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Abstract The BRAF and MEK inhibitors combined strategies have dramatically changed the outcome of BRAF-mutated metastatic melanoma patients. However, despite the initial promising results, the onset of primary or acquired resistance occurs in nearly half of the patients at about one year from the diagnosis. Understanding the mechanisms of resistance to these inhibitors is therefore critical for planning more effective therapeutic strategies able to improve patient outcomes. To this aim we generated BRAF and MEK inhibitors resistant melanoma cells starting from the SAN and A375 lines, both harboring the most common BRAF-V600 mutation and sensitive to these drugs. The obtained double-resistant cell lines were characterized by MTT cell proliferation, migration, invasion assays, phosphoarray and western blot analysis. Here we report that the overexpression of several Tyrosine Kinase Receptors (TKRs), such as EphA2 and DDRs, drives the resistance to these drugs and that this resistance can be overcome by treatment with ALW‑II‑41‑27 multikinase inhibitor. ALW‑II‑41‑27 blocks not only TKRs expression, but also the related downstream AKT and MAPK signaling pathways and its efficacy is documented by decreased cell viability and reduced cell invasion/migration of the resistant cells. Our results can delineate a novel promising therapeutic approach to overcoming the drug resistance occurring in BRAF-mutated metastatic melanoma.

Abstract Background Despite the recent progress in the treatment and outcome of Non Small Cell Lung Cancer (NSCLC), immunotherapy has still significant limitations reporting a significant proportion of patients not benefiting from therapy, even in patients with high PD-L1 expression. We have previously demonstrated that the combined inhibition of MEK and PD-L1 in NSCLC patients derived three dimensional cultures exerted significant synergistic effect in terms of immune-dependent cancer cell death. However, subsequent experiments analyzing the expression of Indoleamine 2,3-dioxygenase-1 (Ido-1) gene expression demonstrated that Ido-1 resulted unaffected by the MEK inhibition and even increased after the combined inhibition of MEK and PD-L1 thus representing a potential escape mechanism to this combination. Methods We analyzed transcriptomic profile of NSCLC lung adenocarcinoma cohort of TCGA (The Cancer Genome Atlas), stratifying tumors based on EMT (Epithelial mesenchymal Transition) score; in parallel, we investigated the activation of Ido-1 pathway and modulation of immune cytokines productions both in NSCLC cells lines, in peripheral blood mononuclear cells (PBMCs) and in ex-vivo NSCLC spheroids induced by triple inhibition with an anti-PD-L1 monoclonal antibody, the MEK inhibitor and the Ido-1 inhibitor. Results In NSCLC lung adenocarcinoma patient cohort (from TCGA) Ido-1 gene expression was significantly higher in samples classified as mesenchymal according EMT score. Similarly, on a selected panel of NSCLC cell lines higher expression of MEK and Ido-1 related genes was detected in cells with mesenchymal phenotype according EMT score, thus suggesting a potential correlation of co-activation of these two pathways in the context of EMT, with cancer cells sustaining an immune-suppressive microenvironment. While exerting an antitumor activity, the dual blockade of MEK and PD-L1 enhances the secretion of pro-inflammatory cytokines (IFNγ, TNFα, IL-12 and IL-6) and, consequently, the expression of new immune checkpoints such as Ido-1. The triple inhibition with an anti-PD-L1 monoclonal antibody, the MEK inhibitor and the Ido-1 inhibitor demonstrated significant antiproliferative and proapoptotic activity on ex-vivo NSCLC samples; at the same time the triple combination kept increased the levels of pro-inflammatory cytokines produced by both PBMCs and tumor spheroids in order to sustain the immune response and simultaneously decreased the expression of other checkpoint (such as CTLA-4, Ido-1 and TIM-3) thus promoting an immune-reactive and inflamed micro-environment. Conclusions We show that Ido-1 activation is a possible escape mechanism to immune-mediated cell death induced by combination of PD-L1 and MEK inhibitors: also, we show that triple combination of anti-PD-L1, anti-MEK and anti-Ido-1 drugs may overcome this negative feedback and restore anti-tumor immune response in NSCLC patients’ derived three dimensional cultures.

