CoreGx: Class and Function Abstractions for PharmacoGx, RadioGx and ToxicoGx

In CoreGx: Classes and Functions to Serve as the Basis for Other 'Gx' Packages

CoreGx

library(knitr)
knitr::opts_chunk$set(echo = TRUE)

This package provides a foundation for the PharmacoGx, RadioGx and ToxicoGx packages. It is not intended for standalone use, only as a dependency for the aforementioned software. Its existence allows abstracting generic definitions, method definitions and class structures common to all three of the Gx suite packages.

Importing and Using CoreGx

Load the pacakge:

library(CoreGx)
library(Biobase)
library(SummarizedExperiment)

The CoreSet Class

The CoreSet class is intended as a general purpose data structure for storing multiomic treatment response data. Extensions of this class have been customized for their respective fields of study. For example, the PharmacoSet class inherits from the CoreSet and is specialized for storing and analyzing drug sensitivity and perturbation experiments on cancer cell lines together with associated multiomic data for each sample treatment. The RadioSet class serves a role similar to the PharmacoSet with radiation instead of drug treatments. Finally, the ToxicoSet class is used to store toxicity data for healthy human and rat hepatocytes along with the associated multiomic profile for each treatment.

getClass("CoreSet")

The annotation slot holds the CoreSet name, the original constructor call, and a range of metadata about the R session in which the constructor was called. This allows easy comparison of CoreSet versions across time and ensures the code used to generate a CoreSet is documented and reproducible.

The molecularProfiles slot contains a list of SummarizedExperiment objects for each multi-omic molecular datatype available for a given experiment. Within the SummarizedExperiments are feature and sample annotations for each data type.

The cell slot contains a data.frame with annotations for cell lines used in the sensitivty and/or perturbation slots.

The datasetType slot contains a character vector indicating the experiment type the CoreSet contains.

The sensitivty slot contains a list of raw, curated and meta data for sensitivity experiments.

The perturbation slot contains a list of raw, curated and meta data for perturbation experiments.

The curation slot contains a list of ground truth curations sample identifiers such as cell line names/ids, tissue names/ids, drug names/ids, etc. This slot is to assist in curating across experiment and molecular profile slots to esnure consistent nomenclature.

The class provides a set of standardized accessor methods which allow easy curation, annotation and retrieval of data associated with a specfic treatment response experiment. All accessors are implemented as generics to allow new methods to be defined on classes inheriting from the CoreSet.

methods(class="CoreSet")

We have provided a sample CoreSet in this package. In the below code we load the example cSet and demonstrate a few of the accessor methods.

data(clevelandSmall_cSet)
clevelandSmall_cSet

Access a specific molecular profiles:

mProf <- molecularProfiles(clevelandSmall_cSet, "rna")
mProf[seq_len(5), seq_len(5)]

Access cell-line metadata:

cInfo <- cellInfo(clevelandSmall_cSet)
cInfo[seq_len(5), seq_len(5)]

Access sensitivty data:

sensProf <- sensitivityProfiles(clevelandSmall_cSet)
sensProf[seq_len(5), seq_len(5)]

For more information about the accessor methods available for the CoreSet class please see the class?CoreSet help page.

Extending the CoreSet Class

Given that the CoreSet class is intended for extension, we will show some examples of how to define a new class based on it and implement new methods for the generics provided for the CoreSet class.

Here we will define a new class, the DemoSet, with an additional slot, the demoSlot. We will then view the available methods for this class as well as define new S4 methods on it.

DemoSet <- setClass("DemoSet",
                    representation(demoSlot="character"),
                    contains="CoreSet")
getClass("DemoSet")

Here we can see the class extending CoreSet has all of the same slots as the original CoreSet, plus the new slot we defined: demoSlot.

We can see which methods are available for this new class.

methods(class="DemoSet")

We see that all the accessors defined for the CoreSet are also defined for the inheriting DemoSet. These methods all assume the inherit slots have the same structure as the CoreSet. If this is not true, for example, if molecularProfiles holds ExpressionSets instead of SummarizedExperiments, we can redefine existing methods as follows:

clevelandSmall_dSet <- DemoSet(clevelandSmall_cSet)
class(clevelandSmall_dSet@molecularProfiles$rna)

expressionSets <- lapply(molecularProfilesSlot(clevelandSmall_dSet), as, 'ExpressionSet')
molecularProfilesSlot(clevelandSmall_dSet) <- expressionSets

# Now this will error
tryCatch({molecularProfiles(clevelandSmall_dSet, 'rna')}, 
         error=function(e) 
             print(paste("Error: ", e$message)))

Since we changed the data in the molecularProfiles slot of the DemoSet, the original method from CoreGx no longer works. Thus we get an error when trying to access that slot. To fix this we will need to set a new S4 method for the molecularProfiles generic function defined in CoreGx.

setMethod(molecularProfiles, 
          signature("DemoSet"), 
          function(object, mDataType) {
            pData(object@molecularProfiles[[mDataType]])
          })

This new method is now called whenever we use the molecularProfiles method on a DemoSet. Since the new method uses ExpressionSet accessor methods instead of SummarizedExperiment accessor methods, we now expect to be able to access the data in our modified slot.

# Now we test our new method
mProf <- molecularProfiles(clevelandSmall_dSet, 'rna')
head(mProf)[seq_len(5), seq_len(5)]

We can see our new method works! In order to finish updating the methods for our new class, we would have to redefine all the methods which access the modified slot.

However, additional work needs to be done to define accessors for the new demoSlot. Since no generics are available in CoreGx to access this slot, we need to first define a generic, then implement methods which dispatch on the 'DemoSet' class to retrieve data in the slot.

# Define generic for setter method
setGeneric('demoSlot<-', function(object, value) standardGeneric('demoSlot<-'))

# Define a setter method
setReplaceMethod('demoSlot', 
                 signature(object='DemoSet', value="character"),
                 function(object, value) {
                   object@demoSlot <- value
                   return(object)
                 })

# Lets add something to our demoSlot
demoSlot(clevelandSmall_dSet) <- c("This", "is", "the", "demoSlot")

# Define generic for getter method
setGeneric('demoSlot', function(object, ...) standardGeneric("demoSlot"))

# Define a getter method
setMethod("demoSlot",
          signature("DemoSet"),
          function(object) {
            paste(object@demoSlot, collapse=" ")
          })

# Test our getter method
demoSlot(clevelandSmall_dSet)

Now you should have all the knowledge you need to extend the CoreSet class for use in other treatment-response experiments!

For more information about this package and the possibility of collaborating on its extension please contact [e-mail].

CoreGx documentation built on Nov. 8, 2020, 4:50 p.m.