Mechanisms Of Secondary Resistance Research Articles

Primary resistance to selpercatinib in a patient with advanced medullary thyroid cancer.

Selpercatinib, a selective RET kinase inhibitor, has demonstrated remarkable efficacy in treating patients with advanced medullary (MTC) and differentiated thyroid cancer with RET alterations. Primary resistance to selpercatinib is a very uncommon situation, and its underlying mechanisms are poorly understood. We report the case of a 42-year-old female with advanced MTC harboring a somatic M918T RET mutation who exhibited a primary resistance to selpercatinib. Despite prompt treatment initiation after the diagnosis of progressive disease, the patient continued experiencing rapid spread of disease, characterized by the appearance of new metastatic lesions and increased tumor burden. Genomic analysis revealed no additional mutations associated with on-target or off-target resistance. This case highlights a rare clinical scenario of primary resistance to selpercatinib in advanced MTC. While secondary resistance mechanisms have been well-documented, primary resistance remains poorly understood. Possible explanations include tumor heterogeneity and activation of alternative signaling pathways that stills need to be elucidated. Emerging therapies targeting resistance mechanisms and next-generation RET inhibitors offer promising avenues for further investigation.

Retracted: Molecular Mechanism of Secondary Endocrine Resistance in Luminal Breast Cancer.

[This retracts the article DOI: 10.1155/2021/6618519.].

BRCA1/2 alterations and reversion mutations in the area of PARP inhibitors in high grade ovarian cancer: state of the art and forthcoming challenges.

BRCA1/2 genes are part of homologous recombination (HR) DNA repair pathways in charge of error-free double-strand break (DSB) repair. Loss-of-function mutations of BRCA1/2 genes have been associated for a long time with breast and ovarian cancer hereditary syndrome. Recently, polyadenosine diphosphate-ribose polymerase inhibitors (PARPi) have revolutionized the therapeutic landscape of BRCA1/2-mutated tumors, especially of BRCA1/2 high-grade serous ovarian cancer (HGSC), taking advantage of HR deficiency through the synthetic lethality concept. However, PARPi efficiency differs among patients, and most of them will develop resistance, particularly in the relapse setting. In the current proposal, we aim to review primary and secondary resistance to PARPi in HGSC owing to BRCA1/2 alterations. Of note, as several mechanisms of primary or secondary resistance to PARPi have been described, BRCA1/2 reversion mutations that restore HR pathways are by far the most reported. First, the type and location of the BRCA1/2 primary mutation have been associated with PARPi and platinum-salt sensitivity and impact the probability of the occurrence and the type of secondary reversion mutation. Furthermore, the presence of multiple reversion mutations and the variation of allelic frequency under treatment underline the role of intratumor heterogeneity (ITH) in treatment resistance. Of note, circulating tumor DNA might help us to detect and characterize reversion mutations and ITH to finally refine the treatment strategy. Importantly, forthcoming therapeutic strategies, including combination with antiangiogenics or with targeted therapies, may help us delay and overcome PARPi resistance secondary to BRCA1/2 reversion mutations. Also, progression despite PARPi therapy does not preclude PARPi rechallenge in selected patients.

Overcoming Resistance Mechanisms to Immune Checkpoint Inhibitors: Leveraging the Anti-Tumor Immune Response.

As far back as 3000 years ago, the immune system was observed to play a role in mediating tumor regression. Since then, many strategies have been developed to leverage the anti-tumor immune response. However, while many patients respond to ICIs up front some do not, and many of those that do eventually experience tumor progression. Currently, there are several predictive biomarkers of the immune checkpoint inhibitor response; however, no one test appears to be universally predictive and their application varies by disease site. There are many ways in which cancer cells develop primary or acquired resistance to immune checkpoint inhibitors. Efforts to reverse resistance include ways to combat T cell exhaustion, reprogram the tumor microenvironment, increase the availability of tumor neo-antigens, target alternative immune checkpoints, restore a normal/healthy patient gut microbiome, oncolytic viruses and tumor vaccines. The most studied and most promising methods include combining ICIs with therapies targeting alternative immune checkpoints and restoring a normal/healthy patient gut microbiome. This review will discuss T cell-mediated immunity, how this is leveraged by modern immunotherapy to treat cancer and mechanisms of immune checkpoint inhibitor resistance, while highlighting strategies to overcome primary and secondary resistance mechanisms.

