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SummaryThe dynamics of more than 1900 mitochondrial proteins was explored through quantitative proteomics in 151 melanoma-related tissue samples of both surgical and autopsy origin. Dysregulation of mitochondrial pathways in primary tumors, metastases, and peritumoral tissues was correlated with age and survival of patients, as well as with tumor cell proliferation and the BRAF mutation status of the tumors. The outlined proteomic landscape confirmed the central role of a pathologically upregulated mitochondrial translation machinery and oxidative phosphorylation (OXPHOS) in the development, proliferation, and progression of melanomas. Our results from different melanoma cell lines confirmed our findings and we could document that treatments with selected OXPHOS inhibitors and antibiotics successfully impaired tumor cell proliferation. In addition, we provided proteomic evidence on the mechanism-of-action of the different treatments. These observations could contribute to the development of therapeutic approaches targeting the mitochondrial pathology in melanoma.TOC figureHighlightsMitochondrial proteome landscape outlined in 151 melanoma-related samplesMitochondrial Translation and OXPHOS impact disease severity and survivalBRAF V600E mutation correlates with upregulation of mitochondrial energy productionTargeting the mitochondrial OXPHOS and ribosomes impairs tumor cell proliferationTherapeutic opportunities complementary to the standard of care are proposedIn briefMitochondrial proteome profiling of melanomas reveals dysregulation in major metabolic pathways, suggesting a central role of the mitochondria within the development and progression of melanoma. Targeting mitochondrial pathways has the potential to impact the course of the disease, which provides opportunities for complementary drug interventions.

In 2021, the Asia-Oceania Human Proteome Organization (AOHUPO) initiated a new endeavor named the AOHUPO Online Education Series with the aim to promote scientific education and collaboration, exchange of ideas and culture among the young scientists in the AO region. Following the warm participation, the AOHUPO organized the second series in 2022, with the theme "The Renaissance of Clinical Proteomics: Biomarkers, Imaging and Therapeutics". This time, the second AOHUPO Online Education Series was hosted by the UKM Medical Molecular Biology Institute (UMBI) affiliated to the National University of Malaysia (UKM) in Kuala Lumpur, Malaysia on three consecutive Fridays (11th, 18th and 25th of March). More than 300 participants coming from 29 countries/regions registered for this 3-days event. This event provided an amalgamation of six prominent speakers and all participants whose interests lay mainly in applying MS-based and non-MS-based proteomics for clinical investigation.

Autophagy, the process of lysosomal degradation of biological materials within cells, is often halted abnormally in proteopathies, such as tauopathy and amyloidopathy. Thus, autophagy regulators that rescue dysregulated autophagy have great potential to treat proteopathies. We previously reported that the natural small molecule kaempferide (Kaem) induces autophagy without perturbing mTOR signaling. Here, we report that Kaem promotes lysosomal degradation of microtubule-associated protein tau (MAPT) in inducible MAPT cells. Kaem enhanced autophagy flux by mitigating microtubule-associated protein 1 light chain 3 (LC3) accumulation when MAPT expression was induced. Kaem also promoted activation of transcription factor EB (TFEB) without inhibiting mTOR and without mTOR inhibition-mediated cytotoxicity. In addition, Kaem-induced MAPT degradation was abolished in the absence of mitochondrial elongation factor Tu (TUFM), which was previously shown to be a direct binding partner of Kaem. Collectively, these results demonstrate that Kaem could be a potential therapeutic for tauopathy and reveal that TUFM can be a drug target for autophagy-driven disorders.

