Purpose Patients with anaplastic lymphoma kinase (ALK) gene rearrangements often manifest dramatic responses to crizotinib, a small molecule ALK inhibitor. Unfortunately, not every patient responds and acquired drug resistance inevitably develops in those that do respond. This study aimed to define molecular mechanisms of resistance to crizotinib in ALK+ non-small cell lung cancer (NSCLC) patients. Experimental Design We analyzed tissue obtained from 14 ALK+ NSCLC patients demonstrating evidence of radiologic progression while on crizotinib in order to define mechanisms of intrinsic and acquired resistance to crizotinib. Results Eleven patients had material evaluable for molecular analysis. Four patients (36%) developed secondary mutations in the tyrosine kinase domain of ALK. A novel mutation in the ALK kinase domain, encoding a G1269A amino acid substitution that confers resistance to crizotinib in vitro, was identified in two of these cases. Two patients, one with a resistance mutation, exhibited new onset ALK copy number gain (CNG). One patient demonstrated outgrowth of EGFR mutant NSCLC without evidence of a persistent ALK gene rearrangement. Two patients exhibited a KRAS mutation, one of which occurred without evidence of a persisting ALK gene rearrangement. One patient demonstrated the emergence of an ALK gene fusion negative tumor compared to the baseline sample, but with no identifiable alternate driver. Two patients retained ALK positivity with no identifiable resistance mechanism. Conclusions Crizotinib resistance in ALK+ NSCLC occurs through somatic kinase domain mutations, ALK gene fusion CNG, and emergence of separate oncogenic drivers.

We identified novel gene fusions in patients with lung cancer harboring the kinase domain of the NTRK1 gene that encodes the TRKA receptor. Both the MPRIP-NTRK1 and CD74-NTRK1 fusions lead to constitutive TRKA kinase activity and are oncogenic. Treatment of cells expressing NTRK1 fusions with inhibitors of TRKA kinase activity inhibited autophosphorylation of TRKA and cell growth. Three of 91 lung cancer patients (3.3%), without known oncogenic alterations, assayed by NGS or FISH demonstrated evidence of NTRK1 gene fusions.

Background Prostate cancer that recurs after initial treatment inevitably progresses to castration‐resistant prostate cancer (CRPC), the lethal stage of the disease. Despite improvements in outcomes from next generation androgen receptor (AR)‐axis inhibitors, CRPC remains incurable. Therapeutic strategies to target AR antagonist resistance are urgently needed to improve outcomes for men with this lethal form of prostate cancer. Methods Apoptosis and BCL2 family signaling were characterized in cell line models of CRPC. Quantitative real‐time polymerase chain reaction and Western blot analysis were used to determine BCL2 expression levels. Drug sensitivity was determined by proliferation, survival and apoptosis analysis. Protein‐protein interactions were evaluated by coimmunoprecipitation followed by Western blot detection. Results In the present study, we identify antiapoptotic BCL2 protein signaling as a mechanism of resistance to AR antagonist enzalutamide. In CRPC cell line models, we found that BCL‐xL and MCL‐1 proteins block apoptosis through binding and sequestering proapoptotic proteins BIM and BAX, resulting in cell survival in response to enzalutamide. Treatment with BH3‐mimetics targeting BCL‐xL or MCL‐1 disrupts these interactions and activates apoptosis, sensitizing CRPC cells to enzalutamide. Importantly, we demonstrate that PI3K/Akt signaling is activated in response to enzalutamide and mediates apoptosis evasion through inactivation of BAD, a BH3‐only protein that activates proapoptotic signlaing through inhbition of BCL‐xL. Inhibition of Akt activates BAD, resulting in increased apoptosis and sensitivity to enzalutamide, demonstrating an alternative therapeutic strategy to target drug resistance. Conclusions These results demonstrate that CRPC cells employ multiple mechanisms to mediate apoptosis evasion through BCL2 signaling, suggesting this pathway is critical for survival. This study provides a strong preclinical rationale for developing therapeutic strategies to target antiapoptotic BCL2 signaling in combination with AR antagonists to improve treatment options for patients with advanced prostate cancer.

Aging and DNA polymerase ␤ deficiency (␤-pol ؉/؊ ) interact to accelerate the development of malignant lymphomas and adenocarcinoma and increase tumor bearing load in mice. Folate deficiency (FD) has been shown to induce DNA damage repaired via the base excision repair (BER) pathway. We anticipated that FD and BER deficiency would interact to accelerate aberrant crypt foci (ACF) formation and tumor development in ␤-pol haploinsufficient animals. FD resulted in a significant increase in ACF formation in wild type (WT) animals exposed to 1,2-dimethylhydrazine, a known colon and liver carcinogen; however, FD reduced development of ACF in ␤-pol haploinsufficient mice. Prolonged feeding of the FD diet resulted in advanced ACF formation and liver tumors in wild type mice. However, FD attenuated onset and progression of ACF and prevented liver tumorigenesis in ␤-pol haploinsufficient mice, i.e. FD provided protection against tumorigenesis in a BER-deficient environment in all tissues where 1,2-dimethylhydrazine exerts its damage. Here we show a distinct down-regulation in DNA repair pathways, e.g. BER, nucleotide excision repair, and mismatch repair, and decline in cell proliferation, as well as an up-regulation in poly(ADP-ribose) polymerase, proapoptotic genes, and apoptosis in colons of FD ␤-pol haploinsufficient mice.Folate deficiency is an important public health concern because of the role folate plays in the development of many different health problems, including neural tube defects, cardiovascular disease, Alzheimer disease, and cancer, specifically colon cancer. It has been proposed that the carcinogenic properties of folate deficiency may be related to a decrease in DNA methylation, perhaps as a function of reduced S-adenosylmethionine levels, an increase in the uracil content of DNA, or an increase in oxidative stress by alterations in thiol switches. Folate deficiency has also been shown to increase (in cells, animal models, and humans) levels of single strand breaks (1-5), micronucleus formation (6, 7), chromosomal aberration (8, 9), and mutation frequency (10, 11), all potentially downstream effects of high levels of uracil in DNA and oxidative damage to DNA.The DNA repair pathway for removal of uracil and oxidized bases is the base excision repair (BER) 2 pathway. The BER pathway is believed to repair small, non-helix-distorting lesions in the DNA. It has been estimated to be responsible for the repair of as many as one million nucleotides per cell per day (12), stressing its importance in the maintenance of genomic stability. It has been suggested that BER has evolved in response to in vivo exposure of DNA to reactive oxygen species and endogenous alkylation, and that this pathway suppresses spontaneous mutagenesis (13). In the initial elucidation of the BER pathway the following steps were involved: (i) removal of the damaged base by a DNA glycosylase; (ii) incision of the phosphate backbone by an endonuclease; (iii) synthesis of new DNA by a polymerase; (iv) excision of the deoxyribose phosphate moie...

These findings suggest that IAP antagonists can increase sensitivity and amplify the caspase-mediated apoptotic response to enzalutamide through TNF-α signaling mechanisms. Combination with an IAP antagonist increases enzalutamide sensitivity, lowers the apoptotic threshold and may combat drug resistance in patients with prostate cancer. Prostate 77:866-877, 2017. © 2017 Wiley Periodicals, Inc.