The future paradigm of HMA + VEN or targeted inhibitor approaches: sequencing or triplet combinations in AML therapy.

The routine use of next-generation sequencing methods has underscored the genetic and clonal heterogeneity of acute myeloid leukemia (AML), subsequently ushering in an era of precision medicine-based targeted therapies exemplified by the small-molecule inhibitors of FLT3, IDH1/IDH2, and BCL2. This advent of targeted drugs in AML has broadened the spectrum of antileukemic therapies, and the approval of venetoclax in combination with a hypomethylating agent has been a welcome addition to our AML patients unable to tolerate intensive chemotherapy. Mounting evidence demonstrates that molecularly targeted agents combined with epigenetic therapies exhibit synergistic augmented leukemic cell kill compared to single-agent therapy. With such great power comes greater responsibility in determining the appropriate frontline AML treatment regimen in a molecularly defined subset and identifying safe and effective combination therapies with different mechanisms of action to outmaneuver primary and secondary resistance mechanisms in AML.

Therapeutic Targeting of FLT3 Gate Keeper Mutation with E2082-0047 in Traditional and a Novel Immunocompetent Murine Adoptive Transfer Model of AML

Signaling mutations such as Fms-like tyrosine kinase 3 (FLT3) internal tandem duplication (FLT3-ITD) occur in approximately 30% of AML patients which provide AML cells with a constitutively active aberrant growth advantage, resulting in inferior overall survival. Multiple phase 3 studies with different FLT3 inhibitors validated FLT3-ITD as an important therapeutic target in AML. However, resistance to FLT3-ITD inhibitors occurs via mutations in the tyrosine kinase domain (FLT3-TKD), including the gatekeeper mutation F691L for which all approved FLT3 inhibitors are ineffective. Other mechanisms of secondary FLT3 inhibitor resistance include induction of IRAK4 activity and acquisition of RAS/PTPN11/MAPK activating mutations. New FLT3 inhibitors targeting both intrinsic (FLT3 acquired mutations) and extrinsic mechanisms of FLT3 resistance (e.g. IRAK4 induction) are urgently needed. We demonstrated previously the selectivity and potency of a novel FLT3 inhibitor, E2082-0047, against FLT3-ITD and TKD mutations in vitro using a Ba/F3 cell line harboring different TKD mutations. Guided by KinomeScan data, we demonstrated simultaneous IRAK4 inhibition and verified superior in vivo efficacy compared to gilteritinib using the FLT3-ITD MOLM-13 cell line derived xenograft (CDX) murine model (Elgamal OA et al., ASH 2022). Recognizing the exceptional safety profile of E2082-0047 in pre-clinical IND enabling toxicology studies, we moved forward to test the potency of E2082-0047 versus gilteritinib in cells harboring the FLT3-ITD-F691L gatekeeper mutation using two in vivo models, MOLM-14-F691L CDX model and a novel immunocompetent murine adoptive transfer model that does not require conditioning or irradiation. This model is generated by the crossing of the CD45.2 specific Npm1 cA cre inducible model (Vassiliou et al., 2011) with the Flt3 ITD (Lee et al., 2007) model which was previously reported to harbor a F692L mutation, analogous to the human F691L mutation (Dovey et al., 2016) thus, generating the Npm1 cA;Flt3 ITD-F692L AML murine model. In the MOLM-14-F691L CDX model study, we found a consistent reduction in human CD45 cells in bone marrow and increased survival benefit in mice receiving E2082-0047 compared to gilteritinib. Further, mice in the gilteritinib group with progressing disease (> 50% human CD45+ cells in bone marrow) were switched to E2082-0047 with consequent > 5-fold reduction in bone marrow tumor burden within 8 days. These data suggest that E2082-0047 will be effective in gilteritinib resistant disease. Strikingly, in the AML adoptive transfer model, E2082-0047 resulted in a compelling long-term survival benefit. In our first study (donor #1), vehicle and gilteritinib cohorts had 29- and 32-days median survival, respectively with evident circulating CD45.2 AML. In the E2082-0047 cohort, mice remained on study with an average of <2% circulating CD45.2 cells therefore, we stopped treatment and euthanized three mice for tissue collection, leaving eight mice for disease relapse monitoring for an additional two weeks where we lost 3/8 mice due to early removal criteria (ERC) and 5/8 were euthanized at end of study day 100, with an average of <10% circulating CD45.2 cells. This initial study showed the capacity for E2082-0047 to induce long-term survival in a model with a clinically relevant TKD gatekeeper mutation. We repeated our study with a more aggressive donor (donor #2) where vehicle and gilteritinib arms had a median survival of 22 days. While mice receiving E2082-0047 remain on study (week 8 of an ongoing study), with an average of <5% peripheral blood CD45.2 level (Figure 1). Collectively, our previous and follow-up studies herein demonstrate the superiority of E2082-0047 over gilteritinib against FLT3-ITD and with TKD mutations including the gatekeeper F691L variant. We demonstrate significantly improved survival after E2082-0047 treatment in an immune deficient in vivo model of FLT3-ITD/TKD-F691L MOLM-14 AML and a durable long-term survival in a large subset of mice using two donors in an immune competent adoptive transfer model of NPM1+FLT3-ITD/TKD-F692L AML. Given the curative potential of E2082-0047 in the immune competent model, ongoing efforts are focused on investigating the host immune response to AML. Given the safety and efficacy studies performed with E2082-0047 to date, a healthy volunteer study to best estimate dose for trials in AML is ongoing.