We have previously reported that daptomycin (DAP), a last resort antibiotic, binds to ribosomal protein S19 (RPS19) in humans and exhibits selective anti-cancer activity against MCF7 breast cancer cells. Here, we investigated the role of RPS19 in the anti-cancer effects of DAP and have found that DAP does not induce autophagy, apoptosis or cell viability but does reduce cell proliferation. Our results suggest that an extraribosomal function of RPS19 involves the regulation of vascular endothelial growth factor (VEGF) but not EGF, PDGF or FGF. Engagement of RPS19 by DAP was shown by CETSA and ITDRFCETSA assays, and knocking down of RPS19 with siRNA increased the potency of DAP in MCF7 cells. In addition, DAP suppressed the secretion of VEGF in cancer cells and thereby inhibited cell migration. Collectively, these data provide an outline of the underlying mechanism of how DAP exhibits anti-cancer activity and suggests that RPS19 could be a promising target for the development of new anticancer drugs.

Danshen (Salvia miltiorrhiza) is a traditional medicinal plant widely used in Asian countries for its pharmacological activities (e.g., amelioration of cardiovascular diseases). In this study, we investigated the anti-atherosclerotic activity of raw danshen root extract prepared using high hydrostatic pressure (HHP) at 550 MPa for 5 min and hot water extraction. This method was useful for elimination of bacteria from cultured danshen plants and for better extraction yield of active principles. The HHPtreated danshen extract (HDE) inhibited proliferation of human umbilical vein endothelial cells (HUVECs) and induced autophagy that was assessed by LC3 conversion and p62 degradation. HDE suppressed foam cell formation in oxLDL-induced RAW264.7 macrophages; lysosomal activity simultaneously increased, measured by acridine orange staining. HDE also reduced atherosclerotic plaque development in vivo in apolipoprotein E knock-out (ApoE-/-) mice fed a high cholesterol diet. Taken together, these results indicated that HDE exhibited anti-atherosclerotic activity via autophagy induction. [BMB Reports 2020; 53(12): 652-657].

Small molecules targeting autophagy have been highly implicated as new therapeutic agents to treat diseases of interest. With the increasing demand for autophagy-targeting drugs, this review attempts to provide an efficient strategy to explore major autophagy-based human disease interventions with newly explored mechanisms using small molecules and promising therapeutic approaches.Introduced in this review are direct links and applications among autophagy pathways, their modulators, and phenotypic diseases, along with recent approaches. Autophagy-related diseases, machinery, and compounds are introduced to guide the appropriate investigation of autophagy in the pharmaceutical industry. The authors then provide their expert perspectives on the subject.The self-catabolic intracellular process autophagy occurs in organisms throughout their lifetime, supporting its critical role in organismal health across life stages. Because of the detrimental influence of dysfunctional cells to an organism and their etiology in numerous diseases, maintaining cellular quality control by recycling components through autophagy is essential to prevent health decline.

In the advanced stages, malignant melanoma (MM) has a very poor prognosis. Due to tremendous efforts in cancer research over the last 10 years, and the introduction of novel therapies such as targeted therapies and immunomodulators, the rather dark horizon of the median survival has dramatically changed from under 1 year to several years. With the advent of proteomics, deep-mining studies can reach low-abundant expression levels. The complexity of the proteome, however, still surpasses the dynamic range capabilities of current analytical techniques. Consequently, many predicted protein products with potential biological functions have not yet been verified in experimental proteomic data. This category of ‘missing proteins’ (MP) is comprised of all proteins that have been predicted but are currently unverified. As part of the initiative launched in 2016 in the USA, the European Cancer Moonshot Center has performed numerous deep proteomics analyses on samples from MM patients. In this study, nine MPs were clearly identified by mass spectrometry in MM metastases. Some MPs significantly correlated with proteins that possess identical PFAM structural domains; and other MPs were significantly associated with cancer-related proteins. This is the first study to our knowledge, where unknown and novel proteins have been annotated in metastatic melanoma tumour tissue.

