CDK inhibition results in pharmacologic BRCAness increasing sensitivity to olaparib in BRCA1-WT and olaparib resistant in Triple Negative Breast Cancer

One in three Triple Negative Breast Cancer (TNBC) is Homologous Recombination Deficient (HRD) and susceptible to respond to PARP inhibitor (PARPi), however, resistance resulting from functional HR restoration is frequent. Thus, pharmacologic approaches that induce HRD are of interest. We investigated the effectiveness of CDK-inhibition to induce HRD and increase PARPi sensitivity of TNBC cell lines and PDX models. Two CDK-inhibitors (CDKi), the broad range dinaciclib and the CDK12-specific SR-4835, strongly reduced the expression of key HR genes and impaired HR functionality, as illustrated by BRCA1 and RAD51 nuclear foci obliteration. Consequently, both CDKis showed synergism with olaparib, as well as with cisplatin and gemcitabine, in a range of TNBC cell lines and particularly in olaparib-resistant models. In vivo assays on PDX validated the efficacy of dinaciclib which increased the sensitivity to olaparib of 5/6 models, including two olaparib-resistant and one BRCA1-WT model. However, no olaparib response improvement was observed in vivo with SR-4835. These data support that the implementation of CDK-inhibitors could be effective to sensitize TNBC to olaparib as well as possibly to cisplatin or gemcitabine.

BRCA1-methylated triple negative breast cancers previously exposed to neoadjuvant chemotherapy form RAD51 foci and respond poorly to olaparib

Background

About 15% of Triple-Negative-Breast-Cancer (TNBC) present silencing of the BRCA1 promoter methylation and are assumed to be Homologous Recombination Deficient (HRD). BRCA1-methylated (BRCA1-Me) TNBC could, thus, be eligible to treatment based on PARP-inhibitors or Platinum salts. However, their actual HRD status is discussed, as these tumors are suspected to develop resistance after chemotherapy exposure.

Methods

We interrogated the sensitivity to olaparib vs. carboplatin of 8 TNBC Patient-Derived Xenografts (PDX) models. Four PDX corresponded to BRCA1-Me, of which 3 were previously exposed to NeoAdjuvant-Chemotherapy (NACT). The remaining PDX models corresponded to two BRCA1-mutated (BRCA1-Mut) and two BRCA1-wild type PDX that were respectively included as positive and negative controls. The HRD status of our PDX models was assessed using both genomic signatures and the functional BRCA1 and RAD51 nuclear foci formation assay. To assess HR restoration associated with olaparib resistance, we studied pairs of BRCA1 deficient cell lines and their resistant subclones.

Results

The 3 BRCA1-Me PDX that had been exposed to NACT responded poorly to olaparib, likewise BRCA1-WT PDX. Contrastingly, 3 treatment-naïve BRCA1-deficient PDX (1 BRCA1-Me and 2 BRCA1-mutated) responded to olaparib. Noticeably, the three olaparib-responsive PDX scored negative for BRCA1- and RAD51-foci, whereas all non-responsive PDX models, including the 3 NACT-exposed BRCA1-Me PDX, scored positive for RAD51-foci. This suggested HRD in olaparib responsive PDX, while non-responsive models were HR proficient. These results were consistent with observations in cell lines showing a significant increase of RAD51-foci in olaparib-resistant subclones compared with sensitive parental cells, suggesting HR restoration in these models.

Conclusion

Our results thus support the notion that the actual HRD status of BRCA1-Me TNBC, especially if previously exposed to chemotherapy, may be questioned and should be verified using the BRCA1- and RAD51-foci assay.

Regulation of RAD51 at the Transcriptional and Functional Levels: What Prospects for Cancer Therapy?

The RAD51 recombinase is a critical effector of Homologous Recombination (HR), which is an essential DNA repair mechanism for double-strand breaks. The RAD51 protein is recruited onto the DNA break by BRCA2 and forms homopolymeric filaments that invade the homologous chromatid and use it as a template for repair. RAD51 filaments are detectable by immunofluorescence as distinct foci in the cell nucleus, and their presence is a read out of HR proficiency. RAD51 is an essential gene, protecting cells from genetic instability. Its expression is low and tightly regulated in normal cells and, contrastingly, elevated in a large fraction of cancers, where its level of expression and activity have been linked with sensitivity to genotoxic treatment. In particular, BRCA-deficient tumors show reduced or obliterated RAD51 foci formation and increased sensitivity to platinum salt or PARP inhibitors. However, resistance to treatment sets in rapidly and is frequently based on a complete or partial restoration of RAD51 foci formation. Consequently, RAD51 could be a highly valuable therapeutic target. Here, we review the multiple levels of regulation that impact the transcription of the RAD51 gene, as well as the post-translational modifications that determine its expression level, recruitment on DNA damage sites and the efficient formation of homofilaments. Some of these regulation levels may be targeted and their impact on cancer cell survival discussed.

Genetic variation among quince (Cydonia oblonga Mill.) genotypes sampled from the Coruh valley in Turkey

Turkey has very rich quince genetic resources, and the country currently dominates world quince production. In particular, the northeastern part of the country has notable Cydonia oblonga Mill. germplasm. Authenticating the identity of germplasm resources of C. oblonga Mill. would be of great value for breeding practices. In the present study, genetic variations of 14 C. oblonga Mill. genotypes sampled from the Coruh valley of Turkey were investigated. Ten random primers generated 53 DNA markers. The highest polymorphism ratio was observed in the OPA07 primer (86%), while the lowest was observed in OPA03 (29%). The percentage of polymorphic bands was 51%, which demonstrated the efficiency of the primers used. The similarity matrix revealed that the similarity among genotypes ranged between 0.42 and 0.96. The identified random amplified polymorphic DNA markers enabled clear discrimination among all genotypes considered.

