Targeting HER2 heterogeneity in breast and gastrointestinal cancers

About 20% of breast and gastric cancers and 3% of colorectal carcinomas overexpress the human epidermal growth factor receptor 2 (HER2) and are sensitive to HER2-directed agents. The expression of HER2 may differ within the same tumoral lesion (spatial intralesional heterogeneity), from different tumor locations (spatial interlesional heterogeneity), and throughout treatments (temporal heterogeneity). Spatial and temporal heterogeneity may impact on response and resistance to HER2-targeting agents and its prevalence and predictive role changes across HER2-overexpressing solid tumors. Therefore, the definition and the characterization of HER2 heterogeneity pose many challenges and its implementation as a reproducible predictive biomarker would help in guiding treatment modulation.

Improving Outcome of Selected Patients With Non-Resectable Hepatic Metastases From Colorectal Cancer With Liver Transplantation: A Prospective Parallel Trial (COLT trial)

BACKGROUND

Patients with unresectable Colorectal Liver Metastases (CLM) receiving palliative chemotherapy have a 5-year overall survival (OS) of less than 30%. Liver transplantation (LT) can improve OS up to 60%-83% (SECA-I and SECA-II trials). The aim of the study is to assess the efficacy of LT in liver-only metastatic CRC compared with a matched cohort of patients included in a phase III trial on triplet chemotherapy + antiEGFR.

PATIENTS AND METHODS

The COLT trial is an investigator-driven, multicenter, non-randomized, open-label, controlled, prospective, parallel trial (ClinicalTrials.gov NCT03803436). Hyperselected patients with liver-limited unresectable CLM, RAS and BRAF wild-type and curatively removed primary colon cancer are included. The observed post-transplant outcomes will be prospectively compared 1:5 with those obtained in a matched cohort from the TRIPLETE trial (NCT03231722).

RESULTS

Primary endpoint is to compare the 3 and 5-years OS of patients enrolled in the COLT trial with COLT-eligible population enrolled in the TRIPLETE trial. An expected gain in OS of 40% at 5-years is predicted for the COLT population (the expected OS at 5-years in COLT vs. TRIPLETE is 70% vs. 30%). Secondary endpoints are to compare the 5-years disease-free survival and to assess the safety of LT (Dindo-Clavien Classification and the Comprehensive Complication Index).

CONCLUSION

LT offers the longest OS reported in selected patients with CLM. Improving the selection strategies can give patients a 5-year OS similar to other indications for LT and a better outcome than those undergoing chemotherapy alone.

Abstract CT215: Pharmacological inactivation of DNA repair to improve response to immunotherapy: The Arethusa trial in metastatic colorectal cancer

Background. Metastatic colorectal cancer (CRC) remains mostly incurable, with a survival of about two years only. It has been recently proved that CRCs with genetic defects in the mismatch-repair pathway (MMRd), occurring in 15% of early CRC but only in 5% of metastatic CRC, present with a high tumor mutational burden (TMB), which results in an increased number of neoantigens that can be recognized by the immune system. Indeed, treatment with the anti-programmed cell death protein 1 (PD-1) immune checkpoint inhibitor pembrolizumab or nivolumab is effective in inducing durable objective responses in metastatic CRC MMRd cases. These results are quite remarkable considering that the clinical efficacy was independent from RAS mutations, which constrain the use of targeted treatments and negatively affect prognosis. We recently showed in preclinical models that the pharmacological treatment with temozolomide (TMZ) can induce the inactivation of MMR genes and consequently trigger an increase in immunogenic neoantigens. This suggests that TMZ could be used to prime MMR proficient (MMRp) tumors for response to checkpoint inhibitors. Accordingly, mCRC patients recruited in previous clinical trials where TMZ was administered, acquired alterations of MMR genes upon treatment and showed remarkable increase in TMB at disease progression (PD). We thus designed the ARETHUSA clinical trial to test whether a priming course with TMZ in patients can sensitize mCRC to the anti-PD1 inhibitor pembrolizumab.