Human colon carcinomas, including HCT116 cells, often exhibit high basal autophagic flux under nutrient deprivation or hypoxic conditions. Mitochondrial ROS (mROS) is known as a “molecular switch”’ for regulating the autophagic pathway, which is critical for directing cancer cell survival or death. In early tumorigenesis, autophagy plays important roles in maintaining cellular homeostasis and contributes to tumor growth. However, the relationships between mROS and the autophagic capacities of HCT116 cells are poorly understood. Ubiquinol cytochrome c reductase binding protein (UQCRB) has been reported as a biomarker of colorectal cancer, but its role in tumor growth has not been clarified. Here, we showed that UQCRB was overexpressed in HCT116 cells compared to CCD18co cells, a normal colon fibroblast cell line. Pharmacological inhibition of UQCRB reduced mROS levels, autophagic flux, and the growth of HCT116 tumors in a xenograft mouse model. We further investigated mutant UQCRB-overexpressing cell lines to identify functional links in UQCRB-mROS-autophagy. Notably, an increasing level of mROS caused by UQCRB overexpression released Ca2+ by activation of lysosomal TRPML1 channels. This activation induced transcription factor EB nuclear translocation and lysosome biogenesis, leading to autophagy flux. Collectively, our study showed that increasing levels of mROS caused by overexpression of UQCRB in human colon carcinoma HCT116 cells could be linked to autophagy for cell survival.

Direct identification of the proteins targeted by small molecules can provide clues for disease diagnosis, prevention, and drug development. Despite concentrated attempts, there are still technical limitations associated with the elucidation of direct interactors. Herein, we report a target-ID system called proximity-based compound-binding protein identification (PROCID), which combines our direct analysis workflow of proximity-labeled proteins (Spot-ID) with the HaloTag system to efficiently identify the dynamic proteomic landscape of drug-binding proteins. We successfully identified well-known dasatinib-binding proteins (ABL1, ABL2) and confirmed the unapproved dasatinib-binding kinases (e.g., BTK and CSK) in a live chronic myeloid leukemia cell line. PROCID also identified the DNA helicase protein SMARCA2 as a dasatinib-binding protein, and the ATPase domain was confirmed to be the binding site of dasatinib using a proximity ligation assay (PLA) and in cellulo biotinylation assay. PROCID thus provides a robust method to identify unknown drug-interacting proteins in live cells that expedites the mode of action of the drug.

The MM500 meta‐study aims to establish a knowledge basis of the tumor proteome to serve as a complement to genome and transcriptome studies. Somatic mutations and their effect on the transcriptome have been extensively characterized in melanoma. However, the effects of these genetic changes on the proteomic landscape and the impact on cellular processes in melanoma remain poorly understood. In this study, the quantitative mass‐spectrometry‐based proteomic analysis is interfaced with pathological tumor characterization, and associated with clinical data. The melanoma proteome landscape, obtained by the analysis of 505 well‐annotated melanoma tumor samples, is defined based on almost 16 000 proteins, including mutated proteoforms of driver genes. More than 50 million MS/MS spectra were analyzed, resulting in approximately 13,6 million peptide spectrum matches (PSMs). Altogether 13 176 protein‐coding genes, represented by 366 172 peptides, in addition to 52 000 phosphorylation sites, and 4 400 acetylation sites were successfully annotated. This data covers 65% and 74% of the predicted and identified human proteome, respectively. A high degree of correlation (Pearson, up to 0.54) with the melanoma transcriptome of the TCGA repository, with an overlap of 12 751 gene products, was found. Mapping of the expressed proteins with quantitation, spatiotemporal localization, mutations, splice isoforms, and PTM variants was proven not to be predicted by genome sequencing alone. The melanoma tumor molecular map was complemented by analysis of blood protein expression, including data on proteins regulated after immunotherapy. By adding these key proteomic pillars, the MM500 study expands the knowledge on melanoma disease., The MM500 meta‐study aims to establish a knowledge basis of the tumor proteome to serve as a complement to genome and transcriptome studies. The melanoma proteome landscape, obtained by the analysis of 505 well‐annotated melanoma tumor samples, is defined based on almost 16 000 proteins, including mutated proteoforms of driver genes. This data covers 65% and 74% of the predicted and identified human proteome, respectively.