Abstract Background We recently conducted Cetuximab-AVElumab-Lung (CAVE-Lung), a proof-of-concept, translational and clinical trial, to evaluate the combination of two IgG1 monoclonal antibodies (mAb): avelumab, an anti-PD-L1 drug, and cetuximab, an anti-epidermal growth factor receptor (EGFR) drug, as second- or third-line treatment in non-small cell lung cancer (NSCLC) patients. We have reported clinically relevant anti-tumor activity in 6/16 patients. Clinical benefit was accompanied by Natural Killer (NK) cell-mediated antibody-dependent cell cytotoxicity (ADCC). Among the 6 responding patients, 3 had progressed after initial response to a previous treatment with single agent anti-PD-1, nivolumab or pembrolizumab. Methods We report long-term clinical follow-up and additional findings on the anti-tumor activity and on the immune effects of cetuximab plus avelumab treatment for these 3 patients. Results As of November 30, 2021, 2/3 patients were alive. One patient was still on treatment from 34 months, while the other two patients had progression free survival (PFS) of 15 and 19 months, respectively. Analysis of serially collected peripheral blood mononuclear cells (PBMC) revealed long-term activation of NK cell-mediated ADCC. Comprehensive genomic profile analysis found somatic mutations and germline rare variants in DNA damage response (DDR) genes. Furthermore, by transcriptomic analysis of The Cancer Genome Atlas (TCGA) dataset we found that DDR mutant NSCLC displayed high STING pathway gene expression. In NSCLC patient-derived three-dimensional in vitro spheroid cultures, cetuximab plus avelumab treatment induced additive cancer cell growth inhibition as compared to single agent treatment. This effect was partially blocked by treatment with an anti-CD16 mAb, suggesting a direct involvement of NK cell activation. Furthermore, cetuximab plus avelumab treatment induced 10-, 20-, and 20-fold increase, respectively, in the gene expression of CCL5 and CXCL10, two STING downstream effector cytokines, and of interferon β, as compared to untreated control samples. Conclusions DDR mutations may contribute to DDR-induced STING pathway with sustained innate immunity activation following cetuximab plus avelumab combination in previously treated, PD-1 inhibitor responsive NSCLC patients.

Abstract Background Despite the advancements in new therapies for colorectal cancer (CRC), chemotherapy still constitutes the mainstay of the medical treatment. For this reason, new strategies to increase the efficacy of chemotherapy are desirable. Poly-ADP-Ribose Polymerase inhibitors (PARPi) have shown to increase the activity of DNA damaging chemotherapeutics used in the treatment of CRC, however previous clinical trials failed to validate these results and pointed out dose-limiting toxicities that hamper the use of such combinations in unselected CRC patients. Nevertheless, in these studies little attention was paid to the mutational status of homologous recombination repair (HRR) genes. Methods We tested the combination of the PARPi niraparib with either 5-fluorouracil, oxaliplatin or irinotecan (SN38) in a panel of 12 molecularly annotated CRC cell lines, encompassing the 4 consensus molecular subtypes (CMSs). Synergism was calculated using the Chou-Talalay method for drug interaction. A correlation between synergism and genetic alterations in genes involved in homologous recombination (HR) repair was performed. We used clonogenic assays, mice xenograft models and patient-derived 3D spheroids to validate the results. The induction of DNA damage was studied by immunofluorescence. Results We showed that human CRC cell lines, as well as patient-derived 3D spheroids, harboring pathogenic ATM mutations are significantly vulnerable to PARPi/chemotherapy combination at low doses, regardless of consensus molecular subtypes (CMS) and microsatellite status. The strongest synergism was shown for the combination of niraparib with irinotecan, and the presence of ATM mutations was associated to a delay in the resolution of double strand breaks (DSBs) through HRR and DNA damage persistence. Conclusions This work demonstrates that a numerically relevant subset of CRCs carrying heterozygous ATM mutations may benefit from the combination treatment with low doses of niraparib and irinotecan, suggesting a new potential approach in the treatment of ATM-mutated CRC, that deserves to be prospectively validated in clinical trials.