Molecular and morphological characterization of pomegranate (Punica granatum L.) genotypes sampled from Coruh Valley in Turkey

The pomegranate is one of the oldest fruits that are traditionally consumed by the local inhabitants of the Coruh Valley, Turkey. In this study, the molecular and morphological characteristics of 19 promising pomegranate genotypes selected from the Coruh Valley were evaluated. For the morphological evaluation, 22 quantitative fruit characteristics were used. For the molecular evaluation, 47 random amplified polymorphic DNA (RAPD) primers were used for polymerase chain reaction analysis. The principle component analysis of 22 quantitative fruit characteristics revealed that fruit weight and skin color are dominant traits for genotype discrimination. The unweighted average distance cluster of fruit characteristics revealed 3 distinct groups. Among the 47 RAPD primers, 9 exhibited reliable polymorphic patterns, and generated a total of 63 RAPD bands, of which 49.2% were polymorphic. The similarity matrix showed that the highest (0.920) and lowest (0.556) genetic similarities occurred between the APS13 and APS28 genotypes and the APS12 and APS42 genotypes, respectively. We determined clear discrepancies between the morphological and molecular data; consequently, the differences obtained among genotypes for fruit characteristics did not support genetic relationships among genotypes. In conclusion, molecular data provided the most reliable results at the DNA level.

Molecular and morphological characterization of pomegranate (Punica granatum L.) genotypes sampled from Coruh Valley in Turkey

The pomegranate is one of the oldest fruits that are traditionally consumed by the local inhabitants of the Coruh Valley, Turkey. In this study, the molecular and morphological characteristics of 19 promising pomegranate genotypes selected from the Coruh Valley were evaluated. For the morphological evaluation, 22 quantitative fruit characteristics were used. For the molecular evaluation, 47 random amplified polymorphic DNA (RAPD) primers were used for polymerase chain reaction analysis. The principle component analysis of 22 quantitative fruit characteristics revealed that fruit weight and skin color are dominant traits for genotype discrimination. The unweighted average distance cluster of fruit characteristics revealed 3 distinct groups. Among the 47 RAPD primers, 9 exhibited reliable polymorphic patterns, and generated a total of 63 RAPD bands, of which 49.2% were polymorphic. The similarity matrix showed that the highest (0.920) and lowest (0.556) genetic similarities occurred between the APS13 and APS28 genotypes and the APS12 and APS42 genotypes, respectively. We determined clear discrepancies between the morphological and molecular data; consequently, the differences obtained among genotypes for fruit characteristics did not support genetic relationships among genotypes. In conclusion, molecular data provided the most reliable results at the DNA level.

Genetic relationships between selected Turkish mulberry genotypes (Morus spp) based on RAPD markers

Mulberry (Morus spp, Moraceae) is an important horticultural crop in Turkey, which is one of the main world producers of mulberry fruit. We evaluated the genetic relationships among 26 mulberry genotypes selected for agronomic characteristics, using RAPD markers. A total of 367 DNA markers were generated with 34 random primers. The highest genetic similarity (0.80) was observed between Oltu58 (M. nigra) and Olur90 (M. nigra) genotypes. The genotypes Oltu3 (M. alba) and Oltu18 (M. rubra) were the most distant (0.36). We found that the RAPD technique is a useful tool to discriminate mulberry genotypes at both the intra- and interspecific level. This type of information will aid in accurate identification of useful genotypes for breeding programs.

Genetic variation among date plum (Diospyros lotus) genotypes in Turkey

Turkey is one of the most important genetic resources of the date plum, Diospyros lotus, especially in the northeastern part of the country. Authenticating the identity of germplasm resources of D. lotus would be of great value for breeding. We examined the genetic variability of 11 D. lotus genotypes sampled from Coruh Valley in Turkey. One hundred and twenty-eight DNA markers were generated by 12 random primers. The highest polymorphism ratio was observed with the primer OPA-01 (71%) while the lowest was with OPY-01 (36%). The band size was between 350 and 2500 bp for these primers. The percentage of polymorphic bands was 58%, which demonstrated the efficiency of these primers. The similarity between genotypes ranged from 0.48 to 0.76. The RAPD markers permitted us to distinguish all the genotypes.

An assessment of genetic variability and relationships among wild-grown blackthorn (Prunus spinosa L.) plants based on RAPD markers

Prunus spinosa, blackthorn, exists as wild populations that inhabit uncultivated uplands of Coruh Valley in the northeastern part of Turkey; the fruit is used to make preserves. We examined genetic diversity in wild-grown Prunus spinosa; 16 individual plants from wild populations of Coruh Valley were sampled and subjected to RAPD (random amplified polymorphic DNA) analysis. We tested 51 random decamer primers; 15 of them gave reproducible polymorphic patterns. These 15 primers produced 226 bands, of which 65% were polymorphic. A UPGMA dendrogram clearly divided the genotypes into four groups; we concluded that RAPD analysis can be used for examining genetic relatedness among blackthorn genotypes.