Genomic analysis of the clavulanic acid (CA)-high-producing Streptomyces clavuligerus strains, OL13 and OR, developed through random mutagenesis revealed a frameshift mutation in the cas1 gene-encoding clavaminate synthase 1. Overexpression of the intact cas1 in S. clavuligerus OR enhanced the CA titer by approximately 25%, producing ~ 4.95 g/L of CA, over the OR strain in the flask culture. Moreover, overexpression of the pathway-specific positive regulatory genes, ccaR and claR, in the OR strain improved CA yield by approximately 43% (~ 5.66 g/L) in the flask. However, co-expression of the intact cas1 with ccaR-claR did not further improve CA production. In the 7 L fermenter culture, maximum CA production by the OR strain expressing the wild-type cas1 and ccaR-claR reached approximately 5.52 g/L and 6.01 g/L, respectively, demonstrating that reverse engineering or simple rational metabolic engineering is an efficient method for further improvement of industrial strains.

A pyrrolo[1,2-a]pyrazine-based chemical territory was expanded via construction of new chemical library with distinctive substitution patterns, which was made possible by regiodivergent electrophilic acylation followed by aldol condensation. Biological screening of the compounds in this class revealed that the viability of human lymphoma U937 cells was strongly inhibited by 6b with a methoxy group at the o-position of the aromatic ring, but not by compounds 6t-w bearing a halogen at the o-position. Furthermore, 6x having a 2,4-dimethoxyphenyl group inhibited the survival of U937 cells more potently than 6b. In contrast, 6y possessing a 2,5-dimethoxyphenyl moiety did not show effective inhibition, implying the importance of orientation of the substituent(s) around the benzene ring. The anticancer action of 6x with safe therapeutic window could be associated with the FTase-p38 signaling axis.

Melanoma of the skin is the sixth most common type of cancer in Europe and accounts for 3.4% of all diagnosed cancers. More alarming is the degree of recurrence that occurs with approximately 20% of patients lethally relapsing following treatment. Malignant melanoma is a highly aggressive skin cancer and metastases rapidly extend to the regional lymph nodes (stage 3) and to distal organs (stage 4). Targeted oncotherapy is one of the standard treatment for progressive stage 4 melanoma, and BRAF inhibitors (e.g. vemurafenib, dabrafenib) combined with MEK inhibitor (e.g. trametinib) can effectively counter BRAFV600E-mutated melanomas. Compared to conventional chemotherapy, targeted BRAFV600E inhibition achieves a significantly higher response rate. After a period of cancer control, however, most responsive patients develop resistance to the therapy and lethal progression. The many underlying factors potentially causing resistance to BRAF inhibitors have been extensively studied. Nevertheless, the remaining unsolved clinical questions necessitate alternative research approaches to address the molecular mechanisms underlying metastatic and treatment-resistant melanoma. In broader terms, proteomics can address clinical questions far beyond the reach of genomics, by measuring, i.e. the relative abundance of protein products, post-translational modifications (PTMs), protein localisation, turnover, protein interactions and protein function. More specifically, proteomic analysis of body fluids and tissues in a given medical and clinical setting can aid in the identification of cancer biomarkers and novel therapeutic targets. Achieving this goal requires the development of a robust and reproducible clinical proteomic platform that encompasses automated biobanking of patient samples, tissue sectioning and histological examination, efficient protein extraction, enzymatic digestion, mass spectrometry-based quantitative protein analysis by label-free or labelling technologies and/or enrichment of peptides with specific PTMs. By combining data from, e.g. phosphoproteomics and acetylomics, the protein expression profiles of different melanoma stages can provide a solid framework for understanding the biology and progression of the disease. When complemented by proteogenomics, customised protein sequence databases generated from patient-specific genomic and transcriptomic data aid in interpreting clinical proteomic biomarker data to provide a deeper and more comprehensive molecular characterisation of cellular functions underlying disease progression. In parallel to a streamlined, patient-centric, clinical proteomic pipeline, mass spectrometry-based imaging can aid in interrogating the spatial distribution of drugs and drug metabolites within tissues at single-cell resolution. These developments are an important advancement in studying drug action and efficacy in vivo and will aid in the development of more effective and safer strategies for the treatment of melanoma. A collaborative effort of gargantuan proportions between academia and healthcare professionals has led to the initiation, establishment and development of a cutting-edge cancer research centre with a specialisation in melanoma and lung cancer. The primary research focus of the European Cancer Moonshot Lund Center is to understand the impact that drugs have on cancer at an individualised and personalised level. Simultaneously, the centre increases awareness of the relentless battle against cancer and attracts global interest in the exceptional research performed at the centre.