Metastatic ER+ Breast Cancer: Mechanisms of Resistance and Future Therapeutic Approaches.

Endocrine therapy is the main treatment for hormone receptor-positive (HR+) breast cancer. However, advanced tumors develop resistance to endocrine therapy, rendering it ineffective as the disease progresses. There are several molecular mechanisms of primary and secondary endocrine resistance. Resistance can develop due to either alteration of the estrogen receptor pathway (e.g., ESR1 mutations) or upstream growth factors signaling pathways (e.g., PI3K/Akt/mTOR pathway). Despite progress in the development of molecularly targeted anticancer therapies, the emergence of resistance remains a major limitation and an area of unmet need. In this article, we review the mechanisms of acquired endocrine resistance in HR+ advanced breast cancer and discuss current and future investigational therapeutic approaches.

Immunotherapy of gastrointestinal stromal tumors: current view and future directions

Gastrointestinal stromal tumors (GIST) are most common mesenchymal tumors in gastrointestinal tract which originate from interstitial cells of Cajal and characterized by the mutations in the KIT or PDGFRA tyrosine kinase receptors. Thus, the common therapeutic approach for GIST therapy (including metastatic, recurrent and non-resectable forms) is based on inhibiton of activities of receptor tyrosine kinases indicated above by corresponding receptor tyrosine kinase inhibitors, including first-line therapeutic agent imatinib mesylate – Gleevec. Despite of high efficacy of IM-based therapy, most of GIST patients acquire resistance to this receptor tyrosine kinase inhibitor, which in turn requires second-, third- and fourth-line therapies. The review also describes the common molecular and genetic variants of GIST and the mechanisms of primary and secondary GIST resistance to the targeted-based therapies. In addition, the role of immune microenvironment in GIST and its relationship with tumor’s mutational burden are discussed in detail, thereby illustrating the immunotherapy as one of the attractive future directions for GIST therapy. Lastly, the manuscript provides the information about the ongoing clinical trials of GIST immunotherapy.

Double Guard Efficiency and Safety—Overcoming Resistance to Immunotherapy by Blocking or Stimulating Several Immune Checkpoints in Non-Small Cell Lung Cancer Patients

Immunotherapy is one of the leading systemic therapies in non-small cell cancer (NSCLC) patients, but it is not effective in an important proportion of them due to primary or secondary resistance mechanisms. Clinicians do not have the tools to predict immunotherapy resistance, and thus, many patients still fail initial treatment. One of the scientific concepts to avoid resistance and/or offer the patient effective salvage second-line treatment is the dual immunologic checkpoint blockade. We aimed to review published and available data on combination immunotherapy in terms of mechanisms, efficacy, and safety data on many different dual blockades. We discussed the potential of combined CTLA-4 (Cytotoxic T Lymphocyte Antigen 4), PD-1 (Programmed Death 1) or PD-L1, TIGIT, LAG-3, TIM-3, macrophage leukocyte immunoglobulin-like receptor B2 (LILRB2/ILT4), S15-mediated immune suppression (SIGLEC-15), CD137, ICOS, and OX40 inhibitors in NSCLC treatment.

A multi-center natural history study of precision-based genomics in prostate cancer (PC).