Methods. Arethusa is a 2-cohorts, phase II trial consisting of three different phases (NCT03519412). During screening-phase, 344 mCRC patients with RAS-extended mutations who failed standard therapies will be tested for MMR status. MMRd CRC patients will proceed directly to trial-phase for immediate pembrolizumab treatment (expected N=14). MMR-proficient (MMRp) patients will be further tested for TMZ sensitivity via assessment of expression of O6-methylguanine-DNA methyltransferase (MGMT) by immunohistochemistry and by promoter methylation analysis. Expected 67 IHC-negative, promoter methylation-positive MMRp patients will thus be eligible for priming-phase and will receive TMZ until PD; TMB will then be assessed on tumor biopsies at resistance. Those patients that will have >20 mutations/megabase (expected N=20) will proceed to that trial-phase and will be treated with pembrolizumab. Overall response rate (primary outcome), Progression Free, and Overall Survival, and treatment related toxicities (secondary outcomes) in MMRp pembrolizumab-treated patients will be estimated. Treatment efficacy and toxicity within pembrolizumab-treated MMRd cohort will be used for comparison. Pre- and post-TMZ biopsies and longitudinal blood and stool collection during priming and trial phases will allow for discovery of predictive molecular markers and for the assessment of integrated tumor and (immune)environment evolution in response to therapy.

Citation Format: Silvia Marsoni, Giovanni Germano, Andrea Sartore Bianchi, Filippo Pietrantonio, Nicola Personeni, Alessio Amatu, Emanuela Bonoldi, Emanuele Valtorta, Ludovic Barault, Federica Di Nicolantonio, Filippo de Braud, Lorenza Rimassa, Armando Santoro, Silvia Ghezzi, Andrea Cassingena, Giovanna Marrapese, Loredana Lupica, Giulia Siravegna, Giuseppe Rospo, Cosimo Martino, Luca Lazzari, Paolo Luraghi, Nabil Amirouchene-Angelozzi, Alberto Bardelli, Salvatore Siena. Pharmacological inactivation of DNA repair to improve response to immunotherapy: The Arethusa trial in metastatic colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT215.

Acquired Resistance to the TRK Inhibitor Entrectinib in Colorectal Cancer

Entrectinib is a first-in-class pan-TRK kinase inhibitor currently undergoing clinical testing in colorectal cancer and other tumor types. A patient with metastatic colorectal cancer harboring an LMNA-NTRK1 rearrangement displayed a remarkable response to treatment with entrectinib, which was followed by the emergence of resistance. To characterize the molecular bases of the patient's relapse, circulating tumor DNA (ctDNA) was collected longitudinally during treatment, and a tissue biopsy, obtained before entrectinib treatment, was transplanted in mice (xenopatient), which then received the same entrectinib regimen until resistance developed. Genetic profiling of ctDNA and xenopatient samples showed acquisition of two point mutations in the catalytic domain of NTRK1, p.G595R and p.G667C. Biochemical and pharmacologic analysis in multiple preclinical models confirmed that either mutation renders the TRKA kinase insensitive to entrectinib. These findings can be immediately exploited to design next-generation TRKA inhibitors.

SIGNIFICANCE

We provide proof of principle that analyses of xenopatients (avatar) and liquid biopsies allow the identification of drug resistance mechanisms in parallel with clinical treatment of an individual patient. We describe for the first time that p.G595R and p.G667C TRKA mutations drive acquired resistance to entrectinib in colorectal cancers carrying NTRK1 rearrangements.

Abstract 616: Blood-based molecular landscapes of resistance to EGFR blockade in colorectal cancer patients

The molecular landscape of colorectal cancers (CRC) is presently assessed by genotyping neoplastic tissue obtained through surgical or bioptic procedures. We evaluated whether blood-based molecular profiles could be used to perform diagnostic determinations and monitor resistance to therapy in colorectal cancer patients. We find that RAS pathway mutations, which are commonly evaluated prior to administration of anti-EGFR antibodies, can be ascertained directly in the blood. Sequencing of circulating DNA identified genomic alterations in KRAS, NRAS, MET, ERBB2, FLT3, and MEK1 in patients with primary or acquired resistance to cetuximab or panitumumab. Secondary resistance to EGFR blockade is frequently accompanied by emergence of mutant RAS clones, which can be tracked in blood. We find that upon withdrawal of anti-EGFR antibodies, KRAS alleles decline in circulating DNA indicating that clonal evolution continues beyond clinical progression. Functional analysis of CRC cell populations, which had acquired resistance to cetuximab, revealed that KRAS mutant clones can decay when EGFR blockade is suspended. These results establish proof of principle that genotyping colorectal cancers using circulating DNA can inform therapeutic decisions, identify mechanisms of drug resistance and provide insights for further lines of therapy.