Sphingolipid metabolism plays an important role in determining the fate of a cell. Among several sphingolipid metabolites, ceramide is a key player in intracellular signal transduction. Ceramide is usually converted to various metabolites such as sphingomyelin, sphingosine, ceramide-1-phosphate, and glucosylceramide. If ceramide is accumulated in the cell, it induces apoptosis. On the other hand, its metabolite sphingosine is converted to sphingosine-1-phosphate (S1P), which promotes angiogenesis via G protein coupled receptor signaling. Therefore, the equilibrium in ceramide and S1P levels in cells plays an important role in angiogenesis as well as cell death. Acid ceramidase (AC) is a promising target protein in the development of multi-targeted anticancer drugs as its inhibition can simultaneously inhibit angiogenesis via the Akt and ERK 1/2 pathway and limit cancer growth through ceramide-induced apoptosis. Although some inhibitors of AC have been reported, they have not been proven effective for human therapy. Recent advancement in the elucidation of AC structure will facilitate the development of better inhibitors for treating human diseases.

Clavulanic acid (CA) produced by Streptomyces clavuligerus is a clinically important β-lactamase inhibitor. It is known that glycerol utilization can significantly improve cell growth and CA production of S. clavuligerus. We found that the industrial CA-producing S. clavuligerus strain OR generated by random mutagenesis consumes less glycerol than the wild-type strain; we then developed a mutant strain in which the glycerol utilization operon is overexpressed, as compared to the parent OR strain, through iterative random mutagenesis and reporter-guided selection. The CA production of the resulting S. clavuligerus ORUN strain was increased by approximately 31.3% (5.21 ± 0.26 g/l) in a flask culture and 17.4% (6.11 ± 0.36 g/l) in a fermenter culture, as compared to that of the starting OR strain. These results confirmed the important role of glycerol utilization in CA production and demonstrated that reporter-guided mutant selection is an efficient method for further improvement of randomly mutagenized industrial strains.

Disorders of autophagy, a key regulator of cellular homeostasis, cause a number of human diseases. Due to the role of autophagy in metabolic dysregulation, there is a need to identify autophagy regulators as therapeutic targets. To address this need, we conducted an autophagy phenotype-based screen and identified the natural compound kaempferide (Kaem) as an autophagy enhancer. Kaem promoted autophagy through translocation of transcription factor EB (TFEB) without MTOR perturbation, suggesting it is safe for administration. Moreover, Kaem accelerated lipid droplet degradation in a lysosomal activity-dependent manner in vitro and ameliorated metabolic dysregulation in a diet-induced obesity mouse model. To elucidate the mechanism underlying Kaem’s biological activity, the target protein was identified via combined drug affinity responsive target stability and LC–MS/MS analyses. Kaem directly interacted with the mitochondrial elongation factor TUFM, and TUFM absence reversed Kaem-induced autophagy and lipid degradation. Kaem also induced mitochondrial reactive oxygen species (mtROS) to sequentially promote lysosomal Ca2+ efflux, TFEB translocation and autophagy induction, suggesting a role of TUFM in mtROS regulation. Collectively, these results demonstrate that Kaem is a potential therapeutic candidate/chemical tool for treating metabolic dysregulation and reveal a role for TUFM in autophagy for metabolic regulation with lipid overload., Kim, Hwang et al. use in vitro and in vivo models of autophagy disorder/metabolic dysfunction to show that in this context, the natural compound kaempferide is an autophagy enhancer and reveal that one of the underlying mechanisms governing this is mediated by the mitochondrial elongation factor TUFM. This insight may have therapeutic value in the treatment of metabolic disorders.