TPS5121 Background: With genomic-based therapies approved for advanced PC, there has been a substantial rise in the clinical use of genomic sequencing. In addition to identifying actionable targets, there is a long list of less common ‘tail’ alterations in metastatic PC with unclear prognostic or predictive significance. We hypothesize that integrative clinico-genomic studies of uncommon subgroups of PC, defined based on a molecular biomarker of low-prevalence or based on an exceptional clinical outcome to therapy, can lead to the identification of new predictive and resistance biomarkers and will accelerate the development of precision medicine strategies for patients with PC. Methods: This is a multi-institutional prospective observational study for longitudinal collection of clinical and genomic data from participants (prts) with distinct molecular alterations of interest and/or exceptional phenotypes. The primary objectives are: 1) to define the natural history of men with select molecular alterations and/or exceptional clinical responses, 2) to establish a biospecimen repository for extensive molecular analyses to study the biology of PC and mediators of therapeutic response and resistance. Exploratory objectives include: 1) understanding the impact of co-occurring genomics alterations and other molecular alterations on the natural history of PC in these defined subsets, 2) identifying biologic mechanisms of exceptional response, primary and secondary resistance, and tracking evolutionary patterns that occur during acquired resistance. Eligible prts have a diagnosis of PC with known germline and/or somatic variants in PIK3A, PIK3CB, and/or AKT, PALB2, BRIP1, RAD50, RAD51, RAD54, RB1, SPOP, Wnt/B-catenin pathway, MMR genes ( MLH1, MSH2, MSH6, PMS2), EPCAM and/or TMB-high (as defined by TMB ≥ 10 mut/Mb). Any platform for genomic testing is acceptable and data is collected centrally. Prts deemed exceptional responders (with or without mutational aberrations) are defined as those with a complete response or a confirmed partial response of any duration of time to systemic therapies or any response of exceptional duration (particularly with therapies targeting PARP, the androgen receptor, and/or immunotherapies). Data including demographic, disease characteristics, treatment outcomes including response to therapies, and survival are collected along with other pathologic, radiographic, and molecular/genomic data. Correlative sample collection includes archival primary and metastatic biopsy specimens and prospective collection of blood for future analyses. This study will provide insights into the significance of individual and co-occurring alterations and will help establish a path forward for the expansion of drug indications for PC patients with rare variants. 37 prts have been accrued with an accrual ceiling of 2000 prts. Clinical trial information: NCT04706663 .

Targeting Pro-Survival Autophagy Enhanced GSK-3β Inhibition-Induced Apoptosis and Retarded Proliferation in Bladder Cancer Cells.

Advanced bladder cancer (BC) (local invasive and/or metastatic) is not curable even with cytotoxic chemotherapy, immune checkpoint inhibitors, and targeted treatment. Targeting GSK-3β is a promising novel approach in advanced BC. The induction of autophagy is a mechanism of secondary resistance to various anticancer treatments. Our objectives are to investigate the synergistic effects of GSK-3β in combination with autophagy inhibitors to evade GSK-3β drug resistance. Small molecule GSK-3β inhibitors and GSK-3β knockdown using siRNA promote the expression of autophagy-related proteins. We further investigated that GSK-3β inhibition induced the nucleus translocation of transcription factor EB (TFEB). Compared to the GSK-3β inhibition alone, its combination with chloroquine (an autophagy inhibitor) significantly reduced BC cell growth. These results suggest that targeting autophagy potentiates GSK-3β inhibition-induced apoptosis and retarded proliferation in BC cells.

Abstract 4010: Inhibition of PERK by HC-5404 sensitizes clear cell renal cell carcinoma tumor models to anti-angiogenic tyrosine kinase inhibitors

