However, the key transcriptional factor RelA/p65 in canonical NF-κB pathway functions to promote OC precursor survival but not terminal OC differentiation. Here, we found that plumbagin inhibited the activity of NF-κB inducing kinase, the key molecule that controls noncanonical NF-κB signaling, in an ATP/ADP-based kinase assay. Consistent with this, plumbagin inhibited processing of NF-κB2 p100 to p52 in the progenitor cells of both OCs and osteoblasts (OBs). Interestingly, plumbagin not only inhibited OC but also stimulated OB differentiation in vitro. Importantly, plumbagin prevented trabecular bone loss in ovariectomized mice. This was associated with decreased OC surfaces on trabecular surface and increased parameters of OBs, including OB surface on trabecular surface, bone formation rate, and level of serum osteocalcin, compared to vehicle-treated mice. In summary, we conclude that plumbagin is a NF-κB-inducing kinase inhibitor with dual anabolic and antiresorptive effects on bone and could represent a new class of agent for the prevention and treatment of osteoporosis.

SLPI suppresses hepatocellular carcinoma progression via endoplasmic reticulum stress induced apoptosis.

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. Secretory leukocyte protease inhibitor (SLPI) has been reported to function as a regulatory factor in several cancers. However, its biological functions and underlying mechanisms in HCC remain to be uncovered. Here, we aimed to explore the effect of SLPI in HCC. In our study, we found that the mRNA and protein expression levels of SLPI were significantly down-regulated in HCC tissues and hepatoma cell lines and low level of SLPI predicted worse survival in our HCC cohorts. In term of function, silencing of SLPI markedly promoted whereas overexpression SLPI suppressed proliferation, migration and invasion capabilities of HCC cells in vitro, and ectopic expression of SLPI inhibited the tumorigenicity of HCC cells in vivo. Mechanistic studies demonstrated that SLPI played a protective role in HCC progression via activating endoplasmic reticulum stress (ER stress)-mediated apoptosis of hepatoma cells, which could be regulated by MAPK signaling pathways. In summary, our findings highlight that SLPI could serve as a potential prognostic biomarker and putative tumor suppressor by enhancing ER stress-induced apoptosis in HCC cells mediated by MAPK signaling pathways, which provides new insights into promising therapeutic targets for HCC treatment.

Identification of raloxifene as a novel α-glucosidase inhibitor using a systematic drug repurposing approach in combination with cross molecular docking-based virtual screening and experimental verification.

α-Glucosidase is a promising target for the treatment of diabetes. Drug repurposing can increase the chances of discovering an active inhibitor. Therefore, this study aimed to identify potential α-glucosidase inhibitor using drug repurposing and in silico strategies. We identified critical amino acid residues of the three α-glucosidase proteins. Based on cross molecular docking studies of three α-glucosidase proteins and drugs in the FDA database, we screened hits with the favorable binding affinities and modes targeting the three proteins. Subsequently, an in vitro activity assay showed that raloxifene was an excellent inhibitor of α-glucosidase. Moreover, molecular dynamics simulations of raloxifene and three proteins were performed to assess the stability of the protein-hit systems in physiological conditions and clarify protein-hit interactions. We also performed the binding free energy calculation, Hirshfeld surface and alanine scanning mutagenesis analyses. These results demonstrated that binding between raloxifene and the three proteins was stable, and the critical amino acid residues of the three proteins formed stable contacts with raloxifene. The molecular mechanisms agree well with its activity, reinforcing that raloxifene is a candidate α-glucosidase inhibitor. Our study smoothes the path for the development of novel a-glucosidase inhibitors with high efficacy and low toxicity for the treatment of diabetes.

Isolating Polaritonic 2D-IR Transmission Spectra.

Strong coupling between vibrational transitions in molecules within a resonant optical microcavity leads to the formation of collective, delocalized vibrational polaritons. There are many potential applications of "polaritonic chemistry", ranging from modified chemical reactivity to quantum information processing. One challenge in obtaining the polaritonic response is removing a background contribution due to the uncoupled molecules that generate an ordinary 2D-IR spectrum whose amplitude is filtered by the polariton transmission spectrum. We show that most features in 2D-IR spectra of vibrational polaritons can be explained by a linear superposition of this background signal and the true polariton response. Through a straightforward correction procedure, in which the filtered bare-molecule 2D-IR spectrum is subtracted from the measured cavity response, we recover the polaritonic spectrum.