Citation Format: Giulia Siravegna, Benedetta Mussolin, Michela Buscarino, Giorgio Corti, Andrea Cassingena, Giovanni Crisafulli, Ryan B. Corcoran, Agostino Ponzetti, Alfredo Budillon, Patrizia Racca, Silvia Marsoni, Federica Di Nicolantonio, Fotios Loupakis, Salvatore Siena, Andrea Sartore Bianchi, Alberto Bardelli. Blood-based molecular landscapes of resistance to EGFR blockade in colorectal cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 616. doi:10.1158/1538-7445.AM2015-616

Phase II study of dacarbazine for metastatic colorectal cancer: Final results with MGMT analysis

3581

Background: O6-methylguanine-DNA-methyltransferase (MGMT) is a DNA repair protein removing mutagenic and cytotoxic adducts from O6-guanine in DNA. Approximately 40% of colorectal cancers (CRCs) display MGMT deficiency due to promoter hypermethylation leading to silencing of the gene. Alkylating agents, such as dacarbazine, exert their antitumor activity by DNA methylation at the O6–guanine site, inducing base pair mismatch, therefore activity of dacarbazine could be enhanced in CRCs lacking MGMT. We conducted a phase II study with dacarbazine in CRCs who had failed standard therapies (oxaliplatin, irinotecan, fluoropyrimidines, and cetuximab or panitumumab if KRAS wild type). Methods: All patients had tumor tissue assessed for MGMT as promoter hypermethylation in double-blind for treatment outcome. Patients received dacarbazine 250 mg/m2 i.v. qd for 4 consecutive days q21 until PD or intolerable toxicity. We employed a Simon two-stage design to determinate if the ORR would be ≥ 10%. Secondary endpoints included association of response, PFS and disease control rate with MGMT status. Results: Sixty-eight patients were enrolled from May 2011 to March 2012. Patients received a median of 3 cycles of dacarbazine [range 1-12]. Grade 3-4 toxicities included: fatigue (41%), nausea/vomiting (29%), constipation (25%), platelet count decrease (19%), anemia (18%). Overall, 2 patients (3%) achieved partial response (PR) and 8 patients (12%) had stable disease (SD). Disease control rate (PR+SD) was significantly associated with MGMT promoter hypermethylation in the corresponding tumors. Conclusions: Objective clinical responses to dacarbazine in metastatic CRC patients are confined to those tumors harbouring epigenetic inactivation of the DNA repair enzyme MGMT. Clinical trial information: 2011-002080-21.

Abstract LB-75: Blood-based molecular detection of acquired resistance to anti-EGFR therapies in colorectal cancer patients

The anti EGFR monoclonal antibodies cetuximab and panitumumab are used to treat metastatic colorectal cancer patients. The clinical efficacy of EGFR inhibitors is limited by the development of acquired resistance, which typically occurs within 3-12 months since starting of therapy. We recently reported that secondary KRAS mutations are responsible for acquired resistance in approximately 50% of patients (Misale et al.; Diaz et al., Nature 2012). We reasoned that the detection of KRAS mutant alleles in the plasma of cetuximab treated patients may enable the early identification of secondary resistance to anti EGFR blockade before radiographic documentation of relapse. Using the highly sensitive BEAMing approach we have examined cell-free circulating tumor DNA (ctDNA), a form of "liquid biopsy". KRAS mutant alleles emerged in the circulation of approximately 50% of patients treated with anti-EGFR antibodies months before radiographic documentation of disease progression. The liquid biopsy approach was then used to select patients in which KRAS mutations did not emerge during anti-EGFR therapy. Exome sequencing identified amplification of the MET proto-oncogene in biopsies from patients who did not develop KRAS mutations. Using an innovative approach, we find that MET amplification can be identified in a non-invasive manner through the examination of ctDNA months before relapse becomes clinically manifest. As multiple anti-MET therapeutic strategies are available, these findings offer immediate novel opportunities to design clinical studies.