Abstract Anti-angiogenic agents form the backbone of standard of care for advanced clear cell renal cell carcinoma (ccRCC), but their clinical impact is limited by primary and secondary resistance mechanisms that remain a critical problem. Furthermore, the approvals for VEGFR-targeting receptor tyrosine kinase inhibitors (VEGFR-TKIs), cabozantinib in second-line, and tivozanib in third-line RCC patients were based on modest objective response rates and median progression-free survival. There is an urgent need for novel mechanisms that target adaptive tumor responses that drive resistance to these agents, as well as combination drug partners that improve outcomes for patients. As part of their mechanism, VEGFR-TKIs induce oxygen- and nutrient-deprivation that drives ER stress. Tumors can evade deleterious ER stress by activating PERK branch of the integrated stress response, which arrests global translation and restores homeostasis. We hypothesized that inhibiting PERK would enhance the anti-tumor activity of VEGFR-TKIs in vivo and tested this using HC-5404, a potent and selective PERK inhibitor currently in Ph1 clinical testing (NCT04834778). Here, we present preclinical evidence that supports combining HC-5404 with VEGFR-TKIs in ccRCC. We demonstrate that axitinib, cabozantinib, lenvatinib, and sunitinib all activate PERK in 786-O ccRCC xenografts in a dose-responsive manner. The addition of HC-5404 significantly enhanced the tumor growth inhibition (TGI) of VEGFR-TKIs across multiple ccRCC tumor models, resulting in tumor stasis or regression in combination groups. Expression profiling and IHC analysis of tumor sections revealed that HC-5404 enhanced the anti-angiogenic effects of axitinib and lenvatinib in 786-O tumors, highlighting the protective role of PERK in response to anti-angiogenics. To evaluate whether the combination treatments could benefit a diverse patient population, sensitivity to HC-5404 and axitinib was evaluated across a panel of patient-derived xenograft (PDX) models. This experiment confirmed widespread responsiveness to the combination treatment that in some cases achieved >50% tumor regression. As tumor progression on VEGFR-TKIs limits the success of these agents in the clinic, we evaluated the effect of adding HC-5404 to tumors that have previously progressed on axitinib. In this study, 786-O xenografts were treated with axitinib for 2-weeks and non-responders were rerandomized into groups of either single agent or combination of HC-5404 and axitinib. The combination treatment significantly improved TGI relative to either monotherapy, resulting in tumor regression of ~20%. Taken together, these findings highlight that by disrupting an adaptive stress response evoked by VEGFR-TKIs, HC-5404 presents a clinical opportunity to enhance the anti-tumor effects of well-established standard of care therapies in ccRCC. Citation Format: Michael E. Stokes, Veronica Calvo, Crissy Dudgeon, Sho Fujisawa, Sharon Huang, Leyi Shen, Nupur Ballal, Joe McGinley, David Liu, Mark J. Mulvihill, Alan C. Rigby, Nandita Bose, Eric S. Lightcap, David Surguladze. Inhibition of PERK by HC-5404 sensitizes clear cell renal cell carcinoma tumor models to anti-angiogenic tyrosine kinase inhibitors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4010.

Abstract 940: Comprehensive characterization of MET exon 14 skipping mutations in non-small cell lung cancer

Abstract Background: MET exon 14 skipping mutation (METΔex14) is a key driver event in non-small cell lung cancer (NSCLC), and can be acquired following drug resistance to MET, EGFR or ALK inhibitors. Clinical and genomic features of METΔex14 in NSCLC remain to be further characterized. Methods: A total of 556 baseline samples, 54 MET inhibitor-resistant samples and 16 EGFR/ALK inhibitor-resistant samples from 586 METΔex14 NSCLC patients were included in the analysis. Tissue and/or plasma samples were subjected to targeted next-generation sequencing (NGS) using Geneseeq’s 139/425 cancer-relevant gene panels. Results: The overall frequency of METΔex14 was 1.1%, with a total of 266 distinct variants detected. Of these, 40.2% were base substitutions in the intronic non-coding region immediately adjacent to the splice acceptor site, followed by indels (25.6%) and base substitutions (4.5%) in the splice donor site, and indels (21.4%) and base substitutions (2.3%) in the splice acceptor site, etc. No associations with clinical features were found among different variants. At baseline, METΔex14 commonly co-occurred with TP53 mutations (40.8%), and CDK4 (15.8%) and MET (7.9%) amplifications. In 42 (7.6%) patients, concurrent oncogenic mutations in EGFR, KRAS, ALK, RET, BRAF, and ERBB2 were also detected. Such patients displayed a different spectrum of METΔex14 variants compared with those without concurrent oncogenic mutations (P=0.08). In patients treated with MET inhibitors, no difference in survival was seen among different METΔex14 variants (P=0.38). Notably, activation of EGFR or MET (kinase domain mutations/amplification) conferred primary resistance to savolitinib and crizotinib. In addition, patients with high chromosomal instability or low intratumoral heterogeneity had unfavorable PFS. Secondary resistance to MET-TKI included MET activation (D1228N/H, Y1230C/S, amplification), EGFR activating mutations/amplification, KRAS G12V, as well as FGFR2/4 amplification. Surprisingly, we identified a FGFR3-TACC3 fusion as a previously unreported secondary resistance mechanism to savolitinib in the second line setting. Finally, we found that MET exon 14 skipping mutation might be a rare secondary resistance mechanism to EGFR/ALK inhibitors. Conclusion: In this study, we characterized METΔex14 in a large cohort of NSCLC patients and explored potential primary and secondary resistance mechanisms to savolitinib and crizotinib, which may facilitate drug development and help inform clinical actions. Citation Format: Xue Wu, Yaru Zhang, Jiaohui Pang, Li Lin, Jiani C. Yin, Haimeng Tang, Yang Shao. Comprehensive characterization of MET exon 14 skipping mutations in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 940.

