Periodic Reporting for period 4 - onCOMBINE (Towards evidence-based combinations of approved and novel cancer drugs)
Berichtszeitraum: 2022-04-01 bis 2023-06-30
Lung cancer is not only the Number 1 killer in oncology; it is also one of the major types of cancer that might be significantly prevented by changing lifestyle and improving atmospheric air quality. Our research focuses on a major type of lung cancer, called non-small cell type of lung cancer (NSCLC). Patients with NSCLC are often grouped according to the type of mutations their tumors harbor. The major sub-group expresses oncogenic forms of the RAS protein. Mutant forms of the RAS proteins are induced primarily by tobacco smoking and polluted air. In contrast, the mutations affecting another molecule, EGFR, might be due primarily to polluted air.
This second large subtype of NSCLC is highly responsive to anti-cancer drugs called tyrosine kinase inhibitors (TKIs), but the corresponding patients poorly respond to immune checkpoint blockers (ICBs). However, despite the initial high activity of TKIs, within one year almost all patients acquire resistance to the first-generation TKIs. Although newer generation drugs have been developed, resistance to the new drugs is almost inevitable. As a result, patients with mutant EGFR lung cancer who sequentially underwent treatment with the 1st-, 2nd- and 3rd-generation inhibitors have no viable treatment options other than chemotherapy.
Resolving the molecular mechanisms that drive emergence of new mutations, when patients are under treatment with TKIs, is a major objective of our research project. Once fully resolved, drugs that can block the mechanism behind the emergence of new mutations might lengthen response to TKIs, thereby prolong patient survival.
This second large subtype of NSCLC is highly responsive to anti-cancer drugs called tyrosine kinase inhibitors (TKIs), but the corresponding patients poorly respond to immune checkpoint blockers (ICBs). However, despite the initial high activity of TKIs, within one year almost all patients acquire resistance to the first-generation TKIs. Although newer generation drugs have been developed, resistance to the new drugs is almost inevitable. As a result, patients with mutant EGFR lung cancer who sequentially underwent treatment with the 1st-, 2nd- and 3rd-generation inhibitors have no viable treatment options other than chemotherapy.
Resolving the molecular mechanisms that drive emergence of new mutations, when patients are under treatment with TKIs, is a major objective of our research project. Once fully resolved, drugs that can block the mechanism behind the emergence of new mutations might lengthen response to TKIs, thereby prolong patient survival.
Our research efforts have resolved a mechanism that permits emergence of new mutations in TKI-treated animal models of NSCLC. We attribute this process to the ability of EGFR-specific TKIs to instigate apoptosis of EGFR mutation-bearing cells. The many attempts to find a mechanism that possibly underlies the apparent drug-induced accelerated evolution led us to the response of bacteria to antibiotics. In 1975 Miroslav Radman reported an inducible bacterial DNA mutagenesis system, the SOS response, which might explain the link between genotoxic stress and adaptive mutagenesis of EGFR. He found that released fragments of single stranded DNA act as the sensors that initiate transcriptional programs and mutate the bacterial genome. The major endogenous mechanism of mutagenesis (i.e. mutator) in E. coli is DNA polymerase V (polV), which initiates virtually all SOS mutagenesis. PolV belongs to the group called Y family DNA polymerases, which promote translesion synthesis (TLS) of DNA. These polymerases exhibit low fidelity, thereby increase mutagenesis rates when they are engaged in DNA replication. We previously investigated whether the treatment of lung cancer with TKIs similarly engages hypermutators. Because GAS6 (growth arrest-specific protein 6), AXL’s ligand, is upregulated in cycling drug-persister cells and it binds with externalized phosphatidylserine of apoptotic bodies, we assumed that the GAS6-AXL module acts as a sensor that stimulates SOS-like reactions in response to TKIs. In line with this prediction and with previous reports that associated AXL and GAS6 with intrinsic resistance to TKIs, we found that AXL overexpression can up-regulate low-fidelity DNA polymerases and downregulate DNA repair enzymes. Moreover, simultaneously inhibiting AXL and EGFR completely blocked relapses in animal models. Metabolomic analysis uncovered yet another intrinsic mutator that relates to the dependency of DNA replication on balanced pools of deoxyribonucleotides (dNTPs). By activating MYC and purine synthesis, AXL disbalances the pools of dNTPs, which can influence polymerase proofreading and mutator phenotypes. In conclusion, pharmacological stress-driven mutagenesis might be shared by eukaryotes and unicellular organisms, arguing against prevailing assumptions that mutations occur purely stochastically. Moreover, blocking the mutators and their upstream control might identify new strategies to prevent or significantly delay the onset of cancer relapse post treatment.