Citation Format: Giulia Siravegna, Andrea Sartore Bianchi, Andrea Cassingena, Katia Bencardino, Luis A. Diaz, Mark Sausen, Victor E. Velculescu, Federica Di Nicolantonio, Salvatore Siena, Alberto Bardelli. Blood-based molecular detection of acquired resistance to anti-EGFR therapies in colorectal cancer patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-75. doi:10.1158/1538-7445.AM2013-LB-75

Abstract B229: Molecular mechanisms of resistance to cetuximab and panitumumab in colorectal cancer

Personalized cancer medicine based on the genetic milieu of individual tumors has long been postulated but until recently this concept was not supported by clinical evidence. The advent of the EGFR-targeted monoclonal antibodies cetuximab and panitumumab has revolutionized the therapy of colorectal tumors and paved the way to the individualized treatment of this cancer type. From the initial observation that cetuximab or panitumumab as monotherapy are effective only in 10–20%, of mCRCs, knowledge has being gained on the molecular mechanisms underlying primary resistance to these agents. It has already been unequivocally established that KRAS mutations, which occur in 35–45% of colorectal cancers, preclude responsiveness to EGFR-targeted therapy. However, less than 20% patients displaying wild-type KRAS tumors achieve objective response. Alterations in other effectors downstream of the EGFR, such as BRAF, and deregulation of the PIK3CA/PTEN pathway have independently been suggested to give rise to resistance.

Molecular profiling of tumor samples and functional analysis of cellular models were preformed to clarify the relative contribution of molecular alterations to resistance. We retrospectively analyzed objective tumor response, progression-free (PFS) and overall survival (OS) together with the mutational status of KRAS, BRAF, PIK3CA and expression of PTEN in 132 tumors from cetuximab or panitumumab treated mCRC patients. Among the 106 non responsive patients, 74 (70%) had tumors with at least one molecular alteration in the four markers. The probability of response was 51% (22/43) among patients with no alterations, 4% (2/47) among patients with 1 alteration, and 0% (0/24) for patients with ≥ 2 alterations (p<0.0001). Accordingly, PFS and OS were increasingly worse for patients with tumors harboring none, or ≥ 2 molecular alteration(s) (p<0.001).

When expression of PTEN and mutations of KRAS, BRAF and PIK3CA were concomitantly ascertained, up to 70% of mCRC patients unlikely to respond to anti-EGFR therapies can be identified. We propose to define as ‘quadruple negative’, the CRCs lacking alterations in KRAS, BRAF, PTEN and PIK3CA. The functional role of mutated KRAS, BRAF and PIK3CA alleles in modulating resistance to cetuximab was evaluated in multiple cellular models in the presence or absence of ligands of the EGF receptor. The introduction of these oncogenic alleles in colorectal cancer cells impaired the therapeutic effect of cetuximab. Accordingly, we propose a molecular mechanism whereby the occurrence of KRAS and BRAF mutations together with the availability of EGF receptor ligands modulate the response to anti EGFR monoclonal antibodies.

Comprehensive molecular dissection of the EGFR signaling pathways should be considered to select mCRC patients for cetuximab- or panitumumab based therapies. The rapid and effective translation of these findings into predictive biomarkers to couple EGFR-targeted antibodies to the patients that benefit from them represent a paradigm of modern clinical oncology.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B229.

Participation of the SOS system in producing deletions in E. coli plasmids

The participation of the SOS response in the deletion of palindromic and non-palindromic inserts of about 66 and 100 bp cloned within the EcoR1 site of the chloramphenicol acetyl transferase (cat) gene of plasmid pBR325 was tested after introducing the derived plasmids into strains containing different combinations of lexA, recA and umuC alleles and the auxotrophic mutation trpE65. This allowed for a comparison of deletion frequency in the plasmids, measured as the reversion of chloramphenicol sensitivity to resistance (Cms-->Cmr), to point-mutation frequency measured from the reversion of trpE65 to tryptophan independence (Trp(-)-->Trp+). We found that the spontaneous deletion frequency of palindromic inserts was increased by the overproduction of activated RecA* and UmuC+ in lexA (Def) backgrounds but the deletion of the non-palindromic inserts was unaltered. Overproduction of RecA+ had no significant effect on deletion incidence but it did increase Trp(-)-->Trp+ reversions. The SOS stimulation of palindrome deletions paralleled the SOS mutator effect of certain recA and umuC alleles on Trp(-)-->Trp+ reversions, suggesting that some form of SOS processing was responsible for the observed increases. The results further suggest that the SOS effect on deletions depends on the distinction between palindromy vs. non-palindromy, rather than on the sizes or sequences of the inserts or those of the terminal homologies bracketing them.