The MM500 study is an initiative to map the protein levels in malignant melanoma tumor samples, focused on in‐depth histopathology coupled to proteome characterization. The protein levels and localization were determined for a broad spectrum of diverse, surgically isolated melanoma tumors originating from multiple body locations. More than 15,500 proteoforms were identified by mass spectrometry, from which chromosomal and subcellular localization was annotated within both primary and metastatic melanoma. The data generated by global proteomic experiments covered 72% of the proteins identified in the recently reported high stringency blueprint of the human proteome. This study contributes to the NIH Cancer Moonshot initiative combining detailed histopathological presentation with the molecular characterization for 505 melanoma tumor samples, localized in 26 organs from 232 patients., The MM500 study is an initiative to map the protein levels in malignant melanoma tumor samples, focused on in‐depth histopathology coupled to proteome characterization. The protein levels and localization were determined for a broad spectrum of diverse melanoma tumors originating from multiple body locations. More than 15,500 proteoforms were identified by mass spectrometry, from which chromosomal and sub‐cellular localization was annotated within both primary and metastatic melanoma.

Ciliogenesis is often impaired in some cancer cells, leading to acceleration of cancer phenotypes such as cell migration and proliferation. From the investigation of primary cilia of 16 gastric cancer cells (GCs), we found that GCs could be grouped into four primary cilia (PC)–positive GCs and 12 PC-negative GCs. The proliferation of the PC-positive GCs was lower than that of PC-negative GCs. To explore the role of fatty acid binding protein 4 (FABP4), which is a known oncogenic factor, in ciliogenesis, FABP4 expression and function were inhibited by transfection of cells with short interfering RNA targeting FABP4 (siFABP4) or FABP4 inhibitor treatment. Notably, the proliferation and migration of the cilia-forming GCs was effectively suppressed by inhibition of FABP4. In addition, the primary cilia in GCs were restored by a factor greater than two, suggesting a negative role of FABP4 in ciliogenesis in these GCs and FABP4 as a potential anticancer target.

The Asia-Oceania Human Proteome Organization (AOHUPO; www.aohupo.org) was officially founded on June 7, 2001, by Richard J. Simpson (Australia), Akira Tsugita (Japan), and Young-Ki Paik (Korea) and launched on October 1–4, 2001, at the second scientific meeting of the International Proteomics Conference held in Canberra, Australia. Inaugural council members of the AOHUPO elected were Richard J. Simpson (Australia, president), Qi-Chang Xia (China), Kazuyuki Nakamura (Japan), Akira Tsugita (Japan, VIce President), Young-Ki Paik (Korea, secretary general), Mike Hubbard (New Zealand), Max C. M. Chung (Singapore), Shui-Tien Chen (Taiwan), and John Bennett (Philippines). The first AOHUPO conference was held on March 26–27, 2002, at the Seoul National University, Seoul, Korea, conjointly with the second Annual Meeting of KHUPO. Since then, biennial AOHUPO conferences have been held in Taipei (2004), Singapore (2006), Cairns (2008), Hyderabad (2010), Beijing (2012), Bangkok (2014), Sun Moon Lake (2016), and Osaka (2018). The 10th AOHUPO conference is scheduled to be held in Busan on June 30 to July 2, 2021, to celebrate our 20th anniversary., Graphical Abstract, Highlights • AOHUPO celebrates its 20th anniversary in 2021. • The diversity of the AOHUPO society is featured. • The past and current activities as well as the future direction are reported., In Brief We summarized the activities of the AOHUPO over the past 20 years, from its foundation to the present. The AOHUPO is the only regional HUPO organization that straddles the northern and southern hemispheres, and the needs of the society for proteomics are not uniform. Despite this diversity, the research in the AOHUPO has made steady progress, and we believe that this pace of evolution can be further accelerated in the next 20 years with the addition of younger generations.