In parallel to our attempts to resolve EGFR secondary mutagenesis and delay onset of resistance to TKIs, we studied yet another strategy, namely: enhancing responses of patients with EGFR mutations to immune checkpoint blockers (ICBs). It is well documented that EGFR mutant tumors exhibit relatively low response rates to ICBs. Therefore, understanding mechanisms underlying resistance of EGFR mutant patients to immunotherapy is urgently needed. An important clue as to the mechanism driving resistance of the EGFR mutant group to ICBs has been provided by clinical observations made with patients expressing rare mutant forms of EGFR, who respond relatively well to ICBs. Because treatment outcomes vary by EGFR allele, we assumed that features intrinsic to the tumor cells drive the relatively high resistance of the EGFR+ group. While studying intrinsic factors that potentially underlie immunosuppression, we discovered previously unknown strong physical and functional interactions between phospholipase C gamma (PLC-g) and PD-L1. These observations might guide future attempts to combine anti-PLC drugs and PD-L1 inhibitors for the benefit of patients with lung cancer.
In parallel to our attempts to resolve EGFR secondary mutagenesis and delay onset of resistance to TKIs, we studied yet another strategy, namely: enhancing responses of patients with EGFR mutations to immune checkpoint blockers (ICBs). It is well documented that EGFR mutant tumors exhibit relatively low response rates to ICBs. Therefore, understanding mechanisms underlying resistance of EGFR mutant patients to immunotherapy is urgently needed. An important clue as to the mechanism driving resistance of the EGFR mutant group to ICBs has been provided by clinical observations made with patients expressing rare mutant forms of EGFR, who respond relatively well to ICBs. Because treatment outcomes vary by EGFR allele, we assumed that features intrinsic to the tumor cells drive the relatively high resistance of the EGFR+ group. While studying intrinsic factors that potentially underlie immunosuppression, we discovered previously unknown strong physical and functional interactions between phospholipase C gamma (PLC-g) and PD-L1. These observations might guide future attempts to combine anti-PLC drugs and PD-L1 inhibitors for the benefit of patients with lung cancer.
Our studies advanced the field of lung cancer treatment in two ways:
(i) Contrary to the dominance of TKIs as anti-NSCLC drugs, we demonstrated that antibodies and especially combinations of different antibodies might be effective. These observations may lead to the development of antibody and TKI combinations, as well as to the design of bi-specific antibodies.
(ii) Most recently, we obtained evidence supporting the possibility that anti-EGFR antibodies might inhibit a certain mutant form of EGFR (i.e. L858R-EGFR), while it may not inhibit other mutant forms. Translating this to clinical application will likely change the way a large fraction of patients, who are currently treated with the mutation-prone TKIs, will be treated with antibodies like cetuximab. Conceivably, resistance to the antibodies, if it occurs, may not involve the emergence of secondary mutations.
(i) Contrary to the dominance of TKIs as anti-NSCLC drugs, we demonstrated that antibodies and especially combinations of different antibodies might be effective. These observations may lead to the development of antibody and TKI combinations, as well as to the design of bi-specific antibodies.
(ii) Most recently, we obtained evidence supporting the possibility that anti-EGFR antibodies might inhibit a certain mutant form of EGFR (i.e. L858R-EGFR), while it may not inhibit other mutant forms. Translating this to clinical application will likely change the way a large fraction of patients, who are currently treated with the mutation-prone TKIs, will be treated with antibodies like cetuximab. Conceivably, resistance to the antibodies, if it occurs, may not involve the emergence of secondary mutations.