Abstract P4-01-38: A single arm phase II trial of Palbociclib in combination with Tamoxifen as first line therapy for metastatic hormone receptor positive breast cancer

Abstract Background: Palbociclib is a CDK4/6 inhibitor used to treat metastatic hormone receptor-positive (HR+) breast cancer (MBC) in combination with endocrine therapy. Tamoxifen is an effective treatment for HR+ MBC, with different toxicity profile compared with aromatase inhibitors (AI) and fulvestrant. Preclinical data demonstrated synergy for the combination of tamoxifen and palbociclib, being effective in a model of acquired tamoxifen resistance. Methods: We conducted a non-randomized, open-label, single-arm, multicenter, phase II trial of palbociclib in combination with tamoxifen in patients with HR+/HER2 - advanced BC, with no prior therapy for MBC. Ovarian suppression was recommended for pre-menopausal women. Primary objective was progression free survival, PFS. Secondary objectives: objective response rate, ORR (CR or PR) based on RECIST 1.1 or MDA Criteria (for patients with bone only disease); safety and tolerability (using CTCAE v4); clinical benefit rate, CBR (CR, PR or SD lasting min 24 weeks); 2-year overall survival. Correlative objectives: proteomic analysis of plasma exosomes to identify mechanisms of primary and secondary resistance to tamoxifen/palbociclib. Results: Between 6/30/2016 and 7/02/2019, we enrolled 49 patients (47 evaluable): 23 pts with de-novo metastatic disease and 24 pts with recurrent BC (12 pts were on adjuvant treatment with AI at time of recurrence and 12 pts on surveillance). As of 6/30/2022 data cut-off, 2 pts were still on treatment. This is an updated analysis with median follow-up time of 24 months (range 8-51). Median age was 60 (range 39-82). The median PFS was 19.8 months with 95% CI (8-41) for pts with de-novo MBC and 7 months (2-12) for pts with recurrent BC. The ORR was 30% overall, 39% for pts with de novo MBC, 21% for pts with recurrent BC. CBR was 64% overall, 77% for pts with de novo MBC and 50% for pts with recurrent BC. CBR was 65% for white pts and 55% for AA pts. Best response per RECIST1.1: 14 pts (34%) had PR, 18 pts (44%) had SD, 9 pts (22%) had PD. All 6 pts with bone only disease had SD. The most common drug related grade ≥ 3 AE was neutropenia (51%), transient and manageable by dose modifications, no cases of febrile neutropenia. Four patients (8%) developed thromboembolic events (grades 2, 3, 4) and discontinued treatment. One patient died while on treatment from PD. More than 800 exosome proteins were detected in the samples analyzed so far. Exosomal protein networks in pretreatment samples predicted treatment response with 89% sensitivity and 95% specificity in unsupervised clustering. Data on correlative objectives will be presented in a separate abstract. Conclusions: The combination of palbociclib and tamoxifen showed tolerable, expected safety profile. This may be an alternative approach for selected patients in first line treatment of HR+ MBC, especially those who present with de-novo metastatic disease and are intolerant to AI; although this small study indicates a lower PFS. Table 1: Baseline Demographics Citation Format: Oana C. Danciu, Kent Hoskins, Jennifer Weiss, Cristina I. Truica, Anne Blaes, Deimante Tamkus, Jatin Rana, Tandra Pavankumar, Lauren Green, Yu Gao, Menggang Yu, Qianqian Zhao, Deborah Toppmeyer, Ruth O’Regan, Kari B. Wisinski. A single arm phase II trial of Palbociclib in combination with Tamoxifen as first line therapy for metastatic hormone receptor positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-38.

Effect of Janus kinase (JAK) signaling inhibition on lineage plasticity and drug sensitivity in castrate resistant prostate cancer.