Simple Summary Non-small-cell lung carcinoma (NSCLC) covers for almost 85% of all lung cancers and a major contributor to the overall cancer death rate. Erlotinib is used to treat NSCLC via inhibition of epithelial growth factor receptor (EGFR) kinase activity. Despite its high efficacy, recurrence can occur in patients who become resistant to the drug. We performed DARTS LC-MS/MS with SWATH of DIA analysis and identified a novel binding protein of Erlotinib that may underlie NSCLC resistance. Our study indicated that Erlotinib binds POLA2 in addition to EGFR. This was confirmed by DARTS and CETSA results. Importantly, POLA2 expression levels in four NSCLC cell lines were positively correlated with anti-proliferative Erlotinib efficacy (Pearson correlation coefficient, R = 0.9886). These results suggest that POLA2 is a novel complementary target protein of Erlotinib, and could clinically provide validity as a surrogate marker for drug resistance in patients with NSCLC. Abstract Erlotinib inhibits epithelial growth factor receptor (EGFR) kinase activity and is used to treat non-small cell lung cancer (NSCLC). Despite its high efficacy, recurrence can occur in patients who become resistant to the drug. To address the underlying mechanism of Erlotinib resistance, we investigated additional mechanisms related to mode-of-drug-action, by multiple protein-binding interactions, besides EGFR by using drug affinity responsive target stability (DARTS) and liquid chromatography-mass spectrometry (LC-MS/MS) methods with non-labeled Erlotinib. DNA polymerase alpha subunit B (POLA2) was identified as a new Erlotinib binding protein that was validated by the DARTS platform, complemented with cellular thermal shift assays. Genetic knock-down of POLA2 promoted the anti-proliferative effect of the drug in the Erlotinib-resistant cell line H1299 with high POLA2 expression, whereas the overexpression of POLA2 restored anti-proliferative effects in the Erlotinib-sensitive cell line HCC827 with low POLA2 expression. Importantly, POLA2 expression levels in four NSCLC cell lines were positively correlated with anti-proliferative Erlotinib efficacy (Pearson correlation coefficient, R = 0.9886). These results suggest that POLA2 is a novel complementary target protein of Erlotinib, and could clinically provide validity as a surrogate marker for drug resistance in patients with NSCLC.

Erlotinib inhibits epithelial growth factor receptor (EGFR) kinase activity and is used to treat non-small cell lung cancer (NSCLC). Despite its high efficacy, recurrence can occur in patients who become resistant to the drug. To address the underlying mechanism of Erlotinib resistance, we investigated additional mechanisms related to mode-of-drug-action, by multiple protein-binding interactions, besides EGFR by using drug affinity responsive target stability (DARTS) and liquid chromatography-mass spectrometry (LC-MS/MS) methods with non-labeled Erlotinib. DNA polymerase alpha subunit B (POLA2) was identified as a new Erlotinib binding protein that was validated by the DARTS platform, complemented with cellular thermal shift assays. Genetic knock-down of POLA2 promoted the anti-proliferative effect of the drug in the Erlotinib-resistant cell line H1299 with high POLA2 expression, whereas overexpression of POLA2 restored anti-proliferative effects in the Erlotinib-sensitive cell line HCC827 with low POLA2 expression. Importantly, POLA2 expression levels in four NSCLC cell lines were positively correlated with anti-proliferative Erlotinib efficacy, verified by bio-statistical analysis (Pearson correlation coefficient, R=0.9886). These results suggest that POLA2 is a novel complementary target protein of Erlotinib, and could clinically provide validity as a surrogate marker for drug resistance in patients with NSCLC.