Abstract Background Targeting the epidermal growth factor receptor (EGFR) either alone or in combination with chemotherapy is an effective treatment for patients with RAS wild-type metastatic colorectal cancer (mCRC). However, only a small percentage of mCRC patients receive clinical benefits from anti-EGFR therapies, due to the development of resistance mechanisms. In this regard, HER2 has emerged as an actionable target in the treatment of mCRC patients with resistance to anti-EGFR therapy. Methods We have used SW48 and LIM1215 human colon cancer cell lines, quadruple wild-type for KRAS, NRAS, BRAF and PI3KCA genes, and their HER2–amplified (LIM1215-HER2 and SW48-HER2) derived cells to perform in vitro and in vivo studies in order to identify novel therapeutic strategies in HER2 gene amplified human colorectal cancer. Results LIM1215-HER2 and SW48-HER2 cells showed over-expression and activation of the HER family receptors and concomitant intracellular downstream signaling including the pro-survival PI3KCA/AKT and the mitogenic RAS/RAF/MEK/MAPK pathways. HER2-amplified cells were treated with several agents including anti-EGFR antibodies (cetuximab, SYM004 and MM151); anti-HER2 (trastuzumab, pertuzumab and lapatinib) inhibitors; anti-HER3 (duligotuzumab) inhibitors; and MEK and PI3KCA inhibitors, such as refametinib and pictilisib, as single agents and in combination. Subsequently, different in vivo experiments have been performed. MEK plus PI3KCA inhibitors treatment determined the best antitumor activity. These results were validated in vivo in HER2-amplified patient derived tumor xenografts from three metastatic colorectal cancer patients. Conclusions These results suggest that combined therapy with MEK and PI3KCA inhibitors could represent a novel and effective treatment option for HER2-amplified colorectal cancer.

Abstract Background Previous studies showed that the combination of an anti-Epidermal growth factor (EGFR) and a MEK-inhibitor is able to prevent the onset of resistance to anti-EGFR monoclonal antibodies in KRAS-wild type colorectal cancer (CRC), while the same combination reverts anti-EGFR primary resistance in KRAS mutated CRC cell lines. However, rapid onset of resistance is a limit to combination therapies in KRAS mutated CRC. Methods We generated four different KRAS mutated CRC cell lines resistant to a combination of cetuximab (an anti-EGFR antibody) and refametinib (a selective MEK-inhibitor) after continuous exposure to increasing concentration of the drugs. We characterized these resistant cell lines by evaluating the expression and activation status of a panel of receptor tyrosine kinases (RTKs) and intracellular transducers by immunoblot and qRT-PCR. Oncomine comprehensive assay and microarray analysis were carried out to investigate new acquired mutations or transcriptomic adaptation, respectively, in the resistant cell lines. Immunofluorescence assay was used to show the localization of RTKs in resistant and parental clones. Results We found that PI3K-AKT pathway activation acts as an escape mechanism in cell lines with acquired resistance to combined inhibition of EGFR and MEK. AKT pathway activation is coupled to the activation of multiple RTKs such as HER2, HER3 and IGF1R, though its pharmacological inhibition is not sufficient to revert the resistant phenotype. PI3K pathway activation is mediated by autocrine loops and by heterodimerization of multiple receptors. Conclusions PI3K activation plays a central role in the acquired resistance to the combination of anti-EGFR and MEK-inhibitor in KRAS mutated colorectal cancer cell lines. PI3K activation is cooperatively achieved through the activation of multiple RTKs such as HER2, HER3 and IGF1R.