227 Background: Despite the remarkable successes of targeted cancer therapies, certain cancers, including lung, breast, and prostate cancer and melanoma, invariably become resistant to therapy. One mechanism of secondary resistance—lineage plasticity—arises when cells alter their identity and transition into aggressive states. In the case of prostate cancer, cells can acquire a neuroendocrine histology. This is often associated with a loss of tumor suppressor genes, such as TP53, RB1, and PTEN. However, while these genomic events initiate plasticity, tumor progression is not always associated with successive genomic alterations. This, in essence, not only poses a clinical challenge, but also confronts us with a wide-open biological question—what are the molecular underpinnings of lineage plasticity, and importantly, can the process be reversed? Methods: To study the temporal evolution of lineage plasticity and its relationship to androgen receptor signaling inhibitor (ARSI) resistance, we utilized genetically engineered mouse models (GEMMs) and murine organoids that were deleted for Tp53, Rb1, and/or Pten. Single cell RNA analyses were utilized to dissect which genes and pathways were up-regulated and most associated with the progression of plasticity. Plasticity-associated genes and pathways were perturbed using FDA-approved inhibitors or genetic editing tools. The presence of these pathways was confirmed in a subset of metastatic index lesions obtained by radiologically guided biopsies and as visualized by metabolic imaging. Furthermore, relevant findings were functionally validated in human tumor derived organoids (“tumoroids”). Results: Using GEMMs and organoid models, we found the lineage plasticity depended on increased Janus Kinase (JAK) and fibroblast growth factor receptor (FGFR) activity. Pharmacologic inhibition using FDA–approved inhibitors of JAK/STAT (ruxolitinib) and FGFR (erdafinitib), or through genetic knockdown, demonstrated increased androgen receptor (AR) signaling and restored ARSI sensitivity. These findings were further validated in a subset of ARSI-insensitive human tumoroids. By performing single cell RNA sequencing on mCRPC tumors biopsies, the presence of highly plastic JAK/STAT- and FGFR-high cells were confirmed, with implications for stratifying patients for clinical trials. Conclusions: JAK/STAT and FGFR signaling pathways promote lineage plasticity and result in complete insensitivity to androgen receptor signaling inhibitors (ARSIs). FDA-approved inhibitors of JAK/STAT (ruxolitinib) and FGFR (erdafitinib) synergize to reverse lineage plasticity and restore ARSI sensitivity.

Breast Cancer Brain Metastases: Achilles' Heel in Breast Cancer Patients' Care.

Brain metastases (BM) significantly affect the prognosis as well as the quality of life of breast cancer (BC) patients. Although advancements in neurosurgical and radiotherapy techniques improve local control and symptom management, BM remains associated with a poor prognosis. In addition, the efficacy of currently approved systemic therapies in central nervous system (CNS) compartment is still limited, especially after progression on local therapy. The blood-brain barrier (BBB) has been recognized as amechanism of primary resistance to many chemotherapeutic agents and targeted therapies due to low drug penetration. Other mechanisms of primary and secondary resistance are still unclear and may vary across the BC subtypes. New small molecules have demonstrated efficacy in BM, in particular for the HER2-positive subtype, with a benefit in survival. A new era has begun in the field of BM, and many trials specifically designed for this population are currently ongoing. The BC research community needs to address this call with the final aim of improving the efficacy of systemic therapy in CNS compartment and ultimately preventing the occurrence of BM.

Therapies in Refractory Metastatic Renal Cell Carcinoma

As the therapeutic landscape for metastatic clear cell renal cell carcinoma (mccRCC) expands to include vascular endothelial growth factor receptor tyrosine kinase inhibitors (VEGFR TKIs) and immunotherapies, new challenges are in place for evaluating and treating refractory disease. Assessing and managing refractory disease has several elements: (1) the mechanism(s) of front-line treatment, (2) timing of progressive disease, (3) rapidity and sites of progressing disease, (4) use of adjuvant therapy, and (5) incorporation of surgical and radiation techniques. These variables all have distinct impact on the biology of refractory or resistant mccRCC. A better understanding of the essential mechanisms of both primary and secondary immunotherapy resistance will inform biomarker development and therapeutic strategies in the refractory setting. This paper addresses the current understanding of treatment sequencing in refractory mccRCC, focusing on treatment options with prospective clinical trial data, considers refractory mccRCC after adjuvant immunotherapy, and incorporates radiation or surgical resection for oligoprogressive disease.

SOHO State of the Art Updates and Next Questions | Mechanisms of Resistance to BCL2 Inhibitor Therapy in Chronic Lymphocytic Leukemia and Potential Future Therapeutic Directions.

Chronic lymphocytic leukaemia (CLL) constitutively overexpresses B-cell lymphoma 2 (BCL2) with consequent dysregulation of intrinsic apoptosis leading to abnormal cellular survival. Therapeutic use of BCL2 inhibitors (BCL2i, eg, venetoclax) in CLL, as both continuous monotherapy or in fixed duration combination, has translated scientific rationale into clinical benefit with significant rates of complete responses, including those without detectable minimal residual disease. Unlike with chemotherapy, response rates to venetoclax do not appear to be influenced by pre-existing chromosomal abnormalities or somatic mutations present, although the duration of response observed remains shorter for those with traditional higher risk genetic aberrations. This review seeks to describe both the disease factors that influence primary venetoclax sensitivity/resistance and those resistance mechanisms that may be acquired secondary to BCL2i therapy in CLL. Baseline venetoclax-sensitivity or -resistance is influenced by the expression of BCL2 relative to other BCL2 family member proteins, microenvironmental factors including nodal T-cell stimulation, and tumoral heterogeneity. With selection pressure applied by continuous venetoclax exposure, secondary resistance mechanisms develop in oligoclonal fashion. Those mechanisms described include acquisition of BCL2 variants, dynamic aberrations of alternative BCL2 family proteins, and mutations affecting both BAX and other BH3 proteins. In view of the resistance described, this review also proposes future applications of BCL2i therapy in CLL and potential means by which BCL2i-resistance may be abrogated.

Mechanisms of Primary and Acquired Resistance to Immune Checkpoint Inhibitors in Patients with Hepatocellular Carcinoma.

Simple SummaryImmune checkpoint inhibitors (ICIs) are now a cornerstone of systemic treatment for hepatocellular carcinoma (HCC). However, their efficacy is blunted by mechanisms of tumour resistance in many patients. This review reports on the state of the art of resistance to ICIs, focusing on HCC, with the aim to provide clear and direct information to clinicians and researchers. Growing knowledge on the mechanisms of resistance to immunotherapy can indeed guide the choice of and expand the application of novel combined treatments.Hepatocellular carcinoma (HCC) is the most common liver cancer and a relevant global health problem. Immune checkpoint inhibitors (ICIs) represent the most effective systemic treatment for HCC. However, due to primary resistance, approximately 40% of HCC patients do not achieve a disease control with ICIs. Moreover, a similar proportion will experience disease progression after an initial response caused by secondary resistance. This review describes the mechanisms of primary and secondary resistance and reports the ongoing therapeutic strategies to overcome these obstacles.

Advances in the research of the mechanism of secondary resistance to imatinib in gastrointestinal stromal tumors.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. At present, surgery is the first-line treatment for primary resectable GISTs; however, the recurrence rate is high. Imatinib mesylate (IM) is an effective first-line drug used for the treatment of unresectable or metastatic recurrent GISTs. More than 80% of patients with GISTs show significantly improved 5-year survival after treatment; however, approximately 50% of patients develop drug resistance after 2 years of IM treatment. Therefore, an in-depth research is urgently needed to reveal the mechanisms of secondary resistance to IM in patients with GISTs and to develop new therapeutic targets and regimens to improve their long-term prognoses. In this review, research on the mechanisms of secondary resistance to IM conducted in the last 5 years is discussed and summarized from the aspects of abnormal energy metabolism, gene mutations, non-coding RNA, and key proteins. Studies have shown that different drug-resistance mechanism networks are closely linked and interconnected. However, the influence of these drug-resistance mechanisms has not been compared. The combined inhibition of drug-resistance mechanisms with IM therapy and the combined inhibition of multiple drug-resistance mechanisms are expected to become new therapeutic options in the treatment of GISTs. In addition, implementing individualized therapies based on the identification of resistance mechanisms will provide new adjuvant treatment options for patients with IM-resistant GISTs, thereby delaying the progression of GISTs. Previous studies provide theoretical support for solving the problems of drug-resistance mechanisms. However, most studies on drug-resistance mechanisms are still in the research stage. Further clinical studies are needed to confirm the safety and efficacy of the inhibition of drug-resistance mechanisms as a potential therapeutic target.